Welding Mechanical Fastening - Manufacturing Laboratoryma.gnu.ac.kr/course/mp/12_Welding.pdf · AC or DC Power source Electrode, Coating Shielding gas & slag ... Manufacturing Processes

© Pearson & GNU Su-Jin Kim

Welding & JoiningManufacturing Processes

Manufacturing Processes

Welding & Mechanical Fastening(용접과조립)

Associate Professor Su-Jin Kim

School of Mechanical EngineeringGyeongsang National University



Welding

• Welding(용접) joins metals by melting it and adding a filler metals to form a pool of molten metal that cools to become a strong joint.

• Energy sources: gas flame, electric arc, laser, friction.



Fusion Welding (Liquid State Welding)

• Heat source: Oxyfuel fire, Arc, Laser• Filler: Additional metals are supplied to the weld zone.• Retarding Oxidization: Flux, shielding Gas• Slag protects molten puddle from oxygen and spatter

1. Oxyfuel Gas Welding2. Arc Welding3. Laser Beam Welding4. Resistance Welding



Oxyfuel Gas Welding

Touch

Filler

Flame

Oxygen, Fuel gas

http://www.youtube.com/watch?v=y3E_MWG9Q0M

• Oxyfuel gas welding (산소용접) uses acetylene(C2H2) gas combined with oxygen to produce a flame.

• The flame melts the filler metals to be joined.• Flame types: OxidizingCutting, NeutralWelding,

CarburizingHeating



Pressure Gas Welding

2 components welded by heating at their interface using a torch with oxyacetylene gas mixture and pressure.

Rail : http://www.youtube.com/watch?v=B8XLVBYFxyk



Arc Welding

Arc Welding (아크용접) : Electric discharge is heat source.

1. Shield metal AW2. Gas metal AW (MIG)3. Gas tungstem AW (TIG)



Shielded metal arc welding

• SMAW (피복금속AW) is the simplest and most versatile joining process.

• It uses a consumable electrode coated in flux giving off a shielding gas.

https://youtu.be/DcIM73AXLsg

http://www.youtube.com/watch?v=TeBX6cKKHWY&feature=related

AC or DC Power source Electrode, Coating Shielding gas & slag



Gas metal arc welding

• GMAW(가스방호AW)= MIG (metal inert‐gas welding)• Weld area is shielded by gas (Ar, He, CO2) to prevent

oxidation.

MIG: http://ma.gnu.ac.kr/vod/Joining/Metal_Inert_Gas_Welding.MP4

Shield gas, wire electrode

Shield gas

Supply wire electrode (filler) in tube



Gas tungsten arc welding• GTAW(텅스텐AW)=TIG(Tungsten inert gas)• A filler metal is supplied from a filler wire.

http://www.youtube.com/watch?v=VEEpikDY058

Filler wireTungsten electrode

Arc + shield gas



Submerged arc welding

• Weld arc is covered by a flux powder which is fed into the weld zone by gravity through a nozzle.

• Flux completely covers the molten metal and prevents weld from oxidization and spatter.

http://www.youtube.com/watch?v=Uns93e4HaNU&feature=related



Flux‐cored arc welding

• FCAW (유심용제AW) is similar to MIG but electrode is tubular and filled with flux.

• Continuous and automatic electrode feeding.

FCAW vs. MIG: http://www.youtube.com/watch?v=chE6RPhM3xE



Electrogas welding

• EGW welds thick vertical edges in one pass with special equipment. A shielding gas is sometimes used. Used in shipbuilding and storage tanks.

http://www.youtube.com/watch?v=8nwP0JYQIdg



Electroslag welding

• ESW is for thick (25~300mm) vertical edges.• Flux is added. After the molten slag reaches the tip of

the electrode, arc is extinguishes and energy is supplied through the electrical resistant of the molten zone.

http://www.youtube.com/watch?v=rCL8NCy2eg8



Welding speed

• Arc welding speede = efficiencyV = voltage appliedI = currentu = specific energyA=weld section area

uAVIev

Material Specific energy(J/mm3)

Aluminum alloys 2.9

Bronze(90Cu‐10Sn) 4.2

Copper 6.1

Cast iron 7.8

Steels 9.1‐10.3

Titanium 14.3



Plasma arc welding

• A concentrated plasma arc is produced and directed toward the weld area.

