A method for generating machining trajectories of two-dimensional cavity multi-tool combination machining with constant load rate

Abstract

The present invention discloses a method for generating a two-dimensional cavity multi-tool combination machining trajectory with a constant load rate, including determining the allowable load of each tool; obtaining the allowable material removal rate of each tool according to the tool allowable load; dividing the cavity into machining areas according to cavity contour information and the size of each tool; calculating the machining time of each tool according to the allowable material removal rate, and obtaining the tool machining sequence with the shortest total machining time and each tool machining area; generating a circular cutting trajectory in the corresponding area according to the determined tool sequence and the allowable material removal rate of each tool; dividing the initial circular cutting trajectory into two parts; replacing the original circular cutting trajectory with a cycloidal trajectory in the part where the material removal rate is higher than the allowable material removal rate, and outputting a multi-tool combination machining trajectory. The present invention can generate a multi-tool combination machining trajectory with a constant load rate, and in multi-tool combination machining, it can have the best overall machining efficiency while maintaining consistent machining safety.

Description

Technical Field

[0001] The invention relates to the field of mechanical processing, and in particular to a method for generating a two-dimensional cavity multi-tool combination processing trajectory with a constant load rate. Background Art

[0002] In the field of processing, since most of the mold processing belongs to cavity processing, cavity processing plays a very important role. In the traditional processing field, one or two tools are used for cavity processing, because for traditional machine tools, tool change requires workers to change tools manually, which is very time-consuming, and the selection of tool radius depends heavily on the workers' experience. Therefore, in traditional cavity processing, multiple tool processing will be avoided as much as possible. However, with the rapid development of CNC processing technology, CNC machining centers with high efficiency, high precision and high automation have been widely used in processing, and machining centers with tool libraries can realize rapid tool replacement, which also makes multi-tool processing have a basis for application.

[0003] As for the newly emerged multi-tool machining, various mature machining software do not have suitable machining strategies, but many scholars at home and abroad have done a lot of research in different aspects of the field of multi-tool machining. Some have conducted in-depth research on the division of machining areas, and some have optimized the sequence of tools, but most of them are based on a constant feed speed for optimization, or for machining time or machining energy consumption, but this cannot give full play to the machining potential of each tool and maximize machining efficiency. At the same time, when selecting the tool sequence, the optimization algorithm needs to re-plan the machining path every iteration, which is very time-consuming and resource-intensive. In order to fully utilize the advantages of multi-tool machining, an efficient cavity multi-tool machining method is urgently needed. Summary of the invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a method for generating a two-dimensional cavity multi-tool combination machining trajectory with a constant load rate. This method is aimed at the machining of complex cavities, can efficiently select the best tool sequence according to the optional tools provided, and can stabilize the tool machining load by controlling the material removal rate to stabilize, and can fully improve the machining efficiency under the premise of safety by unifying the load rate of each tool, thereby providing a more efficient and high-quality machining method for the machining of complex cavities.

[0005] The present invention adopts the following technical solution:

[0006] A method for generating a two-dimensional cavity multi-tool combined machining trajectory with a constant load rate. It includes:

[0007] Determine the allowable load of each tool based on the set uniform processing load rate and the maximum load that each tool can withstand;

[0008] According to the allowable load of each tool, the allowable material removal rate of each tool is obtained;

[0009] Obtain the contour size information of the cavity to be processed, and divide the cavity into processing areas according to the contour information of the cavity and the size of each tool;

[0010] The processing time of each tool is obtained according to the allowable material removal rate of each tool and the processing area of ​​the cavity, and the tool processing sequence with the shortest total processing time and the processing area of ​​each tool in the processing sequence are obtained;

[0011] Plan the circular cutting trajectory in the corresponding area according to the determined tool processing sequence and allowable material removal rate;

[0012] Obtain the material removal rate of the regional planning circular cutting trajectory, compare the material removal rate with the allowable material removal rate of each tool, and segment the trajectory part with a higher material removal rate;

[0013] The segmented trajectory part is replaced by the cycloid trajectory to obtain the load-stable cavity processing trajectory. Each processing area is respectively obtained by obtaining each tool processing area, planning the circular cutting trajectory and the segmented trajectory part, and further obtaining the multi-tool cavity processing trajectory.

