JPH05228956A - Manufacture of slender article - Google Patents

Abstract

PURPOSE:To ensure the accuracy of outside dimensions by a method wherein a plastic molded form is divided into unit structure, the quantity of warpage is predicted regarding each unit structure, the quantity of warpage of unit structure is totalled regarding the whole article and balance in the asymmetric direction is measured. CONSTITUTION:When an asymmetric sectional article having a structure unit consisting of a rib 1 and a main body 2 joined in the longitudinal direction and being made of slender plastics is manufactured through injection molding, bending moment M at both ends of unit structure is obtained by using a distortion factor (n) capable of being predicted on the basis of the thickness R of the rib 1, the thickness S of the main body 2 and the height H1 of the rib 1 the elastic modulus of a plastic material and the dimensions of the rib l and the main body 2. The quantity of warpage D of unit structure is calculated from formula 5 of ML<2>/48EI (L represents the overall length of unit structure and El the sum of the product of the modulus of longitudinal elasticity and the moment of inertia of the section regarding the main body 2 and the rib 1), and the quantity of warpage regarding the whole structure of the asymmetric article is balanced including the factors of a thick-wall section, lightening, a groove, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a warp countermeasure in a method of manufacturing an elongated asymmetric cross-section article by injection molding of plastics. INDUSTRIAL APPLICABILITY The present invention can be applied to plastic molded articles in general, but is particularly useful in the industrial field that requires elongated molded articles of accurate dimensions, for example, in the manufacture of parts such as connector boards for electronic devices.

[0002]

2. Description of the Related Art An example of a connector (hereinafter simply referred to as a connector) substrate for electronic equipment, which is a typical field of use of the present invention, will be described. The connector is usually elongated (50 to 200 mm) compared to its width and height (both are 5 to 20 mm).
It is a box-shaped substrate with many terminals embedded in it. There are two types, a header and a socket, and it is necessary for the outer diameter dimension to be accurate in order to bring the terminals into electrical contact and to exert their functions when they are fitted together.

The connector base has electrical insulation and moldability,
Injection moldings of plastics are generally used in consideration of factors such as price, and engineering plastics (eg, PPS, LCP, polyamide, PBT, PE) are used to meet the requirements for heat resistance, rigidity, and dimensional stability.
T), especially injection molded products reinforced with glass fiber etc. are often used. However, when an article having an elongated box-like structure, such as a connector substrate, is to be obtained by injection molding, warping often occurs due to unequal shrinkage during molding and cooling. Molded products that cannot ensure the accuracy of the outer diameter required for precision equipment parts must be removed as defective products, which requires not only a thorough inspection system, but also a reduction in product yield and product reliability. It causes many problems such as deterioration.

In general, the warpage (hereinafter referred to as warpage) associated with injection molding occurs remarkably in an elongated article having an asymmetric cross section. The cross-section asymmetry is most common in shape, but the essence of the problem is similar when there is asymmetry in material properties. Conversely, design changes such as shortening the length or eliminating asymmetry can be a powerful means of preventing warpage. However, the length, cross-sectional outer shape, and material are determined by the needs of the user, and cannot be freely changed depending on the convenience of the molding person. A general technical method for obtaining an injection-molded product with less warpage within the constraints of the required length, cross-sectional outer shape, and material has not been known.

[0005]

The injection-molded article is designed with a wall thickness that satisfies the strength and other necessary conditions for use based on the outer diameter dimension specified by the user, for example, the connector designer. 1 and 2 are perspective views of a model of such an elongated injection molded product. In reality, two side plates of the shape shown in FIG. 1 are arranged side by side and connected by partition walls, or a basic structure such as a box with end plates at both ends of the shape of FIG. 2 is added with positioning pins and other parts. Although it has a complicated shape, the practical prediction of warpage, which is the object of the present invention, can be approximately considered by a simplified model as shown in the figure.

In FIG. 1, the upper portion is a plate-shaped portion having a smaller thickness than the lower portion, and is called a rib. The lower part has a larger cross-sectional area than the rib, and usually has a width and height that are greater than the thickness of the rib, and is called the main body. The cross section of the main body does not necessarily have to be a quadrangle, but for convenience sake, the case of a quadrangle will be mainly described. Circles, hexagons, and other irregular cross-sections can be approximated by squares. Although FIG. 1 shows an example in which the height of the main body portion is larger than the width, the width and the height may be the same or the width may be larger than the height (FIG. 3). In the cross-sectional shape, the one shown in FIG. 1 is an L-shape in which the rib is located at the end of the main body, but is not limited to this.
For example, it may be convex. If two L-shaped sections are connected to the left and right, a groove-shaped section, that is, FIG. 2 is obtained. In this case, we will call them side plates and bottom plates. Either the side plate or the bottom plate may be thick, and the thicker one can be considered as the main body and the thinner one as the rib. As shown in Fig. 2, when there is almost symmetry in the left-right direction (for convenience, it is referred to as the x-direction), the contraction in the left-right direction that occurs during molding balances as internal stress, and a large strain occurs in the x-direction. Hateful. The same applies to the case where the two shown in FIG. 1 are connected symmetrically by a partition wall. However,
The vertical direction (the y direction, in the case of a connector, the inserting direction) is essentially asymmetrical structure.

