With the vigorous development of auto industry, industry competition is intensifying, how to reduce vehicle manufacturing costs and improve production efficiency has become the focus in automotive enterprises.
Body cost is an important part of the cost of the vehicle, of which the stamping production costs are mainly composed of the development costs of mold inspection tools, stamping part costs, mold stamping costs, equipment depreciation costs and labor costs.
From the perspective of process design, reducing material costs and die punching costs is an effective way to reduce stamping costs.
Reducing material cost
Reducing material costs can be studied in terms of both reducing material purchase costs and improving material utilization of stamped parts.
Reducing material purchase cost
The entire body-in-white consists of about 400 stamping parts, and the combination of material and thickness of auto stamping parts can be as high as 60 to 80.
Reasonable selection of material and grade can effectively improve material utilization and reduce purchasing costs.
The material and thickness of stamping parts of previous car models will be unified management, and a material selection library will be established.
When selecting materials for new car models, it gives priority to materials and material thicknesses that have been verified for previous models.
It also avoids using uncommon or hard to purchase materials, such as extra-wide sheets and special thickness sheets etc.
The complex procurement process of special materials will severely restrict the development cycle of stamping parts, resulting in multiple purchases of sheet materials, which will increase the cost of transportation, storage and management.
In addition, it is necessary to choose the appropriate material and material thickness according to the performance indexes and process requirements of stamping parts to prevent the quality of stamping parts from being excessive and material costs from increasing.
Improve the material utilization rate
1) Optimization of the forming process.
Stretching and forming are the commonly used forming process of stamping parts.
For stamped parts with stretched forming process, due to the increase of process supplementary profile, the material utilization rate is limited.
Some structural parts with simple shapes and small undulating characteristics adopt the blanking forming process, and the material utilization rate will be significantly improved.
Fig. 1 Mold of stamping part
The stamping parts shown in Figure 1 can be achieved by both drawing and forming processes.
The drawing process needs to be completed in 3 sequences.
The process include: drawing→trimming + punching→flanging,
The drawing process increases the supplementary surface of the process, and in order to ensure the quality of the trimming, the drawn part needs to reserve a trimming allowance of about 10mm.
As shown in Figure 2, the material utilization rate of the drawing process is 59.1%.
The forming process can also be completed in three sequences, strip blanking → forming → shaping + punching, but the material utilization rate of stamping parts is increased to 65.9%.
Therefore, when the quality of the stamping parts meets the use requirements, the blanking forming process is preferred, which can effectively improve the material utilization rate and reduce the stamping production cost.
Fig.2 Drawing process plan
2) Choose a reasonable layout method.
The layout is divided into single row layout, double row layout, two-piece mixed layout, stagger layout etc.
The choice of layout method directly affects the material utilization of stamping parts.
Figure 3 shows a single-row layout scheme for a stamping part, with a material utilization rate of 61.4%, and Figure 4 shows 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 -row layout
Fig.4 Stagger layout
The material of the stamping parts is DC01, the material thickness is 2.0mm, the weight of the parts is about 0.14kg, and the amount of each piece is 1 piece
The plate price is calculated at 4500 yuan/ton, and the material cost of a stamping part is reduced by 0.16 yuan.
If the production plan for this model is 50,000 vehicles per year, Figure 4 will save 8,000 yuan per year compared to Figure 3.
Therefore, in the process design stage, it is necessary to continuously optimize the layout method, determine the best plan, and improve the material utilization rate of the vehicle;
In the manufacturing and production stages, reconfirm the layout method to ensure that the best plan is implemented.
3) Waste utilization.
There are usually two schemes for waste utilization.
One scheme is to use large blank waste as small blanks, and the other scheme is kit production.
The use of waste materials can indirectly increase the utilization rate of materials and reduce the cost of stamping production.
In practice, some large stamped parts need to be cut with a drawing or drop material process to ensure formability, such as the drop material for side surround door openings.
After these scraps are collected, they can be used for forming small stamping parts directly or after cutting after matching the material and thickness.
Figure 5 is a truck side of the outer plate uncoiling material pattern, in which the door position of the scrap cut can be used for the production of the vehicle model of two small stamping parts, and the production quantity is just enough to meet the requirements of a single small stamping part.
