A multi-layer machining path adaptive planning method for complex cavity type part additive and subtractive composite manufacturing

Abstract

A kind of complex cavity class part additive-subtractive composite manufacturing multilayer machining path adaptive planning method, first STEP model analysis is carried out, the mapping between computer and STEP model and topological relationship are established;Then carry out composite machining feature identification, according to the topological relationship between STEP model entity, based on feature map and composite machining judging criterion, identify composite machining feature in STEP model, and extract each composite machining internal topological ring and boundary;Finally, multilayer machining path planning is carried out, according to the boundary of topological ring extracted, using boundary guide method, obtain each topological ring tool shaft vector, tool contact point and extended tool path, according to the layer height interval of additive-subtractive alternation surface, according to G code rule, output corresponding machining path file;The present application can realize the required multilayer, multi-axis, precision controllable non-interference machining path fast generation of additive-subtractive composite manufacturing, effectively reduce the machining preparation time and workload of additive-subtractive composite manufacturing, improve the automation degree of entire composite manufacturing process.

Description

Technical Field

[0001] This invention relates to the field of machining path planning technology in additive and subtractive composite manufacturing, specifically to an adaptive planning method for multi-layer machining paths in the additive and subtractive composite manufacturing of complex cavity parts. Background Technology

[0002] Additive-subtractive composite manufacturing is a manufacturing method that combines additive manufacturing with CNC machining. Its forming principle is: during the near-net-shape forming process of parts, the reasonable alternation of additive and subtractive processes is used to improve the quality and precision of the internal structure of the parts, and realize the integrated precision forming of complex internal structure parts. This method can improve the accessibility of tools and the surface precision of additive parts, and provide a solution for the integrated precision manufacturing of parts that are difficult to manufacture by CNC machining (such as parts with complex cavities).

[0003] Machining path planning is a crucial step in data preparation before composite manufacturing, directly impacting the surface quality and performance of parts. When the part structure is relatively simple, commercial CAM software can be used for overall machining path planning. However, when dealing with complex part structures (especially those with intricate internal structures), considering tool accessibility, commercial software does not support direct machining path planning.

[0004] Existing methods for multi-layer processing path planning in additive and subtractive hybrid manufacturing can be divided into two categories: Method 1 uses CAD software to decompose the model into multiple sub-models from which processing paths can be planned at once, and then uses CAM software to plan the processing path for each sub-model individually (Y. Wang et al, The process planning for additive and subtractive hybrid manufacturing of powder bed fusion (PBF) process. Mater. Design. 227 (2023) 111732). Method 2 uses model slicing and a tracking method to generate the outer contour, which is then used as the processing path (A. Roschli et al, ORNL slicer 2: a novel approach for additive manufacturing tool path planning, Solid Free. Fabr. Symp. 7 (2017)).

[0005] While the above two methods can plan multi-layer machining paths required for additive and subtractive manufacturing, the first method is particularly complex and inefficient when dealing with complex internal features of the model and the need for multiple model decomposition surfaces. The second method's machining accuracy is limited by the accuracy of the model slices, and there is no topological relationship between the slices, making it unsuitable for multi-axis machining path planning. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide an adaptive planning method for multi-layer machining paths in the additive-subtractive composite manufacturing of complex cavity parts. This method can quickly and intelligently identify the additive-subtractive composite manufacturing features inside complex cavity parts and the interference planes at cavity transitions. It can also quickly and adaptively plan multi-layer, multi-axis, precision-controllable, interference-free machining paths required for additive-subtractive composite manufacturing, greatly reducing the machining preparation time and workload of additive-subtractive composite manufacturing and improving the automation level of the entire composite manufacturing process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An adaptive planning method for multi-layer machining paths in the additive and subtractive manufacturing of complex cavity parts includes the following steps:

[0009] (a) STEP model analysis: Establish the mapping relationship a1 between the computer and the STEP model, and establish the topological relationship a2 between the entities in the STEP model;

[0010] (b) Composite processing feature identification: Based on the topological relationship between entities in the STEP model (a2), a face-edge graph (b1) is constructed using the feature graph construction method. The concavity and convexity of each face and adjacent edge are determined, and an attribute adjacency graph (b2) is constructed. Only concave faces and concave edges are retained to construct a minimum subgraph (b3). Then, the quasi-processing features (b4) in the STEP model are extracted from the minimum subgraph (b3) using a breadth-first search algorithm. Based on the attribute adjacency graph (b2), only nodes and connections related to the quasi-processing features (b4) are retained to construct a feature attribute adjacency graph (b5). The topological loops within the features (b6) and the boundaries of each topological loop (b7) are extracted. According to the composite processing feature judgment criteria, it is determined whether each quasi-processing feature is a composite processing feature (b8). Combining the topological loop boundaries (b7), each composite processing feature (b8) is transformed into a "boundary-loop-boundary" form (b9).

