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[分享]stamping process

Stamping Processes

Conventional Stamping. Simply put, stamping is a method of cold-working sheet metal to a prescribed size and shape by means of a die and a press. The die determines the size and shape of the completed workpiece. The press provides the force needed to effect the change.
Each die is specially constructed for the operation to be performed and is not suitable for other operations. The die is in two halves, between which the sheet metal is placed. When the two halves of the die are brought together, the operation is performed. Normally, the upper half of the die is the punch (the smaller member), and the lower half is the die (the larger member). When the two die halves are brought together, the punch enters the die.
The die, or matrix, has the desired opening built into it by various methods. The punch bas a shape which corresponds to that of the die but is smaller by an amount determined by the required "punch and die clearance," which in turn is determined by the type and thickness of the material and the operation to be performed.
figure 1
The two parts are mounted in a die set, or subpress, the die (in a simple blankthrough die) being mounted on the base and the punch on the upper shoe. The use of a die set assures proper alignment of the punch and die regardless of the condition of the press. The simplest dies are those for punching holes in a blank. The machine used to consummate these changes of shape has a stationary bed, or bolster, upon which the die portion is clamped.
A guided slide, or ram, which bas the punch portion clamped to it, moves up and down perpendicularly to the bed. The motion and force of the ram are provided by a crankshaft, eccentric, or other mechanical means. Hydraulically actuated presses are also employed. Figure 1 shows a typical crankshaft-type press.The stamping of sheet metal involves cutting or shearing, bending or forming, and drawing or deep-drawing operations. Cutting around the entire periphery of a part is called "blanking." Cutting holes in a workpiece is called "punching" or "piercing." A description of each category follows:
Blanking (下料, 落料, 冲切, 冲裁, 冲压or Piercing (戳穿, 突破, 冲孔, 穿轧):
Blanking or piercing to a contour (轮廓,周线,等高线) progresses through three stages (see Fig. 2):
1. plastic deformation,
2. penetration, and
3. Fracture. n.破裂, 骨折v.(使)破碎, (使)破裂

figure 2
In stage 1 the punch makes contact with the material, and pressure begins to be exerted until the elastic limit of the stock is exceeded and plastic deformation commences(v.开始,着手). In stage 2 the continuing pressure causes the punch to penetrate the stock, thereby displacing the blank or slug(v.嵌入) into the die opening, the displacement equaling the amount of penetration. In stage 3 the fracturing occurs. At this point, the blank or slug is separated from the parent stock.
Generally, the straight or cut band of the material will average approximately one- third of the stock thickness. This, of course, depends upon the material's brittleness(n.脆性). The punch could penetrate anywhere from 15 to 40 percent of the thickness before fracture occurs.
Forming:
In forming, the operation produces one or more plane surfaces which are at an angle to the original or flat plane of the blank. Any change in the shape of the blank, no matter how small, is classified as forming.
The material to be formed must have the proper ductility(n.延展性,柔顺性,顺从) to ensure its retention of deformation in tension without rupture(n/v.破裂,断裂). A schematic(示意性) of the bending action in a pad die is shown in Fig. 3.

figure 3
Drawing:
When a part is designed so that no seams or other mechanical joints are permissible, it can be described as a "hollow" or "cup-shaped" body. The "body" is manufactured, by using a flat blank, with the drawing method. Drawing probably ranks second in importance to the cutting operations of press-metal working.
Generally speaking, drawing operations require the use of a triple-acting toggle(肘节, 套环, 肘环套接,扭力臂, 曲拐,单向螺杆; 钮扣,拉钳) joint or drawing press. Two or more draws (with necessary heat treatment between draws, depending upon the material used) are required when the depth of the cup-shaped area is more than three-fourths of its diameter or width. In a simplified description, blanks are drawn by first confining(限制的; 拘束的; 狭窄的; 偏狭的) them between the die and a pressure pad (this is where the triple-acting press comes in); then, as the press continues its cycle, the punch (which bas the reverse shape of the die but is smaller by stock thickness) forces the material to flow inwardly from between the two confining surfaces.
The pressure applied between the die and the pressure pad during the entire press cycle must be such that the blank is kept from wrinkling(起皱现象, 起皱纹). Wrinkles will prevent obtaining a smooth cup, and the possibility of tearing the cup increases. The pressure required is mainly the result of experience plus trial and error. For a schematic view of a typical drawing operation, see Fig. 4.

figure 4
In addition to the three basic methods, conventional stamping includes shaving, trimming, embossing, coining, and swaging.
Shaving:
Shaving is a secondary operation after blanking or piercing. It produces a smooth edge on the workpiece instead of the breakaway edge shown in Fig. 2.
This is accomplished by removing only a small amount of stock from the edge of the part. The deformed, fractured portion of the edge is removed, leaving chip-like scrap material and a relatively square and unfractured edge on the part.
Trimming(修剪, 修理; 切屑, 碎料):
This method is similar to blanking except that it occurs after forming, drawing, or other operations when extra metal is left in the part for holding or locating purposes or as a stock allowance. The removal of this extra stock is called trimming.
(TO BE CON'D)
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