brazing, soldering, adhesive bonding and mechanical fastening processes

brazing, soldering

Brazing, Soldering,

Adhesive-Bonding, and

Mechanical-Fastening Processes

Ir Tri Prakosa, M Eng.

Proses Manufaktur II, Januari 2010

Brazed and Soldered Parts

(a) Resistance brazed light bulb filament (b) brazed radiator heat exchangers

Cobe Laboratories Blood Reservoir

 In almost all the joining processes described in previous lectures, the metals to be joined were heated to elevated temperatures by various

means to cause fusion or bonding at the joint

 But how to join materials that cannot withstand high temperatures, such as electronic

components?

 What if the parts to be joined are delicate or

intricate or are made of two or more materials with very different characteristics, properties,

Introduction, con’t

 Today’s lecture first describes two joining

processes, brazing and soldering, which permit lower temperatures than those required for

welding

 In both brazing and soldering, filler metals are placed in or supplied to the joint

 They are then melted using an external source

of heat and, upon solidification, a strong joint results

Introduction, con’t

 Soldering temperatures are lower than those of brazing, and the strength of a soldered joint is not high

 Thus brazing and soldering are arbitrarily

distinguished by temperature

bookbinding, has now developed into an

important technology with wide applications in aerospace and various other industries

replacement, maintenance, repair, or adjustment.

 How to take apart (separating), a product without destroying the joint?

 If we need joints that are truly nonpermanent but are as strong as welded joints-the solution

obviously is to use mechanical means, such as

Effect of Joint Clearance on Strength of Brazed Joints

BRAZING

 Brazing is a joining process in which a filler

metal is placed at or between the faying

surfaces to be joined, and the temperature is

raised to melt the filler metal but not the

workpieces, (Figure a)

 The molten metal fills the closely fitting space by

capillary action.

 Upon cooling and solidification of the filler metal,

a strong joint is obtained

 Brazing comes from the word brass , an archaic

word meaning to harden, and was first used as far back as 3000-2000 B.C

 There are two types of brazing processes:

deposited at the joint with a technique similar to

oxyfuel gas welding.

 Filler metals used for brazing melt above 450 °C (840 °F)

 The temperatures employed in brazing are

below the melting point (solidus temperature) of the metals to be joined

 Thus this process is unlike liquid-state welding processes in which the workpieces must melt in the weld area for fusion to occur

 Problems associated with heat affected zones, warping, and residual stresses are therefore

 The strength of the brazed joint depends on:

filler metal.

 Consequently, the surfaces to be brazed should

be chemically or mechanically cleaned to

ensure full capillary action; hence the use of a flux is important

Filler metals

 Several filler metals (braze metals) are available and have a range of brazing temperatures, see the Table below:

metal), formation of brittle intermetallic

compounds at the joint, and galvanic corrosion

in the joint

 Filler metals for brazing, unlike other welding

Filler metals

 Because of diffusion between the filler metal

and the base metal, mechanical and

metallurgical properties of joints can change in subsequent processing or during the service life

of brazed components

 For example, when titanium is brazed with pure tin filler metal, it is possible for the tin to

completely diffuse into the titanium base metal

by subsequent aging or heat treatment

 When that happens, the joint no longer exists

 The use of a flux is essential in brazing in order

to prevent oxidation and to remove oxide films from workpiece surfaces

 Brazing fluxes are generally made of borax,

boric acid, borates, fluorides and chlorides

 Wetting agents may also be added to improve both the wetting characteristics of the molten filler metal and capillary action

 Surfaces to be brazed must be clean and free

 Clean surfaces are essential to obtain the

proper wetting and spreading characteristics of the molten filler metal in the joint and maximum bond strength

 Sand blasting may also be used to improve

surface finish of faying surfaces

 Because they are corrosive, fluxes should be removed after brazing (usually by washing with hot water)

Brazing methods

Torch brazing

 The heat source in torch brazing (TB) is oxyfuel gas with a carburizing flame

 Brazing is performed by first heating the joint

with the torch, then depositing the brazing rod or wire in the joint

 Suitable part thicknesses are usually in the

range of 0.25-6 mm (0.01-0.25 in.)

