A cutting process planning method to reduce groove wear of turning tools

Abstract

The present invention belongs to the technical field of turning tool wear reduction, and discloses a cutting process planning method for reducing turning tool groove wear. First, the occurrence location and cause of the primary and secondary groove wear are analyzed based on the wear morphology of the turning tool cutting edge; secondly, the cutting depth and tool feed of each step in the turning process are planned so that the contact point between the turning tool cutting edge and the workpiece changes dynamically within a given range; finally, the cutting speed is optimized based on the cutting characteristics of the material to be cut, and the turning process of difficult-to-machine materials is completed in combination with the planned cutting depth and tool feed of each step. Compared with the turning process planning method with constant cutting parameters, the proposed method reduces the cumulative duration of the force and heat load on the same cutting edge contact point during the turning process, and increases the cooling time between two force and heat loads acting on the same contact area. The proposed method not only curbs the turning tool groove wear but also improves the turning efficiency of difficult-to-machine materials.

Description

Technical Field

[0001] The invention belongs to the technical field of turning tool wear reduction, and in particular relates to a cutting process planning method for reducing turning tool groove wear. Background Art

[0002] Metal materials, such as titanium alloys, superalloys, and high-strength steels, exhibit excellent high-temperature strength, good thermal corrosion resistance, and outstanding fatigue resistance, making them widely used in aerospace, defense, and military industries. These materials typically exhibit physical properties such as low thermal conductivity, high hot hardness, and significant cutting deformation, making them typically difficult to machine. During cutting, they experience intense mechanical and thermal reactions, resulting in severe and complex tool wear.

[0003] The wear pattern of turning tools can be divided into rake face wear and flank face wear based on the wear location. Flank face wear is mostly used to evaluate the service life of cutting tools and usually consists of three parts: the tip wear area, the uniform wear area, and the groove wear area. Since the cutting of difficult-to-cut materials is often accompanied by severe surface hardening, this exacerbates the groove wear problem of the cutting tool, and then forms a distinct narrow V-shaped groove on the cutting edge of the tool. As the cutting process progresses, the V-shaped groove widens and deepens, gradually exceeding the wear bandwidth of other areas and eventually becoming the dominant factor restricting the service life of the tool. Invention patent CN104476326A discloses "A method for predicting groove wear of ceramic tools", which is used to predict the shape of the groove wear area of ​​ceramic material turning tools. Invention patent CN108481087A discloses "A method for predicting groove wear of annular tools considering stress concentration effect". By quantifying the influence of stress concentration coefficient on groove wear, it realizes the accurate prediction of the groove wear depth of annular tools during milling of difficult-to-cut materials. Invention patent CN114619057A discloses a workpiece turning method and machine tool, which adjusts the B-axis rotation angle of the lathe to change the main deflection angle of the turning tool during the turning process, thereby suppressing the groove wear of the turning tool while maintaining the rigidity of the tool.

[0004] The current technical solution mainly solves the problem of predicting the shape of tool groove wear. The proposed groove wear suppression technology is only applicable to four-axis lathes with a B-axis and cannot be extended to ordinary three-axis CNC lathes or even three-axis ultra-precision single-point diamond lathes. This means that the current technical solution cannot solve the tool groove wear problem that occurs when using a three-axis lathe for rough machining, semi-finishing, finishing and even precision machining of difficult-to-machine materials. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a cutting process planning method for reducing turning tool groove wear, so as to solve the problem of turning tool groove wear that cannot be solved by the existing technical solutions when using a three-axis lathe to cut difficult-to-process materials.

[0006] The technical solution of the present invention:

[0007] A cutting process planning method for reducing groove wear of a turning tool comprises the following steps:

[0008] Step 1: Select a turning tool based on the material to be machined and conduct a turning test. Use an optical microscope to detect the wear pattern of the turning tool and determine the locations of the primary and secondary grooves. Among them, primary groove wear occurs near the contact point between the primary cutting edge and the machined surface, and secondary groove wear occurs near the contact point between the secondary cutting edge and the machined surface. As the turning process progresses, the above grooves gradually widen and deepen. Comprehensive analysis of factors such as work hardening, chip flow direction, and plastic flow measurement shows that the location of the gradient force and heat load on the cutting edge and the location of chip scratching remain constant and nearly coincident during the turning process. This is the intuitive reason for the groove wear on the turning tool cutting edge.