[0011] (c) Multi-layer machining path planning: Based on the "boundary-loop-boundary" form of each composite machining feature (b9), the boundary guidance method (c1) is adopted. Through cutting depth control (c2) and cutting step length control (c3), the machining path accuracy is controlled to obtain the tool axis vector (c4), tool contact point (c5), and extended toolpath (c6) of each topological loop. The user-defined transformation surface (c7) and the plane between topological loops (c8) are used as the alternating surface (c9). Based on the layer height interval of the alternating surface, a multi-layer machining path file group (c10) is defined. The tool axis vector (c4), tool contact point (c5), and extended toolpath (c6) are output to the corresponding machining path file according to the G-code rules to obtain the multi-layer, multi-axis, precision-controllable, interference-free machining path (c11) required for additive and subtractive composite manufacturing.

[0012] The feature graph construction method in step (b) refers to: taking each face in the STEP model entity as a node and the adjacent edges as node connections, and constructing a face-edge graph b1, an attribute adjacency graph b2, a minimum subgraph b3, and a feature attribute adjacency graph b5 by adding nodes and node connection attributes as needed; in the program, the feature graph is represented by a two-dimensional matrix, where the number of rows and columns of the matrix is ​​equal to the number of faces in the STEP model.

[0013] The method for determining the concavity and convexity of each face and adjacent edge in step (b) is as follows:

[0014] Concavity / convexity determination of surfaces: Planes have no concavity / convexity; The concavity / convexity of cylinders is determined by the direction of the normal vector under the topological logic of the cylinder feature in the STEP model. If the normal vector points into the cylinder, it is a convex cylinder; otherwise, it is a concave cylinder; B-spline surfaces have no global concavity / convexity. Considering that B-spline surfaces are generally used as feature transition surfaces, they are considered as concave surfaces.

[0015] Determining the concavity / convexity of an edge: Determining the concavity / convexity of an edge is transformed into finding the dihedral angle between adjacent faces. For the STEP model, assume that edge E is the intersection of faces F1 and F2, ring L is the boundary ring on face F1 (its direction satisfies the right-hand rule), N1 and N2 are the unit outward normal vectors of faces F1 and F2, point P is a point on edge E, and vector T is the unit tangent vector of edge E at point P along the direction of ring L. Then the concavity / convexity of edge E is determined by the following formula:

[0016] m=(N1×N2)·T (1)

[0017] If m > 0, then edge E is a convex edge; if m < 0, then edge E is a concave edge; if m = 0, then edge E is a tangent edge.

[0018] For edges that come into contact with B-spline surfaces, including B-spline curves, the inner and outer boundary identification method is used. That is, if the edge belongs to the inner contour on a certain surface, it is a convex edge; otherwise, it is a concave edge.

[0019] The quasi-machining feature b4 is: in the smallest subgraph b3, a face-edge group composed of multiple concave attributes, which corresponds to the CNC machining features in the STEP model, namely the features of open cavity, closed cavity, and hole.

[0020] The topological ring b6 is defined as follows: In the smallest subgraph b3, a ring formed by multiple faces or a closed face connected end to end is called a feature topological ring, which represents a cavity feature in the STEP model; if a feature has multiple topological rings, it means that the feature is composed of multiple cavities, and the tool interference of a certain cavity may be affected by other cavities in the same feature.

[0021] The topological ring boundary b7 is constructed by obtaining the adjacent edge information between the constituent surfaces and adjacent surfaces of each topological ring based on the adjacency graph b5 of the feature attributes, thereby constructing the topological ring boundary. Each topological ring has two boundaries. The topological ring boundary contains the edge number, inner and outer boundary identifiers, start point and end point information. The topological ring boundary b7 is a ring with the beginning and end connected.

[0022] The composite processing feature b8 is: a feature that requires additive or subtractive material composite manufacturing to fully perform surface processing is called a composite processing feature, which has two characteristics: non-openness and having a complex internal structure or a large length-to-diameter ratio.

[0023] The criteria for judging composite processing features are as follows: the inner and outer boundary identifiers of the feature starting boundary, i.e. the boundary composed of the outermost topological ring and the non-feature surface, are both inner boundaries, and the feature is composed of multiple topological rings or has a large aspect ratio.

