CN110795886A

CN110795886A - Method for determining dimensional allowance, method for forming dimensional allowance, forming device, and readable storage medium

Info

Publication number: CN110795886A
Application number: CN202010008236.5A
Authority: CN
Inventors: 雷力明; 李雅莉; 侯慧鹏; 付鑫; 王威
Original assignee: China Hangfa Shanghai Aero Engine Manufacturing Co Ltd; AECC Commercial Aircraft Engine Co Ltd
Current assignee: China Hangfa Shanghai Aero Engine Manufacturing Co Ltd; AECC Commercial Aircraft Engine Co Ltd
Priority date: 2020-01-06
Filing date: 2020-01-06
Publication date: 2020-02-14
Anticipated expiration: 2040-01-06
Also published as: CN110795886B

Abstract

The invention relates to a size allowance determining method, a forming device and a readable storage medium for selective laser melting forming of suspended structure parts, wherein the allowance determining method comprises the step of determining the size allowance of the selective laser melting forming of the suspended structure parts according to a size allowance formula d = n multiplied by cos theta for suspended structures with different inclination angles, wherein d is the size allowance, h is the thickness of a powder laying layer formed by selective laser melting forming, theta is the inclination angle of the suspended structure parts, and n is a process constant. The allowance determining method, the forming device and the readable storage medium have the advantages of improving the efficiency of the laser selective melting forming process of the suspended structure part, and ensuring the qualified rate of the part size and the surface quality.

Description

Method for determining dimensional allowance, method for forming dimensional allowance, forming device, and readable storage medium

Technical Field

The invention belongs to the field of additive manufacturing, and particularly relates to a margin determining method, a forming device and a readable storage medium for selective laser melting forming of suspended structure parts.

Background

Additive Manufacturing (AM) is a Manufacturing technology for melting raw materials layer by layer to form a part based on a discrete build-up principle. Selective Laser Melting (SLM) is considered to be one of the most potential Additive Manufacturing (AM) technologies, and since a Laser beam with a fine focused spot is used as a forming energy source, a high-speed and high-precision scanning galvanometer is used as a processing beam control unit, and a thinner layer thickness control technology is adopted, compared with other AM technologies, the SLM technology is more advantageous in obtaining a high-density and high-precision formed part, and can complete direct forming of a complex cavity, a profile, a thin wall and a variable-section part.

Theoretically, the SLM technology can form parts with any complex structure, but is constrained by processing technology, materials, geometric characteristics, technical principles and the like, when some structures with an included angle (inclined angle) smaller than 45 degrees with a horizontal plane are formed, namely, a suspended structure is formed, the printing can be successfully performed only by adding supports on the lower surface of the suspended structure, if no supports are added, the lower surface of the suspended structure is completely made of powder materials, after laser scanning, metal liquid formed by material melting is easy to permeate into gaps among powder particles under the combined action of gravity and capillary force to generate slag, the bonding force of the melted material in the region is weak, and after powder is spread on the next layer, the acting force of a scraper is large, the material in the region is damaged, and the forming failure is caused. After the forming is completed, these support structures that assist in forming need to be removed. The support is usually connected with the surface of a part entity, and after the support is removed, the lower surface of the part has more defects of unevenness, so that the surface roughness is high, the quality is poor, and polishing treatment is required. For example, the Chinese patent application with publication number CN109079143A and publication date of 2018, 12 and 25 and named as a method for removing cracks on the surface of the inner cavity of a part formed by selective laser melting discloses a process for removing opening cracks of the inner cavity of the part by using an abrasive flow process.

However, after the defects of the unevenness are polished and removed, the size of the part is easy to be out of tolerance, and finally the part is scrapped. The problems are all involved when the SLM forms parts of the pre-rotation nozzle, the fuel nozzle, the turbine blade and other aero-engine parts, so that certain size allowance is reserved according to the structural characteristics of the parts and the technological characteristics of the SLM in the model design stage, and the size of the parts after polishing treatment meets the design requirements. In the suspended structure part model processing stage, if the size allowance is added blindly, the polishing removal amount is large when the allowance value is too large, the labor cost is increased, and the size of the polished part is out of tolerance when the allowance value is too small.

In the prior art, a trial and error method is adopted for determining the size allowance of each suspended structure part. And carrying out laser selective melting forming on the suspended structure part to be formed, and then executing a support removing step, wherein in the support removing step, the size allowance of the suspended structure part to be formed is obtained according to the thickness of the removed material of the part body. However, due to the characteristics of the SLM process, the suspension structures with an included angle of less than 45 ° with the horizontal plane all need to be supported, the inclination angles of the suspension surfaces are different, and the size margins to be added are also different, so that when a new suspension structure part is to be formed, the size margins accumulated by early trial and error may be inapplicable, and the new suspension structure part needs to be trial and error again, which greatly affects the processing efficiency of the part.

