Welding is a fabrication process whereby two or more parts are fused together by means of heat, pressure or both forming a join as the parts cool. Welding is usually used on metals and thermoplastics but can also be used on wood. The completed welded joint may be referred to as a weldment.
Some materials require the use of specific processes and techniques. A number are considered 'unweldable,' a term not usually found in dictionaries but useful and descriptive in engineering.
The parts that are joined are known as a parent material. The material added to help form the join is called filler or consumable. The form of these materials may see them referred to as parent plate or pipe, filler wire, consumable electrode (for arc welding), etc.
Consumables are usually chosen to be similar in composition to the parent material, thus forming a homogenous weld, but there are occasions, such as when welding brittle cast irons, when a filler with a very different composition and, therefore, properties is used. These welds are called heterogeneous.
The completed welded joint may be referred to as a weldment.
Joining Metals
As opposed to brazing and soldering, which do not melt the base metal, welding is a high heat process which melts the base material. Typically with the addition of a filler material.
Heat at a high temperature causes a weld pool of molten material which cools to form the join, which can be stronger than the parent metal. Pressure can also be used to produce a weld, either alongside the heat or by itself.
It can also use a shielding gas to protect the melted and filler metals from becoming contaminated or oxidised.
Joining Plastics
Plastics welding also uses heat to join the materials (although not in the case of solvent welding) and is achieved in three stages.
Firstly, the surfaces are prepared before heat and pressure is applied and, finally, the materials are allowed to cool to create fusion. Joining methods for plastics can be separated into external or internal heating methods, depending on the exact process used.
Joining Wood
Wood welding uses heat generated from friction to join the materials. The materials to be joined are subjected to a great deal of pressure before a linear friction movement creates heat to bond the workpieces together.
Common Joint Configurations
Butt Joint
A connection between the ends or edges of two parts making an angle to one another of 135-180° inclusive in the region of the joint.
T Joint
A connection between the end or edge of one part and the face of the other part, the parts making an angle to one another of more than 5 up to and including 90° in the region of the joint.
Corner Joint
A connection between the ends or edges of two parts making an angle to one another of more than 30 but less than 135° in the region of the joint.
Edge Joint
A connection between the edges of two parts making an angle to one another of 0 to 30° inclusive in the region of the joint.
Cruciform Joint
A connection in which two flat plates or two bars are welded to another flat plate at right angles and on the same axis.
Lap Joint
A connection between two overlapping parts making an angle to one another of 0-5° inclusive in the region of the weld or welds.
This is a fast process which allows wood to be joined without adhesives or nails in a matter of seconds.
Different Types of welding
There are a variety of different processes with their own techniques and applications for industry, these include:
Arc
This category includes a number of common manual, semi-automatic and automatic processes. These include metal inert gas (MIG) welding, stick welding, tungsten inert gas (TIG) welding also know as gas tungsten arc welding (GTAW), gas welding, metal active gas (MAG) welding, flux cored arc welding (FCAW), gas metal arc welding (GMAW), submerged arc welding (SAW), shielded metal arc welding (SMAW) and plasma arc welding.
These techniques usually use a filler material and are primarily used for joining metals including stainless steel, aluminium, nickel and copper alloys, cobalt and titanium. Arc welding processes are widely used across industries such as oil and gas, power, aerospace, automotive, and more.
Friction
Friction welding techniques join materials using mechanical friction. This can be performed in a variety of ways on different welding materials including steel, aluminium or even wood.
The mechanical friction generates heat which softens the materials which mix to create a bond as they cool. The manner in which the joining occurs is dependant on the exact process used, for example, friction stir welding (FSW), friction stir spot welding (FSSW), linear friction welding (LFW) and rotary friction welding (RFW).
Friction welding doesn't require the use of filler metals, flux or shielding gas.
Friction is frequently used in aerospace applications as it is ideal for joining otherwise 'non-weldable' light-weight aluminium alloys.
Friction processes are used across industry and are also being explored as a method to bond wood without the use of adhesives or nails.
Electron Beam
This fusion joining process uses a beam of high velocity electrons to join materials. The kinetic energy of the electrons transforms into heat upon impact with the workpieces causing the materials to melt together.
Electron beam welding (EBW) is performed in a vacuum (with the use of a vacuum chamber) to prevent the beam from dissipating.
There are many common applications for EBW, as can be used to join thick sections. This means it can be applied across a number of industries from aerospace to nuclear power and automotive to rail.
Laser
Used to join thermoplastics or pieces of metal, this process uses a laser to provide a concentrated heat ideal for barrow, deep welds and high joining rates. Being easily automated, the high welding speed at which this process can be performed makes it perfect for high volume applications, such as within the automotive industry.
Laser beam welding can be performed in air rather than in a vacuum such as with electron beam joining.
Resistance
This is a fast process which is commonly used in the automotive industry. This process can be split into two types, resistance spot welding and resistance seam welding.
Spot welding uses heat delivered between two electrodes which is applied to a small area as the workpieces are clamped together.
Seam welding is similar to spot welding except it replaces the electrodes with rotating wheels to deliver a continuous leak-free weld.