Experience Sharing on Design and Manufacturing of Metal Stamping Dies

Here, we will share some specific design and manufacturing experiences to provide our understanding of dies accumulated over the years. Through this article, we hope to give you a better understanding of the specific details of metal stamping dies in China.

What is a stamping die?

Stamping dies have various concepts in different places, such as punching dies, metal dies, metal stamping dies, etc. The specific concept refers to the use of dies fixed on a punch press or a press to apply a certain pressure to metal or non-metal sheets, so that the material can be separated or formed to obtain parts with certain size and appearance requirements. There are many types of dies, and here we mainly explain metal stamping dies.

Stamping dies have the characteristics of consistent size and appearance of the products produced, as well as fast forming, high efficiency, stable quality, required precision, high material utilization, simple operation, and low labor intensity for workers. The technical requirements for operators are not high, and they can quickly master the operation after a short period of learning and training. For example, a production line operator needs to learn how to operate a punch press, feeder, straightener, mold disassembly and other operations.

Classification of stamping dies

Stamping dies can generally be classified into two types: progressive dies and transfer dies.

Progressive dies can be further divided into compound dies, stretching dies, riveting dies, etc. Here is a brief introduction to the structure and functions of these dies:

Progressive dies, also known as "single-process dies", refer to dies that can only complete one stamping process in one stroke of stamping. After this process is completed, the product needs to be manually or mechanically removed from the die and then placed into the next die for continuous production until the final process of the die is completed and the entire product is finished. These dies are easy to maintain, but they are time-consuming and labor-intensive in production, with a higher product scrap rate.

Progressive dies (single-process dies).

Compound dies: Common compound die structures include compound blanking and compound stretching, which are slightly different from other progressive die structures. The punch (also known as the male die or punch head) is designed in the lower die, and the other several template blocks are the lower clamp plate (fixing the punch head), the lower stop plate, and the lower discharge plate (external discharge). The upper die consists of the female die (or blade), the inner discharge plate, and the upper cushion plate. The inner discharge plate is hung on the upper cushion plate with an equal height sleeve, and then pushed up with a knock pin or spring. For example, in a compound die used for blanking, the inner discharge plate generally discharges the female die by 0.50mm, which cannot be lower than the female die, otherwise the blade of the female die is prone to break or not discharge. The force of the inner discharge should be strong enough to push the product out of the female die. Generally, if the material is relatively thick, nitrogen gas springs are installed on top of it.

Compound dies

Transfer dies, also known as "progressive dies", refer to dies that can simultaneously complete two or more stamping processes at different stations in one stroke of stamping. These dies are difficult to maintain and require experienced toolmakers to operate. However, they are highly efficient in production. If the speed is fast enough, thousands of products can be produced in an hour, saving labor and time costs, and with a lower product scrap rate.

Transfer dies (progressive dies)

Introduction to the structure of stamping dies

The structure of stamping dies and punching dies are similar, and corresponding dies are designed according to different product characteristics and requirements. The structures of different dies vary and their functions and the products produced are also different. In general, some dies are simple, while others are complex. However, no matter how complex the structure is, the basic structure remains unchanged, consisting of several templates, modules, and standard parts.

Metal stamping dies

Generally, a mold is assembled from several templates and parts (which we call inserts or sub-inserts) and standard parts. The specific templates of a typical stamping die structure, from top to bottom (including code numbers), are as follows:

Templates of the upper die:

upper bolster, upper pad, upper punch unit (UPU), upper backup unit (UBU), upper stripper plate (PHU), upper stop plate (PPS), and upper knockout plate (PSU);

Templates of the lower die:

die block (DIE), lower backup plate (LBD), lower punch unit (LPD), lower pad, and lower bolster;

Other less commonly used templates:

cover plate (CVU), extrusion plate, upper die plate, lower knockout plate, lower stop plate, lower stripper plate, male die, female die, etc.;

Some mold parts include:

Inserts and sub-inserts of the upper die: clamp insert, stripper insert, punch, etc.;

Inserts and sub-inserts of the lower die: die insert, cutting edge, etc.;

Standard parts: spring, hexagon screw, stop screw, wire spring, height equalization bushing, guide pin, guide bushing, height equalization bushing washer, dual-use pin, material stop pin, etc.;

Non-standard parts: external positioning pin, internal positioning pin, pitch positioning pin, external limit pin, internal limit pin, etc.