[0024] The inner and outer boundaries are identified as follows: In the STEP model entity, the FACE_BOUND entity has two types: FACE_INNER_BOUND and FACE_OUTER_BOUND; FACE_INNER_BOUND is used to represent the inner closed boundary of the surface, and FACE_OUTER_BOUND is used to represent the outer boundary of the surface.

[0025] The cutting depth control method c2 includes: constant depth control and constant quantity control. The constant depth control method is suitable for cutting depth planning when there are many model features; the constant quantity control method is only suitable for cutting depth planning when there are few model features or when the height difference between the features is small.

[0026] The cutting step length control method c3 requires different control methods depending on the type of the guiding boundary. The step length of the straight boundary directly follows the boundary length; the step length of the arc boundary is controlled by a constant angle; and the step length of the B-spline curve boundary is controlled by node subdivision.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) The present invention identifies composite processing features in the STEP model and potential interference surfaces at cavity conversion based on rule and feature map method, saving training time based on machine learning feature recognition method.

[0029] (2) The present invention uses the boundary guidance method to plan the tool contact points of cavity-type parts. The machining accuracy is controllable by human, and the topological logic between the tool contact points is preserved, which can be used to generate multi-layer multi-axis machining paths.

[0030] (3) This invention can quickly plan multi-layer, multi-axis, precision-controllable non-interference processing paths required for additive and subtractive composite manufacturing, effectively improving the efficiency of processing path planning and the automation level of the additive and subtractive composite manufacturing processing preparation process. The final processing path file is based on G-code rules and can be directly used for various types of additive and subtractive composite manufacturing equipment, and has wide applicability. Attached Figure Description

[0031] Figure 1 This is a flowchart of the present invention.

[0032] Figure 2 This is a STEP model diagram of an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram illustrating how the determination of the concavity / convexity of an edge in this invention is transformed into the problem of finding the dihedral angle between adjacent surfaces.

[0034] Figure 4 Figure (I) is a face-edge graph; Figure (II) is an attribute adjacency graph; Figure (III) is a minimum subgraph; and Figure (IV) is an attribute adjacency graph.

[0035] Figure 5 Figure (I) shows the comparison between the STEP model and features in the embodiment of the present invention; Figure (II) shows the comparison between some topological loops in the STEP model and features of the embodiment; Figure (II) shows a schematic diagram of the boundary form of a certain topological loop.

[0036] Figure 6 This is a schematic diagram of the inner and outer boundary markings of the present invention.

[0037] Figure 7 This is a schematic diagram of the cutting depth control method of the present invention; wherein, Figure (I) is a constant depth control method; and Figure (II) is a constant quantity control method.

[0038] Figure 8 This is a schematic diagram of the cutting step length control method of the present invention; wherein, Figure (I) shows the step length control method for straight lines and arcs; and Figure (II) shows the step length control method for B-spline curves.

[0039] Figure 9 This is a diagram illustrating the implementation of adaptive planning for multi-layer processing paths in the STEP model according to an embodiment of the present invention. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] Reference Figure 1 An adaptive planning method for multi-layer machining paths in the additive and subtractive manufacturing of complex cavity parts includes the following steps:

[0042] (a) STEP Model Analysis: Establish the mapping relationship between the computer and the STEP model a1, and establish the topological relationship between the entities within the STEP model a2, so as to provide a foundation for subsequent composite processing feature recognition based on feature maps;

[0043] (b) Composite Processing Feature Identification: Based on the topological relationship a2 between entities in the STEP model, a face-edge graph b1 is established using the feature graph construction method to store information such as face number, adjacent edge number, start point, end point, and inner and outer boundary markers; the concavity and convexity of each face and adjacent edge are determined, and an attribute adjacency graph b2 is established; only concave faces and concave edges are retained to establish a minimum subgraph b3; then, the quasi-processing features b4 in the STEP model are extracted from the minimum subgraph b3 using a breadth-first search algorithm; based on the attribute adjacency graph b2, only nodes and connections related to the quasi-processing features b4 are retained to establish a feature attribute adjacency graph b5, and the topological loops b6 and the boundaries of each topological loop are extracted; according to the composite processing feature judgment criteria, it is determined whether each quasi-processing feature is a composite processing feature b8; combined with the topological loop boundaries b7, each composite processing feature b8 can be transformed into a "boundary-loop-boundary" form b9 to facilitate subsequent processing path planning;

[0044] (c) Multi-layer machining path planning: Based on the "boundary-loop-boundary" form of each composite machining feature (b9), the boundary guidance method (c1) is adopted. Through cutting depth control (c2) and cutting step length control (c3), the machining path accuracy can be controlled, and the tool axis vector (c4), tool contact point (c5), and extended toolpath (c6) of each topological loop are obtained. The user-defined transformation surface (c7) and the plane between topological loops (c8) are used as the alternating surface (c9). Based on the layer height interval of the alternating surface, the multi-layer machining path file group (c10) is defined. The tool axis vector (c4), tool contact point (c5), and extended toolpath (c6) are output to the corresponding machining path file according to the G-code rules, and finally, the multi-layer, multi-axis, precision-controllable, interference-free machining path (c11) required for additive and subtractive composite manufacturing is obtained.

