WO2021153407A1 - Residual stress measurement method and residual stress measurement device - Google Patents

Abstract

Provided is a method for measuring residual stress accurately by reducing the effect of heat generation and the like during piercing when residual stress inside a resin molded article is measured at a predetermined location therein by a piercing method. This residual stress measurement method determines residual stress inside a resin molded article by measuring the amount of release strain which is released in a main piercing step for providing a piercing portion in the resin molded article and piercing the piercing portion using a drill. The measurement of the amount of release strain includes performing, prior to the main piercing process, at least: a preliminary piercing step for piercing the piercing portion of the resin molded article by advancing the drill to a preliminary piercing depth location, and then retracting the drill out of the resin molded article; and a piercing condition setting step for setting at least one of the revolving speed and the feed rate of the drill in the main piercing step so that a strain difference Δε, which is the absolute value of a difference between a first strain amount ε₁ detected upon completion of the preliminary piercing step and a second strain amount ε₂ detected when or after the resin molded article has been left to stand until the amount of strain is stabilized after the preliminary piercing step is complete, is less than or equal to 50 μst.

Description

Residual stress measuring method and residual stress measuring device

The present invention relates to a residual stress measuring method and a residual stress measuring device for measuring the residual stress inside a resin molded product.

Conventionally, as a method of measuring the residual stress inside the resin molded product, there are a perforation method and a surface layer sequential removal method which are methods of measuring while breaking the resin molded product, and a photoelasticity method which is a method of not destroying the resin molded product. The law is known.

Of these, in the drilling method, a strain gauge is attached in advance around the portion of the resin molded product to be measured to measure the strain amount, and the strain amount when the resin molded product is punched along the thickness direction. It is a method of measuring a change and measuring a residual stress, and is mainly used for measuring a residual stress in a flat portion of a plate-shaped product or a three-dimensional three-dimensional shape product. However, since there is a distance between the perforated portion and the strain gauge for measuring the amount of strain, it is not possible to accurately measure the residual stress generated during the molding process.

The surface layer sequential removal method is a method in which a strain gauge is attached to one surface of a plate-shaped resin molded product, and the amount of strain is measured while removing the other surface in thin layers to obtain residual stress. In this method, not only the in-plane of the resin molded product but also the residual stress in the wall thickness direction can be measured.

However, in the surface layer sequential removal method, the resin molded product to be measured is limited to a simple shape such as a plate shape or a pipe shape. Further, the surface layer sequential removal method has drawbacks that it cannot be applied when the strain gauge does not completely adhere to the resin molded product, and that it takes time and effort to measure.

The photoelastic method is a method in which light polarized by a polarizing plate is applied to a transparent resin molded product to evaluate the residual stress from the striped pattern of transmitted light, and the residual stress in the plane can be easily measured. .. However, the photoelastic method has drawbacks that it cannot measure the residual stress in the wall thickness direction and cannot be applied to an opaque resin molded product.

As described above, further improvement is required for the method of measuring the residual stress inside the resin molded product. Therefore, in Patent Document 1, the drilling method is improved, and the amount of strain of the resin molded product when the drilled portion is drilled to a predetermined first drilling depth in the thickness direction of the resin molded product having the drilled portion. The first stress generated in the resin molded product by drilling was obtained from the obtained strain amount, and then the drilled portion was further drilled in the thickness direction to a predetermined second drilling depth. The strain amount of the resin molded product is measured, the second stress generated in the resin molded product by this drilling is obtained from the obtained strain amount, and then the difference obtained by subtracting the first stress from the second stress is obtained. A method for calculating residual stress, which is calculated as an approximate value of residual stress at an intermediate depth between the first drilling depth and the second drilling depth, is disclosed. In this residual stress calculation method, it is possible to more easily calculate the residual stress at a predetermined position and obtain the residual stress distribution inside the resin molded product regardless of the type of resin material used.

Japanese Unexamined Patent Publication No. 2010-2433335

The perforation method described in Patent Document 1 also has room for further improvement in terms of reducing measurement errors and variations and improving measurement accuracy. In particular, there is room for improvement in reducing variations in the measurement results of strain and residual stress at the same location for a plurality of resin molded products manufactured with the same material and under the same molding conditions. In addition, there is room for improvement in that the effect of the design change is correctly reflected in the measured value of the residual stress of the resin molded product when the design is changed to reduce the residual stress based on the measurement result. was there.

Here, if residual stress exists in the resin molded product, problems such as shortening of product life and deformation after molding occur. Therefore, it is necessary to accurately grasp the residual stress and take measures such as appropriate design changes. However, if it is not possible to perform highly accurate measurement, it becomes difficult to take appropriate measures.

The present invention has been proposed in view of the above circumstances, and is a residual stress measuring method capable of measuring the internal residual stress at a predetermined position of a resin molded product with higher accuracy, and a method for measuring the residual stress therefor. It is an object of the present invention to provide a measuring device.

The present inventor has investigated to solve the above-mentioned problems, and found that the drilling method generates frictional heat due to the rotation of the tool when drilling by cutting with a tool such as a drill or an end mill. It was found that the measurement accuracy of residual stress decreases. More specifically, the frictional heat generated by the rotation of the tool heats or melts the resin around the perforated portion to release the strain in the resin molded product and reduce the residual stress, or the resin ( Re) It was found that the measurement accuracy of the residual stress is lowered because the residual stress is increased due to the strain generated in the resin molded product due to the promotion of crystallization or cross-linking. That is, it is considered that the above-mentioned variation in the measurement results of the residual stress is caused by the process of heat generation and cooling at the time of drilling, and by extension, the state of occurrence of strain and its change are not always constant. Therefore, the present inventor has solved the above-mentioned problems by suppressing heat generation at the time of drilling by the drilling method by the following.

