What are the common problems encountered in the precision machining process of parts

Accuracy issue

Dimensional deviation

Reason: Insufficient precision of processing equipment, such as wear of the machine tool's lead screw and decreased precision of the guide rail, can lead to a decrease in the motion accuracy of the tool or workpiece. For example, the pitch error of the machine tool screw may cause deviation in the axial feed of the tool, resulting in dimensional errors of the part. In addition, improper selection of cutting parameters can also cause dimensional deviations, for example, a feed rate that is too fast may result in excessive cutting of the tool, exceeding the design dimensions.

Solution: Regularly perform precision testing and maintenance on processing equipment, and replace worn parts. At the same time, reasonable selection of cutting parameters, adjustment based on factors such as part materials and tool performance, and real-time monitoring and feedback correction of dimensions using online measurement systems during the machining process.

Shape error

Reason: Vibration during the processing is one of the common causes of shape errors. For example, the vibration of the machine tool itself may come from the unbalanced operation of the motor, changes in cutting force during the cutting process, etc. The wear of cutting tools can also cause changes in the shape of parts, such as the wear of milling cutter blades, which may lead to a decrease in flatness when milling flat surfaces.

Solution: Take vibration reduction measures, such as installing vibration reduction pads on the foundation of the machine tool, optimizing the geometric and cutting parameters of the tool to reduce fluctuations in cutting force. At the same time, regularly replace the cutting tools and check the accuracy of the tools before processing to ensure that they meet the machining requirements.

Surface roughness does not meet the requirements

Reason: Inappropriate cutting parameters, such as low cutting speed or excessive feed rate, can leave obvious machining marks on the surface of the part. The quality and wear of cutting tools also have a significant impact on surface roughness. For example, if the cutting edge of the tool is not sharp, it can cause material tearing during the cutting process, rather than smooth cutting. In addition, improper use of coolant during the processing, such as insufficient coolant flow or inaccurate cooling position, can also affect surface quality.

Solution: Select appropriate cutting parameters based on the part material and tool material, such as increasing cutting speed, reducing feed rate, etc. Choose high-quality cutting tools and replace them promptly after they have worn out to a certain extent. Reasonably use coolant to ensure that it can fully cover the cutting area and provide good cooling and lubrication.

Material issues

Material deformation

Reason: During the cutting process, stress is generated inside the material due to the action of cutting force. When the stress exceeds the yield limit of the material, deformation occurs. For example, for thin-walled parts, due to their poor rigidity, deformation is more likely to occur during processing. In addition, improper heat treatment can also cause material deformation, such as changes in the structure of the material after quenching, resulting in internal stress and ultimately leading to part deformation.

Solution: For parts that are prone to deformation, use a reasonable machining process, such as step-by-step machining, to reduce the depth of each cut and lower the cutting force. Proper straightening or aging treatment should be carried out after heat treatment to eliminate internal stress. At the same time, when designing parts, consider adding reinforcement ribs and other structures to improve the rigidity of the parts.

The material hardness does not meet the processing requirements

Reason: The original hardness of the material may not meet the processing expectations, or the hardness may change during the processing due to factors such as heat treatment. For example, when processing hardened steel, if the hardness is too high, it will increase tool wear and even lead to tool damage; If the hardness is too low, it may not meet the design performance requirements of the part.

Solution: Check the hardness of the material before processing, and choose the appropriate processing method and tool based on the hardness situation. If the material hardness does not meet the requirements, appropriate heat treatment can be carried out first, such as annealing to reduce hardness or quenching to increase hardness, and then processing can be carried out.

Tool issue

Tool wear

Reason: During the cutting process, the tool will generate intense friction and cutting heat with the workpiece material, which can lead to tool wear. Unreasonable cutting parameters, such as excessive cutting speed and feed rate, can accelerate tool wear. In addition, the hardness and toughness of the workpiece material can also affect the tool wear rate. For example, when processing high hardness alloy materials, tool wear will be faster.

Solution: Reasonably select cutting parameters and optimize them based on the properties of the workpiece material and the material of the tool. The use of tool coating technology, such as coating the surface of the tool with titanium nitride (TiN), titanium carbide (TiC) and other coatings, can improve the wear resistance of the tool. At the same time, establish a tool wear monitoring system to determine the degree of tool wear by monitoring signals such as cutting force, cutting sound, and vibration, and replace the tool in a timely manner.

Cutting tool breakage and damage

Reason: When the cutting tool encounters hard spots, uneven machining allowance, or sudden increase in cutting force during the cutting process, it is prone to chipping and damage. For example, when milling castings containing hard inclusions, the tool may collide with the inclusions and break the edge.

Solution: Conduct non-destructive testing on the workpiece material before processing to understand the presence of inclusions inside the material. Optimize the processing technology, such as arranging rough and fine machining processes reasonably to ensure even distribution of machining allowance. Choose appropriate tool geometry and materials to improve tool toughness and cope with possible cutting force impacts.

Process system issues

Clamping problem

Reason: Insufficient positioning accuracy of the fixture can result in inaccurate positioning of the workpiece during the clamping process. For example, after the positioning pin of the fixture wears out, it cannot accurately position the workpiece, resulting in the position tolerance of the processed part not meeting the requirements. In addition, excessive clamping force may cause deformation of the workpiece, especially for thin-walled and high-precision parts.

Solution: Regularly inspect and maintain fixtures, replace worn positioning components. Based on the material and shape of the workpiece, the size and distribution of clamping force should be reasonably determined, and appropriate clamping methods should be adopted, such as using soft claws, elastic fixtures, etc., to reduce workpiece deformation.

Unreasonable process route

Reason: The process route design did not take into account factors such as the precision requirements of the parts, material characteristics, and the performance of the processing equipment. For example, arranging processes with high precision requirements on processing equipment with lower precision, or not properly arranging the sequence of heat treatment processes and mechanical processing processes, can lead to processing problems.

Solution: Based on the specific requirements of the parts, consider various factors comprehensively and design a reasonable process route. For example, for parts with high precision requirements, rough machining is performed on rough machining equipment first, and then precision machining is performed on high-precision machining equipment. Reasonably arrange the heat treatment process in the process route, such as aging treatment after rough machining to eliminate internal stress, and then carry out precision machining.