[0045] In step (a), the mapping relationship a1 between the computer and the STEP model is as follows: Define each entity type in the STEP model in the program, including the number, keyword, name, topology and geometric information of each entity type; Based on the topological logical relationship stored in the STEP model, the topological relationship a2 between each entity in the STEP model can be established.

[0046] Reference Figure 2 The STEP model in the embodiment consists of 97 faces. The feature graph construction method in step (b) refers to: taking each face in the STEP model as a node and the adjacent edges as node connections, and constructing a face-edge graph b1, an attribute adjacency graph b2, a minimum subgraph b3, and a feature attribute adjacency graph b5 by adding nodes and node connection attributes as needed; in the program, the feature graph can be represented by a two-dimensional matrix, where the number of rows and columns of the matrix is ​​equal to the number of faces in the instance model.

[0047] The method for determining the concavity and convexity of each face and adjacent edge in step (b) is as follows:

[0048] Concavity / convexity determination of surfaces: Planes have no concavity / convexity; The concavity / convexity of cylinders is determined by the direction of the normal vector under the topological logic of the cylinder feature in the STEP model. If the normal vector points into the cylinder, it is a convex cylinder; otherwise, it is a concave cylinder; B-spline surfaces have no global concavity / convexity. Considering that B-spline surfaces are generally used as feature transition surfaces, they are considered as concave surfaces.

[0049] Reference Figure 3 The determination of the concavity / convexity of an edge can be transformed into the problem of finding the dihedral angle between adjacent surfaces. Assume that edge E is the intersection of surfaces F1 and F2, ring L is the boundary ring on surface F1 (its direction satisfies the right-hand rule), N1 and N2 are the unit outward normal vectors of surfaces F1 and F2, point P is a point on edge E, and vector T is the unit tangent vector of edge E at point P along the direction of ring L. Then the concavity / convexity of edge E is determined by the following formula:

[0050] m=(N1×N2)·T (1)

[0051] If m > 0, then edge E is a convex edge; if m < 0, then edge E is a concave edge; if m = 0, then edge E is a tangent edge.

[0052] For edges that come into contact with B-spline surfaces, including B-spline curves, the inner and outer boundary identification method is used. That is, if the edge belongs to the inner contour on a certain surface, it is a convex edge; otherwise, it is a concave edge.

[0053] The quasi-machining feature b4 is: in the smallest subgraph b3, a face-edge group composed of multiple concave attributes, which corresponds to the CNC machining features in the STEP model, namely, features such as open cavity, closed cavity, and hole.

[0054] Reference Figure 2 , Figure 4 Based on the topological relationships a2 between model entities, a face-edge graph b1 is constructed using the feature graph construction method, as follows: Figure 4 As shown in (Ⅰ), it is used to store information such as face number, adjacent edge number, start point, end point, and inner and outer boundary identifiers; to determine the concavity and convexity of each face and adjacent edge, the concave attribute feature is represented by bold lines and font, and an attribute adjacency graph b2 is established, as shown in (Ⅰ). Figure 4 As shown in (II); retaining only the concave attribute features, construct the minimum subgraph b3, as follows. Figure 4As shown in (III), it is easy to see from the smallest subgraph b3 that the STEP model consists of 6 quasi-processing features b4. The surfaces of each quasi-processing feature are: b4-1: surface 8-10, b4-2: surface 11-14, b4-3: surface 15, b4-4: surface 16-17, b4-5: 18-41, b4-6: 42-97, which correspond to the features such as open cavity, closed cavity, and hole in the embodiment model, respectively. Based on the attribute adjacency graph b2, only the nodes and connections related to the quasi-processing features b4 are retained to establish the feature attribute adjacency graph b5, as shown in Figure 3. Figure 4 As shown in (Ⅳ).