[0009] Step 2: Propose an overall strategy for turning process planning. For comparison, the turning tool cutting parameters before turning process planning are: cutting depth ap0, feed rate f0, and cutting speed Vc1. The above cutting parameters are kept constant in each process step. This general constant cutting parameter planning method results in the intersection point between the turning tool cutting edge and the machined / unmachined surface not changing, which in turn aggravates the problem of main and secondary groove wear of the turning tool. To this end, a process planning strategy for suppressing the occurrence of turning tool groove wear is proposed, that is, adjusting the cutting depth of each process step so that the contact point between the turning tool main cutting edge and the workpiece to be machined changes dynamically, and adjusting the tool feed rate at different cutting positions in a single process step so that the contact point between the turning tool secondary cutting edge and the machined surface of the workpiece changes dynamically. The above operation helps to reduce the action time of gradient force and heat load at the same cutting edge position. Subsequently, on this basis, the cutting speed of the turning tool in each process step is optimized.

[0010] Step 3: Plan the turning depth for each work step according to the overall strategy. First, divide the turning process into two phases based on the amount of material to be removed. The first phase removes most of the remaining material, and the cutting parameters used in each work step during this phase are different from those before optimization. The second phase completes the remaining material removal, and the cutting parameters used in this phase remain the same as before optimization. Second, for the material removal process in the first phase, with the goal of reducing tool main groove wear and improving cutting efficiency, establish the objective function to be optimized, f(ap), as follows:

[0011]

[0012] Among them, the symbols W1, W2, W3 and W4 represent the weight values ​​of the objective function of each part, ap i Represents the cutting depth of the i-th step, and its range is [ap min,ap max ], N represents the total number of steps to be planned; the above multi-objective function is composed of four cumulative parts, of which the first part represents the cumulative sum of the cutting depth differences between two adjacent steps, and the second part represents the cumulative sum of the lag differences of the cutting depth sequence, where the lag period is 2; the larger the cumulative value of the first two parts of the objective function, the greater the difference in cutting depth used between similar steps, which will help to suppress the wear of the tool main groove; the third part represents the cumulative value of the cutting depth used in all cutting steps, which is used to measure the cutting efficiency; the fourth part is the penalty term, and the weight W4 is set as a piecewise function. When the cutting depth meets the condition ap i >0.9ap max When the value of weight factor W4 is significantly increased, it will help to adjust the cutting depth away from the maximum limit cutting depth;

[0013] Subsequently, the weight factors of each objective function are set, and the PSO particle swarm algorithm is used to solve the objective function. Finally, the solution results are arranged in sequence and supplemented with the cutting depth values ​​of the remaining steps. The resulting parameter sequence represents the complete cutting depth information of all steps from beginning to end.

[0014] Furthermore, the cutting depth of the remaining steps is consistent with the cutting depth ap0 used in the unoptimized process;

[0015] Step 4: Plan the turning feed for each step according to the overall strategy; set the tool feed at the cutting starting point to f min , the tool feed at the cutting end point is f max , the tool feed at the middle position changes linearly along the cutting path, and the feed rate change law in the remaining steps is consistent with the feed rate change law in the above steps;

[0016] Step 5: Optimize the turning speed according to the cutting characteristics of the material to be processed. At the same time, according to the planned cutting depth and tool feed, use the selected turning tool to complete the subsequent processing of the difficult-to-process material.

[0017] Beneficial effects of the present invention:

[0018] The present invention is aimed at the turning process of difficult-to-machine materials and proposes a cutting process planning method that reduces tool groove wear. This method rationally plans the cutting depth and tool feed of each step in the turning process, so that the contact point between the turning tool cutting edge and the workpiece changes dynamically within a given range. Compared with the process planning method with constant cutting parameters, the proposed method reduces the cumulative duration of the force and heat load on the same cutting edge contact point during the turning process, and increases the cooling time between two force and heat loads acting on the same contact area. The proposed method not only curbs the turning tool groove wear but also improves the turning efficiency of difficult-to-machine materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 (a) is a schematic diagram of the turning tool cutting process;

[0020] Figure 1 (b) is a partial enlarged view of the turning tool contact area;

[0021] Figure 1 (c) is a schematic diagram of the positions of the left and right contact points of the cutting edge during turning.

[0022] Figure 2 It is a schematic diagram of the cutting process adjustment strategy used to reduce the groove wear of the turning tool.

[0023] Figure 3 (a) is a schematic diagram of the position change range of the left and right contact points after applying the process adjustment strategy;

[0024] Figure 3 (b) Schematic diagram of the change in the left contact point position induced by the dynamic adjustment of the tool cutting depth;

[0025] Figure 3 (c) Schematic diagram of the change in the right contact point position induced by the dynamic adjustment of the tool feed rate.

