There are many factors affecting the precision of precision parts in the process of machining. Different machining methods can achieve different precision under different machining conditions. If we blindly pursue machining accuracy, it will reduce production efficiency and increase the cost of precision parts processing. Therefore, precision machining enterprises should try their best to improve efficiency and reduce production costs on the premise of ensuring quality. The machining accuracy of precision machinery parts can be divided into dimensional accuracy, shape accuracy and position accuracy. Therefore, the machining accuracy is measured by dimensional tolerance, shape tolerance and position tolerance.
Method of obtaining dimensional accuracy of parts
- Test cutting method:First try to cut out a small part of the processing surface, measuring the size of the test cut, adjust the position of the cutting edge relative to the workpiece according to the processing requirements, then try to cut and measure, after two or three times of test cutting and measurement, when the precision machining size meets the requirements, then the whole surface to be processed for cutting. The test cutting and turning of journal size of precision machinery parts processing, the online measurement and grinding of journal size, the test boring of box parts, the manual fine grinding of precision measuring block, etc., are all through the trial machining shear method.
The precision achieved by the trial cutting method may be very high. It does not require complex equipment, but it is time consuming, requiring many adjustments, test cuts, measurements and calculations. Low efficiency, depending on the worker’s technical water symptoms and the accuracy of measuring instruments; The quality is not stable, only used for single small batch production. - The adjustment method is to adjust the accurate relative position of machine tool, fixture, tool and workpiece with sample or standard parts in advance, so as to ensure the dimensional accuracy of precision mechanical parts processing, and the size remains unchanged in the process of a batch of parts processing. This is the adjustment method. Machining shaft parts on multi-tool lathes or hexagonal automatic lathes, machining grooves on milling machines, grinding cylindrical and hole systems on centerless grinders are all adjustment methods.
If a milling machine fixture is used, the position of the tool is determined by the tool holder; The essence of the adjustment method is to use the distance device on the machine tool or tool device or pre-set tool holder, so that the tool relative to the machine tool or fixture to a certain position. Precision, reprocessing a batch of work pieces. In mass production, it is often used to adjust the tool device with travel limit device, prototype device and so on. Compared with the test cutting method, the adjustment method has better machining accuracy and stability, and the production efficiency is higher. The machine tool operation requirements are not high, but the machine tool adjustment requirements are high. It is often used for mass production and mass production. - Sizing method: precision parts processing using the corresponding size of the tool to ensure the size of the workpiece machining method called sizing method, that is, the use of standard size of the tool for processing, precision machining surface size by the following formula to determine the size of the tool; That is, the tool with a certain dimensional accuracy is used to ensure the accuracy of the workpiece being processed. For example, using a square broach to pull out the square hole, using a drill, reamer, reamer or boring block to process the inner hole, milling grooves on both sides of the workpiece with a combination of milling cutters, all belong to the dimensional tool method.
