Shaft parts are typical parts in mechanical processing that can support transmission components, bearing loads, and transmitting torque. As rotating parts, shaft parts have high machining accuracy and fit tolerance requirements. Therefore, the article briefly introduces the types of shafts parts, discusses the process flow of mechanical processing of shaft parts, explores the key points of mechanical processing of shaft parts, and further analyzes the implementation cases of mechanical processing of shaft parts, hoping to provide some reference for mechanical processing of shaft parts.
Machining is the main way of shaft parts processing and manufacturing. In recent years, the batch machining efficiency and accuracy of shaft parts have improved with the improvement of the machining process. However, many cylindrical parts in mechanical equipment, bearing fit, threaded fit, and bushing fit on the shaft parts with the tolerance and accuracy requirements are also increasing, and the traditional machining process presents a slight shortage. Therefore, based on traditional machining, exploring the main points of the shaft parts machining process has very prominent practical significance.
1. Types of shaft parts
As a more common application of mechanical parts, shaft parts in the entire mechanical industry products in a very wide range of applications. Shaft parts are a length beyond the diameter of the parts, including the concentric axis of the conical surface, the outer cylindrical surface, the inner hole, the end face and threads, and other parts. According to the differences in structural forms, shaft parts mainly include stepped shafts, light shafts, crankshafts, tapered shafts, camshafts, eccentric shafts, hollow shafts, and shaped shafts of several types. In mechanical equipment, shaft parts cannot only support the connecting rod, pulley, gears, cams, and other transmission parts operation and can assume the role of torque transfer.
2. Process flow of shaft parts machining
2.1 Blank selection
Blank selection is the first step in shaft parts machining and an important part of the quality of shaft parts machining. General shaft parts machining blanks for alloy steel, carbon steel, or ductile iron, such as Q235, 0Cr, 45# steel, and 20CrMnTi. Among them, 40Cr is a torsional strength, high impact toughness material not only can ensure the machining accuracy of shaft parts but also reduce the overall weight of shaft parts, which is the preferred material for shaft parts machining.
2.2 Determine the benchmark
After the blank is selected, the processor should determine the machining size of the shaft parts and the initial machining point of the tool according to the drawings of the shaft parts designed in the early stage and speculate the machining size and feasibility of each part of the shaft parts. According to the content of dimensioning (decentralized key labeling), the principle of matching the size of parts is implemented, and the drawing requirements are understood quickly to improve the control accuracy and avoid the cumulative error in the machining stage of shaft parts. Specifically, the same benchmark needs to be selected when marking the machining dimensions of shaft parts. The tediousness of machining is alleviated through the consistent design of the machining process datum, design datum, and measurement datum of shaft parts. At the same time, according to the appropriateness requirements of process dimensions, in the process of datum labeling, the tool tip radius should be fully considered by the processor, and the fillet machining allowance or automatic compensation tool tip radius should be set in advance to avoid the occurrence of over-cutting or under-cutting problems caused by stress concentration.
For shaft parts with various shapes, including arc, cylinder, and sphere, the processor should use the fixed mode of one clamp and one top to complete machining in one clamping to improve machining stability. According to the spindle speed of 800 r/min, the feed rate is 150 mm/r, and the back cutting amount is 3.20 mm. For finishing machining, the large angle knife is selected, the spindle speed is increased from 800r/min to 1200r/min, and the feed and back feed is adjusted to 80mm/r and 0.3mm, respectively. In the thread link of the car, the external thread knife is selected, the spindle speed is 200r/min, and the feed rate is 60mm/r.
2.3 Heat treatment
Heat treatment effectively improves the cutting performance of shaft parts and reduces or even eliminates the internal stress of shaft parts. Before the shaft parts are formally machined, heat treatment is required, covering several operations such as annealing, normalizing, tempering, and nitriding. After initially reducing the hardness of the shaft parts blank, according to the application of high precision requirements of the shaft parts, 2 aging treatments are carried out successively, and the heat treatment is carried out again after semi-finishing machining and before grinding machining.
2.4 Rough turning machining
In the rough turning processing stage, the processor can choose a 45 ° elbow turning tool, with a 90 ° external turning tool and a 90 ° offset left turning tool, by the three-jaw chuck clamping blank parts in the top of the blank parts after the center hole drilling set. At the same time, rough turning processing 3 steps; each step of rough turning processing is left with a margin. After roughly turning one end, use the three-jaw chuck to hold the other end of the blank, drill the center hole after the top, and rough turn the blank with a margin. Repeat the above operation to complete the rough machining of 4 steps. In the rough machining stage, the amount of backdraft directly impacts productivity and machining uniformity. Therefore, to ensure the durability of the tool, the machinist should increase the amount of backdraft as much as possible, with the form of multiple tool travel to carry out cycle machining, smooth removal of machined parts surface energy margin, to avoid uneven machining, the margin is too large and other problems.
