Emerging automotive lightweighting materials and processes
Monday, August 15, 2016
Every car model that is launched over the coming years is expected to include lightweighting measures. Mazda, for example, has set a goal to reduce the curb weight of all its new model cars by 15 percent (up to 220 pounds per car), through material replacement and engineering, redesigning features and shrinking parts dimensions. The company also plans to improve its global corporate fuel-economy average by 30 percent.
Innovative materials together with new production methods and reinforcing structures will play an important role in reducing vehicle weight. Lower vehicle weight not only improves fuel efficiency but also reduces the load on the brakes and suspension systems.
Let's start with a polyetheretherketone (PEEK) resin from Victrex Ltd. that provides automotive weight savings and reliability. Incorporating high-modulus fibers (HMF) into high-flow PEEK material offers the strength and stiffness necessary to displace metals such as steel, aluminum, titanium, brass and magnesium in automotive under-the-hood and industrial applications.
New Victrex PEEK HMF polymers are based on the Victrex 90-Series used to mold tough thin-walled parts. The new material provides mechanical strength and stiffness for high-temperature applications typically requiring metals. Lightweight thermoplastics such as Victrex PEEK HMF polymers can help engineers reduce component weight by up to 80 percent when compared to metals like steel and brass.
PEEK HMF (left) and metal weight reduction comparisons (right).
In addition to lowering part weight, the ability to consolidate parts with more functional designs can help shorten cycle times and reduce production costs because of the efficiencies gained through injection molding. The PEEK HMF polymer has been tested in hydraulic fluid, fuel, oil, grease and lubricants. It also has a long-term temperature use of 260 degrees C. PEEK HMF polymer is being used to replace metal brackets, clips, fasteners and other secondary structures.
Next, advanced nanocellulose reinforced polymers are being biocomposite developed. American Process Inc. (API) and Futuris Automotive have formed a partnership with researchers at the Georgia Institute of Technology, Clark Atlanta University, Swinburne University of Technology, and the U.S. Department of Agriculture's Forest Products Laboratory to develop ultra-strong, lightweight automotive structural components reinforced with nanocellulose.
American Process Inc.
Sub-microscopic nanocellulose from trees at nanometer (nm) lengths.
The goal of the project is to replace heavy steel structures within cars, such as the seat frames, with advanced reinforced polymers that have cost parity with traditional materials. The nanocellulose composites promise to be an economical substitute for expensive lightweight carbon-fiber composites currently used in some luxury automobiles.
API has developed a proprietary manufacturing process that makes renewable, low-carbon-footprint nanocellulose, with strengths equivalent to Kevlar and prices similar to conventional polymers. API began commercial sales of nanocellulose in late 2015, when their demonstration plant came online in Georgia.
According to API, its nanocellulose has even lower weight than carbon fibers, is just as strong and is just a fraction of the price of carbon fibers. In addition, API has made its nanocellulose more thermally stable at high temperatures, and also gave it functionality to blend with hydrophobic polymers — thereby enabling market applications and opening the road to commercial production.
Continuing, there is hybrid technology that significantly reduces infotainment mount weight. The infotainment carrier in the Audi A6 — developed by Audi, Lanxess, KraussMaffei Technologies GmbH and Christian Karl Siebenwurst GmbH & Co. KG. — is based on thermoplastic composite technology and is approximately 50 percent lighter than its steel counterpart. It uses:
- Hybrid technology with fiber-reinforced polyamide composites
- Forming and overmolding in a single mold
- Fully automated production, component requires no reworking
The process involves the use of two inserts made of Tepex Dynalite 102-RG600(2)/47 percent, a polyamide (nylon) 6 composite from Lanxess subsidiary Bond-Laminates, reinforced with continuous glass fibers. The inserts are gradually heated by an infrared heating system from Krelus AG, formed in the injection mold and then directly overmolded with the easy-flow polyamide 6, a Durethan BKV 30 EF H2.0 from Lanxess
Ribs on the side of the component far from the gate are filled by injecting Durethan through the Tepex inserts. The one-shot process enables production of the composite part in a cycle time of less than 50 seconds without requiring any re-working. The handling system and production mold were developed and manufactured by Maier Formenbau GmbH.
Audi A6 thermoplastic composite infotainment carrier.
Finally, let's take a look at a competitive metal material solution for automotive lightweighting namely, nanostructure based advanced high strength steel (AHSS). A new class of AHSS by NanoSteel, a founding member of the American Lightweight Materials Manufacturing Innovation Institute, is based on nanostructured materials that have exceptional combinations of strength and ductility for automotive applications.
Previously, sheet steel made of nanostructures was considered too brittle (no elongation) to form the shapes required for automotive parts. A study by independent engineering firm EDAG Inc. commissioned by Nanosteel shows this new AHSS has the potential to provide a 30 percent reduction of weight in the Body-In-White (BIW) structure of a baseline sedan.
Nanostructured AHSS (left) and an AHSS General Motors sedan frame (right).
These materials are designed with a combination of high strength and formability that permit complex part designs while utilizing conventional manufacturing processes. The NanoSteel sheet steels allow the use of thinner gauges, which provide superior tensile and elongation properties compared to currently available steels.
One of the challenges with currently available AHSS materials is the need to form parts at elevated temperatures increasing cost and production cycle times. The new material's inherent ductility allows cold forming of component parts using room-temperature metal stamping processes on existing manufacturing equipment.
NanoSteel's three classes of AHSS (N1, N2, and N3) were used to replace crush zone parts that require high energy absorption, deep draw parts with significant complexity and structural parts such as B-pillars and cross-members where strength is the overriding consideration to protect the passenger. NanoSteel's three grades of sheet steel offer progressively higher strength and lower elongation, from N1 at 450/950 Mpa (Mega Pascals) with 35 percent elongation, to N2 at 450/1200 MPa with 20 percent elongation and N3 at 1000/1600 MPa and 12 percent elongation, used as follows:
- N1 Grade was used for external body panels due to the need for high formability.
- N2 Grade was used for front and rear crash rails and floor structure due to its high work-hardening capability, which allows for large amounts of energy absorption during a crash event.
- N3 Grade was used for the roof structure and body side structure where the highest possible strength is required to maintain the integrity of the passenger compartment.
In conclusion, plastics and advanced lightweight metals are helping to shed weight without compromising the safety and comfort features mainly responsible for the upward weight spiral. Cost-efficient plastic manufacturing solutions can also help to consolidate parts and reduce the number and scope of processing steps while reducing weight of the finished component or system.
Furthermore, replacement of metal material by engineering thermoplastics, fiber-reinforced composites and hybrid composites in the automotive core structure, body or power train offer significant weight reduction potential. Greater reductions can be achieved in structural components such as underbody covers, dashboards, roof, front end or door modules.
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