Forge welding is an ancient solid-state welding process that joins metals by heating them and hammering them together, causing diffusion or formation of lower-melting eutectics. It can join similar or dissimilar metals without fillers. The metal is heated to 50-90% of its melting temperature then fluxed and pressed together. Diffusion at the atomic level forms a bond through plastic deformation and inter-diffusion at the interface. Forge welding produces a monolithic weld as strong as the base metals through solid-state diffusion or eutectic formation without melting.

1. NATIONAL INSTITUTE OF TECHNOLOGY
WARANGAL, TELANGANA-506004
A report
on
Forge Welding
Submitted by
Chirra Kumara Swamy
Roll No-143503
MANUFACTURING ENGINEERING
Submitted to
Dr. Kanmani Subbu
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING

2. Introduction
Forge welding is a solid-state welding process that joins two pieces of metal by heating them to a
high temperature and then hammering them together. The process is one of the simplest methods
of joining metals and has been used since ancient times. Forge welding is versatile, being able to
join a host of similar and dissimilar metals. With the invention of electrical and gas welding
methods during the Industrial Revolution, forge welding has been largely replaced.
Forge welding between similar materials is caused by solid-state diffusion. This results in a weld
that consists of only the welded materials without any fillers or bridging materials.
Forge welding between dissimilar materials is caused by the formation of a lower melting
temperature eutectic between the materials. Due to this the weld is often stronger than the
individual metals.
The temperature required to forge weld is typically 50 to 90 percent of the melting temperature.
Steel welds at a lower temperature than iron. The metal may take on a glossy or wet appearance
at the welding temperature. Care must be taken to avoid overheating the metal to the point that it
gives off sparks from rapid oxidation (burning).
Solid-state Diffusion Bonding
Solid-state diffusion bonding is a process by which two nominally flat interfaces can be joined at
an elevated temperature (about 50%-90% of the absolute melting point of the parent material)
using an applied pressure for a time ranging from a few minutes to a few hours. The International
Institute of Welding (IIW) has adopted a modified definition of solid-state diffusion bonding,
proposed by Kazakov.
Diffusion bonding of materials in the solid state is a process for making a monolithic joint
through the formation of bonds at atomic level, as a result of closure of the mating surfaces due
to the local plastic deformation at elevated temperature which aids inter-diffusion at the surface
layers of the materials being joined.

3. The Diffusion-welding process consists in bringing together the smoothed surfaces to be
diffusion welded after having eliminated all contaminants and surface oxides. Then pressure is
gradually applied and temperature is elevated to permit diffusion at the atomic level. Local
deformation at the contact points by yield and creep permits increasingly larger areas to touch.
Then diffusion causes the interface to disappear slowly while the remaining voids between the
original surfaces shrink or are absorbed within the grains. Finally the interface cannot be seen
any more (in a metallographic section) and residual voids, if any, result no larger or frequent than
those of the base metals.
Process parameters
Temperature: is the most important variable in Diffusion-welding. It should be selected and
controlled so as not to interfere with metallurgical changes or transformations that may occur in
the materials.
Time: needed to perform atomic diffusion is temperature dependent. Longer times become less
and less effective. The time needed cannot be determined simply but has to be found
experimentally. Once welding is performed, longer times will not add to the properties.
Pressure:directly affects the outcome of Diffusion-welding and its importance is great,
especially in the initial stages of the process. It can be linked to the yield point of the metals
involved but it is difficult to deal in theory as a predetermined value. Although local
deformation is introduced at the contact point as an essential stage in the process, macroscopic
deformations are avoided. Pressure is generally limited to the minimum required to get good
results, because of the high equipment costs associated with high compression.

