1. SHIELDED METAL ARC WELDING (SMAW)

2. Shielded metal arc welding (SMAW),
Also known as Manual Metal Arc (MMA) welding
Informally as stick welding
is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld.
An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined.

3. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.
Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's most popular welding processes.

4. It dominates other welding processes in the maintenance and repair industry, used extensively in the construction of steel structures and in industrial fabrication.
The process is used primarily to weld iron and steels (including stainless steel) but aluminum, nickel and copper alloys can also be welded with this method.
Flux-Cored Arc Welding (FCAW) , a modification to SMAW is growing in popularity

6. SAFETY PRECAUTIONS
Uses an open electric arc, so risk of burns – to be prevented by protective clothing in the form of heavy leather gloves and long sleeve jackets.
The brightness of the weld area can lead arc eye, in which ultraviolet light causes the inflammation of the cornea and can burn the retinas of the eyes.
Welding helmets with dark face plates to be worn to prevent this exposure

7. New helmet models have been produced that feature a face plate that self-darkens upon exposure to high amounts of UV light
To protect bystanders, especially in industrial environments, transparent welding curtains often surround the welding area.
These are made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.

8. ARC EYE
Arc eye, also known as arc flash or welder's flash or corneal flash burns, is a painful condition sometimes experienced by welders who have failed to use adequate eye protection. It can also occur due to light from sunbeds, light reflected from snow (known as snow blindness), water or sand. The intense ultraviolet light emitted by the arc causes a superficial and painful keratitis. Symptoms tend to occur a number of hours after exposure and typically resolve spontaneously within 36 hours. It has been described as having sand poured into the eyes.

9. Signs Intense lacrimation Blepharospasm Photophobia Fluorescein dye staining will reveal corneal ulcers under blue light
Management
Instill topical anaesthesia
Inspect the cornea for any foreign body
Patch the worse of the two eyes and prescribe analgesia
Topical antibiotics in the form of eye drops or eye ointment or both should be prescribed for prophylaxis against infection

10. EQUIPMENT

11. Various welding electrodes and an electrode holder

12. SUBMERGED ARC WELDING (SAW)

13. CONTROL PANEL

14. Submerged Arc Welding (SAW)
Is a common arc welding process.
A continuously fed consumable solid or tubular (metal cored) electrode used.
The molten weld and the arc zone are protected from atmospheric contamination by being “submerged” under a blanket of granular fusible flux.
When molten, the flux becomes conductive, and provides a current path between the electrode and the work

15. Normally operated in the automatic or mechanized mode.
Semi-automatic (hand-held) SAW guns with pressurized or gravity flux feed delivery are available.
The process is normally limited to the 1F, 1G, or the 2F positions (although 2G position welds have been done with a special arrangement to support the flux). Deposition rates approaching 45 kg/h have been reported — this compares to ~5 kg/h (max) for shielded metal arc welding.
Currents ranging from 200 to 1500 A are commonly used; currents of up to 5000 A have been used (multiple arcs).

16. Single or multiple (2 to 5) electrode wire variations of the process exist
SAW strip-cladding utilizes a flat strip electrode (e.g. 60 mm wide x 0.5 mm thick).
DC or AC power can be utilized, and combinations of DC and AC are common on multiple electrode systems.
Constant Voltage welding power supplies are most commonly used, however Constant Current systems in combination with a voltage sensing wire-feeder are available.

17. Material applications
Carbon steels (structural and vessel construction);
Low alloy steels;
Stainless Steels;
Nickel-based alloys;
Surfacing applications (wearfacing, build-up, and corrosion resistant overlay of steels).

18. Advantages of SAW
High deposition rates (over45 kg/h) have been reported;
High operating factors in mechanized applications;
Deep weld penetration;
Sound welds are readily made (with good process design and control);
High speed welding of thin sheet steels at over 2.5 m/min is possible;
Minimal welding fume or arc light is emitted.

19. Limitations of SAW
Limited to ferrous (steel or stainless steels) and some nickel based alloys;
Normally limited to the 1F, 1G, and 2F positions;
Normally limited to long straight seams or rotated pipes or vessels;
Requires relatively troublesome flux handling systems;
Flux and slag residue can present a health & safety issue;
Requires inter-pass and post weld slag removal.

20. Key SAW process variables
Wire Feed Speed (main factor in welding current control);
Arc Voltage;
Travel Speed;
Electrical Stick-Out (ESO) or Contact Tip to Work (CTTW);
Polarity and Current Type (AC or DC).
Other factors
Flux depth/width;
Flux and electrode classification and type;
Electrode wire diameter;
Multiple electrode configurations.

21. GAS TUNGSTEN ARC WELDING (GTAW)

22. GTAW

23. GTAW Fusion Welding Process
Arc Between Non-Consumable Tungsten Rod And Work
Arc & Weld Pool Shielded By Argon/Gas
Filler Wire Separately Added To Weld Pool
Welding Torch & Tungsten Rod Cooled by Flow OF Argon / Cooling Water

24. GTAW Equipment & Accessories
Power Source – Inverter, Thyrister, Rectifier, Generator
High Frequency Unit
Water Cooling System
Welding Torch- (Ceramic Cup, Tungsten Rod, Collet, Gas-lens)
Pedal Switch
Argon Gas Cylinder
Pressure Gauge, Regulator, Flow Meter
Earthing Cable With Clamp

25. Equipment & Accessories
Pressure Regulator
Flow Meter
Tungsten Rod
Argon Gas In
Cooling Water In
Solenoid Valve
Argon Cylinder
Gas Lens
HF Unit & Water Cooling System
Welding Cable & Cooling Water In Tube
Ceramic Cup
Cooling Water Out
Argon Shielding
Arc
High Frequency Connection +
Work
Pedal Switch
Power Source –

26. Equipment
GTAW torch with various electrodes, cups, collets and gas diffusers
GTAW torch, disassembled

27. Gas tungsten arc welding (GTAW), commonly known as Tungsten Inert Gas (TIG) welding
Is an arc welding process that uses a nonconsumable tungsten electrode to produce the weld.
The weld area is protected from atmospheric contamination by a shielding gas (usually an inert gas such as argon), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it.
A constant current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.

