Say Goodbye to Rivets in the Auto Industry
General Motors Co. has claimed that they are the first vehicle manufacturer to eliminate the need to join steel and aluminum with rivets by replacing it with a technique known as resistance spot welding. Although aluminum can be mechanically fastened with relative ease to most metals, it is a costly process that drives up the price of auto making. With over two years of technique development in the process, General Motors says that their new method of fastening will reduce the overall weight of their vehicles and will be a less expensive means of creating high-strength joins.
Making the Bond: Aluminum and Steel Together At Last
Creating a strong weld bond between aluminum and steel has always been notoriously difficult. Attempting to arc weld the two materials together causes weak and brittle intermetallic compounds to form during the process due to the different melting temperatures of the two metals. This causes fragile connections between the two metals and increases the chances of bond failures, which is particularly dangerous in vehicle fabrication. Methods of joining aluminum and steel have existed for some time, but these techniques are not always as affordable or as secure as riveting.
Bimetallic Transition Inserts
One popular method of joining aluminum and steel is through the use of bimetallic transition inserts. These are commonly available in a variety of aluminum and other metal combinations, and they allow arc welders to make steel to steel and aluminum to aluminum bonds in a secure and simple method. Bimetallic transition inserts are essentially two aluminum and steel components that have been pre-bonded through alternative methods such as rolling or hot pressure welding. This allows the arc welder to bond steel to the steel side, and aluminum to the aluminum side of the bimetallic transition insert, which creates a strong connection suitable for high-strength bonds. This is a reliable method, but is not easily applicable to auto manufacturing due to the high cost.
Coating the Dissimilar Materials
Another method of joining aluminum with steel is by coating the steel with aluminum through processes like hot dip aluminizing or brazing. This allows the arc welder to join the two metals if the proper amount of care is taken, but this is typically not reliable for a full strength bond. This makes the process unsuitable for auto manufacturing, and is generally only functions for sealing objectives.
The Benefits of No Rivets
With General Motors new technique of resistance spot welding, they will be able to save on the production of each vehicle depending on the amount of rivets used in the model. This also opens new possibilities for replacing steel components with aluminum, which would allow for significant weight reductions in the vehicle. This weight reduction would have great benefits for fuel economy, and help auto manufacturers meet increasing environmental mandates and objectives.