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Joining Flashcards

1
Q

Benefits of welding

A

-provides permanent joint
-welding joint can be stronger that parent materials if a filled is used with superior strength
-most economical usually in terms of material usage and fabrication cost.
-not restricted to factory environment

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2
Q

Drawbacks of welding

A

-most are performed manually so extensive in labor cost
-inherently dangerous as involve high energy
-permanent bond so can be easily dissembled
-welded joint can suffer from quality defects that are difficult to detect

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3
Q

Welding

A

Involves localized joining of two metallic parts at their fraying surfaces

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4
Q

Fusion welding

A

Heat used to melt the base metals.

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5
Q

Why is filler metal often added to molten pool during fusion welding

A

To facilitate process and provide bulk and strength to the welded joint

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6
Q
A
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7
Q

Autogenous weld

A

A fusion welding operation where no filler metal is added

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8
Q

Weld joint

A

Junction of the edges or surfaces of parts that have been joint by welding

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9
Q

What is a butt joint

A

Parts lie in the same place and are joined at their edges

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10
Q

What is a corner joint

A

Parts in a corner joint form a right angle and are are joined at the corner of the angle

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11
Q

What is a lap joint

A

Joint consists of two overlapping parts

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12
Q

What is a tee joint

A

Perpendicular to each other is shape of T

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13
Q

What is an edge joint

A

Parts are parallel with at least one of their edge in common, and the joint is made at the common edge

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14
Q

Arc welding

A

Uses Heat of an electric arc between an electrode and work. This melts metal. Filler usually added

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15
Q

What is an electric arc

A

Discharge of electric current across a gap in a circuit. Usually sustained by plasma

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16
Q

Consumable electrode in arc we,ding

A

Provides source of the filler material

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17
Q

Disadvantage of consumable electrode

A

Must be changed periodically, reducing arc time of welder.

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18
Q

Advantage of consumable electrode

A

It can be continuously fed into the weld pool, avoiding frequent interruptions

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19
Q

Non consumable electrodes in arc welding

A

Resist melting by arc but do gradually deplete

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20
Q

Arc shielding

A

At high temps metals being joint are chemical,y reactive to oxygen, nitrogen and hydrogen in air shich can degrade properties of weld joint. Arc shielding accomplished by covering the electrode tip, arc and molten weld pool with a blanket of gat or flux or both which inhibits exposure to air

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21
Q

Flux

A

A substance used to prevent formation of oxides and other unwanted contaminants or to dissolve the to facilitate removal. In welding, flux melts and becomes liquid slag, covering operation. Slag harden upon cooling and must be removed later by brushing or chipping

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22
Q

Use of flux

A

-protect from atmosphere
-stabilise arc
-reduce splattering

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23
Q

Stick welding or shielded metal arc welding

A

Uses a consumable electrode consisting of a filler metal coated with chemicals that provide flux and shielding. Filler must be close in composition to welded metal. Stick is clamped to an electrode holder connected to a power source

