(Ye Qingjian) performance comparison of new energy battery trays aluminum alloy casting pallets will become the mainstream in the future [SMM Automotive New Materials Summit]

At the 2021 China Industry Expo New Materials Forum and China Automotive New Materials Application Summit Forum solemnly held by SMM, Ye Qingjian, industry manager of Guangdong Prady Technology Co., Ltd., analyzed and introduced the application and manufacturing process of new energy vehicle battery tray technology. "New energy vehicles will become a landmark and leading product of the new round of scientific and technological revolution and industrial change, promoting the transformation and upgrading of information technology, high-end equipment manufacturing, new materials, new energy and other industries," he said. Aluminum profile welded battery tray is the mainstream battery tray design scheme at present, through the splicing and processing of profiles to meet different needs. Aluminum alloy casting pallet is not the mainstream at present, but with the mature die-casting technology of large tonnage press entering the market, it must be a direction in the future. "

Development status of New Energy vehicles

At present, various countries put new energy vehicles in the core strategic development position, formulate strategic plans and laws and regulations to support industrial development. Low-carbon is the key technology direction that the automobile industry pays close attention to for a long time, and low-carbon has great potential for energy saving and emission reduction, so new energy vehicles are still the main force in the market for a certain period of time. By 2035, new energy vehicles will become mainstream products, and all kinds of intelligent technologies will be widely used in automobiles. New energy vehicles will become the iconic and leading products of the new round of scientific and technological revolution and industrial change, promoting the transformation and upgrading of information technology, high-end equipment manufacturing, new materials, new energy and other industries.

The development of new energy vehicles is becoming more and more mature, the policy and regulatory system has been gradually improved, the capability of technological innovation has been continuously improved, the intensity of business model innovation has been continuously strengthened, and the infrastructure system for recharging electricity has been gradually improved.

The models are becoming more and more abundant, and the hot sales of high and low end models drive the continuous growth of the market. High-quality models such as BYD Han and high performance-to-price models such as Hongguang MINI EV have become the core force driving market growth. The proportion of car purchases by private consumption has increased rapidly, and the proportion of sales in non-restricted cities has increased steadily.

The electrification of multinational brands has led to a substantial increase in market share. BMW, Volkswagen, Toyota and other comprehensive development of new energy vehicle market.

The automobile and electricity separation mode speeds up the innovation, and the charging network speeds up the construction. Weilai, Weimar, Geely, BAIC, Changan, SAIC and other active layout of the power exchange market.

The electrification of multinational brands has led to a substantial increase in market share. BMW, Volkswagen, Toyota and other comprehensive development of new energy vehicle market.

The consumption of lithium iron phosphate has increased, and the technology is becoming more and more mature. The performance-to-price ratio of lithium iron phosphate continues to have an advantage.

From January to May, the production and sales of new energy vehicles completed 970000 and 950000 respectively, an increase of 2.2 times over the same period last year, while that of pure electric vehicles reached 820000 and 790000, respectively, an increase of 2.6 times and 2.5 times over the same period last year. The new energy vehicle industry is in a new stage of development from government-driven to market-driven, from technology-following to technology-leading, and from the maximum production capacity to the leading quality and production capacity of Synchronize. 2021 new energy vehicles will improve steadily, and sales are expected to exceed 2 million, an increase of about 46 per cent over the same period last year.

New energy battery tray structure

Battery tray

The battery tray is mainly composed of lower tray, cooling system, power battery module, battery management system, wire harness, thermal insulation cotton and upper cover. Its function is to carry the protection module.

The battery pack accounts for about 25% of the vehicle weight, and the battery shell accounts for about 15% of the battery package weight. In the context of lightweight, it is necessary to lose weight on the battery pack.

Aluminum battery tray is the mainstream of electric vehicles at present. Mixing materials is the trend, different parts use different materials to achieve the optimal solution of performance and cost.

Steel tray

Steel pallet is the traditional process 400Mpa steel plate stamping + welding (ring beam 2-2.5mm, shell 1mm). 700Mpa and above high-strength steel and hot-formed steel plate tray (ring beam 1.5mm, shell 0.8mm).

The machining procedure of CNC assembly is simple, the precision is not very high, the cutting quantity is small, and the working procedure includes drilling and tapping teeth.

