Author:Wu Xiongwei, Yang Jian, Li Zhaowen, Xie Guowen, Qin Xianfeng, You Binbo (Automotive Engineering Research Institute of Guangzhou Automobile Group Co., Ltd.)
The article has been published in the "Mold Manufacturing" monthly magazine, the copyright belongs to the author, please indicate the source, thank you!
【Abstract】Taking the inner plate of a certain model cover as the research object, based on the results of Autoform analysis, several internal cover forming process schemes are compared, the advantages and disadvantages of different process schemes are summarized, a reasonable cost reduction process scheme model is obtained, and the formability and dimensional accuracy of the parts are verified through actual production, which provides a reference for the process design of the inner plate of the cover of the new model and reduces the development cost of the model.
Keywords: cover inner panel; cost reduction; process; Autoform
1 Introduction
With the development of the automotive industry, the control of automobile manufacturing costs from single pieces to assemblies by various car companies has become more and more refined. As an important part of the body-in-white, stamping parts effectively reduce the cost of stamping parts, and the effect on reducing the manufacturing cost of the whole vehicle is very significant.
Therefore, the industry has also set off a trend of researching stamping parts to reduce costs. Yu Min et al. studied the optimization cost reduction scheme of the side wall outer plate process [1]; Lin Tong et al. studied the cost reduction scheme of optimizing the material grade [2]; and Feng Fenyan et al. studied the cost reduction optimization scheme of stamping parts raw materials [3].
In this paper, the inner plate of a certain model cover is used as the research object, the process scheme is arranged, the process model is constructed based on autoform analysis software, the simulation analysis compares a variety of process schemes, and the feasible cost reduction model is verified physically.
2 Process arrangement
The inner plate structure of the cover is simple, the internal sidewall angle is large, and the formability is good. This is shown in Figure 1.
Figure 1 Detailed structural drawing of the inner plate of the cover
In order to reduce the use of scrap knives and reduce the amount of iron powder generated during the cutting process, the process plan is formulated as a 4-process stamping process.
The detailed process can be arranged as follows: (1) OP10: stretching → (2) OP20: trimming + side trimming + punching → (3) OP30: trimming + side trimming + punching + side punching → (4) OP40: trimming + shaping + punching, as shown in Figure 2.
Figure 2 Layout diagram of the detailed process plan
Based on quality requirements, the content of the post-process process is basically the same. This article focuses on the impact of stretching process schemes on cost reduction.
There are 3 types of drawing processes for the inner plate of the cover:
(1) Option 1: Closed-mouth stretching scheme.
According to previous production experience, the outer plate of the cover often adopts the conventional closed mouth stretching process scheme. The 3D process die face, as shown in Figure 3, affects the cost critical point (i.e., the key point affecting material utilization) as shown at the circle. The detailed cross-sectional diagram is shown in Figure 4.
Fig. 3 Closed-mouth stretching process die surface Figure 4 Closed-mouth stretching key point cross-section
(2) Option 2: Open stretching scheme.
In order to improve the material utilization rate, reduce the production cost, and control the material size of the key point affecting the material utilization rate, the process die surface is optimized based on the closed-mouth stretching process scheme, and the boundary process supplement is adjusted, and the open process die surface is shown in Figure 5, and the detailed section is shown in Figure 6.
Fig. 5 Open stretch process die surface Fig. 6 Closed mouth stretch critical point section
The fundamental difference between closed-mouth stretching and open-mouth stretching is that the key node position of the influencing rate usage rate and whether the forming of the part surrounds the back-end process supplemental surface.
(3) Scheme 3: Floating platen stretch scheme.
Different from the conventional process idea, in order to maximize the optimization of the flow of materials at key points, to ensure the formability of the part. Affecting the material key point area to increase the upper pressure plate, the use of nitrogen cylinder as the pressure source, reduce the size of the blank, increase the feed resistance, control the material flow, thereby reducing the material cost. The process surface is shown in Figure 7 and the cross-section is shown in Figure 8.
Fig. 7 Floating plate stretching process die surface Figure 8 Floating plate stretch key point section
3 Model building
According to the above scheme analysis, three different tensile process schemes of the inner cover plate are built, and the Autoform software is introduced to create the CAE analysis model, and the tool body is shown in Figure 9, Figure 10 and Figure 11 respectively.
Figure 9 Closed-mouth simulation process model
Figure 10 Simulation process model of opening and closing ports
Figure 11 Floating plate stretch simulation process model
In order to ensure a unified benchmark comparison, the analysis material is uniformly GC270F steel plate [4], the part weight is 6.18kg, and the detailed material curve is shown in Figure 12.
