Nine major errors in machining, how many do you know?

There are deviations between geometric parameters such as the actual size, shape and position of the parts after they have been manufactured and those in the ideal state, and theMachining errorsTalk about that level of deviation.

The degree of conformity between the geometrical parameters actually presented by the part after machining and the geometrical parameters in the ideal state is known as themachining accuracyThe smaller the machining error, the higher the degree of conformity and thus the higher the accuracy. The smaller the machining error, the higher the degree of conformity and thus the higher the machining accuracy.

Machining accuracy and machining error are two expressions of the same problem. Thus, the size of the machining error reflects the level of machining accuracy. The main causes of machining error are some of these:

1、Manufacturing errors of machine tools

The manufacturing errors of machine tools mainly include spindle rotation errors, guideway errors and transmission chain errors.

Spindle rotary error, refers to the spindle each moment of the actual axis of rotation, relative to its average axis of rotation of the amount of change, it will directly affect the accuracy of the workpiece being machined. The main reasons for the spindle rotary error, there are spindle coaxial error, there is the error of the bearing itself, there are bearings between the coaxial error, and spindle winding. Guideway, is used to determine the relative position of the machine components of the benchmark, but also the benchmark of the machine movement.

For the cause of the guideway error, the guideway itself exists in the manufacturing error, and the guideway uneven wear, as well as the quality of installation, these are extremely important factors. Transmission chain error refers to the error in the relative motion between the transmission elements at the beginning and end of the transmission chain. This error is caused by manufacturing and assembly errors in the various components of the chain, as well as by wear and tear that occurs in the course of use.

2、The geometric error of the tool

In the cutting process, any tool is bound to wear, and it is precisely because of this wear that the size and shape of the workpiece change. Errors in the geometry of the tool, the error caused by machining, depending on the type of tool is not the same as the difference: when the use of fixed-size tools to start machining, the tool itself has a manufacturing error, will directly affect the machining accuracy of the workpiece; however, for the general use of the tool (such as lathe cutters such as this type of tool), the manufacturing error for machining error does not have a direct effect However, for commonly used tools (such as turning tools), their manufacturing errors do not have a direct impact on machining errors.

3、Geometric error of fixture

The role of the fixture is to allow the correct position between the workpiece and the tool and the machine tool, so the geometric error of the fixture has a great influence on the error generated during machining, especially the positional error.

4. Positioning errors

Positioning errors mainly include datum misalignment errors and inaccuracies in the manufacture of positioning subs. When machining a workpiece on a machine tool, a number of geometric elements on the workpiece must be selected as positioning datums during machining, and if the selected positioning datums and the design datums (in this case, the datums used to determine the dimensions and positions of a surface on the part drawing) do not coincide, then datum misalignment errors will occur.

The positioning surface of the workpiece together with the fixture positioning element constitutes the positioning pair. The maximum amount of positional change of the workpiece caused by the inaccuracy of the positioning pair and the clearance between the positioning pairs is called the inaccuracy of the positioning pair manufacturing, which only occurs when machining by the adjusting method, and does not exist in the test-cutting method.

5. Errors arising from force deformation of the process system

Workpiece stiffness, in the process system, if the workpiece stiffness is relatively low compared to the stiffness of the machine tool, cutting tools and fixtures, then in the cutting forces play a role in the conditions of the workpiece due to the lack of stiffness caused by the deformation of the machine tool, the impact on the machining error will be more significant.

Tool rigidity, cylindrical turning tool in the machining surface normal that is (y) direction of the stiffness is very great, the deformation generated by the negligible, not to mention. For the boring of small diameter holes in this case, the toolpost stiffness is extremely poor, the deformation generated by the toolpost force has a great impact on the hole machining accuracy.

Machine tool component stiffness, machine tool components are composed of many parts, for machine tool component stiffness, there is no suitable simple calculation method, the main use of experimental methods to determine the stiffness of machine tool components. Factors affecting the stiffness of machine tool components exist in the contact deformation of the bonding surface of the influence of friction, as well as the influence of low-stiffness parts, in addition to the influence of the gap.

6. Errors caused by thermal deformation of the process system

Thermal deformation of the process system has a significant impact on the machining error, especially in the case of precision machining and large parts machining, the machining error caused by thermal deformation can sometimes account for 50% of the total error of the workpiece.

7. Adjustment error

For each process step in machining, there is always a need to adjust the process system in one way or another. Since it is not possible to achieve absolute precision in the adjustment, errors in the adjustment can occur. In the process system, the accuracy of the mutual position of the workpiece and the tool on the machine is ensured by adjusting the machine, the tool, the fixture or the workpiece. When the initial accuracy of the machine, tool, fixture, and workpiece blanks are all in accordance with the process specifications and no dynamic elements are taken into account, the adjustment error plays a decisive role in the errors that occur during machining.

8. Measurement errors

Measurements are taken when the part is being machined, and also after machining, however, due to the method of measurement, the accuracy of the gauge, as well as the workpiece and subjective and objective factors, all have a direct impact on the accuracy of the measurements.

9. Internal Stress

The stress that exists inside the part and is not generated by external forces is called internal stress. Workpiece once the internal stress, then the workpiece metal will be in a high-energy level of instability, it will instinctively towards the low-energy level of the stable state, and will be accompanied by the occurrence of deformation, which will make the workpiece to lose the original machining accuracy.