28. Most commonly used to weld thin sections of stainless steel and light metals such as aluminum, magnesium, and copper alloys.
The process grants the operator greater control over the weld than competing procedures such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds.
GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques.
A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.

29. GTAW system setup

30. Applications
Aerospace industry is one of the primary users of gas tungsten arc welding, the process is used in a number of other areas.
Many industries use GTAW for welding thin workpieces, especially nonferrous metals.
It is used extensively in the manufacture of space vehicles, and is also frequently employed to weld small-diameter, thin-wall tubing.
Is often used to make root or first pass welds for piping of various sizes.
In maintenance and repair work, the process is commonly used to repair tools and dies, especially components made of aluminum and magnesium.
Because the welds it produces are highly resistant to corrosion and cracking over long time periods, GTAW is the welding procedure of choice for critical welding operations like sealing spent nuclear fuel canisters before burial.

31. Quality
GTAW ranks the highest in terms of the quality of weld produced.
Operation must be with free from oil, moisture, dirt and other impurities, as these cause weld porosity and consequently a decrease in weld strength and quality.
To remove oil & grease, alcohol or similar commercial solvents used, while a stainless steel wire brush or chemical process remove oxides from the surfaces of metals like aluminum.
Rust on steels removed by first grit blasting the surface and then using a wire brush to remove imbedded grit. These steps important when DCEN used, because this provides no cleaning during the welding process, unlike DCEPor AC.
To maintain a clean weld pool during welding, the shielding gas flow should be sufficient and consistent so that the gas covers the weld and blocks impurities in the atmosphere. GTA welding in windy or drafty environments increases the amount of shielding gas necessary to protect the weld, increasing the cost and making the process unpopular outdoors.

32. Because of GTAW's relative difficulty and the importance of proper technique, skilled operators are employed for important applications.
Low heat input, caused by low welding current or high welding speed, can limit penetration and cause the weld bead to lift away from the surface being welded.
If there is too much heat input, the weld bead grows in width while the likelihood of excessive penetration and spatter increase.
If the welder holds the welding torch too far from the workpiece, shielding gas is wasted and the appearance of the weld worsens.

33. If the amount of current used exceeds the capability of the electrode, tungsten inclusions in the weld may result. Known as tungsten spitting, it can be identified with radiography and prevented by changing the type of electrode or increasing the electrode diameter.
If the electrode is not well protected by the gas shield or the operator accidentally allows it to contact the molten metal, it can become dirty or contaminated. This often causes the welding arc to become unstable, requiring that electrode be ground with a diamond abrasive to remove the impurity.

34. GTAW welding torches designed for either automatic or manual operation and are equipped with cooling systems using air or water. The automatic and manual torches are similar in construction, but the manual torch has a handle while the automatic torch normally comes with a mounting rack.
The angle between the centerline of the handle and the centerline of the tungsten electrode, known as the head angle, can be varied on some manual torches according to the preference of the operator.
Air cooling systems are most often used for low-current operations (up to about 200 A), while water cooling is required for high-current welding (up to about 600 A).
The torches are connected with cables to the power supply and with hoses to the shielding gas source and where used, the water supply.

35. The internal metal parts of a torch are made of hard alloys of copper or brass in order to transmit current and heat effectively.
The tungsten electrode must be held firmly in the center of the torch with an appropriately sized collet, and ports around the electrode provide a constant flow of shielding gas.
The body of the torch is made of heat-resistant, insulating plastics covering the metal components, providing insulation from heat and electricity to protect the welder.

36. GTAW TORCH Cap with collet For Holding Tungsten Torch Handle
Cooling Water Outlet
Argon Gas Inlet
Cooling Water Inlet Tube with cable
Ceramic Cup
Tungsten Rod
Argon Shielding Gas
Base Metal
Earthing Cable
Arc

37. The size of the welding torch nozzle depends on the size of the desired welding arc, and the inside diameter of the nozzle is normally at least three times the diameter of the electrode.
The nozzle must be heat resistant and thus is normally made of alumina or a ceramic material, but fused quartz, a glass-like substance, offers greater visibility.
Devices can be inserted into the nozzle for special applications, such as gas lenses or valves to control shielding gas flow and switches to control welding current.

38. Power supply
GTAW uses a constant current power source, meaning that the current (and thus the heat) remains relatively constant, even if the arc distance and voltage change.
This is important because most applications of GTAW are manual or semiautomatic, requiring that an operator hold the torch.
Maintaining a suitably steady arc distance is difficult if a constant voltage power source is used instead, since it can cause dramatic heat variations and make welding more difficult.

39. The preferred polarity of the GTAW system depends largely on the type of metal being welded.
DCEN is often employed when welding steels, nickel, titanium, and other metals. It can also be used in automatic GTA welding of aluminum or magnesium when helium is used as a shielding gas. The negatively charged electrode generates heat by emitting electrons which travel across the arc, causing thermal ionization of the shielding gas and increasing the temperature of the base material. The ionized shielding gas flows toward the electrode, not the base material, and this can allow oxides to build on the surface of the weld.
DCEP is less common, and is used primarily for shallow welds since less heat is generated in the base material. Instead of flowing from the electrode to the base material, as in DCEN, electrons go the other direction, causing the electrode to reach very high temperatures. To help it maintain its shape and prevent softening, a larger electrode is often used. As the electrons flow toward the electrode, ionized shielding gas flows back toward the base material, cleaning the weld by removing oxides and other impurities and thereby improving its quality and appearance.

40. AC commonly used when welding aluminum and magnesium manually or semi-automatically, combines the two direct currents by making the electrode and base material alternate between positive and negative charge. This causes the electron flow to switch directions constantly, preventing the tungsten electrode from overheating while maintaining the heat in the base material. This makes the ionized shielding gas constantly switch its direction of flow, causing impurities to be removed during a portion of the cycle.
Some power supplies enable operators to use an unbalanced alternating current wave by modifying the exact percentage of time that the current spends in each state of polarity, giving them more control over the amount of heat and cleaning action supplied by the power source.
In addition, operators must be wary of rectification, in which the arc fails to reignite as it passes from straight polarity (negative electrode) to reverse polarity (positive electrode).
To remedy the problem, a square wave power supply can be used, as can high frequency voltage to encourage ignition.