In the case of the example of FIGS. 1 and 2, if the thickness of the upper part is small, the plate on that side is likely to cause a larger contraction,
Therefore, it tends to warp so that the upper part is concave. Naturally, the warp is more remarkable as the total length is larger. According to the present invention, a "slender asymmetric article" which is asymmetric in at least one of the directions perpendicular to the direction having the maximum length (z direction) is formed by injection molding of thermoplastics. The present invention relates to a method for obtaining a molded product having an accurate dimension by preventing warpage during manufacturing. Hereinafter, for convenience, a case where the height direction (y direction) is asymmetric will be described.

That is, the first object of the present invention is that the warp is practically no problem in the injection molding of an elongated plastic article having an asymmetric cross section (simply referred to as an asymmetric article). It is to provide a general technical method for ensuring dimensional accuracy. Furthermore, the present invention also provides a method of manufacturing an injection molded connector substrate having less warpage within the constraints of given length and cross sectional profile.

[0009]

As a result of exploring the warpage phenomenon associated with injection molding, the present inventor can understand the actual warpage to some extent quantitatively by conducting an analysis based on the following idea. Was found, and the warping countermeasure technology of the present invention was completed by utilizing the results. That is, linear polymer molecules and anisotropic shape (eg fibrous) fillers are oriented in the process in which the resin flows while filling the mold, and when this is cooled and solidified, the partial parts are oriented. Therefore, it is possible to obtain a molded product that is a joined body of parts having different shrinkage characteristics because of different orientations and degrees. In this way, the shrinkage characteristics that differ depending on the part generate shearing force that acts inside the molded product, and eventually bending moments that act on both ends of the joined body, causing warpage.

Naturally, the shapes of actual molded bodies are various, and it is difficult to exactly predict the warpage. However, from the viewpoint of practical warpage countermeasures, the present inventor
By considering the molded body by dividing it into appropriate unit structures and introducing the concept of a warpage factor caused by the unit structure, it is possible to think that the warpage that occurs as a whole is due to a collection of the warp amounts of the unit structures. I found that there is no. That is, the technical idea which is the basis of the present invention is that the warpage of an actual asymmetric article having a complicated structure is divided into the warpage factors of the partial structural unit which is a combination of two plates joined in the length direction. Therefore, the amount of warpage caused by the joint portion of the unit structure will be quantitatively predicted to some extent by consideration of the above mechanism. Then, such an attempt is based on the thickness of the rib, the thickness of the main body, and the height of the rib.
The present invention could be completed based on the success of the above concept.

Generally, a plastic injection-molded product is produced by molding a mold based on a structure designed in consideration of a required outer diameter dimension, a strength required for use, a resin flow and the like. For the sake of convenience, the structural design based on the conventionally used design standard will be referred to as a standard structural design. However, a standard structure design that only considers strength and the like often causes warpage, which is a problem as a manufacturing technology for products that require accurate dimensions such as connector boards. Also,
It is extremely inconvenient to change the design after the warp is actually recognized in this way, and there are many trial and error measures against it.

The technical point of the present invention is that it is difficult to quantitatively predict the warp in the past, and in the injection molding technology for which a basic policy effective as a countermeasure has not been known, the warp is quantitatively predicted to some extent and It is possible to take measures against. Such a problem is that the factor that causes the warpage of the molded product as described above is, in effect, a superposition of the warpage amounts of the unit structures, and the overall warpage is predicted in advance. Then, if a large warp is expected,
This is solved based on the technical idea of adding a warpage factor in the direction of canceling this to internally balance the amount of warpage of the entire molded product to prevent warpage. Here, as a basic unit structure, consider a model in which two plate-like portions are joined in the longitudinal direction, first predict the strain ratio n, and calculate the value of n and
The amount of warpage is calculated based on the wall thickness, height and length of each plate. Hereinafter, the present invention will be described in detail including examples.