Super steel pallet manufacturers: Baosteel, ArcelorMittal S-in Motion, ThyssenKrupp selectrify.

At present, A000 mini electric models in mainstream car companies use steel trays: Hongguang MINI EV, Zhi Dou, Mercedes Benz, Chery small ants and so on.

Aluminum alloy tray

Aluminum profile welded battery tray is the mainstream battery tray design scheme at present, through the splicing and processing of profiles to meet different needs. Extruded aluminum alloy battery tray has high rigidity, anti-vibration, extrusion and impact properties. The utility model has the advantages of flexible design, convenient processing, easy modification and so on. However, there are many manufacturing processes, complex welding process, welding deformation and lax welding seal.

At present, the mainstream aluminum profiles use ordinary 6063 or 6016 (10% lighter than 6 series in 7-series research and development), and the tensile strength is basically between 220~240MPa. If the extruded aluminum profiles with higher strength are used, the tensile strength can reach more than 400MPa, and the weight of the lower box of Putong aluminum profiles can be reduced by 20% and 0%. Representative models are mainstream electric platforms such as BAIC, BYD, Great Wall, Xiaopeng P7, BMW ix3 and Volkswagen MEB.

The cast aluminum tray simplifies the complex process of willow joint, stamping and welding, reduces the processing technology, reduces the weight of parts, reduces the cost, and improves the competitiveness of products. The utility model has the advantages of flexible structure and wall thickness design, integrated molding of tray outer frame, lifting lug and cooling channel. The manufacturing process has the advantages of simple process, high production efficiency, high dimensional precision and good air tightness. The wall thickness is generally 2.5mm ~ 4.5mm. At present, the commonly used die-casting materials are AISilOMgMn, AIMg5Si2Mn, AISi9Mn and AISi7, etc. In order to ensure the mechanical properties, vacuum die-casting is generally adopted, and the vacuum of the mold cavity is less than 50mbar. It is usually used in small pallets such as GM and BMW PHEV models. Representative companies include Volkswagen GolfGTE plug-in hybrid die-casting battery tray, BMWX5 plug-in hybrid and Tencent 500.

The technical difficulty of cast aluminum pallet is that aluminum alloy is prone to undercasting, crack, cold isolation, depression, stomata and other defects in the casting process, and the elongation of cast aluminum alloy is low, and deformation and fracture is easy to occur after collision. The whole casting molding needs to be put into the mold at one time, and the cost of the mold is very high, and the corresponding press tonnage is very large. The integral casting molding has many surface and internal defects, and the mechanical properties vary greatly in different positions, which affects the reliability of the pallet. And due to the limitation of casting wall thickness, the lightweight effect of integral casting battery tray is slightly worse than that of profile tray.

Aluminum alloy casting pallet is not the mainstream at present, but with the mature die-casting technology of large tonnage press entering the market, it must be a direction in the future.

The main material of cast aluminum plus profile aluminum tray is welded by profile and some aluminum castings. The pallet bottom plate of Models is 6mm aluminum plate, the mounting points of the surrounding and lower car body are aluminum profiles, the front end is aluminum castings, and the middle is 16 modules with fixed profiles, all connections are basically realized by aluminum arc welding.

Stamping aluminum plate welded battery tray has a very good lightweight effect, compared with steel without reducing the stiffness of the premise, can reduce weight by 40%. And it is made of aluminum plate stamped (BMW 134mm, Tesla 33.2S 6), reinforced bars are arranged in the length direction, a stamping protruding table is uniformly arranged around the bottom plate to connect with the lower car body, and a circle around the base plate is extruded, which is connected with the bottom plate by means of CMT continuous arc welding, the upper surface of the profile is arranged with installation holes connected with the upper cover, and the upper cover is stamped by 0.8mm low carbon steel plate. This form has the advantages of simple structure and good lightweight effect.

At present, the technical difficulties faced by this kind of pallet are the springback of the bottom plate stamping and the warping deformation caused by the full welding of the base plate and the surrounding profiles, especially the warping deformation at both ends of the length direction. Representative models are BMW i3, Tesla Models, Tesla Model3. Because of its drawing depth, battery package vibration, lack of impact strength and other problems, car companies need to have a strong body and chassis integrated design ability to strengthen the structure of the battery package and collision protection.

