Three Types of Fastening Methods in Industrial Assemblies

Three Types of Fastening Methods in Industrial Assemblies

Laura Davis, Manufacturing Technology Insights | Monday, May 10, 2021

Many adhesives and tapes support the advantages and disadvantages of mechanical and thermal attachment. PSA tapes or hot melt adhesives allow quicker assembly than mechanical fasteners; strength can be found in toughened epoxies, exceeding the strength of welded joints of >20 MPa lap shear strength.

Fremont, CA : Humans have found creative ways to mechanically fasten various materials with ropes, pegs, and wedges for as long as they have been using instruments. Someone invented the first adhesive after about a few thousand years of perfecting the art of fastening: some birch-bark tar that could bond rocks together. From pressure-sensitive adhesive (PSA) tapes to structural-strength curing adhesives, the portfolio of available adhesives has since evolved into a textbook of everything. Here are three types of fastening methods:

Adhesives

Adhesive and tape bonding, the latest assembly method to emerge, offers an assembly with unique advantages. It integrates different materials, often with thinner substrates than those that are capable of mechanical or thermal attachment. The surface also preserves the elimination of stress concentration, improves aesthetics, prevents thermal degradation, and maintains protective coatings. Adhesives also simultaneously bond and seal joints, potentially removing other steps in the process and damping vibrations in the final part.

The various benefits come at a price, mostly at the cost of raw materials. In terms of planning, application, and curing, adhesives can also be relatively complex, resulting in a lack of familiarity between engineers and standard requirements. Disassembly is also a challenge, especially when part testing is not generally accepted for non-destructive testing.

Mechanical Fasteners

Mechanical fasteners are user-friendly and require little if any cleaning or preparation for the attached parts. Mechanical fasteners immediately generate strong joints, many of which can be removed when needed. Compared to other methods, such as thermal attachment, they also come with lower labor rates.

Mechanical fasteners have their limitations, however. Many require puncturing the surface of one or more components that are joined. The parts with a visible bond line are distorted by this penetration and possible damage to painted surfaces. Different attachment points also focus stresses on the joint that increase fatigue and may lead to premature failure. And mechanical fasteners do not segregate dissimilar materials, which may cause corrosion.

Thermal Fastening

Similar to mechanical fasteners, thermal attachments offer benefits. Without the need for clamping or healing time, they promise a fast process, and the raw materials are cheap. A broad, standard level of understanding for designers and manufacturers has been created by the wide acceptance of welding and soldering on the market for decades.

However, thermally bonded assemblies must use similar materials, and relatively thick substrates are often required. The joints are strong, but it is also hard to disassemble, rework, or repair them. Aesthetic concerns such as discoloration, distortion, or read-through can also be created. Thermal attachment costs can be very high, including the cost of skilled labor, energy, and safety.

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