How to accurately obtain the machining dimensional accuracy of mechanical parts

During machining, it is practically impossible to machine every geometric parameter of the part due to various factors. There will always be some deviation in the mechanical part to make it exactly the same as the ideal geometric parameters. This deviation is the machining error. To minimize this error, it is necessary to accurately obtain the machining dimensional accuracy of mechanical parts by the following methodsg

(1)Trial cut method

That is, first test cut a small part of the machined surface, measure the size of the test cut, adjust the position of the cutting edge of the tool relative to the workpiece according to the processing requirements, and then test cut. Again, so after two or three test cuts and measurements, when the machine is processed to the required size, the entire surface to be machined is cut.

The test-cutting method is repeated until the required dimensional accuracy is achieved by “test-cutting-measuring-adjustment-retest-cutting”. An example is the test drilling of a box hole system.

The accuracy achieved by the test-cutting method can be very high and does not require complicated equipment, but this method is very time-consuming (requiring several adjustments, test cuts, measurements, calculations), inefficient, and depends on the skill level of the worker and the accuracy of the measuring instrument, and the quality is unstable, so it is only used for small batches of one piece.

As one of the test-cutting methods:Overlap, a method of processing another overlapping workpiece or combining two (or more) workpieces for processing on the basis of the already processed workpiece. The requirements for the final machined dimensions during the fitting process are subject to the fitting requirements with the machined parts.

(2) Adjustment method

The precise relative positions of the machine, fixture, tool and workpiece are set in advance with samples or standard parts to ensure the dimensional accuracy of the workpiece. Since the dimensions are pre-adjusted in place, no test cuts are required during machining and the dimensions are automatically acquired and remain constant during the machining of a batch of parts – this is the adjustment method.

For example, when using a milling unit, the position of the tool is determined by the tool setting block. The essence of the tool setting method is to use a fixed range device or tool setting device or pre-set tool holder on the machine tool to achieve a certain positional accuracy of the tool relative to the machine tool or device, and thus to machine a batch of workpieces

The tool will be fed into the machine tool according to the dial for cutting, is also a tooling method. This method first needs to determine the scale on the dial according to the trial cut method in mass production, often using a fixed-range block, test pieces, fixtures and other tooling devices for tooling.

Tool setting method has better processing accuracy and stability than the trial cut method, and higher productivity. The requirements for machine operators are not high, but the requirements for machine tool setting workers are high. Commonly used in mass production and mass production.

(3) Sizing method

The method of using the corresponding size of the tool to ensure the size of the workpiece to be machined is called sizing method. It is processed with the standard size of the tool, the size of the machined surface is determined by the size of the tool. That is, the use of a certain dimensional accuracy of the tool (such as more knives, reaming drill, drill bit) to ensure the accuracy of the workpiece processing parts (such as holes).

The marking method is easy to operate, with high productivity and relatively stable machining accuracy. It is almost independent of the skill level of workers and has high productivity. It is widely used in all kinds of production.

(4) Active measurement method

During the machining process, the machining dimensions are measured during the machining process, the measurement results will be compared with the design requirements of the size, so that the machine continues to run or stop is the active measurement method.

Currently, the value in the active measurement can be displayed digitally. Active measurement method is in the processing system (i.e., machine tool units, tools, fixtures, workpieces) to include measurement devices.

(5) Automatic control method

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

Automatic completion of dimensional measurement, tool deflection adjustment, cutting processing, machine stopping and a series of other work, automatically achieve the required dimensional accuracy. For example, when machining on a CNC machine tool, the part is controlled by various program instructions for processing sequence and processing accuracy.

To fully obtain the machining accuracy of mechanical parts, it is necessary to consider not only the size but also the shape and position. If you want to know more about this, please continue to follow our news.

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