What factors affect the accuracy of machined parts?
Publish Time: 2024-12-03
The accuracy of machined parts is a key indicator to measure the quality of parts and product performance, and it is affected by a combination of factors.
The accuracy of machine tools is the primary factor. The spindle rotation accuracy of machine tools is directly related to the roundness and cylindricity of the machined surface of parts. If the spindle has radial runout or axial movement, the processed circular parts will have coaxiality errors, and the cylindrical surface will have non-straight generatrix. The straightness and flatness errors of the guide rails will cause deviations in the tool motion trajectory, making the processing plane uneven or the linear dimensions inaccurate. For example, when turning a long shaft, if the guide rail is bent, the straightness of the shaft is difficult to guarantee. In addition, the accuracy of the machine tool's transmission system cannot be ignored. For example, the clearance of the screw nut pair will cause uneven tool feed, thereby forming a pitch error or dimensional error on the surface of the part.
Tool wear has a significant impact on accuracy. As the processing progresses, the tool cutting edge will gradually wear. After the tool is worn, the shape and size of its cutting edge change, which directly leads to changes in the processing size of the part. For example, after the milling cutter is worn, the height dimension of the milled plane will gradually decrease, and burrs will appear on the edge of the contour. Moreover, tool wear will also cause changes in cutting force, which will affect the shape accuracy of the parts. For example, during turning, tool wear increases the cutting force, which may cause the workpiece to bend and deform, affecting the cylindricity.
Clamping error cannot be ignored. The clamping method and positioning accuracy of the parts on the machine tool are crucial. If the positioning reference is not properly selected or the positioning element is not accurate enough, the parts will have position deviations during the processing. For example, when drilling, if the fixture cannot accurately position the part, the position of the drilled hole will deviate from the design requirements. Excessive or uneven clamping force will also cause deformation of the parts, especially thin-walled parts, and the processing accuracy will inevitably decrease after deformation.
Thermal deformation is a complex influencing factor. During the operation of the machine tool, heat is generated due to motor operation, cutting heat, etc., causing the machine tool parts to expand and contract. The heating of the spindle parts will cause the spindle to elongate, affecting the axial dimensional accuracy of the processing. The heat generated by the tool during cutting is transmitted to the workpiece, causing the local temperature of the workpiece to rise and expand, and the size to shrink after cooling, resulting in dimensional errors and shape errors. For example, when grinding the outer circle, the grinding heat may cause thermal stress on the workpiece surface, resulting in surface burns and damage to the shape accuracy.
In short, the accuracy of machined parts is the result of the interaction of multiple factors such as machine tool accuracy, tool condition, clamping accuracy and thermal deformation. In actual processing, these factors must be comprehensively considered and strictly controlled to ensure that high-precision parts are processed to meet the strict requirements of industrial production on part quality.