Numerical control processing method for sharp edge of car outer covering

Abstract

The application provides a numerical control machining method for sharp edges of car outer cover, and relates to the technical field of automobile production and machining, which comprises the following steps: PowerMILL programming is used for machining of the surface of the part where the concave surface is located; sharp edge surfaces near the sharp edge line of the concave surface are extracted and cut; a normal upward bias is formed to form a sharp edge protection surface; super semi-finishing is added; a D6 ball nose tool is used first, and then a D1 ball nose tool is used; one-way spiral continuous milling machining is carried out from the middle of the sharp edge according to the same three-dimensional bias strategy and preset values; the D1 ball nose tool is layered according to the residual machining amount of the D6 ball nose tool, and is combined into an uninterrupted machining program to prevent overcutting of the sharp edge; programming is carried out according to the sharp edge partition, and the trajectory sequence is rearranged through a secondary development tool to realize no-tool joint gap machining, solve the problem that the 5mm inside the sharp angle of the concave surface cannot be repaired by hand, and solve the problem that the sharp edge of the convex mold appears with a half cut and a sharp edge tool joint gap, so that no-repair machining is achieved, and the technical effect of batch processing is increased.

Description

Technical Field

[0001] This invention relates to the field of automobile manufacturing and processing technology, and in particular to a CNC machining method for sharp edges of car body panels. Background Technology

[0002] As the requirements for vehicle body lines and the rounded corners of parts become smaller, they have gradually evolved into a unique sharp-edge process. Sharp edges directly determine the high-end feel and brand recognition of a vehicle, while also having a key impact on the molding precision, assembly consistency and aerodynamic performance of body panels.

[0003] Current machining technologies mostly adopt conventional CNC machining approaches: the machining of sharp edges and concave surfaces is carried out using a roughing process with a large tool and a finishing process with a small tool. The operation space is reserved for subsequent manual finishing by grooving the concave surface, but no special protection and machining strategies are designed for the sharp edge and corner areas. The machining of punches with multiple sharp edges adopts a partitioned programming method, machining each side of the sharp edge separately to ensure basic sharpness. The overall machining relies on the default parameters of conventional programming software, the tool path planning does not consider the machining characteristics of the critical areas of sharp edges, and after machining, manual finishing by a fitter is required to eliminate tool marks and adjust the surface to meet basic forming requirements.

[0004] In traditional machining, tool marks from the large and small cutters near the edge are prone to appear in the high-pressure forming area. Furthermore, the grooved design of the sharp-edged concave surface makes manual finishing impossible to reach critical areas like sharp corners. The segmented machining of the punch can also cause tool breakage due to tool wear, which is difficult to eliminate even after finishing. Ultimately, this prevents domestically produced molds from meeting the requirements of high-end automotive exterior body panels for sharp edge precision, surface quality, and consistent appearance. Therefore, existing machining methods suffer from the problem that sharp-edged concave surfaces (especially the 5mm space on both sides of sharp corners) cannot be finished manually, and that tool breakage occurs at the edge joints of multiple sharp-edged parts in the punch. Summary of the Invention

[0005] The purpose of this invention is to provide a CNC machining method for sharp edges of automotive exterior body panels, so as to alleviate the technical problems in the prior art where the sharp corners on both sides of the concave surface cannot be manually repaired within 5mm, and where the sharp edges of the punch cause edge breakage at the halfway point.

[0006] This invention provides a CNC machining method for sharp edges of automotive exterior body panels, comprising: Step 1: For the sharp edges and concave surfaces during the overall machining of the profile, the PowerMILL programming developed in the secondary development is used to machine the profile surface where the concave surface is located. The sharp edges and concave surfaces near the sharp edge edge are extracted and cut off. The upward offset of the normal direction forms a sharp edge protection surface to obtain the machining allowance. Then, a super semi-finishing with a D30 ball allowance is added between the conventional semi-finishing and finishing. Step 2: For the sharp corners of the concave surface of the sharp edge, first use a D6 ball end mill, then use a D1 ball end mill. Both are machined in a single-direction spiral climb mill starting from the middle of the sharp edge with the same three-dimensional offset strategy according to the preset value. The machining range exceeds the allowance range of the sharp edge protection surface in Step 1. At the same time, the starting trajectory of the D1 ball end mill is layered according to the residual machining amount of the D6 ball end mill and merged into an uninterrupted machining program to prevent overcutting of the sharp edge. Step 3: For the part of the punch with multiple sharp edges and half edges, program according to the sharp edge partition and rearrange the trajectory sequence through the secondary development tool to achieve seamless tool breakage machining.

