A stamping press is a processing machine commonly used in the manufacturing industry, used for forging, stamping and plate processing. It's an extensive machine in its own right.
Stamping presses come in several types, so when purchasing one, it is important to consider the finished products being manufactured, the type of stamping die, the characteristics of the stamping process, production efficiency and investment budget. Careful consideration and research will help ensure a positive return on investment for your stamping press.
Selecting a stamping press mainly focuses on two critical factors: type and specification.
Selection of stamping press type
There are several types of stamping presses, and the type selection is mainly based on the material, specifications, dimensions and size requirements of the finished products.
Selection based on stamped part product type
Punch type selection is largely determined by the type of stamped part, including the material, specifications and final size of the stamped part.
For example, a C-frame punch is suitable for small to medium-sized metal blind parts, bent parts or shallow drawing parts. However, the elastic deformation of its structure can compromise the uniform distribution of the die gap, affecting the precision of the finished stamped products and reducing the die's useful life.
Despite these limitations, the C-frame punch has several advantages, such as its open frame on three sides, which facilitates the operation and installation of molds, feeders and automatic mold changing devices for automated production, and its economical cost.
For large, medium or high precision stamping products, it is recommended to choose an H-frame punch or a double-axis punch.
For specialized stamping processes such as leveling, bend correction and shaping, a stamping press with high strength and rigidity should be selected. If a high level of machining accuracy is a priority, a stamping press with high rigidity or a punch with high capacity (with sufficient pressure capacity for the machining process) should be selected.
However, even if a large capacity punch is used with a C-frame punch, it will not have a significant impact. It is important to highlight that a stamping press with high rigidity should be chosen in this scenario.
Selection based on production efficiency of stamping parts
When manual feeding is used, it is important not to choose a stamping press with a lot of strokes. During automatic stamping, whenever possible, a punch with more strokes should be selected.
However, during deep drawing, you should not choose a punch with many blows, as the stamping process would be very fast, leaving no time for the material to deform completely, which could result in the parts cracking.
If the production volume exceeds 3,000 batches, it is more advantageous to use automatic feeding.
For multiple batches and large quantities, it is recommended to consider continuous processing methods such as high-speed automatic punches and transfer punches. The choice between a universal punch or an automatic punch must also take into account future production plans, market conditions and technical trends.
Selection of stamping press specifications
After selecting the type of stamping press, the equipment specification must also be determined. This is achieved by coordinating the die size and equipment parameters according to the processing plan and the results of processing calculations.
The selection of stamping equipment specifications is mainly based on the following technical parameters.
(1) Rated pressure
The force generated by the press slider during the downward movement is called stamping pressure. The pressure of a mechanical stamping press changes depending on the downward position of the slider (or the rotation angle of the crank in the case of a crank punch).
Nominal pressure is the maximum impact force that the slider can withstand at a specific distance before reaching bottom dead center, or at a specific angle of crank rotation before reaching bottom dead center. This specific distance is referred to as the nominal pressure stroke and the corresponding crank angle is the nominal pressure angle. The nominal pressure reflects the impact force that the punch itself can withstand.
Nominal pressure is a critical technical parameter in selecting punch specifications. To ensure the safety of the stamping process, the tonnage of the selected punch must be greater than the actual stamping pressure and must ensure that the partial load curve does not exceed the allowable load curve of the punch.
The general principles of tonnage selection are:
- For shear and bending correction, the punching pressure should not exceed 80% to 90% of the tonnage.
- For deep drawing, the drawing force should not exceed 50% to 60% of the tonnage.
- For shallow drawing, the drawing force should not exceed 70% to 80% of the tonnage.
For combined stamping, bending or stamping, the tonnage value must be determined based on the specific conditions and allowable load curve of the machine tool being used.
When stamping thicker parts, it is important to consider not only the permissible punch pressure, but also its power.
The change in punching force during stamping varies for different types of stamping, and the maximum impact force of the punch slider also changes.
Therefore, the nominal pressure should be selected based on the allowable pressure curve of the punch and the actual force curve of a specific stamping process, so that the actual stamping pressure curve remains below the allowable pressure curve of the punch.
(2) Closing height and die mounting height
When the press slider is at bottom dead center, the distance between its lower end face and the upper surface of the work table is called the press closing height.
