A method for scanning path planning in laser additive manufacturing considering overhang feature recognition

Abstract

The present invention discloses a laser additive manufacturing scanning path area planning method considering overhang feature recognition, taking the three-dimensional model file of the part as the object, dividing the triangular facets into a set of overhang triangular facets and a set of non-overhang triangular facets; marking the overhang edge and establishing the overhang edge index when the tangent segment is intersected, and by traversing the slice contour, the slice contour line segment of the overhang mark is offset to the internal area of ​​the slice contour; the offset line segment contour is used as a dividing line to further divide the overhang area and the non-overhang area, and the laser additive manufacturing scanning path planning is performed on the overhang area and the non-overhang area. The present invention identifies and extracts the overhang triangular facets based on the three-dimensional model file information, and then divides the overhang area of ​​the two-dimensional slice contour, and performs path planning by deciding the appropriate scanning method for the feature area and the non-feature area, thereby ensuring the forming quality of the overhang structure of the part.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser powder bed fusion additive manufacturing, and in particular relates to a laser additive manufacturing scanning path regional planning method considering overhang feature recognition. Background Art

[0002] Laser powder bed fusion is one of the main technologies for metal additive manufacturing. According to the three-dimensional design model of the part, a high-power laser beam is used as the energy source to selectively melt solid metal powder along a certain scanning path, and high-density parts are directly formed by layer-by-layer powder laying, layer-by-layer solidification and superposition. Laser powder bed fusion (LPBF) has the advantages of short manufacturing cycle, high material utilization rate, high dimensional accuracy of formed parts, and brings considerable flexibility to part design. In recent years, LPBF technology has received much attention from the aviation, aerospace, biomedical and other industries, and has shown good application results.

[0003] Laser scanning path planning is an important factor affecting the quality of parts formed by LPBF technology. Reasonable process strategies, such as reasonable laser power, scanning speed, scanning path, scanning line spacing, etc., can effectively improve the forming quality of parts. Due to the special structure of overhanging structural features, lower laser power and faster scanning speed should be used when printing. Different from the process parameters used in the solid area, the forming quality of typical structural features such as overhanging features can be improved by controlling the process parameters.

[0004] However, when existing equipment forms parts, it only uses different process parameters for printing the solid and the contour respectively, without fully considering the differences in process strategies for the structural characteristics of the parts, and without taking into account the relationship between the structural characteristics and the forming quality. Due to the asymmetry of the cut layer contour and the difference in the contour morphology between layers, a single fixed general process strategy is difficult to effectively balance the stress distribution during the LPBF technology forming process, and it is difficult to more effectively improve the forming quality. It is necessary to realize the adaptive allocation of process strategies according to the morphological characteristics of the parts. Summary of the invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a laser additive manufacturing scanning path regional planning method that takes overhang feature recognition into consideration. The three-dimensional model file information is identified and overhang triangular facets are extracted. The overhang area is then divided in combination with the two-dimensional slice contour. By assigning different scanning modes to the overhang area and the non-overhang area, regional path planning is achieved, thereby ensuring the forming quality of the overhang structure of the part.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0007] A laser additive manufacturing scanning path regional planning method considering overhang feature recognition, the method specifically comprising:

[0008] Taking the 3D model file of the part as the object, the triangular facets of the 3D model file are divided into a set of overhanging triangular facets and a set of non-overhanging triangular facets according to the normal vector directions of the triangular facets of the 3D model file;

[0009] Then, when the tangent segment is intersected, the overhang edge is marked and the overhang edge index is established. By traversing the slice contour, the slice contour line segment of the overhang mark is offset to the inner area of ​​the slice contour by a custom distance.

[0010] The offset line segment contour is used as the dividing line to divide the overhang area and the non-overhang area, and the laser additive manufacturing scanning path planning is performed on the overhang area and the non-overhang area.