[0007] Furthermore, the specific steps of step 1 are as follows: Step 1.1: Use the PowerMILL programming method based on secondary development to perform surface machining on the part containing the sharp edge and concave surface. Number the tools used in programming so that the output machining program carries instructions for automatic head changing, automatic tool changing and automatic tool measurement of the machine tool, thereby realizing the automated machining of the surface of the part containing the sharp edge and concave surface. Step 1.2: First, extract the sharp edge concave surface from the processing data, cut the sharp edge surface within a preset range near the edge line and offset it upward in the normal direction by a preset thickness to form a sharp edge protection surface that is only used for surface finishing programming. Step 1.3: Between the standard D30 ball end mill semi-finishing allowance of 0.1mm and the standard D30 ball end mill finishing allowance of 0mm, add a super semi-finishing process with D30 ball allowance; Step 1.4 Finally, follow the rule of one procedure and one tool for each edge to perform fine machining of the concave surface of the sharp edge, eliminating the tool marks near the edge line caused by the traditional large tool to small tool.

[0008] Furthermore, in step 1.2, the cutting range of the sharp edge surface is 5 to 10 mm near the edge line, the preset thickness of the upward offset in the normal direction is 0.1 to 0.15 mm, and the sharp edge protection surface range retains a machining allowance of 0.1 to 0.15 mm after the surface finishing is completed.

[0009] Furthermore, in step 1.3, the allowance for the semi-finishing of the D30 ball end mill is 0.03mm to 0.04mm, which is used to reduce the impact of tool wear on machining accuracy during subsequent finishing and to minimize the tool marks between the sharp edge concave surface and the finishing of the D30 ball end mill.

[0010] Furthermore, the specific steps of step 2 are as follows: Step 2.1: Machining of sharp edges and concave corners. First, use a D6 ball end mill, according to the preset speed, feed rate, step distance and calculated tolerance, and use a three-dimensional offset strategy and follow the reference line to start the unidirectional spiral milling from the middle of the sharp edge. The machining range exceeds the allowance range of the sharp edge protection surface in Step 1. Step 2.2: Then, using a D1 ball end mill, calculate the tolerance according to the preset high speed, low feed rate, small step distance and high precision, and use the same three-dimensional offset strategy to start the unidirectional helical climb milling from the middle of the sharp edge, and set the arc entry and exit between the step distances. Step 2.3: Simultaneously, the starting trajectory of the D1 ball end mill is layered according to the residual machining amount of the D6 ball end mill and merged into an uninterrupted machining program to prevent overcutting of sharp edges.

[0011] Furthermore, in step 2.1, the preset parameters for machining the D6 ball end mill are a rotational speed of 10000 r / min to 11000 r / min, a feed rate of 4000 mm / min to 4500 mm / min, a step distance of 0.2 mm, a calculated tolerance of 0.005 mm, and the machining range exceeds the allowance range for the sharp edge protection surface in step 1 by 2 to 3 mm.

[0012] Furthermore, in step 2.2, the preset parameters for machining with the D1 ball end mill are: rotational speed of 14000-15000 r / min, feed rate of 2000-2500 mm / min, step distance of 0.05 mm, and calculated tolerance of 0.001 mm; and except for the center trajectory of the Y-shaped edge, a single sharp edge is continuously machined by a single D1 ball end mill, with no tool skipping along the trajectory.

[0013] Furthermore, in steps 2.1 and 2.2, the reference line for the starting tool path of the concave surface of the sharp edge is obtained by using PowerMILL to perform a single-stroke root clearing calculation path at the part where the included angle between the two sides of the sharp edge is less than 170° to 180° with the same tool allowance and a calculation tolerance of 0.001mm, and generating a reference line from the path; at the part where a path cannot be generated, the intersection line is obtained by offsetting to the concave side by the distance of the tool radius plus the machining allowance, and used as the reference line.

[0014] Furthermore, in step 2.3, the layer thickness of the starting trajectory of the D1 ball end mill is 0.005mm. After layering, it is merged with the trajectory generated by the three-dimensional offset strategy into a single uninterrupted machining program to eliminate sharp-edged local groove defects caused by tool heat accumulation effect.