[0013]

[Distortion ratio] In order to understand the actual state of warpage during plastics injection molding, the present inventor first installed an elongated ribbed plate (Fig. 3: perspective view) from the gate provided at one end in the direction of length L. Injection molding was performed to collect basic data. The material used is a glass fiber reinforced liquid crystal polymer. Based on these results, the strain ratio n (the maximum strain is 1) is set to the rib and body thicknesses (R, S) and the rib height H ₁
Is shown in FIG. 4 as a parameter. The horizontal axis of the figure is the thickness of the main body, and the vertical axis is the strain ratio n. When the value of the strain ratio n is below the baseline, the rib side warps concavely, and when it is above the baseline, the rib side warps convexly. Figure 4 shows R /
5 levels of S, 2 levels of H ₁ , a total of 10 cases (Fig. 4A
~ Fig. 4J), but of course it can be shown in more detail if necessary. Although the illustrated one is based on experimentally obtained data, it can be interpreted in relation to the flow of the resin to some extent, and thus a predicted value obtained by using a theory can be used as the strain ratio n.

Taking the cases of FIGS. 4A and 4B as an example, the results obtained are interpreted as follows from the flow of resin. In this case, since the thickness of the rib is as small as ⅓ of the main body, the main stream of the resin injected from the gate at one end goes straight through the main body cavity in the length z direction, and the rib cavity is filled with the resin filled in the main body. Is partially filled with the tributary whose flow is changed in the height y direction. Therefore, the body is oriented in the z direction and the ribs are oriented in the y direction to some extent. Ribs that tend to be oriented in the y-direction have a greater shrinkage in the length z-direction than a body oriented in the z-direction, and cause a rib-shaped concave warpage in the molded product.
The strain ratio n indicates the degree thereof, and in the case of FIG. 4B in which the height of the rib is large, the strain becomes large because the tendency of the flow in the y direction is larger. However, if the molded product has a relatively large cross-sectional size, the absolute value of R will also increase, and the rib cavity will also be filled with the flow in the z direction from the beginning, and the difference with the main body will be small, so both FIGS. 4A and 4B are right. Approaching the baseline.

[0015]

[Amount of Warp] The present inventor created such a concept of the strain ratio n, and then performed the following quantitative analysis of the amount of warp (deformation amount). First, with respect to a model (Fig. 1) in which two parts having different contractions, that is, a rib (i = 1) and a main body (i = 2) are vertically joined in the longitudinal direction, Consider a force W (y) that is proportional to some strain. W
Since (y) is the derivative of shearing force, the distribution of strain magnitude can be expressed by the exponential function a _i * exp (−k _i y) (1) of y. k _i can be determined from the longitudinal elastic modulus of the plastics material E _i, shear modulus G, and the length dimension L. SQRT (N) means the square root of N. k _i = SQRT (8E _i / GL ² ) (2).

A _i is a strain at the joint surface (y = 0), and a ₁ and a _{2 are obtained} from the condition that the shearing force at the joint surface calculated from the integral of W (y) is equal for the rib and the main body. Are related. On the other hand, a ₁ + a ₂ = d
S is the difference between the rib shrinkage and the body shrinkage. This 2
It is possible to solve a ₁ and a ₂ from one relationship. a ₂ = dS / (1+ (E2 * k1 * (1-EXP (-k2 * H2))) / (k2 * E1 * (1-EXP (-k1 * H1)))) (3) a ₁ = dS-a ₂ (4).

Next, the bending moment acting on both ends of the unit structure joint surface is M ₁ as a value obtained by integrating yW (y) over the heights of the rib (i = 1) and the main body (i = 2). It is the sum of M ₂ and the equation M _i = (a _i E _i / k _i ² ) (1- (k _i H _{i +} 1) exp (−k _i H _i ) (5) M = M ₁ + M ₂ (6 ) Can be calculated.

Assuming a quadratic function m (z) = M-4M (Lz) z / L ² (7) of the longitudinal coordinate z which is M at both ends of the beam-shaped structure, The second derivative with respect to z is -m
Using the general formula of (z) / EI, the maximum warp amount D at the center of the beam can be calculated from the total length L and the bending moments M at both ends by the following formula. ^{D = 5ML 2 / 48EI (8} ).