41. Tungsten Rod Tungsten Rod Non Consumable Electrode.
Maintains Stable Arc
Tip to be Ground to a cone Shape of 60º to 30º angle
Thoriated Tungsten for General Application, Zerconiated Tungsten for Aluminium Welding
Sizes :- 2, 2.4 & 3 mm Ø
Ground to 50º ankle

42. ISO Class
ISO Color
AWS Class
AWS Color
Alloy [18] WP
Green
EWP
None
WC20
Gray
EWCe-2
Orange
~2% CeO2
WL10
Black
EWLa-1
~1% LaO2
WL15
Gold
EWLa-1.5
~1.5% LaO2
WL20
Sky-blue
EWLa-2
Blue
~2% LaO2
WT10
Yellow
EWTh-1
~1% ThO2
WT20
Red
EWTh-2
~2% ThO2
WT30
Violet
~3% ThO2
WT40
~4% ThO2
WY20
~2% Y2O3
WZ3
Brown
EWZr-1
~0.3% ZrO2
WZ8
White
~0.8% ZrO2
The electrode used in GTAW is made of tungsten or a tungsten alloy, because tungsten has the highest melting temperature among metals, at 3422 °C.
The electrode is not consumed during welding, though some erosion (called burn-off) can occur.
Electrodes can have either a clean finish or a ground finish—clean finish electrodes have been chemically cleaned, while ground finish electrodes have been ground to a uniform size and have a polished surface, making them optimal for heat conduction.
The diameter of the electrode can vary between 0.5 mm and 6.4 mm, and their length can range from 75 to 610 mm .

43. A number of tungsten alloys have been standardized by the International Organization for Standardization and the American Welding Society in ISO 6848 and AWS A5.12, respectively, for use in GTAW electrodes- refer table
Pure tungsten electrodes (classified as WP or EWP) are general purpose and low cost electrodes. Cerium oxide (or ceria) as an alloying element improves arc stability and ease of starting while decreasing burn-off. Using an alloy of lanthanum oxide (or lanthana) has a similar effect. Thorium oxide (or thoria) alloy electrodes were designed for DC applications and can withstand somewhat higher temperatures while providing many of the benefits of other alloys.
However, it is somewhat radioactive, and as a replacement, electrodes with larger concentrations of lanthanum oxide can be used. Electrodes containing zirconium oxide (or zirconia) increase the current capacity while improving arc stability and starting and increasing electrode life.
Electrode manufacturers may create alternative tungsten alloys with specified metal additions, and these are designated with the classification EWG under the AWS system.
Filler metals are also used in nearly all applications of GTAW, the major exception being the welding of thin materials. Filler metals are available with different diameters and are made of a variety of materials. In most cases, the filler metal in the form of a rod is added to the weld pool manually, but some applications call for an automatically fed filler metal, which is fed from rolls.

44. shielding gases
Necessary in GTAW to protect the welding area from atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. The gas also transfers heat from the tungsten electrode to the metal, and it helps start and maintain a stable arc.
The selection of a shielding gas depends on several factors, including the type of material being welded, joint design, and desired final weld appearance.
Argon is the most commonly used shielding gas for GTAW, since it helps prevent defects due to a varying arc length. When used with alternating current, the use of argon results in high weld quality and good appearance.
Another common shielding gas, helium, is most often used to increase the weld penetration in a joint, to increase the welding speed, and to weld conductive metals like copper and aluminum.
A significant disadvantage is the difficulty of striking an arc with helium gas, and the decreased weld quality associated with a varying arc length.

45. Shielding Gas Inert Gas - Argon , Helium Common Shielding Gas – Argon
When Helium Is Used – Called Heli – Arc Welding
When Argon Is Used – Called Argon Arc Welding
Inert Gas Prevents Contamination Of Molten Metal
It Prevents Oxidation Of Tungsten Rod
It Ionizes Air Gap and Stabilizes Arc
It Cools Welding Torch & Tungsten Rod

46. Shielding Gas Argon - Purity 99.95% Impure Argon Results In Porosities
Purity Verified by Fusing BQ CS plate
Leakage of Argon in Torch Results in Porosity.
Check Leakage by Closing the Ceramic Cup With Thump

47. Argon Gas Cylinder Light Blue In Colour
Full Cylinder Pressure: 1800 psi ( 130 Kgs / Cm2 )
Volume Of Argon In Full Cylinder: 7.3 M3
Commercial Argon (99.99%) Cost: Rs 70/- Per M3
High Purity Argon (99.999) Cost: Rs 87/- Per M3

48. Purging Gas Commercial Argon or Nitrogen
Back Purging
Purging Gas Commercial Argon or Nitrogen
Applicable to Single Sided full penetration
Prevents oxidation of root pass from opposite side of weld
Essential for high alloy steels, nonferrous metals and alloys
Desirable For All Material
Filler Wire
Welding Torch
Purging Gas Out
Purging Gas In
Root Pass
Purging chamber

49. Argon-helium mixtures are also frequently utilized in GTAW, since they can increase control of the heat input while maintaining the benefits of using argon. Normally, the mixtures are made with primarily helium (often about 75% or higher) and a balance of argon. These mixtures increase the speed and quality of the AC welding of aluminum, and also make it easier to strike an arc.
Argon-hydrogen, is used in the mechanized welding of light gauge stainless steel, but because hydrogen can cause porosity, its uses are limited.
Nitrogen can sometimes be added to argon to help stabilize the austenite in austentitic stainless steels and increase penetration when welding copper. Due to porosity problems in ferritic steels and limited benefits, however, it is not a popular shielding gas additive.

50. Materials
Most commonly used to weld stainless steel and nonferrous materials, such as aluminum and magnesium, but it can be applied to nearly all metals, with notable exceptions being lead and zinc.
Its applications involving carbon steels are limited not because of process restrictions, but because of the existence of more economical steel welding techniques, such as gas metal arc welding and shielded metal arc welding.
GTAW can be performed in a variety of other-than-flat positions, depending on the skill of the welder and the materials being welded.