The design numbering rules of stamping dies

The numbering of stamping dies is generally written as follows (taking examples):

Engineering model：90-KNMF0125RAH，90-KNMF0125RAA，90-KNMF0125RBB

Continuous model：90-KNMF0125SAA，90-KNMF0125SBB

The "R"  in "RAH" stands for engineering model, while the "H" represents a total of eight sets (from A-H, which are respectively RAH, RBH… RHH). “A” represents the first set. "RAA" or “RBB” refers to riveting models, such as riveting screws, riveting spring plates, and so on.

The "S" in "SAA" and  "SBB" represents the continuous model, while “0125” represents the mold number. The “F” in front represents the year the mold was produced. If a mold was produced in 2010, it would be represented by “F0125”. In this case, the mold produced in 2010 can be referred to as the “125 mold”. If a mold was produced in 2011, it would start with “G”. Therefore, if you say “125 mold,” people may assume you’re referring to the mold “G0125”.

Other examples include the upper plate (PHU) with the code 90-KNMF0125SAAPHU, and the block for the upper plate with code 90-KNMF0125SAAPHPA001.

If this continuous model has two parts, then “A” and “B” are used to indicate them after the code “90-KNMF0125SAAPHU”. The upper plate for the first segment should be “90-KNMF0125SAAPHUA”, while the one for the second segment should be “90-KNMF0125SAAPHUB”. The blocks for the upper plate are “90-KNMF0125SAAPHPA001” and “90-KNMF0125SAAPHPB001”.

Lower template (DIE)：90-KNMF0125SAADIE，90-KNMF0125RAHDIE

Regarding other codes that have not been explained here, a brief explanation can be made.

Code comparison table

Stamping common materials and selection criteria

The properties of materials used in stamping are closely related to stamping production, and their properties directly affect the design of stamping process, the quality of stamping parts and the service life of products, and also affect the organization of balanced production and production costs of stamping parts.

metallic material

When selecting the material of stamping parts, not only the use performance should be considered, but also the performance requirements of stamping processing and subsequent processes should be met. The basic requirements for stamping processing materials are as follows.

Good stamping performance

For the forming process, such as stretching, bending, step difference, convex hull, etc., the material should have good stamping performance, that is, it should have good crack resistance, good mold fit and shape fixability, otherwise the product is prone to deformation , cracking, etc., causing difficulties in mold repair. For the separation process, the material is required to have a certain degree of plasticity.

High surface quality

The surface of the material should be smooth and smooth without defects or damage. Materials with good surface quality are not easy to break during molding, and are not easy to scratch the mold, and the surface quality of the workpiece is also good.

The thickness tolerance of the material should meet the national standard

Because a certain mold gap is only suitable for materials with a certain thickness range, if the material thickness tolerance is too large, it will not only directly affect the quality of the parts, but may also lead to the appearance of waste products. In the process of correcting bending and shaping, the mold or press may be damaged due to excessive thickness positive deviation.

Commonly used materials for stamping dies

The most commonly used materials in stamping production are metallic materials (including ferrous and non-ferrous metals), but sometimes non-metallic materials are also used. Among them, ferrous metals mainly include ordinary carbon structural steel, high-quality carbon structural steel, alloy structural steel, carbon tool steel, stainless steel, electrical silicon steel, etc.; non-ferrous metals mainly include pure copper, brass, bronze, aluminum, etc.; non-metallic materials There are cardboard, laminated board, rubber board, plastic board, fiber board and mica etc.

The supply status of metal materials for stamping is generally sheets and strips of various specifications. The sheet material can be used in the production of engineering molds, the strip material (coil material) can be used in the production of continuous molds, and can also be used in the production of engineering molds. The size of the sheet material is large, which can be used for stamping large parts, or the sheet material can be cut into strips according to the layout size and used for stamping small and medium-sized parts; strip materials (also known as coil materials) have various widths , the unfolded length can reach tens of meters, and it is supplied in rolls, which is suitable for automatic feeding of continuous mold mass production.

