CNC lathe processing technology of the hottest dis

2022-10-24
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With the popularization of numerical control processing technology and the continuous improvement of product quality requirements, a large number of disk parts have been processed by numerical control lathes. The correct process and tooling design make the CNC lathe show many characteristics, such as high machining accuracy and flexible machining

engine diagram the use of ABS in automobiles flywheel, brake disc, etc. are typical automobile disc parts. This paper will analyze and elaborate some key points in process design and tooling design of such parts and the selection opinions of common equipment through processing examples

process design

for the NC machining process design of disk parts, the most important thing is to arrange the machining surfaces with mutual row position tolerance requirements in one process, complete the machining under one-time clamping, and eliminate the secondary clamping error

1. Finish machining an engine flywheel (Figure 1)

if the vertical multi tool automatic lathe shown in Figure 2 is used for machining, the machining process is:

(1) finish turning the large plane. Arrange one of the left and right carriage planes and the other carriage inner hole( φ 438mm、 φ 50mm)。

(2) refinish datum plane a. Arrange one of the left and right carriage planes and the other carriage inner hole( φ 128mm) and excircle( φ 412mm)。

Figure 2 vertical multi tool automatic lathe

this process is limited by the action function of the machine tool φ 128mm hole and φ The 50mm hole cannot be completed in the same process, and it needs to be clamped twice. Due to the existence of repeated positioning error and fixture manufacturing error, it is difficult to stably meet the coaxiality requirements of the two holes of the product

in order to meet the requirements of product design and stabilize the control of product quality, the CNC lathe shown in Figure 3 can be used for processing. In the process design, the automatic tool change function of the CNC lathe is used, and the internal hole back boring tool is used to process from side a with program control φ 50mm inner hole, set φ 128mm、 φ 50mm is arranged to be processed in the same process. Avoid the influence of repeated positioning error and fixture manufacturing error on machining accuracy, and ensure the product quality φ Coaxiality requirement of 0.03mm

Figure 3 vertical CNC lathe

2. Finish machining the positive and negative planes of an engine flywheel (Figure 4)

generally, the traditional process is to finish one side first, and then finish the other side in the next process. The quality of re clamping of the second order workpiece has a great impact on the machining accuracy (parallelism) (when clamped with a general three jaw chuck, the workpiece is easy to be clamped and lifted). If the CNC lathe is used, the special tool (as shown in Figure 5) can be designed according to the structural characteristics of the workpiece in the process design to finish machining on both sides in one process: the large plane is upward, and the special tool controlled by the program is back boring the f surface. Because the inner hole diameter is φ 48mm, maximum machining diameter of F surface φ 100mm, cutting width 26mm, the dimension of the weakest part of the special tool bar shown in the figure is 20mm, which is sufficient for finishing. The process plan makes full use of the structural characteristics of products and the flexible action control characteristics of CNC equipment, which can not only reduce a processing procedure, save equipment and processing costs, but also stably ensure the processing quality

3. Finish machining a brake disc

finish machining the datum a plane and the upper and lower brake surfaces shown in Figure 6. To meet the product requirements, the three planes must be clamped at one time in the same process, and the special tool holder and claw shown in Figure 7 should be used, and the upper and lower brake surfaces should be finished at the same time. Such processing is not entirely to improve the processing efficiency, but mainly to meet the quality requirements of "the thickness change of two braking surfaces in a week is not greater than 0.01mm". Although the CNC lathe can use two cutters to process separately through program control

the upper and lower brake surfaces are affected by the swing difference of the main shaft, processing deformation and other factors, so it is difficult to meet the above requirements. We can only use "simultaneous" processing to reflect the system error "at the same time" on the upper and lower brake surfaces to meet the quality requirements of the product. After the two knives are processed, the knives cannot be returned directly, otherwise, the traces of knife withdrawal will be left on the brake surface. Therefore, the next knife must have a downward "let knife" action, and then the machine tool program controls the knife tower to move up, so that the upper knife "let knife" and the next two knives retreat together. Finally, the next knife must be "reset" upward to ensure the size of the upper and lower brake surfaces. In this way, the CNC lathe should be equipped with a special "hydraulic double-sided tool rest"

although the CNC lathe has high machining accuracy and flexible machining, it still needs to carefully analyze the process design according to the product characteristics. Without the correct process design, no matter how advanced the equipment can play its value

tooling design

the main clamping tool of CNC lathe is chuck. When designing and using, we should focus on the centering accuracy of chuck to avoid workpiece clamping deformation and lifting