 More than one torch may be used in this

process

Jenis-jenis nyala las oxyfuel

Brazing methods

Torch brazing

 Although it can be automated as a production process, torch brazing is difficult to control and requires skilled labor

 This process can also be used for repair work

 The basic equipment for manual brazing costs about $300 but can run more than $50,000 for automated systems

Brazing methods

Furnace brazing

 As the name suggests, furnace brazing (FB) is

carried out in a furnace

 The parts are re-cleaned and re-loaded with brazing metal in appropriate configurations

before being placed in the furnace

Brazing methods

Furnace brazing

 Furnaces may be batch type for complex

shapes or continuous type for high production runs, especially for small parts with simple joint designs

 Vacuum furnaces or neutral atmospheres are used for metals that react with the environment

 This process is similar to using shielding gas in welding operations

Brazing methods

Furnace brazing

 Skilled labor is not required, and complex

shapes can be brazed since the whole

assembly is heated uniformly in the furnace

 The cost of furnaces varies widely, ranging from about $2,000 for simple batch furnaces to more than $300,000 for continuous vacuum furnaces

Brazing methods

Induction brazing

 The source of heat in induction brazing (IB) is

induction heating by high-frequency ac current

 Parts are preloaded with filler metal and are

placed near the induction coils for rapid heating

 If a protective atmosphere is not utilized, fluxes are generally used

 Part thicknesses are usually less than 3 mm

(0.125 in.)

Brazing methods

Induction brazing

 Induction brazing is particularly suitable for

brazing parts continuously (Figure below)

 The cost for small units is about $10.000

Ilustrasi skematik setup brazing

Brazing methods

Resistance brazing

 In resistance brazing (RB), the source of heat is

through electrical resistance of the components

to be brazed

 Electrodes are utilized for this purpose, as in

resistance welding

 Parts are either preloaded with filler metal, or it

is supplied externally during brazing

 Parts that are commonly brazed by this process have thicknesses of 0.1 - 12 mm (0.004-0.5 in.)

Brazing methods

Resistance brazing

 As in induction brazing, the process is rapid, heating zones can be confined to very small areas, and the process can be automated to produce uniform quality

 Equipment costs range from $1,000 for simple units to more than $10,000 for larger, more

complex units

Brazing methods

Dip brazing

 Dip brazing (DB) is carried out by dipping the

assemblies to be brazed into either a molten

filler-metal bath or a molten salt bath (at a

temperature just above the melting point of the filler metal), which serves as the heat source

 All workpiece surfaces are thus coated with the filler metal

 Consequently, dip brazing in metal baths is used only for small parts, such as sheet, wire, and

 Depending on the size of the parts and the bath,

as many as 1000 joints can be made at one

time by dip brazing

 Cost of equipment varies widely: from about

$2,000 to more than $200,000; the more

expensive equipment comes with various

computer controls

 The radiant energy is focused on the joint, and the process can be carried out in a vacuum.

 Equipment cost ranges from $500 to $30,000

Brazing methods

Diffusion brazing

 Diffusion brazing (DFB) is carried out in a

furnace wherewith proper control of temperature and time the filler metal diffuses into the faying surfaces of the components to be joined

 The brazing time required may range from 30

minutes to 24 hours

 Diffusion brazing is used for strong lap or butt

joints and for difficult joining operations

Braze welding

 Thus considerably more filler metal is used,

compared to brazing

 However, temperatures in braze welding are

generally lower than in fusion welding, and part distortion is minimal

 The use of a flux is essential in this process

 The principal use of braze welding is to maintain and repair parts, such as ferrous castings and steel components

Brazing process capabilities

 Desain Sambungan yang digunakan di Brazing

Desain sambungan yang sering digunakan di operasi brazing Celah/kelonggaran

antara dua komponen yang dibraze adalah faktor penting bagi kekuatan

Brazing process capabilities

 In general, dissimilar metals can be assembled with good joint strength, including carbide drill bits or carbide inserts on steel shanks (see the Figure)

Brazing process capabilities

 The shear strength of brazed joints can reach

800 MPa (120 ksi) using brazing alloys

containing silver (silver solder)

 Intricate, lightweight shapes can be joined

rapidly and with little distortion

 Brazing can be automated and used tor mass production

Design for brazing

 As in all joining processes, joint design is

Brazing Design

Design for brazing

 The typical joint clearance in brazing ranges

from 0.025 mm to 0.2 mm (0.001 in to 0.008

in.)

 The clearances must fit within a very small

tolerance range because larger clearances

reduce the strength of the brazed joint

 A variety of special fixtures may be used during brazing to hold the parts together, some with

provision for thermal expansion and contraction

SOLDERING

 In soldering, the filler metal (solder), melts

below 450 °C (840 °F)

 As in brazing, the solder fills the joint by

capillary action between closely fitting or closely placed components

 Heat sources for soldering are usually soldering irons, torches, or ovens

 Soldering with copper-gold and tin-lead alloys was first practiced as far back as 4000-3000

Gambar Screening

atau stenciling pasta

ke atas printed circuit board: 1 Ilustrasi

Wave Soldering

(a) Ilustrasi skematik proses wave

Wave-Soldering

(WS)

the molten solder to ultrasonic cavitation, which

removes the oxide films from the surfaces to be

joined The need for a flux is thus eliminated.