For the grades, specifications and performance of various materials, you can refer to relevant manuals and standards.

Reasonable selection of stamping materials

The selection of stamping materials should consider the use requirements of stamping parts, stamping process requirements and economy.

lReasonable material selection according to the use requirements of stamping parts

The selected material should enable the stamping to work properly in the machine or component and have a certain service life. For this reason, according to the use conditions of the stamping parts, the selected materials should meet the requirements of the corresponding strength, stiffness, toughness, corrosion resistance and heat resistance.

lReasonable material selection according to stamping process requirements

For any kind of stamping parts, the selected material should be able to stably form a qualified product without cracking or wrinkling according to the requirements of its stamping process. This is the most basic and important material selection requirement. To this end, the following methods can be used to select materials reasonably.

①Test punch. According to previous production experience and possible conditions, select several sheets that can basically meet the requirements of stamping parts for trial punching, and finally choose the one that has no cracks or wrinkles and has a low scrap rate. The results of this method are more intuitive, but with greater blindness.

②Analyze and compare. On the basis of analyzing the properties of stamping deformation, compare the maximum deformation degree during stamping forming with the limit deformation degree allowed by the sheet metal stamping forming performance, and use this as a basis to select a sheet suitable for the stamping process requirements of this type of part.

In addition, plates of the same grade or thickness can be divided into cold rolling and hot rolling. Among the domestically produced plates in my country, thick plates (t>4mm) are hot-rolled plates, and thin plates (t<4mm) are cold-rolled plates (there are also hot-rolled plates). Compared with hot-rolled sheets, cold-rolled sheets have precise dimensions and small deviations,

Less surface defects, bright, dense internal structure, better stamping performance. (Note: t generally represents the thickness in the mold. For example, the thickness of the template and the thickness of the material can be expressed by t.)

lReasonable selection of materials according to economic requirements

The selected materials should be as cheap as possible, easy to source, and economical on the premise of meeting the requirements of performance and stamping technology, so as to reduce the cost of stamping parts.

Stamping die development process

How is the stamping die processed step by step?

For a complete stamping die development process, the customer should first send the product drawing to the head of the stamping die design department, and the design supervisor will confirm whether the product can be made with the technology of the department. If possible, then hand it over to the designer for drawing and preparing materials. Buy all the boards needed for the mold first, make way for rough machining, and grind the template thickness to a certain size. Generally, a total of 50 (0.50mm) margins are left on both sides. After rough machining, send it to heat treatment.

At the same time, the staff of the design department held a seminar to formulate the step-by-step process drawings of the product and discharge the material belt diagram. A product cannot be produced through only one process, and must cooperate with other processes to produce qualified products. After the product process diagram is determined, the designer starts to design the mold.

After the design has drawn all the parts of the entire mold, the mold can be formally processed. First, the template is ground to the correct size, then discharged, put through the hole, and then wire cut, cut into the block hole, knife edge, Blanking, etc., will be sent to milling machine or CNC to process countersunk head, give way, etc., and finally inspected by quality assurance. If it fails to pass, it will be returned to the responsible department for further processing.

Finally, the fitter takes it away from the warehouse and starts the preparatory work before assembly, such as chamfering, removing burrs, rust, confirming the size, checking whether each place is processed in place, whether there are holes or holes, whether the screw teeth are missing, etc., the mold When the parts arrive, you can start to assemble the mold temporarily, and install a little bit at a time. After the mold parts are in place, the mold is almost ready, which saves a lot of time than starting to assemble when all the parts are in place.

After the mold assembly is completed, start to test the mold and debug the mold until the mold can produce products that meet the requirements of dimensional accuracy and appearance quality, and then send the customer to sign the sample. After the customer confirms, all the work of this set of mold is officially completed , just wait for the production on the machine. In the future, it will be repairing and maintaining the mold. The mold is fine, and the fitter workers are fine. Working as a fitter is quite worrying. I don’t know when the mold will break. As soon as it breaks, I have to repair it immediately. If there are too many repairs, it will be more annoying. Of course, if your mold is installed well and everything that should be done is done, the mold will not have so many problems.