Cold extrusion forming technology

Cold extrusion is an important part of precision plastic volume forming technology. Cold extrusion refers to the cold metal blank into the mold cavity, under strong pressure and velocity, forcing the metal extrusion from the cavity, so as to obtain the required shape and size of the extrusion and has certain mechanical properties. It is clear that the cold extrusion process is to rely on the mold to control the metal flow, by a large number of metal volume transfer to the forming part of the.

Cold extrusion technology is a kind of high precision, high efficiency, high quality and low cost advanced production technology, widely used in small and medium scale production of forgings. Compared with hot forging, warm forging process, the material can be 50% ~ 30%, energy saving 40% ~ 80% and can improve the quality of forgings, improve the working environment.

At present, the cold extrusion technology has been widely used in fasteners, machinery, instruments, electrical appliances, light industry, aerospace, marine, military and other industries, has become one of the important means of processing technology indispensable metal plastic bulk forming. After World War II, the cold extrusion technology has been widely used in the development of foreign automobile, motorcycle, household appliances and other industries in developed countries, and the emergence of new extrusion materials, mold steel and large tonnage presses will expand its development space. Japan in 80s claimed that its car production in the forging process of the production of parts, there are 30% ~ 40% is the production of cold extrusion process. With the continuous improvement of the technical requirements of the product of the progress of science and technology and automobile, motorcycle, household appliances and other industries, the production of cold extrusion technology has gradually become the development direction of small and medium-sized forging production. Compared with other processing technology, cold extrusion has the following advantages:

1) saving raw materials. Cold extrusion is the use of plastic deformation of metal to make the desired shape of the parts, which can greatly reduce the cutting process, improve the utilization of materials. The material utilization ratio of cold extrusion can reach more than 80%.

2) improve labor productivity. Cold extrusion process instead of machining parts, the productivity can be increased several times, several times, and even hundreds of times.

3) the ideal surface roughness and dimensional accuracy can be obtained. The precision of parts can reach IT7 ~ IT8, the surface roughness can reach R0.2 ~ R0.6. Therefore, the parts used in cold extrusion processing is generally very little machining, only in the requirements of special high precision grinding.

4) improve the mechanical properties of parts. After cold extrusion, the metal cold work hardening, as well as the formation of a reasonable distribution of fiber lines within the parts, so that the strength of parts is much higher than the strength of raw materials. In addition, the reasonable cold extrusion technology can make the surface of the parts to form compressive stress and improve fatigue strength. Therefore, some of the original parts heat treatment can save heat treatment process for cold extrusion process, some parts of the original need made of high strength steel, cold extrusion process after available low strength steel for use.

5) can be processed in the shape of complex, difficult to machining parts. Such as profiled, complex inner, and the surface of the invisible tank etc..

6) reduce the cost of parts. The cold extrusion technology has the advantages of saving raw materials, improving the productivity, reducing the amount of machining of parts, and the poor quality materials, which can be used to reduce the cost of parts.

There are some difficulties in the application of cold extrusion technology:

1) on the high requirements of the mold. Cold extrusion blank in the die by three to stress and the deformation resistance increases significantly, which makes the mold under stress than the general stamping, cold extrusion die steel, stress often up to 2000MPa ~ 2500MPa. For example, a diameter of 38mm, thickness of 5.6mm, high 100mm low carbon steel cup as an example, using the method of drawing processing, the maximum deformation force is only 17T, and adopting cold extrusion processing method, is the deformation force of 132t, then the role in more than 2300MPa of cold extrusion punch on the pressure unit. In addition to the needs of the mold with high strength, but also need to have enough impact toughness and wear resistance. In addition, the metal blank in the mold strong plastic deformation, will make the mold temperature to 250 degrees Celsius to 300 degrees Celsius, thus, the mold material needs certain tempering stability. Due to the above situation, the life of the cold extrusion die is much lower than that of the punch die.

2) press with large tonnage. Due to the large deformation of the cold extrusion force, the need for hundreds of tons or even a few thousand tons of press.

3) due to the high cost of cold extrusion die, the parts are generally only suitable for mass production. It is suitable for the minimum volume is 100 thousand ~ 5 pieces.

4) surface treatment before extrusion. This not only increases the working process, it is necessary to occupy a larger production area, and it is difficult to realize the automation of production.

5) should not be used for high strength materials processing.

6) the plastic and impact toughness of the cold extruded parts becomes poor, and the residual stress of the parts is large, which can cause the reduction of the deformation and corrosion resistance of the parts (stress corrosion resistance).