The original error is the error existing at the beginning of the milling machine process. The common errors are geometric error, positioning error, machining error caused by stress deformation, machining error caused by thermal deformation, and error caused by the internal stress distribution of the workpiece.
Set error of process system
1. Geometric error of milling machine: the forming movement of the machined tool to the workpiece is completed by the milling machine, so the machining accuracy is inseparable from the accuracy of the milling machine. The manufacturing error of milling machine mainly includes spindle rotation error, guide rail and transmission chain error, as well as the error caused by precision reduction caused by long-time work.
2. Geometric error of cutter: cutter is one of the important parts of milling machine, and the error of cutter has great influence on the forming of workpiece. There are many kinds of influence of tool error on machining accuracy. If it is a fixed size tool, the manufacturing error will directly affect the workpiece. The general tool has little influence on the accuracy of the workpiece.
3. Geometric error of fixture: fixture mainly indicates the correct position of workpiece and tool. Once the fixture has accuracy error, it will have a great impact on the machining accuracy of milling machine.
1. Non coincidence error of datum: there is an error between the positioning datum and the design datum. The two do not coincide, and can only be processed by the adjustment method. It will not occur during trial cutting.
2. Inaccuracy of positioning pair manufacturing: the correct position of the workpiece in the fixture is determined by the positioning element. The direction of the reference misalignment error may be different from the direction of the positioning pair manufacturing inaccuracy error. The positioning error may be the vector sum of the reference misalignment error and the positioning pair manufacturing inaccuracy error.
Error caused by stress deformation of process system
1. Rigidity of workpiece: the rigidity of workpiece is lower than that of milling machine, cutter and fixture. Under the action of cutting, the workpiece will be deformed due to insufficient rigidity, which has a great impact on the machining accuracy of milling machine.
2. Tool rigidity: the rigidity of the cylindrical turning tool on the normal of the machining surface is very high, and the deformation can be ignored. When milling small-diameter inner holes, the rigidity of the cutter bar is very poor, which will have a certain impact on the accuracy of the holes.
3. Component stiffness of milling machine: each mechanical manufacturing equipment is composed of a variety of components, and the component stiffness has a great impact on the machining accuracy of the milling machine. The main factors affecting the rigidity of milling machine parts are the contact deformation of the joint surface, the influence of friction, the influence of low rigidity parts and the influence of clearance.