Polyurethane Battery Pack Upper Shell Solution for High Pressure Resin Transfer Molding (HP-RTM) Process

 

Composite Materials For Electric Vehicle Battery Boxes

 

 

On January 12, 2023, the China Association of Automobile Manufacturers released the production and sales data of the automobile market in 2022. In 2022, my country’s automobile production and sales reached 27.021 million and 26.864 million respectively, up 3.4% and 2.1% year-on-year. Among them, the excellent performance of new energy vehicles in 2022 has become the key to maintaining positive growth in my country’s automobile market.

 

In 2022, my country’s annual production and sales of new energy vehicles reached 7.058 million and 6.887 million respectively, up 96.9% and 93.4% year-on-year, and the market share reached 25.6%, 12.1 percentage points higher than in 2021.

 

And network data shows that in November 2022, global electric vehicle sales continued to maintain a double-digit year-on-year growth (46%), and electric vehicle sales accounted for 18% of the global overall automobile market, of which the market share of pure electric vehicles increased to 13%.

 

There is no doubt that electrification has become the development direction of the global automotive industry. With the explosive growth of new energy vehicles around the world, composite materials for electric vehicle battery boxes have also ushered in great development opportunities. Major automakers have also put forward higher requirements on the technology and performance of composite materials for electric vehicle battery boxes.

 

Accelerating Lightweighting of Vehicles – Battery Housing

 

Another important driver for automotive composites is the global push to achieve zero emissions by 2050, which will promote a significant increase in the development and production of electric vehicles (EVs).

 

In September 2020, California announced that it would require all new passenger cars and trucks sold in the state to be emission-free by 2035. At the same time, the European Union has proposed a 2030 target of 37.5% reduction in new car CO2 emissions.

 

Julia Atwood, head of advanced materials at BloombergNEF, said at the IACMI Fall 2020 Member Meeting that by 2025, the average price of electric vehicles is expected to fall below that of internal combustion engine (ICE) vehicles. She predicts that global electric vehicle sales will exceed ICE vehicles by 2037 and reach 50 million vehicles/year by 2050.

 

The paradigm shift in powertrain technology is introducing a need for robust battery enclosure systems that can meet stringent mechanical and impact requirements, as well as fire, smoke and toxicity performance to protect vehicle occupants in the event of a battery fire.

 

In addition, since the battery pack adds significant weight to the vehicle, there is a demand to reduce the weight of the enclosure as much as possible.

 

For all these reasons, composites are proving to be very advantageous in battery enclosure applications, and these structures are providing major opportunities for the use of composites in ground transportation, such as cars, trucks, buses and other vehicles.

 

Assembled Battery Enclosures

 

Multiple material suppliers, automakers, and composite manufacturers announced solutions for battery enclosures for electric vehicles.

 

As OEMs seek to increase the driving range of BEVs, composites can help offset battery weight while improving safety through lightweight battery enclosures.

 

For example, Teijin Automotive Technologies (Auburn Hills, Michigan, U.S.) has been compression molding composite electric vehicle battery covers and full enclosures in North America, Europe, and Asia for more than a decade, primarily using short-fiber/thermoset sheet molding compound (SMC). However, the company has begun exploring continuous reinforcements using resin transfer molding (RTM) and wet compression molding processes.

 

Teijin is also investigating a hybrid material approach, using long fibers to partially reinforce chopped fiber materials, and is working on creating material cards (for use in simulation software) for its higher-capacity materials to help its customers develop new products.

 

Composite wind blade producer TPI Composites Inc. (Scottsdale, Arizona, U.S.) is also producing composite battery enclosure components, including for large-scale projects in multiple regions, as well as developing battery enclosures for Class 4-8 electric trucks expected to be launched in 2023-2024.

 

The company spent six years developing and validating various material/process options to meet a range of quality, cost and other performance requirements. These are primarily based on continuous fibers (glass, carbon or a blend) impregnated with phenolic or high-temperature flame-retardant epoxy resins for use in high-pressure RTM, wet composite molding and other techniques.

 

Polyurethane HP-RTM battery upper shell – integrating safety, efficiency and lightweight

 

High-tech enterprise Kalai Technology and Covestro jointly launched a polyurethane battery pack upper shell solution using high-pressure resin transfer molding (HP-RTM) technology, and achieved mass production with mainstream power battery manufacturers. This cooperative research and development pioneered the application of polyurethane composite materials in the field of new energy vehicle battery packs.

 

The polyurethane HP-RTM manufacturing process achieves “plastic instead of steel” and can be used for battery packs.

