Weak-rigidity flexible rod cutting deformation control method

Abstract

The invention provides a cutting deformation control method for a weak-rigidity flexible rod. The cutting deformation control method comprises the steps that the size and source of a blank and the heat treatment mode of the blank are optimized; carrying out preferable heat treatment on the preferable blank; optimizing turning parameters of finish machining and rough machining; a residual stress release groove is machined in the slender neck position of the part; the part is subjected to stress relief aging heat treatment; the part is externally ground to the designed maximum outer circle size, and stress relief aging heat treatment is carried out; processing shapes of two ends of the part; the clamping mode for machining the slender neck part of the part is optimized; under the optimized clamping mode, the slender neck part of the part is machined through the optimized material removal sequence; and the part is subjected to stress relief aging heat treatment. Based on the technical scheme, the design requirement can be met without excessively depending on resources such as a high-precision lathe in the machining process, the reshaping rate of the part is reduced to 13.3% from 25%, and the production efficiency is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of cutting processing, and in particular to a method for controlling cutting deformation of a weak-rigidity flexible rod. Background Art

[0002] Flexible rods are widely used in key aircraft components such as electro-hydraulic servo valves and aircraft engine control shafts. Their tiny size and shape changes will cause changes in component performance and affect control accuracy. Due to the extremely large aspect ratio, weak rigidity, and high straightness requirements of flexible rods, deviations are very likely to occur, resulting in a high rework rate and low yield rate, which greatly increases production costs and time. The use of resources such as high-precision lathes can alleviate the problem of deformation deviations, but they occupy a long machine time and have limited machine tool resources, which cannot effectively improve processing efficiency and greatly restrict product delivery. Residual stress is the main reason for the final deformation deviation of weak rigidity parts such as flexible rods. The residual stress inside the parts is mainly the result of the superposition of the residual stress of the blank and the residual stress introduced by machining. Reasonable control of the residual stress inside the parts can effectively reduce the deformation of weak rigidity parts such as flexible rods, thereby solving the problem of deformation deviations.

[0003] With the widespread application of weak rigidity parts in aircraft, their processing deformation control has received a lot of attention and research. However, most of the existing related research focuses on the residual stress law and processing deformation control of aerospace structural parts, engine casings, blades and other parts. There is no effective deformation control strategy and system solution for large aspect ratio weak rigidity rotating parts such as flexible rods. In actual production, in order to ensure the final processing quality, high-precision lathes and conservative cutting parameters are usually used, resulting in low production efficiency and high cost. Therefore, designing residual stress and deformation control methods for such parts has important theoretical significance and practical application value. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a method for controlling the cutting deformation of a weak-rigidity flexible rod, so that the processing efficiency of parts can be improved and the production cost can be reduced while ensuring that the processing quality does not exceed the tolerance, so as to fill the gaps in the above-mentioned existing research and lay a methodological and technical foundation for the cutting deformation control of flexible rods with large aspect ratios.

[0005] Expected technical effect: Through the method proposed in the present invention, the initial processing blank can be optimized according to the residual stress distribution law of the raw material, and an effective processing method and processing parameter optimization method can be provided to achieve the flexible rod parts production process without relying on high-precision machine tools, reduce the rework rate, and at the same time reduce costs and increase efficiency.

[0006] In order to achieve the above object, the present invention provides the following scheme:

[0007] A method for controlling cutting deformation of a weak-rigidity flexible rod, comprising:

[0008] Optimize the blank size, source and heat treatment method of the blank;

[0009] Performing optimal heat treatment on the selected blank;

[0010] Optimize turning parameters for finishing and roughing;

[0011] Process residual stress relief grooves at the slender neck of the part;

[0012] Perform stress relief and aging heat treatment on parts;

[0013] Grind the parts to the designed maximum outer diameter and perform stress relief aging heat treatment;

[0014] Process the shapes of both ends of the parts;

[0015] Optimize the clamping method of the slender neck part of the processed parts;

[0016] Under the optimized clamping mode, the slender neck part of the part is machined with the optimized material removal sequence;

[0017] The parts are subjected to stress relief and aging heat treatment.

[0018] Optionally, the blank size, source and blank heat treatment method optimization method specifically include:

[0019] First, the existing blanks are classified according to the differences in factory processes and specifications of different manufacturers, and different heat treatment methods suitable for blank materials are selected. Then samples are extracted from different types of blanks, and different heat treatments are performed. The residual stress test of the blanks after heat treatment is performed to obtain the residual stress distribution law of blanks from different sources and under different heat treatment conditions. Finally, according to the principle that the better the uniformity and symmetry of the residual stress field distribution and the smaller the stress value of the blank core, the best combination of heat treatment method and blank source is determined.