Therefore, there is a need in the art for an efficient method for determining the size margin of the suspension structure of the laser selective melting part, so as to improve the efficiency of the laser selective melting forming process of the suspension structure part.

Disclosure of Invention

The invention aims to provide a high-efficiency method for determining the size allowance of a suspended structure of a selective laser melting part, so as to improve the efficiency of a selective laser melting forming process of the suspended structure part.

The invention provides a size allowance determining method, which is used for selective laser melting forming of suspended structure parts and comprises the following steps: for the suspended structures with different inclination angles, the size allowance of selective laser melting forming of the suspended structure parts is determined by a size allowance formula: d = nxh multiplied by cos theta, wherein d is the size allowance, h is the thickness of the powder laying layer formed by selective laser melting, theta is the inclination angle of the suspended structure part, and n is the process constant.

In one or more embodiments, the method for determining the process constant includes performing at least one trial-and-error step, in the trial-and-error step, selecting a first suspended structure with an inclination angle of a first angle, performing selective laser melting forming under a first forming process parameter including a powder layer thickness, and then performing a step of removing a support to obtain a first size margin of the first suspended structure according to the removed material thickness of the part body; and obtaining a process constant corresponding to the first forming process parameter according to the first size allowance, the thickness of the powder spreading layer, the first angle and the size allowance formula.

The invention provides a forming method for selective laser melting forming of suspended structure parts, which comprises the following steps:

step S1: modeling the suspended structure part to obtain an initial model of the suspended structure part;

step S2: converting the initial model, adding a size allowance and a supporting structure corresponding to a forming process parameter to a suspension surface of the suspension structure part under the forming process parameter, converting the initial model into a printing model formed by selective laser melting, wherein the size allowance is determined by any one of the size allowance determination methods;

step S3: and under the forming process parameters, carrying out selective laser melting forming according to the printing model to obtain a preliminary formed part of the suspended structural part.

In one or more embodiments, the forming method further includes step S4: and removing the supporting structure of the preliminary formed part, and carrying out surface treatment on the suspended surface of the suspended structure after the supporting structure is removed.

In one or more embodiments, the material of the flying structure part is Hastelloy X alloy.

The present invention provides a readable storage medium having stored thereon a computer program, the program being executable by a processor to perform the steps of:

adding a size allowance to a suspension surface of a suspension structure part subjected to selective laser melting forming, wherein the size allowance is determined by a size allowance formula: d = n × h × cos θ; wherein d is the size allowance, h is the thickness of the powder laying layer formed by selective laser melting, theta is the inclination angle of the suspended structure part, and n is the process constant.

The invention provides a forming device for selective laser melting forming of suspended structure parts, which comprises a computer readable storage medium for storing instructions executable by a processor; and a processor to execute the instructions, the instructions comprising: adding a size allowance to a suspension surface of a suspension structure part subjected to selective laser melting forming, wherein the size allowance is determined by a size allowance formula: d = n × h × cos θ; wherein d is the size allowance, h is the thickness of the powder laying layer formed by selective laser melting, theta is the inclination angle of the suspended structure part, and n is the process constant.

In conclusion, by adopting the method for determining the size allowance, the size allowance is directly determined through the size allowance formula, the process constant corresponding to the process parameter can be obtained at least by one trial and error, namely, the size allowance formula corresponding to the process parameter can be obtained only by one trial and error. In addition, the size allowance adding formula of the suspension surface established by the invention provides a reference basis for the model design of the selective laser melting forming process, and fills the blank of the design rule aiming at the selective laser melting forming process.

Drawings

The above and other features, properties and advantages of the present invention will become more apparent from the following description of the embodiments in conjunction with the accompanying drawings, it being noted that the drawings are given by way of example only and are not drawn to scale, and should not be taken as limiting the scope of the invention which is actually claimed, wherein:

fig. 1 is a schematic view of a suspended structure part with an inclination angle of 0 °.

Fig. 2 is a schematic view of a structure of a printing model without dimensional margins of parts according to the structure of fig. 1.

Fig. 3 is an optical microscope photograph of a part according to the structure of fig. 1 with the dangling surfaces of the part removed from support.

Fig. 4 is a schematic view of a suspended structural part having an angle of inclination of 20 °.

FIG. 5 is a schematic diagram of a printing model of a part according to FIG. 4.

Fig. 6 is an optical microscope photograph of the part according to fig. 4 with the overhanging surface of the part removed from support.

