A powder bed support-free printing method based on additive and subtractive composite manufacturing technology

Abstract

A powder bed support-free printing method based on additive and subtractive composite manufacturing technology, firstly, a design model is self-supported to obtain an optimized model; then, the optimized model is decomposed according to processing tool parameters to obtain a construction sequence and a sub-model group; finally, each sub-model in the sub-model group is additively manufactured in sequence according to the construction sequence, and a subtractive strategy is used to alternately perform subtractive processing on each sub-model after the additive construction is completed, and its appearance is controlled to be the same as the design model until all sub-models are completed, that is, a design part with a support-free structure is obtained; the present invention utilizes additive and subtractive composite manufacturing technology to replace the original support structure with a self-supporting design of the model, and intermittent CNC machining is used to control the part shape, which can realize high-quality integrated precision manufacturing of large-angle overhang structures, and there is no need to remove the support structure later, and the surface forming quality of the part is high.

Description

Technical Field

[0001] The present invention relates to the field of additive and subtractive composite manufacturing technology, and in particular to a powder bed support-free printing method based on additive and subtractive composite manufacturing technology. Background Art

[0002] Powder bed additive manufacturing technology can be used to form complex and precise parts in one piece. However, it is limited by the maximum build angle (the angle between the tangent direction of the model surface and the build direction (Z direction)). When printing large-angle overhanging structures, it is often necessary to add support structures to these parts to resist thermal deformation and scraper forces. After printing is complete, the support structures need to be removed. However, some internal structural supports are often difficult to remove, and removing the supports can release internal stress in the part, causing deformation and affecting the overall part accuracy.

[0003] The essence of additive and subtractive composite manufacturing is a manufacturing solution that intermittently adds CNC machining steps to the surface of parts during the additive process. It can remove material from the internal and external surfaces before the model is fully constructed, thereby improving surface accuracy.

[0004] Existing powder bed support-free printing technology is mostly achieved by using a non-contact scraper or real-time optimization of process parameters (ZL 201810265567.X "Equipment, System and Method for Three-Dimensional Printing"). Although it can reduce the number of supports for parts, it still requires additional supports for overhang structures close to 90°. In addition, the lower surface forming quality of large-angle overhang structures is poor and there are many internal defects. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a powder bed support-free printing method based on additive and subtractive composite manufacturing technology. By utilizing additive and subtractive composite manufacturing technology, the original support structure is replaced by a self-supporting design of the model, and the shape of the part is controlled by intermittent CNC machining, which can realize high-quality integrated precision manufacturing of large-angle overhang structures, and there is no need to remove the support structure subsequently, and the surface forming quality of the part is high.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A powder bed support-free printing method based on additive and subtractive composite manufacturing technology comprises the following steps:

[0008] First, the design model is self-supported to obtain the optimized model;

[0009] Then, according to the machining tool parameters, the optimization model is decomposed to obtain the construction sequence and sub-model group;

[0010] Finally, each sub-model in the sub-model group is additively manufactured in sequence according to the construction sequence, and a subtractive strategy is used to alternately perform subtractive processing on each sub-model after the additive construction is completed, controlling its appearance to be the same as the design model, until all sub-models are completed, and the designed part without support structure is obtained.

[0011] The self-support design is as follows: first, the maximum build angle of the powder bed additive manufacturing equipment is determined; then, a surface in the design model whose angle between the tangent and the build direction is greater than the maximum build angle is found, namely, a large-angle overhang surface; finally, the angle of the large-angle overhang surface is compensated to the maximum build angle of the equipment, so that it can achieve self-support during the printing process, and an optimized model is obtained.

[0012] The self-supporting structure added in the self-supporting design can be removed in subsequent subtractive processing.

[0013] The processing tool is a T-type milling cutter, which is used to process the self-supporting structure with a negative angle; according to the different forms of the processed curved surface, T-type milling cutters with different specifications and parameters are selected.

[0014] The model is decomposed as follows: according to the optimized model characteristics, machining tools and CNC system parameters, the maximum Z-direction depth of single machining at different positions is determined; according to the maximum Z-direction depth of single machining at different positions, the optimized model is divided along the Z-direction to obtain a construction sequence and a sub-model group.

[0015] The construction sequence is the manufacturing order of sub-models after the initial model is decomposed. In powder bed additive and subtractive composite manufacturing, the construction sequence is the manufacturing order of sub-models from small to large along the Z direction.

[0016] The additive manufacturing and subtractive processing are both performed on the same machine tool, and according to the construction sequence of the sub-model group, each sub-model in the sub-model group is alternately manufactured by additive and subtractive methods.