[0055] Reference Figure 4 Middle (III) Figure 4 Middle (Ⅳ) Figure 5 In (I), the topological ring b6 is: in the smallest subgraph b3, a ring formed by multiple faces or a closed face connected end to end is called a feature topological ring, which can represent a cavity feature in the STEP model; if a feature has multiple topological rings, it can represent that the feature is composed of multiple cavities, and the tool interference of a certain cavity may be affected by other cavities in the same feature.

[0056] Reference Figure 4 Middle (Ⅳ) Figure 5 In section (II), the topological ring boundary b7 is: based on the adjacency graph b5, it is easy to know the adjacent edge information between the constituent surfaces and adjacent surfaces of each topological ring, thus forming the topological ring boundary. Each topological ring has two boundaries; the topological ring boundary contains the edge number, inner and outer boundary identifiers, start point and end point information. Since the topological ring b6 is a ring with its head and tail connected, the topological ring boundary b7 is also a ring with its head and tail connected.

[0057] The composite processing feature b8 is: a feature that requires additive or subtractive material composite manufacturing to fully perform surface processing is called a composite processing feature, which often has two characteristics: non-openness; and a relatively complex internal structure or a large length-to-diameter ratio.

[0058] The criteria for judging composite processing features are as follows: the inner and outer boundary identifiers of the feature starting boundary (i.e. the boundary composed of the outermost topological ring and the non-feature surface) are both inner boundaries (closed features), and they satisfy the condition of being composed of multiple topological rings (composed of multiple cavities) or having a large aspect ratio.

[0059] Reference Figure 6 The inner and outer boundaries are identified as follows: In the STEP model entity, the FACE_BOUND entity has two types: FACE_INNER_BOUND and FACE_OUTER_BOUND; where FACE_INNER_BOUND is used to represent the inner closed boundary of the surface, and FACE_OUTER_BOUND is used to represent the outer boundary of the surface.

[0060] In step (c), the boundary guidance method c1 is as follows: considering that the feature surface of the cavity type can generally be formed by boundary sweeping, the boundary guidance method can generate the tool axis vector c4 and tool contact point c5 required for the machining of the cavity type surface.

[0061] Reference Figure 7 The cutting depth control method c2 includes: constant depth control and constant quantity control. The constant depth control method is suitable for cutting depth planning when there are many model features; the constant quantity control method is only suitable for cutting depth planning when there are few model features or the height differences between features are small. The calculation rules for each cutting depth are as follows:

[0062] Constant depth cutting depth control methods, such as Figure 7 As shown in Figure (Ⅰ), the cutting depth value d0 and the depth direction N0 (usually selected as -z direction) are manually input according to the accuracy requirements; considering that the cavity features are not entirely along the N0 direction, it is necessary to calculate the cutting direction N of each adjacent edge in each cavity. m and single-layer cutting depth d m Assume P m0 and P m Let P be the two endpoints of the m-th adjacent edge within a cavity (corresponding to points on the upper and lower boundaries of the cavity). mi For the i-th layer of the m-th adjacent edge of the cavity, N m d m P mi The calculation formula is determined by the following equation.

[0063] N m =(P m -P m0 ) / |P m -P m0 | (2)

[0064] d m =d0 / cos <N0,N m > (3)

[0065] P mi =P m0 +N m ·d m ·i,i>0 (4)

[0066] The constant depth control method requires a termination condition, i.e., the tool contact point is planned to extend to the lower boundary of each cavity at most; let L mi For P mi to the lower endpoint P of the adjacent edge m The distance is easily determined by the termination condition: if L mi >d m Then continue planning the adjacent edge knife contact points downwards; otherwise, make P... mi=P m And terminated.

[0067] The constant quantity control method is relatively simple, such as Figure 7 As shown in (II), assuming that each cavity feature is planned as an n-layer tool contact point, then the cutting direction N of the m-th adjacent edge of the topological loop is... m and the i-th layer knife contact point P mi The calculation formula is the same as that in equations (2) and (4), and the single-layer cutting depth d m Determined by equation (5);

[0068] d m =|P m -P m0 | / n (5)

[0069] Cutting direction N m The derived vector is the tool axis vector c4 for each cavity feature. Through cutting depth planning, the adjacent edge tool contact group {P(m,i)} within each layer of each cavity feature can be obtained as follows:

[0070]

[0071] Where M represents the number of adjacent edges in the topology ring, and I represents the number of knife contact layers in the topology ring.

