Professor Hu Yamin, a professor and industry expert at Chongqing University of Technology
Multi-station forming
The basic process of stamping processing means that the metal material is deformed in the mold in one stroke of the press. With the development of productivity, the simple stamping production process often fails to meet the production needs.
In the actual process of stamping production, for different purposes and requirements, or to increase productivity, or to shorten the production cycle, or to save raw materials and save energy, or to improve the accuracy and quality of parts, different or the same basic process of stamping The combination is integrated and completed in one stamping stroke or multiple stamping strokes, that is, a plurality of various deformation zones are combined, and all the stamping deformations are realized in one cycle or multiple cycles of the slider operation during operation, which is a multi-station Forming.
Multi-station forming has two types of composite forming and progressive forming.
Composite forming is to complete more than two basic punching processes at the same coordinate position of the die plane in one stroke of the press, that is, to complete a basic stamping process at different height positions.
Composite forming includes: 1 separation process compounding, such as one-time forming to complete blanking (or fine blanking) - punching, trimming - punching, punching - refurbishing, fine blanking - extrusion (semi-punching), etc. . 2 The composite of the forming process, such as one-time forming to complete the drawing - flanging, drawing - bulging, forward and reverse drawing, positive and negative bending. 3 Separation and forming process compounding, such as one-shot forming blanking-drawing, cutting-drawing-bulging, blanking-draw-punching-flanging, etc. In this composite forming process, the basic process of 2 to 4 stamping processes can be completed, which is called a two-station composite die, a three-station composite die, and a four-station composite die.
Progressive forming is a mold that has several or more basic stamping processes in two strokes before and after the stroke of the press in a single stroke of the press slide, generally up to more than 10 passes. It is characterized by feeding one step per billet blank and completing the production process at the end of the last stroke.
The development direction of multi-station forming
Modern composite forming has achieved a single stroke to achieve more basic process forming than the four-station, and an eight-station composite mold has been successfully developed in Japan. Figure 1 shows the longitudinal progressive action of the eight-station composite mold structure. Multi-station composite forming enables precision forming of high concentric products. After the outer peripheral deep drawing, it is also possible to perform thinning drawing and tooth forming into equal volume forming.
Fig.1 Schematic diagram of the longitudinal progressive action of the eight-station composite mold structure
Japan's Ministry of Economy, Trade and Industry's 2007 Strategic Basic Technology Advanced Research Support Project has been successfully developed for low-cost eight-cylinder servo control (including two auxiliary cylinders) for multi-variety and small-volume production. The name is a One Shot Forming Press, model number MMF1000-MM332. Among the three digits after "-MM", the first number indicates the number of upper cylinders, the second number indicates the number of lower cylinders, and the third number indicates the number of auxiliary cylinders.
The modern progressive forming die has been able to achieve more than 20 basic process forming at one time. For example, the progressive die for producing brass connector terminals is 24 steps, and the progressive die for producing the spring ball for the mouse ball is 30 steps, and the plug is produced. The progressive die of the reed is 38 steps. The plug reed is shown in Figure 2.
Fine-punching multi-station forming of 3D complex parts
More and more three-dimensional complex parts need to adopt multi-station forming process, that is, in the fine punching process, through the progressive die (multi-station forming die), or with bending, deep drawing, bending, flanging, countersinking The sheet material is finely stamped and formed into a composite punching-sheet forming composite forming. Or combined with the volume forming of upsetting, pressing, embossing, crushing, shearing, extrusion, etc. into a fine-punching-volume forming composite forming, the product object is developed from equal-thickness stamping parts to unequal thickness. Stamping parts, from two-dimensional flat stamping parts to three-dimensional precision punching parts, such as outer chain plates and automobile gearbox gears, helical gears, oil pump sprocket, Z-shaped connecting rod (see Figure 3).
Figure 3 (a) Car Z-shaped connecting rod
Figure 3 (b) Gearbox helical gear disc gear
Figure 3 (c) Fine punching
Because the stamping itself is sheet metal forming, we refer to the fine punching-sheet stamping forming composite forming as the fine punching composite forming; the fine punching-volume forming composite forming is referred to as fine punching-extrusion forming.
Fine punching—Extrusion The workpiece and the strip are always kept in one piece during the blanking process. That is, the thickness of the punch entering the material is not enough to cause cracks in the sheet, and the blind hole shape and the cross-sectional shape of the punch are identical or similar. For example, the balance weight of the crankshaft (see Figure 4a) is a φ30mm, 11.5mm deep guide ring on a 8.5mm QSTE420TM steel plate. In this case, the material formation is thickened from thin to partially 11.5 mm thick. The fine forming process is divided into three steps (see Figure 4b): the first step is shown in Figure 4b. After the upper die contacts the steel plate, the upper punch presses the blank and presses the material into the lower model cavity, which is fine punching. - extrusion, or extrusion - fine forming. The center of the secondary punch has a pointed cone that presses the material from the center outward. At other gaps in the upper or lower mold, the workpiece must be firmly clamped, which not only ensures that the material does not extrude from this particular area, but also strengthens the material passing through the walls of the concave mold cavity. The second step is as shown in Figure 4b, punching the center hole. The third step is as shown in the lower part of Fig. 4b. The metal material entering the die-forming die cavity is press-formed to fill the corners of the concave mold cavity which are difficult to fill.
(a) Crankshaft balance weight
(b) Balanced hub body forming process
Figure 4
With this fine-extrusion-compression molding, 1350 workpieces per hour can be produced, which is equivalent to 25 workpieces per minute. The disadvantage of this process is that it requires a large forming force during the forming process and requires a large fine punching machine.
Generalized multi-station forming
The generalized multi-station forming also has multi-station cold and hot volume forming, such as multi-station automatic cold heading for producing screws and nuts. A multi-station process such as punching, upsetting, squeezing and necking is carried out in several forming dies by an automatic upsetting machine. The number of forming stations (excluding the cutting station) is generally 3 to 4, and now there are automatic cold dies for up to 5 stations or more, which can be used to form hex nuts or particularly complex medium carbon steel parts. This automatic cold heading machine not only has a large number of forming stations, but also can be inverted by 180° during the transfer of the blank between the forming stations, and can process more complicated high-quality parts with sharp edges and corners.
Generally, only one of the simplest shape parts can be obtained in one process, such as cup parts, lead rods, etc. Most of the parts are more complicated in shape and require several forming.
The factors affecting the accuracy of the part are firstly the accuracy of the raw materials, and the raw materials should be cold drawn materials. When producing extremely precise parts on an automatic cold heading machine, the roundness should be limited to the diameter tolerance. If the diameter of the material is larger than the specified size, the upset or head of the part may be creased or burr formed; if it is smaller than the specified size, the head will be filled with dissatisfaction, and the corners or upsets are not clear.
The multi-station automatic cold heading machine uses the original blank for holding 6~7m or weighing 900~1000kg. The blank needs to be shaped before extrusion. Generally, the blank is sent to the roughing and shaping station immediately after cutting, and the blank which meets the process requirements can be obtained by shaping, so that the forming force of the next station is reduced. When cold forming is performed on an automatic cold heading machine, it is generally necessary to perform a phosphating saponification treatment on a long bar or coil.
The generalized fine-punching composite forming process can also be extended to different types of equipment. For example, the bar billet is used, and then the precision forging-fine punching composite forming process is used; the sheet blanking is performed, and then the precision punching-finishing forging composite forming process is performed. There are also many parts that are machined from cast and forged blanks. After the cutting process, they are assembled by riveting and welding.
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