• Higher quality and speed than the TIG.

http://www.youtube.com/watch?v=jo376zPns8I

Negativeelectrode

Cutting gas

-

+

Shielding gas

Plasma channel

Positive metalFiller



Plasma cutting

http://www.youtube.com/watch?v=mJJydOxHwZU&feature=results_main&playnext=1&list=PL8EE6E5350B31D89B

• Plasma: gas -(heat)> plasma ( +ions + -electrons )• Focused stream of plasma cut sheet metal.• Cutting speed ≈ efficiency, power / thickness, specific

heat, melting point : v ≈ η P / (t w c Tm)



Electron‐beam Welding

• Kinetic energy of high‐velocity electrons is converted into heat to strike the workpiece.

• The higher the vacuum the more the beam will be able to penetrate the part and the greater depth‐to‐width ratio.

http://www.youtube.com/watch?v=NONurFigP5I



Resistance Welding(전기저항용접)

• Welding is produced by means of electrical resistance between 2 joined members.

• Heat generated is RtIH 2 H = heat generated (J)I = current (A)R = resistance in ohmst = time (s)



Resistance Welding

• Contact resistance of electrode‐workpiece < Faying surface resistance of workpiece surface

• Pressure reduces contact resistance and is increased after solidification for forging

• Rapid, small heat affected zone, no filler, high reliability, automation possible

• Mostly lap joint, thickness is limited<12mm, clean interface is needed

• Difficult to weld high conductivity material (Al, Cu)



Resistance spot welding• Tips of the 2 opposing electrodes contact surfaces of lap

joint and resistance heating produces a spot weld.• Good bond in the weld nugget is obtained by having

pressure continually applied till current is turned off.• Strength of weld depends on surface roughness and

cleanliness of mating surfaces.

http://www.youtube.com/watch?v=AwL1CAg43PU&p=9B6D9EAE75875D9D

http://ma.gnu.ac.kr/vod/Joining/Resistance_spot_welding_aluminume.MP4



Resistance Welding

Resistance Seam Welding• Current and pressure is continuous or

on‐off through rolls

Resistance Projection Welding• Many welds simultaneously

Rolls

Plates

Electrode



High frequency welding (고주파용접)

• High frequency current up to 450 kHz Localize heat Forge the joint

• Used for pipe and structural beam welding• Small heat affected zone• Highly conductive material can be easily joined (up to 20

mm)



용접기호 KS B 0052

양쪽플랜지형

한쪽플랜지형

I형맞대기

V형맞대기

X형맞대기

L형

K형

Welding Symbols 1: https://youtu.be/g3MT5R61StI



용접기호 KS B 0052

J형

U형

필랫(Fillet)

플러그, 슬롯

비드

점용접

심(Seam)용접

Welding Symbols 2: https://youtu.be/PlaLdWU8DuI



The Fusion Welded Joint

3 distinct zones of weld are:• base metal• heat‐affected zone (HAZ)• fusion zone



Weld quality

• Discontinuities that affect weld quality are:1. Porosity• trapped gases, chemical reactions, contaminants2. Slag inclusions• Slag is trapped in the weld zone.



Weld quality

3. Incomplete fusion and incomplete penetration

4. Weld profile• Affects the strength and appearance of the weld.

5. Cracks



Design for Welding

http://www.youtube.com/watch?v=pVyYvcEqkcQ&feature=related



Ex) Design frame for welding



Ex) Welding

Gas metal arc welding



Problem of Fusion Welding

• Composition change• Cavity, inclusion• Grain growth, phase transformation• Residual stress, crack

• Most failures start at heat affected zone• Sharpness of variation of heat affected zone may be

reduced by preheating• When C is more than 0.3%, Martensite may form



Solid State Welding

1. Cold Welding (냉간압점)2. Ultrasonic Welding (초음파용접)3. Friction Welding (마찰용접)4. Diffusion Bonding (확산접합)



Cold Welding (냉간압접)

• Localized pressure is applied to mating faces of parts through dies or rolls.