[0011] To optimize the above technical solutions, the specific measures taken also include:

[0012] The above methods include:

[0013] Step 1: Taking the 3D model file of the part as the object, traverse the triangular facets of the 3D model, and read the external normal vector of the triangular facet, identify the dangling triangular facets in the 3D model according to the spatial angle between the external normal vector of the triangular facet and the printing direction, and mark the dangling triangular facets to obtain a set of dangling triangular facets and a set of non-dangling triangular facets;

[0014] Step 2: Solve the tangent segment of the triangle. If it is a hanging triangle, mark the tangent segment as hanging until all triangles are traversed and all the cut contours are obtained;

[0015] Step 3: Traverse the obtained slice contour and find the marked dangling edges;

[0016] Step 4: Determine the correct offset direction according to the position of the point on the hanging edge, and obtain the point after the custom distance offset according to the direction;

[0017] Step 5: Make a boundary judgment on the offset point, perform corresponding processing according to its position, and obtain the corresponding overhang point set and overhang offset point set;

[0018] Step 6: Merge the overhang point set and the overhang offset point set to obtain the overhang area corresponding to the slice contour, and obtain the non-overhang area through Boolean operation;

[0019] Step 7: Traverse each slice contour in turn, obtain the overhang area and non-overhang area of ​​each slice contour, and perform customized planning of the laser additive manufacturing scanning strategy.

[0020] In the above step 1, the critical angle θ required to identify the overhanging inclination angle is customized and compared with the complementary angle (180° -α) between the external normal vector of the triangle and the angle α of the forming direction, and the triangles less than the critical value are marked as overhanging triangles.

[0021] In step 4 above, the method to determine the correct bias direction is as follows:

[0022] When the dangling point is the first point of the dangling edge, the two unit vectors formed by the dangling point and the previous point are and With ∠p i-1 p i p i+1 Compare the angle formed by the angle bisector vector of the angle bisector, and select the unit vector that forms an acute angle with the angle bisector vector as the correct bias direction;

[0023] When the overhang point is the middle point of the overhang edge, select the angle bisector vector as the correct offset direction;

[0024] When the dangling point is the last point of the dangling edge, the two unit vectors formed by the dangling point and the last point are and With ∠p i-1 p i p i+1 Compare the angle formed by the angle bisector vector of the angle, and select the unit vector that forms an acute angle with the angle bisector vector as the correct bias direction.

[0025] In the above step 5, the ray method is used to determine whether the offset point is within the slice contour. If so, it does not cross the boundary and the point is placed in the set for storing overhang offset points. Otherwise, the intersection of the line segment composed of the offset point and the overhang point and the slice contour is solved and the intersection is placed in the set for storing overhang offset points.

[0026] In the above step 7, for the overhanging area and non-overhanging area after the slice contour is divided, the overhanging area can be assigned with variable angle parallel scanning and serpentine scanning strategies, and the non-overhanging area can be assigned with variable angle parallel scanning, serpentine scanning and island scanning strategies.

[0027] In the above step 7, two scanning strategies, serpentine scanning and island scanning, are allocated according to the size of the bounding box of the non-overhanging area. If the bounding box size is less than 5×5 mm, parallel scanning or serpentine scanning strategy is allocated, and if it is larger than 5×5 mm, island scanning strategy is allocated.

[0028] The present invention has the following beneficial effects:

[0029] The present invention identifies and extracts overhanging triangular facets based on the three-dimensional model file information, and then divides the overhanging area of ​​the two-dimensional slice contour. The path planning is performed by deciding the appropriate scanning method for the feature area and the non-feature area, thereby ensuring the forming quality of the overhanging structure of the part.

[0030] 1. The present invention uses a three-dimensional model as an object, identifies and extracts the overhanging area, and plans the scanning path for the overhanging area and the non-overhanging area respectively, so as to avoid a single scanning method from generating an inappropriate scanning path in the overhanging area;

[0031] 2. The present invention utilizes the structural characteristics of the overhanging area and the non-overhanging area to allocate appropriate process parameters, thereby avoiding local heat accumulation and even thermal deformation, and ensuring the forming quality of the overhanging structure of the part. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A flow chart of a method for regional planning of laser additive manufacturing scanning paths considering overhang feature recognition according to the present invention;

[0033] Figure 2 This is a schematic diagram of normal vector determination based on triangular facets of the present invention;

[0034] Figure 3 This is a triangle patch marking effect diagram based on a custom range of triangle patch normal vectors according to the present invention.

