Average vehicle weight has increased at a rate of 1.2% annually over the past three decades, with the only exception being a slight reduction during the late 1970s in response to the oil crisis. The average light-duty vehicle manufactured today weighs about 1730 kg (3814 lb).
In addition to vehicle electrification, friction reduction, variable valve timing, and a number of other means, automakers are taking weight out of the car to improve fuel economy and reduce greenhouse gas emissions. A vehicle weight reduction of just 10% translates into a 7-8% fuel savings. But while use of alternative materials steadily increases, average vehicle weight continues to climb, commensurate with increases in safety, performance, and convenience.
From a weight and cost perspective, it pays to examine more closely material substitution as a frontline strategy in the weight loss battle. Any material substitution has the potential to yield benefits or, conversely, create issues that did not previously exist. For example, switching from steel to carbon-fiber doors may decrease weight, but increase cost. So, it is critically important to thoroughly assess trade-offs between material weight, performance, cost, etc.
In general, the amount of weight reduction obtained by replacing steel is greatest when replaced by polymer composites, followed by magnesium and aluminum. Recyclable aluminum has proved a sound alternative in terms of cost, corrosion resistance, yield, and tensile strength. Die-cast parts represent roughly 80% of the aluminum used in vehicles.
Die-cast aluminum and plastic/die-cast aluminum combinations are commonly used in electronic modules. Today’s average vehicle has between two and six electronic module assemblies of various die-cast materials. Replacing die-cast aluminum with stamped aluminum cases results in reduced weight, reduced cost (at least 30%), improved environmental performance, and added manufacturing efficiencies. A typical stamped aluminum case is half the weight of a similar die-cast aluminum design.
As with any commodity, the price of aluminum fluctuates. The volatility of the aluminum market and die-cast sourcing add layers of costs and complexity to the manufacturing process. While nobody can control the aluminum market, any reduction in material requirements pays dividends. The stamping process requires less aluminum, which translates into savings.
In a finished product, the use of stamped aluminum can reduce case weight from 25 to 50%; cost savings increase as case size increases. Case cost is further reduced by eliminating secondary manufacturing steps, such as machining, deflashing, and deburring—all of which are required in die casting.
The primary purposes of metal cases—die-cast or stamped—are thermal management and protection from the environment. Metal cases dissipate heat generated by the microprocessors and other power components. Both die-cast and stamped aluminum can handle the job effectively; preliminary testing results show minimal differences in thermal performance.
Rigorous tests show that stamped cases demonstrate excellent resistance to environmental corrosion—specifically from abrasive salt spray, which is one of the most corrosive substances encountered on the road. Molex carried out salt-spray testing to compare performance between the two types of cases.
After multiple cycles, the stamped case demonstrated much better corrosion resistance than the die-cast one. When the test samples were pulled apart and analyzed, there was no visible indication of salt intrusion beyond the cover or shroud seal on any of the stamped samples.
A proven technology, stamped aluminum is widely used across diverse industries. In terms of manufacturing efficiencies, use of stamped aluminum cases eliminates the need for a die-cast suppliers and tools. Die casting can be process-heavy and maintenance-intensive, and molds require frequent maintenance and replacement after 50,000-100,000 parts. Stamped dies can produce millions of parts without need for replacement.
Stamped cases provide a cleaner, faster process, as well as greater overall design flexibility for the customer. Processed in a progression die, raw alloy aluminum is de-reeled onto a stamping machine and moves down an automated stamping press, with each station manipulating the sheet metal to produce a case design. The process culminates with the adhesive attachment of connectors to the case and assembly of the PCB, which is populated with microprocessors and other electronic components.
The progressive stamping process is not only cleaner, but also faster than die casting. Stamped aluminum cases also improve part-to-part consistency by eliminating surface cracks, heat checking, flaking, and delamination, in addition to reducing staining and other cosmetic problems.
Potential applications for stamped aluminum alloy include all electronic control modules, including ECM shielded and/or filtered applications for use on-engine, underhood, and in the passenger compartment.
The conversion to stamping needs to begin as early in the design phase as possible to optimize thermal management performance and maximize weight reduction. The PCB layout, component placement, and heat-sink requirements must be determined very early. In addition, the stamped-component supplier must work closely with the end customer to understand the anticipated wattage, thermal requirements, cover attachment, and sealing preferences of the module. For these reasons, it’s essential to collaborate during the design phase with an experienced partner. Doing so will ensure an optimized design that leverages the full benefits of stamped aluminum for electronic module assemblies.
Rand Wilburn, Global Marketing Manager – Automotive, Molex, wrote this article for Automotive Engineering.