Abstract: Through dozens of production tests, on the basis of previous mold design and manufacturing innovation and improvement, a series of new energy vehicles extruded aluminum profiles were successfully produced, which realized the new energy vehicles material without coarse grain defects inside and outside, greatly improved the extrusion productivity and yield, and better met the quality requirements of new energy vehicles materials for enterprise production.
Preface
With the enhancement of environmental protection awareness, the development and advocacy of new energy around the world make the promotion and application of new energy vehicles imminent. Meanwhile, the requirements for the lightweight development of automotive materials, the safe application of aluminum alloy, and its surface quality, size and mechanical properties are also increasingly high [1]. Taking a new energy vehicle with a vehicle weight of 1.6t as an example, the material of aluminum alloy is about 450kg, accounting for about 30%. The surface defects in the extrusion production process, especially the coarse grain problems on the inner and outer surfaces, seriously affect the production progress of aluminum profiles of new energy vehicles, and become the bottleneck of its application and development.
For extrusion profiles, the design and manufacture of extrusion dies are the most important, so the research and development of new energy vehicles aluminum profiles is imperative. Propose scientific and reasonable die solutions, so as to further improve the qualified rate of new energy vehicles aluminum profiles and extrusion productivity, in order to meet the market demand.
At present, the traditional extrusion die design and manufacturing process cannot meet the demand of producing qualified aluminum profiles for new energy vehicles, and the development of the die in the domestic market is still in its infancy [2]. After dozens of tests, the company has developed a series of new energy materials. This paper introduces one of the successfully developed and mass-produced new energy vehicle battery pack installation beam aluminum extrusion die solutions, which can be used for reference.
1 Product Features
(1) The materials of parts, surface treatment and antisepsis shall be implemented according to the relevant provisions in the standards of ETS-01-007 "Technical Requirements for Aluminum Alloy Profile Parts" and ETS-01-006 "Technical Requirements for Anodizing Surface Treatment".
(2) surface treatment: anodizing, the surface can not have coarse grain.
(3) No cracks, wrinkles or other defects are allowed on the surface of the parts. The oxidized parts are not allowed to be polluted.
(4) The prohibited substances of the product meet the requirements of Q/JL J160001-2017 "Requirements for prohibited and restricted substances of automotive parts and materials".
(5) mechanical properties requirements: tensile strength ≥ 210 MPa, yield strength ≥ 180 MPa, elongation after fracture A50 ≥ 8%.
(6) The composition requirements of aluminum alloys for new energy vehicles are shown in Table 1.
The size of battery pack mounting beam component of new energy vehicle accessories is shown in Figure 1.
2 Optimization and comparative analysis of extrusion die structure Large-scale power restriction occurs
(1) Traditional scheme 1#, i.e. the design of extrusion die before improvement, is shown in Fig. 2. According to the conventional design idea, as indicated by the arrows in the figure, the intermediate rib position, the drainage under the tongue, the upper and lower drainage unilateral 20°, the drainage height H15 mm supplies aluminum water to the rib, the right angle of the empty knife under the tongue is excessive, the residual aluminum water is in the corner, which is prone to the existence of aluminum slag in the dead zone, and the surface is extremely prone to coarse grain problem after oxidation verification [1].
The following preliminary optimization is carried out on the traditional mold manufacturing process scheme: 1 on the basis of this mold, try to increase the aluminum supply of the rib; 2 deepen the depth of the empty knife under the tongue on the original basis, that is, increase 5mm on the original 15mm; 3 widen the width of the empty knife under the tongue by 2mm on the basis of the original 14mm. The physical picture after optimization is shown in Figure 3.
The verification results show that after the above three preliminary improvements, the coarse grain defects still exist after the oxidation treatment of the profile, which has not been reasonably solved, indicating that the preliminary improvement plan before this time still cannot meet the production requirements of aluminum alloy materials for new energy vehicles.
