Lec16 Flashcards
Brazing is
process in which filler metal is placed between surfaces to be joined - used as glue
Brazing filler metal
melts about 450 C BELOW the melting temp of metals to be joined
Strength of brazed joint depends on
joint design
adhesion at the interface
filler metal
Preparing of brazing surfaecs
chemically or mechanically cleaned to ensure full capillary action
Brazing
temp raised enough to melt the filler metal but not the workpiece
molten metal fills the closely fitted space by capillary action
Braze welding
filler metal is deposited at the joint with technique similar to oxyfuel gas welding
Brazing vs welding process
1 composition of brazing alloy is different from base metal
2 strength of brazing alloy is lower than base metal
3 melting point of brazing alloy lower than base metal
4 bonding requires capillary action
Braze joints of desired strength must
have sufficient area of joint to form bond
Adv of brazing
virtually all metals can be joined
ideal for dissimilar metals (ferrous to non ferrour different melting points)
less heating is required compared to welding (quicker and more eonomical small HAZ)
Shapes brazing is good for
thinner and more complex assemblies wont melt through materal
disadv of brazing
subsequent heating of the assembly can cause inadvertent melting of the braze metal (weaken or destroying joint)
brazed joints fail when workers apply hear in an attempt to straighten or repair damaged assemblies
Brazing vs welding
brazing is fast parent metal doesnt metal like to unlike
welding stronger joint higher temp needed join zone at temp for longer
differences between welding and brazing
brazing always uses filler different to parents welding sometimes uses filler metal
welding does always need a flame
brazing is quicker and cheaper
welding typically temp hot enough to melt parents
brazing never melt parents
Soldering
filler metal called solder relatively low temps 450C
solder fills joint by capillary action
high wetting capability and low surface tension
soldering heat source
soldering irons torches ovens
Brazing vs soldering
solder temps relaively low - limited use at elevated temps - solder filler metals at less than 450 C
Adv of soldering
solder metals are cheap and have acceptable mech prop
can be used to join a wide variety of sizes shapes and thickness
applications of soldering
electronis industry
electrial coupling
gas/airtight seals
aluminium radiators in automotive industry
Mechanical fastening
no fusion or adhesion of surface
mechanical interlocking and interference of surfaces brought about by clamping forces
Selection of type of fastener depends on
materials to be joined function of joint strength and reliability required weight limitations dimensions of components environmental condition
Choose mechanical fastening based on
cost - cheap
appearance - is it gonna be okay with additional fixing
need for future disassembly - quickly and easily
When using mechanical fastenings you should
use fewer but larger faseners less coslty
minimum number of fasteners req
use standardised fasteners
holes should be far from edges or corners
Adv of mechanical fastening
ease of manufacture ease of assembly and transportation easy of disassembly maintenance repair ease of design - movable joints low cost
Mechanical fastening types
metal stitching or stapling
seaming
crimping
snap in fasteners
metal stitching
joining thin metallic and non metallic materials eg staples in carboard
seaming
folded two thin pieces of materials (coke can)
crimping
caps are fastened to bottles tubular or flat parts - forcing two parts together
snap fasteners
classic mechanical fastening
automotive bodies and household appliances
