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Flashcards in Lec16 Deck (28)
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1

Brazing is

process in which filler metal is placed between surfaces to be joined - used as glue

2

Brazing filler metal

melts about 450 C BELOW the melting temp of metals to be joined

3

Strength of brazed joint depends on

joint design
adhesion at the interface
filler metal

4

Preparing of brazing surfaecs

chemically or mechanically cleaned to ensure full capillary action

5

Brazing

temp raised enough to melt the filler metal but not the workpiece
molten metal fills the closely fitted space by capillary action

6

Braze welding

filler metal is deposited at the joint with technique similar to oxyfuel gas welding

7

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

8

Braze joints of desired strength must

have sufficient area of joint to form bond

9

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)

10

Shapes brazing is good for

thinner and more complex assemblies wont melt through materal

11

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

12

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

13

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

14

Soldering

filler metal called solder relatively low temps 450C
solder fills joint by capillary action
high wetting capability and low surface tension

15

soldering heat source

soldering irons torches ovens

16

Brazing vs soldering

solder temps relaively low - limited use at elevated temps - solder filler metals at less than 450 C

17

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

18

applications of soldering

electronis industry
electrial coupling
gas/airtight seals
aluminium radiators in automotive industry

19

Mechanical fastening

no fusion or adhesion of surface
mechanical interlocking and interference of surfaces brought about by clamping forces

20

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

21

Choose mechanical fastening based on

cost - cheap
appearance - is it gonna be okay with additional fixing
need for future disassembly - quickly and easily

22

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

23

Adv of mechanical fastening

ease of manufacture
ease of assembly and transportation
easy of disassembly maintenance repair
ease of design - movable joints
low cost

24

Mechanical fastening types

metal stitching or stapling
seaming
crimping
snap in fasteners

25

metal stitching

joining thin metallic and non metallic materials eg staples in carboard

26

seaming

folded two thin pieces of materials (coke can)

27

crimping

caps are fastened to bottles tubular or flat parts - forcing two parts together

28

snap fasteners

classic mechanical fastening
automotive bodies and household appliances