Figure 12 GC270 material curve
The meshing and detailed parameter settings are shown in Figure 13.
Figure 13 Autoform mesh parameter setting diagram
After the model creation and meshing settings are completed, submit the calculations and complete the simulation analysis.
Scheme 1 uses trapezoidal material, double ribs. The blank size is: 1,780×1,185mm, and the material utilization rate is about 59.5%. After forming, the front end is almost no feeding, the rear end key point position is fed about 35mm, the maximum feeding on the left and right sides is about 10mm, the overall stretch is more sufficient, and the blank and forming cloud diagram are shown in Figure 14.
Fig. 14 Scheme 1 Blank and forming FLD diagram
Scheme 2 uses trapezoidal material, double ribs. The size of the blank is: 1,780×1,140mm; the material utilization rate is about 61.9% after the forming of the front end is almost no feeding, the rear end key point position is fed about 20mm, the maximum feed on the left and right sides is about 17mm, the local part area is not stretched sufficiently, there is a trend of thickening and dimensional accuracy. The blank and forming cloud diagram is shown in Figure 15.
Fig. 15 Scheme 1 Blank and forming FLD diagram
Scheme 3 uses square material, single rib. Blank sizes: 1,710×1,130 mm, material utilization rate: 62.6%.
After forming, the front end is almost no feeding, the rear end key point position is fed about 7mm, and the maximum feeding on the left and right sides is about 19mm. The overall stretch is relatively sufficient, the stretch state is basically consistent with scheme 1, and the blank and forming cloud diagram are shown in Figure 16.
Fig. 16 Scheme 1 Blank and forming FLD diagram
4 Floating pressure structure and physical verification
From the perspective of process and CAE simulation, the solution 3 floating platen process, formability and material utilization are the optimal solutions.
4.1 Mold structure
At present, there are few applications of floating platen process, and the production stability needs to be further verified. Based on the stability requirements, the mold is developed for production verification.
Scheme 3 requires an increase of 40 t nitrogen cylinder pressure sources in the upper mold than scheme 1 and 2, and 4 nitrogen cylinders are added to the maximum nitrogen cylinder of 10t each. The mold structure is shown in Figure 17.
Fig. 17 Tensile die structure of floating pressure plate
4.2 Stamping commissioning
Taking the CAE simulation process production parameters as a reference, the benchmark pressure of the press is set to 140t for debugging and retrieval. Due to the small resistance of the left and right end ribs, the material inflow deviates from the CAE analysis by about 10 mm. The feed in the critical area of the front and back end is basically consistent with the CAE analysis, and the middle of the back end has more material flow. The final sheet size is 1,730× 1,130mm, and the actual rate usage rate is 61.9%.
The pressure force rises by 10%, that is, 155T stamping and retrieving, the formability of the part is relatively stable, and there is no cracking and wrinkle.
The pickup status is shown in Figure 18.
Figure 18 On-site commissioning workpiece drawing
4.3 Quality Inspection
In order to further verify the dimensional accuracy of the part, after the punching edge is completed, the part placement is scanned in the free state blue light, and the scanning result is output to the rebound deviation cloud map compared with the digital module. As shown in Figure 19 and Figure 20.
Figure 19 Physical mold scan
As can be seen from Figure 20, the key area and the internal surface rebound reference of the part are within 0.5mm of ±. The maximum rebound on the left and right sides is about 2mm, and the maximum rebound in the middle of the rear end is about 2mm. It is basically the same as the first sampling state of the conventional scheme, and the subsequent surface grinding, increased reinforcement debugging, and local surface compensation can better solve the problem point, and the production stability of the parts is better.
Figure 20 Workpiece blue light scan cloud diagram
5 Conclusion
In this paper, several different process schemes of the inner cover plate of a certain model are compared and analyzed, combined with CAE simulation and production verification, and the following conclusions are drawn:
(1) The floating platening process scheme effectively improves the material rate and reduces the production cost per vehicle by about 3.6 yuan.
In the case of ensuring the formability and quality of the parts, the floating platen process is adopted, which increases the material rate by about 3% compared with the conventional process scheme, and the cost is saved by about 3.8 yuan per vehicle.
The total cost of making and repairing four nitrogen cylinders using this process is about 80,000 yuan, and the cost per vehicle is increased by about 0.2 yuan for 400,000 production capacity.
(2) There is a certain deviation between the size of the simulation and analysis sheet and the actual production.
Due to the first round of debugging, the sheet inflow deviates from the actual simulation analysis, resulting in a certain deviation between the blank size and the actual analysis, but within the scope of debugging, the problem can be solved through later debugging.
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