2.5 Precision turning
Precision turning is to reduce the roughing error further and ensure that the processed parts meet the requirements of the specified accuracy and the surface roughness of the operation; you can choose a 45 ° cylindrical turning tool and molding turning tool, external thread turning tool, in the double top clamping.
In the background of the double center clamping, turning 3 steps and thread large diameter turning. The remaining 2 steps are left for 3 grooves and 3 chamfers. After turning one end of the workpiece, the other end is clamped with a double center, 4 steps are turned, and the thread is turned to a large diameter. The remaining steps are left for 3 grooves and 4 chamfers. On this basis, the two ends of the workpiece are clamped with double centers, and the corresponding end threads are turned according to the design basis. Subsequently, 2 keyways are scribed, and the keyway position is milled more to provide a basis for later grinding. Grinding is a commonly used process for ELID (synchronous electrolytic sharpening), mainly in the role of the metal bond to promote the power supply positive, super abrasive grinding wheel connected to the power supply cathode for the tool electrode; at the same time, the electrolytic grinding fluid into the grinding wheel, electrode in the middle of the use of the anodic dissolution effect to remove the surface of the grinding wheel metal poles, to promote the grinding wheel in the optimal state of precision or even ultra-precision machining of shaft parts. The grinding process is a dynamic equilibrium process; in the process of processing the grinding wheel surface, sharp abrasive grains can be gradually exposed to repair the grinding wheel and generate passivation film, while the workpiece material can continue to scrape off the surface of the grinding wheel passivation film, to ensure that the whole process is repeated. High volume fraction (40%) SiCp/Al composite shaft parts processing, for example, according to the characteristics of the workpiece internal silicon carbide particles, to achieve long life, high performance, high reliability of the precision machining requirements, the processor can choose the universal cylindrical grinder with a cast iron bond diamond grinding wheel W40/W10/W5, special grinding fluids, and special motors, adjust the voltage to 12.0 -15.0V, duty cycle of 1:3, grinding wheel grain size of W5μm, spindle speed of 1500r/min, feed rate of 2mm/min, to obtain a cylindricity of 0.80μm, surface roughness of 0.16μm precision workpiece.
3. Process points of shaft parts machining
Compared with other parts, shaft parts machining has more stringent requirements for tool selection. Before formal machining, the processor should select the tool based on the criteria of high chip removal, high durability, high precision, high durability, easy to replace, and easy to adjust, such as the secondary deflection angle of 55˚, the main deflection angle of 93˚ of the large declination cutters, to meet the needs of high-precision machining, arc position overcutting avoidance. After the tool is determined, the processor should start according to the machining process of multi-part machining error and machining vibration control, choose a three-jaw chuck, fixed in the way of one clamp and one top, automatic feed blank material to meet the batch processing consistency requirements. Especially for vertical milling small diameter outer circle on a flat surface, you can choose two of the same specifications and straightening treatment of the vise as a small end of the outer circle at both ends of the clamping tool, and then use the jack to assist in supporting the suspension of the large end of the outer circle, to improve the clamping firmness and reliability. In the clamping mode, the processor should be selected beforehand the origin of the shaft workpiece, that is, before tool machining, the relative starting point of the shaft parts. The starting point as the origin of building the vertical and horizontal coordinate system, to avoid the tool replacement stage and the role of interference with the parts simultaneously for the late correction and the whole error control process, provides the basis. General shaft parts, tool processing before the relative starting point for the right end face, the center axis intersection.
3.2 Determination of parameters
In the shaft parts machining process, most of the parts in the high temperature, high pressure environment, the original existence of scratches, small holes, and cracks very easy to expand the overall failure of the parts. Therefore, according to the shaft parts machining standards, the processor should start from the actual surface requirements, combined with the specific type of machining, and the reasonable formulation of machining parameters, to avoid crack failure. For the tool cutting amount, the processor should start from each process according to the standard form, the cutting speed, the cutting speed, the cutting speed, the cutting speed, the cutting speed, and the cutting speed.
According to the standard form, the cutting, backdraft, and feed speeds are reasonably set to improve parts machining accuracy and surface finish. Among them, the cutting speed is affected by the type of parts and lathe turning speed limit. When the part blank is Q235 carbon steel material, the roughing and finishing cutting speed can be set to 800r/min and 1200r/min, respectively. In contrast, in the thread processing stage, according to the characteristics of the external threading tool application process of turning volume and chip removal, the cutting speed can be adjusted to 200r/min; the backdraft amount needs to be close or equal to the machining allowances of the shaft parts to improve the machining efficiency and control the lathe walking. Machining efficiency controls the number of times the lathe tool. Considering the conventional roughing large back draft by the hardness of the workpiece material, machine conditions and other factors need to be set in advance for finishing allowances, 0.20-0.50mm. Feed rate by the shaft parts surface roughness requirements, precision requirements, workpiece blanks, and other factors, and the lathe’s performance on the maximum permissible feed rate also has a greater impact. Generally speaking, in the roughing stage, you can choose a faster feed rate to remove the blank allowance in a short time. In the finishing stage, it is necessary to appropriately reduce the feed rate to achieve better accuracy and surface roughness control.