51. A TIG weld showing an
accentuated AC etched zone
Closeup view of an
aluminium TIG weld AC etch zone

52. Aluminum and magnesium are most often welded using alternating current, but the use of direct current is also possible, depending on the properties desired. Before welding, the work area should be cleaned and may be preheated to  °C for aluminum or to a maximum of 150 °C for thick magnesium workpieces to improve penetration and increase travel speed.
AC current can provide a self-cleaning effect, removing the thin, refractory aluminium oxide (sapphire) layer that forms on aluminium metal within minutes of exposure to air. This oxide layer must be removed for welding to occur. When alternating current is used, pure tungsten electrodes or zirconiated tungsten electrodes are preferred over thoriated electrodes, as the latter are more likely to "spit" electrode particles across the welding arc into the weld.
Blunt electrode tips are preferred, and pure argon shielding gas should be employed for thin workpieces. Introducing helium allows for greater penetration in thicker workpieces, but can make arc starting difficult.

53. Direct current of either polarity, positive or negative, can be used to weld aluminum and magnesium as well.
DCEN allows for high penetration, and is most commonly used on joints with butting surfaces, such as square groove joints. Short arc length (generally less than 2 mm or 0.07 in) gives the best results, making the process better suited for automatic operation than manual operation. Shielding gases with high helium contents are most commonly used with DCEN, and thoriated electrodes are suitable.
DCEP is used primarily for shallow welds, especially those with a joint thickness of less than 1.6 mm. While still important, cleaning is less essential for DCEP than DCEN, since the electron flow from the workpiece to the electrode helps maintain a clean weld. A large, thoriated tungsten electrode is commonly used, along with a pure argon shielding gas.

54. Steels
For GTA welding of carbon and stainless steels, the selection of a filler material is important to prevent excessive porosity. Oxides on the filler material and workpieces must be removed before welding to prevent contamination, and immediately prior to welding, alcohol or acetone should be used to clean the surface.
Preheating is generally not necessary for mild steels less than one inch thick, but low alloy steels may require preheating to slow the cooling process and prevent the formation of martensite in the heat-affected zone.
Tool steels should also be preheated to prevent cracking in the heat-affected zone. Austenitic stainless steels do not require preheating, but martensitic and ferritic chromium stainless steels do. A DCEN power source is normally used, and thoriated electrodes, tapered to a sharp point, are recommended. Pure argon is used for thin workpieces, but helium can be introduced as thickness increases.

55. Dissimilar metals
Welding dissimilar metals often introduces new difficulties to GTA welding, because most materials do not easily fuse to form a strong bond. Welds of dissimilar materials have numerous applications in manufacturing, repair work, and the prevention of corrosion and oxidation. In some joints, a compatible filler metal is chosen to help form the bond, and this filler metal can be the same as one of the base materials (eg:, using a stainless steel filler metal stainless steel and carbon steel as base materials), or a different metal (such as the use of a nickel filler metal for joining steel and cast iron). Very different materials may be coated or "buttered" with a material compatible with a particular filler metal, and then welded. In addition, GTAW can be used in cladding or overlaying dissimilar materials.
When welding dissimilar metals, the joint must have an accurate fit, with proper gap dimensions and bevel angles. Care should be taken to avoid melting excessive base material. Pulsed current is particularly useful for these applications, as it helps limit the heat input. The filler metal should be added quickly, and a large weld pool should be avoided to prevent dilution of the base materials.

56. Process variations Pulsed-current
In the pulsed-current mode, the welding current rapidly alternates between two levels.
The higher current state is known as the pulse current, while the lower current level is called the background current.
During the period of pulse current, the weld area is heated and fusion occurs. Upon dropping to the background current, the weld area is allowed to cool and solidify.
Pulsed-current GTAW has a number of advantages, including lower heat input and consequently a reduction in distortion and warpage in thin workpieces. In addition, it allows for greater control of the weld pool, and can increase weld penetration, welding speed, and quality. A similar method, manual programmed GTAW, allows the operator to program a specific rate and magnitude of current variations, making it useful for specialized applications.

57. Dabber
The Dabber variation is used to precisely place weld metal on thin edges. The automatic process replicates the motions of manual welding by feeding a cold filler wire into the weld area and dabbing (or oscillating) it into the welding arc. It can be used in conjunction with pulsed current, and is used to weld a variety of alloys, including titanium, nickel, and tool steels. Common applications include rebuilding seals in jet engines and building up saw blades, milling cutters, drill bits, and mower blades

58. Heat-affected zone
The cross-section of a welded butt joint, with the darkest gray representing the weld or fusion zone,
the medium gray the heat affected zone, and
the lightest gray the base material.

59. The heat-affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which has had its microstructure and properties altered by welding. The heat from the welding process and subsequent re-cooling causes this change in the area surrounding the weld. The extent and magnitude of property change depends primarily on the base material, the weld filler metal, and the amount and concentration of heat input by the welding process.
The thermal diffusivity of the base material plays a large role – if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Alternatively, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat inputted by the welding process plays an important role as well, as processes like oxyfuel welding use high heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input

60. To calculate the heat input for arc welding procedures, the formula used is:
where Q = heat input (kJ/mm), V = voltage (V), I = current (A), and S = welding speed (mm/min). The efficiency is dependent on the welding process used, with shielded metal arc welding having a value of 0.75, gas metal arc welding and submerged arc welding, 0.9, and gas tungsten arc welding, 0.8.

61. Types Of GTAW Power Source
Inverter- DC
Thyrister – DC
Motor Generator – DC
Rectifier – DC
Transformer – AC (For Aluminium Welding Only)

62. Power Source Provides Electric Energy – Arc – Heat
Drooping Characteristic
OCV – Appx. 90V,
Current Range 40 A to 300 A ( Capacity Of M/s)
Arc Voltage 18V to 26V

63. Characteristic Of GTAW Power Source
Drooping – Constant Current V V1
Vertical Curve V2 A A1 A2

64. High Frequency Unit
Provides High Voltage Electric Energy With Very high Frequency – Cycles / Sec.
Initiates low energy Arc / Spark & Ionize Air Gap.
Electrically charges Air Gap For welding Current to Jump Across the Tungsten Tip & BM to Form An Arc.
HF Gets Cut Off, Once Welding Arc Struck.