 

 

Compared with other processes, the new HP-RTM process uses automated layering technology, which greatly improves efficiency and reduces manufacturing costs. Life cycle assessment shows that compared with traditional metal processes, the use of HP-RTM process also produces lower carbon dioxide emissions.

 

In addition, battery pack weight reduction can reduce carbon emissions for the entire vehicle while increasing the range of electric vehicles, killing two birds with one stone. The battery pack upper shell made of this HP-RTM polyurethane composite material can easily achieve mass production of thin and light battery shell solutions due to its strong physical properties and low density advantages.

 

The average thickness of the entire shell is about 1.5mm, and the thinnest can be 0.8mm. While ensuring lightweight, it can also maintain high strength and high toughness. Among all current non-metallic solutions, it has outstanding advantages.

 

✔ 60% lighter than high-strength steel

✔ 50% lighter than SMC

✔ 20% lighter than aluminum alloy

 

 

Compared with the prepreg process, the HP-RTM process has achieved automation of the fiber layering to a considerable extent by optimizing the fiber layering design, which has greatly improved the production efficiency. In addition, its mold costs, operating labor, operating costs and quality stability have all been greatly improved.

 

 

The HP-RTM process only requires a small number of stations in the preforming stage, and uses a “one-to-two” design of one injection machine and two presses, which shortens the product molding cycle to improve production efficiency while ensuring cost control. In addition, the storage of prepregs has strict production management requirements for temperature and humidity, while the HP-RTM process route is more tolerant.

 

Producing Complex Vehicle Structural Parts With Preforms

 

Cannon Tipos and Coriolis Composites have jointly developed a manufacturing process that can manufacture complex carbon fiber reinforced composite (CFRP) parts as semi-finished products from near-net-shape preforms.

 

The key components of the process are the high-pressure resin transfer molding (HP-RTM) process and Coriolis’s automatic fiber positioning (AFP). The components produced by this collaboration are currently being tested for mass production. The process achieves a production cycle time of 20 seconds and shows mechanical properties that meet the requirements, but with a weight reduction of up to 80%.

 

The company’s automatic fiber placement (AFP) equipment allows continuous or short fibers to be placed in different directions, even on complex geometric surfaces, while minimizing material waste.

 

 

The dry AFP 2D preform consists of an optimized fiber sheet of unidirectional (UD) oriented carbon fibers, with a fiber weight of 280 g/m2 per layer and a fiber volume fraction of 55%. A special binder technology is used to inject a compatible epoxy resin system that cures quickly.

 

Improving the preform’s plasticity, fiber impregnation and trimmability (using a 3D waterjet process) to achieve near-net-shape geometries can reduce overall scrap rates by up to 50%.

 

The Cannon Tipos steel mold is designed for pressures up to 120 bar. Minimized microporosity ensures an optimal reaction of the resin and curing agent at a constant temperature with a maximum deviation of 2°C. In addition, there is minimal back pressure during the injection phase and the vacuum time should be maximized to avoid flushing losses and the generation of bubbles. The surface quality of the components is particularly good due to the highly polished cavity combined with Coriolis’ preform technology.

 

Source: Covestro, Epoxy Resin Exchange and Trading, RIO Materials, etc., summarized by Composites Network.

 

my country’s composite materials account for about 30% of the global market share. Therefore, it is of great significance to analyze the development background, production and sales, market size, competition pattern and other industry status of the composite materials industry in a forward-looking and timely manner, and explore the future of the composite materials industry in combination with the development trajectory and practical experience of the composite materials industry over the years.

 

HP-RTM process is a new RTM process technology introduced in recent years to cope with the mass production of high-performance thermosetting composite parts. It adopts matching preforming technology and completes the impregnation and curing of resin to the fiber through high-pressure mixed injection in a closed vacuum cavity, which can achieve low-cost, short-cycle (large-scale) and high-quality production.

 

The conference is hosted by Composites Network and Tianjin Tianduan Press Co., Ltd., and co-organized by Langfang Feize Composite Materials Technology Co., Ltd. and Hunan Jingzheng Equipment Manufacturing Co., Ltd. The “2023 First Composite Materials HP-RTM Process Technology Exchange and Automated Forming Equipment Demonstration Training” will be held in Tianjin from August 3 to 5.

 

During the meeting, visits to Tianjin Tianduan Press Co., Ltd. and Langfang Feize Composite Materials Technology Co., Ltd. will be arranged to observe the molding equipment and on-site production operation demonstrations, learn efficient, low-cost, customized lightweight solutions in practice, and jointly explore new technologies, new applications and new developments in composite materials, to assist enterprises in top-level design and strategic planning, and to gain a leading edge in market competition.