Profile precision improvement method for electron beam selective melting product

Abstract

The invention provides an electron beam selective melting product profile precision improving method, and belongs to the field of additive manufacturing of alloy structural parts. According to the method, firstly, surface allowance and lap joint area allowance are added to a target part, then auxiliary support is added and printed, after the part is post-processed, three-dimensional scanning is conducted on the obtained target part, the target part is compared with a theoretical blank model, and a deformation value is displayed according to a comparison result. And reverse kneading compensation is conducted on the theoretical blank model through engraving software, a theoretical model after reverse deformation is obtained, printing is conducted again according to the theoretical model, and a target part with the higher profile precision is obtained.

Description

Technical Field

[0001] The invention belongs to the field of additive manufacturing of alloy structural parts, and in particular relates to a method for improving the surface accuracy of an electron beam selective melting product. Background Art

[0002] Electron beam selective melting (EBSM) has the advantages of high energy utilization, no reflection, high power density, fast scanning speed, no pollution in vacuum environment, and low residual stress. It is particularly suitable for the direct forming of active, refractory and brittle metal materials, and has broad application prospects in aerospace, biomedicine, automobiles, molds and other fields.

[0003] The process advantages of this molding technology are as follows: (1) The working environment is a vacuum environment, and the molding process does not consume protective gas; (2) Since the molding is carried out in a vacuum environment, there are no other impurity elements mixed into the molded parts; (3) During the titanium alloy electron beam selective melting molding process, the working temperature of the molding chamber is extremely high, reaching 600℃~800℃, and the temperature gradient of the printed parts is small. There is no quenching phenomenon, so the thermal stress is small. During the molding process, the parts are not sensitive to warping, and generally no additional dimensional support is required. Only a small amount of auxiliary support is required to conduct heat on the suspended surface printing.

[0004] Compared with laser selective melting additive manufacturing technology, electron beam selective melting can greatly reduce the deformation of printed products and improve product surface accuracy due to the smaller stress caused by its high temperature working environment. In terms of product surface accuracy, electron beam printed titanium alloy products are not like laser printed products, which will greatly increase the difficulty of surface accuracy control as the product size increases and the wall thickness decreases. Regardless of the size and wall thickness of the product, the deformation of electron beam printed titanium alloy products is controlled in a relatively stable state, not too large or too small, and the surface accuracy can be guaranteed to be controlled within ±1.2mm. But similarly, when the parts are small enough to be printed, even if the parts are small, it is difficult to achieve 100% surface accuracy within the range of ±0.3mm.

[0005] The purpose of using electron beam equipment to print parts is to take advantage of its good surface precision control and relatively low molding cost. From the current level of surface control, compared with laser selective melting, its shape control effect on small parts is not friendly, and in terms of the molding size of the current electron beam equipment, it cannot form parts that are too large. This results in the electron beam selective melting additive manufacturing technology having no obvious advantages over laser selective melting, and even due to the problem of the surface loose layer, its cost is not necessarily lower than laser selective melting.

[0006] Due to its working principle, the electron beam selective melting technology cannot ensure the surface accuracy of parts by adding dimensional supports. There is currently no simulation software and simulation method that matches it, so the parts printed using the electron beam selective melting technology are directly divided and printed after adding simple auxiliary supports on the basis of the blank model. This method cannot predict deformation in advance and tests the experience of the process personnel. When the printed product is unqualified, it is difficult to make adjustments. At present, the corresponding amount is added to the concave position by the method of compensation, and finally the fitter is asked to grind the excess position according to the requirements. If there are structures and positions that are inaccessible or difficult to grind in place by the fitter, the use of compensation and grinding cannot achieve full compliance with the surface accuracy standards, and it is also difficult to achieve the weight index. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a method for improving the surface accuracy of titanium alloy products by electron beam selective melting. The theoretical blank model is inversely deformed through a blank model iteration method, and the inverse deformation model is used for printing. There is no need for post-grinding, which greatly reduces the workload of fitters and improves the surface quality and step difference of the overlap area.

[0008] The above-mentioned purpose of the present invention is mainly achieved through the following technical solutions:

[0009] A method for improving the surface precision of an electron beam selective melting product comprises the following steps:

[0010] (1) Processing the target component model, adding allowance to the surface based on the blank model, and obtaining the target model with added allowance;

[0011] (2) performing surface mapping processing on the inner and outer surfaces of the overlapped area of ​​the target model with added margin obtained in step (1) to obtain the target model;

[0012] (3) adding block supports to the target model obtained in step (2), then performing program segmentation and importing it into an electron beam additive manufacturing device for printing;

[0013] (4) After printing is completed, the target parts are taken out and powder is blown off to remove supports and surface excess;

[0014] (5) grinding and smoothing the surface of the target component obtained in step (4) to obtain the target component;

[0015] (6) Performing a three-dimensional scan on the target component obtained in step (5), comparing it with the theoretical blank model, and performing reverse kneading compensation on the theoretical blank model through engraving software according to the deformation value displayed by the comparison result;

[0016] (7) The theoretical blank model after reverse deformation obtained in step (6) is processed in sequence from step (1) to step (5) to obtain the target component.