65. Water Cooling System Provides Cooling Water To Welding Torch.
Cools Tungsten Rod, Torch handle & Welding Cable.
Cooling Water Returns through Flexible Tube Which Carries welding cable within.

66. Pedal Switch Switches system on And off in sequence When Pedal Pressed
Solenoid valve opens, Argon gas flows
High Frequency current jumps from tungsten rod generating sparks
Welding current flows generating an arc across tungsten rod and work.
High frequency gets cut off from the system & welding continues.
When Pedal Released
Current gets cut off, Arc extinguishes
Gas flow remains for few more seconds before it stops.
Switches system
on And off in sequence

67. Argon Gas Cylinder- Pressure Regulator + Flow Meter
Cylinder Stores Argon At High Pressure
Regulator Regulates Cylinder Pressure to Working Pressure
Flow Meter Controls Flow Rate
Cylinder Valve
Pressure gauges
Flow Meter
Flow Regulator
Pressure Regulator
Connection To Torch
Argon Cylinder

68. Tools For GTAW Head Screen Hand gloves Chipping Hammer Wire Brush
Spanner Set

69. Filler Wire Added Separately to the weld pool.
Compatible to base metal
Used in cut length for manual welding.
Used from layer wound spool for automatic welding.
Sizes :- 0.8, 1, 1.2, 1.6, 2, 2.4 & 3 mm

70. ASME Classification Of Filler Wire
SS Filler Wire:
SFA-5.9, ER 308, 308L, 316, 316L, 347, 309
LAS Filler Wire:
SFA 5.28, ER 70S A1, ER 80S B2, ER90S D2,
ER 80S Ni2
CS Filler Wire:
SFA , ER 70S2
C = 0.07%, Mn = 0.9% – 1.4%, Si = 0.4 – 0.7%, P = 0.025%, S = 0.035%

71. Dos & Don'ts In GTAW Always Connect Electrode – Ve
Keep Always Flow Meter Vertical
Check & Confirm Argon Purity
Clean Groove & Filler wire With Acetone
Grind Tungsten Tip to Point
Don’t Strike Arc With Electrode + Ve
Don’t strike Arc Without Argon Flow
Don’t Strike Arc By touching Tungsten Rod
Don’t Touch Weld Pool With Tungsten Rod
Don’t Lift and break Arc

72. Dos & Don'ts In GTAW Break The Arc Only By Pedal Switch
Lift The Torch only After 5 Sec Of Arc Break.
Ensure Pre Purging & Post Purging of 5Sec
Ensure Argon Flow & Water Circulation To Torch
When Arc is Stopped Don’t Lift Torch immediately.
Don’t Weld With Blend Tungsten Rod
Don’t Weld With Argon Leaking Torch
Don’t Weld Without Water Circulation

73. Dos & Don'ts In GTAW
Dos Don’ts
Provide Back Purging For Single Sided Full Penetration Welds
Use N2 or Argon as Back Purging Gas For CS & LAS
Use Argon As Back Purging Gas For SS & Non Ferrous Alloys
Don’t Weld Single Sided Full Penetration Welds Without Back Purging
Don’t Use N2 As Back Purging Gas For Non Ferrous Alloys
Don’t Empty Ag Cylinders Fully.

74. Defects In GTAW 1. Cracks 2. Lack Of Fusion 3. Porosity 4. Undercut
5.Lack Of Penetration Excess Penetration
7.Overlap Suck Back
9. Under Flush Burn Through
11. Tungsten Inclusion Stray Arcing

75. Crack Cause Remedy Wrong Consumable Wrong Procedure Improper Preheat
Inadequate Thickness In Root Pass
Use Right Filler Wire
Qualify Procedure
Preheat Uniformly
Add More Filler Wire in root Pass
crack

76. Lack Of Fusion Cause Remedy Inadequate Current Wrong Torch angle
Improper bead placement
Use Right Current
Train /Qualify welder
Train/Qualify Welder
Lack Of Fusion

77. Porosity Cause Remedy Impure Argon Gas Argon Leak Within Torch
Defective Filler Wire
Wet surface of BM
Rusted / Pitted Filler wire
Improper Flow Of Argon
Replace Argon Cylinder
Replace Leaking Torch
Replace Filler Wire
Clean & Warm BM
Clean Filler Wire
Provide Gas lens
Porosity
. .

78. Undercut Cause Remedy Excess Current Excess Voltage
Improper Torch angle
Reduce the Current
Reduce Arc length
Train & Qualify the Welder
Under cut

79. Lack Of Penetration* Cause Remedy Excess Root Face
Inadequate Root opening
Over size Filler Wire
Wrong Direction of Arc
Improper bead placement
Improper weaving technique
Reduce Root Face
Increase Root Opening
Reduce Filler Wire size
Train / Qualify Welder
Train & Qualify Welder
* Applicable to SSFPW
LOP

80. Excess Penetration* Cause Remedy Excess root opening Excess Current
Inadequate root face
Excess Weaving
Wrong Direction Of Arc
Reduce root gap
Reduce Current
Increase Root face
Train Welder
* Applicable to SSFPW
Excess Penetration

81. Overlap Cause Remedy 1) Wrong Direction Of Arc Inadequate Current
Excess Filler Wire
Train & Qualify Welder
Increase Current
Reduce Filler Metal
Overlap

82. Suck Back* Cause Remedy Excess weaving in root Excess Current
Inadequate root face
Wrong Electrode angle
Reduce weaving
Reduce Current
Increase root face
Train / Qualify Welder
* Applicable to SSFPW in 4G, 3G & 2G
Suck Back

83. Under flush Cause Remedy Inadequate weld beads in final layer
2) Inadequate understanding on
weld reinforcement
3) Wrong selection of filler wire
size
Weld some more beads
in final layer
2) Train / Qualify welder
3) Train / Qualify Welder
Under flush

