Basic knowledge of sheet metal

The object of sheet metal workers is to use metal plates or various profiles to process metal components with different shapes through sheet metal processing technology. Automobile sheet metal parts are widely used in automobile manufacturing and automobile maintenance. In particular, automobile panels are mostly sheet metal, which is easy to be corroded and damaged, so sheet metal work plays an extremely important role in automobile maintenance industry. As an excellent sheet metal worker, you must be familiar with all kinds of metal materials used in automotive sheet metal, know the mechanical properties of all kinds of materials, know the knowledge of lofting, unfolding and blanking of sheet metal, and know how to use materials reasonably to ensure the quality and efficiency of sheet metal work.

The first chapter preparation

Section 1 Metal materials commonly used in automotive sheet metal

Metal materials commonly used in automotive sheet metal include ferrous metals and non-ferrous metals. Due to the relationship between performance and price, ferrous metal accounts for more than 90% of automobile body sheet metal materials, while other materials only account for less than 10%. To understand the metal materials used in automotive sheet metal, we must understand the following aspects:

(1) automotive sheet metal's requirements for metal materials.

(2) Properties of common metal materials, including mechanical properties, service properties and chemical properties.

(3) Specifications and varieties of common metal materials and their applications in automobiles.

First, automotive sheet metal's requirements for metal materials

In modern life, the automobile is not only one of the most important means of transportation in industry, agriculture and even all walks of life, but also one of the most important tools of activities in human daily life. In use, automobiles often work in extremely harsh environments, with heavy load, high speed, high vibration, high dust, frequent sun and rain, and great differences in working temperatures. Therefore, strict requirements are put forward for automobile sheet metal parts, especially sheet metal parts.

1. Good mechanical properties

Because the automobile is often in the state of high speed, heavy load and frequent vibration in work, the automobile sheet metal parts must have sufficient strength, suitable hardness, good toughness and good fatigue resistance to ensure that the automobile is not deformed or damaged in normal operation and meet the needs of transportation.

2. Good process performance

Page 1 In automobile manufacturing and repair, the shapes of many sheet metal structural parts are very complicated. In order to avoid the difficulty of sheet metal processing, it is required that sheet metal materials must have good technological properties, namely:

(1) Sheet metal materials must have good pressure workability to ensure the smooth forming of sheet metal workpieces, that is, good plasticity. Must have the ability to produce permanent deformation under the action of external force without being destroyed. For cold-worked parts, good cold plasticity is required, such as stamping parts of automobile parts; For hot working parts, good thermoplasticity is required, such as hot forgings, spring steel plates, hot rivets, etc.

(2) Good weldability. Many automobile sheet metal parts are welded together by spot welding, oxygen welding, arc welding or gas shielded welding, so it is required that the sheet metal parts must have good welding performance. This is especially important in automobile maintenance and repair. Materials with good weldability have high welding strength and low cracking tendency.

3. Good chemical stability

Most automobile panels work outdoors, often in contact with water and steam, especially mufflers, and often work at high temperatures and corrosive gases. This requires that sheet metal parts must have good chemical stability, which requires not only strong corrosion resistance and rust prevention ability at room temperature, but also that they will not be corroded or deformed at high temperature or in the sun.

4. Good dimensional accuracy and internal quality of the plate.

The dimensional accuracy and internal quality of sheet metal have great influence on sheet metal processing, especially on molded parts. The specific requirements are:

(1) The plate has high dimensional accuracy, uniform thickness and no deformation.

(2) The surface is smooth, with high smoothness and no defects such as bubbles, shrinkage cavities, scratches and cracks.

(3) No serious corrosion, scale and other attachments.

(4) The structure is uniform, and there is no obvious difference in crystal structure and hardness.

5. Low price, economy and practicality.

For any part of an automobile, the economy should be considered under the condition of meeting the working conditions. You can use ferrous metals instead of nonferrous metals; If you can use non-ferrous metals, never use precious metals. The service life of automotive sheet metal parts should be compatible with the service life of other automobile parts.

Second, the mechanical properties of automotive sheet metal materials

The mechanical properties of metal materials refer to the properties of metal materials under the action of external forces. It mainly includes strength, plasticity, elasticity, hardness and fatigue.

1. Power

Strength refers to the ability of metal materials to resist deformation and failure under static load. Yield strength and tensile strength are commonly used indicators to measure metal strength.

1) yield strength

Yield strength is also called yield limit. When the external force reaches a certain level, even if the external force does not increase, the deformation of the metal material will continue. This phenomenon is called "submission". The stress point at which the yield phenomenon begins is called the yield point, which is represented by the symbol o8.

The yield point is a sign that metal materials will undergo significant plastic deformation. The higher the yield point of the material, the greater the load required for plastic deformation. In sheet metal processing, materials are usually changed into various shapes, so the yield point of rice materials must meet the needs of sheet metal processing.

2) Tensile strength

Tensile strength refers to the maximum tensile force that a material can bear before it breaks, which is represented by the symbol ob.