[1] A perforated portion is provided in a resin molded product to be measured, the amount of release strain released during the main drilling step of perforating the perforated portion with a drill is measured, and the resin molding is performed from the obtained release strain amount. A method for measuring residual stress by a drilling method for obtaining residual stress inside a product, wherein the strain measuring means is provided on the surface of the resin molded product before the main drilling step. When the pre-drilling step of advancing the drill from the surface to the pre-drilling depth position and then retreating the drill to remove the drilled portion from the resin molded product and the pre-drilling step are completed. It is the absolute value of the difference between the detected first strain amount ε _{1 and the second strain amount ε 2} detected at the time of standing still until the strain amount stabilizes after the completion of the preliminary drilling step or thereafter. A method for measuring residual stress, wherein at least one of a drilling condition setting step of setting at least one of the rotation speed and the feed rate of the drill in the main drilling step is performed so that the strain amount difference Δε is 50 μst or less.
[2] In the drilling condition setting step, a multi-axis gauge having two or more axes is used, and the first strain amount ε ₁ , the second strain amount ε _2, and the strain amount difference Δε are set for each axis of the multi-axis gauge. The above [1], wherein at least one of the rotation speed and the feed rate of the drill in the main drilling step is set so that the strain amount difference Δε obtained for each of the axes is 50 μst or less. Residual stress measurement method.
[3] During the preliminary drilling step, the temperature of the drilled portion is measured, and in the drilling condition setting step, the temperature is equal to or lower than the glass transition temperature of the resin constituting the resin molded product. The residual stress measuring method according to the above [1] or [2], wherein at least one of the rotation speed and the feed speed of the drill in the drilling step is set.
[4] The method for measuring residual stress according to any one of [1] to [3], wherein the drilling condition setting step is set so that the rotation speed of the drill is 100 rpm or less.
[5] The method for measuring residual stress according to any one of [1] to [4], wherein the drilling condition setting step is set so that the feed rate of the drill is 4.0 mm / min or less.
[6] The perforated portion and the strain measuring portion are provided on a surface perpendicular to the thickness direction, and the perforated portion is configured to perforate the resin molded product in the thickness direction in the preliminary drilling step. and, and, the strain measuring unit, in the drilling condition setting step, occurs perpendicular to the thickness direction, configured to measure the first amount of distortion epsilon ₁ and the second amount of distortion epsilon ₂ The method for measuring residual stress according to any one of the above [1] to [5].
[7] The residual stress measuring method is a method of obtaining an internal residual stress in the thickness direction of the resin molded product, and in the main drilling step, the drilled portion is drilled to the first drilling depth in the thickness direction. The first stress measurement is performed by measuring the amount of strain in the resin molded product and using the obtained strain amount to measure the first stress generated in the resin molded product by drilling to the first drilling depth. The step and the strain amount in the resin molded product when the drilled portion was drilled to a second drilling depth different from the first drilling depth in the thickness direction were measured by the strain measuring section and obtained. It is obtained by a second stress measuring step of measuring the second stress generated in the resin molded product by drilling to the second drilling depth using the strain amount, and by subtracting the first stress from the second stress. The residual stress measuring method according to the above [6], further comprising a residual stress calculation step of calculating the difference as a residual stress at an intermediate depth between the first drilling depth and the second drilling depth.
[8] A residual stress measuring device used in the residual stress measuring method according to any one of [1] to [7], wherein the residual stress measuring device rotates the drill to form the resin. The drilling means includes a punching means for punching an article, a strain measuring means for detecting the strain amount of the resin molded product, and a recording means for recording the strain amount detected by the strain measuring means. A drill, a rotating portion that rotates around the central axis of the drill, a holding portion that fixes the resin molded product so that the perforated portion is located on the central axis, the rotating portion, and the holding portion. A residual stress measuring device including a drive unit for advancing or retreating at least one of them along a central axis of the drill.

According to the present invention, the residual stress at a predetermined position of the resin molded product can be measured more accurately. Therefore, it is possible to change the product design in consideration of the influence, which can lead to effective reduction of the residual stress inside the resin molded product.

FIG. 1 is a plan view showing a plane perpendicular to the direction in which the residual stress is measured in the resin molded product, and FIG. 1A is a view showing the positional relationship between the strain measuring portion and the perforated portion, and FIG. (B) is a diagram showing the positional relationship between the strain measuring means and the perforated portion. FIG. 2 is a side sectional view of the resin molded product showing the positional relationship of each numerical value used for measuring the strain amount, and FIG. 2 (a) is a view showing the resin molded product before drilling. b) is a figure which shows the resin molded article after drilling. FIG. 3 is a graph showing the results of measuring the amount of strain for each axis of the 3-axis strain gauge in Example 1. FIG. 4 is a graph showing the results of measuring the amount of strain for each axis of the 3-axis strain gauge in Example 2. FIG. 5 is a graph showing the results of measuring the amount of strain for each axis of the 3-axis strain gauge in Comparative Example 1. FIG. 6 is a graph showing the results of measuring the amount of strain for each axis of the 3-axis strain gauge in Comparative Example 2. 7 (a) and 7 (b) are polarizing microscope photographs of the microstructure in the cross section of the perforated portion of the resin molded product in Example 2, of which FIG. 7 (b) is FIG. 7 (b). It is an enlarged photograph of the frame enclosure part of a). 8 (a) and 8 (b) are polarizing microscope photographs of the microstructure in the cross section of the perforated portion of the resin molded product in Comparative Example 3, of which FIG. 8 (b) is a diagram. It is an enlarged photograph of the frame enclosure part of 8 (a).

Hereinafter, one embodiment of the present invention will be described in detail, but the present invention is not limited to the following embodiments, and may be carried out with appropriate modifications within the scope of the object of the present invention. can.

In the present embodiment, a perforated portion is provided in the resin molded product to be measured, and the strain is released when the perforated portion is drilled with a drill, resulting in a change in the amount of strain on the surface of the resin molded product (due to perforation). The amount of strain released) is measured by a strain measuring means, and the change in the amount of strain is converted into stress to obtain the residual stress at a predetermined position inside the resin molded product. Here, before measuring the residual stress, a preliminary drilling step of advancing the drill from the surface to the pre-drilling depth position to drill the resin molded product, and then retracting the drill to remove the resin molded product from the resin molded product, and pre-drilling. _{The first strain amount ε 1} detected when the process is completed and the second strain amount ε detected _{when the first strain amount ε 1} is allowed to stabilize after the preliminary drilling process is completed or after that. It is characterized in that at least a drilling condition setting step for setting the number of rotations of the drill and the feed rate of the drill is performed so that the strain amount difference Δε, which is the absolute value of the difference from _{2, is 50 μst or less.} As a result, the state of generation of distortion of the resin around the perforated portion due to the heat generated by the drill and the influence on the change are suppressed, so that the residual stress of the resin molded product can be measured accurately. In the following, first, the resin molded product will be described.

<Resin molded product>
The resin molded product of the present embodiment (hereinafter, also simply referred to as “molded product”) is a target for measuring residual stress and has a predetermined thickness. This resin molded product is provided with a strain measuring portion and a perforated portion. Preferably, the perforated portion and the strain measuring portion are provided on a surface perpendicular to the thickness direction of the resin molded product, respectively, and the perforated portion is configured to perforate the resin molded product in the thickness direction and is strained. The measuring unit is configured to measure the amount of strain (hereinafter, also referred to as “release strain amount”) generated by releasing the stress inside the resin molded product by this drilling. Further, the strain measuring unit is configured to measure the first strain amount ε ₁ and the second strain amount ε ₂ generated perpendicularly to the thickness direction in the drilling condition setting step described later.

This embodiment is particularly effective when the resin molded product is an injection-molded product of a crystalline thermoplastic resin. When molding a thermoplastic resin by injection molding, cooling generally proceeds quickly near the surface of the molded product, and cooling progresses relatively slowly inside the molded product, so that the molten resin injected into the mold solidifies. It progresses unevenly. As a result, inside the molded product, the molten resin solidifies while being pulled by the shrinkage of the resin near the surface of the molded product that has solidified earlier, so that tensile stress is generated. On the other hand, in the vicinity of the surface of the molded product, compressive stress is generated because the resin after solidification is pulled by shrinkage when the molten resin inside the molded product solidifies.

