Mold Design

According to the national occupation definition, mold design is: a person who is engaged in the digital design of enterprise molds, including cavity molds and cold stamping dies, on the basis of traditional mold design, fully applies digital design tools, improves mold design quality, and shortens mold design cycle.

The Concept Of Mold Design

The overall structure of the stamping die can be divided into two parts:

• Common parts.
• The part that varies depending on the product. Common parts can be standardized or standardized, and parts that vary by product are difficult to standardize.

The Specification Of Mold Design

1.The composition of the template

The composition of the stamping die will vary according to the type and composition of the die, and there are two major types: the forward configuration and the reverse configuration. The former is the most commonly used structure, and the latter structure is mainly used for drawing forming molds or matching special molds.

2.Mold specifications

(1) Mold size and locking screw

The size of the template should be larger than the working area, and the standard template size should be selected. The position configuration of the template locking screw is related to the mold type and template size. Among them, single-engine molds are most commonly used with locking screws arranged at the four corners, and the most standard form of work area can be widely used. Long-shaped molds and continuous molds are most commonly used with locking screws arranged at the four corners and the middle position.

(2) The thickness of the template

The thickness of the template has an absolute relationship with the structure of the mold, the type of stamping processing, the processing force of the stamping, and the precision of the stamping processing. It is difficult to determine the thickness of the mold based on theoretical calculations. Generally, it is determined by experience. The thickness of the template used in the design should be as small as possible, and the mold height and clamping height should be standardized to facilitate purchase and inventory management.

Mold Template Design

The main templates of continuous molds include punch fixing plates, press plates, concave templates, etc. The structure design depends on the accuracy of the stamping product, the production quantity, the machining equipment and machining methods of the mold, and the maintenance methods of the mold. There are the following three types Forms:

• Monolithic type
• Yoke type
• Embedded type.

1. Monolithic

The monolithic template is also called an integral structure type, and its machining shape must be closed. The monolithic template is mainly used for molds with simple structure or low precision. The machining method is mainly cutting (no heat treatment is required). The heat-treated template must be subjected to wire cutting or electric discharge machining and grinding. When the template size is long (continuous mold), two or more integrated types will be used together.

2. Yoke

The central part of the yoke template is processed into a groove shape to assemble block products. Its structure is based on application requirements, and the grooves can be constructed with other templates. The advantages of this yoke template structure are: the groove is easy to process, the width of the groove can be adjusted, and the machining accuracy is good. However, low rigidity is its disadvantage.

The design precautions of the yoke template are as follows:

• The fitting of the yoke plate structure and the block parts adopts intermediate fitting or light fitting. For example, the use of strong press fitting will change the yoke plate.
• The yoke plate has the holding function of the block parts. In order to withstand the side pressure and surface pressure of the block parts, it must have sufficient rigidity. In order to make the groove of the yoke plate and the block parts tightly combined, the corners of the grooves are made clearance machining. If the corners of the yoke plate grooves cannot be made clearance machining, the block parts must be made clearance machining.
• The division of block parts should also consider its internal shape, and the reference plane must be clarified. In order to prevent deformation during stamping, attention should also be paid to the shape of each block part.
• When the yoke plate is assembled with many pieces of block parts, the pitch will change due to the accumulated error in the machining of each block part. The solution is to design the middle block part in an adjustable way.
• The block parts adopt a side-by-side mold structure. Because the block parts will be subjected to lateral pressure during the punching process, there will be gaps between the block parts or the inclination of the block parts. This phenomenon is an important cause of poor stamping such as poor stamping dimensions and chip clogging, so adequate countermeasures must be taken.
• There are five ways to fix the block parts in the yoke plate according to their size and shape: A. Fix with a locking screw, B. Fix with a key, C. Fix with a button, D. Fix with a shoulder Fixed, E. The above pressing parts (such as the guide plate) are pressed and fixed.

3. Built-in

Round or square recesses are processed in the template, and the block-shaped parts are embedded in the template. This template is called an embedded structure. This structure has a small machining tolerance, high rigidity, and accuracy and reproducibility during disassembly and assembly. good. Due to the advantages of easy machining, machining accuracy determined by the working machine, and fewer final adjustments, the built-in template structure has become the mainstream of precision stamping dies, but its disadvantage is that it requires a high-precision hole machining machine.

