Joining Processes

1. Joining Processes Contains • Introduction • Classification • Applications • Gas Welding • Oxy-acetylene Welding • Arc Welding • Equipment's & Method • Welded Joint • Soldering, Brazing & Braze Welding • Comparison Study

2. Introduction • Used for Joining metal parts in fabrication works. • Process are also applied when steam or water tight joints are needed. • Commonly used joining processes are • Welding • Soldering • Brazing • Adhesive Bonding

3. Introduction • Process is use for joining of various materials. • Most essential requirement is Heat. • Pressure is also required, but not in all processes. • Heat is supplied either electrically or by using gas torch. • Capacity of a material to be welded under fabrication conditions & suitable designed structure to perform satisfactorily service is called as weldability. • Weldability includes :- i) Metallurgical compatibility of a metal. ii) Ability to be welded with Mechanical soundness. iii) Serviceability of the resulting welded joint.

4. Classification Modern method classification under Two broad categories. • Plastic / Pressure Welding Metal pieces heated up to plastic state then forced together by external pressure. Filler metal is not required. e.g. Forged welding, Electric resistance welding. • Fusion / Non-Pressure welding Metal pieces heated up to molten state & allowed to solidify. Filler metal is required during processes. e.g. Gas welding, Arc welding

5. classification Gas Welding • oxy-acetylene welding • Air acetylene welding • oxy-hydrocarbon welding • Pressure gas welding Arc welding • Carbon-arc welding • Flux-cored welding • Gas tungsten arc welding (TIG) • Gas metal arc welding (MIG) • Plasma arc welding • Electro-slag welding • Stud arc welding • Shielded metal arc welding • Submerged arc welding

6. classification Resistance welding • Spot welding • Seam welding • Projection welding • Percussion welding • Flash butt welding • Resistance butt welding • High frequency resistance welding Solid state welding • Cold welding • Friction welding • Explosive welding • Roll welding • Ultrasonic welding • Diffusion welding • Forge welding • Hot pressure welding

7. classification • Thermo-chemical welding • Thermite welding • Atomic hydrogen welding • Radiant energy welding • Electron Beam welding (EBW) • Laser Beam welding (LBW)

8. Application Aircraft Construction • Welding of engine parts • Turbine frame for jet engine • Ducts, fittings Automobile Construction • Arc welded alloy wheels • Rear axle housing • Frame, brackets Buildings • Column base plates, trusses Ships • Shall frames Pressure vessels & tanks • Shell construction • Oil, gas & water storage Piping's & pipeline • Open pipe joints • Oil & gas pipeline

9. Gas Welding Processes It is a fusion-welding / non pressure welding method. It join the metals, by using combustion heat of oxygen/air & fuel gas mixture. Edges of the parts to be welded, generally by adding a filler metal.

10. Gas Welding Processes • Oxy-acetylene Welding • Consist of two cylinders, One contain oxygen & other contain acetylene • Heat is generated to melt & join the parent metals. • Oxy-acetylene flame reaches a temp of about 3200 ͦͦ c • Metal can flow together to form a complete bond. • Does not required pressure during welding.

11. Gas Welding Processes Flame :- • Correct type of flame is req. for production of satisfactory welds. • Temp 3100 0c to 3300 0c • Natural flame (Equal oxygen & acetylene) • Oxidising Flame (Excess of oxygen) • Reducing Flame/ carburising flame (Excess of acetylene)

12. Gas Welding Processes • Leftward ( forward) Welding Method :- • Welding torch in right hand & filler rod in the left hand & flame is directed from right to left. • Torch angle is 600- 700 & Filler rod is 300_ 400 • Used on thin metals, thickness less than 5mm. • Rightward ( Backward) Welding Method :- • Welding torch in right hand & filler rod in the left hand but flame is directed from left to right • Torch angle is 400- 500 & Filler rod is 300_ 400 • Speed increases by 20-25% & lower fuel consumption by 15-25%

13. Gas Welding Equipment's

14. Gas Welding • Advantages :- • Control of temperature • Low cost, generally portable. • Maintenance cost is low • Disadvantages :- • Gas flame give long time for heat. • More safety problems during handling. • Filler materials fumes are irritating the eyes, nose, throat & lungs. • Heavy section can not be welded economically. • Application :- • Joining thin materials ( ferrous/nonferrous) • Used in automobile & aircraft industries. • Also used in sheet fabrication plant.

15. Arc Welding Process • Fusion welding process, heat is obtained from an electric arc. • Electrode is touch the work piece to form electric circuit. • Temperature produced is 60000 C to 70000 C • Consist of Parent metal, Deposited metal, Crater, Electrode • Base metal & electrode is melted by temp of arc & deposited around the edges. • The distance between centre of electrode tip & the bottom of arc is called as arc length. • Arc length is 3 to 4 mm. • Either A. C. or D. C. supply is used.

16. Arc Welding Equipment's • A.C. or D.C. machine • Electrode & Holder • Cables & Connectors • Earthing Clamps • Chipper hammer • Wire brush • Helmet • Safety Goggles • Hand gloves • Apron

17. Arc Welding Methods Shielded Metal Arc Welding (SMAW) • Also called as Flux shielded metal arc welding ( FSAW) • The electrode itself melts & supplies the necessary filler metal. • By supply of current, control the temp of work piece. & is about 24000 C to 26000 C • Material droplets are transferred from the electrode to work piece through arc & deposited along the welded joint. • Coating flux produces a gaseous shield & slag to prevent molten metal from atm.