1. Methods to ensure centering accuracy

when the machining surface and clamping surface have high requirements for coaxiality, the jaw of the chuck generally needs to go through "self turning" on the equipment itself to ensure the concentricity of the positioning surface and the spindle axis. When "self turning", try to simulate self turning in the processing state: for example, when "self turning" positive claw, clamp an auxiliary tool in the middle of the claw stroke (as shown in Figure 8), and the oil cylinder pressure during "self turning" should be consistent with the pressure during normal operation

the diameter of the arc surface after the "self turning" of the jaw should be consistent with the diameter of the clamping outer circle of the workpiece as far as possible. Similarly, it is best to tighten an auxiliary device when "self driving" anti claw

2. Methods to ensure the accuracy of end face runout

the axial positioning support of the workpiece can be adjusted or "self turning" to ensure that the positioning points of the computer and printer are "coplanar". However, for the three jaw chuck with traditional structure, if the jaw wants to move in the jaw seat, there must be a certain sliding gap. In the clamping process, it is inevitable to produce

workpiece "lifting" phenomenon. When the workpiece requires strict jumping requirements between the machining surface and the positioning surface, the three jaw chuck with system structure is difficult to ensure the clamping accuracy. Figure 9 shows the flywheel for an engine. In order to ensure the coaxiality of the inner hole and the outer circle, they must be arranged in the same process (clamping upward on the large plane). However, when the workpiece is turned over to process side a, it is necessary to ensure the runout requirements in the figure, and the positioning surface of the workpiece must be close to the axial positioning surface of the chuck during processing. It is difficult to meet the processing requirements if the three jaw disc clamping with traditional structure is adopted. Therefore, the chuck with "downward tension" should be used. When the workpiece is clamped, there is a downward component to keep the workpiece close to the positioning surface. In addition, as a key component of the CNC lathe, the chuck should be lubricated, disassembled and cleaned on time according to the method specified in the manual to prevent debris from aggravating the wear of the sliding surface

equipment selection opinions

1. Selection of machine tool structure

(1) horizontal "simple CNC lathe" (as shown in Figure 10). This kind of machine tool adopts the layout of flat bed, which has good manufacturing technology and is convenient for the processing of guide rail surface. The horizontal bed is equipped with a horizontally placed tool rest, which can improve the motion accuracy of the tool rest. However, due to the small space in the lower part of the horizontal bed, it is difficult to remove debris. In terms of structural dimensions, the horizontal placement of the tool rest makes the horizontal dimension of the sliding plate longer, thus increasing the structural dimension of the machine tool in the width direction. The main feature of the equipment is that it has the function of two axis linkage and the equipment is cheap. However, the reason why it is called "simple CNC lathe" is that its spindle can not be stepless speed regulation, the number of tool holders installed is small, the fast-moving speed is slow, and there is no automatic chip removal mechanism. The overall structure of the bed is less rigid and the machining accuracy is lower than that of the CNC horizontal lathe. However, after years of improvement, the equipment has mature technology and stable operation. The machining accuracy can reach it7 ~ it8. It can be used for rough machining, semi precision machining and simple surface machining of parts

Figure 10 horizontal simple CNC lathe

(2) horizontal CNC lathe (as shown in Figure 11). This kind of machine tool structure I strives to build and put into operation three berths of more than 50000 tons in the first half of this year. There are two layouts: inclined bed structure and inclined slide plate structure. The inclination angle of the guide rail is small, which is inconvenient for chip removal; The inclination angle is large, and the guide rail has poor guidance and stress. The size of its tilt angle also directly affects the proportion of the height and width of the overall dimension of the machine tool. Considering the above factors, the former fixtures generally adopt mechanical locking. For small and medium-sized CNC lathes, the inclination of the bed is 60 °. The flat bed inclined sliding plate structure

Figure 11 horizontal CNC lathe

on the one hand, it has the characteristics of good processability of horizontal bed. On the other hand, the machine tool has the advantages of small size in the width direction of inclined bed structure, convenient chip removal, small floor area of the machine tool, beautiful appearance, easy to realize closed protection, etc. These two layout forms are widely used by small and medium-sized CNC lathes. When selecting, the rigidity of the overall inclined bed structure is slightly higher than that of the flat bed inclined sliding plate structure, and the equipment price is also slightly higher. When there is heavy cutting content, it is best to choose the overall inclined bed structure. Horizontal CNC lathe is suitable for shaft parts and small diameter(

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