[0017] The excess thickness in step (1) is 0.4 mm to 0.8 mm.

[0018] The surface treatment range of step (2) is 3-5 mm extending outward from the overlap line of the overlap area, and the height of the treatment is 0.5-1.5 mm.

[0019] The powder blowing method in step (4) is as follows: the forming cylinder and the parts are placed in the equipment together, and the powder is cleaned using high-pressure gas with an air pressure of 7 MPa.

[0020] The support and surface excess removal method in step (4) is mechanical grinding, laser cleaning, electrochemical corrosion or chemical milling.

[0021] After the chemical milling treatment, the target parts are subjected to heat treatment at a temperature of 600-700° C. and the cooling method is furnace cooling.

[0022] The target component described in step (7) is subjected to a three-dimensional scan and compared with the blank model before inverse deformation. If the three-dimensional scanning result cannot meet the requirements of the surface accuracy, steps (6) and (7) can be repeated until the surface accuracy meets the requirements.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] (1) The method for improving the surface accuracy of titanium alloy products by electron beam selective melting of the present invention does not require post-grinding, which greatly reduces the workload of fitters.

[0025] (2) The present invention can achieve the required surface accuracy without any additional compensation, and there is no need for excessive wall thickness. The weight index can be controlled relatively well without the need for grinding.

[0026] (3) The present invention can improve the surface quality and step difference of the overlapping area. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the target component structure of Example 3 of the present invention;

[0028] Figure 2 The three-dimensional scanning result diagram of the actual and theoretical blank models of the present invention;

[0029] Figure 3 The three-dimensional scanning result diagram of the actual object and the theoretical blank model after reverse deformation of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0031] Example 1

[0032] The target titanium alloy component is a barrel-shaped structure with an inner diameter of 400mm, an outer diameter of 410mm, a wall thickness of 5mm, and a component height of 300mm.

[0033] (1) Based on this model, add loose layer margin to all surfaces with an addition amount of 0.5 mm.

[0034] (2) The single-gun molding area of ​​the multi-gun electron beam equipment is 300mm×300mm, and it is impossible to print this part with a single gun. Therefore, it is necessary to add margin to the overlap area. On the basis of adding margin to the loose layer, the overlap area is further added with an addition amount of 0.5mm. The inner diameter of the model cylinder is 399mm and the outer diameter is 411mm. The four overlap areas extend 3mm outward along the overlap line, and the width of the allowance is 21mm.

[0035] (3) Perform program segmentation to ensure the internal quality, density and surface quality of the formed parts. The segmented program is imported into the electron beam additive equipment for printing.

[0036] (4) After the parts are printed, they are taken out of the additive equipment and placed into the RPS equipment together with the forming cylinder. High-pressure gas is used to blow the powder to impact the semi-sintered powder preheated by the powder layer, and the powder adhered to the parts is cleaned and collected.

[0037] (5) Use electrochemical corrosion to evenly remove the loose layer on the surface and improve the surface quality. The fitter will grind the amount of the overlap area and smooth the surface to ensure that the state is the state of the theoretical blank model.

[0038] (6) The printed object is three-dimensionally scanned and compared with the theoretical blank model. According to the deformation value shown in the comparison result, the model is reversely kneaded and compensated using the Rreeform software.

[0039] (7) Repeat the processes from step (1) to step (5) to obtain the target parts.

[0040] (8) The printed anti-deformation blank model is subjected to three-dimensional scanning and compared with the blank model before anti-deformation. The surface accuracy of 100% of the area reaches ±0.3mm, which meets the technical requirements.

[0041] Example 2

[0042] The target titanium alloy component is a conical barrel structure with an outer diameter of 500mm at the large end and 400mm at the small end. Both the upper and lower end faces have large cross-sectional mutations, the wall thickness of the thin-walled area is 4mm, and the component height is 125mm.

[0043] (1) Based on this model, loose layer excess is added to all surfaces with an addition amount of 0.7 mm.

[0044] (2) On the basis of the addition of the loose layer, the overlap area is further added with an amount of 0.5 mm. The four overlap areas extend 4 mm outward along the overlap line, and the width of the subsidy is 23 mm.

[0045] (3) Process the blank model after pasting, add auxiliary support structure at the position of the suspended surface, and perform program segmentation to ensure the internal quality, density and surface quality of the formed parts. Import the segmented program into the electron beam additive equipment for printing.

[0046] (4) After the parts are printed, they are taken out of the additive equipment and placed in the RPS equipment with the forming cylinder. High-pressure gas is used to blow the powder to impact the semi-sintered powder preheated in the powder layer, and the powder adhered to the parts is cleaned and collected. The parts are handed over to the fitter to remove the auxiliary printing support and grind the support surface.

[0047] (5) Use electrochemical corrosion to evenly remove the loose layer on the surface and improve the surface quality. The fitter will grind the amount of the overlap area and smooth the surface to ensure that the state is the state of the theoretical blank model.

