Brazing, Soldering

What is the difference between Welding and Soldering ?

Welding is a cohesive bond , whereas Soldering/Brazing is the adhesive bond.

Brazing & soldering come in between Solid State welding and Fusion welding

Brazing, Soldering or Braze Welding

In both these processes , the parental material does not melt, but only filler material melts thus filling the joint through capillary action.

Soldering ( or soft Soldering): The filler material has melting point lower than 450 deg C and also less than that of parental material

Brazing ( or hard Soldering): The filler material has melting point higher than 450 deg C and also less than that of parental material

Braze Welding is different than above two. In this case , both components are joined by a V-joint.

Brazing vs. Welding Advantages

1. Dissimilar metals which can’t be welded can be joined by brazing

2. Very thin metals can be joined

3. Metals with different thickness can be joined easily

4. In brazing thermal stresses are not produced in the work piece, hence there is no distortion.

5. Problems of Heat Affected Zone (HAZ) is avoided.

6. Less power is required and process is faster

Disadvantages

1. Brazed joints have lower strength compared to welding2. Joint preparation cost is more3. Colour of the metal in the brazed joint is different and aesthetic problem4. high service temperature can cause failure to a brazed joint.

Applications

-Automotive ( joining tubes and pipes)-Electrical equipments (joining wires and cables)- cutting tool ( brazing cemented carbide tips to steel shanks)- repairs and maintenance in many fields

Brazing

Soldering

- electronics parts like PCB

Joint preparation1. Both Butt –Joint and Lap joints are used in brazing , but Lap joint is preferred.2. In case of Lap joints, an overlap of at least 3 times of the thickness of thinner

parts is recommended3. The clearance between mating parts is very important. Very small gap will

restrict material gap, very large gap will reduce capillary action.4. The gap is usually 0.025-0.25 mm

clearance

Join

t str

engt

h

Strength of the filler metal as cast

Strength of the filler metal in brazed joint

Recommended clearance

BrazingTypes

1. Torch brazing2. Furnace brazing3. Induction brazing4. Resistance brazing5. Dip brazing6. Infrared brazing7. Braze welding

Types of brazing

Torch Brazing

-Fuels used are same type as used in Gas welding-Reducing flame is used to reduce oxidation- can be mechanised

Brazing

(a) Before (b) After

Note that the filler metal is a shaped wire.

2. Furnace Brazing

• Good for medium / high production volume• Electrical heated furnace• Inert gases or vacuum condition helps to avoid oxidation

Types of Brazing

3. Induction Brazing

One of the widely used process ( compared to resistance brazing)

Types of Brazing

4. Dip Brazing

•Molten salt or molten metal is used to heat the surfaces to be brazed. •Many brazing can take place at time

Types of Brazing

5. Braze Welding

•Like the welding process where more filler material is used.• Normally V-groove is used for such braze welding.• No capillary action takes place unlike some other above type brazing

Flux Material (Brazing/Soldering)

Flux is used for following reasons :

1. Dissolve oxides from the surfaces to be joined2. Reduce surface tension of molten material capillary action3. Protect from further oxidation to parental material

Borax and Boric acid are commonly used Flux material in Brazing

Ammonia Chloride, Zinc Chloride are commonly used Flux material in Soldering.

Filler Material for Brazing

Properties :-1. Melting temp compatible with the base metal.2. Low surface tension for higher wettability3. Higher fluidity for faster metal penetration4. No chemical reaction with the base metal

Forms of filler material:1.Rod2.Wire3.Sheets and strips4.Powder5.Paste

Typical Filler Metals for Brazing Various Metals and Alloys

Most common filler is copper base Zinc alloy ( 50-60% Cu, 40% Zn, 1% Ni,) known as “Spelter”

Base metal Filler metal

Brazing temperature,

(°C)Aluminum and its alloys Aluminum-silicon 570–620

Magnesium alloys Magnesium-aluminum

580–625

Copper and its alloys Copper-phosphorus 700–925

Ferrous and nonferrous (except aluminum and magnesium)

Silver and copper alloys, copper- phosphorus

620–1150

Iron-, nickel-, and cobalt-base alloys

Gold 900–1100

Stainless steels, nickel- and cobalt-base alloys

Nickel-silver 925–1200

Soldering

Soldering process is similar to brazing

Advantages of Soldering Vs Brazing

1. Low energy consumption2. Good thermal and electrical conductivity3. Easy to repair and rework

Disadvantages of Soldering Vs Brazing

1. Low joint strength2. Not good at high pressure/ high temperature working

Soldering

Types of Soldering Process

1. Hand soldering 1. Uses a hot soldering iron/ soldering guns2. Fast ( one solder joint/ second)

2. Wave soldering1. Mostly used to make PCB2. Passes over a wave of molten solder 3. Can be mechanized

3. Reflow soldering 1. Solder paste is applied between the parts to be soldered2. Complete set up is heated and the solder melts .

Types of Solders and their Applications

Tin-lead General purpose Tin-zinc Lead-silver Cadmium-silver Zinc-aluminum Tin-silver Tin-bismuth

Aluminum Strength at higher than room temperature Strength at high temperatures Aluminum; corrosion resistance Electronics Electronics

Recall the Eutectic composition of Sn-Pb !