Five Prone Errors In Machining

1.Machine manufacturing error

The manufacturing errors of machine tools mainly include spindle rotation errors, guideway errors and transmission chain errors. Spindle rotation error refers to the variation of the actual rotation axis relative to its average rotation axis at each instant of the spindle, and it will directly affect the accuracy of the workpiece being machined.

The main reasons for the rotation error of the main shaft are the coaxiality error of the main shaft, the error of the bearing itself, the coaxiality error between the bearings, and the main shaft winding. The guide rail is the reference for determining the relative positional relationship of various machine tool components on the machine tool, and it is also the reference for machine tool movement. The manufacturing error of the guide rail itself, the uneven wear of the guide rail, and the installation quality are important factors that cause the guide rail error. Transmission chain error refers to the error of the relative movement between the transmission elements at both ends of the transmission chain. It is caused by manufacturing and assembly errors of the various components in the transmission chain, and wear during use.

2. Geometric error of the tool

It is inevitable that any tool will wear during the cutting process, which will cause the workpiece size and shape to change. The effect of tool geometric errors on machining errors varies with the type of tool: when a fixed-size tool is used for machining, the manufacturing error of the tool will directly affect the machining accuracy of the workpiece; for general tools (such as turning tools), the manufacturing error It has no direct impact on machining errors.

3. Geometric error of fixture

The role of the fixture is to make the workpiece equivalent to the tool and the machine tool have the correct position, so the geometric error of the fixture has a great impact on the machining error (especially the position error).

4.Positioning error

Positioning errors mainly include reference misalignment errors and inaccurate positioning manufacturing errors. When machining a workpiece on a machine tool, several geometric elements on the workpiece must be selected as the positioning reference during machining. If the selected positioning reference and design reference (the reference used to determine the size and position of a surface on the part drawing) ) If they do not coincide, a reference mismatch error will occur.

The positioning surface of the workpiece and the positioning element of the fixture together form a positioning pair. The maximum position variation of the workpiece caused by the inaccuracy of the positioning pair and the gap between the positioning pairs is called the inaccuracy of the positioning pair. The inaccuracy of the positioning sub-manufacturing will only occur when the adjustment method is used for machining and will not occur during the trial cutting method.

5. Errors caused by deformation of the process system

Workpiece rigidity: If the workpiece rigidity in the process system is relatively low compared to machine tools, tools, and fixtures, under the effect of cutting force, the deformation of the workpiece due to insufficient rigidity will have a greater impact on machining errors.

Tool rigidity: The rigidity of the external turning tool in the normal (y) direction of the machining surface is very large, and its deformation can be ignored. When boring a small diameter inner hole, the rigidity of the tool bar is very poor, and the deformation of the tool bar under force has a great influence on the accuracy of hole machining.

Machine tool component rigidity: Machine tool components are composed of many parts. So far, there is no suitable simple calculation method for machine tool component rigidity. Currently, experimental methods are mainly used to determine the machine tool component stiffness. The factors that affect the rigidity of machine tool components include the influence of contact deformation of the joint surface, the influence of friction, the influence of low-rigidity parts, and the influence of clearance.

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Link to this article：Five Errors That Are Prone To Occur During Machining

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