[0017] The subtractive strategy is as follows: the design model is divided using the same Z value plane in the model decomposition to obtain a sub-design model group; the sub-design model and sub-model of the same layer are set as the target part and the blank respectively for subtractive tool path planning; the first layer cutting area is set as the lower 9 / 10 part of the first layer self-supporting structure, and the upper 1 / 10 part is retained; the nth (n>1) layer cutting area is set as the lower 9 / 10 part of the nth layer self-supporting structure and the upper 1 / 10 part of the n-1 layer; the last layer cutting area is set as the last layer self-supporting structure part and the upper 1 / 10 part of the second to last layer; and the subtractive machining tool path of each layer is generated for subtractive machining according to the selected machining tool parameters and the set cutting area.

[0018] The powder bed support-free printing method based on additive and subtractive composite manufacturing technology is suitable for the integrated precision manufacturing of large-angle overhanging inner cavity structures.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The powder bed support-free printing method proposed in the present invention is combined with additive and subtractive composite manufacturing technology, and a self-supporting optimized design is used to replace the original support structure during additive manufacturing of large-angle overhang structures, which can improve the printing quality of large-angle overhang structures.

[0021] (2) The present invention realizes the support function of the lower structure for the subsequent layers through the formulated additive and subtractive composite manufacturing strategy and T-shaped tool, which is conducive to the integrated precision manufacturing of parts with large-angle overhang structures.

[0022] (3) The method proposed in the present invention is also applicable to the integrated precision manufacturing of large-angle overhanging inner cavity structures. Compared with the traditional method, which has the disadvantages of difficult removal of internal supporting structures and poor surface forming quality, the present method can remove the internal self-supporting structure in steps during the additive and subtractive composite manufacturing process, and can realize the integrated precision manufacturing of parts with large-angle overhanging inner cavity structures without the need to remove the supporting structure later. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the overall flow chart of the present invention.

[0024] Figure 2 This is a flow chart of the self-supporting design scheme of the present invention.

[0025] Figure 3 This is a flow chart of the model decomposition strategy of the present invention.

[0026] Figure 4 Develop a flow chart for the material reduction strategy of the present invention.

[0027] Figure 5 These are examples of the self-supporting design of the present invention; (a) is the design model, and (b) is the optimized model.

[0028] Figure 6 This is an example diagram of the model decomposition of the present invention; (a) is the model decomposition strategy judgment, and (b) is the sub-model group after decomposition.

[0029] Figure 7 Schematic diagram of the additive and subtractive composite manufacturing process and subtractive strategy of the present invention.

[0030] Figure 8 This is a flow chart of the unsupported forming of a large-angle overhanging inner cavity structure of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0032] Reference Figure 1, a powder bed support-free printing method based on additive and subtractive composite manufacturing technology, comprising the following steps:

[0033] First, the design model 101 is subjected to self-supporting design 2 to obtain an optimized model 102;

[0034] Then, according to the parameters of the machining tool 103, the optimized model 102 is subjected to model decomposition 3 to obtain a construction sequence 104 and a sub-model group 105;

[0035] Finally, each sub-model in the sub-model group 105 is additively manufactured 4 in sequence according to the construction sequence 104, and a subtractive strategy 6 is used to alternately perform subtractive processing 5 on each sub-model after the additive construction is completed, so as to control its appearance to be the same as the design model 101, until all sub-models are constructed, and the design part 106 without a support structure can be directly obtained.

[0036] Reference Figure 2 、 Figure 5 , the specific scheme of the self-supporting design 2 is:

[0037] Step 201, determining the maximum build angle of the powder bed additive manufacturing equipment;

[0038] Step 202: Find a surface in the design model 101 whose angle between the tangent direction and the build direction is greater than the maximum build angle (large-angle overhang surface);

[0039] In step 203 , the angle of the large-angle overhang surface is finally compensated to the maximum construction angle of the device so that it can achieve self-support during the printing process, thereby obtaining the optimized model 102 ; the self-support structure 102 - 1 added in the self-support design 2 can be removed in the subsequent subtractive processing 5 .

[0040] Reference Figure 6 The processing tool 103 is a T-type milling cutter, which can process the self-supporting structure with a negative angle; according to the different forms of the processed surface, T-type milling cutters with different specifications and parameters are selected.

[0041] Reference Figure 3 、 Figure 6 , the model decomposition 3 strategy is:

[0042] Step 301 , determining the maximum Z-direction depth of a single machining operation at different positions based on the features of the optimization model 102 , the machining tool 103 , and the parameters of the numerical control system, and obtaining multiple Z-direction cutting planes such as P1 to P7 ;

[0043] In step 302 , the optimized model 102 is divided along the Z direction according to the maximum Z-direction depth of a single machining operation at different positions to obtain a construction sequence 104 and a sub-model group 105 .

[0044] Reference Figure 6The construction sequence 104 is the order in which the sub-models are manufactured after the initial model is decomposed. In this embodiment, the construction sequence 104 is the sub-model group 105 numbered sub-models 105 - 1 , 105 - 2 , ... 105 - 8 .