Here, EI is the product of the longitudinal elastic modulus E _i and the second moment of area I _i . EI = E ₁ I ₁ + E ₂ I ₂ (9) Since the stress due to the shrinkage difference between the rib and the main body is generated in the joint surface, I _i is calculated for the width of the joint for convenience. I ₁ = ((H ₁ −η) ³ + η ³ ) / 3 (10) I ₂ = ((H ₁ + H ₂ −η) ³ − (H ₁ −η) ³ ) / 3 (11) where η is It is the position of the neutral line in the height direction and is calculated by the following formula. η = (E ₁ H ₁ ² + E ₂ H ₂ ² ) / (2 * (E ₁ H ₁ + E ₂ H ₂ )) (12) Ignoring the influence of the part outside the joint in this way, However, as in the case of the example, a result which is not practically acceptable was obtained.

The symbols indicating the respective parts in the dimensions including the following examples are as follows, and the units are all mm (see FIG. 1). R: the rib thickness H _1: rib height S: thickness of the main body H _2: body height W: length of the unit structure: the unit structure overall height _{(H 1 + H 2) L} : Width H of the main body The body thickness is the dimension of the smaller side in the case of a rectangular cross section. However, in the case of the groove-shaped cross section shown in FIG. 2, the thickness of the side plate is represented by R and the thickness of the bottom plate is represented by S. Therefore, there are cases where R> S.

The plastics used in the examples are glass fiber reinforced liquid crystal polymers, which are significantly affected by the orientation in injection molding and warp is likely to be a problem in precision parts. Longitudinal elastic modulus of the oriented material 140,000, perpendicular direction of the longitudinal elastic modulus 70000 shear modulus G = 20000 (Unit Modulus kgf / cm ^2), shrinkage (parallel) 0.001, shrinkage (perpendicular) 0.006 Is. Therefore, when the rib and the body are oriented at right angles, the difference in shrinkage at the joint surface is 0.00
5, and in this case, the strain becomes maximum (strain rate n = 1). If there is no difference in the orientation direction between the rib and the main body, there is no difference in the shrinkage rate at the joint surface, and the strain rate is n = 0. Generally speaking, the strain of this material can be regarded as a value obtained by multiplying the maximum shrinkage difference by the strain rate, dS = 0.005 n.

Since the strain rate reflects the orientation direction of the rib, it also affects the longitudinal elastic modulus in the z direction. In the case of this material, since the body is oriented in the z direction, the longitudinal elastic modulus E ₂ = 14
0000, but E ₁ is n = 0 and is the same as E ₂ 140000, n =
Since 1 is 70,000, it can be approximated by E ₁ = E ₂ (1-0.5n) (13).

[0023]

[Embodiment 1] When the reference structural design of a box having a groove cross section having the shape of FIG. 2 is given by R = 1, S = 2, H = 8, W = 5, L = 140, first, FIG. Use to predict the strain ratio. H ₁ = 6, R / S =
This is the case of FIG. 4D because it is 1/2, and when S = 2 on the horizontal axis is read, a strain ratio of about n = 0.2 is predicted for the concave surface. From n = 0.2, E ₁ = 126000, dS = 0.001. Using this value together with other condition values, calculation from equations (2) to (6) yields M = 723. On the other hand, since the EI = 8.35 million from the calculation of the second moment of area, the maximum warpage amount D at the center of L = 140 can be calculated from equation (8) to be 0.177 mm. In the case of this embodiment, since there is one unit structure in the height direction, this value becomes the predicted value as it is. The measured value was 0.19 mm. Therefore, changing to S = 3mm changes to R / S = 1/3, so the strain ratio decreases, and together with the tendency for warpage to decrease with S, thickening the bottom plate is expected to be an effective measure. It Obtaining n = 0.05 from Fig. 4B and recalculating for S = 3, it is significantly reduced to M = 227 and D = 0.04.
It will be 7 mm. The actual value of the amount of warpage was 0.04 mm, which was a level with no practical problems.

[0024]

Embodiment 2 The target article of this embodiment is a connector substrate having a shape shown in FIG. 5 (side view) and FIG. 6 (AA cross-sectional view of FIG. 5). It can be considered that they are connected symmetrically. The values of the standard structure design are R = 0.4, S = 1.2, H = 7.3, H
₁ = 4.5 and L = 80, and the strain ratio is almost the maximum value (n = 1) from FIG. 4B (top concave). From n = 1, E ₁ =
70000, dS = 0.005. Calculation using this value together with other condition values gives M = 2646. On the other hand, from the calculation of the moment of inertia of area, since EI = 75,100, the maximum warp amount D at the center of L = 80 can be calculated from equation (8) to be 0.235 mm. Since the calculation conditions are approximate (excluding both ends), the measured value is 0.3
0.14mm smaller than 5mm. In the case of this example, the maximum value of S allowed from the external dimensions is about 1.8 mm, and S is within this range.
When is increased, it decreases to about n = 0.7, but D = 0.18
At 6 mm, the amount of warp does not become small enough.