Types of solders and fluxes

 Solders (from the Latin solidare, meaning to

make solid) are usually tin-lead alloys in various proportions

 For better joint strength and special applications, other solder compositions that can be used are tin-zinc, lead-silver, cadmium-silver,

and zinc

aluminum

alloys

Types of solders and fluxes

 Because of the toxicity of lead and its adverse effects on the environment, lead-free solders

are being developed and are now in wider use

 Typical compositions are 96.5% Sn-3.5% Ag and 42% Sn-58% Bi

 In soldering, fluxes are used as in welding and brazing and for the same purposes

Types of solders and fluxes

 Fluxes are generally of two types:

chloride solutions, which clean the surface rapidly

applications.

 Moreover, because solders do not generally

have much strength, they are not used for load bearing structural members

 Aluminum and stainless steels are difficult to

solder because of their strong, thin oxide film

(see Figure next page)

Struktur Permukaan Logam

atasnya tertutup lapisan tebal Aluminium oksida

hidrat berpori

Process capabilities

 However, these and other metals can be

soldered using special fluxes that modify

surfaces

 Soldering can be used to join various metals

and thicknesses

 Although manual operations require skill and

are time-consuming, soldering speeds can be high with automated equipment

 The cost of soldering equipment depends on its

Process capabilities

 It ranges from less than $100 for industrial

soldering irons to more than $50,000 for

automated equipment

 Design guidelines for soldering are similar to those for brazing

 Some frequently used joint designs are shown

in Figure next page

 Note again the importance of large contact

surfaces to develop sufficient joint strength in soldered products

Desain Sambungan yang digunakan

pada penyolderan

Desain sambungan yang biasa digunakan pada Penyolderan

Perhatikan contoh (e), (g), (i), dan (j) adalah disambung secara mekanik sebelum

ADHESIVE BONDING

Adhesive Bonding

 Numerous components and products can be

joined and assembled using an adhesive, rather

than by any of the joining methods described

thus far

 Adhesive bonding has been a common method

of joining and assembly for applications such as labeling, packaging, bookbinding, home

furnishings, and footware

Adhesive Bonding

 Plywood, developed in 1905, is a typical

example of adhesive bonding of several layers

of wood with glue

 Adhesive bonding has been gaining increased acceptance in manufacturing ever since its first use on a large scale in assembling load-bearing components in aircraft during World War 2

(1939- 1945)

 Three basic types of adhesives are:

substance obtained from starch), soya flour, and

animal products.

magnesium oxychloride.

thermoplastics (used for nonstructural and some

structural bonding) or thermosetting polymers (used primarily for structural bonding).

Sifat-sifat Umum Adhesif

Sifat-sifat Umum Adhesif (lanjutan)

 Because of their strength, synthetic organic

adhesives are the most important in

manufacturing processes, particularly for bearing applications

load- They are classified as:

silicones, epoxies, cyanoacrylates, modified acrylics, phenolics, polyimides, and anaerobics.

styrene-butadiene rubber, butyl rubber, nitrile rubber,

ethylene-vinyl acetate copolymers, polyolefins, polyamides, polyester, and thermoplastic elastomers.

d Evaporative or diffusion ; including vinyls, acrylics,

phenolics, polyurethanes, synthetic rubbers, and

natural rubbers.

elastomer-epoxies, nitrile-phenolics, vinylphenolics, and

polyimides.

epoxies, polyurethanes, silicones, and polyimides Electrical conductivity is obtained by addition of

fillers such as silver (used most commonly), copper, aluminum, and gold.

 Fillers that improve the electrical conductivity of adhesives generally also improve their thermal conductivity

 The least expensive of adhesives are epoxies and phenolics, followed by polyurethanes,

acrylics, silicones, and cyanoacrylates

 Adhesives for high-temperature applications in a range up to about 260 °C (500 °F), such as

polyimides and polybenzimidazoles, are

 Adhesives are available in various forms, such

as liquids, pastes, solutions, emulsions, powder, tape, and film

 When applied, adhesives generally are about

0.1 mm (0.004 in.) thick

 Depending on the particular application, an

adhesive must have one or more of the

following properties (see Table next page):