[0014] Further, the set uniform processing load rate is defined as:

[0015] K safe =F allow / F max ×100%

[0016] Where K safe is the uniform machining load rate of the tool sequence, K safe ∈[0,1], used to obtain the value of the allowable load based on the maximum load determined by the specific conditions of different tools after determining the processing conditions, and to unify the load conditions when processing with different tools; F allow is the allowable load of the tool, which is the safe load of the tool based on the load factor; F max It is the maximum load that the tool can reach.

[0017] Furthermore, the maximum load that the tool can reach is the value of the cutting force when the maximum stress experienced by the tool during machining is equal to the allowable stress.

[0018] Furthermore, the relationship between the material removal rate and the tool force is proportional under certain processing parameters:

[0019] F=K m ×MRR

[0020] Where MRR is the material removal rate, K m is the correlation coefficient between MRR and force F, which can be determined experimentally. Therefore, the allowable material removal rate can be defined as:

[0021] MRR allow =F allow / K m

[0022] MRR allow is the allowable material removal rate, F allow is the permissible load.

[0023] Further, the contour size information of the cavity to be processed is obtained, and the cavity is divided into processing areas according to the contour information of the cavity and the size of each tool, specifically:

[0024] The central axis of the cavity boundary is established according to the acquired information of the cavity boundary. The central axis is formed by connecting the centers of the inscribed circles of the cavity boundary.

[0025] The passability of each tool in the area is determined based on the inscribed circle radius corresponding to the middle axis. If the minimum value of the inscribed circle radius corresponding to the middle axis end is smaller than the selected tool radius, the tool cannot be used to process the corresponding area of ​​the middle axis segment, and a tool with a smaller radius must be selected.

[0026] The corresponding areas of each central axis segment that can be processed by each tool are combined as the processable area of ​​the tool to complete the division of the processing area.

[0027] Furthermore, the processing time of each tool is Mi The allowable material removal rate of the tool is directly calculated by the volume of the processing area. The specific calculation method is as follows:

[0028]

[0029] Where V i For the tool sequence Tools{T i The area that can be processed by the i-th tool in}, MRR i is the allowable material removal rate corresponding to the corresponding tool.

[0030] Further, the calculation process of the processing time is:

[0031]

[0032] Among them, Time totle Is to use the tool sequence Tools{T i The total processing time of the tool is the actual processing time of each tool. Mi, advance and retract time Ri And the total tool change time c Obtained by addition.

[0033] Furthermore, the offset distance of the circular cutting trajectory is determined according to the tool processing sequence and the allowable material removal rate, and the circular cutting trajectory is further generated. The offset distance calculation process is as follows:

[0034] D = MRR akkow / f

[0035] Among them, D is the offset distance of the circular cutting trajectory, and f is the initial feed speed of machining.

[0036] Furthermore, the segmented trajectory part is replaced with a cycloid trajectory to obtain a load-stable cavity machining trajectory, and further obtain a multi-tool cavity machining trajectory, specifically:

[0037] The corresponding medial axis is generated according to the inner and outer rings of the annular tangent trajectory to be inserted into the cycloid trajectory as the boundary.

[0038] The generated middle axis segment is used as the guide line of the cycloid and the radius of the inscribed circle corresponding to the middle axis is used as the radius of the cycloid trajectory to generate the cycloid trajectory.

[0039] The original tangential trajectory segment in the area is deleted, and then the generated cycloid trajectory is connected at the beginning and end with the retained tangential trajectory.

