Faced with the pressure of global energy crisis and environmental protection, energy conservation and emission reduction have become the development trend of the automobile manufacturing industry. By using high-strength steel plate thermoforming production and manufacturing technology, while achieving lightweight body and collision safety, it has become a car in recent years. Hot spots in manufacturing research. The thermoforming technology started late in China and has been in the experimental stage of research institutes such as universities or research institutes. However, with the intervention of automobile companies, thermoforming technology has developed rapidly. At present, hot stamping technology has been applied to the automobile manufacturing industry. And to achieve mass production, our company has established a hot stamping production line for mass production, and can design and develop hot stamping molds.
1. The principle of hot stamping and its application in the whole vehicle
In the hot stamping forming process, the boron-containing steel sheet is heated to an austenitic temperature range (900 ° C or higher) and then transferred to a hydraulic press to be stamped while the steel sheet is still ductile. The water-cooled mold ensures that the steel sheet is quenched to obtain a martensite structure, resulting in a finished product with a perfect shape and tensile strength of up to 1500 MPa (see Figure 1).
Hot-formed steel is the steel with the highest strength among automotive steels. It is suitable for automotive body parts such as anti-collision reinforcement beams and skeleton support beams. The advantage of using hot-formed parts is that ultra-high-strength parts can be obtained (1500MPa). ), improve the collision performance of the whole vehicle; it can simplify the structure of the whole vehicle and reduce the weight of the whole vehicle; the dimensional accuracy of the parts is improved, and the resilience is reduced by more than 90% (see Figure 2); high temperature forming, lifting sheet elongation, shape is obtained Complex parts (see Figure 3).
2. Hot stamping process and equipment
(1) Hot stamping process The hot stamping production process is: forklift or bridge crane feeding to sheet unpacking system (marking) → manipulator device grabs the sheet and transfers the sheet to the heating furnace → the sheet is heated Controlled and monitored heating in the furnace → After the sheet is heated, the sheet is picked up by the automatic device → from the heating furnace to the hot forming press → hydraulic press, cooling system and mold work → hot stamping forming and cooling – the robot device is from the mold Cutting to conveyor belt → manual basket loading → transfer → laser or mechanical cutting → finished product (see Figure 4).
(2) Hot stamping automatic stamping line key equipment Hot stamping automatic stamping line equipment includes: controllable atmosphere heat treatment heating furnace, loading and unloading robot equipment, CNC high-strength parts thermoforming hydraulic press (including temperature monitoring system, hydraulic system, cooling system) , mold change system, control system, sheet metal removal system, component transmission system, safety protection, nitrogen generator, emergency generator set, mold cooling unit, etc. (see Figure 5).
The demolition system consists of a fast robot and universal end picker, and two magazines. The demolition system enables continuous production and separates the dip into a single layer of material. The production requirements can meet the 500mm high material stacking and unloading, can meet the final 3.0mm sheet material unpacking, transfer the separated sheet material to the marking station for production number, and can carry out double-layer (or multi-layer) material inspection. The high-speed loading automation system passes the sheet through the conveyor belt to the inlet of the controlled atmosphere heat treatment furnace.
The high-speed feeding robot device is responsible for quickly taking out the heated sheet material from the centering table of the furnace, and feeding the heated sheet material into the press in the shortest time and distance. The high-speed blanking manipulator device is responsible for accurately and quickly removing the formed workpiece from the press and placing it on the tail-end transmission system. The feeding robot device has a reciprocating action time of no more than 5 s.
The controlled atmosphere heat treatment heating furnace is filled with protective gas, and the sheet is heated from normal temperature to 930 ° C (normal value is 930 ° C, maximum 940 ° C), and maintained for a period of time, real-time dynamic monitoring system for temperature unqualified board Material is automatically alarmed. The tail discharge has a centering system to accurately position the heated sheet.
The thermoforming press adopts an open structure, the forming force is controllable, the slider speed and stroke are adjustable, and the ability to hold the mold is closed after the mold is closed, and the pressure and time should be controlled. A temperature monitoring system is required, and the surface temperature of the workpiece is detected by an infrared technology non-contact temperature sensor. The measurement accuracy should be kept at ±5 °C, and the alarm can be automatically performed.
3. Hot stamping quality requirements and testing methods
(1) The hot stamping quality requirements are detailed in the attached table.
(2) Test method Mechanical properties Sample sampling method, according to Q/CCJT148-2009 metal tensile specimen sampling standard; mechanical properties testing method according to GB/T228.1-2010 metal material tensile test part 1 : Room temperature test method. The metallographic test method is based on the metal microstructure inspection method of GB/T13298-1991, and the test results are based on the metallographic structure test (see Figure 6).
4. Conclusion
Thermoforming technology is more and more widely used in automobile enterprises, but domestic manufacturing technology is not very mature. Various auto companies are constantly researching and exploring, and shortening foreign thermoforming technology by introducing foreign advanced thermoforming equipment and hot forming molds. The gap has made progress in stages, but how to ensure the rationalization and economical production of hot forming molds and solve the problem of mass production process will be the next research direction for domestic auto companies.
About the author: Zhao Shichao, Yang Shaofeng, Liu Yansheng, Technology Center of Great Wall Motor Co., Ltd. / Hebei Automotive Engineering Technology Research Center.
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