SPRING 2023

10 THE DISTRIBUTOR’S

10 THE DISTRIBUTOR’S LINK Bruno Marbacher Bruno Marbacher earned his mechanical engineering degree in Switzerland, he also holds a business degree. He started out as a tool and die maker (poly-mechanic) and over the years he has held various management positions in quality and engineering. During his time in America he has developed and given numerous seminars on topics related to the proper use of mechanical fasteners and machine elements, and assists engineers in solving fastening/assembly issues. His has groomed and directed many young engineers in fastening/assembly technology. He now offers his 40 years of experience through writing and lecturing. THREAD-FORMING SCREWS FOR A COST-EFFICIENT FASTENING SOLUTION Dear Reader: In the last Link issue, we focused on tapping screws; in this article we continue with the thread-forming screws that form regular threads. There are quite a few different styles to cover. It is not always easy to find the advantages of one over the other. Advantages Of Thread-Forming Screws When driven into a work piece, thread-forming screws produce their own mating thread. The following processes can then be omitted: ¤ No Thread tapping ¤ No Removal of chips ¤ Inspecting screw thread is not necessary ¤ Other operations associated with the assembling process not required ¤ Since each screw produces its own mating thread, there are no problems with thread tolerances ¤ The screws sit play-free in their mating threads and thus they have an excellent vibration TECHNICAL ARTICLE resistance. Thread-forming screws are extremely reliable and safe They are very cost-efficient and should be used instead of regular screws whenever this is feasible. Thread-forming screws are usually available in the diameters ranging from 2-8 mm ( 2-56 to 5/16”). They are used in metals and plastics. Consequently, their specific threads are different. Fastening of the screws is different to that of regular screws. The forming of threads produces a certain resistance therefore they need to be installed with a power screwdriver. This type of fastener is tightened after they have been driven in. However, typically the final tightening is just snugging up the parts. One does not induce a controlled preload, as this is the case with regular screws. “Thread-forming screw” is the generic term for these screws. Thread-Forming Process There are no chips produced during the threadforming process. Instead, the material is displaced in the mating part, it strengthens the material of the host part. Thread-forming screws form regular threads in malleable steels and non-ferrous metals without a tapped hole. The play-free thread fit in the mating thread ensures that the screws are firmly retained. Additional locking elements are generally not needed. CONTINUED ON PAGE 104