What Is Friction Welding?- Working, And Application

What Is Friction Welding?

Friction welding is a solid-state welding process that welds two workpieces together through mechanical friction at the interface of the workpieces in relative motion with an additional lateral “upset” force to plastically displace and weld the two pieces together.

Friction welding is not a fusion welding process since there is no melting of the materials being joined. Friction welding is more comparable to forge welding and is commonly used for joining metals and thermoplastics for many aviation/automotive applications.

When observing a surface, it appears smooth but in reality comprises a large number of very fine protrusions or defects called asperities.

When a surface moves relative to another surface, the asperities interact, creating a friction effect that prevents the motion of the two surfaces through interference.

The contact forces acting on these asperities generate heat through elastic and plastic yielding. Frictional performance welding utilizes this phenomenon as an industrial joining application.

The frictional interface through the induced mechanical motion creates heat causing the materials to be joined to soften and flow viscously. While the workpieces are in a flow state, the mechanical motion through friction effectively mixes the two materials for bonding.

The mechanisms by which the frictional heat, and mixing of material occurs during the process, are very dependent on the process condition used the four primary process types are friction stir welding (FSW), friction stir spot welding (FSSW), linear friction welding (LFW), and rotary friction welding (RFW).

How does friction welding work?

FSW utilizes a tool that is non-consumable, and is inserted with enough force into the interface of the two workpieces.

The tool is rotated and axially inserted into the interface; once inserted into the interface it travels or gaits through the interface causing frictional heat to develop, heating and softening the material.

The material surrounding the rotating tool is then mechanically mixed to produce a bond. FSSW is essentially FSW, except it rotates, plunges, and retracts at the workpieces in lap-joint configuration to produce a “spot” weld, meaning during FSSW there is no traverse or gaiting.

LFW and RFW do not utilize a non-consumable tool; in other words the individual workpieces to be joined create the frictional heat and subsequent mechanical mix. In LFW an individual workpiece is linearly oscillated against another workpiece while a compressive force is applied.

The frictional heat generated by the oscillating surfaces softens and mechanically mixes the interface material. RFW is similar to LFW with the exception that typically the workpieces are round and rotate relative to one another.

The workpieces typically shorten (“burn-off”) in the direction of the compressive force forming a flash during LFW and RFW.

During burn-off, the young surface of the interface releases contaminants such as oxides and foreign particles. Once contaminants are expelled free and clear, pure metal-to-metal mixing can begin, forming an integral bond.

While the temperatures generated in friction welding are extremely hot, the material remains a solid-state condition (i.e., no melting occurs).

Applications

Friction welding can create better industrial rollers, tubes, and shafts for many applications. While this is more often used as a way to make subassemblies for industrial printers and material handling equipment, it also has automotive, aerospace, marine, and oil applications.

Other examples of components include gears, axle tubes, drivelines, valves, hydraulic piston rods, truck roller bushes, pump shafts, drill bits, connection rods, etc.

Advantages Of Friction Welding

• Enables joining of dissimilar materials typically not joining compatible through welding by others joining methods.
• Creates a narrow, heat-affected zone.
• Consistent and repeatable process of full metal fusion.
• Joint preparation is minimal – usually a saw-cut surface but everything is possible.
• Faster Turn-around Times – than long lead time of forgings, currently 6 months or more.
• Greatly improves design flexibility – select the proper material for each area of a blank.
• Allows for different quantities – 1 off prototypes to high volumes.
• Does not require, fluxes, filler materials or gases.
• Environmentally friendly process – process does not create any fumes, gases or smoke.
• Solid state process – there is no chance for porosity or slag inclusions.
• Creates cast or forge like blanks – without costs associated with tooling or minimum quantities.
• Reduces machining labor, which also reduces perishable tooling costs and increases capacity.
• Full surface weld gives much greater strength in critical areas.
• Reduces raw material costs in bi-metal applications. Expensive materials are used only were needed in the blank.

Disadvantages of friction welding

• This process is suitable only for round bars with the same crossing section.
• It is limited to butt joints that are angular and flat.
• The set up is very expensive.
• It is very difficult to prepare the workpiece.
• Welding is not possible for non forgeable material.
• It is only suitable for small parts of machines, large parts cannot be worked with it.

FAQs