1、 Original error
The original error is the error existing at the beginning of the milling machine process. The more 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, etc.
2、 Process system set error
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 errors of milling machines mainly include spindle rotation errors, guide rail and transmission chain errors, as well as errors caused by the decline in accuracy 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 a great impact on the forming of workpiece. There are many kinds of influence of tool error on machining accuracy. If it is a tool with fixed size, the manufacturing error will directly affect the workpiece, and 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 cutter. Once the fixture has accuracy error, it will have a great impact on the machining accuracy of milling machine.
3、 Positioning error
1. Non coincidence error of datum: there is an error between the positioning datum and the design datum, and the two do not coincide. It can only be processed by adjustment method, which will not occur during trial cutting.
2. Positioning pair manufacturing inaccuracy: 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 can be the vector sum of the reference misalignment error and the positioning pair manufacturing inaccuracy error.
4、 Error caused by force 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 deform due to insufficient rigidity, which has a great impact on the machining accuracy of milling machine.
2. Tool stiffness: 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 a small-diameter inner hole, the stiffness of the cutter bar is very poor, which will have a certain impact on the accuracy of the hole.
3. Component stiffness of milling machine: each mechanical manufacturing equipment is composed of a variety of components, and the component stiffness also has a great impact on the machining accuracy of milling machine. The factors that affect the stiffness of milling machine components mainly include the contact deformation of the joint surface, the influence of friction, the influence of low stiffness parts, the influence of clearance and so on.