[0035] Figure 4 It is a verification model case of the method of the present invention;

[0036] Figure 5 This is a schematic diagram of the cut contour of a layer with an overhanging structure;

[0037] Figure 6 Schematic diagram of the scanning path of the overhanging area after custom path planning;

[0038] Figure 7 Schematic diagram of the scanning path in the non-overhanging area after customized path planning. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0040] The present invention discloses a laser additive manufacturing scanning path sub-area planning method considering overhang feature recognition, the process is as follows: Figure 1 As shown in the figure, this method can identify and extract overhanging triangular facets based on the 3D model file information, and then divide the overhanging area of ​​the 2D slice contour, and plan the path by deciding the appropriate scanning method for the feature area and the non-feature area, so as to ensure the forming quality of the overhanging structure of the part. The method is as follows:

[0041] Taking the 3D model file of the part as the object, the triangular facets of the 3D model file are divided into a set of overhanging triangular facets and a set of non-overhanging triangular facets according to the normal vector directions of the triangular facets of the 3D model file;

[0042] Then, when the tangent segment is intersected, the overhang edge is marked and the overhang edge index is established. By traversing the slice contour, the slice contour line segment of the overhang mark is offset to the inner area of ​​the slice contour by a custom distance.

[0043] The offset line segment contour is used as the dividing line to divide the overhang area and the non-overhang area, and the laser additive manufacturing scanning path planning is performed on the overhang area and the non-overhang area.

[0044] In an embodiment, the method comprises the following steps:

[0045] Step 1: Take the 3D model file of the part as the object, traverse the triangular facets of the 3D model, and read the external normal vector of the triangular facet. According to the spatial angle between the normal vector of the triangular facet and the printing direction, identify the overhanging triangular facets in the 3D model and mark the overhanging triangular facets, such as Figure 2 As shown, the following formula is used:

[0046]

[0047] in, Represents the normal vector direction of the triangle patch, Represents the direction of the external normal vector of the triangular face. Given the custom critical angle θ required to identify the overhang inclination, it is compared with the complementary angle of α (180-α). The triangular facets smaller than the critical value are marked. Taking the spherical model as an example, the marking effect is as follows: Figure 3 shown.

[0048] Figure 2 The schematic diagram of the normal vector judgment based on the triangular facet of the present invention is shown in FIG. The printing direction is generally the Z-axis direction, which is the vector The normal vector of the triangle patch is The overhanging triangular facets whose overhanging inclination angle is less than the critical value are determined by comparing the supplementary angle (180° -α) of the space vector angle α with the custom critical value angle θ.

[0049] Figure 3 This is the effect diagram of the triangle patch marking based on the self-defined range of the triangle patch normal vector of the present invention. Taking the spherical model as an example, a self-defined critical value is defined, the triangle patches of the spherical model are traversed and the triangle patches within the critical value range are marked, and the effect is shown in the figure.

[0050] Step 2: Solve the tangent segment of the triangle. If it is a hanging triangle, mark the tangent segment as hanging until all triangles are traversed and all the cut contours are obtained;

[0051] Step 3: Traverse the obtained slice contour and find the marked dangling edges;

[0052] Step 4: Determine the correct offset direction based on the position of the point on the hanging edge, and obtain the point after the custom distance offset is performed according to the direction. The correct offset direction is determined by the following formula:

[0053]

[0054] in, is the correct bias direction vector, is the angle bisector vector of the point inside the slice contour. The angle between the two vectors must be an acute angle to ensure that the offset point is inside the slice contour.

[0055] Step 5: Check the out-of-bounds status of the offset points and process them accordingly based on their positions to obtain the corresponding overhang point set and overhang offset point set. Specifically:

[0056] The ray method is used to determine whether the offset point is within the slice contour. If so, it does not cross the boundary and the point is placed in the set for storing overhang offset points. Otherwise, the intersection of the line segment composed of the offset point and the overhang point and the slice contour is solved and the intersection is placed in the set for storing overhang offset points.

[0057] Step 6: Merge the overhang point set and the overhang offset point set to obtain the overhang area of ​​the slice contour, and obtain the non-overhang area through Boolean operation;

[0058] Step 7: Traverse each slice contour in turn, obtain the overhang area and non-overhang area of ​​each slice contour, and perform customized planning of the scanning strategy.

[0059] Among them, when performing custom planning, the two scanning strategies of serpentine scanning and island scanning can be customized according to the size of the bounding box of the non-overhanging area. If the bounding box size is less than 5×5mm, parallel scanning or serpentine scanning can be allocated, and if it is larger than 5×5mm, island scanning can be allocated.