Therefore, the countermeasure in this case is to remove the meat. Fig. 7 shows the cross-sectional shape after taking countermeasures by removing a 0.8 mm deep hole 1.3 mm above the side surface of the body plate. In this case, we consider two unit structures that combine the central body and the upper or lower ribs. Predicting the amount of warpage due to the upper rib, R = 0.4, S = 1.2, H ₁
= 4.5 does not change, so n = 1, therefore H = 5.8 (H
₁ + H ₂ ), H ₂ = 1.3, a warp of D = 0.338 mm concave on the upper surface is predicted. On the other hand, the warp related to the unit structure in the opposite direction (thickened side, that is, the lower surface is concave) formed by lightening is R = 0.4 (1.2−0.8), S = 1.2, H ₁ =
From 1.5 (2.8-1.3), n = 0.5 (FIG. 4A), and from H = 2.8 and H ₂ = 1.3, D = 0.413 mm. The calculated value of the warp applied in the opposite direction cancels the calculated value of the warp of the upper surface concave, and it is judged that the countermeasure by lightening is effective, but as described above, the measured value before the countermeasure is larger than the calculated value. Considering the above, it is expected that some warpage of the concave surface will remain. Measured value 0.1 mm concave on the upper surface.

[0026]

[Third Embodiment] A target article of this embodiment is a connector substrate having a shape shown in FIG. 8 (side view) and FIG. 9 (AA sectional view of FIG. 8), and a side wall having an L-shaped section of FIG. It can be considered that the two are connected to each other by a partition wall. The standard structure design value of the side wall is R = 0.5,
S = 1.5, H = 3.5, is _{H 1 = 2, L = 80} .
Although n = 0.5 from FIG. 4A, n may be larger in consideration of the presence of partition walls. When n = 0.5 L =
At 80 mm, the warp of the bottom surface is 0.33 mm. When calculated with n = 1, it is 0.53 mm. The measured value was 1.0 mm (the groove of the lower rib was not included in the calculation). In order to deal with this, a measure was taken to add a warpage factor for the upper surface recess by grooving the upper surface (depth 0.7, width 0.3) (FIG. 10). In this case as well, the warp is divided into two unit structures and the warp is superposed. As for the warpage factor due to the main body and the lower rib, the height H _{2 of the} main body is reduced to 0.8 mm, so the warp amount of the lower concave is D = 0.72.
However, since the upper side also contracts due to the influence of the groove (H ₁
= 0.7, n = 0.4, calculated as D = 0.655), and the former warpage is almost cancelled. Measured value 0.02 mm.

[0027]

[Influence of Various Factors on Warp Amount] FIG. 11 exemplifies the influence of the strain rate n on the warp amount D. Dimension is H
= 2 mm of 8 mm and 12 mm, L = 80 mm, R / S = 1 /
3, E 2 and G have the same values as in Examples 1 to 3, and E ₁ is (13)
According to the formula. As shown in this figure, the warp amount D is almost proportional to the strain rate n until n = 0.5. FIG. 12 shows the warp amount D
It illustrates the effect of the length L on the. Distortion rate n
= 0.5, the dimensions other than the length and the elastic modulus are the same as in the case of FIG. From the gradient of the log-log graph, D is 2.5 of L
It can be seen that it changes almost in proportion to the power.

FIG. 13 exemplifies the influence of the heights (H ₁ , H ₂ ) of the rib and the main body on the warpage amount D. Total height H = 8 mm, 2 cases of 12 mm, L = 80 mm, H ₁ ,
The dimensions other than H ₂ , the strain rate, and the elastic modulus are the same as in the case of FIG. The effect of H ₁ and H ₂ on D is relatively gentle except when either H ₁ or H ₂ is close to 0 (both ends of the graph). Naturally, the warp amount D is larger when the total height H is lower. FIG. 14 illustrates the influence of the magnitude of the longitudinal elastic modulus on the warp amount D. E ₂ = 60,000 to 140,000, E
₁ is a value obtained by the equation (13) when n = 0.5. L = 80 mm (2 cases of H = 6 and 8), L =
Although 120 mm (H = 12 mm) is shown, it can be seen that the influence of E on D is small in any case. Therefore, it can be seen that almost the same results can be obtained when a plastic material having a longitudinal elastic modulus different from that used in the above description is used.

