The automotive industry has utilized several technologies and materials to reduce vehicle weight in both conventional internal combustion engine and electric-powered vehicles. The use of aluminum and magnesium has provided lightweight solutions in some applications. However, there are several areas where the use of steel sheets is still preferred due to the increased mass and size required for aluminum and magnesium components to attain the equivalent strength of steel.
Advancements in sheet steel composition have produced high-strength-low-alloy (HSLA) and ultra-high-strength-low-alloy (UHSLA) sheet steels. These grades are being used more extensively today as they help vehicle assemblers achieve their weight-reduction goals. The higher-strength steel grades not only allow for thinner sections to be used but also reduce weight while not increasing mass.
Many of these new grades of sheet steel work harden dramatically when fabricated into specific components. Consequently, manufacturers experience assembly problems with the higher-hardness materials. Tapping high-strength steel, creating usable extruded holes and attaching weld nuts are all difficult operations, which are encountered when using high-strength steel. These materials are too hard and thin to use a thread-forming screw and a weld nut cannot be effectively attached. Therefore, automotive assemblers often prefer to use self-piercing clinch nuts, particularly when a structural joint is required.
Self-piercing clinch nuts are specially designed nuts that pierce a hole and become staked in-place. They are typically installed in sheet metal parts during the fabrication of the component, utilizing specifically designed insertion mechanisms which are integrated into the stamping process. The nut pilot, which has mechanical features that resist pullout and rotation, pierces the sheet metal and secures itself in place. Several self-piercing clinch nut suppliers produce design variations that are mildly heat treated in order to pierce high-hardness thinner-sheet steel. In the past, self-piercing clinch nuts were normally supplied with internal nut threads. Now there is a trend to supply self-piercing clinch nuts with plain-bore holes which are suitable for using TAPTITE® thread-rolling screws.
REMINC/CONTI have worked with some nut suppliers to make their self-piercing clinch nuts compatible for use with TAPTITE 2000® and TAPTITE PRO® CORFLEX®-I™ thread-rolling fasteners. The nut's plain-bore hole size and length of engagement are optimized so that grade strength Class 10 TAPTITE® bolts can be driven into these nuts creating a joint which meets Class 10 strength levels. TAPTITE® CORFLEX®-I™ screws have proven to be capable of thread forming into these mildly hardened self-piercing clinch nuts.
The combination of TAPTITE® thread-rolling screws and clinch nuts has been popular in the assembly of automotive vehicle seats. Seat assembly is an application where weight savings must be achieved without increasing mass so that the seat design remains compact. Chassis and body-in-white applications are also popular applications. The body-in-white typically requires several fastening sites that usually become coated with e-coat and primer. Pre-threaded nuts, when filled with e-coat, create the possibility of the joint having e-coat remaining between the machine screw and the internal thread. This undesirable scenario can be avoided by driving a TAPTITE® screw into a plain-bore hole where the screw will push the e-coat out through the end of the nut during thread forming. A TAPTITE® screw and self-piercing clinch nut combination also provides a solution when the sheet material is aluminum, yet a high-strength structural joint is required.
Here are several benefits when TAPTITE® fasteners are driven into plain-bore hole self-piercing clinch nuts.
Cost Savings Benefits
- No cross threading will occur.
- No pre-tapping is necessary.
- No secondary operation is required to install the nut.
- No welding is required.
- No additional locking element required due to inherent prevailing torque provided by TAPTITE® screw.
- No pre-punched hole is required.
- Accurate nut positioning.
- A proven workable HSLA and UHSLA solution for structural joints.
- Joint performance not compromised by e-coat/primer due to thread-forming when using a TAPTITE® screw.
- No pre-punched holes are required.
- Accurate nut placement.
- No cross threading will occur.
We encourage all vehicle assemblers and tier-1 suppliers to investigate the use of TAPTITE® screws with plain-bore self-piercing clinch nuts. REMINC/CONTI engineering staff members are ready to assist you with your potential fastener applications.