[0015] Furthermore, the specific steps of step 3 are as follows: For the punch with multiple sharp edges and half edges, the punch is programmed in sections according to the sharp edge machining method. During programming, tangential extension surfaces are made on both sides of the sharp edge so that the machining trajectory is tangentially fed in and out. The trajectory of different areas is rearranged in a unified order by a secondary development tool to ensure that the area with half edges is machined sequentially from one side to the other.

[0016] Beneficial effects: The CNC machining method for sharp edges of automotive exterior body panels provided by this invention constructs a protective surface for sharp edges through secondary development of PowerMILL programming in the overall surface machining stage, controls the machining allowance near the edge line, and reduces the impact of tool wear in subsequent finishing by adding a D30 ball end mill for semi-finishing. This avoids tool marks caused by the connection between large and small tools in traditional machining from the source. For the machining of the concave corner of the sharp edge, a combination strategy of pre-machining with a D6 ball end mill and finishing with a D1 ball end mill is adopted. Combined with a three-dimensional offset spiral climb milling method starting from the middle of the sharp edge, the machining quality of the critical area within 5mm on both sides of the sharp corner is ensured. At the same time, the layered merging design of the D1 ball end mill trajectory completely solves the groove defects caused by heat accumulation of small diameter tools, so that the sharpness of the sharp edge can stably meet the requirements of high-end models. The trajectory rearrangement design of the punch with multiple sharp edges and half edges eliminates the tool breakage difference in partition machining with the help of secondary development tools, avoids the coloring problems caused by manual finishing, and achieves standardization and consistency in the machining of sharp edges.

[0017] This invention solves the problem of non-refining machining of sharp edges and concave surfaces in dies and punches with half-cut edges and multiple sharp edges. It achieves a breakthrough from ordinary sharp edges (sharp edges with grooved concave surfaces, and the sharpness of the product cannot be effectively controlled due to processing capacity limitations) to a high-pressure design that achieves no hollow grooves on sharp edge concave surfaces and non-refining machining of punches with half-cut edges and multiple sharp edges; without significantly increasing processing costs, it achieves non-refining machining of the surface near the sharp edges of ordinary sharp edge dies. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a CNC machining method for sharp edges of a car exterior body panel provided in an embodiment of the present invention; Figure 2 A schematic diagram showing the distribution of sharp edges on the outer panel of a high-end car engine hood with a half-cut edge, in the processing method provided in the embodiment of the present invention. Figure 3 This is a schematic diagram showing the distribution of sharp edges on a high-end car fender with Y-shaped edges in the processing method provided in this embodiment of the invention. Figure 4 This is a partially enlarged cross-sectional view of the sharp edge in the processing method provided in the embodiment of the present invention; Figure 5 This is a schematic cross-sectional view of the sharp edge reference line in the processing method provided in the embodiment of the present invention; Figure 6This is a schematic diagram of the trajectory at the bifurcation of the Y-shaped edge on the concave surface in the processing method provided in the embodiment of the present invention; Figure 7 This is a schematic diagram of the anti-overcutting trajectory of the sharp concave surface edge line in the processing method provided in the embodiment of the present invention; Figure 8 This is a schematic diagram of the rearrangement sequence trajectory at the disappearance of the punch half-edge in the processing method provided in the embodiment of the present invention.

[0020] Explanation of reference numerals in the attached drawings: 1-Sharp edge; 2-Half edge; 3-Disappearing part of half edge; 4-Y-shaped edge; 5-Sharp angle of sharp edge; 6-Shaped areas on both sides of the intersection of concave surfaces; 7-Reference line section point; 8-Section of tool radius and machining allowance. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0024] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] like Figure 1As shown, the CNC machining method for sharp edges of car body panels provided by the present invention includes: Step 1: For the concave surface of the sharp edge during the overall machining of the profile, the PowerMILL programming developed in the secondary development is used to machine the profile of the part where the concave surface is located, extract and cut the sharp edge surface near the edge line of the concave surface of the sharp edge, and offset the normal upward to form a sharp edge protection surface to obtain the machining allowance; and add a super semi-finishing with D30 ball allowance between the conventional semi-finishing and finishing. Step 1.1: The PowerMILL programming method based on secondary development was used to perform surface machining on the part containing the sharp edge and concave surface. The tools used in the programming were numbered so that the output machining program carries instructions for automatic head changing, automatic tool changing and automatic tool measurement of the machine tool, thereby realizing the automated machining of the surface of the part containing the sharp edge and concave surface. Step 1.2: First, extract the sharp edge concave surface from the processing data, cut off the sharp edge surface within a preset range near the edge line and offset it upwards in the normal direction with a preset thickness to form a sharp edge protection surface used only for surface finishing programming; the cutting range of the sharp edge surface is 5-10mm near the edge line, preferably 10mm, and the preset thickness offset upwards in the normal direction is 0.1-0.15mm, preferably 0.1mm, and the sharp edge protection surface range is retained at 0.1-0.15mm, preferably 0.1mm, after surface finishing is completed, as a processing allowance.

