Cold rolling is a processing method in which a metal blank is placed in a cold rolling equipment, and a pressure is applied to the blank through a convex die fixed on a press at room temperature, so that the metal blank undergoes plastic deformation to produce a part.
First, the fundamental type
1. Cold-rolled precision tube: When cold-rolled, the direction of metal movement is the same as that of the punch. Cold rolling can make solid and hollow pieces of various shapes.
2. Inverse cold rolled precision tube: In the case of reverse cold rolled, the movement direction of the metal is opposite to that of the punch. Back-kneading can obtain cup-shaped pieces of various shapes.
3. Composite cold-rolled precision tube: During cold-rolling, some of the blanks move in the same direction as the punches, while the other moves in the opposite direction to the punches. Compound kneading can produce various cup, rod and tube parts.
4. Radial cold-rolled precision tube; during cold-rolling, the direction of metal movement is straight with the direction of the punch movement. Radial kneading can be divided into centrifugal kneading and centrifugal kneading. Radial kneading is used to make helical gears, keyboards and other parts.
5. Forging precision tube: When pressing, the metal blank moves radially outward. Pressing is used to make shaft parts with flanges or cup-shaped parts with flanges.
Positive cold-rolling, reverse cold-rolling and composite cold-rolling are the three most widely used cold-rolling precision tube skills. Their metal movement direction is parallel to the axis of the punch. Therefore, many materials also call these three methods as axial kneading. As mentioned before, axial kneading can produce various solid and hollow parts, such as ball pins, bobbin cases, cartridge cases, and the like. Radial cold rolling has only been developed in the past ten years, and it is mainly used for dials of communication equipment and bicycle keyboards.
The above are several fundamental cold-rolled precision tube deformation methods. Following the development of cold-rolled precision tube skills, sometimes cold volume die forging is also classified as cold kneading.
Cold-rolled precision tubes are widely used in the electromechanical production of cars, tractors, bearings, telecommunications equipment, and exteriors, and are still widely used in light industries such as bicycles and sewing machines, as well as in the national defense industry system. This is because it has significant advantages.
Second, the characteristics of cold-rolling skills
1 Cold-rolled precision pipe fittings with precise dimensions and smooth appearance: Nowadays, the cold-rolled parts developed in China generally have a scale accuracy of 8-9, and if the ambition is smooth, its accuracy is second only to the polished surface. Therefore, the parts produced by the cold rolling method generally do not require reprocessing, and a small amount only needs finishing (grinding).
2 Save the original data: The utilization rate of cold rolled precision pipe fittings data can generally reach more than 80%. For example, the utilization rate of the piston pin machining data of Jiefang brand car is 43.3%, and the utilization rate of the data is increased to 92% when cold kneading is used. From 27.8% to 64%. It can be seen that the use of cold kneading methods to produce mechanical parts can save a lot of steel and non-ferrous metal materials.
3 High yield: The power of mechanical parts produced by cold-rolled precision tubes is very high, especially for large-volume parts. The cold kneading method can produce several times, dozens of times, or even hundreds of times compared with cutting. Times. For example, the cold kneading method for passenger car piston pins is 3.2 times faster than that of cutting, and now the cold rolling kneading piston pin driver is used to further improve the yield. The yield of a cold kneading active machine is equivalent to that of 100 ordinary lathes or 10 four-axis active lathes.
4 It can process parts with complicated shapes: such as special sections, internal teeth, special holes and blind holes. These parts are difficult to complete by other processing methods, but cold kneading is very convenient.
5 Cold-rolled precision pipe fittings have high strength, good rigidity and light weight: because of cold kneading, cold working strengthening characteristics of metal materials are used for cold kneading, that is, the metal blank is under three-dimensional compressive stress during kneading. And it has continuous fiber flow direction, so the strength of the product has been greatly improved. In this way, high-intensity data can be replaced by low-intensity data. For example, in the past, 20Cr steel was used to produce Jiefang brand piston pins through cutting. Now, 20 # steel is used to produce piston pins through cold rolling. After measuring the various functions by function, the cold rolling method is higher than the cutting method to produce piston pins.
This shows that cold-rolled precision tube processing piston pins can replace 20Cr steel with 20 # steel.
From the above characteristics, it can be seen that the cold rolling skills have outstanding advantages compared with various current processing methods. This opens up a broad road for cold rolling to replace cutting, forging, forging and drawing skills to make machine parts.
III. Unfolding of cold-rolled precision tube skills
The early stage of cold rolled precision tube skills is very slow. For a long time, only a few soft metals (lead and tin) have been kneaded. It was not until the end of the 19th century and the beginning of the 20th century that it began to knead harder non-ferrous metals (zinc, aluminum, copper, brass, etc.). As for cold rolling of steel, because of the great pressure required during cold rolling, kneading could not be solved at that time. Questions about the mold materials used for pinching steel, suitable smoothing agents, and large tonnage presses, etc., have long thought that cold-rolled steel pipes are difficult or even impossible.