[0026] Figure 4 It is a convergence curve diagram of the optimization process of the cutting depth used in each working step of the turning tool.

[0027] Figure 5 It is a curve chart of the change of feed rate used in a single step of the turning tool at different cutting positions. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings and in conjunction with specific embodiments:

[0029] Taking the turning process of pure iron DT4E as an example, the turning tool cutting parameters planned using a general constant cutting parameter planning method are as follows: the cutting length in each step is 500 mm, the lathe spindle speed is 800 rpm, the tool feed rate f0 = 0.1 mm / r, the cutting depth ap0 = 0.11 mm, the number of steps is 26, and the cutting method is dry cutting. In addition, the spindle speed can be adjusted within the range of [600 rpm, 1200 rpm], the tool feed can be adjusted within the range of [0.05 mm / r, 0.15 mm / r], and the cutting depth can be adjusted within the range of [0.05 mm, 0.2 mm]. After completing the cutting according to the current process, groove wear occurs on both the primary and secondary cutting edges of the turning tool. To reduce groove wear of the turning tool and improve cutting efficiency, a turning process planning method is proposed, which includes the following steps:

[0030] Step 1: Select the DCGT11T302-KC5010 brand turning tool insert to carry out pure iron material turning test, use an optical microscope to detect the wear form of the turning tool, and determine the location of the main and auxiliary grooves; Figure 1 As shown in the figure, the main groove wear occurs near the contact point between the main cutting edge and the surface to be machined, and the secondary groove wear occurs near the contact point between the secondary cutting edge and the machined surface. As the turning process progresses, the above grooves gradually widen and deepen. Taking into account factors such as work hardening, chip flow direction, and plastic flow measurement, it can be seen that the position of the gradient force and heat load on the cutting edge and the position of chip scratching remain constant and almost coincident during the turning process. This is the intuitive reason for the groove wear on the turning tool cutting edge.

[0031] Step 2: Propose an overall strategy for turning process planning, such as Figure 2 As shown, by adjusting the cutting depth ap of each step i The contact point position between the main cutting edge of the turning tool and the workpiece surface to be processed is dynamically changed, and the tool feed f at different cutting positions in each step is adjusted. i The contact point position between the secondary cutting edge of the turning tool and the machined surface of the workpiece changes dynamically. The moving range of the two contact points on the cutting edge is as follows: Figure 3 As shown, the above operation helps to reduce the action time of the gradient force and heat load at the same tool position;

[0032] Step 3: Plan the turning depth for each work step according to the overall strategy. First, divide the turning process into two phases based on the amount of material to be removed. The first phase removes most of the remaining material, and the cutting parameters used in each work step during this phase are different from those before optimization. The second phase completes the remaining material removal, and the cutting parameters used in this phase remain the same as before optimization. Second, for the material removal process in the first phase, with the goal of reducing tool main groove wear and improving cutting efficiency, establish the objective function to be optimized, f(ap), as follows:

[0033]

[0034] The above multi-objective function is composed of four parts, and the symbols W1, W2, W3 and W4 represent the weight values ​​of the objective functions of each part; i Represents the cutting depth used in the i-th step, and its range is [ap min ,ap max ], in this example, ap min =0.05mm,ap max =0.2mm; N represents the total number of steps to be planned in the first stage. In this example, N=20;

[0035] Subsequently, the accumulated data involved in the first three parts of the objective function are standardized, and the range of the standardized data is [1,5]. The weight factors of the above three parts of the objective function are set as W1 = -3, W2 = -0.6, and W3 = -4 respectively. The accumulated data involved in the fourth part of the objective function are not standardized, and the corresponding weight factor W4 is set when the cutting depth meets ap i When the value is greater than 0.18 mm, it is set to 500, otherwise it is set to 5. The objective function is solved using the PSO particle swarm algorithm, and the convergence curve of the solution process is as follows: Figure 4 As shown; Finally, the solution results are arranged in sequence, and the cutting depth values ​​of the remaining steps are added afterwards. The parameter sequence formed represents the complete cutting depth information of all steps from beginning to end. The cutting depth planning results of each step are shown in Table 1;

[0036] Step 4: Plan the turning feed for each step according to the overall strategy; set the tool feed at the cutting starting point to f min , the tool feed at the cutting end point is f max , the tool feed at the middle position changes linearly along the cutting path, and the feed rate change law in the remaining steps is consistent with the feed rate change law in the above steps; in this example, f min =0.05mm / r,f max =0.15mm / r, the planning result of turning tool feed is as follows Figure 5 As shown;

