Material selection and application in mechanical design

With high speed of industrial development, people's choice of mechanical design material and application requirements also more and more high, do a good job in mechanical design of the choice of materials is very important, it has become the emphasis and difficulty of the mechanical design industry, under the guarantee normal strength of the stiffness of machine, material saving, environmental protection, energy conservation, improve the economic benefit of mechanical, applicability to become the research focus in the industry. This paper briefly introduces the significance of material selection and application in mechanical design, and analyzes the characteristics and selection of mechanical design materials.

1, the choice of materials in mechanical design and application analysis

With the rapid development of economy, environment, resources, and many other problems also slowly rise to the surface, after a lot of development in the design of some mechanical important resource has become less and less, although our country is humongous, but large population led to the per capita in the world at the end of the instability of some competition triggered the resources at the same time, the higher the cost of materials of mechanical manufacturing, The application space is further compressed, so we should do more research in the material selection of mechanical design, in order to reduce the burden of mechanical manufacturing, increase mechanical efficiency, improve mechanical life, but also achieve energy conservation and emission reduction, protect the environment, and make contributions to sustainable development.

2, mechanical design commonly used materials

1. Metal materials

In all kinds of engineering materials, metal materials (especially iron and steel) are the most widely used. According to statistics, in machinery manufacturing products, steel materials account for more than 90%. Steel is widely used, in addition to its good mechanical properties (such as strength, plasticity, toughness), because it is relatively cheap and readily available, and can meet the requirements of a variety of properties and uses. Among all kinds of steel, alloy steel is often used to make various parts because of its excellent properties.

All metal materials except iron and steel are non-ferrous metals. In non-ferrous metals, aluminum and other alloys are the most widely used. Some of them have the smallest quality, and some of the advantages of good thermal conductivity and electric conductivity, usually can also be used to reduce friction and corrosion resistance requirements of the occasion.

2, polymer materials

Polymer materials usually contain three categories, namely plastic, rubber and synthetic fiber. Polymer materials have many advantages, such as rich raw materials, can be extracted from oil, natural gas and coal, or the area is required by low energy consumption; The average density is only 1/6 of steel. Good elasticity in the right temperature range; Good corrosion resistance, etc. For example, polytetrafluoroethylene, known as the "king of plastics," has strong corrosion resistance and strong chemical stability, not becoming brittle at very low temperatures and not softening in boiling water. Therefore, polytetrafluoroethylene is widely used in chemical equipment and refrigeration equipment, but polymer materials also have obvious shortcomings, such as: easy to aging, many of them poor flame retardant, generally speaking, poor heat resistance.

3. Ceramic materials

As engineering structural ceramic materials, there are high temperature structural ceramics with silicon nitride and silicon carbide as the main components, and there are tool structural ceramics with alumina as the main component. The main characteristics of ceramic materials are: high hardness, wear resistance, corrosion resistance, high melting point, stiffness and low density than steel. Ceramic materials are often described as "strong as steel, hard as diamond, light as aluminum" materials. At present, ceramic materials have been used in seals, rolling bearings and cutting tools, but the main shortcomings of ceramic materials are relatively brittle, low fracture toughness, high price and poor processing performance.

4. Composite materials

Composite material is composed of two or more kinds of materials with obviously different physical and mechanical properties. Different materials can be used as the basic phase and reinforcement phase of the material respectively. The reinforcing phase plays a role in improving the strength and stiffness of the basic phase, and the basic phase plays a role in shaping the reinforcing phase, so as to obtain excellent performance that is difficult to achieve by a single material.

3, the principle of selection of mechanical design materials

(1) The magnitude and nature of load stress

This aspect of factors is mainly considered from the strength point of view, with a full understanding of the mechanical properties of the material under the premise of selection. Brittle materials are in principle only suitable for parts that operate under static load only. In the case of more or less impact, plastic materials should be used as the main material. Generally, the properties of metal materials can be improved and improved by heat treatment. Therefore, it is necessary to make full use of heat treatment to develop the potential of materials. For the most commonly used tempered and tempered steel, the blank with different mechanical properties can be obtained due to the different tempering temperature.

(2) The working conditions of the machinery

The influence of working temperature on material selection, on the one hand, we should consider the linear expansion coefficient of the materials of the two parts with each other can not differ too much, so as not to produce too much stress when the temperature changes, or with loose; On the other hand, the change of mechanical properties of materials with temperature should also be considered. Mechanical wear in the work is likely to occur, to improve the surface hardness, to enhance wear resistance. Therefore, suitable for surface treatment of hardened steel, carburized steel, nitriding steel and other varieties should be selected.

(3) The complexity of the parts and the possibility of material processing

The parts with complex structure should be cast blank or welded after stamping out components with sheet metal. Parts of simple structure can be obtained by forging.

(4) Economy of machinery

1, the relative price of the material itself. When the use of low-cost materials can meet the requirements of use, it should not choose high prices of materials. This is especially important for mass-manufactured parts.

2. Processing costs of materials. For example, some box parts, although cast iron is cheaper than steel plate, but in batch hours, steel plate welding is more favorable, so you can save the production cost of cast iron.

3, the utilization rate of materials. For example, using blank without cutting or less cutting (such as investment casting, die forging, cold drawing blank, etc.) can improve the utilization rate of materials.

4. Combined structure. For example, a train wheel is a general material of the wheel core external hot sleeve on a hardness and wear resistant hub.

5, save rare materials. For example, aluminum bronze is used instead of tin bronze for bearing bush, and manganese-boron alloy steel is used instead of nickel alloy steel.

6. Material supply. For small batch parts should minimize the variety and specifications of materials used on the same machine.