[0026] Step 1.3: Between the standard D30 ball end mill semi-finishing allowance of 0.1mm and the standard D30 ball end mill finishing allowance of 0mm, add a super semi-finishing process with a D30 ball end mill allowance. In Step 1.3, the allowance for the super semi-finishing of the D30 ball end mill is 0.03mm to 0.04mm, which is used to reduce the impact of tool wear on machining accuracy during subsequent finishing and to minimize the tool marks between the sharp edge concave surface and the D30 ball end mill finishing.

[0027] Step 1.4 Finally, according to the rule of one procedure and one tool for each edge, the concave surface of the sharp edge is finished to eliminate the tool marks near the edge line caused by the traditional large tool to small tool.

[0028] Specifically, such as Figure 2 , Figure 3As shown, the machining method based on PowerMILL programming developed by secondary development is used for the surface machining of the concave part. Its feature is that it is conducive to the output tool of secondary development. The tool used in programming is numbered and the output program has instructions to realize automatic head changing, tool changing and tool measurement during machine tool processing, so as to realize automatic machining. Among them, the finishing of the sharp edge concave surface requires the sharp edge protection surface. Its feature is that except for the area near the concave surface, all are machined in place by conventional methods. The finishing of the sharp edge concave surface with the allowance uses a special programming method to ensure that each edge is machined continuously in one go with one program and one tool without defects, achieving the standard of no rework. It can eliminate the tool joint marks near the edge line in the traditional method of using a large tool to a small tool. The distance between the position of the tool joint mark and the edge line is outside the forming strong pressure zone. Through targeted treatment, the tool joint mark is controlled within a certain range, so that coloring can be achieved after less rework, ensuring the needs of later debugging work. In step 1.2, the sharp edge concave surface allowance protection before finishing is to extract the sharp edge concave surface from the machining data and cut off the sharp edge surface within a 10mm range near the edge line, with the normal direction offset upward by 0.1mm, as the sharp edge protection surface. It is only used when programming the surface finishing to ensure that there is a 0.1mm machining allowance in the sharp edge protection surface range after finishing. In step 1.3, before finishing the surface area where the sharp edge is located, the pre-processing is performed so that the area where the sharp edge is located is the outer surface of the part product area. Between the conventional machining allowance of 0.1mm for the D30 ball semi-finishing and the finishing machining of 0mm for the D30 ball, an additional 0.03mm for the D30 ball ultra-semi-finishing is added to minimize the impact of tool wear on machining accuracy and ensure that the tool marks between the sharp edge concave surface and the finishing machining of 0mm for the D30 ball are minimized.

[0029] Step 2: For the sharp corners of the concave surface of the sharp edge, first use a D6 ball end mill, then use a D1 ball end mill. Both are machined in a single-direction spiral climb mill starting from the middle of the sharp edge with the same three-dimensional offset strategy according to the preset value. The machining range exceeds the allowance range of the sharp edge protection surface in Step 1. At the same time, the starting trajectory of the D1 ball end mill is layered according to the residual machining amount of the D6 ball end mill and merged into an uninterrupted machining program to prevent overcutting of the sharp edge. Step 2.1: Machining of sharp edges and concave corners. First, a D6 ball end mill is used. According to the preset speed, feed rate, step distance, and calculated tolerance, a three-dimensional offset strategy is employed, and the milling is carried out from the middle of the sharp edge using a unidirectional spiral milling method based on the reference line. The machining range exceeds the allowance range of the sharp edge protection surface in Step 1. In Step 2.1, the preset parameters for machining with the D6 ball end mill are: speed of 10000r / min~11000r / min, preferably 10000r / min; feed rate of 4000mm / min~4500mm / min, preferably 4000mm / min; step distance of 0.2mm; calculated tolerance of 0.005mm; and the machining range exceeds the allowance range of the sharp edge protection surface in Step 1 by 2~3mm, preferably 2mm.

