The problem of workpiece deformation in the machining of precision parts is a problem that is difficult to solve. First, you must analyze the cause of the deformation before you can take countermeasures.
First, the material and structure of the workpiece will affect the deformation of the workpiece
The amount of deformation is proportional to the complexity of the shape, the aspect ratio and the wall thickness, and is proportional to the rigidity and stability of the material. Therefore, the influence of these factors on the deformation of the workpiece is minimized when designing the part.
Especially in the structure of large parts, the structure should be reasonable. Before processing, the defects such as hardness and looseness of the blank should be strictly controlled to ensure the quality of the blank and reduce the deformation of the workpiece.
Second, the deformation caused by the workpiece clamping
When clamping the workpiece, first select the correct clamping point and then select the appropriate clamping force according to the position of the clamping point. Therefore, the clamping point and the supporting point should be made as close as possible, so that the clamping force acts on the support, the clamping point should be as close as possible to the working surface, and the position where the force is not easy to cause the clamping deformation is selected.
Increasing the contact area between the workpiece and the fixture can effectively reduce the deformation of the workpiece when it is clamped. For example, when milling thin-walled parts, a large number of elastic pressure plates are used, the purpose is to increase the force receiving area of ​​the contact parts; when turning the inner diameter and the outer circle of the thin-walled sleeve, whether using a simple open transition ring or an elastic mandrel The entire arc claws, etc., are used to increase the contact area when the workpiece is clamped. This method is advantageous for carrying the clamping force and thus avoiding deformation of the part. The axial clamping force is also widely used in production. The special fixture designed and manufactured can make the clamping force act on the end surface, which can solve the bending deformation of the workpiece due to the thin wall of the workpiece and the poor rigidity.
Third, the deformation caused by the workpiece 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 often call the knife phenomenon. In response to such deformation, corresponding measures should be taken on the tool. The precision of the tool is required for finishing. On the one hand, the resistance formed by the friction between the tool and the workpiece can be reduced, and on the other hand, the heat dissipation capability of the tool when cutting the workpiece can be improved, thereby reducing the workpiece. Residual internal stress.
The heat generated by the friction between the tool and the workpiece during machining also deforms the workpiece, so high-speed machining is often chosen. In high-speed machining, since the chips are cut off in a short time, most of the cutting heat is carried away by the chips, which reduces the thermal deformation of the workpiece. Secondly, in the high-speed machining, due to the reduction of the softened portion of the cutting layer material, It can reduce the deformation of the part processing, and is beneficial to ensure the size and shape accuracy of the part. In addition, the cutting fluid is mainly used to reduce the friction during cutting and to reduce the cutting temperature. Reasonable use of cutting fluid plays an important role in improving tool durability, machining surface quality and machining accuracy. Therefore, it is necessary to use a sufficient cutting fluid in order to prevent deformation of the part during processing.
The use of reasonable cutting amounts in machining is a key factor in ensuring part accuracy. In the case of thin-walled parts with high processing precision, symmetric machining is generally adopted to equalize the stress generated on the opposite sides to reach a stable state, and the workpiece is flat after processing. However, when a certain process takes a large amount of knife, the workpiece will be deformed due to the unbalanced tensile stress and compressive stress.
The deformation of thin-walled parts during turning is multi-faceted. The clamping force when clamping the workpiece, the cutting force when cutting the workpiece, the workpiece hindering the elastic deformation and plastic deformation caused by the cutting of the tool, and the temperature of the cutting zone is increased to cause thermal deformation.
Fourth, stress deformation after processing
After processing, the internal stress of the part itself is a relatively balanced state. The shape of the part is relatively stable, but after removing some materials and changing the internal stress after heat treatment, the workpiece needs to reach the balance of force again, so the shape is A change has taken place. To solve such deformation, the workpiece to be straightened can be stacked to a certain height by a heat treatment method, and a certain tooling is pressed into a flat state, and then the tooling and the workpiece are placed together in a heating furnace, and the material is selected according to the material of the part. Different heating temperatures and heating times. After the heat is straightened, the internal structure 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 further facilitates further finishing of the part.
In summary, for the easily deformable workpiece, the corresponding countermeasures should be adopted in the blank and the processing technology, and it is necessary to analyze according to different situations, and a suitable process route will be found. Of course, the above method only further reduces the deformation of the workpiece. If you want to obtain a higher precision workpiece, you need to continuously learn, explore and study.