[0072] Reference Figure 8 The cutting step size control method c3 requires different control methods depending on the type of the guiding boundary. For straight boundary boundaries, the step size can directly follow the boundary length; for curved boundary boundaries, a constant angle control can be used; and for B-spline curve boundary boundaries, node subdivision control can be used. The calculation rules for each cutting step size are as follows:

[0073] like Figure 8 As shown in (Ⅰ), assume P 1i ~P 4i This represents the knife contact point on the 1st to 4th adjacent edges of the i-th layer of a certain topological ring. Based on the topological ring surface markings and guiding boundaries, P... 1i P 2i The adjacent edges are planes, and the guiding boundary is a straight line; P 2i P 3i The adjacent edges are cylindrical, and the guiding boundary is an arc; therefore, connecting P... 1i With P 2i At that time, the guide boundary is directly connected in a straight line, and the cutting step size is |P 2i -P 1i |;Connect P 2i With P 3i At this time, a constant angle can be used to control the cutting step size, approximating the circular arc curve; assuming the step angle is manually input as θ, the center of the arc is C, the radius of the arc is R, and the guiding boundary unit normal vector is N (right-hand rule), P2ik For P 2i The position of the tool contact point after the k-th step is to find P. 2ik A new local coordinate system needs to be established at the arc, with the coordinate system from the center C to P. 2i Connecting the lines gives the x-axis, and the x-axis unit vector satisfies equation (7). Combining this with the guiding boundary unit normal vector N, we obtain the y-axis unit vector that satisfies equation (8).

[0074] x=(P 2i -C) / |P 2i -C| (7)

[0075] y = N × x (8)

[0076] Based on the knowledge of trigonometric functions, it is easy to obtain P. 2ik The calculation formula is:

[0077] P 2ik =C+R(cos(kθ)·x+sin(kθ)·y),k>0 (9)

[0078] The constant angle step size control method still needs a termination condition, that is, the tool contact can be planned up to the next adjacent edge of the same layer (e.g., Figure 8 P in (Ⅰ) 3i Let L 2ik For P 2ik To the next adjacent edge knife contact P of this layer 3i Given the distance, the termination condition is easily determined as follows:

[0079] L 2ik =|P 3i -P 2ik |<2R·sin(θ / 2)=L ch (10)

[0080] Among them, L ch The length of the chord corresponding to the central angle θ in the arc;

[0081] That is, when L 2ik >L ch If necessary, continue planning the next contact point; otherwise, make P... 2ik =P 3i And terminate; by controlling the value of θ, the fitting accuracy of the knife contact point can be controlled.

[0082] If the surface between two adjacent edges of a topological ring is a B-spline surface and the guiding boundary is a B-spline curve, the cutting step size can be controlled by node subdivision; for example... Figure 8 As shown in (II), P 1i With P 2i The guiding boundary is a B-spline curve, assuming the B-spline curve has a degree of p and n+1 control points Q0 to Q1.n and m+1 nodes u0~u m And satisfy m=n+p+1; the principle of the node subdivision method is: divide each node interval [u j ,u j+1 The data is divided into 'a' parts, where the value of the kth subdivision node is:

[0083] u jk =u j +k(u j+1 -u j ) / a,0≤j <m,0≤k<a (11)

[0084] The B-spline curve formula can be used to solve for the point P(u) on the B-spline corresponding to the subdivision node within each node interval. jk As shown in equation (12);

[0085]

[0086] Where, N j,p (u) is a B-spline function basis function that satisfies equations (13) and (14);

[0087]

[0088]

[0089] For B-spline curves in the STEP model, they are often non-uniform rational B-splines with positive repetition at nodes and weighted control points. For nodes with positive repetition, when calculating the basis functions within the node interval, a denominator of 0 may be encountered. In this case, if the numerator is also 0, the entire term is defined as 0; otherwise, the denominator is defined as 1. Furthermore, it is assumed that the weights of each control point of the NURBS curve are w0 to w0. n Then the calculation formula for each subdivision point on the NURBS curve is shown in equation (15);

[0090]

[0091] By sequentially outputting the adjacent edge knife contacts and the knife contacts on the surface within each feature topology ring, the complete knife contact group c5{P(m(i),i)} within each feature topology ring can be obtained, as shown in Equation (16).

[0092]

[0093] Where I represents the number of knife contact layers in the topology ring, and m(i) represents the total number of knife contacts in the i-th layer.

[0094] The extended toolpath c6 is defined as follows: To improve the surface quality of the cavity at the alternating surface c9, an extended toolpath should be added during machining path planning, while avoiding interference. The presence of interference in the extended toolpath of this layer is determined by whether the alternating surface c9 below the current layer's machining path is a topological loop surface c8. If not, there is no interference, and an extended toolpath for the corresponding feature can be introduced. The extended toolpath c6 can be obtained from some of the tool contact points c5 below the current layer's machining path.

