outlook Doug Richman
Joining Methods Enable Increased Aluminum Use
T
he industry’s ongoing shift to multimaterial design optimization can be challenging for engineers unfa- miliar with appropriate design practices when work- ing with dissimilar materials. According to a survey released during the 2015 CAR Management Briefi ng Seminars, engi- neers and designers favor aluminum alloys as the lightweight material of choice. Most respondents indicated aluminum is an important part of their strategy to meet 2025 fuel economy and CO2
standards. The rapid growth of aluminum use in multimaterial vehicle applications demands technical feasibil- ity of reliable and safe joints with high process capability and optimum cost effi ciency.
Aluminum design and manufacturing practices are similar
to processes used for other metals but require revisions in light of aluminum’s specifi c properties and characteristics. Once individuals and organizations gain experience success- fully designing and manufacturing with aluminum they fi nd it as easy to work with as other commonly used materials. Joining is a critically important technology in auto manu- facturing. Independent of material, joining processes are critical as they infl uence vehicle durability, NVH performance, handling and collision energy management. Current high- volume aluminum joining processes have been in production for more than 20 years and a broad range of well-developed practices are available to meet the functional requirements of a specifi c OEM application. These processes are proven to be cost effective and compatible with high-volume produc- tion rates and environments, include bolting, welding, fl ow screws, clinching, adhesive bonding, rivet bonding and others (for a full list see “2015 Automotive Aluminum Joining Manual” on
drivealuminum.org). Manufacturers select the most appropriate joining system for individual joints based on functional requirements, pro- duction rates and specifi c manufacturing plant constraints. Lightweight vehicle bodies and structures using an optimized combination of two or more materials are already prevalent. As a result, most are assembled using hybrid joining—two or more joining operations either carried out simultaneously or sequentially leading to enhanced properties of the joint. In auto applications, the most important task is joining aluminum to steel. Joining dissimilar materials is generally
Technical Committee Chairman Aluminum Transportation Association Arlington, VA
more diffi cult than joining the same material or alloys with minor differences in composition. The number of applicable joining techniques also decreases. When joining aluminum to dissimilar materials, those unfamiliar in working with alu- minum must learn new techniques to address key consid- erations such as material thicknesses, thermal expansion- contraction mismatch during joining and in service, and the potential for galvanic corrosion. Major OEMs and Tier One fabricators have successfully made the transition to ma- jor aluminum components through education and training, dispelling the myth that aluminum is diffi cult to work with. As with any advancement in the industry, to become knowledge- able, skillful and comfortable in deploying a new technology, process experience in repeat applications is required. Audi, Jaguar Land Rover and Ford have mastered rivet bonding, combining adhesives with joining technologies in- cluding rivets, fl ow screws or clinch joints for their aluminum- intensive designs. Rivet bonding enables a signifi cant com- ponent weight reduction, increased body stiffness, improved crash performance, and enhanced NVH characteristics, all without slowing down the assembly process. Adhesive bond- ing also establishes an excellent barrier to galvanic corrosion and offers the designer additional possibilities to exploit new, innovative designs and manufacturing concepts. Other manufacturers prefer spot welding or friction stir spot welding process in body joint applications. The GM process is one of several innovative spot welding practices. Resistance spot welding remains the dominant joining tech- nique for steel-bodied cars and may be the fi rst choice of design engineers when looking to incorporate more alumi- num. However, joining aluminum components by resistance spot welding may deteriorate mechanical properties of work-hardened or age-hardened aluminum alloys due to heat generated during the welding process. Where weld appearance is critical, some applications re-
quire laser welding. With its high processing speeds, low heat input and resultant low distortion, and overall fl exibility of ap- plication, this process has become a key assembly technol- ogy during the last two decades. Another advantage of laser welding is high accessibility as it only needs single-sided access and welds can be carried out in narrow places.
29 — Motorized Vehicle Manufacturing 2015
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