[0037] Step 5. Optimize the turning speed based on the cutting characteristics of pure iron DT4E. As the cutting speed decreases, the plastic flow phenomenon on the machined surface of the pure iron material gradually intensifies, which will further worsen the problem of secondary groove wear of the tool. Therefore, within the given spindle speed range, the optimal speed is 1200 rpm. Then, combined with the planned cutting depth and tool feed, a turning tool insert with the brand DCGT11T302-KC5010 is used to complete the cutting of pure iron DT4E material.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0039] Table 1 Comparison of cutting depth of each step before and after optimization

[0040]

[0041]

Claims

1. A cutting process planning method for reducing groove wear of a turning tool, characterized in that: The following steps are involved: Step 1: Select a turning tool based on the material to be machined and conduct a trial turning test to detect the wear pattern of the turning tool and determine the locations of the primary and secondary grooves. Primary groove wear occurs near the contact point between the primary cutting edge and the machined surface, while secondary groove wear occurs near the contact point between the secondary cutting edge and the machined surface. As the turning process progresses, these grooves gradually widen and deepen. Based on this, the causes of groove wear are analyzed. Step 2: Propose an overall strategy for turning process planning. For comparison, the turning tool cutting parameters before turning process planning were as follows: cutting depth ap0, feed rate f0, and cutting speed Vc1. The above turning tool cutting parameters were kept constant in each process step. This constant cutting parameter planning method resulted in no change in the intersection point between the turning tool cutting edge and the machined and unmachined surfaces, which in turn exacerbated the problem of wear on the main and secondary grooves of the turning tool. To this end, a process planning strategy for suppressing the occurrence of turning tool groove wear was proposed, namely, adjusting the cutting depth of each process step so that the contact point between the turning tool main cutting edge and the workpiece unmachined surface changes dynamically, adjusting the tool feed rate at different cutting positions in a single process step so that the contact point between the turning tool secondary cutting edge and the machined surface of the workpiece changes dynamically, and on this basis, optimizing the cutting speed of the turning tool in each process step. Step 3: Plan the turning depth for each process step according to the overall strategy. First, divide the turning process into two phases based on the amount of material to be removed. The first phase removes the majority of the remaining material, and the cutting parameters used in each process step during this phase are different from those before optimization. The second phase completes the remaining material removal process, and the cutting parameters used in this phase remain the same as before optimization. Second, for the material removal process in the first phase, with the goal of reducing tool main groove wear and improving cutting efficiency, establish the objective function to be optimized, f(ap), as follows: Among them, the symbols W1, W2, W3 and W4 represent the weight values ​​of the objective function of each part, ap i Represents the cutting depth of the i-th step, and its range is [ap min ,ap max ], N represents the total number of steps to be planned; The above multi-objective function is composed of four cumulative parts, where the first part represents the cumulative sum of the cutting depth differences between two adjacent steps; the second part represents the cumulative sum of the lag differences of the cutting depth sequence, where the lag period is 2; the larger the cumulative value of the first two parts of the objective function, the greater the difference in cutting depth used between similar steps, which will help to suppress the wear of the tool main groove; the third part represents the cumulative value of the cutting depth used in all cutting steps, which is used to measure the cutting efficiency; the fourth part is the penalty term, and the weight W4 is set to a piecewise function. When the cutting depth meets the condition ap i >0.9ap max When the value of weight factor W4 is significantly increased, it will help to adjust the cutting depth away from the maximum limit cutting depth; Subsequently, the weight factors of each objective function are set, and the PSO particle swarm algorithm is used to solve the objective function. Finally, the solution results are arranged in sequence and supplemented with the cutting depth values ​​of the remaining steps. The resulting parameter sequence represents the complete cutting depth information of all steps from beginning to end. Furthermore, the cutting depth of the remaining steps is kept consistent with the cutting depth ap0 used in the unoptimized process; Step 4: Plan the turning feed of each step according to the overall strategy; set the turning tool feed at the cutting starting point to f min , the tool feed at the cutting end point is f max , the turning tool feed at the middle position changes linearly along the cutting path, and the feed rate change law in the remaining steps is consistent with the feed rate change law in the above steps; Step 5: Optimize the turning speed Vc1 based on the cutting characteristics of the material to be processed. At the same time, according to the planned cutting depth and tool feed, use the selected turning tool to complete the subsequent processing of the difficult-to-process material.

2. The cutting process planning method according to claim 1, characterized in that: The wear pattern of the turning tool cutting edge was detected using an optical microscope.

3. The cutting process planning method according to claim 1, characterized in that: The total amount of material removed in the first stage accounts for 75% to 95% of the total remainder.

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