18. Arc Welding Methods Submerged Arc Welding • It also called as hidden arc or sub-arc welding. • Electrode & molten pool remains completely hidden & submerged under a blanket of flux material which protect the weld pool from atm. Impurity. • Electrode melts & acts as a filler rod , Pressure is not required. • Welding is carried out without sparks, smoke, flash or spatter. • No edge preparation is required for welding up to 12 mm thickness.

19. Arc Welding Methods Gas Tungsten Arc Welding (GTAW) • Also called as Tungsten Inert Gas (TIG) welding. • To avoid atm. impurity shielding gas is used, filler metal may be added. • Kept distance of electrode 2 to 3 mm form work piece, • Angle of 700 to 800 in welding torch & filler rod, no cleaning is required. • No flux is used, Operator can better control on welding process with clear visibility

20. Arc Welding Methods Gas Metal Arc Welding (GMAW) • Also called as Metal Inert Gas (MIG) welding. • Continuously fed metal electrode & workpiece. • Flux is not used, but arc & molten metal are shielded by inert gas (argon, helium, etc.) • Current ranges 100 to 400 Amp. Depending up on dia.(0.09 to 1.6 mm) & melting pt. of wire. • It is faster process. Produced joint with deep penetration. • Both thin & thick work pieces can be welded. • Process is more complicated.

21. Arc Welding Methods Plasma Arc Welding System • The process employs two inert gases, one forms plasma & other forms shields the plasma. • Filler rod may or may not be added, & pressure is not required. • Temp is about 50,0000 F • It employs a constricted arc process. With the help of a water-cooled small dia. nozzle which squeezes the arc, increases its pressure, temperature, heat & thus improve the arc stability, arc shape & heat transfer characteristic.

22. Arc Welding Methods Flux-cored Arc Welding (FCAW) • Electrode is flux cored . • Electrode is supplied to the arc as a continuous wire. • Additional shielding may or may not be obtained from an externally supplied gas. • It provides high quality weld metal at lower cost for wide thickness range. • Arc is visible hence, easy to weld. • Electrode wire is more expensive & used only to weld ferrous metals.

23. Resistance Welding Process • Heat is obtained from resistance by flowing electric current in a circuit & by application of pressure. • Filler metal (rod) is not required during the process. • Factors are involved • Amount of current. • The pressure that electrode (copper) transfer to the workpiece. • Time during which current flows. • Area of electrode tip in contact with the workpiece.

24. Resistance Welding Process • Advantages • Rate of production is high. • Filler rod is not required. • The equipment used are semi-automatic. • Both similar & dissimilar metals can be welded. • Disadvantages • Initial cost of equipment is very high. • Skilled persons are required for maintenance. • Special surface preparation is required for some materials. • Workpiece of higher thickness cannot be welded. • Applications • Joining of sheets, bars, rods & tubes. • Welding of aircraft & automobile parts. • Making of cutting tools, fuel tanks of cars, etc.

25. Resistance Welding Process • Types of resistance welding • Spot welding • Seam welding • Projection welding • Percussion welding • Flash butt welding • Resistance butt welding • High frequency resistance welding

26. Resistance Welding Process Spot Welding • Sheets are joined by local fusion at one or more spots • Used for joining sheets, sheet rolled sections, also for light gauge parts (up to 3 mm) • Amount of current is 3,000 to 1,00,000 Amp for fraction of second. • Temperature of weld zone is 8150 C to 9300 C • Edge preparation is not required.

27. Resistance Welding Process • Seam Welding • Workpiece is placed between the wheels (electrode) for producing continuous weld. • As pressure is applied, the drive is started & welding current is switched on. • It can produced gas tight & liquid tight joint. • A single seam weld or parallel seams weld is possible. • Weld can be provided only in straight or uniformly curved line. • It difficult to weld workpiece with thickness greater than 3 mm.

28. Types of Welded Joints Lap Joint or Fillet Joint

29. Types of Welded Joints Butt Joint

30. Typical defects in Weld Joints

31. Adhesive Bonding • Use adhesives for joining materials. • Strong adhesive bond required considerable energy to separate the pieces. • Adhesive Bonding Procedure:- i) Surface Preparation. ii) Appling the primer. iii) Appling the adhesive. iv) Assembling adhesive coated components. v) Curing the assembly vi) Testing the joints.

32. Adhesive Bonded Joints

33. Types of Adhesives • Point to be considering while selecting Adhesives :- • Type of materials required to be joined. • Service requirements of the assembly. • Method of applying the adhesive on surface to be joined. • Thermoplastic Adhesives :- • This type adhesive soften at high temperature. • Are easy to use • Thermosetting adhesives :- • Once hardened cannot be remelted & a broken joint cannot be rebounded by heating also. • In this type adhesives cure or harden by chemical reactions

34. Soldering • Is the process for joining steel, copper & other materials at low temperature. • Filler material is required, temperature up to 4270 C • Divided into two type • Soft solder :- wires & small parts • Hard solder :- which melts at high temp

35. Brazing • Filer material is required. • The filler metal is distributed between the closely fitted surface of the joint by capillary action. • Filler materials used in the process are divided • Copper base alloys • Silver base alloys • Borax is commonly used flux in brazing process.

36. Brazing • Various method are :- • Torch Brazing • Resistance Brazing • Immersion Brazing • Furnace Brazing • It is suitable for mass production . • Brazing produces a clean joint. • Filler metals used in the process are costly.