[0030] Step 2.2, as follows Figure 6 , Figure 7 As shown, a D1 ball end mill is then used, with preset high speed, low feed rate, small step distance, and high-precision tolerance calculation. The same three-dimensional offset strategy is used to start the unidirectional helical climb milling from the middle of the sharp edge, and arc entry and exit are set between the step distances. In step 2.2, the preset parameters for the D1 ball end mill machining are a speed of 140000r / min~15000r / min, preferably 14000r / min, a feed rate of 2000~2500mm / min, preferably 2000mm / min, a step distance of 0.05mm, and a calculated tolerance of 0.001mm. In addition, except for the center trajectory of the Y-shaped edge, a single sharp edge is continuously machined by a single D1 ball end mill, and there is no tool skipping on the trajectory.

[0031] The method for obtaining the reference line for the starting tool path of the concave surface of the sharp edge is as follows: in the part where the included angle between the two sides of the sharp edge is less than 170° to 180°, the single-stroke root clearing calculation path is calculated using PowerMILL with the same tool allowance and a calculation tolerance of 0.001mm, and the reference line is generated from the path; in the part where the path cannot be generated, the intersection line is obtained by offsetting the tool radius plus the machining allowance to the concave side, and this line is used as the reference line.

[0032] Step 2.3: Simultaneously, the starting trajectory of the D1 ball end mill is layered according to the residual machining amount of the D6 ball end mill, and merged into a continuous machining program to prevent overcutting of sharp edges. In Step 2.3, the layer thickness of the starting trajectory of the D1 ball end mill is 0.005mm. After layering, it is merged with the trajectory generated by the three-dimensional offset strategy into one continuous machining program to eliminate the local groove-like defects of sharp edges caused by the tool heat accumulation effect.

[0033] Specifically, such as Figure 4 As shown, in the design data, the concave edge of the sharp edge is the sharp corner formed by the intersection of two concave surfaces. In the programming stage, a ball end mill with a reasonable diameter is selected, and special programming requirements and methods are used to understand and control the key factors in the correlation between the actual processing results and the forming quality. That is, to control the residual R value of the sharp corner after the design data calculation and the processing accuracy and quality of the concave surfaces on both sides, in a state without refinishing, to ensure the sharpness of the edge forming of the outer surface of the car product and other general quality requirements. In order to ensure the processing accuracy and quality of the sharp edge and the area near the concave surface, the program starts the cut at the sharp edge, processes along the sharp edge from one end to the other end completely, and then performs climb milling outward. In order to strictly ensure the sharpness of the sharp edge and the force on both sides of the sharp edge during mold closing, the cutting trajectory must be tangent to the concave surfaces on both sides of the sharp edge at the same time. The cutting in and cutting out between the step distances are connected outside the product area to ensure the sharpness and aesthetics of the sharp edge. like Figure 5As shown, the reference line needs to be determined by considering the tool radius and machining allowance. The included angle between the two sides of the sharp edge is generally between 170 and 180 degrees. In the part with less than 176 degrees, the trajectory is calculated by using PowerMILL software with the same tool allowance and a calculation tolerance of 0.001mm. The trajectory is used to generate the reference line. In the part where the trajectory cannot be generated, the intersection line is obtained by offsetting to the concave side by the tool radius and machining allowance respectively using CATIA software. Due to the product shape and strong pressure design, there may be local offset near the edge end or even the intersection cannot be obtained after the offset surface is extended. In this case, the obtained reference line needs to be extended tangentially to the concave end of the sharp edge. If the reference line is obtained by two methods or is broken, the joint needs to be checked, the smooth part is retained and the smooth joint is ensured. One reference line is extracted for each sharp edge. For Y-shaped edges, two reference lines of different lengths are extracted and placed on one reference line. For overcutting prevention of sharp edges, due to the slow heat conduction of small-diameter tools, the machining volume is largest at the starting point. During high-speed machining, a heat accumulation effect occurs, causing the tool to extend beyond its original length. This heat accumulation effect is related to the machining volume, duration, and heat dissipation conditions, making it a dynamic process where heat generation and dissipation are difficult to balance. When the included angle between the two sides of a sharp edge is 170°, and the D6 allowance is 0.03mm, during machining with a D1 ball end mill starting from the middle of the sharp edge with a machining allowance of 0.04mm, the extension range of the D1 ball end mill is 0–0.02mm. This creates localized groove-like defects of varying depths at the sharp edge, which cannot be detected by conventional white light, coordinate measuring machine, and online inspection methods. The tool is in a non-thermal accumulation state before and after processing, and the tool length detection data cannot be correlated with the occurrence of this defect. It can only be detected by the debugging expert through visual inspection and fingertip touch. After this processing defect enters the debugging process, it will directly affect the quality and sharpness of the sharp edge on the outer surface of the part, and cannot be eliminated by refining. This will cause the design department to obtain an incorrect correspondence between the pressure and deformation data of the sharp edge surface and the forming result. By using the D1 ball end mill starting trajectory according to the D6 residual machining amount in layers of 0.005mm, and then using the three-dimensional offset strategy to calculate the unidirectional spiral climb milling from the middle of the sharp edge according to the reference line, and combining the two into one program to maintain uninterrupted processing, the occurrence of the sharp edge machining depth can be guaranteed to be eliminated.