When the continuous stamping die adopts this template structure, in order to make the template have high rigidity requirements, an empty station is designed. The precautions for the construction of the built-in template are as follows:

• Machining of embedded holes: Vertical milling machines (or fixture milling machines), integrated machining machines, fixture boring machines, fixture grinders, wire-cut electrical discharge machines, etc. are used to process the embedded holes of the template. The machining standard for inserting holes, when using a wire-cut electric discharge machine, in order to improve its machining accuracy, two or more wire-cutting processes are performed.
• Fixing method of inserts: The determinants of the fixing method of inserts are the accuracy of machining, the ease of assembly and disassembly, the possibility of adjustment, etc. There are four ways to fix the inserts: A. Fix with screws, B. Fix with shoulders, C. Fix with toes, and D. Fix the upper part with plates. The method of fixing the inserts of the concave template also adopts press-fitting. At this time, the looseness caused by the machining thermal expansion should be avoided. When using the round mold inserts to process irregular holes, the rotation prevention method should be designed.
• Considerations for assembly and disassembly of inserts: The machining precision of inserts and their holes is required to be high for assembly operations. In order to obtain that even a slight dimensional error can be adjusted during assembly, it is advisable to consider the countermeasures in advance. The specific considerations for insert machining include the following five items: A. With a press-in lead-in part, B. Adjust the insert with spacers The press-in state and correct position of the piece, C·The bottom surface of the insert is provided with a hole for pressing out, D. Screws of the same size should be used when tightening with screws, to facilitate locking and loosening, E. To prevent the direction of assembly Mistakes should be designed for fool-proof chamfering.

Mold Unit Design

1. UNIT

The mold alignment unit is also called the alignment guide device of the mold blade. In order to ensure the alignment of the upper mold and the lower mold and shorten the preparation time, according to the requirements of product accuracy and production quantity, there are mainly the following five types of mold alignment units:

• Non-guided type: When the mold is installed on the punching machine, the pairing of its blades is directly performed, without the use of guiding devices.
• Outer guide type: this type of device is the most standard structure. The guide device is installed on the upper mold base and the lower mold base, and does not pass through each template. It is generally called the mold base type.
• Combined use of external and internal guidance (1): This device is the most commonly used structure for continuous molds. An internal guiding device is installed between the punch fixing plate and the pressing plate. The combination of the punch and the die utilizes a fixed pin and an outer guide device. Another function of the inner guiding device is to prevent the pressure plate from tilting and protect the small punches.
• Combined use of outer guide and inner guide (2): This device is a high-precision and high-speed continuous mold structure, and the inner guide device penetrates the punch fixing plate, the pressing plate and the die fixing plate, etc. . The inner guiding device itself also has the function of aligning and protecting small punches. The main function of the outer guiding device is to get a smooth goal when the mold is disassembled and installed on the punching machine.
• Inner guide type: This structure does not use outer guide device. The inner guide device penetrates the punch fixing plate, the pressing plate and the die fixing plate, etc., to correctly maintain the positional relationship of each plate for protection shower.

2. Guide post and guide sleeve unit

There are two types of mold guiding methods and accessories: guide posts and guide sleeve units:

• (A). Outer guide type (mold base type or main guide)
• (B). Inner guide type (or auxiliary) lead).

In addition to meet the requirements of precision molds, there is a high demand for the use of both external and internal guidance.

• (1) External guide type: Generally used for molds that do not require high precision, most of them are sold as a unit with the mold base. The main function is to match the blades when the mold is installed on the punching machine. There is almost no stamping process. Dynamic accuracy retention effect.
• (2) Inner-guided type: Due to the development of mold processing machines, it is rapidly popularized. The main function is not only the matching of the blades when the mold is installed on the punching machine, but also the dynamic accuracy maintenance effect in the stamping process.
• (3) External guiding and internal guiding combined use type: a pair of molds simultaneously use external guiding and internal guiding devices.

3. Punch and die unit (round)

• (1) Punch unit: According to its shape (shoulder type and straight type), length, and convenience of maintenance, the use of the punch unit should be matched with the blank guide sleeve unit.
• (2) Concave die unit: The circular die unit is also called the die guide sleeve unit. Its forms are monolithic and separate. It depends on the production quantity, service life, and the location of the product or punching. The combination series are: (A). Use the template to directly process the shape of the die, (B). The escape part with two bevel angles, (C). Whether to use the back plate, (D). Irregular die shape must There is a rotation prevention design.

