Nine kinds of errors are prone to machining aluminum
Nine kinds of errors are prone to machining aluminum
The machining error of aluminum profile refers to the degree of deviation between the actual geometric parameters (geometry, geometry and mutual position) of the part after processing and the ideal geometric parameters. The degree of correspondence between the actual geometric parameters and the ideal geometric parameters after aluminum profile processing is the aluminum profile processing accuracy. The smaller the processing error, the higher the degree of compliance, and the higher the processing accuracy. The processing accuracy and processing error of aluminum profiles are two ways of thinking about a problem. Therefore, the size of the processing error determines the level of processing accuracy.
Main reasons for machining errors of aluminum profiles
First, the error of machine tool manufacturing
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 processed aluminum profile. The main reasons for the spindle rotation error are the coaxiality error of the spindle, the error of the bearing itself, the coaxiality error between the bearings, and the spindle winding degree. The guide rail is the reference for determining the relative positional relationship of each machine tool part 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.
Second, the error caused by the fixture
In the machining of aluminum profiles, 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 influence on the machining error (especially the position error).
Third, the error caused by the tool
Any tool will inevitably wear during the cutting process, which will cause the size and shape of the aluminum workpiece to change. The effect of tool geometry error on machining error varies with the type of tool: when using fixed-size tools, the manufacturing error of the tool will directly affect the machining accuracy of aluminum profile machining parts; and for general tools (such as turning tools), Its manufacturing error has no direct impact on machining errors.
Fourth, positioning error
Positioning errors mainly include reference misalignment errors and inaccurate positioning manufacturing errors. When machining aluminum profiles on a machine tool, several geometric elements on the workpiece must be selected as the positioning reference during processing. If the selected positioning reference and design reference (which are used to determine the size and position of a surface on the part drawing) If the reference is not coincident, a reference misalignment error will occur.
The positioning surface of the aluminum profile processing part and the positioning element of the fixture together form a positioning pair. The maximum position variation of the workpiece caused by the inaccurate 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 processing and will not occur during the trial cutting method.
Fifth, the process system is deformed by heat
The thermal deformation of the process system has a relatively large impact on the processing error, especially in precision machining and long material processing, the processing error caused by thermal deformation can sometimes account for 50% of the total workpiece error.
Six, process system deformation
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 aluminum profiles due to insufficient rigidity has a greater impact on machining errors.
Tool stiffness: 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 will greatly affect the accuracy of hole processing.
Machine tool component stiffness: Machine tool components are composed of many parts. So far, there is no suitable simple calculation method for machine tool component stiffness. At present, the experimental method is 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 bonding surface, the influence of friction, the influence of low-rigidity parts, and the influence of clearance.
Seven, adjustment error
In each process of aluminum profile machining, the process system must be adjusted in one way or another. Since the adjustment cannot be absolutely accurate, adjustment errors occur. In the process system, the mutual position accuracy of the workpiece and tool on the machine tool is ensured by adjusting the machine tool, tool, fixture or workpiece. When the original accuracy of machine tools, tools, fixtures, and aluminum workpiece blanks meets process requirements without considering dynamic factors, adjustment errors play a decisive role in machining errors.
When the part is measured during or after processing, the measurement accuracy, the accuracy of the measuring tool, and the workpiece and subjective and objective factors directly affect the measurement accuracy.
Nine, internal stress
The stress that exists in the aluminum profile without external force is called internal stress. Once internal stress is generated on the aluminum part, the workpiece metal will be in an unstable state with a high energy level. It instinctively changes to a stable state with a low energy level, and is accompanied by deformation, thereby causing the workpiece to lose its original processing. Precision.