~ Article courtesy of PennEngineering

Today’s design engineers have more flexibility when choosing a fastening solution than ever before. The need for parts that are lighter and thinner, yet stronger is pushing fastening innovations forward. One alternative to the more conventional self-tapping screws for metal is the self-clinching fastener. Before discussing the benefits of self-clinch fasteners, it’s important to understand how self-tapping screws work and what sets them apart from self-drilling fasteners.

Self-tapping versus self-drilling
It’s a common question: is there a difference between self-tapping and self-drilling screws? The answer is yes, but the terms are sometimes used interchangeably. As for similarities, both types of screws can fasten metal components and can tap their own threads.

A self-tapping screw removes the need for a tap because it cuts its own thread when driven into a mating material, such as metal. However, some self-tapping screws are unable to drive through metal, so a pre-drilled pilot hole may be required for the fastening process.

For the screw to be securely fastened to the mating material, the diameter of the pilot hole should be smaller than the screw. In the extrude and tap process, the panel must first be punched to extrude the sheet metal, which effectively thickens the sheet metal. Then, a self-tapper screw is inserted.

While a self-tapping screw often requires a pre-drilled pilot hole, a self-drilling screw does not. Its sharp threads and drill-bit-shaped point let it easily self-drill through a range of metal materials. This makes installation faster, saving time and costs by removing the need for a pilot hole.

Technically, all self-drilling screws are self-tapping screws. But not all self-tapper screws are self-driller screws.

The self-clinching fastener
A self-clinching fastener offers an alternative to conventional self-tapping screws for metal. It’s a threaded or non-threaded component permanently inserted into sheet metals.

When pressed into ductile material, a self-clinching fastener displaces the host material around the mounting hole, causing it to cold flow into a specially designed annular recess in the shank or pilot of the fastener. A serrated clinching ring, knurl, ribs, or hex head prevents fastener rotation in the host material once inserted — becoming a permanent part of the piece into which it’s installed.

Self-clinching fasteners install with any parallel-acting press that can be adjusted to optimum installation forces.

Self-clinching fasteners have greater reliability and holding power than extruded/tapped or stamped threads, achieving strong threads/attachment in metal as thin as 0.20 mm/.008 inches. They’re a reliable choice where high pushout and torque-out resistance are required in sheet metal that’s too thin to provide secure fastening by other methods.

The ideal choice
In applications where aesthetics do not matter, a self-tapping screw can do the trick. With the use of a simple drill press, a strong attachment can be achieved as long as the mating material has good thickness. Just note that the thread will be limited in strength based on the material.

Another important consideration is that the extrude and tap method can create chips of metal in between the mating parts when using a thread-cutting screw. This is problematic for certain assemblies, including electrical or food applications.

It’s possible to achieve a stronger joint with self-clinching technology, especially in thinner mating materials. For applications requiring sleek cosmetics, a self-clinching solution is typically the better, more reliable choice.

Ultimately, your application will drive which fastening option is ideal.

Self-clinch in three easy steps
In just three steps, self-clinching fasteners install with any parallel-acting press that can be adjusted to optimum installation forces.

• Step 1: Place the fastener into the anvil hole and place the mounting hole over the shank of the fastener.
• Step 2: With the installation punch and anvil surfaces parallel, apply squeezing force until the head of the clinch nut comes in contact with the sheet material.
• Step 3: Install the mating piece from the side opposite the head of the fastener.

Advantages
Self-clinching fasteners offer additional advantages:

• Clean process – cleaner and more environmentally friendly than other joining methods such as welding (no weld splatter and less energy consumption)
• Design flexibility – can fasten to dissimilar materials, including common steel, HSS, and others
• In-process installation – easily and efficiently installed into a plain round hole, with no secondary options needed
• Cost reduction – decrease installation cycle times for medium and high-volume applications

 

 

 

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Filed Under: Fastener Engineering • Screws, Fastener screws • nuts • bolts
Tagged With: PennEngineering
 

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