Simple Guidance For You in Design of Blanking Dies

Estimated reading time: 27 minutes

Among the six major parts of stamping dies, many have completed standardization work. The standardization and typification of die design is an effective method to shorten the mold manufacturing cycle and simplify the mold design. It is the prerequisite for the application of mold CAD/CAM and the basis for the industrialization and modernization of molds. The State Administration of Standards has successively formulated basic standards for die, die product (parts) standards and die process quality standards for stamping dies. See the table below.

Standard type	Standard name	Standard number	Brief content
Basic standards for stamping dies	Die terms	GB/T 8845-2006	A definitive exposition is made on the types of commonly used dies, components and structural elements and functions of the parts. Each term has both Chinese and English.
	Dimensional tolerance of stamping parts	GB/T 13914-2002	Gives a more reasonable technical and economical stamping part size tolerance, shape and position tolerance
	Angle tolerance of stamping parts	GB/T 13915-2002
	Blanking gap	GB/T 16743-2010	Gives a reasonable range of blanking gap
Standards for Die Products (Parts)	Die parts	GB/T 2855，1~2-2008	Die sliding guide diagonally, middle, back side, four-corner guide post upper and lower die seat
		GB/T 2856，1~2-2008	Die rolling guide diagonal, middle, back side, four-corner guide post upper and lower die seat
		GB/T 2861，1~11-2008	Various guide posts, guide sleeves, etc.
		JB/T 7646.1~6-2008JB/T 5825~5830-2008	Die handle, round convex, concave mold, quick-change round convex mold, etc.
		JB/T 7643~7652-2008	Universal fixed plate, backing plate, small guide post, various mold handles, guide pins, side blades, guide plates, starting stopper device; steel plate sliding and rolling guide diagonally, middle, rear, on the four-corner guide post , Die seat and guide post, guide sleeve, etc.
	Die base	GJB/T 2851-2008	Sliding guide diagonal, middle, rear side, four-corner guide pillar mold base
		GJB/T 2852-2008	Rolling guide diagonal, middle, rear side, four-corner guide pillar mold base
Quality standards for die craftsmanship	Technical conditions of die	GB/T 14662-2006JB/T 8053-2008	Various mold parts manufacturing and assembly technical requirements, as well as technical requirements for mold acceptance, etc.
	Technical conditions of die base	JB/T 8050-2008JB/T 8070-2008JB/T 8071-2008	Technical requirements for mold parts manufacturing and assembly, as well as technical requirements for mold base acceptance, etc.

Work parts design

Punch

1. The structure of the circular stamping dies

Figure 1-1 shows the structure of the round punch. The punch in Figure 1-1 (a) can punch workpieces with a diameter of 1 to 8 mm, and the punch in Figure 1-1 (b)can punch workpieces with a diameter of 8 to 30 mm. The punch in Figure 1-1 (c) can make workpieces with larger diameters. The circular convex model of the national standard in Figure 1-1 (d) ~ (f). According to the national standard (JB/T5825 ~ 5829-1995), the punch material uses T10A, Cr6WV, 9Mn2V, Cr12, Cr12MoV. The heat treatment hardness of the cutting edge part is 58~60 HRC for the first two materials, 58~62 HRC for the last three materials, and the tail is to 40~50 HRC. The latest national standard for round punches is JB/T5825-5829-2008.

2. The structure of the non-circular stamping dies

When punching non-circular holes and non-circular blanking workpieces, the structure of the punch is in Figure 1-2. Figure 1-2 (a) shows the integral type, Figure 1-2 (b) shows the combined type, and Figure 1-3 (c) shows the mosaic type. In order to save high-quality materials and reduce mold costs, the base part material of punches is ordinary steel such as 45 steel, and only the working edge part is made of mold steel such as Cr12, TI0A.

3.  Fixing of the stamping dies

The punch structure consists of a working part and an installation part. People use the working part of the punch to complete the punching process. Its shape and size should be designed according to the shape and size of the punched part, and the nature and characteristics of the punching process. The installation part of the convex mold is mostly installed on the mold base after being combined with the fixed plate. The installation form of the punch mainly depends on the stress state of the punch, the limitation of installation space, relevant special requirements, its own shape and process characteristics and other factors.

