BRAZING NOTES
AN INTRODUCTION TO AUTOGENOUS WELDING
Welding is a manufacturing process used to join two or more individual pieces. It
can be broadly categorized into two classifications: fusion welding and solid-state
welding. Fusion welding encompasses all of the processes that utilize direct heat
applied from an external source to fuse or melt contact surfaces of metals to weld
them together, while solid-state welding encompasses all of the processes that
require external pressure to weld materials together.
Fusion welding processes can be further classified by method. There are three main
fusion welding methods: autogenous welding, homogeneous welding, and
heterogeneous welding. They differ with regard to the application and nature of filler
material (i.e., whether or not filter material is used and, if filler material is used, what
it is made from). The following blog post focuses on autogenous welding. It
highlights how it compares to the homogeneous welding and heterogeneous welding
methods, what types of welding processes use it, and what advantages it offers.
AUTOGENOUS VS. HOMOGENEOUS VS. HETEROGENEOUS
WELDING
Autogenous welding is a fusion welding method that does not require the
application of filler material to form a weld. Since solid-state welding processes
generally do not use filler materials, they may also be classified as autogenous.
In contrast to autogenous welding, both homogeneous welding and heterogeneous
welding require the application of filler material to form a weld. Welding operations
that use the homogeneous welding method need filler material that has the same
composition as the base material, while welding operations that use
the heterogeneous welding method need filler material that has a different
composition than the base material.
TYPES OF AUTOGENOUS WELDING PROCESSES
Autogenous welding is a method of performing fusion welding processes rather than
a specific fusion welding process. Some of the fusion welding processes that use it
include:
• Laser beam welding. This welding process uses a concentrated laser beam to melt
the material and form the desired weld.
• Gas tungsten arc welding. This welding process uses a non-consumable electrode
to form an high temperature arc to form the desired weld.
• Electron beam welding. This welding process uses a high-energy electron beam to
form the desired weld.
• Plasma arc welding. This welding process uses an ionized plasma arc to form the
desired weld.
ADVANTAGES OF AUTOGENOUS WELDING
Compared to the other two fusion welding methods, autogenous welding offers a
number of advantages, such as:
• Better looking welds. Autogenous welding processes are less likely to create
inconsistent or uneven weld bead patterns.
• Lesser post-grinding requirements. Since material is not added during autogenous
welding operations, welded components do not have excess material that needs to
be removed.
• Lower material costs. Since autogenous welding operations do not need filler, they
have lower material costs.
• Greater suitability for thin materials. Autogenous welding is suitable for welding
thin sheets since it makes controlling heat, weld bead profile, and arc start/stop easy.
• Easier automation. Autogenous welding operations readily accept automation
technology.
While the above characteristics make autogenous welding ideal for many
applications, the method is not suitable for all welding applications. For example, it
is not appropriate for welding projects involving/requiring:
• Non-butt joints
• High-strength reinforced joints
• Plates over 2–3 mm in thickness and requiring full penetration
• Edge preparation for filler material
WHAT IS BRAZING?
Brazing is a process by which non-ferrous filler metals or braze alloys are melted
between two or more close-fitting base metal parts to form a joint. The technique
involves heating components above the braze alloy melt temperatures and below the
melting temperature of the base metal, allowing capillary action to distribute the
molten filler throughout the joint between the two pieces to be brazed. As the braze
alloy cools, a strong joint or seal forms.
Laser brazing replaces the use of an oxy-acetylene flame, the most common heat
source in other brazing techniques, with a laser to allow for more localized heat
application.
WHAT METALS CAN BE BRAZED?
Laser brazing is compatible with a variety of metals, including:
• Brass
• Copper
• Stainless steel
• Aluminum
• Zinc-coated steels
It is also effective in joining mixed materials like tungsten carbide or silicon
nitride—a highly durable ceramic—to itself or metal parts.
Brazing procedure:
The procedure includes the following steps-
• Cleaning and preparing the surface to be brazed
• Fluxing the base metal and filler metal surfaces.
• Aligning the base metal parts to be joined
• Heating the joint
• Applying brazing filler metal on to the joint
• Cooling of the joint
• Removing flux residue from the completed joint
Function of the filler metal
• It wets the base metal surfaces
• Spreads along the joint by capillary action
• Adheres and solidifies to form the brazed joint.
The flux which is employed during brazing melts at a lower temperature bend the
brazing filler material. It wets the surface to be brazed, removes the oxide film and
gives clean surface.
The filler metals used in brazing are of copper base alloys and silver base alloys. For
brasses up to 20% tin are mostly used mainly for the brazing of the ferrous metals.