[0040] Beneficial effects of the present invention:

[0041] The present invention ensures that after inputting the tool sequence, workpiece information and a set uniform load factor, a multi-tool combination processing trajectory with a constant load rate can be generated. When the multi-tool combination is processed, the load of each tool is at the same ratio relative to its respective maximum load, so that the processing capacity of each tool can be fully utilized, while keeping each tool in the same risk range, ensuring processing safety while also improving processing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a flow chart of a cavity multi-tool machining method considering load optimization of the present invention;

[0043] Figure 2 It is a schematic diagram of the cavity model to be processed in the present invention;

[0044] Figure 3 yes Figure 2 A schematic diagram of the center axis of the cavity generation;

[0045] Figure 4 It is a schematic diagram of the division of the processable area of ​​the present invention;

[0046] Figure 5 It is a schematic diagram of the processing area corresponding to the tool sequence of the present invention;

[0047] Figure 6 is a schematic diagram of the circular cutting trajectory generated by the smaller tool of the present invention;

[0048] Figure 7 is a schematic diagram of the circular cutting trajectory generated by the larger tool of the present invention;

[0049] Figure 8 It is a schematic diagram of replacing the cycloid trajectory at the corner of the annular cutting trajectory of the present invention;

[0050] Fig. 9 It is a schematic diagram of replacing the cycloid trajectory in the innermost area of ​​the annular cutting trajectory of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0052] Example

[0053] like Figure 1 As shown, a method for generating a two-dimensional cavity multi-tool combination machining trajectory with a constant load rate is applicable to milling machining of various cavities and planes, and applicable equipment includes but is not limited to machining centers, milling machines, robots and other equipment with multi-tool machining capabilities.

[0054] The specific steps include:

[0055] S1 determines the allowable load of each tool based on the set uniform processing load rate and the maximum load that each tool can bear. Specifically, a suitable load factor K is selected based on the processing conditions, such as tool shape, machine type and model. safe In this embodiment, a load factor of 70% is selected, and the reasonable load of the tool is calculated based on this, including:

[0056] S1.1 First, the maximum load that the tool can withstand is calculated based on the tool material and the allowable load of the machine tool. There are many ways to calculate the maximum load of the tool. This embodiment uses the finite element analysis method for calculation. In this embodiment, the tool sequence is only different in tool size, and the tool material is the same, so each tool has the same allowable stress [σ]. Then, a corresponding tool model is established in the finite element software to simulate the state during processing. By applying a load to the tool, when the equivalent stress of the tool reaches the allowable stress, it is the maximum load F of the tool. max .

[0057] S1.2 Then calculate the safe load or allowable load of each tool based on the load factor of the selected tool:

[0058] F allow =K safe ×F max

[0059] F allow is the allowable load of the tool, which is calculated to be 0.7F in this embodiment. max .

[0060] S2 obtains the allowable material removal rate of each tool based on the allowable load of each tool.

[0061] The specific implementation is:

[0062] By calculating the material removal rate and the tool load, a relationship is established between the two. The optimal material removal rate of the tool is calculated using the optimal load obtained previously. There are many methods for establishing the relationship between the material removal rate and the tool load. This embodiment uses a machining experiment to determine the optimal material removal rate under the condition of the optimal cutting force. First, it is stipulated that the axial cutting depth a of the tool during the cavity machining process p It is constant. According to experiments, it can be found that the tool force is proportional to the material removal rate, so the fitting calculation formula can be analyzed as follows:

[0063] MRR allpw =K m ×F allow

[0064] The best material removal rate MRR allow The optimal tool load F is calculated allow Based on the correlation coefficient K m In this embodiment, T can be calculated by this method. 4 Material removal rate MRR 4 , and other material removal rates MRR 6 , MRR 8 , MRR 12 .

