What is Friction?
Friction is an essential part of our lives. We may not realise, but without Friction, even a bicycle will not move an inch on road, leave alone vehicles and trains running!
Yes, we do need to spend energy to overcome Friction, but if it were not to be there, we will not be able to get any Controlled Motion at all.
Friction is rubbing resistance to motion when 2 adjoining objects are made to move relative to each other. The materials of the 2 objects can be anything - paper to wood, rubber to flooring material, steel to steel, oil to surrounding copper tube and so on. By keeping anyone object as non-moving, if we try to move the adjoining object, there is a rubbing resistance getting generated between the two, and we do need to give adequate Force, for the relative motion to start and then to continue.
The Object, even though on an inclined plane, may not easily slide down. This is due to the friction between adjoining surfaces of the object and the inclined Slope material!
- Friction Force - this terminology is used for Linear Motion between adjoining objects
- Frictional Torque - this terminology is used for Rotary Motion between adjoining objects
Values of Friction Force / Torque
Coefficient of friction is denoted by µ. Itis a number (without any Engg Unit) which indicates the Index of Rubbing Resistance between 2 adjoining objects.
Value of µ depends on various factors-
- Material characteristics of the 2 objects
- Profile of Contact Surfaces
- Relative Speed of motion between the 2 objects
The value is thus not very straightforward and may require many references/studies. One important misconception is that the maximum value of µ is 1. But this need not be true as the value can go even higher than 1, under some combinations of attributes mentioned above.
What is Friction Welding?
This is a solid-phase joining process developed through years of research to join 2 parts. Please note that even though Friction Welding is generally referenced from the context of metal parts joining, it can even be used for joining plastics.
There are various types of friction welding - Rotary, Stir, Linear etc. In this writeup, we will look at Rotary Friction Welding.
In Rotary Friction Welding, out of the 2 jobs to be welded (end surfaces), one is rigidly held while the other one rotates. The part that rotates is held in a chuck while the other job is rigidly fixed on a slide. The job fixed to the slide cannot rotate but can linearly move towards the job held onto the chuck. While the chuck is made to rotate at a certain speed, the other part is made to move axially and touch the rotating job. When they touch under application of linear force, their surfaces start rubbing against each other, and both parts become hot. The rotation and linear force applications are continued till both jobs attain a certain temperature wherein they change from Elastic to Plastic stage. At this time, the rotary motion is suddenly stopped, and an upset force is linearly applied through the slide.
As a consequence of this lateral force, metal to metal bonding happens between the 2 objects and both the parts get forged.
Component before Friction Weld
Component after Friction Weld
Two key aspects of this process:
- Apart from the electricity supply, there is just no other consumable for this process.
- The strength of welded joint (Tensile / Shear / Bending etc) is better than the parent material. Microstructure analysis of a properly welded joint shows better granular arrangement at the joint, compared to the parent parts.
What is described above is the basic principle of Friction Welding. With today’s level of Machine Building, coupled with an innate knowledge of metallurgy, the Friction welding machines has reached an extreme level of sophistication, productivity and accuracy. ETA Technology has been a trailblazer in this field and continues to innovate in helping our customers build their best product ever.