When to Say No: 5 Materials Where Thread Forming Screws May Fail

Veröffentlicht: February 12, 2026

Kategorien: Neuigkeiten

Choosing the correct fastener for any task often involves a blend of careful engineering and some practical testing. For numerous professionals in the industrial field, Trilobular Thread Forming Screws, such as the DIN 7500 CE or ME types available in the Qewit lineup, prove to be extremely helpful. These screws do not cut threads; instead, they shape them. As a result, there are no scattered metal shavings, and the connection becomes much more secure because the metal retains its form and grips the screw firmly. However, these fasteners are not perfect solutions. If someone attempts to insert them into an unsuitable material, problems like broken heads, damaged drives, or fractured components can occur quickly.

Recognizing the boundaries where these fasteners might not perform well is key to maintaining an efficient production process and avoiding frustrating delays. It is essential to consider that the base material under the screw is just as important as the screw itself, and understanding this helps prevent issues down the line.

Why Is Material Selection Critical for Thread Forming Success?

The core principle of thread forming relies on plastic deformation. In simple terms, the process involves shifting the metal aside to create a threaded path. This method succeeds well when the metal is flexible enough to adjust. But if the material resists movement or lacks toughness, it will not yield properly; rather, it will resist strongly or shatter under pressure.

The Physics of Material Displacement and Plasticity

Ein Trilobular DIN 7500 screw features a somewhat triangular design that minimizes resistance during insertion. For it to function effectively, the surrounding material must be pliable, allowing it to bend or reshape without fracturing. As the screw advances, it pushes the material along the natural lines of the part, which ultimately strengthens the overall joint. Yet, if the material lacks sufficient flexibility to shift, the resistance increases rapidly, and typically, the screw fails first under the strain.

Limitations of High-Hardness Base Metals

Fasteners undergo specific hardening processes, often through controlled heating. When the base metal approaches the hardness level of the screw, the screw struggles to penetrate it. For example, Qewit’s standard-grade fasteners are durable, but attempting to insert a DIN 7500 CE Pan Head into tempered steel leads to the trilobular tips wearing down quickly. This results in torque-out, where the tool spins endlessly while the screw remains stuck, eventually breaking apart.

Risks of Material Fatigue and Stress Cracking

Materials that are prone to breaking easily pose significant challenges for thread forming. Since these screws apply considerable outward force in various directions, they can behave like a splitting wedge. In substances unable to withstand such internal tension, the part may divide cleanly right away, or it could appear stable initially only to develop cracks later, perhaps while stored in inventory for weeks.

Which Five Materials Pose the Highest Risk of Failure?

While theoretical knowledge is valuable, identifying the particular materials to avoid in real-world settings is what ensures smooth operations. Drawing from widespread industry experiences and the inherent constraints of typical steel fasteners, the following list highlights the five most common materials that lead to thread-forming issues.

Brittle Cast Iron and High-Carbon Steels

Cast iron is well-known for its strength, yet it remains highly fragile. It lacks the necessary resilience for a DIN 7500 screw to shape threads effectively. Rather than the metal adapting around the screw, it tends to break into fine particles. Similarly, high-carbon steels reaching Grade 10.9 or above present comparable difficulties because their rigidity demands insertion forces that exceed the screw’s own breaking point.

Heavily Reinforced Thermoset Plastics

Plastics generally work well with thread forming, but thermoset varieties differ markedly from everyday thermoplastics. When a plastic contains substantial glass reinforcement, with numerous fine glass fibers added for added durability, it turns highly abrasive. During insertion of a Trilobular screw, these fibers function like coarse grit, wearing away the screw’s threads well before it reaches the hole’s depth.

Non-Ductile Die-Cast Alloys

One might assume all aluminum variants are soft enough for thread forming, but certain die-cast alloys have uneven internal compositions that make them unreliable. If the alloy includes significant porosity, featuring many small voids within, the forming action simply enlarges those spaces. Consequently, instead of producing a solid, reliable thread, the result is an irregular cavity resembling damage from pests, which provides minimal resistance to pulling out.

Cold-Worked Stainless Steels

Stainless steel can be deceptive in its behavior. Although Qewit provides reliable A2 and A4 stainless fasteners, the properties of the target material are crucial. When the base stainless steel has undergone cold working, such as through pressing or rolling at low temperatures, it hardens considerably beyond its initial condition. Inserting a thread former in this scenario frequently causes galling, where the screw and the hole fuse together midway through the process.

Ceramics and Highly Crystalline Materials

This category may appear straightforward, but it arises surprisingly often in advanced industrial applications. Substances with a crystalline makeup, such as certain high-tech ceramics or rigid composites, resist deformation entirely. Under the force from a DIN 7500 ME Countersunk Head screw, they fracture immediately. For these, pre-threaded holes or custom inserts are nearly always necessary.

How Can You Ensure Optimal Fastener Performance?

To sidestep these common problems, preparation is vital before any assembly begins. Qewit’s “Western Style” business approach emphasizes technical reliability, ensuring that the “Far Eastern Value” delivers consistent results in actual use.

Verification of Substrate Hardness and Ductility

It is crucial to assess the hardness and flexibility of your components beforehand. For a typical steel DIN 7500 CE, the base material should stay under HV 350 in hardness. Exceeding this level raises the chance of hydrogen embrittlement, where the metal weakens and fails under stress. Therefore, always align the screw’s hardening process with the specific demands of the application.

Precise Pilot Hole Diameter Optimization

The starting hole’s size is a critical factor in success. If the pilot hole is slightly too narrow, even by a small amount, the required turning force will rise sharply, potentially damaging tools and screws alike. On the other hand, if it is overly wide, the screw will not engage enough threads, leading to easy removal. Achieving the ideal dimension usually involves some experimentation tailored to the material in question.

Utilization of Qewit Technical Support and Testing

Avoid relying on assumptions alone. Qewit maintains comprehensive testing resources, including Tensile Strength Testers and Vickers Hardness equipment. If uncertainty exists about whether a DIN 7500 screw suits a particular new alloy, request a evaluation. They can supply 3.1 certifications or Initial Sample Inspection Reports (ISIR), offering evidence of performance prior to large-scale orders.

FAQ (häufig gestellte Fragen)

Q1: Can I use thread forming screws in pre-drilled holes in hardwood?

A: In principle, thread forming suits metals and plastics best. For wood applications, a Wood Screw with sharp, deep threads and a cutting tip is far more appropriate. Wood’s lower density means that attempting to form threads can damage the fibers instead of creating a firm hold.

Q2: What is the main difference between DIN 7500 CE and ME?

A: The distinction lies in the head design. The CE features a Pan Head, which rests atop the surface and offers broad contact for stability. In contrast, the ME has a Countersunk (Flat) Head, designed to align flush for a clean appearance. Both share the trilobular shank mechanism.

Q3: Will thread forming screws damage the plating on my parts?

A: Because these screws displace material without cutting, they tend to be kinder to surface finishes than cutting types. That said, the friction involved can cause slight surface marks. To prevent corrosion, Qewit provides options like Zinc Plating, Geomet, or Zinc Flake coatings for added protection.