In an actual resin molded product, the stress distribution does not always have a clear compression-tension relationship depending on the shape and molding conditions, but what kind of stress and distribution state are, resin molding If the residual stress distribution in a predetermined region can be accurately grasped and the residual stress at a predetermined position can be accurately grasped inside the product, the deformation and fracture of the molded product due to it can be more accurately grasped. Predicting can lead to countermeasures.

The resin molded product used in this embodiment has a predetermined thickness. Here, the present embodiment refers to a predetermined position (for convenience, a region specified by a perforated portion and a strain measuring portion described later) in the resin molded product in the thickness direction, that is, the thickness. The directional position is specified by the bottom of the hole in the perforation, and the surface position is specified by the strain measuring part, eg, the center of the strain measuring means) and the residual stress in a predetermined region with respect to the thickness direction. Find the residual stress distribution.

Any resin molded product has a thickness in all directions, but the method of determining the thickness direction is not particularly limited, and a desired direction in the resin molded product can be set in the above-mentioned thickness direction. can.

FIG. 1 is a plan view showing a plane of a resin molded product having a predetermined thickness extending in the z direction, which is perpendicular to the direction in which the residual stress is measured. As shown in FIG. 1A, the resin molded product used in the present invention includes a perforated portion for perforating the resin molded product in the thickness direction on a surface perpendicular to the thickness direction, and the perforated portion when perforated. An example can be illustrated of one provided with a strain measuring unit for measuring the amount of strain generated on a surface perpendicular to the thickness direction.

In FIG. 1, the perforated portion is provided in the central portion of the surface perpendicular to the thickness direction. The perforated portion is perforated in the thickness direction (z direction in FIG. 1) from the plane having the perforated portion perpendicular to the thickness direction. The perforated portion is represented by a circle in FIG. 1, but it is not necessary to add a pattern or the like to serve as a mark. Further, the perforated portion does not need to be provided at the central portion of the surface perpendicular to the thickness direction, and can be provided at a desired position.

In FIG. 1, three strain measuring portions are provided around the perforated portion. When the perforated portion is perforated along the thickness direction, the amount of strain generated by the stress released by the perforation is measured. Here, the number of strain measuring units is not particularly limited, and may be a single strain measuring unit or may be provided with a plurality of strain measuring units. The positional relationship between the perforated portion and the strain measuring portion is not particularly limited, but as described above, since the amount of strain generated by the stress released by the perforation is measured, the perforated portion and the strain are measured as much as possible from the viewpoint of measurement sensitivity. If the strain measuring part is placed around the drilling part while keeping the measuring part close to each other, considering the shape of the resin molded product and the size of the device and tool used for drilling, within the range that does not impair the workability at the time of drilling. good. In addition, the eccentric residual stress of the strain measuring part can be quantitatively evaluated, and in particular, the value and direction of the maximum principal stress and the value and direction of the minimum principal stress can be evaluated. It is preferable to enclose it in the strain measuring unit of the above, and it is more preferable to enclose it in three strain measuring units from the viewpoint of the accuracy of strain measurement and the ease of data processing.

The thickness of the resin molded product is preferably 1.2 times or less of the drilling diameter (hole diameter). As a result, the measured residual stress can be made more accurate. Further, in the conventional method, the thickness of a thin resin molded product such as 1.2 times or less of the hole diameter (1.2 times or less of the hole diameter of the hole in the 3-axis rosette type strain gauge) remains in the thickness direction. Measuring the stress was outside the guaranteed range of ASTM, and it was difficult to obtain it substantially accurately. In this regard, according to the present embodiment, the residual stress in the thickness direction can be accurately obtained even for the resin molded product having a very thin thickness as described above.

By reducing the thickness of the resin molded product to a predetermined thickness or less, the obtained residual stress value becomes more accurate. If the resin molded product has a line-symmetrical shape with the center in the thickness direction (z direction) as the target axis and the length in the thickness direction is Lz, the thickness is (1/2) Lz from the surface. By obtaining the residual stress distribution up to the vertical position, the residual stress distribution for the entire length Lz in the thickness direction may be obtained. This is because if the resin molded product has a line-symmetrical shape with the center in the thickness direction (z direction) as the target axis, the residual stress distribution is also line-symmetrical.

The resin contained in the resin molded product used in the present embodiment is not particularly limited, and a conventionally known general resin can be used. Further, the resin molded product may contain a plurality of resins. In addition, resin molded products include pigments such as nucleating agents, carbon black and inorganic fired pigments, reinforcing materials such as glass fibers, inorganic fillers such as talc, antioxidants, stabilizers, plasticizers, lubricants and mold release agents. Also included is a resin molded product obtained by adding an additive such as a flame retardant to form a composition imparted with desired properties.

As described above, since this embodiment can be applied regardless of the type of resin material, it can be preferably used when an appropriate material is selected from a plurality of candidate resin materials. Further, by obtaining and comparing the residual stresses of a plurality of resin materials by the same method, the difference in the residual stresses of the resin materials can be evaluated more accurately.

The resin molded product may be molded by any molding method and may have any usage history, but a resin molded product molded by an injection molding method in which residual stress is likely to occur is particularly preferable. It is effective. Further, as the resin molded product used in the present invention, a product molded under desired conditions can be used.

The resin molded product may be provided with a perforated portion and a strain measuring portion on the surface, and even if it is made of a single resin, it may be laminated or composited with a plurality of resins or resins and other materials. You may be there. Further, the resin molded product may have a shape in which shapes such as a flat shape, a curved shape, and a refracted shape are combined, and may have any shape.

The resin molded product is configured so that the strain amount of the resin molded product can be detected by a strain measuring means, and then the perforated portion is drilled in the measurement of the residual stress described later. As an example, a strain gauge, which is a strain measuring means, is attached to the surface of a strain measuring portion of a resin molded product, and then the drilled portion is drilled in the residual stress measurement described later. .. Here, as the strain measuring means, it is preferable to use a strain gauge, and it is more preferable to use a multi-axis gauge having two or more axes (for example, a rosette type three-axis strain gauge). The strain measuring means is preferably attached to each surface of the strain measuring portion of the resin molded product.

<Measurement of residual stress on resin molded products>
The residual stress measuring method of the present invention is a method of measuring a resin molded product in a state where a strain measuring means is provided on the surface of the resin molded product before the main drilling step of drilling the drilled portion with a drill to measure the release strain amount. The perforated portion is detected when the pre-drilling step of advancing the drill from the surface of the resin molded product to the pre-drilling depth position to perforate and then retracting the drill to remove it from the resin molded product and the pre-drilling process are completed. The strain amount which is the absolute value of the difference between the first strain amount ε _{1 to be formed and the second strain amount ε 2} detected at the time when the strain amount is allowed to stabilize after the preliminary drilling process is completed or after that. It has at least a drilling condition setting step of setting at least one of the number of rotations and the feed rate of the drill in the main drilling step as a drilling condition so that the difference Δε is 50 μst or less. By performing perforation in the main perforation step under the perforation conditions set in this way, the influence of heat generated during perforation on the state of crystallization and strain of the resin is suppressed, so that the residual stress inside the resin molded product can be reduced. It can be measured accurately.