4. Calculation of stamping dies length

The specific structure of the mold determines the length of the punch, considering the needs of grinding, the safety distance between the fixed plate and the unloading plate, and assembly.

Figure 1-4 (a) shows a fixed discharge plate and a guide plate. The length of the punch is calculated by the following formula.

L=h₁+h₂+h₃+h

When using elastic unloading plate, as shown in Figure 1-4 (b), the length of the punch is calculated by the following formula.

L=h₁+h₂+t+h

In the formula, L—-the length of the punch, mm;

         h₁—-Fixed plate thickness , mm;

         h₂ —-Discharge plate thickness, mm;

         h₃—-It means the guide plate thickness, mm;

t—-material thickness, mm;

h—-Increase the length. It includes the grinding amount of the punch, the depth of the punch into the female mold (0.5~1mm), the safety distance between the punch fixing plate and the discharge plate, etc., generally 10~20 mm.

After calculating the length of the punch according to the above method, the upper standard replaces the actual length of the punch.

Stamping Dies

1. The structure of the stamping dies

Figure 1-5 shows the main structure of the commonly used die for punching dies. Figure 1-5(a) shows the integral concave mold. The mold has a simple structure and good strength. It is suitable for small and medium-sized stamping parts and molds that require relatively high dimensional accuracy. In use, if the cutting edge of the concave die is partially worn or damaged, it must be replaced as a whole. At the same time, since the non-working part of the concave die also uses mold steel, the manufacturing cost is relatively high.

Figure 1-5 (b) shows the combined die, the working part and non-working part are manufactured separately. The working part is made of die steel, and the non-working part is made of ordinary materials. The mold manufacturing cost is low, and the maintenance is convenient. It is suitable for large and medium-sized stamping parts with low precision requirements.

Figure 1-5 (c) shows the mosaic die, which has the advantages of convenient processing and easy replacement of vulnerable parts, which reduces the processing difficulty of complex molds, and is suitable for punching narrow and long stamping parts with complex shapes.

2. Determining the form of the stamping dies edges

Figure 1-6 shows the main form of the straight-cylinder cutting edge of the punching die. This type of die has high strength and convenient processing. The size and clearance of the edge will not change due to grinding during stamping, and the quality of stamping parts is stable. The disadvantage is that it is not easy to eliminate blanking parts or blanking waste. Mainly used in the blanking of complex shapes or high precision workpieces with a diameter of less than 5mm.

Figure 1-5 (a), (c) shown in the concave die cutting edge is often used for composite molds with ejector devices. The cutting edge of the die shown in Figure 1-5 (b) is often used in single-process die and continuous die. The lower taper of the die is mainly to facilitate the removal of parts. In the design, it is generally 2-3″. Figure 1-6 ( d) ~(g) shows the circular concave model type listed in the national standard (JB/T8057. 3~4-1995). The recommended material for the die is T10A, Cr6WV, 9Mn2V, Cr12, and the heat treatment hardness is 58~ 62 HRC.

Figure 1-7 shows the tapered edge form of the punching die. This kind of die has poor strength. During use, the gap will increase due to the wear of the cutting edge, but because the cutting edge is tapered, the workpiece or waste is easy to discharge, and the friction and pressure of the punch on the hole wall are also small, so The life of the die can be increased. This type of die edge is mostly used for blanking parts with simple shapes and low precision requirements, and the inclination of the edge is related to the thickness of the material.

Figure 1-8 shows the convex table edge form of the blanking dies and concave die, which is suitable for punching workpieces below 0.3 mm. The quenching hardness of the die is generally 35-40 HRC, and the gap can be adjusted by hammering the inclined surface of the boss during assembly until a qualified workpiece is punched out.

The latest national standard for circular die is JB/T5830-2008.