(2) Propose new scheme 2 on the basis of preliminary optimization. The mold design of new scheme 2# is shown in Figure 4. According to the "principle of metal fluidity" and "the law of minimum resistance" [2], the improved auto parts mold 2# adopts the "open back hole" design scheme, the rib position plays a direct impact role, reducing friction resistance; the feed surface is designed as "cauldron shape", the bridge is processed into an amplitude type, aiming to reduce friction resistance, improve fusion degree, and reduce extrusion pressure; try to sink the bridge to prevent coarse grain problems at the bottom of the bridge, the width of the empty knife under the bridge tongue is ≤ 3mm; the step difference between the working belt of the male head and the working belt of the lower die is ≤ 1.0mm; the empty knife under the tongue of the upper die is smooth and uniform, without leaving a flow block, try to directly into the molding hole; the working belt between the two male heads in the middle inner rib is as short as possible, which is generally 1.5~2 times the wall thickness; the drainage groove is smooth, which meets the needs of enough metal aluminum water flow into the cavity, which is fully fused, and no dead zone is left everywhere [3] (the empty knife after the upper die is not more than 2~2.5mm). The structure of the extrusion die before and after the improvement is shown in Figure 5.
(3) pay attention to the improvement of processing details. The bridge is polished and connected smoothly, the upper and lower mold working belt is smooth, the deformation resistance is reduced, the metal flow is improved to reduce the uneven deformation, and the coarse crystal and welding problems can be effectively suppressed, so as to ensure the position of the reinforcement discharge and the speed of the bridge root is synchronized with other parts, and the surface problems such as the welding of the coarse crystal on the surface of the aluminum profile are reasonably and scientifically suppressed. The comparison of the mold drainage before and after the improvement is shown in Figure 6.
3 Extrusion Process
For 6063-T6 aluminum alloy of new energy vehicles, according to the calculation of the extrusion ratio of the shunt mold at 20~80, the extrusion ratio of this aluminum extruded by the 1800t machine is 23, which meets the production performance requirements of the machine [4]. The extrusion process is shown in Table 2.
When extruding, pay attention to the following points[5]:
(1) It is forbidden to stack the molds in the same furnace(1) It is forbidden to stack the molds in the same furnace, otherwise it will lead to uneven mold temperature and easy to crystallize.
(2) If abnormal stop occurs during extrusion, the stop time shall not exceed 3min, otherwise the mold must be unloaded.
(3) It is forbidden to(3) It is forbidden to heat and extrude directly after unmolding.
4 Modification Measures and Effects
After dozens of mold repair and mold test improvement, the following reasonable mold repair scheme is proposed.
(1) modify and adjust the original 1# mold: 1 sink the bridge as far as possible, the width of the bridge bottom ≤ 3mm; 2 the step difference between the working belt of the male head and the working belt of the lower mold ≤ 1.0mm; 3 do not leave the flow block; 4 the working belt between the two male heads at the inner rib is as short as possible, the drainage groove is smooth, as large and smooth as possible; 5 the working belt of the lower mold is as short as possible; 6 no dead zone is left everywhere (no more than 2mm for the back empty knife); 7 the inner cavity coarse crystal repairs the upper mold, the outer surface coarse crystal reduces the working belt of the lower mold and flattens the flow block, or do not leave the flow block, and reduce the working belt of the lower mold [6].
(2) On the basis of further modification and improvement of the above 1# mold, 2# mold is modified as follows: 1 eliminate the dead zone of the two male heads; 2 level the flow block; 3 reduce the drop between the male head and the working belt of the lower mold; 4 reduce the working belt of the lower mold.
(3) After modifying and improving the mold, the surface quality of the finished product reaches an ideal state, with a bright surface and no coarse grains, which excellently solves the problems of coarse grains and welding defects on the surface of such new energy aluminum profiles.
(4) The extrusion capacity was increased from 5 t/d to 15 t/d, and the production efficiency was greatly improved.
The before and after improvement comparison is shown in Figure 7.
5 Conclusion
Through repeated optimization and improvement of the original mold, the problem of coarse grain and welding on the surface of aluminum profiles of new energy vehicles has been completely solved.
(1) The weak link of the original mold--the middle rib position line was reasonably optimized. By eliminating the dead zone of the two studs, leveling the flow block, reducing the drop between the stud and the working belt of the lower mold, shortening the working belt of the lower mold and other improvement measures, the surface defects such as coarse grain and welding of 6063 aluminum alloy used in such vehicles were successfully overcome.
(2) The extrusion capacity was increased from 5 t/d to 15 t/d, and the production efficiency was greatly improved.
(3) This successful case of extrusion die design and manufacturing is representative and referential in the production of the same type of material, and it is worth promoting.
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