[0095] The alternating surface c9 is the upper surface of the model during the transition between additive manufacturing and subtractive machining processes. It is mainly composed of the user-defined transition surface c7 and the inter-topological ring plane c8. The user-defined transition surface c7 primarily functions to average the thickness of the alternating layer and reduce the cutting amount in each subtractive machining operation. The inter-topological ring plane c8 corresponds to the plane at the cavity transition point in the STEP model, and its function is to reduce the risk of tool collisions and improve the global tool reachability of the STEP model.

[0096] Reference Figure 9 The present invention is illustrated using an example of a complex internal cavity component with multiple features.

[0097] After mapping the STEP model of the embodiment row by row to the mapping relationship a1 between the computer and the STEP model, the topological relationship a2 between entities can be quickly extracted using a hash algorithm. Based on the topological relationship, feature graph matrices are established, where the number of rows and columns of the matrix is ​​equal to the number of faces in the STEP model. The main diagonal of the face-edge graph b1 matrix stores the face number, and the remaining elements store the starting point, ending point, edge number, and inner / outer boundary identifier of the intersection edge (or 0 if there is no intersection edge). Elements in the attribute adjacency graph b2 store different types of face and line concavity / convexity attribute characters. The minimum subgraph b3 retains only elements less than 0 in the attribute adjacency graph b2 and sets them to 1, while all other elements are set to 0. A breadth-first search algorithm is used to extract quasi-processing features b4 from the minimum subgraph b3. This embodiment's STEP model has six quasi-processing features: b4-1 to b4-6, corresponding to features such as open mouth, closed mouth, and hole in the embodiment's STEP model. A feature attribute adjacency graph b5 is then established. Extract the topological loop b6 and topological loop boundary b7. According to the composite machining feature judgment criteria, it can be determined that there are three quasi-machining features b4 in the STEP model of the embodiment that satisfy the composite machining feature judgment criteria, namely: b8-1, b8-2, and b8-3, corresponding to the large aspect ratio hole and two complex cavities in the embodiment. Using the extracted composite machining feature topological loop boundary b7, the "boundary-topological loop-boundary" combination b9 of each composite machining feature is obtained. The tool axis vector c4, tool contact point c5, and extended toolpath c6 of each composite machining feature topological loop are planned using the boundary guidance method c1. Combined with the user-defined transformation surface c7, the topological loop inter-surface c8 is extracted as the alternating plane. According to the layer height interval of the alternating plane, the multi-layer machining path file group c10 is defined. The tool axis vector c4, tool contact point c5, and extended toolpath c6 are output to the corresponding machining path file according to the G-code rules, and the multi-layer machining path file group of the embodiment model can be obtained.

[0098] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An adaptive planning method for multi-layer machining paths in the additive and subtractive material composite manufacturing of complex cavity parts, characterized in that, Includes the following steps: (a) STEP model analysis: Establish the mapping relationship a1 between the computer and the STEP model, and establish the topological relationship a2 between the entities in the STEP model; (b) Composite processing feature identification: Based on the topological relationship between entities in the STEP model (a2), a face-edge graph (b1) is constructed using the feature graph construction method. The concavity and convexity of each face and adjacent edge are determined, and an attribute adjacency graph (b2) is constructed. Only concave faces and concave edges are retained to construct a minimum subgraph (b3). Then, the quasi-processing features (b4) in the STEP model are extracted from the minimum subgraph (b3) using a breadth-first search algorithm. Based on the attribute adjacency graph (b2), only nodes and connections related to the quasi-processing features (b4) are retained to construct a feature attribute adjacency graph (b5). The topological loops within the features (b6) and the boundaries of each topological loop (b7) are extracted. According to the composite processing feature judgment criteria, it is determined whether each quasi-processing feature is a composite processing feature (b8). Combining the topological loop boundaries (b7), each composite processing feature (b8) is transformed into a "boundary-loop-boundary" form (b9). (c) Multi-layer machining path planning: Based on the "boundary-loop-boundary" form of each composite machining feature (b9), the boundary guidance method (c1) is adopted. Through cutting depth control (c2) and cutting step length control (c3), the machining path accuracy is controlled to obtain the tool axis vector (c4), tool contact point (c5), and extended toolpath (c6) of each topological loop. The user-defined transformation surface (c7) and the plane between topological loops (c8) are used as the alternating surface (c9). Based on the layer height interval of the alternating surface, a multi-layer machining path file group (c10) is defined. The tool axis vector (c4), tool contact point (c5), and extended toolpath (c6) are output to the corresponding machining path file according to the G-code rules to obtain the multi-layer, multi-axis, precision-controllable, interference-free machining path (c11) required for additive and subtractive composite manufacturing.