[0045] Reference Figure 4 、 Figure 7 , the material reduction strategy 6 is:

[0046] Step 601 , using the same Z-value plane as in step 3 of model decomposition to divide the design model 101 into sub-design model groups;

[0047] Step 602 , setting the sub-design model and sub-models 105 - 1 to 105 - 8 on the same layer as the target part and blank, respectively, for subtractive tool path planning;

[0048] Step 603 , setting the first-layer cutting area to the lower 9 / 10 portion of the first-layer self-supporting structure, retaining the upper 1 / 10 portion, and obtaining the sub-designed part 106 - 1 by additive manufacturing 4 of the sub-model 105 - 1 and subtractive processing 5 ;

[0049] Step 604 , setting the cutting area of ​​the nth layer (n>1) to the lower 9 / 10 portion of the self-supporting structure of the nth layer and the upper 1 / 10 portion of the n-1th layer. When the sub-model 105-n is additively manufactured 4 , the uncut self-supporting structure of the sub-designed part 106-(n-1) provides support for it, allowing the additive manufacturing 4 process to proceed smoothly. Subsequently, part of the self-supporting structure is removed through subtractive processing 5 to obtain the sub-designed part 106-n.

[0050] In step 605 , the last cutting area is set to be the last self-supporting structure part and the upper 1 / 10 part of the second-to-last layer, and the designed part 106 is finally obtained through additive manufacturing 4 sub-models 105 - 8 and subtractive processing 5 .

[0051] The additive manufacturing and subtractive processing are both carried out on the same machine tool. For specific forms, please refer to: ZL202110598775.3 "A powder bed five-axis additive and subtractive composite manufacturing equipment"; according to the construction sequence of the sub-model group, each sub-model in the sub-model group is alternately manufactured by additive and subtractive methods.

[0052] Reference Figure 8The powder bed support-free printing method based on additive and subtractive composite manufacturing technology is suitable for the integrated precision forming of large-angle overhanging internal cavity structures. Through self-supporting design 2, the designed model 101 is converted into an optimized model 102. The model decomposition plane is then determined based on the parameters of the machining tool 103, resulting in a build sequence 104 and a sub-model group 105. Finally, according to the build sequence 104, the sub-models in the sub-model group 105 are additively manufactured 4 and subtractively processed 5. After all sub-models are fully processed, the designed part 106 is obtained. This method overcomes the difficulty of removing traditional internal cavity support structures, effectively improving the size and surface accuracy of additively manufactured large-angle overhanging internal cavities.

Claims

1. A powder bed unsupported printing method based on additive and subtractive composite manufacturing technology, characterized in that: The following steps are involved: First, the design model is self-supported to obtain the optimized model; Then, according to the machining tool parameters, the optimization model is decomposed to obtain the construction sequence and sub-model group; Finally, each sub-model in the sub-model group is additively manufactured in sequence according to the construction sequence, and a subtractive strategy is used to alternately perform subtractive processing on each sub-model after the additive construction is completed, controlling its appearance to be the same as the design model, until all sub-models are constructed, thus obtaining the designed part with no support structure. The self-support design involves first determining the maximum build angle of the powder bed additive manufacturing equipment; then finding a surface in the design model whose angle between the tangent direction and the build direction is greater than the maximum build angle, i.e., a large-angle overhang surface; and finally compensating the angle of the large-angle overhang surface to the maximum build angle of the equipment, so that the surface achieves self-support during printing, thereby obtaining an optimized model. The model is decomposed as follows: determining the maximum Z-direction depth of a single machining at different positions according to the optimized model characteristics, machining tools, and CNC system parameters; dividing the optimized model along the Z-direction according to the maximum Z-direction depth of a single machining at different positions to obtain a construction sequence and a sub-model group; The subtractive strategy is as follows: the design model is divided using the same Z-value plane in the model decomposition to obtain a sub-design model group; the sub-design models and sub-models at the same layer are set as the target part and blank, respectively, for subtractive tool path planning; the first-layer cutting area is set as the lower 9 / 10 part of the first-layer self-supporting structure, and the upper 1 / 10 part is retained; The cutting area of ​​the nth layer is set to the lower 9 / 10 part of the nth layer self-supporting structure and the upper 1 / 10 part of the n-1th layer, where n>1; the cutting area of ​​the last layer is set to the last layer self-supporting structure part and the upper 1 / 10 part of the second to last layer; and the subtractive machining tool path of each layer is generated for subtractive machining according to the selected machining tool parameters and the set cutting area.

2. The method according to claim 1, characterized in that The processing tool is a T-type milling cutter, which is used to process the self-supporting structure with a negative angle; according to the different forms of the processed curved surface, T-type milling cutters with different specifications and parameters are selected.

3. The method according to claim 1, characterized in that The construction sequence is the manufacturing order of sub-models after the initial model is decomposed. In powder bed additive and subtractive composite manufacturing, the construction sequence is the manufacturing order of sub-models from small to large along the Z direction.

4. The method according to claim 1, wherein The additive manufacturing and subtractive processing are both performed on the same machine tool, and according to the construction sequence of the sub-model group, each sub-model in the sub-model group is alternately manufactured by additive and subtractive methods.

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