Precision part machining accuracy refers to the degree to which the actual geometric parameters (dimension, shape, position) after part machining match the ideal geometric parameters specified in the drawing. The higher the degree of fit, the higher the machining accuracy. In machining, due to the influence of various factors, it is not actually possible to process each geometric parameter of a part to exactly match the ideal one, and there are always some deviations. This difference is a processing error.

To guarantee the accuracy of a part, we offer the following guarantees.

(1) test method

That is to say, first cut the working surface of the very small part, measure the dimension obtained in the cutting, adjust the position of the cutting edge of the tool relative to the workpiece according to the processing requirements, try again, and measure again, as shown in 2. After three trials and measurements, the entire surface of the workpiece is again cut when the required dimensions are met.

The testing method is repeated until the required dimensional accuracy is reached by "testing, measurement, adjustment, and re-testing". For example, the test boring of box hole system.

The accuracy achieved with the try-on method can be high and does not require complex equipment, but this method is time consuming (requires multiple adjustments, try-on, measurements and calculations), is inefficient, depends on the technical level of the worker and the accuracy of the weighing instrument, and is not suitable for quality testing. Due to its small size, it is only used for small scale production.

For example, in the case of a computer computer, it is possible to combine two (or more) components into one (or more) component. The requirement that the final dimensions to be processed during compounding are achieved is based on the compounding requirement with the processed parts.

(2) adjustment method

The exact relative position of the machine tool, jigs, tools and the workpiece is adjusted in advance with samples or standard parts to ensure the dimensional accuracy of the workpiece. Since the dimensions have been adjusted in advance, the method of adjustment is to automatically acquire the dimensions without retrying during machining and keep them constant during the machining process of the part. For example, when using a milling fixture, the position of the tool is determined by the cutter block. The essence of the adjustment method is to make the tool reach a certain position accuracy with respect to the machine tool or jig by using a positioning device or anti-knife device on the machine tool or a pre-arranged tool post, and then process a series of workpieces.

Another adjustment method is to cut the machine tool with a scalpel according to the dial. This method requires first determining the scale on the dial based on the test method. In mass production, a constant stopper, a sample, a template, etc. are often used to adjust the knife device.

The adjustment method has higher machining accuracy stability and higher productivity than the test cutting method, and the requirements for machine tool operators are not high, but the requirements for machine tool adjusters are high, and it is often used in mass production.

(3) dimensional determination method

The method of guaranteeing the dimension of the workpiece part according to the dimension of the tool is called the constant dimension method. This is a tool machining with standard dimensions, and the dimensions of the surface to be machined are determined by the tool dimensions. That is, a tool (reamer, drill, drill, etc.) with a certain dimensional accuracy is used to ensure the accuracy of the workpiece part (hole, etc.).

Dimension is convenient to operate, high productivity, relatively stable processing accuracy, has almost nothing to do with the technical level of workers, high productivity, widely used in all types of production. Examples include drill holes and hinge holes.

(4) active measurement method

Active measurement methods measure the machining dimension during machining and compare the measurement results with the dimensions required for design, or continue or stop the machine tool.

Select. The values of the active measure are already displayed numerically. Active measurement became the fifth element of the process system, incorporating the measuring device into the process system (i.e. a unified body consisting of machine tools, tools, jigs and workpieces).

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

(5) automatic control method

This method consists of a measuring device, a feed device, and a control system. It combines the measurement, feeding device and control system into an automatic processing system, and the processing process is automatically completed by the system.

A series of tasks such as dimensional measurement, tool compensation adjustment and cutting machining and machine tool parking are automatically completed and automatically reach the required dimensional accuracy. For example, when machining with an NC machine tool, the parts control the machining order and machining accuracy according to various program instructions.

There are two concrete methods for automatic control.

The machine tool has a device that automatically measures the size of the workpiece, and when the workpiece reaches the required size, the measuring device automatically retracts the workpiece and instructs it to stop working.

(2) digital control, that is, the machine tool has a servo motor that controls the precise movement of the turret or table, a pair of rolling screw nuts, and a series of digital control devices. The program is automatically controlled by a computer digital control unit.

Early automated control methods used active measurements and control systems such as mechanical and hydraulic pressure. At present, a program that is pre-organized according to the processing request, a program control machine tool that issues instructions to perform the work by the control system, or a digital control machine tool that issues digital information instructions to perform the work by the control system, and a processing process Automatic control machining is carried out by widely adopting adaptive control machine tools that can adapt to changes in machining conditions, automatically adjust the machining dose, and optimize the machining process according to predetermined conditions.

The quality of machining by the automatic control method is stable, the productivity is high, the machining flexibility is good, and it can be adapted to multi-product production, which is the basis of the current development direction of machine manufacturing and computer assisted manufacturing (CAM).