Stamping press is a common processing equipment in the manufacturing industry, which is used for forging, stamping and plate processing, but the stamping press itself is a large aggregate.
It can also be divided into many types.
Therefore, when purchasing stamping press, it also needs to be selected according to the finished products to be manufactured, stamping die type, stamping process characteristics, production efficiency and investment budget.
Only after careful consideration and investigation can we ensure the return on investment of purchasing stamping press.
The selection of stamping press mainly focuses on two key points, that is, the selection of type and specification.
Selection of stamping press type
There are many types of stamping presses, and the selection of types is mainly based on the materials, specifications, dimensions, sizes and requirements of finished products.
Select according to the product type of stamping parts
The selection of punch type is mainly determined by the type of stamping parts, such as the material, specification and finished product size of stamping parts.
For example, C-frame punch is recommended for small and medium-sized metal blanking parts, bending parts or shallow drawing parts, although the elastic deformation of its body will destroy the uniform distribution of the gap of the die, affect the accuracy of the finished stamping products and reduce the service life of the die.
However, its body is open on three sides, easy to operate, easy to install molds, feeders and automatic mold changing devices to realize automatic production, and the price is economical;
For large and medium-sized or high precision stamping products, H-frame punch and double shaft punch should be selected.
For special stamping processes such as leveling, bending correction and shaping, stamping press with high strength and rigidity shall be selected;
If high machining accuracy is particularly required, a stamping press with high rigidity or a punch with large capacity (one with sufficient pressure capacity for its machining) shall be selected.
However, even if the C-type punch uses a punch with large capacity, it does not have much effect. It should be noted that the stamping press with high rigidity should be selected.
Select according to the production efficiency of stamping parts
When feeding manually, do not select a stamping press with too many strokes;
During automatic stamping, the punch with more strokes shall be selected as far as possible.
During deep drawing, the punch with too many strokes cannot be selected, because the drawing is too fast, the material has no time to fully deform, and the parts are easy to crack.
If there are more than 3000 batches, it is more advantageous to use automatic feeding.
In case of multiple batches and large quantities, continuous processing methods such as high-speed automatic punch and transfer punch shall be considered.
The selection of universal punch or automatic punch should also be combined with future production, market situation, technical trend, etc.
Selection of stamping press specifications
Selection of punch specification after the type of stamping press is selected, the specification of the equipment must also be determined.
This work is determined by coordinating the die size and equipment parameters according to the process scheme and the process calculation results.
The selection of stamping equipment specifications is mainly based on the following technical parameters.
(1) Nominal pressure
The impact force generated by the sliding block of the press in the downward process is the pressure of the stamping press.
The pressure of the mechanical stamping press varies with the downward position of the slider (for the crank punch, it can also be regarded as the angle of crank rotation).
Nominal pressure refers to the maximum impact force that the slider can withstand when the slider slides to a specific distance before the bottom dead center, or when the crank rotates to a specific angle before the bottom dead center.
This specific distance is called 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 bear.
Nominal pressure is an important technical parameter for selecting punch specifications. In order to ensure the safety of stamping production, the tonnage of the selected punch must be greater than the stamping pressure during actual stamping production, and it must be ensured that the part load curve cannot exceed the allowable load curve of the punch.
The general tonnage selection principles are as follows:
- When blanking and correcting bending, the punching pressure shall not be greater than 80% ~ 90% of the tonnage;
- During deep drawing, the drawing force shall not be greater than 50% ~ 60% of the tonnage;
- In shallow drawing, the drawing force shall not be greater than 70% ~ 80% of the tonnage
When blanking bending or blanking drawing combined stamping, its tonnage value shall be determined according to its specific conditions and the allowable load curve of the machine tool used.
For thicker stamping parts, not only the allowable pressure of the punch, but also the power of the punch should be considered.
In the process of stamping, the change law of punching force is also different for different types of stamping, and the maximum impact force of punch slider is also changing.
Therefore, the nominal pressure should be selected according to the allowable pressure curve of the punch and the actual force curve of a specific stamping processing type, so that the actual stamping pressure curve is completely below the allowable pressure curve of the punch.
(2) Closing height and die mounting height
When the sliding block of the press is at the bottom dead center, the distance between its lower end face and the upper surface of the worktable is called the closing height of the press.