The drill used in the present invention does not only refer to a so-called drill used for general drilling, but may be a milling cutter such as an end mill, and is used for drilling a resin molded product using a drilling machine, a milling machine, a machining center, or the like. The tool is not particularly limited as long as it can be used. Since a drill is a tool for drilling by cutting or grinding by rotating a blade with respect to a resin molded product, heat generation and pressurization are likely to occur during drilling. As described above, the heat generation and pressurization during drilling affect the crystallization and strain state of the resin molded product, and eventually the residual stress, which can reduce the measurement accuracy of the residual stress. From the viewpoint of suppressing the influence on such residual stress, a preliminary drilling step and a drilling condition setting step are performed.

Hereinafter, the preliminary drilling step and the drilling condition setting step in the residual stress measuring method of the present invention will be described.

[Preliminary drilling process]
In the pre-drilling step, the drill is rotated and advanced at a predetermined rotation speed and feed rate to drill the drilled portion of the resin molded product from the surface of the resin molded product to the pre-drilling depth position, and then the drill is retracted. This is the process of removing the drill from the hole. Here, when the drill is advanced and drilled in the preliminary drilling step, it is preferable to advance the drill at a constant feed rate for drilling. Further, the preliminary drilling depth position for drilling in the preliminary drilling step is preferably a depth position in the range of 0.01 mm or more and 0.50 mm or less from the surface of the resin molded product, and 0.05 mm from the surface of the resin molded product. It is more preferably at a depth position of 0.30 mm or more, and particularly preferably at a depth position of 0.10 mm or more and 0.20 mm or less from the surface of the resin molded product. Further, when the drill is removed from the hole, the drill may be rotated in the same rotation direction as at the time of drilling, may be rotated in the reverse direction, or may be stopped. Among them, from the viewpoint of minimizing the influence on the amount of strain due to the extra load applied to the resin, when removing the drill from the hole, it is preferable to retract the drill at the same speed as the feed rate at the time of drilling. .. At this time, it is more preferable to retreat while rotating in the direction opposite to that at the time of drilling at the same rotation speed and the same feed rate as at the time of drilling.

Hereinafter, an example of the preliminary drilling process will be described in detail with reference to the drawings.

FIG. 2A shows a resin molded product before drilling. Here, the resin molded product 1 has a length Lz along the z direction, and has a cylindrical shape having an xy cross section having a radius R. As shown in FIG. 1B, the upper end surface 11 of the resin molded product 1 has a circular radius R. The upper end surface 11 is provided with a perforated portion 111 and strain measuring means 112, 112, 112.

As shown in FIG. 2B, the perforated portion 111 has a circular radius r and is provided at the center of the upper end surface 11. As will be described later, the perforated portion 111 is a portion that is perforated along the thickness direction (z direction). The shape and size of the perforated portion 111 are not particularly limited, and can be appropriately changed to a desired shape and size.

Here, when a 3-axis rosette type strain gauge is used as the strain measuring means, the strain measuring means 112, 112, 112 for measuring the strain for each axis are around the perforated portion 111 as shown in FIG. 1 (b). Is provided at intervals of, for example, 90 °, 135 °, and 135 °. Here, the strain measuring means 112, 112, 112 are portions (length (Rr)) of the upper end surface 11 excluding the perforated portion 111, which is generated when the perforated portion 111 is perforated in the thickness direction (z direction). ) Part) is configured so that the amount of strain can be measured (hereinafter, the part of length (Rr) may be referred to as "the part for measuring the amount of strain"). In the present embodiment, the strain measuring means 112, 112, 112 are provided in the strain measuring unit. The strain measuring unit is not limited to the strain measuring means as described above, and may be another strain measuring means capable of measuring the amount of strain of the upper end surface 11 generated when the perforated portion 111 is perforated. ..

As another strain measuring means, for example, a method of indirectly measuring the strain amount by using a correlation system that calculates the strain amount by image analysis of the deformation of the surface of the resin molded product may be used. .. Further, when the position for measuring the amount of strain is not flat, a conventionally known three-dimensional image analysis means may be used as the strain measuring means. For example, in a correlation system, it is possible to perform three-dimensional measurement by combining two imaging devices.

FIG. 2B shows a cross-sectional view of the resin molded product after drilling in the preliminary drilling step. FIG. 2B shows an example in _{which the drilling portion 111 is drilled to a drilling depth z 2} in the thickness direction (z direction) in the preliminary drilling step.

Here, when the drill is advanced and drilled at a constant feed rate, and the drill is retracted and removed from the hole at the same rate as the feed rate at the time of drilling, the time when the preliminary drilling process is completed (the drill is formed). The drilling depth is divided by the drill feed speed to calculate the drill advance time, and by doubling this, the drilling time including the drill retreat time is calculated. The time point at which the drilling time elapses from the time point at which drilling in the preliminary drilling step is started can be grasped as the time point at which the preliminary drilling process is completed. Further, when drilling with a drill, the detection value of the strain measuring means often fluctuates greatly due to the influence of the vibration of the drill during drilling. Therefore, the data is obtained from the result of recording the detected value of the strain measuring means over time. These may be grasped by reading the drilling start time and the drilling completion time based on the start time and the end time of the region where the fluctuation range of is large and unstable.

To perform the above drilling, a drill, a rotating portion that rotates around the central axis of the drill, and a holding portion that fixes the resin molded product so that the drilled portion is located on the central axis of the drill. A drilling device including a driving unit for advancing or retreating at least one of the rotating portion and the holding portion along the central axis of the drill can be used, and it is preferable to use the same device as the residual stress measuring device described later. ..

[Punching condition setting process]
_{In the drilling condition setting step, after obtaining the first strain amount ε 1} detected by the strain measuring means when the preliminary drilling step is completed, the resin molded product is allowed to stand while the strain measuring means continues to measure the strain amount. and, seeking second strain amount epsilon ₂ distortion amount detected is detected in the stable when or after the absolute value of the first strain of epsilon ₁ and a second strain of epsilon ₂ of the difference strain This is a step of calculating the quantity difference Δε and setting at least one of the drill rotation speed and the feed speed in the main drilling step described later so that the strain amount difference Δε is 50 μst or less. This makes it possible to perform drilling under drilling conditions that suppress heat generation and pressurization, which can affect the crystallization and strain state of the resin molded product. It can be measured well.

Here, the internal strain of the resin molded product remaining between the surface of the resin molded product and the position of the preliminary drilling depth is released at the time of drilling to the drilling depth in the drilling condition setting step, and is released in the preliminary drilling and drilling step. Is detected as the first strain amount ε _{1 at the time of completion.} The strain amount of the resin molded product after drilling should be stable unless additional heat or load is applied to the resin molded product after drilling. Therefore, the first strain amount ε normally measured at the completion of drilling. _{It is considered that 1 is equivalent to the second strain amount ε 2} measured after being allowed to stand after the completion of drilling (the strain amount difference Δε is close to zero). However, if the number of rotations of the drill is excessively high or the feed rate of the drill is excessively high, heat may be generated in the perforated portion of the resin molded product due to friction with the drill, or the resin molded product may be pressurized by the drill. Therefore, the state of crystallization and strain of the resin molded product is affected by it. In particular, when the resin in the perforated portion melts due to heat generation, the amount of strain changes significantly during the cooling and solidification process, so the difference between _{the first strain amount ε 1} at the time of completion of perforation and the second strain amount ε _{2 after standing.} The strain difference Δε, which is the absolute value of, can be large.