84. Burn through* Cause Remedy Excess Current Excess Root opening
Inadequate Root face
Improper weaving
Reduce the Current
Reduce root opening
Increase root face
Train / Qualify Welder
*Applicable to root pass
Burn trough

85. Tungsten Inclusion Cause Remedy Ineffective HF
Improper Starting of Arc
3) Tungsten Tip Comes in
Contact With Weld
Rectify HF Unit
Never Touch Weld
With Tungsten Rod
3) Train / Qualify welder
Tungsten Inclusion

86. Stray Arcing Cause Remedy HF Not In Operation
Inadequate Skill of Welder
Rectify HF Unit
Train the Welder
Arc Strikes

87. Gas Metal Arc Welding

88. What Is GMAW ? A Fusion Welding Process – Semi Automatic
Arc Between Consumable Electrode &Work
Arc Generated by Electric Energy From a Rectifier / Thyrester / Inverter
Filler Metal As Electrode Continuously fed From Layer Wound Spool.
Filler Wire Driven to Arc By Wire Feeder through Welding Torch
Arc & Molten Pool Shielded by Inert Gas through Torch / Nozzle

89. Gas Metal Arc Welding MIG – Shielding Gas Ar / Ar + O2 / Ar + Co2
MAG – Shielding Gas Co2
FCAW – Shielding Gas Co2 With Flux cored Wire
Note:- Addition of 1 – 5% of O2 or 5 – 10% of Co2 in Ar. increases wetting action of molten metal

90. Power Source For MIG / MAG
Inverter- DC
Thyrister – DC
Motor Generator – DC
Rectifier – DC

91. Characteristic Of GMAW Power Source
Constant V / Linear Characteristic V
Appx. Horizontal Curve V1 V2 A A1 A2

92. Current & Polarity DC- Electrode +Ve Stable Arc
Smooth Metal Transfer
Relatively Low Spatter
Good Weld Bead Characteristics
DC- Electrode – Ve, Seldom Used
AC- Commercially Not In use

93. Accessories Of GMAW Power Source Wire Feed Unit
Shielding Gas Cylinder, Pressure gauges/ Regulator, Flow meter (Heater For Co2 )
Welding Torch
Water Cooling System (For Water cooled Torch)
Earthing Cable With Clamp

94. Tools For GMAW Head Screen With DIN 13 / 14 Dark Glass
Hand Wire Brush / Grinder With Wire Wheel
Cutting Pliers
Hand Gloves
Chipping Hammer / Chisel & hammer
Spanner Set
Cylinder Key
Anti-spatter Spray
Earthing Cable With Clamp

95. Filler Wire - Electrode
GMAW Torch
On / Off Switch
Shielding Gas
Torch Handle
Spring Conduit
Gas Cup
Nozzle Tip
Filler Wire - Electrode
Arc
Job

96. Equipment & Accessories
Pressure Regulator
Flow Meter
Shielding Gas
Heater (Only For Co2)
Solenoid Valve
Switch
Shielding Gas Cylinder
Welding Torch
Wire Feeder
Copper Cup
Wire Inside Spring Lining
Contact Tip
Electrode / Wire
Wire Spool
Argon / Co2 Shielding
Arc –
Work
Power Source
With Inductance
Torch With Cable Max. 3Mtr –

97. Types Of Wire Feeding In GMAW
Push Type
Wire fed in to The torch by Pushing through Flexible Conduit From A Remote Spool
Pull Type
Feed Rollers Mounted on The Torch Handle Pulls the Wire From A Remote spool
Self Contained
Wire Feeder & The Spool On the Torch

98. Function Of Shielding Gas In GMAW
Prevents Air contamination of weld Pool
Prevents Contamination During Metal Transfer
Increases fluidity of molten metal
Minimizes the spatter generation
Helps in even & uniform bead finish

99. Shielding Gases For GMAW
MIG: Argon Or Helium
For SS, CS, LAS & Non-ferrous Mt & Al
MIG: Ar + 1 to 2 % O2, Wire With Add. Mn & Si
MIG: Ar + 5 to 20 % Co2 Wire With Add. Mn & Si
MAG: Co2 With Solid Wire
For CS & LAS
FCAW: Co2 With Flux Cored Wire
For CS, LAS & SS Overlay

100. ASME Classification For CS GMAW Wire
SFA 5.18 : - CS Solid Wire
ER 70 S – 2, ER 70 S – 3
ER 70 S – 6, ER 70 S – 7
SFA 5.20 :- CS Flux Cored Wire
E 71 T-1, E 71 T-2 ( Co2 Gas )
E 71 T-1M, E 71 T-2M ( Ar + Co2 Mix)

101. GMAW CS Wire Generally Copper Coated Available In Solid & Flux Cored
Prevents Oxidation / rusting in Storage
Promotes Electric Conductivity in Arcing
Available In Solid & Flux Cored
Size in mm 0.8, 1, 1.2, 1.6, 2, 2.4, 3
Manganese & Silicon ( Mn 1 – 2 %, Si Max 1%)
Act As Deoxidizing Agents
Eliminate Porosity
Increase Wetting Of Molten Pool

102. Metal Transfer In MIG Short-Circuiting / Dip Transfer
Globular Transfer
Spray Transfer

103. Metal Transfer In MIG CS Solid Wire 1.2 mm Φ 120 to 250A 16 – 24 V
Above230A
24 – 35 V
Up to 120A
14 – 22V
Dip/Short Circuiting
Globular
Spray
Co2 or Ar
Co2 or Ar
Only Ar / Ar+O2

104. Short-Circuiting / Dip Transfer
Wire In Contact With Molten Pool 20 to 200 times per Second
Operates in Low Amps & Volts – Less Deposition
Best Suitable for Out of Position Welding
Suitable for Welding Thin Sheets
Relatively Large opening of Root Can be Welded
Less Distortion
Best Suitable for Tacking in Set up
Prone to Get Lack of Fusion in Between Beads