3. Design of the shape of the stamping dies

The external dimensions of the blanking die can be calculated based on experience.

h_a = K_b (h_a>15 mm)

C=(1.5~2.0)h_a

In the formula, h_a—-thickness of the cavity, mm;

K—-correction factor; see the table below;

b —-Maximum orifice size, mm;

C—-The wall thickness of the cavity, and c≥30~40 mm;

Die thickness correction factor K	0.5 mm	1.0 mm	2.0 mm	3.0 mm	>3.0 mm
<50 mm	0.30	0.35	0.42	0.50	0.60
50~100 mm	0.20	0.22	0.28	0.35	0.42
100~200 mm	0.15	0.18	0.20	0.24	0.30
>200 mm	0.10	0.12	0.15	0.18	0.22

4. Convex and concave blanking molds

Convex and concave molds are working parts in the composite mold that have the functions of a blanking convex mold and a punching concave mold at the same time. Its inner and outer edges are both cutting edges, and the wall thickness between the inner and outer edges depends on the size of the punched part. In terms of strength, the minimum wall thickness should be limited, and the minimum wall thickness of the convex and concave dies is affected by the structure of the punching die.

For the front-mounted composite punching die, because the convex and concave die is mounted on the upper die, the inner hole will not accumulate waste, the expansion force is small, and the minimum wall thickness can be smaller; for the flip-chip composite punching die, the minimum wall thickness is due to the accumulation of waste in the hole. The wall thickness should be larger.

The minimum wall thickness of convex and concave molds is currently generally determined according to empirical data. Then the minimum wall thickness of the convex and concave molds of the inverted compound mold is shown in the table below. The minimum wall thickness of the convex and concave molds of the positive compound mold can be smaller than that of the inverted mold.

Material thickness t（mm）	0.4	0.6	0.8	1.0	1.2	1.4	1.6	1.8	2.0	2.2	2.5
Minimum wall thickness d（mm）	1.4	1.8	2.3	2.7	3.2	3.6	4.0	4.4	4.9	5.2	5.8
Material thickness t（mm）	2.8	3.0	3.2	3.5	3.8	4.0	4.2	4.4	4.6	4.8	5.0
Minimum wall thickness d（mm）	6.4	6.7	7.1	7.6	8.1	8.5	8.8	9.1	9.4	9.7	10.0

Positioning part design on blanking dies

The positioning parts of the die are used to ensure the correct feeding of the strip and the correct position in the stamping dies. The positioning of the strip in the mold has two aspects: one is the limit in the direction perpendicular to the feeding direction of the strip to ensure that the strip is fed in the correct direction, which is called feeding guide, or guide; The second is the limit in the feeding direction. The distance (step distance) that controls the feeding of the strip at one time is called the feeding distance, or the stop. For the positioning of blocks or process parts, it is basically a limit in two directions, but the structure of the positioning parts is different from that of the strip.

The positioning device of the die can be divided into stopper pin, positioning plate (nail, block), guide pin, fixed distance side edge, etc. according to its working mode and function.

Stop pin

The function of the stop pin is to ensure that the strip or strip has an accurate feeding distance. It can be divided into fixed stopper pin, movable stopper pin, automatic stopper pin and start stopper pin, etc., as shown in Figure 1-10.

Figure 1-10(a) shows a fixed stopper pin, which is simple in structure but inconvenient to operate. Figure 1-10 (b) shows the hook-shaped fixed stopper pin. The hook-shaped stopper pin is set farther from the cutting edge of the die, and the die has good strength. Figure 1-10 (c) shows the adjustable stopper pin. During use, the position can be adjusted according to the feed distance of the material. It is mostly used for general cutting die.

Figure 1-10 (d) shows the movable spring stopper pin, which is mostly used for stamping dies with a fixed discharge plate. The thickness of the material should not be less than 0.8 mm. The strip should be pulled back slightly during operation, so production efficiency is low. Figure 1-10(e) shows the structure of the automatic stopper pin, which is pressed into the hole as the die descends during punching. It is easy to operate and is mostly used in the compound die of the spring-loading plate. Figure 1-10 (f) shows the initial stopper pin, which is mostly used for positioning in the first step of the continuous die.

The stop pin is generally made of 45 steel, and the quenching hardness is 43~48 HRC. When designing, the height of the stop pin should be slightly larger than the material thickness of the stamping part.

Positioning plate and positioning nail

Positioning plate and positioning nails are parts for positioning a single blank or semi-finished product according to its shape or inner hole. Due to the different shapes of the blanks, there are many positioning forms, as shown in Figure 1-11, where Figure 1-11 (a) shows the shape positioning, and Figure 1-11 (b) shows the inner hole positioning.

