New Technology to Join Sheet Metals Unconventionally

BTM Corporation USA has developed a technique for joining sheet metals without using fasteners of any kind. The patented Tog-L-Loc sheet metal joining system is capable of joining plain, coated and dissimilar metals, combining the economy of a mechanical clinch with the integrity of an impervious and fatigue-resistant leak-proof joint. Two or more layers of metals can be reliably joined using this process. The typical sheet metal thickness can range from 0.2 mm to 3 mm. The joint is formed by drawing the metals into a circular 'cup' and then expanding the diameter to form a 360-degree radial lock below the bottom sheet. The basic tooling consists of a punch with a spring-loaded stripper and a die with spring-loaded, expanding die blades. The joining process goes as follows:

• The two sheet metals that are to be joined are kept on a die,
• The punch along with the stripper descends on sheet metal,
• The stripper clamps the metals between punch and die,
• The punch draws the metals into the die
• The punch continues to travel, directions, and the die blades open out to accommodate the squeezed metal
• As the punch retracts, the stripper allows the punch to be removed. The punch and die sets are available in various sizes to cater to various combinations of metal thickness. 

This process offers many advantages over conventional methods of sheet metal joining. It can join plain, coated and dissimilar metals. It does not need any surface preparation as required     for spot welding, and also does away with heat and sparks so typical of welding. The operation is clean and distortion-free. The joint formed is strong, fatigue-resistant, and leak-proof (as no hole is produced). The joint can also be checked non-destructively, using a simple gauge. Besides, this process does not need additional components like rivets, screws, etc and hence is more economical. It is fast, as the joining takes place in a single press stroke. The process has wide applications in the automobile, furniture, home appliance, switchgear, and office equipment manufacturing industries.  
 
Source: Search, Vol 4 No 9, September 2001