105. Globular Transfer
Metal transferred in droplets of Size grater than wire diameter
Operates in Moderate Amps & Volts – Better Deposition
Common in Co2 Flux Cored and Solid Wire
Suitable for General purpose Welding

106. Spray Transfer Metal transferred in multiples of small droplets
100 to 1000 Droplets per Second
Metal Spray Axially Directed
Electrode Tip Remains pointed
Applicable Only With Inert Gas Shielding – Not With Co2
Operates in Higher Amps & Volts – Higher Deposition Rate
Not Suitable for Welding in Out of Position.
Suitable for Welding Deep Grooves

107. Pulsed Spray Welding
Power Source Provides Two different Current Levels“Background” and “Peak”at regular interval
“Background” & “Peak” are above and below the Average Current
Best Suitable for Full Penetration Open Root Pass Welding
Good Control on Bead Shape and Finish

108. Synergic Pulse GMAW
Parameters of Pulsed Current (Frequency, Amplitude, Duration, Background Current) Related to Wire feed Rate
One Droplet detaches with each pulse
An Electronic Control unit synchronizes wire feed Rate with Pulse Parameters
Best Suitable for Most Critical Full Penetration Open Root Pass Welding
Good Control on Open Root penetration, Bead Shape and Finish

109. GMAW Process Variables
Current
Voltage
Travel Speed
Stick Out / Electrode Extension
Electrode Inclination
Electrode Size
Shielding Gas & Flow Rate
Welding Position

110. Parameter For 1.2 ф FC Wire Current – 200 to 240 A Voltage – 22-24
Travel Speed 150 to 250 mm / min
Stick Out / Electrode Extension – 15 to 20 mm
Electrode Inclination – Back Hand Technique
Shielding Gas – Co2, 12 L/Min

111. Parameter For 1.2 ф Solid Wire
Current – 180 to 220 A
Voltage – 20-22
Travel Speed 150 to 200 mm / min
Stick Out / Electrode Extension – 10 to 20 mm
Electrode Inclination – Back Hand Technique
Shielding Gas – Co2 – 12 L/Min

112. Results In Change Of Parameters
Increase In Current
More deposition, More Penetration, More BM Fusion
Increase In Voltage
More Weld Bead Width, Less Penetration, Less Reinforcement, Excess Spatter
Increase In Travel Speed
Decrease in Penetration, Decrease in Bead Width,
Decrease In Gas Flow rate
Results In porosity
Long Stick Out / Electrode Extension
Excess Weld Deposit With Less Arc intensity, Poor Bead Finish, Shallow Penetration

113. Common Defects In GMAW 1. Porosity 2. Spatters
3. Lack Of Fusion Under Cut
5. Over Lap Slag
7. Crack Lack Of Penetration
9. Burn Through Convex Bead
11. Unstable Arc Wire Stubbing

114. Porosity Cause Remedy Less Mn & Si In Wire
Rusted / Unclean BM / Groove
Rusted wire
Inadequate Shielding Gas
Use High Mn & Si Wire
Clean & warm the BM
Replace the Wire
Check & Correct Flow Rate
Porosity
. .

115. Spatters Cause Remedy Low Voltage Inadequate Inductance
Rusted BM surface
Rusted Core wire
Quality Of Gas
Increase Voltage
Increase Inductance
Clean BM surface
Replace By Rust Free wire
Change Over To Ar + Co2
Spatters
• • •

116. Lack Of Fusion Cause Remedy Inadequate Current Use Right Current
Inadequate Voltage
Wrong Polarity
Slow Travel Speed
Excessive Oxide On Joint
Use Right Current
Use Right Voltage
Connect Ele. + Ve
Increase Travel speed
Clean Weld Joint
Lack Of Fusion

117. Undercut Cause Remedy Excess Voltage Excess Current
Improper Torch angle
Excess Travel Speed
Reduce Voltage
Reduce Current
Train & Qualify the Welder
Reduce Travel Speed
Under cut

118. Overlap Cause Remedy 1) Too Long Stick Out 2) Inadequate Voltage
Reduce Stick Out
2) Increase the Voltage
Overlap

119. Slag Cause Remedy Inadequate Cleaning Inadequate Current
Wrong Torch angle
Improper bead placement
Clean each bead
Use Right Current
Train / Qualify welder
Train / Qualify Welder
Slag

120. Crack Cause Remedy Incorrect Wire Chemistry Too Small Weld Bead
Improper Preheat
Excessive Restrain
Use Right Wire
Increase wire Feed
Preheat Uniformly
Post heating or ISR
crack

121. Lack Of Penetration* Cause Remedy Too Narrow Groove Angle
Inadequate Root opening
Too Low Welding current
Wrong Torch angle
Puddle Roll In Front Of Arc
Long Stick Out
Widen The Groove
Increase Root Opening
Increase Current
Train / Qualify Welder
Correct Torch Angle
Reduce Stick Out
* Applicable to SSFPW
LOP

122. Burn through* Cause Remedy Excess Current Excess Root opening
Inadequate Root face
Too Low Travel Speed
Quality Of Gas
Reduce the Current
Reduce root opening
Increase root face
Increase Speed
Use Ar + Co2
*Applicable to root pass
Burn trough

123. Convex Bead Finish Cause Remedy Low Current Low Voltage
Low Travel Speed
Low Inductance
Too Narrow Groove
Increase Current
Increase Voltage
Increase Travel Speed
Increase Inductance
Increase Groove Width
Uneven bead finish

124. Unstable arc Cause Remedy Improper Wire Feed Improper Gas Flow
Twisted Torch Conduit
Check Wire Feeder
Check Flow Meter
Straighten Torch Cab

125. Wire Stubbing Cause Remedy Too Low Voltage Too High Inductance
Excess Slope
Too Long Stick Out
Increase Voltage
Reduce Inductance
Adjust Slope
Reduce Stick Out

126. Important Terminology used in Critical Welding
Preheating
Post Heating or Dehydrogenation
Intermediate Stress leaving
Inter pass Temperature
Post Weld Heat Treatment