2. The planning method according to claim 1, characterized in that, The feature graph construction method in step (b) refers to: taking each face in the STEP model entity as a node and the adjacent edges as node connections, and constructing a face-edge graph b1, an attribute adjacency graph b2, a minimum subgraph b3, and a feature attribute adjacency graph b5 by adding nodes and node connection attributes as needed; in the program, the feature graph is represented by a two-dimensional matrix, where the number of rows and columns of the matrix is ​​equal to the number of faces in the STEP model.

3. The planning method according to claim 1, characterized in that, The method for determining the concavity and convexity of each face and adjacent edge in step (b) is as follows: Concavity / convexity determination of surfaces: Planes have no concavity / convexity; The concavity / convexity of cylinders is determined by the direction of the normal vector under the topological logic of the cylinder feature in the STEP model. If the normal vector points into the cylinder, it is a convex cylinder; otherwise, it is a concave cylinder; B-spline surfaces have no global concavity / convexity. Considering that B-spline surfaces are generally used as feature transition surfaces, they are considered as concave surfaces. Determining the concavity / convexity of an edge: Determining the concavity / convexity of an edge is transformed into finding the dihedral angle between adjacent faces. For the STEP model, assume that edge E is the intersection of faces F1 and F2, ring L is the boundary ring on face F1, N1 and N2 are the unit outward normal vectors of faces F1 and F2, point P is a point on edge E, and vector T is the unit tangent vector of edge E at point P along the direction of ring L. Then the concavity / convexity of edge E is determined by the following formula: m=(N1×N2)·T (1) If m > 0, then edge E is a convex edge; if m < 0, then edge E is a concave edge; if m = 0, then edge E is a tangent edge. For edges that come into contact with B-spline surfaces, including B-spline curves, the inner and outer boundary identification method is used. That is, if the edge belongs to the inner contour on a certain surface, it is a convex edge; otherwise, it is a concave edge.

4. The planning method according to claim 1, characterized in that, The quasi-machining feature b4 is: in the smallest subgraph b3, a face-edge group composed of multiple concave attributes, which corresponds to the CNC machining features in the STEP model, namely the features of open cavity, closed cavity, and hole.

5. The planning method according to claim 1, characterized in that, The topological ring b6 is defined as follows: In the smallest subgraph b3, a ring formed by multiple faces or a closed face connected end to end is called a feature topological ring, which represents a cavity feature in the STEP model; if a feature has multiple topological rings, it means that the feature is composed of multiple cavities, and the tool interference of a certain cavity may be affected by other cavities in the same feature.

6. The planning method according to claim 1, characterized in that, The topological ring boundary b7 is constructed by obtaining the adjacent edge information between the constituent surfaces and adjacent surfaces of each topological ring based on the adjacency graph b5 of the feature attributes, thereby constructing the topological ring boundary. Each topological ring has two boundaries. The topological ring boundary contains the edge number, inner and outer boundary identifiers, start point and end point information. The topological ring boundary b7 is a ring with the beginning and end connected.

7. The planning method according to claim 1, characterized in that, The composite processing feature b8 is defined as follows: a feature that requires additive or subtractive material composite manufacturing to fully perform surface processing is called a composite processing feature. It has two characteristics: non-openness and complex internal structure or large aspect ratio. The criteria for judging the composite processing feature b8 are: the inner and outer boundary identifiers of the feature starting boundary, i.e. the boundary composed of the outermost topological ring and the non-feature surface, are both inner boundaries, and it satisfies the requirement of being composed of multiple topological rings or having a large aspect ratio.

8. The planning method according to claim 1, characterized in that, The inner and outer boundaries are identified as follows: In the STEP model entity, the FACE_BOUND entity has two types: FACE_INNER_BOUND and FACE_OUTER_BOUND; FACE_INNER_BOUND is used to represent the inner closed boundary of the surface, and FACE_OUTER_BOUND is used to represent the outer boundary of the surface.

9. The planning method according to claim 1, characterized in that, The cutting depth control method c2 includes: constant depth control and constant quantity control. The constant depth control method is suitable for cutting depth planning with many model features; the constant quantity control method is only suitable for cutting depth planning with few model features or small height differences between features.

10. The planning method according to claim 1, characterized in that, The cutting step length control method c3 requires different control methods depending on the type of the guiding boundary. The step length of the straight boundary directly follows the boundary length; the step length of the arc boundary is controlled by a constant angle; and the step length of the B-spline curve boundary is controlled by node subdivision.

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