[0065] S3 obtains the contour size information of the cavity to be processed, and divides the cavity into processing areas according to the contour information of the cavity and the sizes of each tool;

[0066] The specific implementation is:

[0067] S3.1 In this embodiment, the center axis of the cavity is used to determine the machinability of the tool, and then the area is divided; first, the model information of the workpiece to be processed is obtained, see Figure 2 , which is a cavity model provided by an embodiment of the present invention;

[0068] Then, the data of the surface to be processed is used to calculate the median axis of the surface to be processed. In this embodiment, the Voronoi diagram algorithm is used to calculate the median axis of the surface to be processed. Specifically, a local inscribed circle can be generated along the contour of the surface to be processed. When the inscribed circle covers the entire area to be processed, the motion trajectory of the center of the local inscribed circle is the median axis. The result generated in this embodiment is as follows: Figure 3 shown.

[0069] S3.2 According to the determined center axis and the tool sequence {T 2 ,T 4 ,T 6 ,T 8 ,T 12} to divide the processing area of ​​the processing surface. The specific algorithm for area division according to the central axis has the following steps:

[0070] S3.2.1 Using the medial axis generated previously, calculate the radius of the inscribed circle at any point on the medial axis as follows:

[0071]

[0072] In the formula, R is O i The radius of the inscribed circle corresponding to the point, where Φ(x,y) is any point on the contour of the surface to be processed, O i is any point on the central axis.

[0073] S3.2.2 Based on the obtained inscribed circle radius R, use the given tool sequence {T 2 ,T 4 ,T 6 ,T 8 ,T 12}, the area can be divided as follows:

[0074] Reg(T n )={O i |R(O i )≥n / 2}

[0075] In the formula, Reg(T n ) is the maximum area that can be processed by a tool with a diameter of n. Reg is determined by the median axis, which represents the area formed by the union of the inscribed circles of the workpiece contour generated by a series of circles with the corresponding median axis as the center. Therefore, the radius of the inscribed circle R(O i ) is greater than the corresponding tool radius n / 2 to determine the tool T n The processable area Rreg(T n). In this embodiment, the largest tool that can be used is a tool with a diameter of 12, and the smallest tool that can be used is a tool with a diameter of 2. By analyzing this embodiment, it is found that according to the machinability, the tool with a minimum diameter of 4 can complete the processing, so the tool with a diameter of 2 can be excluded, and its corresponding processing area is the same as that of the tool with a diameter of 4. The division result is as follows: Figure 4 As shown, region 1 is Rreg(T 4 ), that is, the minimum tool diameter is 4, and area 2 is Reg(T 6 ), Region 3 is Reg(T 7 ), Region 4 is Reg(T 12 ).

[0076] S4 obtains the processing time of each tool according to the allowable material removal rate of each tool and the processing area of ​​the cavity, and obtains the tool processing sequence with the shortest total processing time and the processing area of ​​each tool in the processing sequence;

[0077] Specifically, the processing time required for each tool processing is calculated according to the allowable material removal rate of each tool and the divided processing areas, so as to calculate the tool processing sequence with the shortest total processing time, that is, the highest processing efficiency, and determine the processing areas of each tool.

[0078] The steps include:

[0079] S4.1 First, select a set of tool sequences. In this embodiment, select T 4 , T 8 , T 12 , use the material removal rate to calculate the specific processing time required for each tool:

[0080]

[0081] Among them, V i For the tool sequence Tools{T i The area that can be processed by the i-th tool in}, MRR i is the optimal material removal rate corresponding to the corresponding tool. In this embodiment, time is calculated to be M4 V Reg4 / MRR 4 , the processing time calculation of other tools is the same as above.

[0082] S4.2 calculates the total time required to complete the machining of the current tool sequence:

[0083]

[0084] Time totle Is to use the tool sequence Tools{T iThe total processing time of the tool is the actual processing time of each tool. Mi , advance and retract time Ri And the total tool change time C In this embodiment, the processing time obtained by this round of calculation is Time totle =time M4 +time R4 +time M8 +time R8 +time M12 +time R12 +time C .