The difference between the closing height of the punch and the thickness of the base plate of the machine tool is the die mounting height.
In case of inorganic mattress board, the closing height is equal to the mold mounting height.
The adjusting screw in the adjusting connecting rod can adjust the die mounting height within a certain range.
When the sliding block is adjusted to the upper limit position, the mold mounting height reaches the maximum value, which is the maximum mold mounting height;
On the contrary, when the slider is adjusted to the lower limit position, its die mounting height is the minimum die mounting height. The difference between the two is the adjustment of the die mounting height.
When the punch is selected, the closing height of the stamping die should be between the large closing height and the small closing height of the punch.
Because the connecting rod will be shortened after wear, and the closing height of the stamping die will be reduced by future die repair, the height of the stamping die is generally close to the die mounting height of the stamping press when designing the stamping die.
(3) Slider stroke
Slider stroke refers to the distance the slider passes from the top dead center to the bottom dead center.
For crank punches, the slider stroke is equal to twice the crank radius.
Its size reflects the working range of the punch, and long stroke can punch parts with high height.
The determination of the stroke of the press slider mainly considers the smooth placement of the stamping blank into the die and the smooth removal of the stamping parts.
The stroke of the press slider shall be 2 times the height of the stamping parts.
When feeding manually, do not select a stamping press with too many strokes.
During automatic stamping, the stamping press with more strokes shall be selected as far as possible.
During deep drawing, the stamping press with too many strokes cannot be selected, because the drawing is too fast, the material has no time to fully deform, and the parts are easy to crack.
(4) Number of strokes
The number of strokes refers to the number of times that the sliding block of the press moves back and forth at the upper and lower dead points per minute.
The number of trips has a great impact on the productivity, which is mainly determined according to the productivity requirements, the allowable deformation speed of materials and the feasibility of the continuous operation.
(5) Worktable size
The punch table shall be determined according to the size of the actually installed mold. If the mold is large, the size of the worktable can be increased according to the needs of customers.
The size of the punch table (or the plane of the backing plate) shall be greater than the horizontal size of the lower die. Generally, each side shall be 50 ~ 70mm larger to facilitate the installation of the die;
At the same time, the plane size of the lower die must also be greater than the size of the worktable face, generally 45-50mm larger on each side, and the size of the worktable hole must be greater than the size of possible missing parts.
(6) Die handle hole size
A die handle hole is opened at the center of the lower end of the sliding block of small and medium-sized punch to facilitate the installation of the upper die.
The diameter of the die handle of the die shall be consistent with the diameter of the die handle hole of the punch, and the length of the clamping part of the die handle shall be slightly less than the depth of the die handle hole of the punch.
When selecting stamping equipment, the actual conditions of the production site shall also be considered.
If there is no ideal equipment to choose from, we should try to use the existing equipment to realize stamping production;
If more than one equipment meets the requirements, the production requirements of other products and the rational utilization of equipment resources shall be comprehensively considered.
Other selection considerations
- Easy maintenance
Stamping press with large output, high batch, high flexibility, easy maintenance and high reliability often have a great impact on the overall production.
Stamping operation is a relatively dangerous operation, and the safety problem can not be ignored.
When choosing a punch, we must choose a punch with safety equipment. Even if there is wrong operation, there will be no accident and can operate safely.
- Environmental protection
Environmental protection is increasingly put on the agenda. Choosing a punch with low noise and low earthquake is also one of the development directions in the future.
Punch die selection standard
How to choose the die for the stamping press?
First of all, you need to select the punch die according to the blanking force of your punch, actually measure the closing height and die seat of the punch, and select the appropriate die unit according to the actual situation.
Secondly, the manufacturing materials of the mold are selected according to the material of the product to be processed.
The higher the hardness of the die material is not necessarily the better.
When the hardness is too high and the stamping force is too large, the tool die will be broken and there will be fine cracks, which will affect the product accuracy.
Mold materials should be flexible, but not too soft. They should be reasonably selected according to the material of processed products.
Finally, we should also consider one of the most important issues, whether the tool and die manufacturing level of the die manufacturer can meet the accuracy standard you want, which is the fundamental to ensure the accuracy of the production and processing products.
Be sure to find a regular mold manufacturer. Don’t be greedy for cheap and choose one poor quality stamping press.