What are the factors that affect grinding accuracy? How to control the workpiece to meet the accuracy requirements?

Geometric accuracy and running accuracy of the machine tool itself; The rigidity of the parts, the rationality of the clamping and positioning of the parts, the correctness of the selection of the processing technology benchmark, the rationality of the heat treatment process of the parts themselves, and the scientificity of the processing technology (the separation of rough and finish machining, the suitability of the selected processing equipment, etc.). ), the accuracy and reliability of the selected tools, the influence of temperature change on machine tools and parts, and the technical level of operators.

The factors affecting numerical control are: factors affecting machining accuracy and measures to improve machining accuracy. All components in the process system, including manufacturing error, installation error and wear in use, directly affect the machining accuracy of the workpiece. That is to say, in the process of machining, the process system will produce various errors, thus changing the mutual position relationship between the tool and the workpiece in the process of cutting movement and affecting the machining accuracy of the parts. These errors are related to the structural state of the process system itself and the cutting process, and the main factors causing machining errors are:

Geometric error of (1) system

(1) Error of machining principle The error of machining principle is due to the adoption of approximate machining motion mode or approximate tool profile. Because of the error of machining principle, it is called machining principle error. As long as the principle error is within the allowable range, this treatment method is still feasible.

(2) Geometric error of the machine tool The manufacturing error, installation error and wear in use of the machine tool directly affect the machining accuracy of the workpiece. Among them, the errors are mainly the rotary motion of the machine tool spindle, the linear motion of the machine tool guide rail and the machine tool transmission chain.

(3) Tool manufacturing error and tool wear manufacturing error, installation error and wear all affect the machining accuracy of the workpiece. In the process of cutting, the cutting edge, cutting surface, workpiece and chip produce strong friction, which makes the tool wear. When the tool wear reaches a certain value, the surface roughness of the workpiece increases, the color and shape of the chip change, and it is accompanied by vibration. Tool wear will directly affect cutting productivity, machining quality and cost.

④ Fixture error Fixture error includes positioning error, clamping error, fixture installation error and tool alignment error. These errors are mainly related to the manufacturing and assembly accuracy of the fixture. The positioning error of the fixture will be analyzed in detail below. The position of the workpiece in the fixture is determined by the contact (cooperation) between its positioning base surface and positioning element. However, the actual position of each workpiece in the fixture will be inconsistent due to the manufacturing error between the positioning base surface and the working surface of the positioning element. After machining, the machining size of each workpiece must be different, resulting in errors. This kind of machining error caused by the inaccurate positioning of the workpiece on the fixture is called positioning error, which is expressed by △ d and includes reference displacement error and reference misalignment error. When machining a batch of workpieces by adjustment method, the essence of positioning error is the maximum variation of process benchmark in the machining dimension direction. There is no positioning error through trial cutting. The causes of positioning error are the manufacturing error of workpiece and positioning element, the fit gap between them and the non-coincidence of process benchmark and positioning benchmark.

● Datum misalignment error The machining error caused by misalignment between the positioning datum and the process datum is called datum misalignment error, and its size is equal to the dimensional tolerance between the positioning datum and the process datum, which is expressed by △ B. ..

● Datum displacement error When the workpiece is positioned in the fixture, due to the influence of the manufacturing tolerance and the minimum fit clearance between the workpiece positioning base surface and the positioning element positioning base surface on the fixture, the positioning datum and the positioning datum cannot overlap, which makes the positions of the workpieces inconsistent and causes the machining dimension error. This error is called reference displacement error, which is expressed by △ y .. Figure 1- 12a is a schematic diagram of the process of milling keyway with circular sleeve, and the process dimensions are A and B. ..

The technological datum of dimension A is the axis of the inner hole, and the positioning datum is also the axis of the inner hole, which are coincident, and △ b = 0. However, due to the manufacturing tolerance and minimum fit clearance between the surface of the inner hole of the workpiece and the cylindrical surface of the spindle, the positioning datum (the axis of the inner hole of the workpiece) and the limit datum (the axis of the spindle) cannot coincide, and the positioning datum moves down a certain distance relative to the limit datum, because the position of the cutter will not change (the position of the limit datum will not change) during the process of machining a batch of workpieces after the position adjustment. Therefore, the position change of positioning datum affects the size of dimension A, resulting in the error of dimension A, which is the datum displacement error.