Recognize the Structure of Stamping Die of Hardware Stamping Die

The punching die is the die used in the punching process. There are many structure types of blanking dies, and for the convenience of research, blanking dies can be classified according to different characteristics. 

1.according to the nature of the process can be divided into drop die, punching die, cutting die, cutting die, cutting die, etc.;

2.The process combination can be divided into single process die, compound die, and progressive die.

3.according to the guideway of the upper and lower die, it can be divided into open die without a guide and guide plate die, guide column die, guide cylinder die, etc.

4.according to the material of convex and concave dies, they can be divided into carbide dies, steel dies, zinc-based alloy dies, polyurethane dies, etc.

5. The structure and arrangement of the convex and concave dies can be divided into the integral die and inserted die, front-mounted die, and reverse-mounted die. 

6.According to the degree of automation, it can be divided into manual, semi-automatic, and automatic die. 

There are more classification methods, and the above classification methods reflect the different characteristics of the mold structure from different angles. In the following, we will analyze the structure and characteristics of various blanking dies in process combination. 

Single Process Punching Die

Single-process blanking dies to refer to the blanking dies that complete only one punching process in one press stroke, such as drop dies, punching dies, cutting dies, notching dies, edge-cutting dies, etc. 

Drop die

There are three common forms of drop dies:

1) Open-type unguided drop die, characterized by unguided upper and lower die, simple structure, easy manufacturing, and the punching clearance is determined by the guiding accuracy of the punch slider. It can be used to punch the edge residue. It is commonly used to produce small batch punching parts with thick material and low precision requirements. 

2)The guide plate type drop die has a gap fit of H7/h6 between the convex die and the guide plate (a fixed discharge plate), which is smaller than the blanking gap. The die is not allowed to leave the guide plate during the return stroke to ensure the guiding effect of the die. Compared with the open die, it has higher precision and longer die life. Still, it is more complicated to manufacture and is often used for simple stamping parts with material thickness greater than 0.3mm (Figure 1).

 

1-lower die holder;2-pin;3-guide plate;4-pin;5-stall peg;6-bump die;7- screw;8 – upper die holder; 9 – pin; 10 – pad; 11 – die fixing plate; 12 – screw; 13 – guide plate; 14 – concave die; 15 -screw

Fig. 1 Guide plate type drop die

3.Fig. 2 is a top pop-up drop die with a guide pillar. The upper and lower dies are guided by a guide pillar and guide bush, so the clearance is easy to guarantee. This die adopts the structure of pop-up unloading and pop-up ejecting, so the material is pressed up and down to complete the separation when stamping. The deformation of the parts is small, and the flatness is high. This structure is widely used for metal parts with small material thickness and flatness requirements and non-metal parts that can be easily layered. 

 

1-Upper die holder; 2-Discharge spring; 3-Discharge screw; 4-Screw; 5-Die handle; 6-Anti-rotation pin; 7-Pin; 8-Pad plate; 9-Die fixing plate; 10-Drop die; 11-Discharge plate; 12-Drop concave die.

13-Top plate; 14-Lower die holder; 15-Top bar; 16-Plate; 17-Bolt; 18-Fixed stopper pin; 19-Column; 20-Guide sleeve; 21-Nut; 22-Rubber

Fig. 2 Guide pillar type drop die

Punching die

The structure of the punching die is similar to the general drop die. However, the punching die has its characteristics, especially for small holes; the strength and stiffness of the die must be considered, as well as the structure of the quick change die. When punching holes in the sidewalls of formed parts, the conversion mechanism for the horizontal movement of the die should be designed. 

1.Side hole punching die

Figure 3 shows punching a hole in the side wall of a formed part. Figure a) shows the cantilevered concave die structure, which can be used for punching holes and slots in the side wall of cylindrical parts. The blank is inserted into the concave die body 3, and the axial position is controlled by the positioning ring 7. This structure allows the punching of multiple holes in the side wall. The structure considers the indexing and positioning mechanism in the case of multiple holes. In Fig. b), the sliding block 4 is pushed by the inclined wedge 1 fixed to the upper die, and the convex die 5 is moved horizontally to complete the punching, grooving, and notching of the side wall of the cylindrical or U-shaped parts.

