Mechanical fastening is a process used to affix or join two or more components together, typically non-permanently. This allows for the assembly and disassembly of items without causing significant damage to the components involved.
Mechanical fasteners provide a robust solution for permanent and non-permanent joints across a range of industries, from automotive and construction, to aircraft and agricultural machinery:
- Permanent Joint: Achieved through methods like riveting, where the fastener is deformed mechanically to hold parts together
- Non-Permanent Joint: Utilises threaded fasteners such as screws and bolts, allowing for easy disassembly
Mechanical fastening provides repeatability and reliability in joining components as well as enabling non-destructive inspection, ensuring that the quality of the joint can be tested without taking the assembly apart.
This flexibility is one reason mechanical fastening remains a popular choice in the manufacturing and engineering industries.
Contents
Click the links below to skip to the section in the guide:
Mechanical fastening is a process whereby two or more parts are joined together using various types of fasteners such as nuts and bolts, machine screws, or sheet metal screws, often in conjunction with lock washers.
Understanding the functionality of the different mechanical fastening methods helps decide which technique is preferable for a given application.
The effectiveness of these fasteners - and thus the integrity of the mechanical fastening itself - is influenced by factors such as the materials you're joining, the environment they're in, and the stresses they will endure.
By selecting the appropriate fastener for your task and applying the right amount of force, you can achieve a strong, durable connection. However, it is important to regularly inspect and maintain the fastenings to prevent failures due to environmental conditions or fatigue.
The choice of fastening used for a mechanical assembly is critical to the integrity and function of your end product. Different fastening methods can be used to mechanically join parts for different applications, considering the function and the environment in which the fastener will be used.
Temporary solutions such as screws, nuts, and bolts allow for maintenance and adjustments to be made, providing flexibility and reusability. However, if you want a more robust and tamper-proof solution, then more permanent fasteners like rivets may be preferable. Either way, it is important to ensure the type of screw or bolt you select matches your application requirements.
Mechanical fastening solutions can be split into temporary, permanent, or specialised methods, as follows:
Temporary Fasteners
- Screws: Typically externally threaded, screws are categorised by their head types (e.g., Philips, flat) and their thread patterns. Machine screws have a uniform diameter and are useful for fastening metal parts with tapped holes. Sheet metal screws, by contrast, are designed to create mating threads when you drive them into metal, meaning that there is no need to pre-drill holes
- Bolts: Externally threaded and used in conjunction with nuts, bolts are selected based on the required strength and environment. Nuts and bolts provide a secure hold by placing a bolt through the parts to be joined and then fastening a nut on the other end. The clamping force generated when you tighten the nut against the bolt head compresses the parts together
- Nuts: Internally threaded, nuts are designed to mate with bolts to hold two or more parts together. They come in various types, such as locknuts, which resist loosening
- Lock Washers: These can ensure a bolt or screw doesn't loosen due to vibration or movement. They are circular pieces with a split that lets them exert a spring force between your fastener and substrate, thereby enhancing the grip
Permanent Fasteners
- Rivets: Used to create permanent joints, once installed, they cannot be removed without damaging the parts
Specialised Fasteners
- Anchors: These are used for attaching objects to concrete or masonry, where traditional fasteners aren’t suitable
- Pins: Used for aligning or joining components, they can be either threaded or smooth
Mechanical fastening offers versatility in your installation methods, whether manual, robotic or in-die, according to your task, requirements, or production line. Mechanical fasteners require minimal space requirements, making them suitable for applications where space is at a premium and aesthetics are of concern. Another key advantage is the ease of installation in any direction, which allows you to work efficiently without concern for special tool orientations or workpiece positioning.
Mechanical fasteners can be used with dissimilar and diverse materials, including high-strength steels, and are robust enough to join materials with a high tensile strength, providing durability under demanding conditions.
In addition, mechanical fasteners can offer corrosion resistance, which is essential for maintaining both structural integrity and appearance over time while ensuring joint longevity and reliability.
Properly-chosen fasteners can help deliver an adequate bearing surface, which reduces stress and wear, preventing damage and extending the lifespan of your assembly.
Despite the advantages of mechanical fastening, there are a number of potential disadvantages to be considered:
1. Susceptibility to Stress Concentration:
Mechanical fasteners, like bolts and screws, can introduce stress concentration points at the area of application, potentially leading to cracking or crazing. This is especially concerning under tensile stress, which is less desirable compared to compressive stress
2. Reduced Structural Integrity:
A fastened joint is generally less strong than a continuous material. For example, a welded joint is often intrinsically stronger than one created with mechanical fasteners because there are no breaks in the material
3. Potential for Loosening:
Over time, mechanical fasteners may loosen. This can happen especially if they are subjected to vibrations or dynamic loads. These can compromise the stability of the joint and may necessitate regular maintenance or tightening
4. Ease of Disassembly:
Although often seen as an advantage for maintenance, the fact that mechanical joints are typically designed for easy disassembly can also be a downside. It makes these joints more prone to accidental disassembly under the wrong conditions
5. Weight Increases:
Some mechanical fasteners can add weight to a structure when compared to other joining solutions. For example, using rivets rather than an adhesive will increase the weight of the final part. This is crucial, particularly in sectors like automotive and aviation, where weight efficiency translates to performance excellence.