Figure 7 is a schematic flow diagram of a process for obtaining the suspended structural feature of figure 4 by selective laser melting.

Figure 8 is an optical microscope photograph of a suspended surface-removed support having a suspended structural feature inclined at an angle of 30.

Figure 9 is an optical microscope photograph with the suspended surface of the suspended structural part at a 45 ° angle of inclination removed from support.

Detailed Description

The following discloses many different embodiments or examples for implementing the subject technology described. Specific examples of components and arrangements are described below to simplify the present disclosure, but these are merely examples and do not limit the scope of the invention. "one embodiment," "an embodiment," and/or "some embodiments" mean a certain feature, structure, or characteristic described in connection with at least one embodiment of the present application. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the present application may be combined as appropriate.

Flow charts are used herein to illustrate operations performed by systems according to embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in the exact order in which they are performed. Other operations may also be added to, or removed from, the processes.

Referring to fig. 1-3, in one embodiment, the suspension structure component is a suspension structure component 1 with an inclination angle of 0 ° as shown in fig. 1. The size allowance of the laser selective melting forming of the suspended structure part is determined by a size allowance formula:

d=n×h×cosθ

wherein d is the size allowance, h is the thickness of the powder laying layer formed by selective laser melting, theta is the inclination angle of the suspended structure part, and n is the process constant. n can be obtained by table look-up or by a trial and error procedure.

In the embodiment, an EOS M280 selective laser melting device is adopted to form a suspended structure part, the part is made of Hastelloy X alloy, and the forming process parameters are as follows: the laser scanning power is 180W, the scanning speed is 1100mm/s, the layer thickness is 20 microns, the scanning interval is 90 microns, and the rotation angle of the laser scanning direction between adjacent layers is 67 degrees.

An embodiment of obtaining process constants by trial and error steps is described in connection with fig. 2 and 3. Under the forming process parameters, carrying out laser selective melting forming on the suspended structure part 1, as shown in fig. 2, processing an initial model of the suspended structure part 1 in magics software, adding a net-shaped supporting structure 2 on a suspended surface 3, after forming, executing a step of removing the supporting structure 2, and shooting by using an optical microscope to remove the supported suspended surface structure. As shown in fig. 3, the measurement can be obtained according to a photomicrograph, a part body material with a certain thickness needs to be removed, the suspended surface 3 can be polished to be smooth and free of defects, since the unevenness of the wave crests and the wave troughs of the suspended surface is removed after the support, in order to ensure reasonable removal amount, the selected measurement points can represent the average value of the whole wave crests, the specific measurement method can be as shown in fig. 3, values of a plurality of wave crest points are selected from the photomicrograph, for example, the measured values of seven point positions in fig. 3 are selected to calculate the average value, and the specific values are as shown in table 1:

table 1: the peak height corresponding to each measurement point in FIG. 3

Therefore, the part body material with the thickness of 0.250mm needs to be removed, namely, the size allowance d =0.25mm needs to be added, and the forming process parameters are obtained by combining the known powder laying layer thickness h =20 μm and the inclination angle θ =0 ° and substituting the size allowance formula d = n × h × cos θ: the laser scanning power is 180W, the scanning speed is 1100mm/s, the layer thickness is 20 microns, the scanning interval is 90 microns, and the process constant n corresponding to the rotation angle of 67 degrees between adjacent layers in the laser scanning direction is 12.5.

Through the foregoing embodiments, it can be understood that, for different process parameters, the corresponding data table may be established in advance through trial and error steps, and in the subsequent forming process, the process parameters may be determined only by looking up the table according to the process parameters.

For the process parameters of the foregoing embodiment, knowing that the powder layer thickness h =20 μm and n equals 12.5, the suspended structure parts for different suspension angles can be determined quickly and at low cost by the dimensional margin formula, which is described later with reference to fig. 4 to 9.

Referring to fig. 4-7, selective laser melting of the suspended structure part 101 includes the following steps:

s1: modeling the suspended structure part 101 to obtain an initial model of the suspended structure part 101, for example, three-dimensionally designing the suspended structure 101 in computer aided design software such as UG, and drawing a part diagram model of the suspended structure part 101 as shown in fig. 4;