4. Pressure bolt and spring unit

• (1), pressure bolt unit: the types of pressure plate bolts are: (A). External screw type, (B). Sleeve type, (C). Internal screw type. In order to maintain the parallel state of the pressing plate at the specified position, the stopping method of the pressing bolt (shoulder contact part): (A). Die seat cavity receiving surface, (B). Punch fixing plate top surface, (C). The top surface of the punch back plate.
• (2) Pressing spring unit: the movable pressing plate pressing spring unit can be roughly divided into: (A). Single use type, (B). Combined use with pressing bolt

When selecting a pressing spring unit, it is best to consider the following points before deciding:

• (A). Ensure the free length of the spring and the necessary compression (the spring with large compression should be placed in the cavity of the pressure plate).
• (B) Whether adjustment of initial spring compression (pre-compression) or load is necessary.
• (C) Consider the ease of mold assembly or maintenance.
• (D) Consider the relationship with the length of the punch or pressing bolt.
• (E), consider safety (to prevent the spring from flying out when it is broken).

5. Guide pin unit (positioning of the feeding direction of the strip)

• (1) Guide pin unit: The main function of the guide pin is to obtain the correct feeding pitch during continuous stamping. There are two types of guide units for stamping dies: indirect (guide pins are used alone) and direct (guide pins are installed inside the punch).
• (2) The assembly method of the guide pin is the same as that of the punching punch (installed on the punch fixing plate). The spring is used to constrain it to the punch fixing plate.
• (3) The guide pin is additionally installed on the binder plate, because the guide pin is required to protrude from the binder plate to a certain amount and to prevent the material to be processed when the mold rises, the rigidity of the binder plate and the It is necessary to pay attention to the guidance form.
• (4) The guide pin unit has a direct type, which is installed in the punch, and is mainly used for shape punching (cutting processing) or edge trimming processing of extension engineering, and its position positioning is based on the hole and extension part of the product the inside diameter of.

6. Guide unit

• (1) In the shape of punching (cutting) or continuous punching, in order to guide the width direction of the processed material and obtain the correct feeding pitch, a guide unit is used.
• (2) The guiding device in the width direction of the strip, the guiding methods are: (A). Fixed plate guide pin type, (B). Movable guide pin type, (C). Plate tunnel guide type ( Single plate), (D). Plate guiding type (two pieces), (E). Lifting pin guiding type (movable type, fixed type and both.
• (3) The guide device for starting and stopping has two forms: (1). Slider type, (2). Movable pin type, etc. The main function is to locate the material at the initial starting position of the mold.
• (4) The feeding stop device can accurately determine the feeding pitch. It is mainly used for manual feeding. Its forms are: (A). Fixed stop pin, (B). Movable stop pin, (C ). Side cutting stop mode, (D). Hook stop mechanism, (E). Automatic stop mechanism.
• (5) Side-pushing material guide mechanism, the material is pressed to one side during stamping processing, which can prevent the material from snaking due to the difference between the width of the strip and the width of the guide.
• (6). Blank material position positioning and guiding mechanism, its forms are: (A). Fixed pin guide type (using the shape of the blank), (B). Fixed pin guide type (using the hole of the blank), (C). Guide plate (for large parts), (D). Guide plate (integrated), (E). Guide plate (divided).

7. Lifting and topping unit

• (1). Lifting pin unit: its main function is to lift the strip to the die during continuous stamping processing (the height of the position is called the feeding height, and achieves the purpose of smooth feeding. Its forms are: (A). The pin type (round, purely for material lifting), is the most common lifting pin unit. (B). Material lifting pin type (round, with holes for guide pins), the lifting pin is equipped with a guide pin The use of holes can prevent the material from bearing the deformation of the guide pin and make the guide pin really work. (C). Material lifting and material guide pin type, both have the function of guiding material, the guiding material of continuous molds is most commonly used in this form of material lifting pin Type. (D). Lifting pin type (square) If required, there are air blow holes. (E). Lifting and guide pin type (square).
• (2) Material ejection unit: During automatic stamping processing, it is necessary to prevent punching products or punching chips from jumping on the surface of the die to avoid mold damage and bad stamping parts.
• (3) Ejection unit: The main function of the ejection unit is to eject products or waste materials from the cavity during each stamping process. The installation site of the ejector unit is two: (A), the reverse configuration mold is installed on the upper mold part, (B). The forward configuration mold is installed on the lower mold part.