The positioning plate and positioning nails are generally made of 45 steel, and the quenching hardness is 43~48 HRC.

Guide pin

Guide pins are mostly used for precise positioning of blanking parts in continuous stamping dies. In order to reduce the feeding error of the strip during blanking and ensure the relative position accuracy of the inner hole and the shape of the workpiece, the guide pin is inserted into the punched hole (or process hole) to accurately position the blank. Figure 1-12 shows the structure of several guide pins. Figure 1-12 (a) is suitable for holes with a diameter of less than 6mm; while figure 1-12 (b) is suitable for holes with a diameter of less than 10 mm; and Figure 1-12 (c) is suitable for holes with a diameter of 10~30 mm. Figure 1-12 (d) is suitable for holes with a diameter of 20-50 mm. Figure 1-12 (e) ~ (f) shows the structure of the movable guide pin.

The use of this guide pin is easy to repair, and it can also avoid stamping accidents such as mold damage and personal safety. The positioning accuracy is better than that of the fixed type. The guide pin is worse. The guide pin can be installed on the blanking punch or on the fixed plate. There must be a certain gap between the guide pin and the guide hole, and the height of the guide pin should be greater than the height of the longest punch in the stamping dies.

The guide pin is generally made of T7, T8 or 45 steel and needs to be heat treated and quenched.

Distance side edge

Fixed-pitch side blades are often used in progressive dies to control the feeding step distance, cut off a small amount of material beside the strip, and obtain a positioning gap to achieve the purpose of stopping the material. While the die is working, the fixed-pitch side edge cuts off the material edge with a length equal to the step length, and the strip can be fed forward by one step. Use fixed-pitch side edges to waste materials, generally used for some small and no waste layout and punching of narrow and long parts with a feed distance of less than 6-8mm. When the progressive die blanks thinner samples, the fixed-pitch side edge is often used.

The form of commonly used side blades is shown in Figure 1-13. According to the cross-sectional shape of the side edge, it is divided into a rectangular side edge and a formed side edge. Figure 1-13 (a) shows a rectangular side blade, which is simple to manufacture, but after the blade tip is worn, burrs are formed on the side of the strip, which affects the feeding accuracy. Figure 1-13 (b) shows the forming side edge. The burr formed on the side of the strip leaves the positioning surface of the guide plate and the side edge baffle. The feeding accuracy is high, but the manufacturing difficulty is increased. Figure 1-13 (c) shows a sharp-angled side edge.

The side edge punches a notch at the edge of the material first. When the strip is fed, the straight edge of the notch slides over the stop pin and then pulls it back, so that the stop pin is blocked by the straight edge. Notch positioning, this kind of side edge material consumes less material, but it is inconvenient to operate.

The thickness of the side edge is generally 6~10 mm, and its length is the length of the strip feeding distance. The stamping dies’ material can be made of T10, T10A, Crl2 steel, and the quenching hardness is 62~64 HRC.

Control of the feeding direction

The control of the feeding direction of the strip is realized by the guide plate or the guide pin. The standard guide plate (guide ruler) can be selected according to the national standard JB/T7648.5-2008. The length dimension should be equal to the length of the die. If the die has a holding plate, the length of the guide plate should be equal to the sum of the length of the die and the length of the holding plate. When guide pins are used to control the feeding direction, two guide pins should be set on the same side. The structure of the guide pin is similar to that of the stop pin.

Unloading device design

The unloading device of the blanking die is a mechanism for pushing, unloading and ejecting strips, blanks, workpieces, and waste materials, so that the next stamping can be carried out normally.

Unloading device

Unloading devices are divided into two categories: rigid unloading devices and elastic unloading devices. The rigid unloading device is shown in Figure 1-14. It has a large unloading force and is often used for punching workpieces with hard materials, large thicknesses and low precision requirements. The elastic discharge device is shown in Figure 1-15. This kind of unloading device relies on the elastic pressure of spring or rubber to push the unloading plate to unload the material. The workpiece punched out by the mold with elastic discharge device is flat and has high precision, and is often used for punching thin and soft workpieces.

