A method for controlling cutting deformation of a weak-rigidity flexible rod

Abstract

The present invention provides a method for controlling deformation during cutting of a weak-rigidity flexible rod, including optimizing the blank size, source, and heat treatment method; performing optimal heat treatment on the optimized blank; optimizing turning parameters for finishing and roughing; machining a residual stress relief groove at the slender neck of the part; performing stress relief and aging heat treatment on the part; grinding the part to the designed maximum outer diameter and performing stress relief and aging heat treatment; machining the shape of both ends of the part; optimizing the clamping method for machining the slender neck portion of the part; machining the slender neck portion of the part using an optimized material removal sequence under the optimized clamping method; and performing stress relief and aging heat treatment on the part. Based on the technical solution of the present invention, the machining process no longer relies excessively on resources such as high-precision lathes to meet design requirements, reducing the part reshaping rate from 25% to 13.3%, significantly improving production efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of cutting processing, 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 can 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 take up a long 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 part 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 part can effectively reduce the deformation of weak rigidity parts such as flexible rods, thereby solving the problem of deformation deviations.

[0003] With the widespread use of weak-rigidity parts in aircraft, their machining deformation control has garnered considerable attention and research. However, existing research focuses primarily on the residual stress patterns and machining deformation control of aerospace structural components, engine casings, and blades. Effective deformation control strategies and system solutions are lacking for low-rigidity, high-aspect-ratio rotating parts, such as flexible rods. In actual production, high-precision lathes and conservative cutting parameters are often used to ensure final machining quality, resulting in low production efficiency and high costs. Therefore, designing methods to control the residual stress and deformation of 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 parts can improve the processing efficiency and reduce the production cost 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 solutions:

[0007] A method for controlling deformation of a weak-rigidity flexible rod during cutting, 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] Processing 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, existing blanks were categorized based on differences in process and specifications among manufacturers, and different heat treatment methods were selected for the blanks. Samples were then taken from each type of blank and subjected to different heat treatment methods. Residual stress tests were then conducted on the heat-treated blanks to determine the residual stress distribution patterns for blanks from different sources and under different heat treatment conditions. Finally, the optimal combination of heat treatment method and blank source was determined based on the principle of achieving the best uniformity and symmetry in the residual stress field distribution and minimizing the core stress.

[0020] The preferred method is a rule 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 were conducted for different cutting parameters (speed, depth of cut, and feed rate) to identify the effects of these parameters on residual stress. The optimal parameters were then selected based on the different goals of the roughing and finishing stages. For roughing, low speeds, large depths of cut, and large feed rates were chosen to improve cutting efficiency. For finishing, higher speeds, small depths of cut, and small feed rates were chosen to improve surface quality and reduce residual stress introduced by cutting.

[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 outward pulling force for the workpiece.

[0025] Optionally, the residual stress relief grooves are designed by optimizing the final dimensions of the stress relief grooves based on the relationship between the groove dimensions and the component stiffness obtained through simulation experiments. The number and location of the residual stress relief grooves can be determined based on the designed dimensions of the component.

[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 for deformation caused by residual stress in parts: in the raw material selection stage, the optimal 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 the part is further reduced by opening stress relief grooves, improving the clamping method and processing procedures to reduce the influence of the internal residual stress of the part on the overall deformation.

[0028] The proposed deformation control method for weak-rigidity flexible rods eliminates the need for excessive reliance on high-precision lathes and other resources to meet design requirements. This reduces the part re-alignment rate from 25% to 13.3%, significantly improving production efficiency. In actual production, the proposed method replaces empirical process design with a mechanism-based analytical process design, significantly reducing the average straightness error of multiple batches of parts processed by approximately 40% compared to the previous process, effectively improving processing quality and reducing processing costs. 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 embodiment of the present invention;

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

[0032] Figure 3 1 is a schematic diagram of a curve showing residual stress and depth during cutting in an embodiment of the present invention;

[0033] Figure 4 1 is a schematic diagram of a simulation of a residual stress relief groove in an embodiment of the present invention;

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

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

[0036] The present invention will be further described below with reference to 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 and an aspect ratio of up to 100, and its shape is as follows: 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 steps are as follows: Figure 2 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 stock; (2) imported 10mm outer diameter bar stock; (3) domestic 10mm outer diameter bar stock. There were five heat treatment methods suitable for the blank materials: (1) no heat treatment; (2) solution treatment (1040℃); (3) solution treatment (1040℃) followed by age hardening (550℃); (4) age hardening (550℃); (5) solution treatment (1040℃) followed by age hardening (480℃).

[0040] Then, the X-ray diffraction method was used to measure the axial and circumferential initial residual stresses of different batches of bar materials under different heat treatment processes. 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, based on the residual stress distribution test results and the straightness error measurement experiment results, we can conclude that 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 it is to deformation control. In this case, the optimal combination is the aging hardening (550°C) heat treatment method for the imported 10mm blank.