8. Fixed pin unit

The shape and size of the fixed pin unit are designed according to the requirements of standard specifications. The precautions for use are as follows:

• (A). The fixed pin hole should be a through hole. If it is not possible, consider the design method that is easy to remove with screws.
• (B). The length of the fixing pin should be moderate, and it should not be longer than the necessary length.
• (C). The fixed pin hole should have a necessary escape part.
• (D). When it is placed in the upper mold part, a mechanism to prevent it from falling should be designed to prevent it from falling.
• (E). When one side is press-fitted and the other side is sliding, the fixed pin hole on the sliding side is slightly larger than the fixed pin.
• (F). The number of fixed pins is based on the principle of two, try to choose the same size.

9. Press plate unit

The particularly important point of the pressure plate unit is that the pressure surface and the die surface have the correct parallelism and the buffer pressure is required to be balanced.

10. Misfeed detection unit

When the continuous die is used for stamping, the die must be designed with a fault detection unit to detect whether the variation of the feeding pitch exceeds its standard and stop the operation of the punch. The error detection unit is installed inside the mold. According to its detection method, there are the following two installation forms:

• (A). The detection pin is installed in the upper mold. When it deviates from the hole of the strip, it will be connected with the strip. Contact and detect.
• (B). The form of the detection pin installed in the lower mold is detected when a part of the strip is in contact with the detection pin.

11. Scrap cutting unit

During the continuous stamping process, the strip (scrap) will leave the mold one after another. There are two ways to handle it:

• (A). Use a coiler to take it up
• (B). Use a die cutting device to refine it.

There are two methods for the latter:

• (A). Use a special scrap cutting machine (installed outside the press machine)
• (B). Install the cutting unit in the final process of the continuous mold.

12. Height stop block unit

The main function of the height stop block unit is to correctly determine the position of the bottom dead center of the upper die. There are two forms:

• (A). It is also often contacted during stamping processing
• (B). It is contacted only during assembly, and stamping processing. Time-free approach. Also, when the mold is transported and stored, in order to prevent contact between the upper mold and the lower mold, it is better to insert a spacer between the upper mold and the lower mold. When the accuracy requirements are not necessary, the use standard can adopt the screw adjustment type.

The Main Components Of Mold

1. Standard parts and specifications

The selection method of standard specifications for molds is best to consider the following items:

• (A). When the specifications used are not restricted, it is best to use the highest level.
• (B). In principle, standard numbers are used.
• (C). When the standard part of the mold does not have this size, the closest one will be used for processing.

2. The design of the punch

Punches can be roughly divided into three parts according to their functions:

• (A). The tip of the cutting edge of the processed material (the cutting edge has irregular, square, round shapes, etc.).
• (B). The contact part with the fixed plate of the punch (fixed part or shank, the cross-sectional shape of which is irregular, square, round, etc.).
• (C). The connecting part of the blade and the handle (middle part).

The design basis of each part of the punch is briefly described from

• (A). Length of the cutting edge
• (B). Grinding direction of the cutting edge
• (C). The fixing method of the punch and the shape of the handle.

3. The design of the punch fixing plate

The thickness of the punch fixing plate is related to the size of the die and the load. Generally, it is 30~40% of the length of the punch, and the length of the punch guide should be 1.5 times higher than the diameter of the punch.

4. Design of guide pin (punch)

The diameter of the guide pin (punch) and the gap between the guide hole of the material, the size and the amount of the protruding pressure plate are designed according to the thickness of the material. The shape of the tip of the guide pin is roughly divided into two types: A. Cannonball Shape, B. Conical (push-pull shape).

• (1). The shell shape is the most common form, and there are also standard parts on the market.

• (2). The conical shape has a certain angle, which is very suitable for high-speed stamping of small parts. The determinants of the push-pull angle are the stamping stroke, the material of the processed part, the size of the guide hole, and the processing speed. When the push-pull angle is large, it is easier to correct the position of the processed material, but the length of the push-pull part will become longer. The connection between the push-pull part and the cylinder part should be smooth.