[0029]

[Illustrative Method 1] The method of calculating D using the equation (8) has been described above. This method can be applied to a wide range of cases, but the calculation is rather complicated. Therefore, in the most basic case of FIG. 1 and FIG.
Constrain only the plate thickness of the type (that is, there is no influence of grooving,
15 to 1 are simplified judgment diagrams in which the distortion rate is estimated from general dimensions and the allowable warpage is fixed at 0.05 mm.
8 15 and 16 are applied when the ribs are joined on the thick body plate as shown in FIG.
Is applied to a groove-shaped cross section that joins two side plates and a bottom plate as shown in FIG. It will be accurate if many figures are shown according to the length, but it is shown in a simplified manner when the length is up to 100 mm (FIGS. 15 and 17) and when the length is up to 200 mm (FIGS. 16 and 18).

According to the graphical method using these figures, whether the relation of the plate thickness of the original design (reference structure design) (relationship between R and S) is within the proper range of the warp amount of less than 0.05 mm. Determining whether or not is extremely easy. If it is found that it is out of the appropriate range, it is easy to know whether it is possible to add the necessary cancellation deformation factor only by changing the bottom plate thickness. The arrows entered in FIG. 18 indicate R (side plate thickness) and S by changing the bottom plate thickness (black circle → white circle) in the first embodiment.
It shows that the relationship with (bottom plate thickness) has moved from the improper region to the proper region. The arrows in FIG. 15 indicate that, in the second embodiment, it is difficult to set the relationship between R (rib plate thickness) and S to a proper range even if S (main body plate thickness) is changed. ing.

[0031]

[Addition of Negative Deformation Factor] As seen in the second embodiment, it is not always possible to balance the warp amount only by changing the wall thickness that does not affect the outer dimensions. In that case, the lightening (Example 2, FIG. 20), It is useful to add a desired canceling deformation factor by means such as grooving (Example 3, Fig. 19). As a countermeasure against deformation by lightening or grooving, it is necessary to form over a certain length. Especially, if a groove is cut at a short length, the rigidity may be deteriorated. For example, as a countermeasure for increasing the thickness of the connecting portion of the connector fitting portion, the deformation in which the lower surface is convex in view of the cross-sectional shape is canceled, and therefore, it is performed from the lower surface side. In that case, groove cutting will result in a loss of rigidity of the base, which is inappropriate. In this case, if the thinning is applied from the lower side of the connecting part of the fitting part, it becomes a warpage factor that the bottom surface becomes concave, and it is possible to cancel the warpage factor due to the standard structure design and balance. When the groove pitch p is about three times the depth d,
The effect of grooving is great (Fig. 19). Even if it is three times or less, some effects can be expected because the number of grooves increases, but there is a disadvantage such as strength reduction. The groove width q is preferably small, and the V-shaped groove is effective. In the case of removing meat, t in FIG. 20 is set to Hd or less. Also in this case, the effect is great when the pitch is about three times the depth.

[0032]

[Method 2] FIGS. 21 to 28 show the distortion rate shown with respect to the horizontal axis He, where the vertical axis is the limit L of the length at which the warp amount D becomes a value that causes a problem in ordinary precision parts. FIG. Here, He is the body height H ₂ in FIG. 1 (bottom surface thickness S in FIG. 2), but H _{2 in} the case of grooving
Since it has a considerable height different from that, it is shown as He. Figure 21
28. FIG. 28 shows the total height H as a parameter for two levels of the allowable value D = 0.05 mm of the normal level and 0.1 mm, which is twice the allowable value, assuming the distortion ratio of four levels. As already explained, the strain ratio can be determined based on the data obtained by actual measurement as shown in Fig. 4, and can also be predicted by taking into consideration the state of resin flow. Figure 21
28. By using FIG. 28, it is possible to predict the warp amount of the injection-molded product for each unit structure by a graphic method instead of the calculation by the formula (8). Balancing the amount of warpage of the entire article based on that knowledge is the same as in previous methods.
Examples 4 to 6 are illustration methods corresponding to Examples 1 to 3, respectively.

[0033]

Fourth Embodiment The size and strain ratio n of the object are the same as in the first embodiment. In FIG. 28, L = 130 mm and D =
Since it is 0.1 mm, n is 1.6 times (0.2 / 0.125)
In this example, where L is also long, the warpage amount D is expected to be too large, near 0.2 mm. When changing to He = 3mm,
The strain ratio n is significantly reduced (FIG. 4B, the same as Example 1). Although the figure for n = 0.1 or less is not shown,
If it is estimated based on FIG. 28 (n = 1/8) in consideration of the influence of n shown in FIG. 11, D = 0.0 even when L = 140 mm.
It can be considered to be improved to 5 mm or less.