Manufacturing technology of new energy battery tray

CNC and processing, profile sawing and cutting according to material section size, product angle, size, need margin, no margin, etc., select sawing machine, single-head sawing machine, double-head sawing machine, angle sawing machine and so on.

Bulk processing is divided into bar processing and sheet processing. Bar machining is characterized by long strip, multi-faceted machining, which requires efficiency and one-time machining, and mostly adopts 3-axis or 4-axis linkage. Plate processing is characterized by a slightly wider material, drilling and splicing.

In the aspect of frame welding, the (MIG) welding process of molten electrode inert gas shielded welding has the advantages of low cost, high production efficiency, flexibility and convenience. The main technical equipment suppliers are Funeng, France Schafu, Shanghai Kenbi welding.

In the aspect of bottom plate friction stir welding, friction stir welding is the mainstream welding technology at present. Friction stir welding ((FSW),) refers to the local plasticity of the welded material due to the heat generated by the friction between the Rapid Spin welding tool and the workpiece. There are five steps in the process of friction stir welding: rotation-drilling-heating-welding-pullout. The utility model has the advantages of good mechanical properties of welded joints, small deformation after welding, good tightness and low welding cost. The disadvantage is that the welded workpiece must be rigid and fixed, and the reverse side should have a bottom plate. A key hole will be left after the exit of the solder needle.

Plate CNC processing, plate processing using gantry CNC machining center (main equipment suppliers: Prady), this kind of gantry machining center is specially designed for plate processing, especially large-scale sheet metal processing, simple loading and unloading, high processing efficiency, coupled with vacuum suction clamping or automatic avoidance pneumatic fixture to maximize performance-to-price ratio. After the completion of the processing of the bottom plate, fill the cushion strip on the side to block the inner chamber of the profile.

In terms of overall welding, the previously welded frame and the bottom plate are welded by assembly friction stir welding and one-time welding around to form a complete battery tray. The main equipment supplier is Aerospace Engineering equipment Beijing Sefoster. The welding process of aluminum profile + stamping aluminum plate is cold metal transition welding (CMT) welding, which is used for hot deformed sheet, precious metal welding, steel-aluminum dissimilar material connection. The biggest advantage of the process is low heat input. The main suppliers are Volunteer and French Schaft.

The total welded workpiece is machined by a large gantry CNC machining center, milling, drilling and tapping teeth. Equipped with special automatic fixture, it can be clamped at one time and multi-process processing can be completed. According to the process characteristics, the conventional three-axis meets the processing requirements. Die-casting pallet, generally only assembly CNC processing needs.

Talking about power battery

New energy vehicle battery category

Classified by vehicle category: 1. HEV hybrid battery pack, only use starting, acceleration, braking and other auxiliary power, small size, light weight. Mostly in the trunk.

2. PHEV plug-in hybrid electric vehicle battery pack, with pure electric working function, large volume. Installation location, floor.

3. EV pure electric vehicle battery pack, completely depends on the form of battery energy, the volume is very large, generally arranged between the front and rear suspension, accounting for about the mass of the whole vehicle.

Classification by cathode material

Classified by cell structure

From January to May 2021, the output of power batteries in China was 59.5 GWH, an increase of 227.3% over the same period last year, of which 29.5 GWH was produced by ternary batteries, accounting for 49.6% of the total output. An increase of 153.4% over the same period last year; the output of lithium iron phosphate battery was 29.9 GWH, accounting for 50.3% of the output, an increase of 360.7% over the same period last year.

From January to May, the installed capacity of power batteries in China was 41.4 GWH, an increase of 223.9% over the same period last year, of which 24.2 GWH was loaded with ternary batteries, accounting for 58.5% of the total output. An increase of 151.7% over the same period last year; lithium iron phosphate batteries accounted for 41.3% of the total, an increase of 456.6% over the same period last year.

Lithium iron phosphate battery market share increased slightly, mainly due to the surge in demand for A00 class models brought about by the demand for lithium iron phosphate battery. With the maturity of lithium iron phosphate technology, it will be more popular in the automobile market.