With the vigorous development of the automobile industry, competition between automobile companies is intensifying. Reducing vehicle manufacturing costs and improving production efficiency has become a crucial focus for them.
The cost of producing the vehicle body is an important component of the total cost of the vehicle. Stamping production costs mainly include inspection tool development costs, stamping parts costs, mold stamping costs, equipment depreciation costs and labor costs.
From a process design perspective, reducing material and punching costs is an effective way to reduce stamping costs.
Reducing the cost of materials
Reducing material costs can be studied both in terms of reducing material purchasing costs and improving material utilization of stamped parts.
Reducing the cost of purchasing materials
The entire white body is made up of approximately 400 stamped parts, with the combination of materials and thicknesses of the automotive stamped parts ranging from 60 to 80.
Choosing the right material and grade can effectively improve material utilization and reduce purchasing costs.
To manage the material and thickness of stamped parts of previous car models, a material selection library will be established.
When selecting materials for new car models, priority will be given to materials and material thicknesses that have been verified for previous models. This will avoid the use of unusual or difficult to acquire materials such as extra-wide sheets and special thickness sheets, etc.
The complex procurement process for specialty materials can severely restrict the development cycle of stamped parts, resulting in multiple purchases of sheet materials, which will increase transportation, storage and management costs.
In addition, it is necessary to choose the appropriate material and material thickness based on the performance indexes and process requirements of stamping parts to avoid excessive quality of stamped parts and increased material costs.
Improve material utilization rate
1) Optimization of the forming process.
Stretching and forming are common forming processes used to stamp parts.
For stamped parts that undergo a stretch forming process, the material utilization rate is limited due to the increased profile of the process.
However, some structural parts with simple shapes and small wavy features can use the blanking forming process, which significantly improves material utilization rates.
Fig. 1 Stamped part mold
Both drawing and forming processes can achieve the stamped parts shown in Figure 1.
The drawing process comprises three sequences: drawing → cutting + punching → flanging.
To guarantee a quality cut, the designed part must reserve a cutting margin of approximately 10mm. This process increases the additional process surface.
As illustrated in Figure 2, the drawing process has a material utilization rate of 59.1%.
The forming process also involves three sequences: strip blanking → forming → forming + punching, but has a higher material utilization rate of 65.9% for stamping parts.
Therefore, if the quality of the stamped parts meets the usage requirements, the blank forming process is preferred. This process can effectively increase the material utilization rate and reduce the stamping production cost.
Fig.2 Drawing process plan
2 ) Choose a reasonable layout method.
The layout of stamping parts can be divided into several types, such as single-line layout, double-line layout, two-piece mixed layout, staggered layout, etc.
The choice of layout method has a direct impact on the use of material for printed parts.
Figure 3 shows a single-line layout scheme for stamping parts, which has a material utilization rate of 61.4%. On the other hand, Figure 4 demonstrates a staggered layout scheme for stamping parts, with a material utilization rate of 73.7%.
The material utilization rate in Figure 4 is 12.3% higher than that in Figure 3.
Fig.3 Single line layout
Fig.4 Staggered layout
The stamped parts are made from DC01 material, with a thickness of 2.0mm and an approximate weight of 0.14kg per piece. The quantity required for each piece is 1.
Based on a sheet price calculation of 4,500 yuan/ton, the material cost for a stamping part is reduced by 0.16 yuan.
Assuming a production plan of 50,000 vehicles per year, Figure 4 can save 8,000 yuan per year compared with Figure 3.
Therefore, it is essential to continuously optimize the layout method during the process design phase, determine the best plan, and improve the material utilization rate of the vehicle.
During the manufacturing and production stages, it is essential to reconfirm the layout method to ensure the best plan is implemented.
3) Use of waste.
There are typically two approaches to waste utilization: using large waste blanks as small blanks or employing kit production.
The use of waste materials can indirectly increase the material utilization rate and reduce the stamping production cost. In practice, some large stamped parts need to be cut with a drawing process or drop material to ensure formability, such as drop material for side door openings.
After collecting these scraps, they can be used to form small printed parts directly or after cutting and adapting the material and thickness.
Figure 5 shows the unwinding pattern of material from the outer plate of a truck, in which the scrap cut at the door position can be used to produce two small stamped parts for the vehicle model. The production quantity is precisely sufficient to meet the requirements of a single small stamped part.