Scrap cutter unloading

For the blanking of large and medium-sized parts or edge trimming of formed parts, scrap cutters are often used to cut and separate the waste edges to achieve the purpose of unloading, as shown in Figure 1-16.

Push device

Pushing device is divided into two categories: rigid pushing device and elastic pushing device. The rigid pusher device is shown in Figure 1-17. It is often used in the pusher device of the flip-chip compound mold and is installed on the upper mold part. There are two types of pusher devices as shown in the figure. When there is a punching punch in the center of the die handle, the structure shown in Figure 1-17 (a) is used, otherwise the simple structure shown in Figure 1-17 (b) is used. . The elastic top piece device is generally installed on the lower die, and is often used in the blanking die for forming a composite die or blanking thin sheet materials. As shown in Figure 1-18, it not only plays the role of spring ejection, but also flattening the blanking part. , Can improve the quality of blanking parts.

Calculation of the relevant dimensions of the unloading device

Calculation of the relevant dimensions of the unloading device

The shape of the discharge plate is generally the same as the shape of the die, and the thickness of the discharge plate can be determined by the following formula.

H_x =(0.8~1.0) h_a

Where H_x is the thickness of the discharge plate, mm;

h_a is the thickness of the die, mm.

The shape of the discharge plate hole is basically the same as that of the stamping die hole (except for the small die hole and special hole), so it is generally processed with the die during processing. In the design, if the unloading plate hole plays a guiding role on the punch, the matching accuracy of the punch and the unloading plate is H7/f6. For the elastic discharge plate that does not serve as a guide, the general discharge plate hole and the single-sided gap of the punch are 0.05~0.1 mm, while the rigid discharge plate punch and the single-sided gap of the discharge plate are 0.2~0.5 mm, and ensure that under the action of the unloading force, the workpiece or waste is not pulled into the gap as the standard.

The discharge plate is generally made of 45 steel and does not require heat treatment.

Fixed part design

Formwork

The blanking mold base is composed of an upper mold base, a lower mold base, a mold handle and a guide device (the most commonly used are guide posts and guide sleeves). The mold base is the support of the entire mold and bears all the loads in the punching process. All parts of the mold are directly or indirectly fixed on the mold base in different ways.

The upper mold base of the mold base is connected with the press slide block through a mold handle, and the lower mold base is usually fixed on the press table with a screw plate. The guide device maintains precise positioning between the upper and lower mold bases to guide the movement of the punch to ensure uniform blanking clearance. The punching mold base is produced by a professional manufacturer according to the national standard (JB/T2851-2008 and JB/T2852-2008). When designing the mold, the standard mold base can be selected according to the perimeter size of the cavity.

Basic requirements for formwork

1.  It should have sufficient strength and rigidity.
2. There should be sufficient accuracy (for example, the upper and lower stamping dies bases should be parallel, the guide post and the center of the guide sleeve should be perpendicular to the upper and lower mold bases, and the mold handle should be perpendicular to the upper mold base, etc.).
3. The guide between the upper and lower stamping dies should be accurate (the gap between the guides should be small, and the movement between the upper and lower molds should be smooth and free from stagnation).

Form of formwork

The most widely used standard mold base is the mold base that uses guide posts and guide sleeves as guiding devices. According to the position of the guide post and the guide sleeve, there are the following 4 basic types, as shown in Figure 1-19.

•  The rear guide pillar mold base. As shown in Figure 1-19 (a), the two guide pillars and guide sleeves of the rear guide pillar mold base are on the back side of the mold base, which can realize vertical and horizontal feeding and convenient feeding. However, due to the offset of the guide pin and the guide sleeve, it is easy to cause unilateral wear, so it is not suitable for the mold with floating mold handle.
•  Intermediate guide column mold base. As shown in Figure 1-19 (b), the two guide pillars and guide sleeves of the middle guide pillar mold base are located on the left and right symmetry lines of the mold. The force is balanced, but the material can only be fed in a single direction forward and backward.
•  Diagonal guide pillar mold base. As shown in Figure 1-19 (c), the two guide pillars and guide sleeves of the diagonal guide pillar mold base are arranged on the diagonal line of the mold, which not only has a balanced force, but also can realize longitudinal and horizontal feeding.
• Four-guide column mold base. As shown in Figure 1-19 (d), the four-guide pillar mold base has four guide pillars and sleeves distributed along the four corners, which are not only balanced in force, strong in guiding function, and large in rigidity, which is suitable for large-scale molds.