[0034] Step 3, as follows Figure 8 As shown, for the part of the punch with multiple sharp edges and half-edges, the programming is done by sharp edge partitioning, and the trajectory sequence is rearranged using a secondary development tool to achieve seamless cutting edge machining. For the part of the punch with multiple sharp edges and half-edges, the punch is programmed by partitioning the multiple sharp edges according to the sharp edge machining method. During programming, tangential extension surfaces are created on both sides of the sharp edge, so that the machining trajectory enters and exits tangentially. The trajectory sequence of different areas is rearranged into a unified area using a secondary development tool to ensure that the part-edge area is machined sequentially from one side to the other.

[0035] Specifically, to ensure the sharpness of the punch's sharp edges, during CNC machining, the trajectory must be machined in a direction roughly perpendicular to the sharp edge. Furthermore, during programming, tangential extension surfaces must be created on both sides of the sharp edge, ensuring the trajectory enters and exits tangentially to maximize the sharpness. Therefore, punches with sharp edges require programming and machining in sections based on the sharp edges; this tool path method is called "sharp edge picking machining." For punches with half-edges, when the trajectory enters the area where the half-edge disappears during section machining, tool wear caused by section machining on both sides of the half-edge will result in machining discrepancies. Even if this discrepancy is eliminated through manual finishing by a fitter, it will still cause poor coloring on the nearby sides, leading to unqualified coloring in the mold product area. The secondary development tool has the following functions: rearranging the trajectory order of different areas with the same number of pieces into a unified area, ensuring that areas with half-edges are machined sequentially from one side to the other using the sharp edge picking tool path method, ensuring that unqualified coloring occurs without finishing.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A CNC machining method for sharp edges of automotive exterior body panels, characterized in that, include: Step 1: For the sharp edges and concave surfaces during the overall machining of the profile, the PowerMILL programming developed in the secondary development is used to machine the profile surface where the concave surface is located. The sharp edges and concave surfaces near the sharp edge edge are extracted and cut off. The upward offset of the normal direction forms a sharp edge protection surface to obtain the machining allowance. Then, a super semi-finishing with a D30 ball allowance is added between the conventional semi-finishing and finishing. Step 2: For the sharp corners of the concave surface of the sharp edge, first use a D6 ball end mill, then use a D1 ball end mill. Both are machined in a single-direction spiral climb mill starting from the middle of the sharp edge with the same three-dimensional offset strategy according to the preset value. The machining range exceeds the allowance range of the sharp edge protection surface in Step 1. At the same time, the starting trajectory of the D1 ball end mill is layered according to the residual machining amount of the D6 ball end mill and merged into an uninterrupted machining program to prevent overcutting of the sharp edge. Step 3: For the punch with multiple sharp edges and half edges, program according to the sharp edge partition and rearrange the trajectory sequence through the secondary development tool to achieve seamless cutting edge machining. The specific steps of step 1 are as follows: Step 1.1: Use the PowerMILL programming method based on secondary development to perform surface machining on the part containing the sharp edge and concave surface. Number the tools used in programming so that the output machining program carries instructions for automatic head changing, automatic tool changing and automatic tool measurement of the machine tool, thereby realizing the automated machining of the surface of the part containing the sharp edge and concave surface. Step 1.2: First, extract the sharp edge concave surface from the processing data, cut the sharp edge surface within a preset range near the edge line and offset it upward in the normal direction by a preset thickness to form a sharp edge protection surface that is only used for surface finishing programming. Step 1.3: Between the standard D30 ball end mill semi-finishing allowance of 0.1mm and the standard D30 ball end mill finishing allowance of 0mm, add a super semi-finishing process with D30 ball allowance; Step 1.4 Finally, follow the rule of one procedure and one tool for each edge to perform fine machining of the concave surface of the sharp edge, eliminating the tool marks near the edge line caused by the traditional large tool to small tool.