Fig. 3 Sidewall punching die.

The return movement of the wedge is done by rubber or spring. The working angle α of the wedge is 40° to 45°. 40° of the wedge slider mechanism has the highest mechanical efficiency, and at 45°, the slider moves the same distance as the stroke of the wedge. For punching parts requiring larger punching force, α can be 35° to increase the horizontal thrust. The convex die of this structure is often symmetrically arranged and is most suitable for punching symmetrical holes in the wall. 

 Small hole punching die (Fig. 4)

The workpiece punched by this die is shown in the upper right corner of the figure. The thickness of the workpiece is 4 mm, and the minimum hole diameter is 05 t. The die structure is designed to shorten the length of the die to prevent it from bending and breaking during the punching process. This structure is more tolerable and has a longer die life. This die uses an impact block 5 to impact the die for punching work. The small die is guided by a small platen 7 and two small guide pillars 6. When the upper die moves down, the large platen 8 and the small platen 7 are pressed against the workpiece. The upper end of the small die 2, 3, and 4, exposing the upper plane of the small platen 7, the upper die compresses the spring and continues to move down, and the impact block 5 impacts the die 2, 3, and 4 to punch the workpiece. The unloading work is done by the big platen 8. The hole of the concave die of the thick material punching small hole die must be open to prevent the waste from blocking and damaging the convex die. The punched parts are positioned on the concave die by positioning plates 9 and 1, and the back side press 10 keeps the punched parts close to the positioning surface.

Fig. 4 Small hole punching die with ultra-short convex die

Compound punching die

Fig. 5 Basic structure of the compound die.

A die that performs several punching processes simultaneously in the same part of the die during one working stroke of the press is called a compound punching die. The difficulty of designing a compound die is how to reasonably arrange several pairs of convex and concave dies in the same working position. 

Figure 5 shows the basic structure of a drop punch compound dies. On one side of the die is a drop die with a punching die in the middle, and on the other is a convex and concave die, with the shape of the drop die, and the inner hole of the punching die. If the drop die is mounted on the upper die, it is called a reverse compound die; on the other hand, it is called a soft compound die. 

The characteristics of the compound die are: compact structure, high productivity, and high accuracy of the part, especially the position of the hole to the shape of the part is easy to ensure. On the other hand, the complex structure of compound die requires high precision of mold parts and high precision of mold assembly. 

(a) Flip-fit composite mold

1 – convex die; 2 – concave die; 3 – upper die fixing plate; 4, 16 – pad; 5 – upper template; 6 – die handle; 7 – push rod 

8-push block; 9-push plate; 10-piece block; 11, 18-moving stopper pin; 12-fixed stopper pin; 13-unloading plate

14 – convex and concave die; 15 – lower die fixing plate; 17 – lower template; 19 – spring.

Fig. 6 Gasket compound punching die.

Fig. 6 shows a flip-flop die for punching washers. Drop die 2 is in the upper die, piece 1 is the punching die, and piece 14 is in the convex and concave die. The flip compound dies generally use a rigid push device to push out the part stuck in the concave die. The rigid pushing device consists of push rod 7, push block 8, and push block 9 to push out the parts. The scrap is pushed out directly from the convex die through the convex and concave die bore. If a straight edge is used in the hole of the convex and concave die, there will be accumulated scrap in the die, and the expansion force will be high, which may lead to an expansion crack when the wall thickness of the convex and concave die is thin. The minimum wall thickness of the concave die of the inverted composite die can be found in the relevant design information. 

With the rigid pushing of the inverted compound die, the strips are not punched in a pressed state. Thus the straightness of the parts is not high. It is suitable for sheet material with more than 0.3mm thickness. If the upper die is equipped with elastic elements and elastic pushers, it is possible to punch softer parts with a thickness of less than 0.3mm and higher straightness. 

Compound die with smooth loading

Fig.7 Compound punching die.