[0085] S4.3 Finally, the selected tool sequence is optimized through continuous iteration, and finally the tool sequence with the shortest total processing time is selected. In this embodiment, the ant colony algorithm is used to optimize it. A directed graph is established according to the size of the tool, and a tool with infinite diameter is added as the end point. Since the entire cavity needs to be processed, all the smallest tools are necessary. Therefore, in the ant colony algorithm, each iteration is the ant moving from the smallest tool to the largest tool. The node passed is the tool selected in this round of iteration, and the path with short time will be marked with more pheromones. When the ant passes here again, it will tend to take the path with more pheromones, and finally the ants choose the shortest path. This embodiment uses this method to obtain the optimal tool sequence selection. In this embodiment, the final optimization result is T 4 , T 12 ,like Figure 5 As shown, area 5 is T 4 Processing area, area 6 is T 12 Processing area.

[0086] S5 plans a corresponding cutting trajectory in a corresponding area according to the determined tool sequence and the allowable material removal rate of each tool.

[0087] The specific algorithm for obtaining the generated line cutting trajectory is as follows:

[0088] According to the selected tool sequence, a circular cutting trajectory is generated for each tool in its corresponding processing area, according to MRR allow Select the machining parameters of the tool. In this embodiment, according to the determined machining speed V f and axial cutting depth a p To determine the trajectory offset D:

[0089]

[0090] After determining the offset distance of the trajectory, generate the spiral cutting trajectory, such as Figure 6 and Figure 7 The figures shown in the figure are the ring cutting trajectories generated for the two areas.

[0091] S6 calculates the material removal rate of the line cutting track, identifies the track with a material removal rate higher than the material removal rate, and divides the circular cutting track into two parts according to whether the material removal rate is higher than the allowable material removal rate. The material removal rate can be calculated by using a pixel method, dividing the cavity area into small pixel blocks, and determining the processing area according to the number of pixel blocks swept by the tool during the processing, and then calculating the material removal rate during the processing.

[0092] S7 generates a cycloidal trajectory for the local area with a material removal rate higher than the allowable material removal rate identified in S6 to replace the original circular cutting trajectory so that the trajectory maintains a material removal rate stable at the MRR allow , thus keeping the machining load stable, due to the change of MRR and the axial cutting depth a p And radial cutting depth R dc And the processing speed V f Relevant, namely:

[0093] MRR = a p ×R dc ×V f

[0094] By using the characteristics of the variable radius cycloid trajectory, the radius of the cycloid trajectory can be adjusted to make the R of the machining trajectory dc Stable, by adjusting R dc To stabilize MRR.

[0095] The following steps are used to generate a cycloid trajectory to replace the tangent trajectory in a local area:

[0096] S7.1 Generate the corresponding medial axis based on the inner and outer rings of the cycloid track to be inserted as the boundary. In this embodiment, the Voronoi diagram algorithm is used to generate the medial axis of the region, such as Figure 8 Shown by the dashed line.

[0097] S7.2 determines the guide line of the cycloid according to the mid-axis segment swept by the circular cutting trajectory segment identified in S6 during processing. The cycloid is generated according to the guide line.

[0098] S7.3 deletes the original circumferential trajectory segment in the area, and then connects the generated cycloid trajectory head and tail with the retained circumferential trajectory. Figure 8 The cycloid trajectory inserted at the corner is shown in Fig. 9 The figure in the middle is the cycloid trajectory inserted at the innermost ring.

