Cars are referred to as “machines that change the world” because the automobile industry is a strong indicator of a country’s economic development level and is therefore considered an important symbol. The automobile has four major processes, with stamping being the top priority and the first of the four processes.
What is stamping?
Stamping is a method of forming and processing in which an external force is applied to a plate, strip, pipe, or profile by a press and die to produce plastic deformation or separation, resulting in a workpiece with the desired shape and size.
Stamping is considered a type of plastic processing, also known as forging, along with forging. The main materials used in stamping are hot-rolled and cold-rolled steel plates and strips, with 60-70% of the world’s steel being made into finished products through stamping.
The automobile body, chassis, oil tank, radiator sheet, boiler drum, container shell, iron core, and silicon steel sheet of motor and electrical appliances are all produced through stamping.
Additionally, there are many stamped parts found in instruments, household appliances, bicycles, office machinery, household utensils, and other products.
Stamping characteristics
1) Stamping is a processing method with high production efficiency and low material consumption.
The stamping process is applicable to the production of large quantities of parts and products, which is convenient to realize mechanization and automation and has high production efficiency.
2) The operation process is convenient and does not require the operator to have a high level of skill.
3) The stamped parts generally do not need to be machined and have high dimensional accuracy.
4) Stamping parts have good interchangeability. The stability of stamping processing is good. The same batch of stamping parts can be used interchangeably without affecting assembly and product performance.
5) Because the stamping parts are made of plates, their surface quality is good, which provides convenient conditions for subsequent surface treatment processes (such as electroplating and painting).
6) Stamping can obtain parts with high strength, high stiffness and lightweight.
7) The cost of stamping parts produced in batch by die is low.
8) Stamping can produce complex parts that are difficult to be processed by other metal processing methods.
Stamping process
The mechanical steering system uses the driver’s physical strength as the source of power, and all its transmission structures are mechanical. It is comprised of a steering control mechanism, a steering gear, and a steering transmission mechanism.
A. Separation process
The sheet metal is separated along a specific contour line under the influence of an external force to obtain finished or semi-finished products with a defined shape, size, and cutting section quality. The separation is due to the stress within the deformed material exceeding its strength limit, σb.
Blanking is a cutting process that uses a die to cut along a closed curve, resulting in a flat part with a specific shape.
Use a die to cut along a closed curve, and the material that is cut out is considered waste. There are several forms of punching, such as positive punching, side punching, and hanging punching.
Trimming
Trim the edges of formed parts neatly or cut into a certain shape.
Separation
The separation process is performed by punching along an unclosed curve using a die. It is more commonly used when the left and right parts are formed together.
B. Forming process
The blank undergoes plastic deformation without breaking to produce finished and semi-finished products with a specific shape and size.
Forming condition: yield strength σs < internal stress of material < strength limit σb.
The blank is formed into various open hollow parts.
Flanging
The edges of sheet metal or semi-finished products are bent to form vertical edges along a specific curve with a certain curvature.
Reshaping
A forming method used to improve the dimensional accuracy of formed parts or obtain a small fillet radius.
Hole turning
Make vertical edges on pre-punched plates or semi-finished products or non punched plates.
Bending sheet metal into various shapes along a straight line can produce parts with highly complex shapes.
Flow chart of the stamping process
Stamping die
The mold is regarded as “the driving force of entering a rich society” in Japan and “the emperor of the metal processing industry” in Germany. The level of mold design and manufacturing technology is a significant indicator of a country’s product manufacturing level.
Mold classification
According to the working principle, it can be divided into:
- Drawing die
- Trimming punching die
- Flanging shaping die
Basic structure of die
Stamping dies are usually composed of upper and lower dies (male and female dies)
Composition: 1 working part, 2 guide, 3 positioning, 4 limit, 5 elastic element, 6 lifting and turnover
Stamping equipment
1. Press machine
1) According to the bed structure, the press can be divided into open press and closed press
The open press is open on three sides and has a C-shaped bed with poor rigidity, making it suitable for small presses. The closed press, on the other hand, has open front and rear sides and a closed bed, providing good rigidity and is therefore typically used for large and medium-sized presses.