[0034]

Fifth Embodiment The size and strain ratio n of the object are the same as in the second embodiment. From FIG. 22, L = 50 mm and D = 0.
It will be 1 mm. Considering that the warp amount D is proportional to the second to third power of L (FIG. 12), L = 80 mm and D = 0.26 to
Expect 0.4mm. The measured value was 0.35 mm. The values of n and dimensions used for the prediction after the lightening countermeasure is the same as in Example 2. The warpage factor (n = 1) of the concave surface is shown in FIG.
Using 2, L = 40 mm and D = 0.1 mm. The warpage factor (n = 0.5) of the bottom concave is L = 45 mm and D = 0.1 mm (see FIG. 2).
4). When L = 40 mm in total, the warp of the concave surface is 0.
It becomes 02 to 0.03 mm. Correcting the effect of length, L =
A warp of about 0.1 mm occurs at 80 mm.

[0035]

Sixth Embodiment The size of the object and the strain ratio n are the same as in the third embodiment. From FIG. 24, L = 45 mm and D = 0.
It is 1 mm, and the expected value for L = 80 mm is D = 0.45 mm. Further, assuming that n = 1, since FIG. 22 is used, L = 30 mm and D
= 0.1mm, L = 80mm, the expected value is D = 1.2mm. In all cases, the warp amount D was corrected as being proportional to L to the 2.5th power. Measured value 1 mm. The countermeasure for grooving the upper surface was based on canceling the warp of L = 30 mm and D = 0.1 mm. Assuming from FIG. 26, H = 1.
When 5, He = 0.8, the desired value is obtained when the distortion ratio n is about 0.3. As described above, the pitch is set to the groove depth of 0.
The strain ratio will be maximized if it is set to about 3 times 7 mm or 2 mm, so this time the groove pitch should be smaller than this.
The fact that the warping was canceled by cutting the groove with a pitch of 7 mm was the same as in Example 3.
As described in.

[0036]

According to the present invention, the plastic molded article is divided into unit structures, the warp amount is predicted for each unit structure, and the warp amounts of the unit structures are overlapped for the entire article to balance in the asymmetric direction. judge. The amount of warpage is predicted by combining equation (8) or FIGS. 21 to 28 derived from some assumptions and theoretical analysis, and the strain ratio n that can be predicted from the parameter mainly including the plate thickness. As a result, the design with the structure required from general specifications such as the external dimensions based on the user's requirements and the wall thickness required for strength (standard structure design) has a well-balanced amount of warpage. Can be determined.

When the balance is not balanced and the amount of warpage in the asymmetrical direction is expected to be large, a canceling factor such as a thick portion, a thinned portion, or a groove is added within a range that does not hinder the external dimensions required by the user. By taking shape measures, the design will be revised to balance the warpage factors for the entire asymmetric article. Here, in introducing the warp factor in the opposite direction, the warp amount prediction technique for the unit structure can be used. For the most basic cases of Fig. 1 (main body and ribs) and Fig. 2 (groove cross section), the reference structure design shows the amount of warpage based on the simplified judgment diagram by narrowing down the parameters to only the two major plate thicknesses. It can be easily determined whether or not it is within the proper range of less than 0.05 mm. If it is out of the range, it is possible to determine whether or not the necessary cancellation deformation factor can be added by changing the bottom plate thickness.

[0038]

EFFECTS OF THE INVENTION According to the present invention, it becomes possible to predict the influence of the unit structure that contributes to the warp in advance when manufacturing a slender asymmetric article by injection molding of plastics, and as a result, it is possible to reduce the warp. A technology to change the design to various dimensions has been realized. If a structural design with a small amount of warpage can be made, it is possible to manufacture an injection-molded product having a correct size by using a mold based on the structural design according to the state of the art of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a perspective view showing a model of an elongated article in which a main body and a rib are joined.

FIG. 2 is a perspective view showing a model of an elongated article having a groove-shaped cross section.

FIG. 3 is a perspective view of a plate with ribs.

FIG. 4 is a diagram showing the relationship between the size of the ribbed plate and the strain ratio. The horizontal axis S, the vertical axis n (the rib side is concave below the base line) H ₁ = 2 mm H ₂ = 5 mm R / S = 1/3 4B R / S = 1/2 FIG. 4C FIG. 4D R / S = 3/4 FIG. 4E FIG. 4F R / S = 1/1 FIG. 4G FIG. 4H R / S = 2/1 FIG.

FIG. 5 is a side view of the substrate according to the second embodiment.

FIG. 6 is a cross-sectional view of the substrate of the second embodiment before countermeasures.

FIG. 7: Substrate of Example 2, cross-sectional view after countermeasures

FIG. 8 is a side view of the substrate of the third embodiment before countermeasures.

