YATIN TAMBE,
Chairman & Managing Director
Friction Welding Technologies Pvt Ltd

DHAYANANTHAN DEVARAJ,
Friction Welding Technologies Pvt Ltd

The Word Friction

The word Friction is viewed by engineers as ‘curse’ as it makes Loss of Production through wear and tear, But Friction can be viewed as a ‘friend’ of Engineers if it is harnessed in a correct manner, where it can join variety of material in solid phase.

Welding process are divided into two streams as Fusion welding – relies on the formation of molten bridge, Solid state welding – rely on the deformation of the metal. In solid state welding process is where we utilize friction as a ‘friend’ to join the materials.

The Theory of Solid Welding

All ductile metals can be cold pressure welded, but the forces required would be prohibitive. Therefore, materials were heated to improve ductility.

  • Flame heating.
  • Induction heating.
  • resistance heating.
  • Heating by Friction.

So, we are here using friction to heat up material in solid state welding. Apart from being a very efficient heat source. Friction provides an effective cleaning action, Various foreign inclusions, surface oxides that opposes formation of bonds are destroyed & removed by abrasion produced by Friction.

Friction Welding Process

Parts are loaded into welder, one in rotating spindle and other in stationary clamp. Component in spindle is brought up to pre-determined rotational speed and then a pre-determined axial force F1 is applied. Rotational speed is then stopped and increased axial force F2 is applied until desired upset is obtained.

As you know there will be variable in friction welding and we categories it as, machine variables, non-machine variables and minor influence variables.

Minor influence variables are as,

  1. Initial condition of friction welding surfaces.
  2. Shapes of the pieces to be welded.
  3. Medium in which the process takes place.

 

Friction welding machine

FWT friction welding machines have a rigid frame construction and a generously designed working space. The machine is designed to grip both components that are to be friction welded together. The component in the spindle side is clamped by means of a Master Collet and the component in the slider side is gripped by means of V-blocks which in turn has a hydraulic clamping mechanism that has been specially designed to withstand the axial loads associated with friction welding. The slider is traversed by means of hydraulic cylinder. The slider is mounted on a linear slide system, which by its nature is very stiff enabling the machinery to work to fine concentricity tolerances.

Adjustable backstops are provided for both components so that different length components are catered for. The machine comes complete with fully integrated hydraulic power pack and one set of tooling to suit the components selected for acceptance and run off trials. Machine cycle time will be dependent on the components to be welded and may vary due to length, form, and diameters and dependent on operator efficiency. The changeover between component types is very quick if performed by competent operator.

The machine mainly comprises of the following,

  1. Mechanical

Machine bed – A rigid frame with fabricated and stress relieved structure with good surface finish. The machine will be designed for low noise and vibrations and the structure would be tested using Ansys software for any deflection, deformation, and stress concentration. The machine structure does not require any special foundation. This is a Fixed head type machine construction.

Headstock – Designed to accommodate the spindle and the spindle is designed in such a way that maximum length of the rotating component as per customer drawing can be accommodated.

Slider advance unit – A moving unit on which the Fixture clamp unit is based, and it is mounted in such way that maximum dia. /length of the non-rotating component as per customer drawing can be accommodated.

Main slide – The main slide will be as per FWTs design on which slider assembly will be mounted.

Self-Centring Clamp – A Self-centring clamp operated by means of a hydraulic cylinder for better accuracy during clamping.

  1. Electrical and Hydraulics

Spindle drive – A Servo spindle motor and an AC asynchronous servo drive is used. The drive to spindle is through a timer belt. The spindle will have forced lubrication system taken directly from the Hydraulic Power Pack. 415V AC, 3 phase, 50 HZ primary power requirements.

Hydraulic powerpack – with suitable powerpack, which will be selected based on upset force required to join the two materials.

Below is the representative image of FWT – 40 Rotary Friction welding Machine

Features of Friction welding

  • Pressure welding process causing forging effect.
  • Fine grained structure.
  • The static strength.
  • The welds are leak-tight.
  • Heat Affected Zone (HAZ).
  • Short welding times.
  • The rotation symmetric heat application, high dimensional accuracy.

 

Advantages of Friction welding

  • Autogenous – No filler material is used.
  • Machine controlled process.
  • Parameters monitoring.
  • Easy automation for high production.
  • Independent of operator skill or attitude.
  • Joint preparation.
  • Low energy & power requirements.
  • 3Ø load on motor & cosψ ≈ 0.85 for arc & flash cosψ ≈ 0.4 to 0.6.
  • No special power supplies.
  • No objectionable smoke, fumes or gases.
  • No weld spatters.
  • No consumables, no fluxes.
  • No solidification defects.
  • Simplifies manufacture of complex forging, saves expensive materials.
  • 2-100 times faster.
  • Superior from Technical & Economical standpoint.
  • Unusually high efficiency coefficient.
  • Dissimilar metals welded. e.g., Al-Cu, Al-Steel.

Weldability Chart