Brazing is a metal joining process where a filler metal with a lower melting point than the base metals is heated to bond them. The filler metal melts and flows into the joint by capillary action without melting the base metals. Proper clearance must be provided in the joint design for the filler metal to flow effectively. Common filler metals include copper, aluminum-silicon alloys, and silver alloys. Brazing allows for dissimilar metal joining and produces stronger joints than soldering but with less distortion than welding.

1.  In welding, base metal melts and hence metallurgical
changes takes place.
 In brazing, the base metal does not melt, but the joint is
obtained by means of a filler metal.
 Brazing is a joining process in which the joint is made
with the help of filler metal whose liquidus temperature
is above 450 0C and is below the solidus temperature of
the base method.
 The filler metal is drawn into the joint by means of
capillary action. Due to this, the joint is to be designed
properly. The clearance between the parts should be
critically controlled.
Brazing , Braze Welding and Soldering.
Brazing

2.  If there is too much clearance, the capillary forces may not
be sufficient to draw the filler metal into the joint where as
insufficient clearance may have too small an amount of
filler metal to give rise to any effective strength.
 Depending on the type of base materials brazed, different
types of filler materials are used.
 Copper based materials are generally used for brazing
ferrous materials.
 Aluminium -silicon filler materials ----- for aluminium.
 Silver alloys ---- for most common metals and alloys.
Brazing ….

3. Process:
 Cleaning of the surfaces.
 Applying flux to the joint (in paste form).
 Heat the joint to bring it to the liquidus temperature
of the filler metal.
 Apply the filler metal so that it flows into the joint
gap by capillary action.
 On solidification of filler metal, joints is formed.
Brazing ….

4. Cleaning the surfaces:
Acid pickling (to remove oxides and scales);
Use of solvents to remove oils, grease etc.
Applying flux to remove oxides:
Flux material -------borax, boric acid, chlorides and fluorides.
For ferrous materials -------- borax and boric acid.
Aluminium copper and stainless steel alloys --- alkaline bi-
fluorides.
For brazing of tungsten to copper ------Sodium cyanide is
used.
Brazing ….

5. Heating the joint: Methods of heating:
1. Torch brazing: Using oxy acetylene torch.
2. Dip brazing: Molten salt bath or metal bath is used to
supply the heat to the base metal.
A brazing joint is prepared and dipped in the bath for quick
melting of the brazing alloy.
3. Induction brazing:
Heat is obtained from the high frequency current induced in
the work by means of electrical coils.
3. Resistance heating: Heat is developed by the resistance of
the joint interfaces.
4. Furnace brazing: Heated under controlled atmosphere in a
furnace.
Brazing ….

6. Advantages:
 Dissimilar metal joining.
 Less distortion.
 Not much skill is required.
 Quick process.
 Economical
Applications:
 For joining dissimilar
materials.
 For cycle and motorcycle
frames, heat exchangers, for
repair of cast iron
components.
Disadvantages:
 Not suitable for joining
aluminium and magnesium.
 Not suitable for high
temperature applications due
to low melting temperature of
filler material.
 Colour of the filler material
may not match with base
material.
 Requires costly equipment for
heating.
Brazing ….

7.  Similar to brazing except that the filler metal reaches
the joint without capillary action but due to gravity.
 Further, the silver base alloys are not generally used
as filler metal, because large amount of filler material
is required to fill the gap, which costs more.
 Generally used for repairing of defective or broken
parts made of steel or cast iron.
Braze (Bronze) welding

8. A method of joining similar or dissimilar materials by
means of a filler metal whose liquidus temperature is
below 450 0C.
The filler metal enter the joint by capillary action.
Process:
Cleaning the joint
Solvent cleaning, acid pickling & mechanical cleaning.
Applying flux:
Purpose:
To remove the oxides from the joint surfaces and to
prevent the filler metal from oxidizing.
Soldering

9. Rosin & Rosin + Alcohol --- most common flux material for
electrical work.
Organic fluxes such as zinc chloride and ammonium chloride for
non electrical soldering work.
Form of flux:
Powder, paste, liquid or solid.
At soldering temperature it must be liquid.
Filler materials:
Lead and Tin------- most common.
Liquidus temperature of eutectic of lead and tin ------ 1830C.
To improve the mechanical properties and temperature
resistance, solders are added to other alloying elements like Zn,
Cd and silver.
Soldering ….

10. Soldering methods:
 Soldering iron
 Dip soldering
 Wave soldering.
Soldering Iron:
 A copper rod with a thin tip.
 For soldering, the heat is supplied by soldering iron, which
is also used to apply solder.
 Soldering iron can be heated using -------furnace or
electrical resistance.
Soldering ….

11. Dip soldering:
 Large amount of solder is melted in a tank which is closed.
 Parts are to be cleaned first and dipped in a flux bath as per
the requirement.
 These are then dipped in a molten solder pool and lifted.
Wave soldering
 In this method, the part to be soldered is not dipped in the
solder tank, but a wave is generated in the tank so that the
solder comes up and make the necessary joint.
 This is normally a continuous process with the PCBs being
continuously moving on top of the solder tank and the waves
become continuously generated.
 Used for mass production.
Soldering ….

12. Sl.
No Welding Soldering Brazing
1 Welding joints are strongest
joints used to bear the load.
Strength of the welded
portion of joint is usually
more than the strength of
base metal.
Soldering joints are weakest
joints out of three. Not meant to
bear the load. Use to make
electrical contacts generally.
Brazing are weaker than
welding joints but
stronger than soldering
joints. This can be used
to bear the load up to
some extent.
2 Temperature required is
3800 degree Centigrade in
Welding joints.
Temperature requirement is up
to 450 degree Centigrade in
Soldering joints.
Temperature may go to
600 degree Centigrade
in Brazing joints.
3 Work piece to be joined need
to be heated till their melting
point.
Heating of the work pieces is
not required
Work pieces are heated
but below their melting
point.
Difference between Welding, Soldering and Brazing.

13. Sl.
No Welding Soldering Brazing
4 Mechanical properties of
base metal may change at
the joint due to heating
and cooling.
No change in mechanical
properties after joining.
May change in
mechanical properties
of joint but it is almost
negligible.
5 Heat cost is involved and
high skill level is required.
Cost involved and skill
requirements are very low.
Cost involved and sill
required are in between
others two.
6 Heat treatment is generally
required to eliminate
undesirable effects of
welding.
No heat treatment is required. No heat treatment is
required after brazing.
7 No preheating of work
piece is required before
welding as it is carried out
at high temperature.
Preheating of work pieces before
soldering is good for making
good quality joint.
Preheating of work
pieces before soldering
is good for making
good quality joint.
Difference between Welding, Soldering and Brazing….

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