1. Chapter 30 Brazing, Soldering, Adhesive, Bonding
& Mechanical Fastening process
Chapter 30

2. Brazing Joining process
A filler metal is placed between two workpieces and heated until melted
Two main types of Brazing
Ordinary
Braze welding
Use of flux is very important

3. Fig: a) Brazing b) Braze welding operation
Filler Metals
Available in a wide range of brazing temperatures
They come in a wide range of shapes
Choice of the filler metal and its composition are important
Diffusion of the filler metal in to the workpeice is an important consideration
Fig: a) Brazing b) Braze welding operation

4. Fluxes The use of flux in brazing is very important Generally made of:
Borax
Boric acid
Borates
Fluorides
Chlorides
Wetting agents may also be added

5. Brazing Methods Torch Brazing
Performed by heating the joint with a torch
Depositing the filler metal in the joint
Suitable part thickness (0.25 – 6.0)mm
Not a automated process
More than one torch can be used in this process

6. Brazing Methods Furnace Brazing
Precleaned & Preloaded with brazing metal
Heated in a furnace
Fig:An example of furnace brazing a)before b) after

7. Other Types Of Brazing Induction Brazing Resistance Brazing
Dip Brazing
Infrared Brazing
Diffusion Brazing

8. Braze Welding Prepared like fusion welding
Filler metal is deposited at the joint with the use of an oxyacetylene torch
Considerably more filler is used
Temperature is minimal compared to that of fusion welding; part distortion is minimal

9. Brazing Process Capabilities
Dissimilar metals can be assembled with good joint strength
Shear strength of brazed joints can reach 800Mpa
Fig:Joint Designs commonly used in brazing operations.The clearance between the two parts being brazed is an important factor in joint strength.If the clearance is to small, the molten braze metal will not fully penetrate the interface.

10. Good/Poor Designs

11. Soldering Different types of soldering Torch Furnace Iron Induction
Resistance
Dip
Infrared
Ultrasonic
reflow (paste)
Wave

12. Reflow Soldering Solvents present in the paste are evaporated
The Flux in the paste is activated and the fluxing action occurs
The components are carefully preheated
The solder particles are melted and wet the joint
The assembly is cooled

13. Wave Soldering
Popular approach to attaching circuits to circuit boards
Fig: a)Screening or stenciling paste onto a printed circuit board: 1) Stenciling process 2) a section of a typical stencil pattern b) wave soldering process

14. Types Of Fluxes Inorganic acids or salts – clean the surface rapidly
Noncorrosive resin-based – used in electrical applications
Soldering is used extensively in electronics industry

15. Adhesive Bonding
Products are joined and assembled by the use of Adhesives
Adhesives properties to be considered
Strength
Toughness
Resistance to various fluids
Ability to wet the surface to be bonded

16. Types of adhesives Surface must be clean for joining parts
Should avoid joints that might be subjected to peeling forces
Design for adhesive bonding

17. Adhesive Peeling Test
Fig : Characteristic behavior of (a) brittle (b) tough adhesive in a peeling test

18. Joint Design in Adhesive Bonding
Fig:Various joint design in adhesive bonding.

19. Configurations for adhesive bonds
Fig : (a) single lap (b) double lap (c) scarf (d) strap

20. Mechanical Fastening Threaded Fasters Other Fastening Methods Bolts
Screws
Nuts
Other Fastening Methods
Stapling
Crimping
Snap-in Fasteners
Shrink and press fits

21. Fig:a)solid b)tubular c) split (bifurcated) d) compression
Rivets
Fig:a)solid b)tubular c) split (bifurcated) d) compression
Fig : Design guidelines for riveting (a)Exposed shank is too long; the result is buckling instead of upsetting (b)Rivets should be placed sufficiently far from edges to avoid stress concentrations (c)Joined sections should allow ample clearance for riveting tools (d) section curvature should not interfere with the riveting process

22. Joining Plastics Heat softens the plastic to a molten state
Then pressure added & fusion takes place
External Heat Sources
Hot air
Heated tools & dies
Electrical-Resistance
Lasers
Internal Heat Sources
Ultrasonic welding
Friction welding

23. THE END