How do ST threading taps form internal threads and simultaneously compress material to enhance connection strength during the tapping process?
Publish Time: 2025-10-29
In modern mechanical manufacturing, electronic equipment assembly, and automotive parts assembly, the demand for lightweight, efficient, and reliable connections is increasing. Traditional threaded connections often require pre-drilling and tapping, a cumbersome process, and are prone to stripping and loosening on thin-walled or soft materials. Therefore, ST threading taps, as a highly efficient and reliable self-tapping tool, are widely used for thread forming in sheet metal, aluminum alloys, and plastics. Their core advantage lies not only in the "one-step" internal thread forming but also in their unique cutting and compressing synergy mechanism, which simultaneously compresses material during tapping, forming a high-strength interlocking structure, significantly improving the tightness and durability of the connection.
1. Definition and Application Background of ST Threads
ST threading taps are specifically designed for machining the mating internal threads required for self-tapping screws, commonly found in thin-plate structural components such as electrical enclosures, lamp housings, ventilation ducts, and automotive brackets. Unlike standard metric threads, ST threads feature a larger tooth angle, deeper tooth height, and optimized pitch design. This allows them to not only cut a thread path during tapping but also to plastically deform the material through compression, resulting in a tight fit.
2. Synergistic Mechanism of Cutting and Compression
The working process of ST threading taps is not simply "cutting," but a composite forming process combining cutting and cold extrusion. The front end is typically designed with 1-3 cutting teeth to create the initial thread groove in the material, reducing cutting resistance. The subsequent main teeth have the complete ST thread profile. As the tap continues to rotate and advance, these teeth do not cut away material but forcefully compress the surrounding metal or plastic, causing it to plastically flow along the thread profile, conforming to the tap profile, and ultimately forming an internal thread that perfectly matches the self-tapping screw. This "compression forming" method avoids the large amount of chips generated in traditional tapping, and is especially suitable for thin sheet materials, preventing complete cutting or burr formation due to the material's thinness.
3. Enhanced Connection Strength Through Material Plastic Deformation
During the extrusion process, the material is subjected to intense compression on the thread flanks, compacting the grain structure and increasing local hardness, creating a "work hardening" effect. Simultaneously, the ST thread's crest and root design ensures an interference fit between the screw and the internal thread upon screwing in, resulting in a large contact area and strong friction, effectively preventing loosening. Experiments show that threaded connections formed by ST tap extrusion exhibit significantly higher tensile strength and resistance to vibration loosening than ordinary machined threads, particularly in aluminum alloys, low-carbon steel, and engineering plastics.
4. Improved Machining Efficiency by Eliminating the Need for a Pilot Hole or a Small Pilot Hole
A major advantage of ST threading taps is their ability to directly tap on materials without drilled holes or with only pre-drilled small holes. For softer materials, even "self-tapping without a pilot hole" is possible; for harder materials, only a pilot hole with a diameter slightly smaller than the thread minor diameter needs to be drilled. This greatly simplifies the machining process, reduces drilling steps, and is particularly suitable for automated assembly lines and mass production.
ST threading taps, through a "cut-then-extrude, extrusion-based" forming mechanism, not only efficiently form internal threads during the tapping process but also significantly enhance connection strength through the plastic deformation of the material. It is not merely a machining tool but also a "structural engineer" for reliable assembly. In modern manufacturing, which pursues lightweight, high efficiency, and high reliability, ST threading taps, with their unique technological advantages, have become an indispensable key component of connection technology.
