How do you choose materials for parts?

The requirements for the use of machine parts are manifested in the following.

(1) The working conditions and load conditions of the part and the requirements to avoid the corresponding forms of failure.

The working condition refers to the characteristics of the environment in which the part is exposed, the working temperature and the degree of friction and wear. For parts working in hot and humid environment or corrosive media, the material should have good rust and corrosion resistance, in this case, stainless steel, copper alloy can be considered first. There are two main aspects of the impact of the working temperature on the choice of materials: on the one hand, to consider each other with the two parts of the material of the linear expansion coefficient can not differ too much, so as not to produce excessive thermal stress in temperature changes or make with the loosening; on the other hand, to consider the mechanical properties of the material with the temperature and change the situation. In the sliding friction under the work of the parts, to improve its surface hardness, in order to enhance wear resistance, should be selected suitable for surface treatment of quenched steel, carburized steel, nitrided steel and other varieties or selection of friction reduction and wear resistance of good materials.

The load situation refers to the size and nature of the load and stress on the part. In principle, brittle materials are only suitable for the manufacture of parts working under static loads; in the case of impact, plastic materials should be used as the main material; for parts subjected to high contact stresses on the surface, materials that can be surface treated, such as surface-hardening steels, should be selected; for parts subjected to strain forces, materials that are resistant to fatigue should be selected; for parts subjected to impact loads, materials with higher impact toughness should be selected. For parts whose size depends on strength and whose size and mass are limited, materials with higher strength should be selected; for parts whose size depends on stiffness, materials with higher modulus of elasticity should be selected.

The properties of metallic materials can generally be increased and improved by heat treatment, so it is necessary to make full use of the means of heat treatment to exploit the potential of the material; for the most commonly used modulated steel, due to its different tempering temperature can be obtained with different mechanical properties of the blank. The higher the tempering temperature, the lower the hardness and stiffness of the material will be, and the better the plasticity. Therefore, when selecting the variety of material, its heat treatment specifications should be specified at the same time and indicated on the drawing.

(2) on the size and quality of the part limits.

Part size and quality of the size and quality of the material species and the manufacturing method of the blank. Production of casting blanks can generally be free of size and quality of the size of the restrictions; and production of forging blanks, it is necessary to pay attention to the forging machinery and equipment production capacity. In addition, the size and quality of the parts and the size of the material is also related to the weight ratio, should be selected as far as possible, the weight ratio of strong materials, in order to reduce the size and quality of the parts.

(3) The importance of the parts in the whole machine and components.

(4) Other special requirements (e.g., whether insulation, magnetic resistance, etc.).

02 Process requirements

In order to make the parts easy to manufacture, the selection of materials should consider the complexity of the structure of the parts, size and type of blank. For complex shape, large size parts, if the casting blank is considered, you need to choose casting performance of good materials; if you consider using welding blank, you should choose welding performance of good mild steel. For parts with simple shape, smaller size and larger volume, suitable for stamping and die forging, the material with good plasticity should be selected. The need for heat treatment of the parts, the material should have good heat treatment properties. In addition, the ease of processing of the material itself and the ease of processing after heat treatment should also be considered.

03 Economic requirements

(1) Relative price of the material itself

As far as possible, inexpensive materials should be used, provided they meet the requirements for use. This is especially important for parts that are manufactured in large quantities.

(2) Processing cost of materials

When the quality of the part is small and the machining volume is large, machining costs can be a large percentage of the total cost of the part. Although cast iron is cheaper than steel plate, but for some single pieces or small batch production of the box class parts, using cast iron than using steel plate welding cost is higher, because the latter can save the manufacturing cost of the mold.

(3) save materials

In order to save materials, heat treatment or surface strengthening (shot blasting, grinding, etc.) process can be used to give full play to and make use of the potential mechanical properties of the material; can also be used surface coating (chrome plating, copper plating, black, blue, etc.) methods to reduce the degree of corrosion and wear, to extend the service life of the parts.

(4) Utilization of materials

In order to improve the utilization of materials, can be used without cutting or less cutting process, such as die forging, precision casting, stamping, etc., which can not only improve the utilization of materials, but also reduce the man-hours of cutting process.

(5) to save valuable materials

By using a combination structure, higher priced materials can be saved, such as the combination structure of the worm gear gear ring with good friction reduction but expensive tin bronze, while the core of the wheel is cheap cast iron.

(6) Savings on rare materials

In this regard, the manganese boron series of alloy steel, which is more abundant in China, can be used in place of the less resourceful chrome-nickel series of alloy steel, as well as the use of aluminum bronze instead of tin bronze, among other methods.

(7) Availability of materials

In the selection of materials, should be used locally and easy to supply materials, in order to reduce the cost of procurement, transportation, storage; from the point of view of simplifying the supply and storage of material varieties, for small batch production of parts, should minimize the use of materials on the same machine varieties and specifications, in order to simplify the supply and management, and can be more easily in the processing and heat treatment process to grasp the most reasonable operating methods, thereby improving manufacturing quality, reduce scrap, and improve labor productivity.