Methods of Joining and Assembly in Manufacturing
By Mary Iannuzzi on February 19, 2020
There are many ways to fasten two parts of an assembly together, each with its own benefits and drawbacks. Choosing the correct method of joining or assembly can make a product more structurally and economically sound. This article will highlight some of the most common methods of joining and assembly.
1. Hardware Assembly
A hardware assembly is any number of parts connected by physical connections such as nuts and bolts. This type of assembly is primarily used when there is a need for or significant benefit to being able to take individual parts out of an assembly throughout the life cycle of the product. It is also used for joints requiring one or more degrees of freedom. Some examples are slider joints, cylindrical joints, and ball joints.
Pros: Hardware assembly allows for easy, low-cost replacement of parts that may break or wear at an increased rate in comparison to the rest of the assembly.
Cons: There is an additional cost associated with the fastening materials. These materials can also add significant weight compared to a permanent joint.
Welding is a permanent joining technique that binds metals together using electricity. In traditional welding, the base metal of both parts being welded together is melted. The connection is formed when this molten metal re-hardens. The weld is often stronger than the metal itself and can add strength to the entire structure. There are many types of welding with subtle differences. A few types are MIG welding, flux-cored welding, TIG welding, and stick welding.
Pros: Welds are lightweight, strong, and can be aesthetically pleasing. Overall, they can add to a structure rather than being a necessary
Cons: Welding requires highly skilled labor and specialized equipment. Many welding techniques require a gas shield. It can also take more time than other methods. This can all lead to high production costs.
Rivets are a type of permanent fastener that binds two plates of metal together. They work similarly to a nut and bolt, however, rather than two separate pieces bound by a screw, a rivet is one solid piece, with both ends flush against each piece of metal.
Two primary types of rivets are used today, solid rivets and blind, or “pop”, rivets.Solid rivets must be installed from both sides. After the rivet is fed through a hole, the back side is manually pushed toward the flat, joined metal. The back end of the rivet expands and fastens the two metal sheets together.
A blind rivet uses a mandrel to achieve a similar outcome without the need to access both sides of the metal. The rivet is fed through the hold and the mandrel is pulled back out, in the reverse direction of insertion. The mandrel causes the back of the rivet to expand before breaking off at a predetermined force. The rivet is left there, binding the two metal plates together.
Pros: Rivets are cost effective, allow for quick production and are generally durable.
Cons: An increased work force is sometimes needed. Each rivet also adds weight, and a stress concentration or weakness near rivet holes is possible.
- Brazing and Soldering
Brazing binds two metal parts together by melting a filler metal in-between them.
The filler metal must become a liquid above 450 degrees Celsius to be considered brazing. Soldering is the same process but uses molten filler metal that melts below 450 degrees Celsius. Both are less structurally strong than welds, but they take less time and you do not need to melt the base metal. Soldering is the weaker of the two, but is often used for electrical parts. It is less likely to cause damage as the molten metal is at a lower temperature.
Pros: Suitable for electronic connections or otherwise heat sensitive connections. Quicker than welding and does not to be shielded with gas or otherwise.
Cons: Can be weak, especially soldering. Not to be used as a primary structural joint and often needs to be reinforced with another joining method to support significant stress.
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