Fig. 7 shows the structure of a smooth-loading compound dies. It is characterized by the fact that the punching waste can be pushed out from the convex and concave die so that the waste will not accumulate in the hole, and the convex and concave die will have a small cracking force so that the wall thickness can be smaller than the minimum wall thickness of the inverted composite die. 

 

Progressive punching die

A progressive die (also called a continuous die or jumping die) is a die that is used to complete multiple punching processes in several different positions of the die in one stroke. The whole part is formed step by step in a progressive process. Progressive forming is a process concentration method that allows multiple processes, such as edge cutting, notching, grooving, punching, plastic forming, and dropping, to be completed on one die. The progressive die can be divided into the ordinary progressive die and multi-station precision progressive die. The multi-station precision progressive die will be discussed in the following chapters. 

Since the progressive die is used for stamping, the punched parts are formed in several different positions in sequence, so the accuracy of the relative position of the hole and the shape of the punched part must be strictly controlled by the feeding step. For this reason, there are two basic types of progressive dies: those with guide pins and those with side edges. 

(a) The progressive die with guide pins

1-Die shank; 2-Screw; 3-Punching die; 4-Falling die; 5-Guiding pin; 6-Fixing pin 6-Fixed gear pin; 7-Starting gear pin

Fig. 8: Punching die with a spacing guide pin

Fig. 8 shows a progressive die for punching a hole with a guide pin. A guide plate guides the upper and lower dies. The distance between the punching die 3 and the drop dies 4 is the feeding step A. The material is initially positioned by the fixed stopper pin 6 during feeding and is precisely positioned by the two guide pins 5 mounted on the drop die. The fit between the guide pin and the drop die is H7/r6, and the connection should ensure easy assembly and disassembly when resharpening the die. The shape of the head of the guiding pin should be conducive to inserting the punched hole during guiding, and it should have a slight clearance with the hole. An initial stopper is often used to ensure the correct spacing of the first part in the progressive die with guide pins. It is installed in the middle of the guide plate under the guide plate. When punching the first part of the strip, the first two holes are punched by pushing the starting stopper pin 7 by hand so that it sticks out from the guide plate against the front end of the strip. Subsequent punches are initially positioned by the fixed stopper pin 6, which controls the feed step. 

The structure is simple, with a guide pin. When the distance between the two positioning holes is larger, the positioning is more accurate. However, its use is limited by certain restrictions. When the sheet is too thin (generally t<0.3mm) or soft material, the hole edge may be deformed when guiding, so it is not suitable. 

The use of a side knife fixed distance of the progressive die

Fig. 9 Double-side blade punching and falling progressive die.

Fig. 9 shows the progressive die with double-side blade pitching for punching the contact ring. Compared with Fig. 2-38, it is characterized by replacing the initial stopper pin, stopper pins, and guide pins with side blades 2. The fixed discharging plate is replaced by the pop-up guide plate 7. This die is arranged diagonally with double side edges at the front and rear so that all parts of the material tail can be punched down. The pop-up unloading plate 7 is mounted on the upper die and connected to the upper die base by the unloading screw 6. Its function is as follows: when the upper die is lowered, and the convex die is punched, the spring 11 (which can be replaced by rubber) is compressed, and the material is pressed; when the convex die is returned, the spring returns to push the unloading plate to unload the material.

Figure 10 shows the spring-loaded guide plate progressive die. The characteristics of this type of die are each convex die (such as piece 7) and the fixed plate 6 into a clearance fit (regular column die mostly a transition fit ), easy loading, unloading, and replacement of the convex die; convex die guided by the pop-up guide plate, high precision guidance; pop-up guide plate 2 by the installation of the lower die base 14 on the guide column 1 and 10 guides, guide plate by six unloading screws 5 and the upper die connection so that it can eliminate the impact of the guide error of the press on the mold, mold Long life and good quality of parts. 

1 – guide pillar; 2 – pop-up guide plate; 3 – guide sleeve; 4 – guide plate insert; 5 – unloading screw; 6 – die fixing

plate; 7 – convex die; 8 – upper die holder 9 – restriction column; 10 – guide pillar; 11 – guide sleeve; 12 – guide plate

13 – concave die; 14 – lower die holder; 15 – side edge block

 

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