What Are The Most Common Mechanical Joining Methods?

Advantages

The advantages of mechanical joining processes include:

• No thermal changing or geometric distortion of materials or work pieces
• Capable of delivering high strength bond
• Structures can be disassembled as required for repair and maintenance (if using temporary fixings)
• Capable of joining materials, including dissimilar materials, that are difficult to weld or join by other means
• Easy to undertake quality control checks
• Little or no damage to pre-coated materials
• No fume or pollution generation, low noise and low energy consumption process
• Wide range of fixings available for different purposes

Disadvantages

Despite the numerous advantages, there are still some disadvantages associated with mechanical joining, including:

• More permanent solutions, such as riveting, can make it difficult to repair joints
• Patented fixings (including rivets) can mean higher costs
• Mechanical fasteners cannot by themselves provide a seal to prevent the escape of gases or liquids
• Holes created for fasteners to pass through create potential weak points where failure could occur as the stresses experienced at these points are accentuated

Processes

As mentioned above, mechanical joining methods can be categorised as those that use an additional fastener and those that do not. Common processes include:

• Processes without an additional fastener:

1. Hemming
2. Clinching
3. Mechanical Interlocking

• Processes with an additional fastener:

1. Screws
2. Threaded Fasteners
3. Rivets
4. Lockbolts
5. Tack Joins

Here, we will take a deeper look at these mechanical joining techniques, including some of their variants:

1. Hemming:

This is a metalworking process that involves folding a sheet of metal back over on itself to connect parts together, improve the appearance of a part or reinforce the edges of a part. Hems come in different designs, including a flat hem, wedge-shaped hem and a droplet-shaped hem.

2. Clinching:

Clinching is a mechanical fastening method that it typically used to join two or more sheet metals, although it can be used for some metal-to-non-metal applications with some modifications to the process.This inexpensive, high-speed method can be divided into round or square clinching and only requires a punch and a die. The punch pushes the sheet metal into the die to form an interlocking friction joint with good static and dynamic strength. Clinching can also be combined with riveting in a combination process called clinch riveting.

3. Mechanical Interlocking:

Also known as snap-fittings, mechanical interlocking joints allow for fast assembly of parts for a range of industries. They typically include two flexible parts that can interlock together to create joints that are easy to disassemble. Snap fit joints are often made from plastic parts although they are also use with aluminium in industries including automotive.

4. Screws:

Screws are widely used to mechanically fasten different materials for a wide range of applications. They come in a range of different types and are able to create large clamping forces yet can also be easily removed for maintenance or repair activities – examples include:

• Self-Tapping Screws: Self-tapping screws, also called thread rolling screws, form threads in a material as they are screwed in. They are designed to be driven into pre-drilled core holes where they can create a mating thread without a cutting action. The thread end is tapered to make it easier to start creating the self-tapped thread, which is often compatible with metric external threads so standard metric screws can also be used for repair.
• Hole and Thread Forming Screws: Hole and thread forming screws have similar advantages to those of self-tapping screws, although no drilling is required when assembling parts from thin sheets. Thin materials can also be joined together without needing a pilot hole, although some materials may still benefit from the use of a pilot hole with these screws. Frequently used in the automotive industry, hole and thread forming screws offer one-sided assembly into hollow profiles without the need for counter support. The screws can be removed for maintenance and repair and the female thread reused for replacement fixings to be used.

5. Threaded Fasteners:

These fasteners are available in a wide range of shapes and sizes. Fully detachable, they provide a strong join and can be designed as blind-hole, pierced, or pierced and protruding joints. Widely used in a range of different industries, threaded joints require either a nut or a separate mating thread into which the bolt can be screwed to secure two or more parts together.

6. Riveting:

Although they can be drilled out, rivets are designed as permanent, non-detachable mechanical fastenings. They can be split into those that require pre-punched holes into which the rivets can be inserted and self-piercing rivets that don’t require these pre-punched holes. Blind rivets can be inserted from a single side of a workpiece, and are sometimes called ‘hollow rivets’ as a result. Used in the aircraft industry, electronics and shipping, blind rivets are fast to install.

7. Lockbolts:

Lockbolts consist of a threaded pin with a break-away tail and a separate closing collar (or ‘collet’). They are used where welding, threaded fasteners or rivets cannot be used. They provide a high strength, vibration-proof and secure mechanical join.

8. Tack Joining:

Tack joining uses a nail-like fastener that is driven through the parts to be joined at high speed. This process doesn’t require pre-punching as the pointed tip of the tack displaces the material being joined to create the join.

Conclusion

Mechanical joining methods fasten or clamp parts together, either with the use of an additional fastener or without. They include the use of screws, threaded fasteners, rivets, lockbolts and tack joins as well as clinching, hemming, and mechanical interlocking.

Mechanical joints can be found in use across all industries, as well as in numerous domestic items from toys to electronic devices.

This wide use comes as a result of their ease of use, versatility, ability to join dissimilar materials, and because some can be unfastened for the purposes of repair and maintenance, among other reasons.