Silver alloys (silver and copper or silver, copper and zinc) having a melting range of
600 to 8500C are suitable for brazing any metal.
Like soldering the parts to be brazed are carefully cleaned, the flux applied, and the
clamped in position for joining process. Borax is mainly used as flux and heated to
a temperature above the melting point.
Other fluxes are-
• Sodium, potassium and lithium borax compounds which is used in high temperature
melting point fluxes
• Chlorides
• Boric acid (mainly employed as a cleaning agent)
Many HVAC and A/C units are made of aluminum components because of the
metal’s high strength, light weight, and resistance to rust. Brazing is commonly used
in these applications to provide reliable, leak-proof connections. However,
aluminum is notoriously challenging to work with as a result of its low melting
temperature and its reliance on selecting the appropriate alloy and flux for the
specific application. In these instances, laser brazing offers an advantage over
traditional brazing because in some cases, it can be used without flux, and its more
precise approach to the heating process allows for filler material to be targeted while
maintaining the integrity of the aluminum base.
Filler materials in laser brazing are often made of aluminum bronzes, a corrosion-
resistant, copper-based alloy noted for its strength.
7 Main differences between brazing and soldering
People often ask about what is the basic difference between brazing and soldering.
They jointly represents one of the several methods used for joining two or more
metal pieces using an alloy(used as filler rods). which is used to stick them together
with proper strength. Both of them involve heating the filler metal and joint surfaces.
The major difference between soldering and brazing is that the temperature at which
the method is being performed. Let’s take a deep look into the two methods.
What is soldering?
Soldering is define as a group of joining processes where coalescence is produced
by heating to a suitable temperature and by using a filler metal having a melting
point not exceeding 8000 F(4270C) and below the melting point of the base metals.
The filler metal is usually distributed between the properly fitted surfaces of the joint
by capillary action. The traditional tool for soldering is the soldering iron with a
copper tip (it has high thermal conductivity) which may be heated electrically or by
oil, coke or o gas flame.
Various soldering methods are –
• Soldering iron method
• Torch method
• Dip metal method
• Spray method
Classifications of soldering:
Soldering is divided into two classifications: soft and hard
Soft soldering is used extensively in sheet metal work for joining parts that are not
exposed to the action of high temperature and are not subjected to excessive loads
and forces. This is also employed for joining wires and small parts.
The solder is mostly composed of led and tin. This has a melting range between 150
to 3500C. A suitable fluxing is always used in soft soldering. The function of this is
to prevent oxidation of the surfaces or to dissolve oxides that settle on the metal
surfaces during the heating process.
A blow torch or soldering iron constitutes the equipment for heating the base metals
and melting the solder and flux.
Hard soldering solders melt at high temperatures and are stronger than those used
in soft soldering. A common method is silver soldering. In this method silver alloyed
with tin is used as solder.
In hard soldering the temperature for various soldering varies from 600 to 9000C. In
this process the fluxes are mostly in paste form.
What is the difference between brazing and soldering?
Brazing is essentially similar to soldering, but it gives much stronger joint than
soldering. The main difference is the use harder filler material which is commonly
known as spelter.
The key differences between brazing and soldering are discussed below.
1.Temperature: Filler metal used in soldering as a melting point less than
8000F(4270c) whereas that in brazing has melting point above
8000F(4270c)
2.Strength: Brazing joints are stronger than soldering.
3.Corrosion resistance: Solder joints do not resist corrosion to the some extent that
brazed or welded joints do.
4.Application of brazing and soldering: Soldering is mainly used in the electrical
industry for permanent connection between the electronic components; it is
commonly used in electronics, arts and crafts, and metal work from flashing to
jewelry. It is mostly used to join wires to leads of components such as switches.
5.Cost: Soldering is a cheap process. Brazing is quite costlier.
6.Preheating: Preheating of base metal does not require in soldering. Preheating
requires in brazing.
7.Types of metals : Soldering is possible only in similar sheet metals as well as thin
metals.
Brazing is suitable in similar or dissimilar as well as thicker metal parts.
Difference of soldering and brazing in tabular form:
Summary of brazing and soldering
Both brazing and soldering are the common methods of joining two or more similar
or dissimilar metals using filler metals. Both of the methods are similar to each other,
the basic difference is that soldering process is done using filler metals less than the
temperature of 8000F. whereas brazing is carried out at temperature above 8000F.
Soldering is mainly used in electronic industry for joining electronic wires and
components and brazing is mainly used to join all kind of metals in industry such as
automotive industry. It takes comparatively more heat than any other soldering
• process.