s2: the initial model in S1 is transformed, for example, by converting the part drawing into a blank drawing with an added dimension allowance in computer aided design software such as UG, and the dimension allowance is determined as follows. As shown in fig. 5, under the following forming process parameters: at a laser scanning power of 180W, a scanning speed of 1100mm/s, a layer thickness of 20 μm, a scanning pitch of 90 μm, a rotation angle of 67 ° in a laser scanning direction between adjacent layers, adding a dimensional allowance to a suspended surface 301 of the suspended structural part 101, for the suspended structural part 101 with θ =20 °, substituting n =12.5, θ =20 °, h =20 μm into a dimensional allowance formula d = n × h × cos θ, and adding a dimensional allowance d =12.5 × 0.02 × cos20 ° =0.235mm, that is, adding a dimensional allowance thickness of 0.235mm to the suspended surface 301 of the suspended structural part 101. After the size allowance is added, the blank graph model is exported from UG software and stored as an STL format file, then the format file can be processed in additive manufacturing process model processing software, such as Magics software, a support structure, such as a block-type support structure 201 shown in fig. 5, is added to the suspension surface of the part blank, and finally the part blank model with the support structure is exported and stored as an SLI format file readable by a selective laser melting and forming device.

S3: and guiding the converted printing model into EOS M280 laser selective melting equipment, wherein the printing model can be the file in the SLI format, and performing laser selective melting forming under the process parameters of 180W of laser scanning power, 1100mm/s of scanning speed, 20 mu M of layer thickness, 90 mu M of scanning interval and 67-degree rotation angle between adjacent layers in the laser scanning direction to obtain a primary formed part of the suspended structural part 101.

S4: the support structure 201 of the preliminary shaped piece of the suspended structural part 101 is removed and a shaped part conforming to the part diagram model shown in fig. 4 is finally obtained. For example, the support structure 201 is removed by a fitter, and then the suspended surface 301 of the suspended structure after the support structure is removed 201 is subjected to surface treatment, for example, polishing by the fitter is performed until the suspended surface is smooth and has no defects such as unevenness. The support removal and/or surface treatment may be performed manually or automatically in a selective laser melting apparatus, all without limitation.

The preliminary formed piece of the suspended structure part 101 with the supporting structure 201 removed is observed by an optical microscope, and the obtained image is shown in fig. 6, and the thickness of the material of the part body to be removed is measured to be 0.231mm, so that the suspended surface 301 can be polished to be smooth and free of defects. The measurement method is similar to the measurement method described in fig. 3 and table 1, and is to measure the values of a plurality of peak points and average them, select twelve peak points in the photomicrograph of fig. 6 for measurement, and average the measured values of each point, and the specific values are shown in table 2:

table 2: the peak height corresponding to each measurement point in FIG. 6

The reason why the average value is 0.231mm and the error is within the allowable range of ± 5 μm compared with the theoretical value of 0.235mm determined by the size allowance formula in S2 is that the measurement is manually performed by taking points, manually performing line drawing, and obtaining the measurement value by distance measurement with a scale, so that the measurement values obtained by different measuring personnel and the same measuring personnel at different times may be different, and the allowable error range of ± 5 μm is the allowable error of manual measurement obtained by the inventor according to a large amount of measurement experience. The optical microscope observation is an observation performed for inspection purposes, and may not be performed in order to improve the forming efficiency in the actual selective laser melting forming, and is used here as a formula for verifying whether the dimensional allowance is accurate.

In one embodiment, an EOS M280 laser selective melting device is used for forming a suspended structural member with θ =30 °, the material is Hastelloy X alloy, and the forming process parameters are as follows: the laser scanning power is 180W, the scanning speed is 1100mm/s, the layer thickness is 20 microns, the scanning interval is 90 microns, the rotation angle of the laser scanning direction between adjacent layers is 67 degrees, the size allowance d =12.5 x 0.02 x cos30 degrees is determined according to a size allowance formula d = n x h x cos theta, the size allowance d =12.5 x 0.02 x cos30 degrees is determined to be 0.216mm, the allowance of 0.216mm is added on the lower surface of the suspended structure, an initial model is converted in magics software, a net-shaped supporting structure is added, and the printing model is led into an EOS M280 device for forming. And after the forming is finished, removing the net-shaped supporting structure and performing surface treatment by a bench worker. The preliminary formed piece of the suspended structure part with the supporting structure removed and the angle of theta =30 degrees is observed by an optical microscope, the obtained image is shown in fig. 8, and the thickness of the part body material needing to be removed is measured to be 0.218mm, so that the suspended surface can be polished to be smooth and flawless. The measurement method is similar to the measurement method described in fig. 3 and table 1, and is to measure the values of a plurality of peak points and average them, select twelve peak points in the photomicrograph of fig. 8 for measurement, and average the measured values of each point, and the specific values are shown in table 3:

table 3: the peak height corresponding to each measurement point in FIG. 8

The average value was found to be 0.218mm, and the error therebetween was within an allowable range of ± 5 μm, compared with the theoretical value of 0.216mm determined by the size margin formula d = n × h × cos θ.

