Some good methods for how to obtain precision of workpiece dimensions

(1) the method of cutting

First try to cut a very small part of the machining surface, measuring the size of the trial-cut, according to the machining requirements appropriate adjustment of the cutting edge relative to the position of the workpiece, then try to cut, and then measure, so after two or three trial-cutting and measurement, when the size of the machining requirements, and then cutting the entire surface to be processed.

Trial-cutting method may achieve high precision, it does not require complex equipment, but this method is time-consuming (need to make many adjustments, test-cutting, measurement, calculation), inefficient, dependent on the technical level of workers and measuring instruments accuracy, quality instability, so only used in single piece of small-batch production.

(2) adjustment method

Precise relative positions of machine tools, fixtures, cutters and workpieces are adjusted in advance with sample or standard parts to ensure dimensional accuracy of workpieces. Because the dimension is adjusted in place beforehand, it is no longer necessary to try cutting, and the dimension is automatically obtained and kept unchanged during the processing of a batch of parts. This is the adjustment method.

In the machine tool, according to the calibration disc feed and then cutting, is also a kind of adjustment method. This method needs to first determine the scale on the dial according to the test cut method. In mass production, the tool setting device is adjusted by using block, sample and template.

The adjustment method has better precision stability, higher productivity and lower requirement for machine tool operators than the trial cutting method, but it has higher requirement for machine tool adjusters, and is often used in batch production and mass production.

(3) fixed size method

The method of determining the size of the workpiece by the corresponding size of the tool is called the fixed size method. It is machined with standard size tools, and the size of the machined surface is determined by the size of the tool. That is, the tool with a certain size accuracy (such as reamers, reaming drills, etc.) to ensure the accuracy of the parts to be processed (such as holes).

Fixed-size method is easy to operate, high productivity, relatively stable processing accuracy, almost independent of the technical level of workers, high productivity, widely used in various types of production. Such as drilling, reaming and so on.

(4) active measurement method

In the process of machining, the method of active measurement is to measure the dimension while machining, and compare the measured result with the dimension required by design, or make the machine tool continue to work or stop working.

At present, numerical values in active measurements have been shown in figures. Active measurement is the fifth factor that adds the measuring device to the process system (that is, the integration of machine tools, fixtures and workpieces).

The active measurement method is stable in quality and high in productivity.

(5) automatic control method

This method is made up of measuring device, feeding device and control system. It consists of measuring, feeding device and control system into an automatic machining system, and the machining process is completed automatically by the system.