4. Pressure and temperature are practically selected so that they will permit the performance of
suitable welds in acceptable time. Although filler metal is in principle not required for
Diffusion-welding, it has been found that a foil of suitable materials placed at the interface can
sometimes facilitate the process. The reasons are for providing a soft layer to maximize surface
contact in the first stage, or to avoid the formation of brittle compounds, or to promote
diffusivity, or to scavenge impurities.
This may result in the opportunity to reduce one or more of the three essential variables
(Pressure, Temperature, Time), with consequent economic gain.
Equipment
Most of the equipment, especially tooling, has to be built specially for the items to be welded.
Presses or autoclaves should be adapted for providing the required atmosphere and the needed
heat source to the parts, sometimes embedded in ceramic molds.
Materials
Materials can be Diffusion-welded are Titanium alloys, nickel alloys, aluminum alloys, as well
as different combinations of materials not easily joined by traditional means. Steels are
preferably welded by alternative more economic methods. But large, flat surfaces of low carbon
steel have been Diffusion-welded without filler metal under the proper conditions.
Advantages:
 This solid state process avoids pitfalls of fusion welding
 Dissimilar materials welds are possible
 Properties and microstructures remain similar to those of base metals
 Multiple welds can be made in one setup at the same time
 Produces a product finished to size and causes minimal deformation
 Presents less shrinkage and stresses compared to other welding processes
 Highly automated process does not need skillful workforce

5. Limitations:
 Costly equipment especially for large weldments
 Costly preparation with smooth surface finish and exceptional cleanliness
 Protective atmosphere or vacuum required
 Long time to completion
 Not suited to high production rates
 Difference in thermal expansion of members may need special attention
 Limited nondestructive inspection methods available
Processofwelding:
There are different approaches to other aspects of forging; the same is true for forge welding. It
cannot be said that any one way is best, as there are many experienced smiths who produce
consistently sound welds in a different manner.
Different scarf forms, different fluxes, and several other aspects of forge welding can be learned
and utilized. To introduce these differences in this lesson would prove confusing to the student.
Thus, this lesson will concentrate on the method taught to me in the 1970’s. Differences aside,
the fundamentals usually prove to be similar or identical
Step one–Preparing the scarf
Then upsetting is done to make enough surface contact between the weld beads, size of upsetting
is depends on the size the weld. See the fig.1 upsetting.
Fig.1. Edge preparation

6. Step Two
Take another yellow heat on the end of the bar, again on the last 1" of the bar, place the end of
the bar (with the 5/8" sides vertical) squarely on the anvil’s face with the end of the bar 1/4" from
the inside edge of the anvil. The edge of the anvil should be somewhat sharp for this step. Hitting
straight down with the hammer’s face halfway above the anvil face and halfway beyond the anvil
face (Figure 2, photo), reduce the cross section to about 1/2 the thickness of the material, in this
case to 5/16". Tip: In order to create a clean shoulder in this operation, put a slight downward
pressure on the bar so the bar stays where you put it. Then after the first or second blow add a
slight forward pressure to keep the bar from “stepping” off the anvil.
Step Three:
The forging dynamics of the material will cause the area of the bar on top of the anvil to slightly
spread wider than desired. In the same heat from step two, turn the bar 90 degrees, and forge this
area back down to 1/2" in thickness.
Step Four:
Take another yellow heat on the last inch of the bar. Place the holder produced on a sharp edge
of the anvil, pressing the shoulder squarely against the side of the anvil. The hand the bar is
holding should be lowered slightly so the face of the scarf is off the anvil face fig.4.
Preparation of sharp edge fig. 4
Move the hand holding the bar to the left of square, and take a blow. Moving the bar back and
forth at a 90 degree angle (right to left), and using each step produced by the previous blow to
brace against the side of the anvil slowly step the bar off the anvil fig. 5.

7. Fig. 5
Step Five:
Repeat steps one through four on the second bar.
Step Six:
Fluxing the scarves Reduce the air blast in the fire if you have an electric blower. If you are
manually applying the air blast, reduce the force of the blast to more of a whisper. This will
reduce the chances of burning the scarves while fluxing by reducing the available oxygen in the
fire. Making sure you have a clean and deep fire, place the scarves into the centre of the fire, face
up. If the bars are not covered with coke, cover them. When the bars reach a bright orange, with
the bars remaining in the fire, take your fire rake make a hole in the fire over the scarves so flux
may be sprinkled on the face of the scarves.
Reference:
[1] http://www.welding-advisers.com/Diffusion-welding.html
[2] Forge Welding by Dan Nauman, Lesson Number 10– Forge Welding
[3] http://en.wikipedia.org/wiki/Forge_welding