[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 using the optimized heat treatment method of age hardening (550°C).

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

[0047] Different key cutting parameters (speed, depth of cut, feed rate) were selected for orthogonal cutting simulation. The experimental scheme was 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 was obtained through simulation analysis and calculation. 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 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 Summary of simulation results

[0052]

[0053] The outermost surface is greatly affected by temperature. The surface residual stress is manifested as residual tensile stress. As the depth increases, it is mainly affected by the tool extrusion effect. The residual tensile stress decreases and transitions to residual compressive stress. The compressive stress first increases and then decreases and finally approaches 0Mpa. Figure 3 As shown. The results of 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. It 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 the cutting is second. So the feed and cutting depth have the greatest impact on σ max and σ min The influence of various factors on residual stress can also be proved by the curve of the influence of various factors on residual stress. At the same time, rough turning should consider improving cutting efficiency, and choose low speed, large cutting depth, and large feed; fine turning should consider surface quality and residual stress introduced by cutting, and choose higher speed, small cutting depth, and small feed. Based on simulation tests and actual processing equipment, the final recommendation is a rough machining spindle speed of 800r / min, a back cutting depth of 1-1.5mm, and a feed rate of 0.06mm / r; a fine machining spindle speed of 1200r / min, a back cutting depth of 0.2mm, and a feed rate of 0.03mm / r.

[0057] Step 104: Process residual stress relief grooves 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 then air-cooled to room temperature.

[0061] Step 106: Grind the slotted part to the designed maximum outer diameter. Then, perform an aging stress relief heat treatment on the part at a temperature of 315°C ± 14°C for 3 hours, followed by air cooling 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. The current clamping methods for turning are mainly "one clamp and one push" and "one clamp and one pull". Figure 5 As shown. Among them, 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 Indicates the friction force between the tool and the workpiece, B indicates the tailstock clamping end, F Brepresents the radial force exerted by the tailstock clamping on the workpiece, F2 represents the axial force exerted by the tailstock clamping on the workpiece, and L represents the length of the workpiece clamped between the three-jaw chuck and the tailstock. Finite element simulations were used to simulate material removal from both clamping methods and compare part deformation under different clamping methods. The results show that the "one clamp, one pull" clamping scheme reduces part deformation by 41.5% compared to the "one clamp, one push" clamping scheme before optimization. Furthermore, the optimized clamping method increases the tailstock's torsional restraint on the part, improving 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 for different sections of the slender neck. Multiple layers of numbers indicate that the processing is carried out in multiple steps, with each layer representing a step, and the numbered layers are executed 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 step. The optimized process is completed in two steps, with the processing sequence 1→2→3→4→5→6→7→8. This symmetrical layer-by-layer removal method allows for smoother residual stress release and uniform overall deformation, thereby reducing deformation.

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

[0066] In summary, the final blank source and heat treatment method selected for this example are imported 10mm blanks that undergo aging hardening (550°C). The cutting parameters selected for roughing are a spindle speed of 800r / min, a back cut of 1-1.5mm, and a feed rate of 0.06mm / r; a spindle speed of 1200r / min, a back cut of 0.2mm, and a feed rate of 0.03mm / r for finishing. The stress relief groove is 2mm deep and 5mm wide. A "clamp and pull" clamping scheme and a layer-by-layer symmetrical removal process are used. After actual production and processing verification, the re-correction rate was reduced from 25% to 13.3%, and the mean straightness error was reduced by approximately 40% compared to the previous process. High-precision machine tools are no longer required, proving 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 illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. A method for controlling deformation of a weak-rigidity flexible rod during cutting, 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 were taken from different types of blanks and subjected to different heat treatment methods. Residual stress tests were then conducted on the heat-treated blanks to determine the residual stress distribution patterns of blanks from different sources and under different heat treatment conditions. Finally, based on the principle that the better the uniformity and symmetry of the residual stress field distribution and the smaller the stress value in the blank core, the optimal combination of heat treatment method and blank source was determined. S2. heat treating the selected blank; S3, adjust the turning parameters for finishing and roughing; S4, machining residual stress relief grooves 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 deformation of a weak-rigidity flexible rod during cutting according to claim 1, characterized in that: The combination of heat treatment method and blank source is determined based on the simulation experiment and cutting test results and the 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 criteria to select the best combination.

3. The method for controlling deformation of a weak-rigidity flexible rod during cutting according to claim 1, characterized in that: The steps for 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 the different goals of the roughing and finishing stages.

4. The method for controlling deformation of a weak-rigidity flexible rod during cutting 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 on the tailstock of the machine tool to provide outward pulling force for the part.

5. The method for controlling deformation of a weak-rigidity flexible rod during cutting 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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