127. What Is Preheating?
Heating the base metal along the weld joint to a predetermined minimum temperature immediately before starting the weld.
Heating by Oxy fuel flame or electric resistant coil
Heating from opposite side of welding wherever possible
Temperature to be verified by thermo chalks prior to starting the weld

128. Why Preheating?
Preheating eliminates possible cracking of weld and HAZ
Applicable to
Hardenable low alloy steels of all thickness
Carbon steels of thickness above 25 mm.
Restrained welds of all thickness
Preheating temperature vary from 75°C to 200°C depending on hardenability of material, thickness & joint restrain

129. How does Preheating Eliminate Crack?
Preheating promotes slow cooling of weld and HAZ
Slow cooling softens or prevents hardening of weld and HAZ
Soft material not prone to crack even in restrained condition

130. What Is Post Heating?
Raising the pre heating temperature of the weld joint to a predetermined temperature range (250° C to 350° C) for a minimum period of time (3 Hrs) before the weld cools down to room temperature.
Post heating performed when welding is completed or terminated any time in between.
Heating by Oxy fuel flame or electric resistant coil
Heating from opposite side of welding wherever possible
Temperature verified by thermo chalks during the period

131. Why Post Heating?
Post heating eliminates possible delayed cracking of weld and HAZ
Applicable to
Thicker hardenable low alloy steels
Restrained hardenable welds of all thickness
Post heating temperature and duration depends on hardenability of material, thickness & joint restrain

132. How does Post Heating Eliminate Crack?
SMAW introduces hydrogen in weld metal
Entrapped hydrogen in weld metal induces delayed cracks unless removed before cooling to room temperature
Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld

133. What Is Intermediate Stress Relieving?
Heat treating a subassembly in a furnace to a predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness
Applicable to
Highly restrained air hardenable material

134. Why Intermediate Stress Relieving?
Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.
Cracks due to entrapped hydrogen and built in stress
Intermediate stress relieving relieves built in stresses and entrapped hydrogen making the joint free from crack prone

135. What Is Inter- Pass Temperature?
The temperature of a previously layed weld bead immediately before depositing the next bead over it
Temperature to be verified by thermo chalk prior to starting next bead
Applicable to
Stainless Steel
Carbon Steel & LAS with minimum impact

136. Why Inter Pass Temperature?
Control on inter pass temperature avoids over heating, there by
Refines the weld metal with fine grains
Improves the notch toughness properties
Minimize the loss of alloying elements in welds
Reduces the distortion

137. What Is Post Weld Heat Treatment?
Heat treating an assembly on completion of all applicable welding, in an enclosed furnace with controlled heating/cooling rate and soaking at a specific temperature for a specific time.
Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness
Applicable to
All type of CS & LAS

138. Why Post Weld Heat Treatment?
Welded joints retain internal stresses within the structure
HAZ of welds remains invariably hardened
Post Weld Heat Treatment relieves internal stresses and softens HAZ. This reduces the cracking tendency of the equipment in service

139. Weldability
The weldability of a material refers to its ability to be welded. Many metals and thermoplastics can be welded, but some are easier to weld than others. It greatly influences weld quality and is an important factor in choosing which welding process to use.

140. Steels
The weldability of steels is inversely proportional to a property known as the hardenability of the steel, which measures the ease of forming martensite during heat treatment. The hardenability of steel depends on its chemical composition, with greater quantities of carbon and other alloying elements resulting in a higher hardenability and thus a lower weldability. In order to be able to judge alloys made up of many distinct materials, a measure known as the equivalent carbon content is used to compare the relative weldabilities of different alloys by comparing their properties to a plain carbon steel. The effect on weldability of elements like chromium and vanadium, while not as great as carbon, is more significant than that of copper and nickel, for example. As the equivalent carbon content rises, the weldability of the alloy decreases. The disadvantage to using plain carbon and low-alloy steels is their lower strength—there is a trade-off between material strength and weldability. High strength, low-alloy steels were developed especially for welding applications during the 1970s, and these generally easy to weld materials have good strength, making them ideal for many welding applications.
Stainless steels, because of their high chromium content, tend to behave differently with respect to weldability than other steels. Austenitic grades of stainless steels tend to be the most weldable, but they are especially susceptible to distortion due to their high coefficient of thermal expansion. Some alloys of this type are prone to cracking and reduced corrosion resistance as well. Hot cracking is possible if the amount of ferrite in the weld is not controlled—to alleviate the problem, an electrode is used that deposits a weld metal containing a small amount of ferrite. Other types of stainless steels, such as ferritic and martensitic stainless steels, are not as easily welded, and must often be preheated and welded with special electrodes.

141. Aluminum
The weldability of aluminum alloys varies significantly, depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem, welders increase the welding speed to lower the heat input. Preheating reduces the temperature gradient across the weld zone and thus helps reduce hot cracking, but it can reduce the mechanical properties of the base material and should not be used when the base material is restrained. The design of the joint can be changed as well, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys should also be cleaned prior to welding, with the goal of removing all oxides, oils, and loose particles from the surface to be welded. This is especially important because of an aluminum weld's susceptibility to porosity due to hydrogen and dross due to oxygen.
[edit]
References
Lincoln Electric (1994). The Procedure Handbook of Arc Welding. Cleveland: Lincoln Electric. ISBN
Residual stress
From Wikipedia, the free encyclopedia
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Residual stresses are stresses that remain after the original cause of the stresses has been removed. Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment. Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. Castings may also have large residual stresses due to uneven cooling.
While un-controlled residual stresses are undesirable, many designs rely on them. For example, toughened glass and pre-stressed concrete depend on them to prevent brittle failure. Similarly, a gradient in martensite formation leaves residual stress in some swords with particularly hard edges (notably the katana), which can prevent the opening of edge cracks. In certain types of gun barrels made with two tubes forced together, the inner tube is compressed while the outer tube stretches, preventing cracks from opening in the rifling when the gun is fired. Parts are often heated or dunked in liquid nitrogen to aid assembly.
Press fits are the most common intentional use of residual stress. Automotive wheel studs, for example are pressed into holes on the wheel hub. The holes are smaller than the studs, requiring force to drive the studs into place. The residual stresses fasten the parts together. Nails are another example.