2) Press can be divided into the mechanical press and hydraulic press according to the type of driving slider force
| Type | Equipment name | Working principle | Characteristic |
| Mechanical press | Friction press | The friction disc and flywheel contact each other and transmit power, and work with the help of the relative motion principle of screw and nut. | The structure is simple. When overloaded, it will only cause the sliding between the flywheel and the friction disc without damaging the parts, but the flywheel rim is worn greatly and the productivity is low. It is suitable for stamping of small and medium-sized parts, especially for stamping processes such as correction, stamping and forming. |
| Crank press | The crank connecting rod mechanism can be divided into open type and closed type. | High productivity, suitable for all kinds of stamping processing | |
| Hydraulic press | Hydraulic press | Based on Pascal principle, water or oil is used as the working medium and static pressure transmission is used to make the sliding block move up and down. | High pressure and static pressure, but low productivity. It is suitable for deep drawing, extrusion and other forming processes |
2. Uncoiling line
3. Plate shears
Plate shears are mainly used to cut straight edges of metal plates of various sizes.
The transmission forms are mechanical and hydraulic.
Stamping material
Stamping materials are crucial for affecting both part quality and die life. Currently, materials for stamping include low-carbon steel, stainless steel, aluminum and aluminum alloys, and copper and copper alloys. Steel plates are the most commonly used raw material for automobile stamping.
However, with the demand for lighter bodies, high-strength steel plates and sandwich steel plates are increasingly being used in automobile body construction.
1. Steel plate performance requirements
1) It has good mechanical properties and large deformation capacity.
The mechanical properties of metal materials refer to tensile strength, yield strength, elongation, hardness and plastic strain ratio.
- High plastic strain ratio R (anisotropic property)
- High work hardening index n value;
- High elongation δ；
- Low yield ratio（ σ s/ σ b)；
- Low aging index.
2) Good surface quality
The surface of the steel plate should be free of noticeable defects such as scabs, cracks, inclusions, and scratches. The inner panel of the vehicle body may have minor defects that do not impact formability and paint adhesion, such as small bubbles, small scratches, small roll marks, slight scratches, and slight oxidation color.
The outer plate should meet the quality level of FD (O5), meaning the better of the two sides should have no defects that affect the appearance after painting or electroplating and the other side should meet the requirements of FB (O3).
2. Steel plate classification
1) Divided by thickness:
The thickness of the stamped parts of the automobile body ranges from thin plates (less than 3mm), medium plates (3-4mm) to thick plates (more than 4mm), with thin plates being the main material used.
2) According to rolling status:
Hot-rolled and cold-rolled steel plates are the two types of steel plates. Hot rolling softens the alloy at a temperature higher than the recrystallization temperature and then presses the material into a thin sheet or billet cross-section with a pressure roller, but the physical properties of the material don’t change.
This results in poor toughness and surface flatness and low prices. Cold rolling, on the other hand, involves further rolling the material with a roller at a temperature lower than the alloy recrystallization temperature, leading to recrystallization at the molecular level and changes in the physical properties of the formed alloy.
As a result, cold-rolled steel plates have good surface quality, high finish, high dimensional accuracy, and can meet some special application requirements. Cold-rolled steel plates mainly include cold-rolled carbon steel plates, cold-rolled low-carbon steel plates, cold-rolled steel plates for stamping, and high-strength cold-rolled steel plates.
Cold-rolled carbon steel sheet
| Grade | Application |
| SPCC | General use |
| SPCD | For stamping |
| SPCE, SPCEN | For deep stamping |
S is the abbreviation of steel, P is the abbreviation of plate, the third letter C is the abbreviation of cold, and N indicates that non-timeliness needs to be guaranteed.
Cold-rolled low carbon steel sheet
| Grade | Application |
| DC01 | General use |
| DC03 | For stamping |
| DC04 | For deep stamping |
| DC05 | For special deep stamping |
| DC06 | For super deep stamping |
Inspection tool
Inspection fixtures are specialized inspection equipment used to measure and assess the dimensional quality of components. In the automotive manufacturing industry, special inspection tools are often utilized, both for large and complex stamped parts, interior trim parts and welding sub-assemblies, as well as for simple small stamped parts and interior trim components, as the primary means of controlling product quality between processes.
Inspection fixtures offer benefits such as speed, accuracy, ease of use, and are ideal for mass production needs.
The inspection tool usually consists of three parts:
① Skeleton and base part;
② Type part;
③ Functional parts (functional parts include: quick chuck, locating pin, detection pin, movable clearance slider, measuring table, profile card, etc.).