4. Example of process implementation for shaft parts machining
4.1 Overview of shaft parts
Taking the machining of two typical shaft parts as an example, the blanks of the parts are all 45# steel. One of the shaft parts A is 50 mm in diameter and 88 mm in length, and the other shaft part B is 50 mm in diameter and 55 mm in length. The machining of workpieces A and B includes turning the outer circle, cone surface, inner hole, 60 ° chamfer in the hole and cylindrical withdrawal groove (depth of 1.50 mm, length of 4mm), hole withdrawal groove (depth of 1.50 mm, length of 5mm), external thread and internal thread. The difficulty of mechanical processing is the dimensional accuracy control of workpiece A and workpiece B, the ellipse machining of matching position, and the total length control.4.2 Machining route
For shaft-type mating parts, the machining sequence is as follows: machining part A → machining part B → mating elliptical surface processing. Among them, the outer contour of machining part A can be divided into 2 times of clamping processing, the end of the left end of the inner hole, outer circle processing in 1 clamping, the second turnaround clamping will end the right side of the outer wheel, external threads and external groove processing. The whole process requires clamping the blank, manually drilling the inner hole to complete the roughing and finishing of the inner hole, and then turning the outer contour roughing and finishing; finally, turnaround clamping for turning the outer contour groove cutting and turning threads. As for the machining of Piece B, it is necessary to complete the left internal hole and internal thread machining in one clamping and complete the machining of Piece A, the elliptic surface of Piece B, and the right external contour of Piece B in the second clamping. During the machining of the left side of Piece A, the machinist needs to carry out the blank face clamping operation according to the standard of blank extending length > 40mm; at this time, manual drilling is carried out, the spindle speed is 500r/min when drilling, and the amount of back-eating is 9mm. after the manual drilling, the machinist can utilize the boring tool to carry out the bore roughing and finishing, the spindle speed is 600r/min when roughing, and the feed amount is 0.12mm/r. The back-eating amount is 0.12mm/r, and the back-eating amount is 1.5mm. 0.12mm/r, and the amount of backtalk is 1mm; the spindle speed is 800r/min at the time of fine boring, the feed is 0.08mm/r, and the back take is 0.30mm. On this basis, the 93˚ external turning tool is utilized to carry out the rough turning of the external contour and the fine-tuning of the external contour successively; the spindle speed is 800r/min at the time of rough turning of the external contour, and the feed is 0.05mm/r, and the amount of backtalk is 1mm; the machine operator carries out the fine-tuning of the external contour. The spindle speed of rough turning is 800r/min, feed quantity is 0.05mm/r, and back eating quantity is 1mm; the spindle speed of fine turning is 1200r/min, feed quantity is 1.50mm/r, and back eating quantity is 0.30mm. On this basis, turn around and clamp the outer circle, utilize the end face turning tool or 93˚ external turning tool to correct it, and then process the right side after the completion of the correction.
During the machining of the right side of Piece A, the machinist can utilize the 93˚ external turning tool to complete the right-side external roughing based on the spindle speed of 800r/min and a back draft of 1mm. Then adjust the spindle speed to 1500r/min and the backdraft to 0.30mm.
Adjust the spindle speed to 1500r/min and the backdraft to 0.30mm to finish the right-side outer finishing. On this basis, a grooving tool with a width of 3mm is utilized for thread turning and grooving; at this time, the spindle speed and back feed amount are 500r/min and 3mm, respectively, and the feed amount is 0.05mm/r.
In processing piece B, the processor should be based on the standard of 30mm or more of the jaws out of the blank clamping operation. Then carry out manual drilling, the rough turning of the left side of the hole and fine-tuning of the left side of the hole, machining tools, and the corresponding spindle speed, back eating amount, and feed amount is the same as the left side of the piece A machining. After the machining of piece A and piece B is completed, clamping along the left side of piece A, causing Piece B to be threaded and tightened in conjunction with Piece A, and carrying out manual drilling of the center hole, the rough turning of the outer contour, and finish turning of the outer contour one after another. Among them, the center hole manual drilling tool used for the center drill, spindle speed of 1000r/min, back draft of 1.50mm; rough turning outer contour, fine turning outer contour of the tool used for the 93 ° cylindrical lathe, spindle speed of 800r/min, 1500r/min, back draft of 1mm, 0.30mm, respectively, the amount of feed for 0.15mm/r, 0.08mm/r.
In summary, shaft parts machining is more difficult and involves more processes. Before the machining of shaft parts, the processor can follow the guidelines of roughing and then finishing, first main and then secondary, first face and then a hole, carry out the feasibility analysis of the process, plan the machining process route, and look for the quality control points from the blank selection, rough machining, finishing, and heat treatment. At the same time, the optimization of the machining process and reduction of machining error are carried out from tool selection, clamping mode adjustment, and parameter setting.
Author: Li Xuemei