[0060] Figure 4 The model used for verification of the present invention. The cut profile at the overhanging structure is as follows: Figure 5 As shown, the scanning path planning is performed by the algorithm of the present invention, and the 0° and 90° serpentine scanning strategies are respectively assigned to the overhanging area, and the 45° serpentine scanning and the 0° island scanning strategy are assigned to the non-overhanging area, as shown in FIG. Figure 6 ,7 shown.

[0061] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for regional planning of laser additive manufacturing scanning paths considering overhang feature recognition, characterized in that: The method comprises: Step 1: Taking the 3D model file of the part as the object, traverse the triangular facets of the 3D model, and read the external normal vector of the triangular facet, identify the dangling triangular facets in the 3D model according to the spatial angle between the external normal vector of the triangular facet and the printing direction, and mark the dangling triangular facets to obtain a set of dangling triangular facets and a set of non-dangling triangular facets; Step 2: Solve the tangent segment of the triangle. If it is a hanging triangle, mark the tangent segment as hanging until all triangles are traversed and all the cut contours are obtained; Step 3: Traverse the obtained slice contour and find the marked dangling edges; Step 4: Determine the correct offset direction according to the position of the point on the hanging edge, and obtain the point after the custom distance offset according to the direction; Step 5: Make a boundary judgment on the offset point, perform corresponding processing according to its position, and obtain the corresponding overhang point set and overhang offset point set; Step 6: Merge the overhang point set and the overhang offset point set to obtain the overhang area corresponding to the slice contour, and obtain the non-overhang area through Boolean operation; Step 7: Traverse each slice contour in turn, obtain the overhang area and non-overhang area of ​​each slice contour, and perform customized planning of the laser additive manufacturing scanning strategy.

2. The method for regional planning of laser additive manufacturing scanning paths considering overhang feature recognition according to claim 1, characterized in that: In step 1, the critical angle θ required to identify the overhanging inclination angle is customized and compared with the complementary angle (180°-α) between the external normal vector of the triangle and the angle α of the forming direction, and the triangles smaller than the critical value are marked as overhanging triangles.

3. The method for regional planning of laser additive manufacturing scanning paths considering overhang feature recognition according to claim 1, characterized in that: In step 4, the method for determining the correct bias direction is as follows: When the dangling point is the first point of the dangling edge, the two unit vectors formed by the dangling point and the previous point are and With ∠p i-1 p i p i+1 Compare the angle formed by the angle bisector vector of the angle bisector, and select the unit vector that forms an acute angle with the angle bisector vector as the correct bias direction; When the overhang point is the middle point of the overhang edge, select the angle bisector vector as the correct offset direction; When the dangling point is the last point of the dangling edge, the two unit vectors formed by the dangling point and the last point are and With ∠p i-1 p i p i+1 Compare the angle formed by the angle bisector vector of the angle, and select the unit vector that forms an acute angle with the angle bisector vector as the correct bias direction.

4. The method for regional planning of laser additive manufacturing scanning paths considering overhang feature recognition according to claim 1, characterized in that: In step 5, the ray method is used to determine whether the offset point is within the slice contour. If so, it does not cross the boundary and the point is placed in the set storing the overhang offset point. Otherwise, the intersection of the line segment composed of the offset point and the overhang point and the slice contour is solved and the intersection is placed in the set storing the overhang offset point.

5. The method for regional planning of laser additive manufacturing scanning path considering overhang feature recognition according to claim 1, characterized in that: In step 7, for the overhanging area and the non-overhanging area divided by the slice contour, the overhanging area is assigned with the variable angle parallel scanning and serpentine scanning strategies, and the non-overhanging area is assigned with the variable angle parallel scanning, serpentine scanning and island scanning strategies.

6. The method for regional planning of laser additive manufacturing scanning paths considering overhang feature recognition according to claim 5, characterized in that: In step 7, two scanning strategies, serpentine scanning and island scanning, are allocated according to the size of the bounding box of the non-overhanging area. If the bounding box size is less than 5×5 mm, parallel scanning or serpentine scanning strategy is allocated, and if the bounding box size is greater than 5×5 mm, island scanning strategy is allocated.

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