2. The CNC machining method for sharp edges of automotive exterior body panels according to claim 1, characterized in that, In step 1.2, the cutting range of the sharp edge surface is 5 to 10 mm near the edge line, the preset thickness of the upward offset of the normal is 0.1 to 0.15 mm, and the sharp edge protection surface range retains a machining allowance of 0.1 to 0.15 mm after the surface finishing is completed.

3. The CNC machining method for sharp edges of automotive exterior body panels according to claim 1, characterized in that, In step 1.3, the allowance for the semi-finishing of the D30 ball end mill is 0.03mm to 0.04mm, which is used to reduce the impact of tool wear on machining accuracy during subsequent finishing and to minimize the tool marks between the sharp edge concave surface and the finishing of the D30 ball end mill.

4. The CNC machining method for sharp edges of automotive exterior body panels according to claim 1, characterized in that, The specific steps of step 2 are as follows: Step 2.1: Machining of sharp edges and concave corners. First, use a D6 ball end mill, according to the preset speed, feed rate, step distance and calculated tolerance, and use a three-dimensional offset strategy and follow the reference line to start the unidirectional spiral milling from the middle of the sharp edge. The machining range exceeds the allowance range of the sharp edge protection surface in Step 1. Step 2.2: Then, using a D1 ball end mill, calculate the tolerance according to the preset high speed, low feed rate, small step distance and high precision, and use the same three-dimensional offset strategy to start the unidirectional helical climb milling from the middle of the sharp edge, and set the arc entry and exit between the step distances. Step 2.3: Simultaneously, the starting trajectory of the D1 ball end mill is layered according to the residual machining amount of the D6 ball end mill and merged into an uninterrupted machining program to prevent overcutting of sharp edges.

5. The CNC machining method for sharp edges of automotive exterior body panels according to claim 4, characterized in that, In step 2.1, the preset parameters for machining the D6 ball end mill are: rotation speed of 10000r / min~11000r / min, feed speed of 4000mm / min~4500mm / min, step distance of 0.2mm, calculated tolerance of 0.005mm, and the machining range exceeds the allowance range of the sharp edge protection surface in step 1 by 2~3mm.

6. The CNC machining method for sharp edges of automotive exterior body panels according to claim 4, characterized in that, In step 2.2, the preset parameters for machining with the D1 ball end mill are: rotational speed of 14000-15000 r / min, feed rate of 2000-2500 mm / min, step distance of 0.05 mm, and calculated tolerance of 0.001 mm; and except for the center trajectory of the Y-shaped edge, a single sharp edge is continuously machined by a single D1 ball end mill, with no tool skipping along the trajectory.

7. The CNC machining method for sharp edges of automotive exterior body panels according to claim 4, characterized in that, In steps 2.1 and 2.2, the reference line for the starting tool path of the concave surface of the sharp edge is obtained by using PowerMILL to perform a single-stroke root clearing calculation path at the part where the included angle between the two sides of the sharp edge is less than 170° to 180° with the same tool allowance and a calculation tolerance of 0.001mm, and generating a reference line from the path; at the part where a path cannot be generated, the intersection line is obtained by offsetting the tool radius plus the machining allowance to the concave side, and used as the reference line.

8. The CNC machining method for sharp edges of automotive exterior body panels according to claim 4, characterized in that, In step 2.3, the layer thickness of the starting trajectory of the D1 ball end mill is 0.005mm. After layering, it is merged with the trajectory generated by the three-dimensional offset strategy into a single uninterrupted machining program to eliminate sharp-edged local groove defects caused by tool heat accumulation effect.

9. The CNC machining method for sharp edges of automotive exterior body panels according to claim 1, characterized in that, The specific steps of step 3 are as follows: For the punch with multiple sharp edges and half edges, the punch is programmed in sections according to the sharp edge machining method. During programming, tangential extension surfaces are made on both sides of the sharp edge so that the machining trajectory is tangentially fed in and out. The trajectory of different areas is rearranged in a unified order by a secondary development tool to ensure that the area with half edges is machined sequentially from one side to the other.

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