[0020] Among them, the preferred method is a law obtained by combining simulation and cutting test results with residual stress distribution, specifically including:

[0021] The simulation experiment adds the obtained residual stress distribution to the finite element model, simulates the material removal process, and compares the deformation of the final model; the cutting test selects the same batch and heat treatment method as the residual stress test experiment for actual processing, and uses straightness error and outer circle roundness as comparison criteria to select the best combination.

[0022] Optionally, the method for optimizing turning parameters for finishing and roughing specifically includes:

[0023] Orthogonal cutting simulation experiments are conducted for different cutting parameters (speed, depth of cut, feed rate) to find out the influence of cutting parameters on residual stress, and select the optimal parameters according to the different goals of roughing and finishing. Among them, rough turning considers improving cutting efficiency, and selects low speed, large cutting depth, and large feed; feed finishing considers surface quality and residual stress introduced by cutting, and selects higher speed, small cutting depth, and small feed.

[0024] Optionally, the optimized clamping method is specifically achieved by fixing the front end with a three-jaw chuck, and the tailstock of the machine tool uses a threaded positioning guide sleeve or other tensioning device to provide an outward pulling force for the workpiece.

[0025] Optionally, the residual stress relief groove design is to obtain the relationship between the slot size and the part stiffness through the results of the simulation experiment, and then optimize the final size of the stress relief groove. The number and position of the residual stress relief groove can be determined according to the size of the part design.

[0026] Optionally, the optimized material removal sequence is to symmetrically remove the material at each slender neck layer by layer.

[0027] The beneficial effects of the present invention are as follows: the method optimizes the important processing steps correspondingly for deformation caused by residual stress in parts: in the raw material selection stage, the best blank source and heat treatment method are selected by evaluating the internal residual stress distribution, thereby reducing the influence of residual stress from the source and achieving twice the result with half the effort; in the processing stage, the processing parameters are optimized to reduce the residual stress introduced by cutting, and the deformation problem caused by the internal residual stress of parts is further reduced by opening stress release grooves, improving clamping methods and processing procedures to reduce the influence of the internal residual stress of parts on the overall deformation.

[0028] By adopting the deformation control method of the weak rigidity flexible rod proposed in the present invention, the processing process no longer relies too much on resources such as high-precision lathes to meet the design requirements, and the re-correction rate of parts is reduced from 25% to 13.3%, which greatly improves production efficiency. In actual production, compared with the traditional processing flow, the method of the present invention replaces the empirical process design with the mechanism analysis process design. The average straightness error of multiple batches of parts after processing can be reduced by about 40% compared with the previous process, which effectively improves the processing quality and reduces the processing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, wherein:

[0030] Figure 1 It is a schematic diagram of the dimensions of the flexible rod part processed in the example of the present invention;

[0031] Figure 2 Schematic diagram of parts processing flow;

[0032] Figure 3 is a schematic diagram of a curve of residual stress and depth during cutting in an example of the present invention;

[0033] Figure 4 is a simulation schematic diagram of a residual stress release groove in an example of the present invention;

[0034] Figure 5 It is a schematic diagram of a clamping scheme in an example of the present invention;

[0035] Figure 6 It is a schematic diagram of the material removal sequence of the slender section processing in the example of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings.

[0037] The present invention provides a method for controlling cutting deformation of a weak rigidity flexible rod, wherein the flexible rod has a length of 267.4 mm, an aspect ratio of up to 100, and a shape of Figure 1 As shown, the straightness requirement is 0.1mm over the entire length. The material used is 17-4PH martensitic precipitation hardening stainless steel. The main processing flow is as follows: Figure 2 As shown, including:

[0038] Step 101: Optimize the blank size, source and heat treatment method of the blank.

[0039] First, the blanks were classified and the heat treatment methods suitable for 17-4PH stainless steel were selected. There were three batches of blank raw materials studied in the experiment: (1) imported 16mm outer diameter bar; (2) imported 10mm outer diameter bar; (3) domestic 10mm outer diameter bar. There were five heat treatment methods suitable for blank materials: (1) no heat treatment; (2) solution treatment (1040℃); (3) solution treatment (1040℃) followed by aging hardening (550℃); (4) aging hardening (550℃); (5) solution treatment (1040℃) followed by aging hardening (480℃).

[0040] Then, the X-ray diffraction method was used to measure the axial and circumferential initial residual stresses of different batches of bars under different heat treatment processes, and the residual stress distribution law and the influence of material batch and heat treatment process on the residual stress were analyzed. The straightness error measurement experiment of the parts after heat treatment was further verified. The experimental results are shown in Table 1.