In such a case, since an error occurs in the measurement of the residual stress due to the change in the strain amount in the drilling portion, the above-mentioned heat generation and pressurization are not generated by the drilling in the main drilling step, that is, the strain amount difference Δε is small. More specifically, it is necessary to set the drilling conditions (at least one of the drill rotation speed and the feed rate) so that the strain amount difference Δε is 50 μst or less. Here, the strain amount difference Δε is preferably 40 μst or less, more preferably 30 μst or less, and further preferably 20 μst or less.

_{The measurement of the first strain amount ε 1} and the second strain amount ε ₂ in the drilling condition setting step is performed by the strain measuring means. As the strain measuring means, the same strain measuring means as that used for measuring the residual stress inside the resin molded product after setting the drilling conditions may be used.

Explaining FIG. 2B as an example, the length (Rr) in the portion where the amount of strain is measured is actually ( _Rr + δ r2) due to the drilling in the preliminary drilling step described above, so that the strain is strained. A strain of quantity δ _{r2 occurs.} The strain amount δ _r2 is measured using the strain measuring means 112, 112, 112. Here, in the measurement of the strain amount δ _{r2 , the first strain amount ε 1} is measured when the preliminary drilling step is completed, and then the second strain amount ε is measured when the detected strain amount becomes stable or thereafter. _Make the measurement of 2. Then, the strain amount difference Δε, which is the absolute value of the difference between the first strain amount ε ₁ and the second strain amount ε _{2, can be obtained.}

At this time, as described above, it is preferable to install a plurality of strain gauges around the perforated portion, such as by using a multi-axis gauge having two or more axes as the strain measuring means. In this case, the perforation condition setting step is described above. The first strain amount ε ₁ , the second strain amount ε ₂ , and the strain amount difference Δε, which is the absolute value of the difference between them, are obtained for each strain gauge (for each axis in the case of a multi-axis gauge), and the strain is obtained. The drilling conditions (drill rotation speed and / or drill feed rate) in this drilling process are set so that the strain amount difference Δε obtained for each gauge (for each axis in the case of a multi-axis gauge) is 50 μst or less. It is preferable to set it. Also, when a strain measuring means other than the strain gauge is used, the drilling conditions (drill rotation speed and / or drill feed rate) in the main drilling step are such that the strain amount difference Δε in the measurement direction is 50 μst or less. ) Is preferably set. As a result, the accuracy of the set strain amount difference Δε is improved, so that heat generation and pressurization due to drilling in the main drilling step can be made less likely to occur.

_{Further, the timing for measuring the second strain amount ε 2} in the drilling condition setting step is performed when the preliminary drilling step is completed, the first strain amount ε ₁ is measured, and then the strain is allowed to stand until the strain amount becomes stable. At this time, due to the influence of the measurement environment and the sensitivity of the strain measuring means, minute fluctuations in the amount of strain (for example, fluctuations of ± 5 μst or less) continue to occur even after standing, and the fluctuations in the detected value are complete. May not be zero. In this case, it is assumed that the strain amount is stable at the time of shifting to the minute fluctuation, and the median value of the fluctuation width at that time may be _{set to the second strain amount ε 2.} Further, when the resin molded product was allowed to stand while the strain amount measurement by the strain measuring means was continued and the strain amount fluctuation range was ± 5 μst or less for the first time for 1 minute (that is, the maximum value of the strain amount). After the absolute value of the difference between the minimum values becomes 10 μst or less, the amount of strain is 30 seconds before that (when 1 minute elapses for the first time without the absolute value of the difference exceeding 10 μst). It is assumed that the strain is stable, and the strain amount at that time may be _{the second strain amount ε 2.} At this time, the fluctuation range of the strain amount is ± 5 μst or less for a total of 1 minute, at least 30 seconds before and after the time when the strain amount stabilizes. The average value of the strain amount for a total of 1 minute may be _{the second strain amount ε 2.} In order to suppress the influence of such minute fluctuations in the detected value, it is preferable to stop the rotating portion and the driving portion when the resin molded product is allowed to stand still.

Generally, the higher the number of rotations of the drill and the feed rate of the drill, the shorter the time required for drilling. Therefore, those skilled in the art who intend to measure the residual stress of the resin molded product by using the drilling method can drill them. There is a tendency to set the conditions as high as the workability allows. On the other hand, in the present invention, by lowering at least one of the rotation speed and the feed rate of the drill, the strain amount difference Δε tends to be reduced and the measurement accuracy of the residual stress tends to be improved. Therefore, in order to surely obtain the effect of the present invention, contrary to the usual case, it tends to approach the condition that requires time for drilling, so that it may take time to measure the residual stress. Therefore, particularly from the viewpoint of shortening the measurement time of the residual stress, it is preferable to increase at least one of the rotation speed and the feed rate of the drill as much as possible within the range in which the strain amount difference Δε can be suppressed to 50 μst or less. Alternatively, it is also preferable to apply the present invention in situations such as design optimization in trials at the development stage.

Here, the drilling conditions (drill rotation speed and / or drill feed rate) for setting the strain amount difference Δε to be 50 μst or less differ depending on the shape of the resin molded product and the type of resin used, but are described above. From this tendency, those skilled in the art can appropriately set the drilling conditions in which the strain amount difference Δε is 50 or less by a finite number of trials. As a specific example of the drilling conditions preferable from the viewpoint of reducing the strain difference Δε, the rotation speed of the drill is preferably 100 rpm or less, more preferably 75 rpm or less, further preferably 50 rpm, and 30 rpm. It is particularly preferably less than or equal to, and most preferably 20 rpm or less. Further, the feed rate of the drill is preferably 4.0 mm / min or less, more preferably 3.0 mm / min or less, further preferably 2.0 mm / min or less, and 1.0 mm / min or less. It is particularly preferably min or less, and most preferably 0.5 mm / min or less.

Further, the above drilling conditions do not have to be fixed to a constant drilling condition as long as the strain amount difference Δε is set to be 50 μst or less. For example, at least one of the rotation speed and the feed rate of the drill may be changed in consideration of the outside air temperature, heat storage in the drill and the drilling device (particularly during continuous processing), and the like.

In the present embodiment, from the viewpoint of more efficiently setting the drilling conditions, the temperature of the drilling portion is measured by using a sensor built in or separately prepared in a drill or a drilling device during the above-mentioned preliminary drilling process. Then, in the subsequent drilling condition setting step, the drilling condition is changed by lowering at least one of the drill rotation speed and the feed speed so that this temperature becomes equal to or lower than the glass transition temperature of the resin constituting the resin molded product. It is also preferable to do so. Here, when a composition containing a plurality of resin components is used as the resin, the glass transition of the resin having the highest content (the resin having the lower glass transition temperature when the contents are the same) is transferred to the glass. The drilling conditions may be set based on the temperature.