Fig. 5 Reuse of waste material from side wall outer door opening
Kit production means a grouping arrangement between stampings in which small stampings are designed directly in the supplemental scrap area of the large stampings process, formed together with the large stampings and then separated by post-sequence slitting.
Alternatively, small stamping parts can be produced in kits by combining left/right parts in a process complementary area, as shown in Figure 6.
The production of the kit can not only improve the utilization rate of materials but also save the cost of small stamping parts and the cost of punching times.
However, the production of the kit increases the process difficulty, and it is necessary to repeatedly optimize the product shape and CAE analysis results in the SE stage to ensure the formability of the two stamping parts.
In addition, it is necessary to consider the collection method of small stamping parts at the design stage to avoid quality defects such as knocks and scratches in the production process.
Fig. 6 Kit stamping process planning
Reducing die stamping cost
There are two main ways to reduce the cost of the whole car stamping, one is to reduce the tonnage of the press and the other is to reduce the number of dies.
Reducing press tonnage
The tonnage of the press is mainly determined by the forming force required for the stamping part, the size of the die, the closing height of the die and the height of the die loading, etc.
When the size of the die is the limiting factor in choosing the tonnage of the press, it is possible to reduce the tonnage of the press by optimizing the internal structure of the die and reducing the size of the die, thus the cost of stamping is reduced.
When the die size becomes the limiting factor for the selection of the tonnage of the press, under the premise of ensuring the performance and structural strength of the die, by optimizing the internal structure of the die, reducing the size of the die, and reducing the tonnage of the press, thus the cost of the die stamping is reduced.
Alternatively, when purchasing press equipment, choose a larger size worktable to reduce the size requirements of the machine tool for the die.
Reducing die numbers
(1) Choose the matched-die production process.
Matched-die production can not only reduce the generation of process supplementary waste, improve material utilization, but also reduce the number of molds, thereby saving die development costs and punching costs, as shown in Figure 7.
Left/right floor through the matched-die production, not only improve the formability of the stamping parts, but also directly save 4 pairs of die stamping costs compared with the single production.
Fig. 7 matched-die production process
The matched-die production is not limited to left/right symmetrical parts.
In the process design stage, it should be fully considered matched-die production process to reduce the cost of stamping the whole car.
(2) The use of multi-position die.
Multi-position die can realize one or more stamping parts on a die for several process content, as shown in Figure 8 (die structure).
The machine tool realizes the three processes of stamping parts in one punch cycle:
OP20 trimming + punching → OP30 flanging + shaping → OP40 trimming + punching + side punching.
The size of the mold is about 1720mm×1940mm×900mm, and it can be produced on a 1000t press.
The cost of one stroke is about 4.5 yuan.
If the content of the 3 processes of the stamping part is 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 punching is about 5.9 yuan.
The use of multi-position die, not only reduces the die development costs and reduce the flow time between the process, but the most direct advantage is to reduce the cost of stamping parts.
Figure 8 multi-station die
(3) Use progressive die.
Figure 9 shows the design drawing of the progressive die process for a car model.
In the production process, only one operator and one press can produce the stamping parts.
Progressive die technology effectively reduces the number of operators and press requirements, and the production of parts of high stability, the quality of parts can be effectively guaranteed.
Fig.9 Design of the progressive die process
- Empty Station
- Empty Station
- Bending 90°
- Cutting& blanking
(4) Adopt the two-mold stamping process layout.
Some stamping manufacturers install the two sets of molds on a large-tonnage press directly or through a template for production to solve the problem of production saturation of small-tonnage presses and waste of resources in single-die production of large-tonnage presses.
This production method needs to ensure that the closing heights of the two molds are the same, and the required forming forces are similar to prevent the uneven force on the left and right from affecting the accuracy of the press.
The effect of improving the material utilization rate and reducing the cost of punching is small for a single stamping part, but the effect of reducing costs and increasing efficiency is significant for a complete vehicle with an annual production of over 10,000 units.
Therefore, automobile companies should be studied and applied with new stamping technologies and processes.
It also needs to continuously improve material utilization and reduce die stamping costs, so that companies can gain a firm foothold in the industry and develop steadily.