[0041] Finally, according to the residual stress distribution test results and the straightness error measurement experimental results, the following conclusions can be drawn: the better the uniformity and symmetry of the residual stress field distribution and the smaller the residual stress value in the blank core, the more conducive to deformation control. For this example, the heat treatment method of aging hardening (550℃) for the imported 10mm blank is the best combination.

[0042] Table 1 Bar straightness error after different heat treatment methods

[0043]

[0044]

[0045] Step 102: heat treat the selected blank imported 10 mm bar material by age hardening (550° C.) using the optimal heat treatment method.

[0046] Step 103: Optimize turning parameters for finishing and roughing.

[0047] Different key cutting parameters (speed, depth of cut, feed rate) are selected for orthogonal cutting simulation. The experimental scheme is designed according to the commonly used processing parameters of actual processing equipment as shown in Table 2. The curve of residual stress and depth of cutting processing is obtained through simulation analysis and calculation as shown in Table 2. Figure 3 As shown. Among them, σ max represents the maximum residual tensile stress on the surface after cutting simulation, σ min represents the maximum residual compressive stress on the surface after cutting simulation, n represents the spindle speed of the simulated machine tool, a p represents the simulated cutting depth, and f represents the cutting feed rate in the simulation. The stress on the material surface after cutting is selected as the standard for measuring the turning process, and the simulation results are shown in Table 3.

[0048] Table 2 Orthogonal experimental design table

[0049]

[0050]

[0051] Table 3 Simulation results summary

[0052]

[0053] The outermost surface is more affected by temperature. The residual stress on the surface is manifested as residual tensile stress. With the increase of depth, it is mainly affected by the extrusion effect of the tool. The residual tensile stress decreases and transitions to residual compressive stress. The compressive stress increases first, then decreases and finally approaches 0Mpa. Figure 3 The above three factors are analyzed using the range as an indicator, where K1, K2, and K3 represent the sum of one level of each factor. represents the average value of K1, K2, and K3. The results are shown in Table 4:

[0054] Table 4 Analysis of orthogonal test results

[0055]

[0056] From the data in the table, we can see that the speed has the smallest range, the feed has the largest range, and cutting is second. Then the feed and cutting depth have a great influence on σ max and σ min The influence of is more significant. This can also be proved by the influence curve of various factors on residual stress. At the same time, rough turning should consider improving cutting efficiency, choose low speed, large cutting depth, and large feed; fine turning should consider surface quality and residual stress introduced by cutting, choose higher speed, small cutting depth, and small feed. Based on simulation experiments and actual processing equipment, the final recommendation is that the rough machining spindle speed is 800r / min, the back cutting amount is 1-1.5mm, and the feed rate is 0.06mm / r; the fine machining spindle speed is 1200r / min, the back cutting amount is 0.2mm, and the feed rate is 0.03mm / r.

[0057] Step 104: Process a residual stress release groove at the slender neck position in the part design to release some residual stress in advance. The processing parameters are selected from the above rough machining parameters. The number and position of the grooves can be changed according to the design requirements. Grooving will cause a decrease in stiffness, so simulation experiments are carried out for different groove widths and groove depths. Figure 4 The results are shown in Table 5. For this workpiece, the influence of groove depth on machining deformation is greater than that of groove width, and the optimal groove parameters are groove depth 2mm and groove width 5mm.

[0058] Table 5 Effect of different groove width and depth on stiffness

[0059]

[0060] Step 105: Perform aging stress relief heat treatment on the parts, specifically, the aging temperature is 315℃±14℃, the aging time is 3 hours, and the parts are air-cooled to room temperature.

[0061] Step 106: Grind the slotted parts to the designed maximum outer diameter. Then perform stress relief heat treatment on the parts, specifically at an aging temperature of 315°C ± 14°C for 3 hours, and air cool to room temperature.

[0062] Step 107: Process the shapes of both ends of the part, and select the above-mentioned finishing parameters for turning parameters.

[0063] Step 108: Optimize the clamping method of the slender neck part of the machined part. At present, the clamping methods for turning are mainly "one clamp and one push" and "one clamp and one pull", such as Figure 5 As shown. A represents the fixed end of the three-jaw chuck, F A It represents the radial force provided by the three-jaw chuck to the workpiece, M represents the torque provided by the three-jaw chuck to the workpiece, and F P Indicates the radial force of the tool on the workpiece, F f represents the friction force between the tool and the workpiece, B represents the tailstock clamping end, and F BIt represents the radial force provided by the tailstock clamping for the workpiece, F2 represents the axial force provided by the tailstock clamping for the workpiece, and L represents the length of the workpiece clamped between the three-jaw chuck and the tailstock. The two clamping methods were simulated for material removal by finite element simulation, and the deformation of parts under different clamping methods was compared. The results show that the "one clamp and one pull" clamping scheme can reduce the deformation of parts by 41.5% compared with the "one clamp and one push" clamping scheme before optimization. At the same time, the optimized clamping method increases the constraint force of the tailstock on the torsion of the parts and improves the clamping rigidity.