Guide post and guide sleeve

The length of the guide post should ensure that when the die is in the lowest working position ( closed position), the distance between the upper end of the guide post and the top surface of the upper die base should not be less than 10~15 mm, and the distance between the bottom surface of the lower die base and the bottom surface of the guide post should be 0.5 ~1 mm, H is the closed height of the mold, as shown in Figure 1-20.

The matching precision of the guide pin and guide sleeve can be selected according to the precision of the stamping dies, the life of the dies, and the size of the gap. When the blanking sheet is thin, and the precision and life of the mold are high, the first-level precision mold base with H6/h5 is selected; when the blanking sheet is thicker, the second-level precision mold with H7/h6 is selected.

Die handle

The upper die of the die is installed on the punch slider through the die handle. There are many forms of blanking mold handles. Commonly used are integral mold handles, press-in mold handles, screw-in mold handles, screw-fixed mold handles, floating mold handles and other structural forms, as shown in Figure 1-21. Floating mold handle structure is often used for high-precision sheet metal workpieces and rolling guide pillar-guided molds. This type of die handle can eliminate the influence of the press guide rail on the guiding accuracy of the die during punching, and improve the punching accuracy, but the processing and manufacturing are complicated.

The mold handle is generally made of Q235 or 45 steel. The diameter must be determined according to the diameter of the mounting hole of the selected press.

Pad

The function of the backing plate is to directly bear and diffuse the pressure transmitted by the punch to reduce the unit pressure of the mold base, prevent the mold base from being pressed out of the pit, and affect the normal operation of the punch. The size of the backing plate is mostly consistent with the circumference of the die, and its thickness is generally 3~10 mm. In order to facilitate the assembly of the mold, the diameter of the pin through the backing plate can be 0.3~0.5 mm larger than the diameter of the pin. The backing plate material is generally made of T7, T8 or 45 steel. The quenching hardness of T7 and T8 is 52~56 HRC, and the quenching hardness of 45 steel is 43-48 HRC.

When designing a composite mold, a backing plate should also be installed between the convex and concave molds and the mold base.

Fixed plate

In the punching die, the convex mold, the convex and concave mold, the insert convex mold and the concave mold are all installed on the mold base after being combined with the fixed plate. The perimeter size of the fixed plate is the same as that of the die, and its thickness should be (0.8~0.9) times the thickness of the punching die. The positions of the various holes on the fixed plate of the convex mould correspond to the holes of the concave mould, and the transitional fit H7/m6, H7/n6 is adopted with the convex mould. After pressing, the end face of the convex mould and the fixed plate are smoothed together. The fixing plate is generally made of Q235, and sometimes 45 steel can be used.

Fastener

The fastening parts in the mold mainly include screws, pins, etc. The screw mainly connects the various parts in the die to make it into a whole, while the pin plays the role of positioning. The screw is best to use the hexagon socket screw. The advantage of this screw is that it is fastened firmly. Because the screw head is buried in the template, the shape of the mold is more beautiful and the installation and disassembly space is small. Cylindrical pins are often used as pins. When designing, there should be no less than two cylindrical pins.

The distance between the pin and the screw should not be too small to prevent the strength from being reduced. The specification, quantity, distance dimension, etc. of screws and pins in the mold can be designed with reference to the typical combination of cold stamping dies in the national standard when selecting.

The closed height of the stamping dies

The closed height of the mold refers to the distance between the upper surface of the upper mold base and the lower surface of the lower mold base when the mold is in the lowest working position.

In order for the mold to work normally, the blanking mold closing height H must be compatible with the press’s installation height, so that it is between the maximum installation height of the press H_max and the minimum installation height H_min, which can generally be determined by the following formula

H_max -5 ≥ Н ≥ H_min+10

When the closing height of the stamping die is less than the minimum closing height of the press, a backing plate can be added.