Fig. 5 Reuse of waste from the side wall of the external door opening
Kit production refers to a grouping of stampings, in which small stampings are designed to fit directly into the supplementary scrap area of the large stamping process. They are then formed together with the large prints and separated by post-sequence cutting. Alternatively, small stamped parts can be produced by combining left/right parts in a complementary process area, as shown in Figure 6.
Kit production can improve material utilization rates, reduce the cost of small stamped parts, and minimize the cost of punching times. However, the production of kits increases the difficulty of the process, making it necessary to repeatedly optimize the product shape and carry out CAE analyzes in the SE stage to guarantee the formability of the two stamped parts.
Furthermore, it is essential to consider the method of collecting small stamped parts at the design stage to avoid quality defects such as bumps and scratches during the production process.
Fig. 6 Planning the kit stamping process
Reducing the cost of stamping
There are two main ways to reduce the cost of automobile stamping: reducing press tonnage and decreasing the number of dies required.
Reducing press tonnage
The tonnage of a press is mainly determined by several factors, including the forming force required for the stamped part, the size of the die, the closing height of the die, and the loading height of the die.
If die size is the limiting factor in selecting press tonnage, it is possible to reduce tonnage by optimizing the internal structure of the die and reducing its size. This, in turn, helps reduce the cost of stamping.
When die size becomes a limiting factor in choosing press tonnage, it is crucial to ensure the performance and structural strength of the die. By optimizing the internal structure of the die and reducing its size, the tonnage of the press can be reduced, thereby reducing the die stamping cost.
Another alternative is to choose a press with a larger work table when purchasing press equipment. This can help reduce machine tool size requirements for the die.
Reducing the number of dice
(1) Choose the combined die production process .
The production of combined dies can not only reduce the generation of supplementary process waste and improve material utilization, but also decrease the number of molds, thereby saving die development and punching costs, as illustrated in Figure 7.
When using combined die production, left/right treading not only improves the formability of stamped parts, but also directly saves 4 pairs of die stamping costs compared with single production.
Fig. 7 Combined die production process
Combination die production is not limited to left/right symmetrical parts. Therefore, during the process design phase, it is important to fully consider the combined die production process in order to reduce the stamping cost of the entire car.
(2) The use of multi-position array.
A multiposition die can be used to produce one or more parts stamped in a single die with different process contents, as illustrated in Figure 8 (die structure).
With this machine tool, three part stamping processes can be carried out in one punching cycle:
Cutting + punching OP20 → flanging + shaping OP30 → cutting + punching OP40 + side punching.
The mold size is approximately 1720mm×1940mm×900mm and can be used in a 1000t press.
The cost of one swipe is about 4.5 yuan.
If the 3 processes of the stamping part are designed according to 3 sets of dies, the press tonnages required by the die are 500t, 630t and 500t respectively, and the cost of one punch is about 5.9 yuan.
Using a multi-position die not only reduces die development costs and minimizes flow time between processes, but also directly reduces the cost of stamping parts.
Figure 8 Multistation Array
(3) you die progressively.
The progressive die process design for a car model is shown in Figure 9.
During production, a single operator and a press are sufficient to manufacture the stamped parts.
The use of progressive die technology significantly reduces the number of operators and presses required, while ensuring high production stability and effectively guaranteeing part quality.
Fig.9 Progressive die process design
- Punch
- Cut
- Cut
- Doubling
- Empty Station
- Flexion 45°
- Empty Station
- Bending 90°
- Punch
- Cropping and erasing
( 4) A equip the two- mold layout of the stamping process.
Some stamping manufacturers install two sets of molds on a large tonnage press directly or through a template for production, to solve the problem of saturation of small tonnage press production and waste of resources in single press mold production of large tonnage.
To implement this production method, it is necessary to ensure that the closing heights of the two molds are identical and that the required forming forces are similar, to prevent unequal forces on the left and right sides from affecting the precision of the press.
Conclusions
Improving the material utilization rate and reducing the punching cost may not have a significant impact on a single stamped part, but it can greatly increase the efficiency and cost-effectiveness of a complete vehicle with an annual production of more than 10,000 units .
Therefore, automobile companies must focus on studying and implementing new stamping technologies and processes to achieve these benefits.
It is also important to continually improve material utilization and minimize stamping costs, which will help companies establish a strong position in the industry and facilitate steady growth.