[0064] Step 109: Under the optimized clamping method, the slender neck part of the part is processed using the optimized layer-by-layer symmetrical removal process, such as Figure 6 As shown in the figure, the numbers represent the processing steps of different sections of the slender neck. The multi-layer numbers indicate that the processing is performed in multiple processes, and each layer of numbers represents a process, which is performed layer by layer from top to bottom. The traditional material removal sequence is 1'→2'→3'→4', which is a sequential processing method and is completed in one process; the optimized process is divided into two processes, and the processing sequence is 1→2→3→4→5→6→7→8, which is symmetrical layer-by-layer removal, so that the residual stress release is smoother and the overall deformation is uniform, thereby reducing deformation.

[0065] Step 110: Perform stress relief aging heat treatment on the processed parts, specifically, the aging temperature is 315°C ± 14°C, the aging time is 3 hours, and the parts are air-cooled to room temperature.

[0066] In summary, the final blank source and heat treatment method selected in this example are imported 10mm blanks that use aging hardening (550℃) heat treatment; the cutting parameters are selected as the rough machining spindle speed of 800r / min, the back cutting amount of 1-1.5mm, and the feed rate of 0.06mm / r; the fine machining spindle speed of 1200r / min, the back cutting amount of 0.2mm, and the feed rate of 0.03mm / r; the groove depth of the stress release groove is 2mm and the groove width is 5mm; the "one clamp and one pull" clamping scheme and the layer-by-layer symmetrical removal processing technology are adopted. After actual production and processing verification, the re-correction rate is reduced from 25% to 13.3%, and the mean straightness error is reduced by about 40% compared with the previous process, and it is no longer dependent on high-precision machine tools, which proves the effectiveness of the method proposed in this invention.

[0067] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A method for controlling cutting deformation of a weak-rigidity flexible rod, characterized in that: The following steps are involved: S1. Classify the existing blanks according to process differences and specification differences, and select different heat treatment methods suitable for the blank materials; Then, samples are extracted from different types of blanks, and different heat treatments are performed. The residual stress test is performed on the blanks after heat treatment to obtain the residual stress distribution law of blanks from different sources and under different heat treatment conditions. Finally, according to the principle that the better the uniformity and symmetry of the residual stress field distribution and the smaller the stress value of the blank core, the best combination of heat treatment method and blank source is determined. S2, heat treating the selected blank; S3, adjust the turning parameters for finishing and roughing; S4, processing residual stress relief groove at the slender neck position of the part; S5. Perform stress relief aging heat treatment on the parts; S6. Grind the parts to the designed maximum outer diameter and perform stress relief aging heat treatment; S7, processing the shapes of both ends of the parts; S8. Adjust the clamping method of the slender neck part of the processed part; S9, symmetrically remove the material at each slender neck layer by layer to process the slender neck part of the part; S10. Perform stress relief aging heat treatment on the parts.

2. The method for controlling cutting deformation of a weak-rigidity flexible rod according to claim 1, characterized in that: The combination of heat treatment method and blank source is determined according to the simulation experiment, cutting test results and residual stress distribution results; the simulation experiment adds the obtained residual stress distribution to the finite element model, simulates the material removal process, and compares the deformation of the final model; the cutting test selects the same batch and heat treatment method as the residual stress test experiment for actual processing, and uses straightness error and outer circle roundness as comparison standards to select the best combination.

3. The method for controlling cutting deformation of a weak-rigidity flexible rod according to claim 1, characterized in that: The steps of adjusting the turning parameters for finishing and roughing include: conducting orthogonal cutting simulation experiments for different cutting parameters, finding the influence of cutting parameters on residual stress, and selecting the optimal parameters according to different goals of the roughing and finishing stages.

4. The method for controlling cutting deformation of a weak-rigidity flexible rod according to claim 1, characterized in that: The slender neck part of the part is clamped by fixing it with a three-jaw chuck at the front end and using a tensioning device at the tailstock of the machine tool to provide outward pulling force for the part.

5. The method for controlling cutting deformation of a weak-rigidity flexible rod according to claim 1, characterized in that: The residual stress relief groove design is to obtain the relationship between the groove size and the part stiffness through the results of simulation experiments, and then obtain the final size of the stress relief groove.

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