Several methods and measures to reduce the cost of stamping

For any enterprise, production cost is a crucial factor. 70% of the metal parts in automobile parts are obtained by stamping, and the cost of stamping parts accounts for more than 30% of the automobile cost. Reducing the cost under the premise of ensuring the quality of parts in the stamping field is an eternal topic in modern automobile manufacturing industry.

Automobile body-in-white is mainly composed of metal stamping parts. If the cost of a single stamping part is reduced, the cost of the whole body-in-white can be reduced. The cost of stamping parts is composed of metal material cost and processing cost, so improving the material utilization rate of stamping parts and reducing the consumption quota of stamping parts, selecting lower-priced steel plates on the premise of ensuring quality and performance, and effectively reducing stamping costs through material performance optimization, product design optimization and process design optimization.

Material performance optimization

Material grade reduction
Under the same tensile strength and yield strength of the same steel grade, the price of materials with high stamping performance is higher than that of materials with low stamping performance. When selecting materials for product design, according to the actual mold debugging situation and the adaptability of the plate, the material grade can be appropriately reduced and low-performance materials can be selected to achieve the purpose of reducing costs.

By checking the drawings and process documents, it is found that the shape of a part is relatively simple and the depth is relatively shallow, and ST14 material with low stamping performance is used for analysis and simulation without cracking. Then do further verification in the field, and try to punch with low-performance test materials. By simply adjusting the die, the parts did not crack during the test punch, and the test punch was qualified. After mass verification in the later period, the production process is stable and the materials can be replaced. Through this test, we screened all the parts with high stamping performance and analyzed the possibility of reducing the material performance. Finally, 20 parts were successfully tested. This work is of great significance to the subsequent development of new vehicles. In the product design and material transformation stage, some parts with shallow drawing depth that can be produced by press bending process can directly use low-performance materials according to experience.

 

Galvanized sheet to cold rolled sheet
Under the same tensile strength and yield strength of the same steel, the price of galvanized materials is higher than that of non-galvanized materials. For some parts with low requirements for corrosion protection, low-priced cold-rolled plates can be used. At the same time, by improving the painting process, some parts with anti-corrosion requirements can also use low-priced cold-rolled plates.

A door lock reinforcement plate originally used galvanized steel plate. Through communication with product designers, it is considered that the requirements for anticorrosion performance here are not high, and painting process can be used instead of galvanized layer for anticorrosion. At the same time, it is stipulated that the part of the chassis near the ground is easy to contact with the road water when the vehicle is driving, which is the key anti-corrosion area. We converted all the galvanized parts in the door assembly, engine cover assembly, side wall assembly and luggage compartment cover assembly of our own models into cold-rolled plates, which greatly reduced the cost of the car body. In the product design stage of new models in the future, the direct use of cold-rolled plates for parts in these areas can effectively reduce the body cost.

 

Application of new materials
In recent years, Baosteel has developed a GI inorganic film material by understanding the demand and cost pressure of automobile enterprises and constantly innovating technology. This material is galvanized sheet. By coating an inorganic film on the lower performance substrate, the lubricity of the material surface is improved, and it can replace the higher performance material in the stamping process. The price of this steel is cheaper than that of high-performance ST07Z material per ton, 500 yuan. Through the trial punching of this material, it is verified that its performance fully meets the stamping requirements, and the trial assembly results meet the loading requirements. The results of part size detection and welding failure are completely qualified, and it is concluded that this new material can completely replace ST07Z.

Material specification consolidation
Material selection optimization, mainly brand merging and coating selection. There is a price difference between different coil widths of the same material, in which the coil width in the range of 1200~1499mm is the optimal coil width, and the coil width smaller than 1200mm and larger than 1499mm has a price difference with this range.

Material thickness control
The thickness of steel coil is qualified in upper or lower difference, which meets the requirements of use, and qualified parts can be punched. However, for users, if the thickness of the steel coil is always in the lower deviation through special control during the rolling process, the steel coil with the same weight can produce more pieces, thus producing more parts, reducing the consumption quota of a single piece, improving the material utilization rate of the steel coil and reducing the weight of waste.

Product design optimization

Platform design
Design determines quality and cost, and the designer’s cost consciousness is very important. Design determines most of the cost of the car body, so good design is very important. The cost of stamping parts includes the cost of tooling such as molds, fixtures and fixtures. Therefore, in the process of vehicle design, if we can adopt the modular design concept, improve the universality of parts, try to design new vehicles under the same platform and use the same parts for multiple vehicles, so that the tooling cost can be dispersed to every part of each vehicle. Reduce the investment in molds, checking tools, fixtures, work station appliances, etc., thus reducing the cost of individual parts.

Develop a variety of common parts under multiple platforms, so that each platform can be used by multiple models at the same time, and the number of platform parts is large, which is beneficial to production organization and reducing procurement costs, greatly improving production efficiency and reducing vehicle costs.

Optimal design of part shape
In product design, it is necessary to optimize the shape of parts, try to avoid big sudden changes in the shape of parts, avoid prominent parts of parts, and avoid too big height difference of parts, so as to improve the utilization rate of parts materials. Table 2 is a case of part shape optimization design.

Optimization of stamping process

Optimize blank shape
In process design, similar parts can meet the requirements of blank materials of multiple products by optimizing the blank shape, using arc knives and adjusting the step distance of arc knives. By adjusting the step distance, the arc knife can meet the requirements of the blank of the outer plate and the inner plate of the hair cover of multiple models. In this way, the universality of tooling is realized and the input cost of tooling is reduced.

 

Residual waste utilization
There are two door openings in the side wall of each car. In the past, the waste at this place used to slide directly into the waste pit in the process of uncoiling and blanking, and was treated as waste. Now, with the progress of production and technology, the utilization scheme of surplus waste has been formulated in the preparation stage of vehicle production. Through simulation analysis, the material grade and material thickness are merged to make full use of large waste.

It should be emphasized that the scheme of waste utilization must be planned before the design of uncoiling blanking die, so that the outflow state of waste and the position of waste knife can be considered in the design of die structure, so as to avoid the situation that useful waste can be chopped up or cannot be discharged out of the press due to the limitation of die structure.

Forming process optimization
In order to ensure the quality stability of stamping parts and reduce the defects such as springback, drawing process is the first choice for many parts in process design. However, through analysis and experiments, some parts with shallow shapes can be produced by forming process even if there is material deformation, thus reducing the waste added by the process; In the second case, some parts are in deep drawing depth, so you can try to use the open drawing method to open the process supplement on the premise of ensuring the trimming amount, which can reduce the use of materials in the process supplement; In the third case, if the part is large, the shape is deformed locally, and other parts are gentle, you can consider setting the drawing parting line in the part, taking the gentle position of the part as the drawing blank holder and the convex part as the drawing punch. Figure 2 shows that the left and right side plates are changed from drawing process to forming process, and the material utilization rate is increased from 45% to 78%.

 

Punching and one-die multi-piece process
Because of the shape of products, some parts must produce large pieces of waste, such as the part where the glass lifter is installed in the middle of the door inner panel and the part where the windshield is installed in the back-up door inner panel. In the original process, these parts are directly cut off after drawing and slide into the waste pit as waste, which has low material utilization rate. In order to solve this problem, we can select suitable parts in the early stage of process review, mainly considering the shape and size of the parts, embed the target parts into the waste parts, make the target parts as drawing shapes, make them together in the drawing sequence, and then cut the parts through trimming and separation, thus effectively using the waste area and improving the production efficiency, as shown in Figure 3. Multiple parts in one module can share the process supplement, effectively reducing the size of the process supplement part of a single part.

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