The accuracy of the machine tool guide rail has a great influence on the accuracy of the entire machine tool. It must be prevented from deformation and wear, so the guide rails of machine tools are usually made of gray cast iron, such as HT200 and HT350. Gray cast iron has good wear resistance under lubricated conditions, but has poor resistance to abrasive wear. In order to improve wear resistance, the surface of the guide rail can be quenched.

Material selection analysis of tractor and auto parts

1. Selection of engine and transmission parts These two parts include quite a few parts. Among them, there are a large number of gears and various shafts, as well as parts that work at high temperatures, such as intake and exhaust valves, pistons, etc. Their materials are more important, and they are generally selected based on experience. For different types of vehicles and different production plants, the selection of engine and transmission system is not the same. Appropriate materials should be selected through a large number of calculations and tests according to the specific working conditions of the part and the actual failure mode.

2. Material selection to reduce the weight of the car With the increasing shortage of energy and raw material supply, people's requirements for energy saving and consumption reduction of automobiles are getting higher and higher. Reducing the self-weight can improve the weight utilization coefficient of the vehicle, reduce material consumption and fuel consumption, which is of great significance in terms of resource and energy conservation and economic value. The material selected to reduce the dead weight should be lighter than the traditional material and can guarantee the performance of the business. For example, replacing cast iron with aluminum alloy or magnesium alloy can reduce the weight to 1/3 to 1/4 of the original, but it does not affect its performance; using new dual-phase steel sheets instead of ordinary low-carbon steel sheets to produce automobiles For stamping parts, thinner plates can be used to reduce the dead weight, but the strength of the components is not reduced at all; in the body and some less important structural parts, the use of plastic or fiber-reinforced composite materials instead of steel can also reduce the dead weight and reduce the energy consumption.

Surface roughness is an important technical indicator reflecting the micro-geometric error of the surface of the part, and it is the main basis for inspecting the surface quality of the part; the rationality of its selection is directly related to the quality, service life and production cost of the product.

There are three methods for selecting the surface roughness of mechanical parts, namely calculation method, test method and analogy method. In the design of mechanical parts, the most common application is the analogy method, which is simple, fast and effective. The application of the analogy method requires sufficient reference materials, and comprehensive information and literature are provided in various existing mechanical design manuals. The most commonly used is the surface roughness that is compatible with the tolerance class. Under normal circumstances, the smaller the dimensional tolerance of mechanical parts is, the smaller the surface roughness value of mechanical parts is, but there is no fixed functional relationship between them. For example, the modified surfaces of some machines, handles, handwheels on instruments, sanitary equipment, and some mechanical parts on food machinery are required to be processed very smoothly, that is, the surface roughness is required to be high, but the dimensional tolerance requirements are very high. Low. In general, for parts with dimensional tolerance requirements, there is still a certain correspondence between the tolerance level and the surface roughness value. ​