[Main drilling process]
In the present embodiment, the residual stress is measured by the drilling method, and as the main drilling step, at least one of the drilling speed and the feed rate set by the drilling condition setting step described above is used. , Further drill the holes provided in the preliminary drilling step. By further drilling the same holes as in the preliminary drilling step and measuring the residual stress, the main drilling process is performed under the suitable drilling conditions obtained for the holes provided in the preliminary drilling step, so that the residual stress is measured with higher accuracy. can do.

In this drilling step, a drill, a rotating portion that rotates around the central axis of the drill, a holding portion that fixes the resin molded product so that the drilling portion is located on the central axis, and a rotating portion and a holding portion. A device including a drive unit for advancing or retreating at least one of them along the central axis of the drill as a drilling means can be used. This device detects the above-mentioned drilling means for drilling a resin molded product by rotating a drill and the amount of strain of the resin molded product from the viewpoint of performing the main drilling step and the residual stress measuring step described later with one device. It is preferable to configure a residual stress measuring device having a strain measuring means and a recording means for recording the amount of strain detected by the strain measuring means. Here, as the drilling means, a so-called drilling machine, milling machine, machining center, or the like can be used. In particular, as described above, the drilling conditions in the present invention are conditions that are not normally set by those skilled in the art, and therefore, if necessary, drilling is provided in at least one of the rotating portion and the driving portion. It is also preferable to use an apparatus.

[Residual stress measurement process]
In the residual stress measuring step, the strain amount (release strain amount) released when the above-mentioned main drilling step is performed is measured by a strain measuring means, and the residual stress inside the resin molded product is calculated from the obtained release strain amount. This is the desired process.

Here, when measuring the residual stress by the drilling method, it is preferable to obtain the internal residual stress in the thickness direction of the resin molded product. As an example, the amount of strain in the resin molded product when the perforated portion is perforated to the first perforation depth in the thickness direction is measured by a strain measuring means, and the obtained strain amount is used to reach the first perforation depth. The first stress measurement step that measures the first stress generated in the resin molded product by drilling, and the strain in the resin molded product when the drilled part is drilled to a second drilling depth different from the first drilling depth in the thickness direction. A second stress measurement step of measuring the amount and using the obtained strain amount to measure the second stress generated in the resin molded product by drilling to the second drilling depth, and subtracting the first stress from the second stress. By performing a residual stress calculation step of calculating the difference obtained as a residual stress at an intermediate depth between the first drilling depth and the second drilling depth, the residual stress at a predetermined position of the resin molded product can be measured. It is what you do. Further specific examples will be shown for each of the above steps.

(First stress measurement process)
Of these, the first stress measuring step includes the case where no drilling is performed. If no perforations are made, the first perforation depth will be zero. That is, the first drilling depth is 0 or more. In particular, when no drilling is performed, the strain amount (δ _r1 ) becomes 0, and the stress released from the resin molded product by drilling also becomes 0, so that the first stress becomes 0.

Hereinafter, a case where the first drilling depth z ₁ is 0 using a resin molded product will be described. When the first drilling depth z ₁ is not 0, the stress obtained by the same procedure as the second stress measuring step below becomes the first stress.

(Second stress measurement process)
In the second stress measuring step, the strain measuring section measures the amount of strain of the resin molded product when the drilled portion drilled in the first stress measuring step is further drilled to a predetermined second drilling depth in the thickness direction. Using the obtained strain amount, the second stress generated in the resin molded product by drilling to the second drilling depth is measured.

In the measurement of the amount of strain in the second stress measurement process, in order to avoid erroneous detection due to vibration of the drilling tool, etc., the resin molded product is measured after the tool is detached from the resin molded product or after the tool is completely stopped. Wait for the condition to stabilize. That is, the strain amount measured in the second stress measuring step can be measured in the same manner as _{the second strain amount ε 2 in the above-mentioned drilling condition setting step.}

The amount of strain obtained by measurement can be converted into stress by a conventionally known method. For example, the strain measuring means 112, 112, 112 provided on the upper end surface 11 of the resin molded product 1 can be connected to an electric resistance wire strain gauge and converted into the stress generated at the time of drilling. That is, when the perforated portion is perforated in the thickness direction, the internal stress of the resin molded product released from the resin molded product can be obtained. The stress obtained here is referred to as the second stress.

(Residual stress calculation process)
In the residual stress calculation step, the difference between the first stress and the second stress of the resin molded product is calculated. For example, the difference obtained by subtracting the first stress (including 0 in this embodiment) from the second stress is calculated as the residual stress at the depth between the perforated portion and the first perforated depth. .. Hereinafter, the residual stress here may be referred to as a first residual stress, and the step of calculating the first residual stress may be referred to as a first residual stress calculation step.

According to the present embodiment, the residual stress at a desired depth can be obtained by adjusting the first drilling depth and the second drilling depth. That is, the residual stress at a desired position in the resin molded product can be obtained. Further, even when the residual stress at the same depth is obtained, the accuracy of the required residual stress can be adjusted by adjusting the distance between the first drilling depth and the second drilling depth. Among them, from the viewpoint of increasing the accuracy of the required residual stress, it is preferable that the distance between the first drilling depth and the second drilling depth is short.

Further, in the residual stress measuring method in the present embodiment, it is preferable that the thickness of the resin molded product is small. By reducing the thickness of the resin molded product, the distance between the first drilling depth and the second drilling depth in the thickness direction is inevitably shortened, so that the strain amount can be measured accurately, and the strain amount can be measured accurately. The measurement accuracy of the stress obtained from the above can also be improved. More specifically, the thickness of the perforated portion of the resin molded product is preferably 1.2 times or less the diameter of the perforated hole.

On the other hand, even if the thickness is large, if the resin molded product has a shape symmetrical in the thickness direction (z direction), the residual stress is also symmetrical in the thickness direction (z direction), so that resin molding If the product has a line-symmetrical shape with the center in the thickness direction (z direction) as the target axis, the residual stress up to half (Lz / 2) of the length (Lz) in the thickness direction is measured. This makes it possible to estimate the residual stress at a deeper position on the opposite side of the target axis.

Following the above residual stress measuring method, drilling deeper third drilling depth z _3, in the same manner as the second stress measurement step with the residual stress measuring method, the third stress generated in the resin molded article The difference between the third stress measuring step to be measured and the difference obtained by subtracting the second stress from the third stress is the second at the intermediate depth between _{the second drilling depth z 2} and the third drilling depth z _3. It can also be calculated as the residual stress, and by repeating this, the residual stress distribution in the thickness direction (z direction) of the resin molded product can be derived.

