Mechanical Joining

Mechanical joining is the process of fastening materials together through physical force without melting them. It includes methods like fastening with nuts and bolts, screws or rivets, as well as the creation of integral joints like snap-fits and clinching.

Mechanical joining typically allows parts to be disassembled and is ideal for dissimilar materials and complex assemblies. However, mechanical joining can add weight and create stress points at the joins.

Types of Mechanical Joining

Mechanical joining can be broadly split into three types; with fasteners, without fasteners, and tube and pipe joins.

With Fasteners: Additional elements are inserted into or through holes to secure the parts

Nuts and Bolts / Screws: Allows for disassembly, versatile, creates strong joins
Rivets: Creates a strong permanent join, includes self-piercing rivets (SPR)
Lockbolts and Pins: Quick-locking and secure

Without Fasteners: Integral joins that use the workpieces themselves

Clinching: Joins sheet metals by creating flanges at the edges
Snap-Fits: Commonly used in plastics, uses integral, moulded features such as clips
Hemming: Folding the edges of parts to create a seam
Mechanical Interlocking: Using specially-created grooves or shapes that lock together

Tube and Pipe Joins:

Tube Rolling: Tube ends expand into fittings with mandrels and rollers, creating a tightly sealed join

Advantages and Considerations

Mechanical joining offers a number of advantages but also some considerations for use. The advantages include:

Versatility: Able to join complex and dissimilar materials
Disassembly: Allowing for ease of repair and recycling
No Heat Input: The lack of heat input avoids thermal distortion and metallurgical / property changes
Environmental Impact: Has a lower energy use than welding processes

Despite these advantages, there are a number of considerations when using mechanical joins:

Added Weight: Fasteners create additional weight to parts and structures
Stress Concentration: Holes used for fastening can weaken materials, with failure being more likely at these points
Material Challenges: Difficulty in forming holes in some ceramic and composite materials
Sealing: Additional gaskets required for fluid and gas-proof sealing

Core Research Programme (CRP) and Joint Industry Projects (JIP)

Core Research

Each year the TWI Core Research Programme (CRP) addresses challenges on behalf of our Industrial Members as well as developing specific technologies and processes. Each of the projects under the CRP is focussed on engineering, materials or manufacturing technologies.

Find out more here

Joint Industry Projects

TWI also conducts Joint Industry Projects (JIPs) that bring together groups of Industrial Members to share the cost of research activities in areas of mutual industrial interest, gaining exclusive access to the outcomes. These projects cover a broad range of topics.

Find out more here

Mechanical Joining at TWI

Resistance welding and mechanical fastening are two of the most widely used, cost-effective, and well-established methods of joining. TWI has a long and rich history of developments in these technologies, providing a range of services to Industrial Members looking for guidance or resources relating to either discipline.

Our expertise in mechanical fastening spans sheet joining, plastics and composites, and structural engineering. Our Members benefit from a range of specialised support services, consultancy and project work.

As well as having expertise in all fastening and non-fastening mechanical joining methods, we offer support with hybrid joining (combining mechanical fasteners with adhesives) and composite-to-metal joining through techniques including laser riveting and transition joints to overcome limitations of traditional fastenings in multi-material structures.

Example Support

commercial clinching and riveting equipment
static, fatigue and impact testing equipment
advice on process selection and best practice
engineering design advice on machine-threaded fasteners
materials science support
expertise on hybrid joints (use of fasteners plus adhesives)
information on the mechanical properties of fastened joints

The high production rate techniques that have been studied at TWI include clinching, which uses a special punch and die to form a mechanical interlock between the sheet metals being joined, and self-piercing riveting, in which a semi-tubular rivet is set using a punch and die to flare the rivet within the lower sheet so that no pre-existing hole is required.

Our experts have also supported industries in mechanical joining of composites to metals through reduced stress concentrations and improved longevity, as well as delivering advanced solutions such as polymer-coated materials (PCMs) joining and laser riveting for high-productivity, robust connections.

All of our confidential consultancy and project work is conducted to ISO 9001 quality standard, while our impartial and independent technical excellence across all industry sectors means that we can find the best solution for your challenges.

For more information, please email contactus@twi.co.uk.

For more information please email:

contactus@twi.co.uk