FIG. 9: Substrate of Example 3; cross-sectional view

FIG. 10 is a substrate of Example 3, a side view after countermeasures (part)

FIG. 11 is a relationship diagram between a distortion ratio and a warp amount.

FIG. 12 is a relationship diagram between the length and the warp amount.

FIG. 13 is a relationship diagram between the height and the warp amount.

FIG. 14 is a relationship diagram between elastic modulus and warpage amount.

[Fig. 15] Warpage determination diagram of rib type model (100 mm or less in length)

[Fig. 16] Warpage determination diagram of rib type model (length 200 mm or less)

[Fig. 17] Warpage determination diagram for a grooved cross-section model (100 mm or less in length)

[Fig. 18] Warpage determination diagram for a grooved section model (length 200 mm or less)

FIG. 19 is a partial side view illustrating groove cutting.

FIG. 20 is a partial perspective view illustrating lightening, FIGS.
8: Relationship between strain rate and size

FIG. 21: Strain ratio n = 1/1, warpage 0.05 mm

FIG. 22: Strain ratio n = 1/1, warpage 0.10 mm

FIG. 23: Strain ratio n = 1/2, warpage 0.05 mm

FIG. 24: Strain ratio n = 1/2, warpage 0.10 mm

FIG. 25: Strain ratio n = 1/4, warpage 0.05 mm

FIG. 26: Strain ratio n = 1/4, warpage 0.10 mm

FIG. 27: Strain ratio n = 1/8, warpage 0.05 mm

FIG. 28: Strain ratio n = 1/8, warpage 0.10 mm

[Explanation of symbols]

R: Rib thickness H ₁ : Rib height S: Body thickness H ₂ : Body height W: Body width H: Overall height of unit structure (H ₁ + H ₂ ) L: Plate length

Claims (6)

[Claims] 1. A method for producing an article having an elongated asymmetric cross section by injection molding of plastics, wherein (1) a structural unit consisting of a rib and a body for joining the articles in the longitudinal direction is considered, and (2) as a main parameter. The warp amount of the unit structure is calculated using the dimensions of the rib and the main body, and (3) the reference structure design that predicts the warp by the judgment method of judging the overall balance from the warp amount of the unit structure. Meat part,
A method for manufacturing a slender article, characterized in that the shape of the slender article is designed so as to balance the warpage amount of the entire asymmetric article by taking geometrical measures such as lightening, a groove and the like to add a canceling deformation factor. 2. A rib thickness R, a body thickness S, and a rib thickness S when a long plastic asymmetric cross-section article having a structural unit consisting of a rib and a body joined in the longitudinal direction is manufactured by injection molding. Strain rate n that can be predicted based on the height H ₁ of the rib, elastic modulus of the plastics material, and the dimensions of the rib and the main body are used to find the bending moment M at both ends of the unit structure.
The warp amount of the unit structure is calculated from the formula D = 5ML ² / 48EI (L is the total length of the unit structure, EI is the sum of the product of the longitudinal elastic modulus and the second moment of area of the main body and the rib), and the thick portion, A method of manufacturing a slender article, characterized in that the design is such that the amount of warpage is balanced for the entire structure of the asymmetric article including factors such as lightening and grooves. 3. The bending moments at both ends of the rib (i = 1) and the main body (i = 2) are expressed by the equations M _i = (a _i E _i / k _i ² ) (1- (k _i H _i +1) exp ( determined by _{-k i H i)), M} = M 1 + a method where k _i and a _i of claim 2, wherein the predicting the bending moment of the unit structure across the M ₂ has a height direction (y It is a constant when the distribution function of the magnitude of the strain of (direction) is expressed by the expression a _i * exp (−k _i y) (* is a multiplicative symbol, exp is an exponential symbol). 4. A method of determining an appropriate region and an unsuitable region of a wall thickness relationship between a rib and a main body or a side wall plate and a bottom plate when manufacturing an elongated plastic asymmetric cross-section article by injection molding. A method for manufacturing an elongated article, characterized in that the thickness of a reference structure design in an inappropriate region is changed to a thickness in an appropriate region by a graphical method using a drawing 5. A method for illustrating a strain rate n and dimensions of a rib and a main body when manufacturing an elongated plastic asymmetric cross-section article having a structural unit consisting of a rib and a main body joined in the longitudinal direction by injection molding. Method for predicting the amount of warpage by the method and balancing the amount of warpage of the entire article based on the knowledge 6. A method of manufacturing a connector substrate for electronic equipment, which comprises using the method according to any one of claims 1 to 5.