The difference between the press closing height and the thickness of the machine tool base plate is called the die mounting height.
If an inorganic mattress plate is used, the closing height is equal to the die mounting height.
The adjusting screw on the connecting rod can adjust the mounting height of the die within a certain range.
When the slider is adjusted to the upper limit, the die mounting height reaches its maximum value, which is the maximum die mounting height.
Conversely, when the slider is adjusted to the lower limit, the array mounting height is at its minimum value, which is the minimum array mounting height. The difference between the two is the die mounting height adjustment range.
When selecting a press, the closing height of the stamping die must be between the maximum and minimum closing heights of the press.
Because the connecting rod can shorten over time due to wear and the closing height of the stamping die can decrease with future repairs, the height of the stamping die is typically designed to be close to the mounting height of the stamping press die.
(3) Sliding stroke
Slider travel refers to the distance traveled by the slider from top dead center to bottom dead center.
For crank punches, the slider stroke is equal to twice the crank radius, which reflects the working range of the punch. A longer stroke allows punching parts with greater height.
The slider stroke selection is based primarily on the ease of inserting the stamped part into the die and removing the stamped parts. It is generally recommended that the slider travel be twice the height of the stamped part.
When manual feeding is involved, it is best to avoid selecting a high-stroke stamping press. For automatic stamping, it is preferable to choose a stamping press with a longer stroke. However, during deep drawing, a high-stroke stamping press should not be selected, as the high stamping speed may cause the material to not deform completely, leading to the parts cracking.
(4) Stroke number is
The number of strokes per minute of a stamping press refers to how often the sliding block moves from top dead center to bottom dead center and back in one minute.
The number of strokes greatly affects the productivity of the stamping process and is mainly determined based on production demands, the acceptable deformation speed of the material and the feasibility of continuous operation.
(5) Work table size
The size of the punching table should be determined based on the size of the mold actually installed. If the mold is large, the size of the working table can be adjusted to meet the customer's needs.
The drilling table (or backing plate surface) must be larger than the horizontal size of the bottom die. It is recommended that each side is 50-70mm larger to facilitate matrix installation.
Furthermore, the size of the bottom surface of the die must be larger than the size of the work table face. It is usually 45-50 mm larger on each side. The size of the work table hole must be larger than the size of possible missing parts.
(6) Die handle hole size
A hole for the die handle is located in the center of the lower end of the small and medium punch slide block to facilitate installation of the upper die.
The diameter of the die handle should correspond to the diameter of the hole for the die handle in the punch, and the length of the die handle fixing part should be slightly less than the depth of the hole for the die handle in the punch.
When selecting stamping equipment, the actual conditions of the production site must also be taken into account.
If suitable equipment is not available, existing equipment must be used to carry out stamping production.
When more than one piece of equipment meets the requirements, the production needs of other products and the efficient use of equipment resources must be comprehensively considered.
Other selection considerations
Easy maintenance
Stamping presses with high output, large batch production, high flexibility and easy maintenance are highly reliable and can have a significant impact on overall production.
Security
Stamping is a dangerous operation and safety cannot be ignored.
When selecting a punch, it is important to choose one that is equipped with safety features, ensuring that even if there is an error in operation, accidents can be avoided and operations can be carried out safely.
Environmental Protection
Environmental protection is becoming a more pressing issue. In the future, choosing a punch with low noise and low vibration levels will be an important development direction in the industry.
Punch Die Selection Pattern
How to choose the die for the stamping press?
To begin with, you should choose the punch die based on the cutting force of your punch. You must accurately measure the closing height and seat of the die, and then select the appropriate die unit that meets your specific needs.
Next, mold materials should be selected based on the product material that needs to be processed.
It is important to note that a higher hardness of the matrix material is not always better. If the hardness is too high and the stamping force is too large, the tool die may break, causing fine cracks that affect the accuracy of the product.
Mold materials must have a balance between flexibility and strength. Material selection should be made based on the material of the product being processed.
Finally, a crucial consideration is whether the manufacturer's tool and die manufacturing level can meet the required standard of accuracy. This is essential to ensure the accuracy of product production and processing.
It is advisable to choose a reliable mold maker rather than opting for a cheap option that may compromise the quality of the stamping press.