• Used to join small workpieces made of soft and ductile metals.

Roll welding• Pressure for long pieces or continuous strips is applied

through a pair of rolls.

Rolls

Separating agent (graphite)



Ultrasonic Welding (초음파용접)

• Ultrasonic vibration of transducer & Pressure Temperature rise to 0.3~0.5 melting point.

• Restricted to thin, small, delicate parts like electric components.

Mass

Force

Couplingsystem

TipWorkpiece

AnvilDirection ofvibration

Powersupply

AC

TransducerDCpolarization supply

TransducerToolholder

Roller

Workpieces

SupportRollerWorkpiecesSupport

©정하림 GNU



Vibration Welding

• Vibrate two plastic parts to be joined by friction heat

http://ma.gnu.ac.kr/vod/Joining/Vibration_welding_plastic.MP4



Friction Welding (마찰용접)

• Heat required is generated from friction at the interface of the 2 members being joined.

http://www.youtube.com/watch?v=-aEuAK8bsQg&p=9B6D9EAE75875D9D Friction Welding

http://ma.gnu.ac.kr/vod/Joining/Friction_Welding.WMV Friction Welding



Diffusion Bonding (확산접합)

• Diffusion bonds two different materials in high pressure, elevated temperature, long time.

• High bond strength, slow process.• Good for Ti, superalloy (Aircraft components)

Copper - Stainless Aluminum - Stainless



Brazing (경납접) & Soldering (연납접)

• Solid base, liquid filler• Filler material: different composition, low melting point,

lower strength



Brazing (경납접)• Filler metal is placed between faying surfaces where the

temperature is raised to melt the filler metal.• Workpieces must melt in the weld area for fusion.• Clearance is important as it affects the strength of the

brazed joint.



Soldering (연납접)

• Filler metal (solder) fills the joint by capillary action.• Can be used to join various metals and to thicken parts.• Temperatures are low and have a low strength as they

are for load‐bearing structural members.• Solders are tin‐lead alloys.



Soldering

• Soldering robot vs. labor



Design for Brazing



Adhesive Bonding

• Numerous components and products can be joined and assembled.

• Adhesive are required to be strong and tough, resistance to fluids, chemicals and environmental degradation.



Design for adhesive bonding



Mechanical Fastening (기계적죔)

1. Bolt, Nut, Thread2. Rivet, Staple3. Snap fit, Shrink fit4. Spring clip, Seaming

• Ease of assembly, disassembly.• Ease of parts replacement, maintenance and repair.



Fastening



Bolt, Nut, Thread



Rivet, Staple



Snap‐in, Thermal shrink



Spring clip, Seaming



Design for Assembly

• Design for assembly (DFA) is to simplify the product so that the cost of assembly is reduced.

• Comparison of Assembly Methods: Manual assembly / Fixed or hard automation / Soft automation or robotic assembly.



Design Guidelines for Manual Assembly • eliminate the need for workers to make decisions or adjustments. • ensure accessibility and visibility. • eliminate the need for assembly tools and gauges (i.e. prefer self‐

locating parts). • minimise the number of different parts ‐ use "standard" parts. • minimise the number of parts. • avoid or minimise part orientation during assembly (i.e. prefer

symmetrical parts). • prefer easily handled parts that do not tangle or nest within one

another.



Design Guidelines for Hard Automation • reduce the number of different components by considering

– does the part move relative to other parts? – must the part be isolated from other parts (electrical, vibration, etc.)? – must the part be separate to allow assembly (cover plates, etc.)?

• use self‐aligning and self‐locating features • avoid screws/bolts • use the largest and most rigid part as the assembly base and fixture.

Assembly should be performed in a layered, bottom‐up manner. • use standard components and materials. • avoid tangling or nesting parts. • avoid flexible and fragile parts. • avoid parts that require orientation. • use parts that can be fed automatically. • design parts with a low centre of gravity.



Design for Assembly

Documents

Welding Mechanical Fastening - Manufacturing Laboratoryma.gnu.ac.kr/course/mp/12_Welding.pdf · AC or DC Power source Electrode, Coating Shielding gas & slag ... Manufacturing Processes