In one embodiment, an EOS M280 laser selective melting device is used for forming a suspended structural member with θ =45 °, a Hastelloy X alloy is used as a material, and the dimensional allowance d =12.5 × 0.02 × cos45 ° =0.177 mm is determined according to the dimensional allowance formula d = n × h × cos θ by using the same forming process parameters as those of the above embodiment. The preliminary formed piece of the suspended structure part with the supporting structure removed and the angle of theta =45 degrees is observed by an optical microscope, the obtained image is shown in fig. 9, and the thickness of the material of the part body to be removed is measured to be 0.172mm, so that the suspended surface can be polished to be smooth and free of defects. The measurement method is similar to the measurement method described in fig. 3 and table 1, and is to measure the values of a plurality of peak points and take an average value, ten peak points are selected from the micrograph of fig. 9 for measurement, and the measured values of the points are averaged, and the specific numerical values are shown in table 4:

table 4: the peak height corresponding to each measurement point in FIG. 9

The average value was found to be 0.172mm, and the error therebetween was within an allowable range of ± 5 μm, compared with the theoretical value of 0.177mm determined by the size margin formula d = n × h × cos θ.

It will be appreciated that the above-described selective laser melting and forming method may be implemented in a computer device, and that a forming apparatus for selective laser melting and forming of suspended structural parts may be implemented, comprising a memory for storing instructions executable by a processor; and the processor is used for executing the instructions to add a size allowance to the suspended surface of the suspended structure part subjected to the laser selective melting forming, wherein the size allowance is determined by a size allowance formula d = n × h × cos θ. Similarly, the laser selective melt shaping method described above may be embodied as a computer readable storage medium having stored thereon computer instructions that, when executed by a processor, perform adding a size margin determined by the size margin formula d = n × h × cos θ.

To sum up, by adopting the method for determining the size margin provided by the embodiment, the size margin is directly determined through the size margin formula, and the process constant corresponding to the process parameter can be obtained at least by one trial and error, namely, the size margin formula corresponding to the process parameter can be obtained only by one trial and error. In addition, the size allowance adding formula of the suspension surface established by the invention provides a reference basis for the model design of the selective laser melting forming process, and fills the blank of the design rule aiming at the selective laser melting forming process.

Although the present invention has been disclosed in the above-mentioned embodiments, it is not intended to limit the present invention, and those skilled in the art may make variations and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope defined by the claims of the present invention, unless the technical essence of the present invention departs from the content of the present invention.

Claims

1. A size allowance determining method is used for selective laser melting forming of suspended structure parts, and is characterized by comprising the following steps:

for the suspended structures with different inclination angles, the size allowance of selective laser melting forming of the suspended structure parts is determined by a size allowance formula:

d=n×h×cosθ

wherein d is the size allowance, h is the thickness of the powder laying layer formed by selective laser melting, theta is the inclination angle of the suspended structure part, and n is the process constant.

2. The method of claim 1, wherein the determining of the process constant includes performing at least one trial and error step in which,

selecting a first suspended structure with a first inclination angle, carrying out selective laser melting forming under a first forming process parameter including the thickness of the powder layer, then executing a support removing step, and obtaining a first size allowance of the first suspended structure according to the removed material thickness of the part body;

and obtaining a process constant corresponding to the first forming process parameter according to the first size allowance, the thickness of the powder spreading layer, the first angle and the size allowance formula.

3. A forming method is used for selective laser melting forming of suspended structure parts and is characterized by comprising the following steps:

step S2: converting the initial model, adding a size allowance and a supporting structure corresponding to a forming process parameter to a suspension surface of the suspension structure part under the forming process parameter, and converting the initial model into a printing model formed by selective laser melting, wherein the size allowance is determined by the size allowance determination method in claim 1 or 2;

4. The forming method of claim 3, further comprising:

step S4: and removing the supporting structure of the preliminary formed part, and carrying out surface treatment on the suspended surface of the suspended structure after the supporting structure is removed.

5. A method of forming as in claim 3 wherein the suspended structural feature is a HastelloyX alloy.

6. A readable storage medium having stored thereon a computer program, the program being executable by a processor to perform the steps of:

adding a size allowance to a suspension surface of a suspension structure part subjected to selective laser melting forming, wherein the size allowance is determined by a size allowance formula:

d=n×h×cosθ

7. A forming device is used for selective laser melting forming of suspended structural parts and is characterized by comprising

A computer-readable storage medium for storing instructions executable by a processor; and

a processor to execute the instructions, the instructions comprising:

d=n×h×cosθ