News Center

Based on the analysis of the grinding and scraping process in the machining of high precision parts, the mechanism of error reduction in the processing of this method is discussed. In the processing of parts with high geometric accuracy, if the accuracy of the processing tools is only improved to ensure that the accuracy of these tools will become higher, the cost will become larger, and even cannot meet the requirements. The basic requirements of machining are high efficiency and low cost, therefore, the method of improving tool accuracy alone does not meet the process principles, and is actually not advisable. Therefore, it is analyzed and discussed in combination with technology knowledge, and the error average method is used to complete the machining of high-precision parts.

1 Principle of average error method

In production, when the precision of the machining tool is not high, the requirements of high-precision machining can be achieved by the scraping motion relative to the tool and the workpiece. This machining method makes use of the micro cutting when the lashing tool and the workpiece are in relative motion during the grinding process. At the beginning of grinding, the lapping tool and the workpiece surface are high point contact, under a certain pressure, the actual contact area is far less than the nominal contact area, so the pressure per unit area is very large, and the surface of the parts is quickly ground. With the gradual grinding of the high point of the workpiece, the matching area is expanded, the pressure per unit area is reduced, the unevenness is gradually reduced, and the geometric shape accuracy is gradually improved. Due to the high hardness and slow wear of the grinding tool, it always maintains a relatively sharp micro edge and has a certain cutting ability. The process of relative friction and wear between the grinding surface is essentially the process of continuous reduction of the geometric error of the workpiece surface, which is called the error average method in the process.

2 Grinding of the surface of the workpiece

The common mating parts in mechanical products are inner holes and outer circles, lead screws and nuts, machine tool guide pairs, etc. In the process of grinding and scraping, although the tools used are different, the mechanism of error reduction of these mating parts is basically the same, and the lapping tool and the workpiece are pairs of each other.

2.1 Cylindrical grinding

Grinding is one of the earliest finishing methods. The lapping sleeve is coupled with the shaft as a lapping tool. The lapping sleeve moves relative to the workpiece under a certain pressure, the workpiece rotates slowly, and the abrasive particles between the lapping sleeve and the workpiece are driven to cut the workpiece. Due to the complexity of the grinding process, the abrasive particles float on the surface of the workpiece, which can respectively play a mechanical, physical and chemical comprehensive role.

1) Mechanical cutting action: The abrasive particles roll, scrape and squeeze under pressure to cut off the fine metal layer.

2) Physical action: The local pressure of the contact point between the abrasive particle and the workpiece is strong, resulting in instantaneous high temperature, extrusion and other effects, which help to form a smooth surface with a small roughness value.

3) Chemical action: The stearic acid or oleic acid added to the grinding liquid reacts chemically with the oxide film on the surface of the workpiece, softening the ground surface and improving the grinding effect.

2.2 Inner hole grinding

The principle of inner hole grinding is the same as that of outer round grinding, and the lapping tool is a grinding rod slotted on the outer round surface to store the grinding agent. Lapping tools are divided into rough lapping tools, fine lapping tools and research tools.

2.3 Scraping of guide rail surface

The process route of machine tool guide surface processing is: casting → rough planing → semi-finishing planing → finishing planing → medium frequency quenching → guide grinding. Due to the long guide rail of the bed, large processing capacity and high precision requirements, it is more suitable to use special guide rail grinding equipment for processing. However, for the movable parts of the guide rail surface of the machine tool tail seat, the bed saddle and the longitudinal and transverse slide board of the tool holder, due to the equal height requirements with the spindle, it must be used in the assembly to meet the assembly accuracy requirements, which is called the repair assembly method in the assembly process. Generally, it is more economical to choose the guide surface of movable parts for scraping. The process of movable parts guide surface is: parts processing → moving guide surface painting → assembly → grinding → measurement → disassembly → scraping → re-assembly → re-grinding → re-measurement → scraping → until the requirements are met. In the above process, grinding is to find the high point, so as to determine the scraping position; Measurement is the measurement of the height size, according to the measurement size to determine the size of the scraping. In the final measurement, if the requirements are met, it is the final size, otherwise it must be scraped again, and the above process is repeated until the requirements are met.

3 Conclusion

1) By studying the mechanism of the error averaging method, the basic law of the action process of the error averaging method is obtained, and the main factors and process parameters affecting the grinding quality are determined.

2) The grinding process includes mechanical, physical and chemical effects, which is a comprehensive error reduction process.

3) The scraping process is actually to use the role of scraping and extrusion to reduce the surface roughness value of the part, improve the contact rate and form compressive stress on the surface of the part, so as to effectively improve the bearing capacity and fatigue life of the part.

4) Using the closed law of circular indexing error, its true value error can be obtained through appropriate measurement methods, error correction and compensation according to the allowable value of indexing error can meet the processing requirements, and play an important role in the processing of high-precision parts.

5) The average error method is an effective method to reduce the difficulty of parts processing, improve the processing quality, and ensure the accuracy of machine assembly, which plays an important role in the design and manufacture of machine tools and other mechanical products.