<Examination of molding materials>
By using the residual stress derived by the residual stress measuring method of the present embodiment, it is possible to derive the residual stress at a predetermined position inside the resin molded product in the resin molded product obtained by molding an arbitrary resin material. .. Further, even in a resin molded product obtained by molding an anisotropic material, the anisotropy of residual stress can be quantitatively evaluated with higher accuracy by calculating the amount of strain in three directions. Here, the resin molded product may be a colored product containing a colorant or a non-colored product containing no colorant. By comparing the residual stress of resin molded products made of different resin materials, it is possible to compare the likelihood of residual stress due to the difference in resin material, so the residual stress can be reduced by changing the resin material (molding material). It can be connected to the examination of.

<Effects in examining molding conditions>
By using the distribution of residual stress derived by the residual stress measuring method of the present embodiment, preferable injection molding conditions can be easily determined. That is, by using the present invention, molding conditions with less residual stress can be easily determined. The molding conditions determined by using the residual stress measuring method of the present invention preferably affect the residual stress inside the resin molded product. Here, examples of molding conditions that affect the residual stress inside the resin molded product include injection speed, mold temperature, and the like.

<Effects in examining the shape of molded products>
Injection molding is a molding method suitable for producing a molded product having a complicated shape. Therefore, there are many injection-molded products having complicated shapes. In particular, in a resin molded product having an uneven thickness portion or a weld portion, molding shrinkage is promoted or suppressed depending on the shape. Therefore, when a complicated shape is formed, the part having a complicated shape has a residual stress distribution with other parts. Is different.

Even when using a cutting piece from which such a complicated shape (the part where the shape changes with respect to the strain measurement part) is used, the residual stress due to shrinkage in the thickness direction and the residual stress due to the shape of the molded product are distinguished. It can be measured, and the measurement direction of the residual stress distribution can be set in various directions. Therefore, according to the method of the present invention, it is possible to derive the residual stress distribution by separating the part having a complicated shape and the other part, and to obtain the difference in the residual stress distribution depending on the thickness of the molded product. ..

Therefore, this embodiment is also useful at the stage of examining the shape in the design of a molded product, etc., and as a technique for predicting residual stress by combining the data of a desired material together with the examination of the above injection molding conditions. It can also be used. As for the existing molded product, a resin molded product having a small residual stress can be easily produced, and it can also be used for failure analysis of the molded product.

The secondary processing referred to here is a processing for relaxing the residual stress inside the resin molded product. Annealing treatment can be mentioned as a method for relaxing the residual stress inside the resin molded product. Conventionally, the usefulness of the effect of the annealing treatment has not been quantitatively evaluated. However, by the residual stress measuring method of the present invention, the residual stress distribution inside the resin molded product before and after the annealing treatment can be derived, so that the change in the residual stress due to the annealing treatment can be confirmed. As a result, according to the present invention, the usefulness of the effect of the annealing treatment can be quantitatively evaluated, and further, preferable treatment conditions for the annealing treatment can be easily determined. As described above, the usefulness of the secondary processing of the resin molded product can be quantitatively evaluated by the residual stress measuring method of the present invention.

In addition, according to the residual stress measuring method of the present invention, when using a resin molded product, the material, shape, molding conditions, and secondary processing of the molded product are used so that the residual stress does not become a problem or becomes as small as possible. It is possible to accurately perform product design such as setting related to resin molded products such as. Further, when using the product, it is possible to accurately prevent the failure by performing a short-term or long-term fracture analysis based on the residual stress of the product.

Hereinafter, examples will be shown and the present embodiment will be specifically described, but the present embodiment is not limited to this example.

<Preparation of resin molded products>
As the resin molded product, a polyacetal resin DURACON (registered trademark) M90-44 manufactured by Polyplastics Co., Ltd. is used as a material, and injection molding is performed under standard molding conditions to obtain a flat resin molded product of 100 mm × 100 mm × 3 mm. (6 mm × 3 mm side gate) was prepared and used as a measurement target.

<Preliminary drilling and setting of drilling conditions based on it>
A perforated portion for perforating with a drill (model number "RS-200", manufactured by Vishay Co., Ltd.) is provided in the center of one side of this resin molded product of 100 mm × 100 mm, and the perforated portion is surrounded as a strain measuring means. 3-axis strain gauge (one gauge length 2 mm (overall strain gauge radius D = 5.13 mm), model number "FRS-2-11", Tokyo (Made by Measuring Instruments Research Institute) is attached.

Next, a rotating portion that rotates around the central axis of the drill, a holding portion that fixes the resin molded product so that the perforated portion is located on the central axis, and a rotating portion that advances or advances along the central axis of the drill. The resin molded product was fixed to a holding portion of a machining center provided with a driving portion for retracting and a drilling means having the same, and the drill was attached to the rotating portion. At the same time, the strain gauge attached to the resin molded product was connected to a data logger (“UCAM-60B”, manufactured by Kyowa Electric Co., Ltd.), which is a recording means for recording the amount of strain detected by the strain gauge.

Subsequently, after setting the number of rotations of the drill and the feed rate of the drill to the respective drilling conditions described later, the drill is advanced while rotating, and the drilled portion of the resin molded product is spared 0.2 mm from the surface. It was drilled to the drilling depth position. At this time, the drilling diameter (hole diameter) was 1.7 mm. That is, when the tip of the drill reaches 0.2 mm in the thickness direction from the surface of the molded product, while measuring the amount of strain with a strain gauge, the drill is rotated in the opposite direction at the same number of rotations as described above. The drill was detached from the hole of the perforated portion by retreating at the same feed rate as the above, and the resin molded product was allowed to stand while continuing to measure the amount of strain with the strain gauge. From the data recorded in the data logger, the first strain amount ε ₁ which is the amount of strain when the drill is removed from the hole of the drilled part and the state where the fluctuation range of the strain amount is ± 5 μst or less for 1 minute for the first time. based on the time and maintained for, was measured with a second strain of epsilon ₂ is a distortion amount at the time the amount of distortion in the 30 seconds before is determined to be stable, the. At this time, as a data logger, a data logger capable of recording the strain amount of each axis (ch1, ch2, and ch3, respectively) of the 3-axis strain gauge over time was used, and the strain amount of each axis (ch) was grasped in real time. .. Then, the resin molded product was allowed to stand while continuing the measurement until all the strain amounts of the above shafts became stable, and the value of the strain amount at the time when the strain amount became stable was set to the second strain amount ε ₂ . .. Further, the absolute value of the difference between the obtained first strain amount ε ₁ and the second strain amount ε ₂ was obtained, and this was defined as the strain amount difference Δε.

In this embodiment, the rotation speed of the drill and the feed rate of the drill are set as shown in Table 1, and the first strain amount under each condition is obtained from each data (FIGS. 3 to 6) recorded in the data logger. ε ₁ and the second strain amount ε ₂ were obtained, and the strain amount difference Δε in each axis was calculated. The results are shown in Table 1. Here, in FIGS. 3 to 6, the vertical axis represents the strain amount of each axis (ch1 to 3) measured by the 3-axis strain gauge, and the horizontal axis represents the elapsed time from the start of drilling. In addition, the time indicated by the downward arrow (↓ mark) in each figure is the time when drilling is completed, and the time indicated by the upward arrow (↑ mark) is the time when the amount of strain stabilizes after standing. The strain amounts are the first strain amount ε ₁ and the second strain amount ε ₂ , respectively. In the case where the fluctuation of the strain amount does not become completely zero even after the time indicated by the upward arrow, the average value of the strain amount for 30 seconds (1 minute in total) before and after the time indicated by the upward arrow is used. The second strain amount was ε ₂ .

