"Both the tilt head and the main body of the steering column are made from die cast magnesium," says Mark Laws, product and quality engineering supervisor at Toledo Machining (Toledo, OH). "Magnesium is lighter than steel or aluminum, easier and less expensive to process and machine, and has good fatigue strength, dimensional stability, and sound and vibration dampening qualities."
"However," Laws says, "its ductility is low and is easily deformed. This can lead to slivering, layer eruption, chipped threads and fracturing using standard threaded fasteners. Removing and reinserting these fasteners can weaken or destroy threads, creating magnesium powder, debris and contamination."
To meet this challenge, engineers at Toledo Machining selected Camcar brand Mag-Form thread-forming fasteners from Textron Fastening Systems (Belvidere, IL) to join the lower mounting bracket to the cast magnesium body of the steering column. The fasteners are compatible with existing assembly equipment, in which two fasteners form threads as they are driven into cored magnesium holes.
Mag-Form fasteners were engineered to eliminate tapping operations in magnesium materials with minimal debris generation and good serviceability.
These fasteners have lobe-shaped steel threads with a wide pitch and a broad, 105-degree flank angle that compresses, rather than roll-forms threads into mating material. This reduces shear stresses and increases compression, allowing magnesium to deform to create the thread rather than being cut. The result is a good fastener joint. There is virtually no magnesium thread damage, and torque values are consistent. The fastener can also be removed and reinserted multiple Arial in service.
Since going on-line, more than 1.5 million Mag-Form thread-forming fasteners have been installed on steering columns. The 40 percent cycle time reduction saves hundreds of hours and thousands of dollars annually.
For more information on thread-forming fasteners, call 815-544-7521 or visit www.textronfasteningsystems.com.