[0099] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for generating machining trajectories of two-dimensional cavity multi-tool combination machining with constant load rate, It is characterized in that These include: Determine the allowable load of each tool based on the set uniform processing load rate and the maximum load that each tool can withstand; According to the allowable load of each tool, the allowable material removal rate of each tool is obtained; Obtain the contour dimension information of the cavity to be processed, and divide the cavity into processing areas according to the contour dimension information of the cavity and the dimensions of each tool; The processing area is divided into: Establishing a central axis of the cavity boundary according to the acquired contour dimension information of the cavity to be processed, wherein the central axis is formed by connecting the centers of the inscribed circles of the cavity boundary; The passability of each tool in the area is determined according to the inscribed circle radius corresponding to the middle shaft segment. Specifically, if the minimum value of the inscribed circle radius corresponding to the middle shaft segment is smaller than the selected tool radius, the tool cannot be used to process the area corresponding to the middle shaft segment, and a tool with a smaller diameter needs to be used. The corresponding areas of each middle shaft segment that can be processed by each tool are combined as the processable area of ​​the tool to complete the division of the processing area; The processing time of each tool is obtained according to the allowable material removal rate of each tool and the processing area of ​​the cavity, and the tool processing sequence with the shortest total processing time and the processing area of ​​each tool in the processing sequence are obtained; Plan the circular cutting trajectory in the corresponding area according to the determined tool processing sequence and allowable material removal rate; Obtain the material removal rate of the regional planning circular cutting trajectory, compare the material removal rate with the allowable material removal rate of each tool, and segment the trajectory part with a higher material removal rate; The segmented trajectory part is replaced with a cycloid trajectory to obtain a load-stable cavity machining trajectory, and further obtain a multi-tool cavity machining trajectory; Specifically: Generate a corresponding medial axis based on the inner and outer rings of the annular tangent trajectory to be inserted into the cycloid trajectory as the boundary; The middle axis segment generated from the segmented trajectory is used as the guide line of the cycloid, and the radius of the inscribed circle corresponding to the middle axis is used as the radius of the cycloid trajectory to generate the cycloid trajectory; The original tangential trajectory segment in the area is deleted, and then the generated cycloid trajectory is connected at the beginning and end with the retained tangential trajectory.

2. The method for generating a two-dimensional cavity multi-tool combined machining trajectory according to claim 1, It is characterized in that The uniform processing load rate of the setting is defined as: K safe =F allow / F max ×100% Where K safe is the uniform machining load rate of the tool sequence, K safe ∈[0,1], used to obtain the value of the allowable load based on the maximum load determined by the specific conditions of different tools after determining the processing conditions, and to unify the load conditions when processing with different tools; F allow is the allowable load of the tool, which is the safe load of the tool based on the load rate; F max It is the maximum load that the tool can reach.

3. The method for generating a two-dimensional cavity multi-tool combined machining trajectory according to claim 1, It is characterized in that The maximum load that the tool can reach is the value of the cutting force when the maximum stress of the tool during machining is equal to the allowable stress.

4. The method for generating a two-dimensional cavity multi-tool combined machining trajectory according to claim 1, It is characterized in that The machining time of each tool is calculated based on the allowable material removal rate of the tool and the volume of the machining area.

5. The method for generating a two-dimensional cavity multi-tool combined machining trajectory according to claim 1, It is characterized in that The total processing time is calculated as follows: Among them, Time totle Is to use the tool sequence Tools{T i The total processing time of the tool is the actual processing time of each tool. Mi , advance and retract time Ri And the total tool change time C Obtained by addition.

6. The method for generating a two-dimensional cavity multi-tool combined machining trajectory according to claim 1, It is characterized in that The circular cutting trajectory is planned in the corresponding area according to the determined tool processing sequence and the allowable material removal rate, and specifically the offset distance of the circular cutting trajectory is determined according to the tool processing sequence and the allowable material removal rate, and the circular cutting trajectory is further generated.

7. The method for generating a two-dimensional cavity multi-tool combined machining trajectory according to claim 6, It is characterized in that The material removal rate of the regional planning circular cutting trajectory is obtained by using a pixel method.

8. The method for generating a two-dimensional cavity multi-tool combined machining trajectory according to claim 2, It is characterized in that The maximum load of the tool is calculated by using a finite element analysis method, and the tool sequence specifically has tools of different sizes but the same material.

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