By setting the rotation speed and feed rate of the drill so that the strain amount difference Δε is all 50 μst or less, an error due to the fluctuation of the strain amount after drilling is less likely to occur, so that the residual stress can be accurately adjusted. It becomes possible to measure.

<Observation of microstructure of perforated part>
With respect to the resin molded product perforated in Example 2 above, a sample was cut out from the cross section of the perforated portion of the resin molded product into strips having a thickness of 10 μm using a microtome (“RM2265” manufactured by Leica), and this sample was obtained. The fine structure of the perforated portion in the above was observed using a polarizing microscope (“BH-2” manufactured by Olympus Corporation). Further, as Comparative Example 3, a resin molded product perforated at high speed under the same conditions as in Example 1 except that the rotation speed of the drill was 4000 rpm and the feed rate of the drill was 1.2 mm / min was similarly perforated. The microstructure of the part was observed. FIG. 7 shows a polarizing micrograph in which the microstructure in the cross section of the perforated portion of Example 2 was photographed, and FIG. 8 shows a polarizing micrograph in which the microstructure in the cross section of the perforated portion of Comparative Example 3 was photographed.

As a result, in the resin molded product of Example 2, as shown in FIG. 7A, the shape along the C surface of the edge of the drill was clearly observed at both ends of the bottom of the drilled portion. On the other hand, in the resin molded product of Comparative Example 3, as shown in FIG. 8A, both ends of the bottom surface of the perforated portion had a gently curved shape. Further, when these were magnified and observed, in the resin molded product of Comparative Example 3, as shown in FIG. 8 (b), a layer structure considered to be a remelted layer was observed on the bottom surface of the perforated portion. In the resin molded product of No. 2, as shown in FIG. 7B, no layer structure was observed on the bottom surface of the perforated portion. Therefore, under the drilling conditions of the comparative example, the resin in the drilled portion is remelted due to heat generated by friction during drilling, and the state of crystallization and strain occurs, while such a change occurs under the drilling conditions of the example. It was found that there was no such difference, and it is considered that this difference leads to the fluctuation of the strain amount immediately after drilling, which is seen in the strain amount difference Δε in Table 1. Therefore, it is measured by performing the drilling condition setting step of setting the drilling condition under the condition that the strain amount difference Δε becomes small, and performing the main drilling step using this drilling condition to measure the strain amount. It is clear that the residual stress can be measured accurately because an error due to the fluctuation of the strain amount immediately after drilling is unlikely to occur in the residual stress.

From the above results, according to the method of the present invention, a pre-drilling step is performed to set a drilling condition so that Δε is 50 μst or less, and a main drilling step is performed using this drilling condition to distort. By measuring the amount, the influence of heat generation during drilling is suppressed, so that the residual stress can be measured accurately.

1 Resin molded product 11 Upper end surface of resin molded product 111 Perforated portion 112 Strain measuring means

Claims (8)

1. A perforated portion is provided in the resin molded product to be measured, the amount of release strain released during the main drilling step of perforating the perforated portion with a drill is measured, and the inside of the resin molded product is obtained from the obtained release strain amount. It is a method of measuring residual stress by the drilling method, which obtains the residual stress in
   Before the main drilling step,
   With the strain measuring means provided on the surface of the resin molded product, the drill is drilled by advancing the drill from the surface to the preliminary drilling depth position, and then the drill is retracted. Preliminary drilling step to remove from the resin molded product
   The first strain amount ε ₁ detected when the pre-drilling step is completed, and the second strain amount ε detected when the strain is allowed to stabilize after the pre-drilling step is completed or after that. A drilling condition setting step of setting at least one of the rotation speed and the feed speed of the drill in the main drilling step so that the strain amount difference Δε, which is the absolute value of the difference from _{2, is 50 μst or less.}
   At least a method for measuring residual stress.
2. In the drilling condition setting step, using a multi-axis gauge having two or more axes, the first strain amount ε ₁ , the second strain amount ε _2, and the strain amount difference Δε are obtained for each axis of the multi-axis gauge. The residual stress measurement according to claim 1, wherein at least one of the rotation speed and the feed rate of the drill in the main drilling step is set so that the strain amount difference Δε obtained for each axis is 50 μst or less. Method.
3. During the pre-drilling step, the temperature of the perforated portion is measured.
   In the drilling condition setting step, at least one of the rotation speed and the feed speed of the drill in the main drilling step is set so that the temperature is equal to or lower than the glass transition temperature of the resin constituting the resin molded product. Item 4. The method for measuring residual stress according to Item 1 or 2.
4. The residual stress measuring method according to any one of claims 1 to 3, wherein the drilling condition setting step is set so that the rotation speed of the drill is 100 rpm or less.
5. The residual stress measuring method according to any one of claims 1 to 4, wherein the drilling condition setting step is set so that the feed rate of the drill is 4.0 mm / min or less.
6. The perforated portion and the strain measuring portion are provided on a surface perpendicular to the thickness direction.
   The perforated portion is configured to perforate the resin molded product in the thickness direction in the pre-drilling step, and
   The strain measuring unit is configured to measure the first strain amount ε ₁ and the second strain amount ε _{2 generated perpendicularly to the thickness direction in the drilling condition setting step.} The method for measuring residual stress according to any one of 1 to 5.
7. The residual stress measuring method is a method for obtaining an internal residual stress in the thickness direction of the resin molded product.
   The main drilling step is
   When the perforated portion is perforated to the first perforation depth in the thickness direction, the amount of strain in the resin molded product is measured, and the obtained strain amount is used to perforate to the first perforation depth. The first stress measurement process that measures the first stress generated in the resin molded product,
   When the perforated portion is perforated to a second perforated depth different from the first perforated depth in the thickness direction, the strain amount in the resin molded product is measured by the strain measuring portion, and the obtained strain amount is measured. A second stress measuring step of measuring the second stress generated in the resin molded product by drilling to the second drilling depth, and a second stress measuring step.
   A residual stress calculation step of calculating the difference obtained by subtracting the first stress from the second stress as a residual stress at an intermediate depth between the first drilling depth and the second drilling depth.
   The method for measuring residual stress according to claim 6.
8. A residual stress measuring device used in the residual stress measuring method according to any one of claims 1 to 7.
   The residual stress measuring device includes a drilling means for drilling the resin molded product by rotating the drill, a strain measuring means for detecting the strain amount of the resin molded product, and a strain amount detected by the strain measuring means. With a recording means to record,
   The drilling means includes the drill, a rotating portion that rotates around the central axis of the drill, a holding portion that fixes the resin molded product so that the drilled portion is located on the central axis, and the rotation. A residual stress measuring device comprising a driving portion that moves at least one of a moving portion and the holding portion forward or backward along a central axis of the drill.
   
   

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