[0048] (6) The printed object is three-dimensionally scanned and compared with the theoretical blank model. According to the deformation value shown in the comparison result, the model is reversely kneaded and compensated using the Rreeform software.

[0049] (7) Repeat the processes from step (1) to step (5) to obtain the target parts.

[0050] (8) The printed anti-deformation blank model is subjected to three-dimensional scanning and compared with the blank model before anti-deformation. The surface accuracy of 100% of the area reaches ±0.5mm, which meets the technical requirements.

[0051] Example 3

[0052] The target titanium alloy parts are variable cross-section barrel structures, with a maximum diameter of 540mm, a minimum diameter of 520mm, an overall wall thickness of 4mm, and a part height of 180mm. Figure 1 shown.

[0053] (1) Based on this model, loose layer excess is added to all surfaces with an addition amount of 0.6 mm.

[0054] (2) Add margin to the overlap area. On the basis of adding margin to the loose layer, add margin to the overlap area again, the added amount is 0.5mm, the maximum outer diameter of the barrel structure is 541.2mm, the minimum outer diameter is 521.2mm, the wall thickness of the thin-walled area is 5.2mm, the four overlap areas extend 4mm outward along the overlap line, and the width of the subsidy is 23mm.

[0055] (3) Process the blank model after pasting, select the optimized electron beam selective melting process parameters for program segmentation to ensure the internal quality, density and surface quality of the formed parts. Import the segmented program into the electron beam additive equipment for printing.

[0056] (4) After the parts are printed, they are taken out of the additive equipment and placed into the RPS equipment together with the forming cylinder. High-pressure gas is used to blow the powder to impact the semi-sintered powder preheated by the powder layer, and the powder adhered to the parts is cleaned and collected.

[0057] (5) Use electrochemical corrosion to evenly remove the loose layer on the surface and improve the surface quality. The fitter will grind the amount of the overlap area and smooth the surface to ensure that the state is the state of the theoretical blank model.

[0058] (6) Perform a 3D scan of the printed object and compare it with the theoretical blank model. The comparison results are as follows: Figure 2 As shown in the figure, the light and dark areas did not meet the technical requirement of ±0.4mm, and only the medium gray area met the standard. According to the deformation value shown in the comparison results, the model was reversely kneaded and compensated using the Rreeform software.

[0059] (7) Repeat the processes from step (1) to step (5) to obtain the target parts.

[0060] (8) Perform a three-dimensional scan of the printed anti-deformation blank model and compare it with the blank model before anti-deformation. The comparison results are as follows: Figure 3 As shown in the figure, the surface accuracy of 100% area reaches ±0.4mm, which meets the technical requirements.

[0061] The above description is only the best specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0062] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for improving the surface accuracy of electron beam selective melting products, characterized in that: The following steps are involved: (1) Processing the target component model, adding allowance to the surface based on the blank model, and obtaining the target model with added allowance; (2) performing surface mapping processing on the inner and outer surfaces of the overlapped area of ​​the target model with added margin obtained in step (1) to obtain the target model; (3) adding block supports to the target model obtained in step (2), then performing program segmentation and importing it into an electron beam additive manufacturing device for printing; (4) After printing is completed, the target parts are taken out and powder is blown off to remove supports and surface excess; (5) grinding and smoothing the surface of the target component obtained in step (4) to obtain the target component; (6) Performing a three-dimensional scan on the target component obtained in step (5), comparing it with the theoretical blank model, and performing reverse kneading compensation on the theoretical blank model through engraving software according to the deformation value displayed by the comparison result; (7) The theoretical blank model after reverse deformation obtained in step (6) is processed in sequence from step (1) to step (5) to obtain the target component.

2. The method for improving the surface accuracy of an electron beam selective melting product according to claim 1, characterized in that: The excess thickness in step (1) is 0.4 mm to 0.8 mm.

3. The method for improving the surface precision of an electron beam selective melting product according to claim 1, characterized in that: The surface treatment range of step (2) is 3-5 mm extending outward from the overlap line of the overlap area, and the height of the treatment is 0.5-1.5 mm.

4. The method for improving the surface precision of an electron beam selective melting product according to claim 1, characterized in that: The powder blowing method in step (4) is as follows: the forming cylinder and the parts are placed in the equipment together, and the powder is cleaned using high-pressure gas with a gas pressure of 5-10 MPa.

5. The method for improving the surface precision of an electron beam selective melting product according to claim 1, characterized in that: The support and surface excess removal method in step (4) is mechanical grinding, laser cleaning, electrochemical corrosion or chemical milling.

6. The method for improving the surface precision of an electron beam selective melting product according to claim 5, characterized in that: After the chemical milling treatment, the target parts are subjected to heat treatment at a temperature of 600-700° C. and the cooling method is furnace cooling.

7. The method for improving the surface precision of an electron beam selective melting product according to claim 1, characterized in that: The target component described in step (7) is subjected to a three-dimensional scan and compared with the blank model before reverse kneading compensation. If the three-dimensional scanning result cannot meet the requirements of the surface accuracy, steps (6) and (7) can be repeated until the surface accuracy meets the requirements.

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