Mechanical fastening is an integral component in various industries and has applications spanning from common household furniture to complex aerospace constructs.
Industries employ different types of fastener to join parts tailored to specific requirements for strength, accessibility, and durability, ensuring the integrity and function of assembled parts:
Construction
Construction projects typically involve heavy duty applications where robust and lasting connections are vital. Mechanical fasteners such as nuts and bolts, metal screws, and threaded fasteners are routinely used to secure beams, roofing, and facades. Components like lock washers ensure a tight fit and maintain clamping force, countering any loosening that vibrations or thermal expansion might cause.
Manufacturing
Mechanical fastening has found diverse applications in the manufacturing sector. Machine screws feature prominently for their precision and strength, adapting to various materials and offering ease of disassembly when needed. Sheet metal screw fasteners and other threaded fasteners provide the essential clamping force to keep components aligned and secure.
Aerospace
Mechanical fastening in the aerospace industry revolves around ensuring maximal reliability under extreme conditions. This sector uses high-grade metal screws and threaded fasteners designed to endure temperature fluctuations and mechanical stresses, with the correct choice of mechanical fasteners critical for both construction and the ongoing maintenance of aircraft and spacecraft.
Automotive
Automobile assembly extensively uses mechanical fastening in systems ranging from simple interior fixtures to critical engine components. Nuts and bolts are ubiquitous, often combined with lock washers for enhanced security. The fasteners used in vehicles must withstand high-level vibrations and thermal variations, so it is vital that they are meticulously chosen and applied.
Electronics
In electronics, mechanical fastening secures components within devices where electrical integrity and precision are essential. Sheet metal screws, machine screws, and various types of nuts and bolts are employed to ensure components remain fixed, providing stable operation despite regular use. Electronics fasteners are selected for their conductor or non-conductor properties, size, and force specifications.
Furniture
Mechanical fastening is widely used for all types of home or office furniture as it provides an easy assembly and durable construction. Threaded fasteners, including nuts, bolts, and screws, provide the necessary holding power for structural stability and mechanical interlocks help to retain functional integrity while maintaining the aesthetic appearance of the furniture.
When you're assembling or repairing machinery, infrastructure, or any structure requiring robust construction, the choice of mechanical fastener is crucial.
Bolts and Nuts
A classic pair, bolts and nuts work together, with the bolt's threaded shaft passing through materials and secured with a nut.
Types:
- Hex bolts: Typically with a hexagonal head, used for construction and repair
- Carriage bolts: Smooth, domed head with a square section underneath to prevent turning during installation
Screws
Screws have a helical thread that enables them to drill into materials.
Types:
- Wood screws: Specifically designed for use in wood
- Machine screws: Used in pre-tapped holes on metal surfaces
Washers
These flat disks help distribute the load of a fastener, diminishing pressure on the secured material.
Types:
- Plain washers: Provide a smooth bearing surface
- Spring washers: Prevent loosening through vibrations
Rivets
Rivets are permanent fasteners that join two pieces of material through pre-drilled holes. After inserting, the tail is deformed to hold the rivet in place.
Pins and Keys
Pins are used to align or join two parts together, with types like split pins or cotter pins ensuring positioned parts remain secure. Keys are used in machine parts to prevent relative rotation between pieces.
Each fastener type has its specific application based on the materials being joined, the environment, load requirements, and accessibility for future maintenance. Your choice will impact the integrity and lifespan of the assembly.
What are the primary uses of mechanical fastening in various industries?
Mechanical fastening is integral to construction, manufacturing, and automotive industries for its ability to robustly join materials, such as wood, metal, and plastic, often allowing for disassembly without damage.
How do different types of mechanical fasteners contribute to joint integrity?
The integrity of a mechanical joint depends on the fastener type. Screws, bolts, and rivets distribute loads differently, with some offering tighter clamping forces and others providing sheer strength, catering to various structural requirements.
What distinguishes mechanical fastening from other joining methods in terms of advantages and disadvantages?
Mechanical fastening offers the benefit of reversible joints and a non-reliance on heat, unlike welding. However, it requires accurate alignment and can sometimes be less aesthetically pleasing than bonded joints.
In what ways is mechanical fastening applied within the automotive sector?
Within the automotive industry, mechanical fasteners are used extensively for assemblies that require regular maintenance or adjustment, such as engine components. They ensure secure joins that can withstand vibrations and stress.
Could you explain the mechanical fastening processes and their applications in mechanical engineering?
Mechanical engineering employs fastening processes like bolting and threading for machinery assembly and maintenance. This ensures components can be disassembled for repairs or upgrades without damage.
What are the alternatives to screw-based mechanical fastenings, and in which scenarios are they most effective?
There are alternatives available to bolt and screw joints, such as snap-fit or press-fit fasteners, which are effective in low-stress applications. They are also useful when quick assembly and disassembly are necessary without the use of tools. These fasteners are often used in consumer electronics and lightweight constructions.