In the previous section, we talked about the causes and solutions of vibration in the CNC cutting process. For this, we will learn more about some of the problems in CNC lathe processing, so that we can better deal with some workpieces in the actual operation process. , And the operation mastery of the craft. The problem of machining workpieces in CNC milling in CNC lathes is a difficult problem to solve. So, for this problem, we must first analyze the cause of the deformation.

 

1. Raw materials will affect the deformation of the workpiece

The aspect ratio of the raw material is proportional to the thickness of the wall, and proportional to the rigidity and stability of the material. Therefore, before processing the workpiece, we should plan in advance how to perform the processing operation. Especially in the structure of large parts, the structure must be reasonable. Before processing, the hardness and slack of the blank must be strictly controlled to ensure the quality of the blank and reduce the deformation of the workpiece.

 

2. The workpiece clamping will cause deformation

For the workpiece, we should find the clamping point when clamping, so that our fixed point and supporting point should be as close as possible, so that the clamping force acts on the support, and the clamping point should be as close to the working surface as possible, and select The force is not easy to cause deformation of the clamping position. When there are clamping forces in multiple directions on the workpiece, the order of the clamping forces must be considered. The clamping force must be applied first to bring the workpiece into contact with the support, not too much. The main clamping force that balances the cutting force should come into play at the end.

 

The contact area between the workpiece and the fixture must be increased or the axial clamping force must be used. The increased rigidity of the sheet is an effective method to solve the deformation of the clamping, but due to the shape and structure of the thin-walled part, it has a lower rigidity. In this way, deformation occurs due to the application of clamping force. Increasing the contact area between the workpiece and the fixture can effectively reduce the deformation of the workpiece during clamping. For example, when grinding thin-walled parts, a large number of elastic pressure plates are used. The purpose is to increase the receiving power of the contact piece, thin the inner diameter and the outer circle of the sleeve wall, and use a simple open transition ring or elastic mandrel. Full-arch claws, etc., are used to increase the contact area during workpiece clamping. This method is conducive to conveying the clamping force and therefore avoids deformation of the workpiece. Axial clamping force is also widely used in production. The special accessories designed and manufactured can make the clamping force act on the end face. Due to the thin wall and low rigidity of the workpiece, the bending deformation of the workpiece can be solved.

 

3. Deformation caused by processing

Due to the cutting force, the workpiece undergoes elastic deformation in the direction of the force during the cutting process, which is what we usually call the blade phenomenon. In order to deal with this deformation, corresponding measures must be taken in the tool. Finishing requires the precision of the tool. On the one hand, it can reduce the resistance generated by the friction between the tool and the workpiece, and on the other hand, it can improve the heat dissipation capacity of the tool when cutting the workpiece, thereby reducing the residual internal pressure of the workpiece.

 

During the machining process, the heat generated by the friction between the tool and the workpiece also deforms the workpiece, so high-speed machining is usually selected. In high-speed processing, since the chip is cut in a short time, most of the cutting heat is carried by the chip, which reduces the thermal deformation of the workpiece. Secondly, in high-speed processing, due to the reduction of the softening of the cut part of the ♂ layer material, it can reduce the deformation of the workpiece, which is beneficial to ensure the accuracy of the size and shape of this piece. In addition. The rational use of cutting fluid plays an important role in improving the durability of the tool, the quality of the machined surface and the machining accuracy. Therefore, sufficient cutting fluid must be used to avoid deformation of the components during machining.

 

The use of reasonable cutting amount in processing is a key factor to ensure the accuracy of parts. When processing thin-walled parts with high precision requirements, symmetrical processing is generally adopted to balance the stresses on the opposite sides to a stable state, and the workpiece is smooth after processing. However, when a large amount of knife is taken in a certain process, the workpiece will be deformed due to the loss of balance between the tensile stress and the compressive stress.

 

4. Stress and deformation after processing

After processing, the part ♪ itself has internal stress. These internal stress distributions are in a relatively balanced state. The shape of the part is relatively stable, but the internal stress changes after removing some materials and heat treatment. At this time, the workpiece needs to reach the balance of force again. The appearance has changed. To solve this kind of deformation, heat treatment can be used to stack the workpiece to be straightened to a certain height, use a certain tooling to compact it into a straight state, and then put the tooling and the workpiece into the heating furnace together. Choose according to the different materials of the parts. Different heating temperature and heating time. After hot straightening, the internal organization of the workpiece is stable. At this time, the workpiece not only has a higher straightness, but also the work hardening phenomenon is eliminated, which is more convenient for the further finishing of the parts. The castings should be aging treated, and the internal residual stress should be eliminated as much as possible, and the method of processing after deformation is adopted. , That is, rough machining-aging-reprocessing. For large parts, it is necessary to use profiling processing, that is, predict the deformation of the workpiece after assembly, and reserve the deformation in the opposite direction during processing, which can effectively prevent the deformation of the parts after assembly.