In 1906, the British T.W. coslett discovered that treating finished steel products with phosphate was a more ambitious method of rust prevention, but had complicated procedures and poor economic benefits, so it was not widely used. However, the appearance of this rust prevention method has greatly stimulated the enthusiasm of everyone to discuss more simple and useful new methods. Later, it took only two minutes to perform zinc phosphate antirust treatment on steel blanks with active continuous equipment. The surface of the zinc phosphate-treated blank is attached with a fat smoothing agent or a sodium soap film, and this film is not easy to fall. When kneading this blank, the pressure is small. This discovery led everyone to find an ambitious steel surface treatment method-phosphating saponification method.
The appearance of the appearance of the saponification treatment of the steel billet makes the kneading of the steel possible. In 1934, the Germans used the phosphating saponification method to successfully cold extrude steel pipes. During the Second World War, the Germans required many cartridge cases, and at the time, brass was in short supply. Therefore, the Germans secretly kneaded the steel cartridges for cold production. Later, they used alloy tool steel as the mold material and successfully squeezed them with cold kneading. Produced a large number of steel bullet shell parts.
In the aftermath of World War II, the Americans stole all the information about German cold kneading of steel, began to use cold kneading to secretly produce ordnance in the United States, and opened many military factories producing steel shells and projectiles.
The cold-rolled steel tube was formally used in the civilian industry only in 1947.
The United States announced in 1949 the test data for the mechanical function of various steels after cold rolling. In 1950 and 1953, Germany released the basic cold rolling skills data and cold rolling force test results of steel.
In 1957, Japan introduced a special cold rolling mill and began to use cold rolling skills in precision instruments and appearance. Japan saw that this new skill had obvious economic benefits, and soon used this skill to make cars and electrical parts. Now it has become the primary processing technique in a wide range of industrial sectors.
In China, the cold rolling process before the founding of the PRC was very backward. At that time, only a small number of factories used non-ferrous metal pipes such as lead and tin or wire cold rolling and pipes.
After Wu Jianguo, cold kneading skills were unfolded. Cold rolling of aluminum, copper and its alloys began in the 1950s; cold rolling of ferrous metals has been used in production in the 1960s. Ten years of catastrophe has greatly affected the development of cold kneading skills. From 1978 onwards, under the guidance of the huge policy of "single side and self-sufficiency", cold kneading skills were rapidly developed. In recent years, with the development of reform and opening up policies, with the vigorous development of national industrial production and scientific skills, cold kneading skills have also been rapidly developed.
At the end of the 1970s, many universities, seminars and factories in China carried out experimental research on cold kneading skills, announced many valuable papers, and began to form a force to study and apply cold kneading skills.
Now, China has been able to cold-knead metals such as lead, tin, aluminum, copper, zinc and their alloys, low carbon steel, medium carbon steel, tool steel, low alloy steel and stainless steel, and even bearing steel, high carbon and high Aluminum alloy tool steel, high-speed steel, and the like can also be cold-kneaded with a certain amount of deformation. The produced cold-rolled parts are of various types, weighing up to 30 kilograms and as light as 1 gram. In the application of mold data, in addition to high-speed steel, bearing steel, high-carbon high-chrome alloy tool steel, many new mold steels such as CG2, 65Nb, LD, etc. have been selected. In terms of kneading skill parameter selection and mold structure planning, optimization planning and computer-aided planning and production (ie CAD / CAM) were started to make the mold structure more reasonable and the kneading skill parameters closer to practice. In terms of cold rolling equipment, China has the ability to plan and manufacture cold rolling presses of various tonnages. In addition to the use of general mechanical presses, hydraulic presses, and cold kneading machines, we also successfully used conflict presses and high-speed high-energy equipment for cold kneading and production.
The development of science has had a serious impact on cold rolling skills, specifically the impact of the use of computers in the analysis of skills, mold planning, production, and skill process control on the occurrence of cold rolling skills. China will further expand the use of this new skill. The development of cold rolling skills should start from the following aspects:
1. Expand the scale of cold rolling skills to gradually replace casting, forging, drawing and cutting within a certain scale;
2. Improve the precision and appearance quality of cold-rolled parts, and produce a few more messy shapes;
3. Expand the variety of raw materials for cold rolling, and discuss more ambitious appearance treatment and smoothing methods;
4. Further use CAD / CAM and optimization planning, improve and accelerate mold planning and production, and develop a more reasonable mold structure;
5. Find the mold information and heat treatment methods that are more suitable for cold rolling to extend the service life of the mold;
6. Further develop the research and application of new skills such as warm rolling, isothermal rolling, hydrostatic rolling and high-speed kneading;
7. Develop a multi-functional cold rolling mill suitable for cold rolling, so that blanks and parts can be safely and actively fed and discharged in order to further improve the yield.