5. Design of the concave mold

(1). Design of punching die

The key items that should be considered in the shape design of the punching die are: A. The life of the die and the shape of the escape angle, B. The shear angle of the die, and C. The division of the die.

• (A). Mold life and shape of escape angle: This design is a very important matter. If the design is not correct, it will cause punch damage, blockage or floating of punching chips, and occurrence of burrs.
• (B). Shear angle of the die: In order to reduce the punching force when the shape is punched, the die can be designed with a shear angle. When the shear angle is large, the punching force will be reduced greatly, but it is easy to cause the product to bend and deform .
• (C). Dividing of the concave mold: The concave mold must be subjected to finishing processing such as forming and grinding. Because of its concave shape, the grinding tool is not easy to enter, so it must be divided.

(2). Design of bending die

The design of the concave mold for bending is to prevent springback and excessive bending. The shape of the concave mold for U-shaped bending is a combination of double R and straight part (30 degrees inclination), preferably approximately R shape. The shape of R part should be polished after forming grinding or NC electric discharge machining.

(3). Design of drawing die

The corner shape of the drawing die and the shape of the escape angle are very important design items. The shapes and characteristics of the corner and escape corner are as follows: When the R angle value of the drawing die is large, it is easier to draw and process, but it also produces the surface of the drawn product. Wrinkles occur, and the thickness of the side wall of the drawn product is greater than the thickness of the plate. When drawing thick plates and difficult ejection, the R value of the die should be small, about 1-2 times the thickness of the plate. Generally, most of the drawing parts of the drawing die of the cylinder and the square tube are made straight, in order to prevent For purposes such as burning, destroying the lubricating oil film and reducing the ejection force, it is advisable to have an escape part (stage-shaped or push-pull-shaped) design under the straight section. Especially in the case of shrinking processing, this straight section must be as small as possible.

6. Side pressure countermeasures for punches

It is the best ideal state for the punch to bear equal load on the left and right sides during the stamping process (ie, the side pressure is zero). When the punch bears the side pressure, the upper die and the lower die will be offset in the horizontal direction, resulting in a part of the die gap. It becomes larger or smaller (uneven gap) and cannot be processed with good precision. The countermeasures for the side pressure of the punch include the following methods:

• (A). Change the processing direction
• (B). Single-sided processing (punching, bending, drawing, etc.) products should be arranged in two rows
• (C). Punching The head or die is equipped with a side pressure stop, and the side of the cutting blade is provided with a guide part (especially for cutting and breaking processing).

7. Design of back pressure plate

The main parts (punch, blanking plate, die) during the stamping process will be subjected to surface pressure afterwards. When the punching pressure is higher than the surface pressure, a back pressure plate (especially the back of the punch and die sleeve) should be used. Back pressure plate There are two forms of use: partial use and full use.

Mold Design Software

Modern industry is developing very fast, basically using computers for design and processing, and its accuracy can be guaranteed to be between 0.002 and 0.01. Engaging in mold design work has a boundless vast world. If you can use computer-aided design, your opponent, invisibly, lags behind you. Commonly used mold design software includes AUTOCAD Pro/E UG SW CImatron, mishiong wait.

Impact On Lifespan

Design is a key step in mold production and the initial link of production, which controls the entire process of mold production. Therefore, design also has a great impact on the service life of molds. Design mainly affects the service life of stamping dies from the following two aspects .

• (1) The precision of the guide mechanism of the mold. Accurate and reliable guidance has a great influence on reducing the wear of mold working parts and avoiding the damage of convex and concave molds, especially the gapless and small gap blanking dies, compound dies and multi-station progressive dies are more effective. In order to improve the service life of the mold, it is necessary to correctly select the guiding form and determine the accuracy of the guiding mechanism according to the nature of the process and the accuracy of the parts.
• (2) The geometric parameters of the cutting edge of the mold (convex and concave mold). The shape, fitting clearance and fillet radius of the convex and concave molds not only have a great influence on the forming of the stamping part, but also have a great influence on the wear and life of the mold. For example, the fit clearance of the mold directly affects the quality of the blanking parts and the life of the mold. For higher precision requirements, a smaller gap value should be selected in the design; otherwise, the gap can be appropriately increased to increase the life of the mold.