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24
Q

How to select power peremetes for stick welding

A

Depends on electrode type length depth and metals being welded

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25
Disadvantages of shielded metal arc welding
Use of consumable stick- reasons on other card. Electrode length varies in length it affects the resistance heating. Current levels should be maintained so it does not overheat
26
Metal arc melding or metal inert gas welding
Electrode is a consumable bare metal wire, and shielding is accomplished by flooding arc with gas
27
Benefit of metal inert gas welding
Eliminates slag covering on the weld bead. As uses wire instead of stick, has advantage in terms of arc time Higher deposition rates Good versatility
28
Tunsten inert gas welding
Uses non consumable tungsten (high melting point) electrode and an inert gas for shielding
29
Advantages of tunsten inert gas welding
Suited for high quality welds No weld splatter as no filler transferred across arc Little or no post weld cleaning as no flux used
30
When is it best to use brazing and soldering
-when metals have poor weldability -dissimilar metals are joined -intense heat may damage components being joined -geometry of the joint does not lend itself to any weld methods -High strength is not required
31
Adhesive bonding
Uses forces of attachment between a filler material and two closely spaced surfaces to bond part. Adhesive (unlike brazing and soldering) is not metallic
32
Brazing
Filler metal is melted and distributed by capillary action between the fraying surfaces of the metal parts being joined. Brazed joint should be stronger than filler material due to small part clearances and bonding between base and filler
33
Benefits of brazing over welding
-any metal can be joined - certain brazing methods can be performed quickly and consistently for high production rates -some allow multiple joints to be brazed simultaneously -can be applied to join thin walled parts -less heat and power required -problems with heat affected zone reduced -joint area inaccessible by welding can be brazed
34
Disadvantages of brazing
-joint strength less -strength of bond usually less than that of base metal -high service temp may weaken brazed joint -colour of joint may not match base
35
Butt joint for brazing
Provides limited area for brazing, reducing strength. To increase racing areas, mating parts are often scarfed or stepped or otherwise altered.
36
Problem with improving brazing of bytt joint by scarfing it
Problem of maintaining the alignment of parts before and during brazing
37
Lap joints in brazing
Provide relatively large interface area.
38
Benefit of brazing old welding lap joint
Filler metal is bonded to the base pats throughout entire interface area rather than just edges
39
What should the clearance between surfaces be during brazing
Be large enough not to restrict molten filler from flowing. Not too great as capillary action would be reduced so parts with no filler.
40
What does clearance in brazing depend on (know diagram)
Base and filler material, joint configuration and processing conditions
41
How is cleanliness of material before brazing maintenaned
Using fluxes. Also promotes wetting for capillary action between
42
Characteristics needed to quantify as a brazing metal
-melting temp compatible with base metal -surface tension in liquid phase must be low for wet ability -fluidity of molten metal must be high for penetration into interface -must be capable of creating strong enough joint -chemical and physical interactions with base must be avoided
43
Characteristics of a good flux
-low melting point -low viscosity so can be displaced by filler metal -facilitates wetting -protects joint -easy to remove
44
Torch brazing
Flux is applied to the part surface and a torch is used to direct a flame against the work in the vicinity of the joint. Reducing flame typically used to inhibit oxidation. After workpart has been heated to suitable temp, flier wire is added to joint
45
Distadvantage of torch blazing
Needs to be done by skilled workers
46
Application of tool blazing
Repair work
47
Furnace blazing
Uses a furnace to supply heat for brazing
48
Medium vs high production furnace brazing
Medium: component parts and brazing metal are loaded into furnace, heated to temp then cooled and removed. High: use flow through furnace, in which parts are are on a conveyor and transported through heating and cooling systems.
49
Atmosphere for furnace brazing
Neutral or reduced
50
Soldering
A joining process in which a filler metal, called solder, with melting point now exceeding 450 degrees is melted and distributed by capillary action between the fraying surfaces of the metal parts being joined.
51
Soldering vs brazing
Soldering occurs at lower temps so usually weaker bonds
52
Advantages of soldering
-low energy in our -various heating methods available -good electrical and thermal conductivity of joint -capable to make air tight seams -easy to repair and rework
53
Disadvantages of soldering
-low joint strength -possible weakening or melting of joint in elevated temperature service
54
Types of joints that can be soldered
Lap and butt types
55
How are the mechanical joints of sheet metal parts usually soldered
The edges are bent over and interlocked before soldering to increase joint strength
56
How is mechanical strength in a soldered electrical connection often achieved
By making the surface area between metal parts larger or deform the to accomplish a mechanical joint between them
57
Hand soldering (there’s also furnace and fourth soldering)
Performed manually using a hot steam iron. A bit, made of copper, is the working end of the soldering iron. Most are heated by electrical resistance
58
Purpose of a soldering iron
-to deliver heat to the parts being soldered -to melt the solder -to convey molten solder to the joint -to withdraw excess solder
59
Wave soldering
Allows multiple lead wires to be soldered to a print board as it passes over a wave of molten solder. Usually a conveyer moves it through wave soldering equipment
60
Steps of wave soldering
Flux is applied using several methods including foaming, spraying or brushing Preheating to evaporate solvent, activate the flux, and raise the temperature of the assembly. Wave soldering, in which liquid solder is pumped from a molten bath through a slit onto the board
61
How to inhibit build up of excess solder during wave soldering
Board is slightly inclined and special tinning oil is mixed with the molten solder to decrease surface tension
62
Reflow soldering
Solder paste consisting of solder powders in a flux binder is applied fo the spots of board where electrical contacts are to be make between surface mount component and the copper circuit. Components are then placed on paste spots and board is heated to melt solder, forming mechanical and electrical bonds
63
Criteria to define a good adhesive
If failure should occur from excessive stress, it should occur in one of the adherents (parts beings joined) rather than at an interface or within the adhesive itself.
64
What is strength of attachment from adhesive depend on
-chemical bonding in which the adhesive units with the adherents -physical interaction where secondary bonding forces result between the atmosphere of the opposing surface -mechanical interlocking where surface roughness of adherents cause the hardened adhesive to become entangled or trapped in its microscopic surface asperities
65
Conditions for good adhesion mechanism
surfaces must be clean to not interfere with achieving intimate contact -helps when surface aren’t perfectly smooth for interlocking -adhesive in its liquid form must achieve wetting of adherent surface
66
Design considerations for adhesivly bonded joints
joint area should be maximized -adhesive are strongest in shear and tension -joint weakest in cleavage or peeling
67
Advantages of adhesives
-process in applicable to wide variety of materials -parts of different sizes and cross sections can be joined -bonding occurs over entire area of joint - some adhesives are flexible so tolerant of cycle loading and thermal expansion - Low temp curing avoids damage of parts being joined - Sealing as well as binding can be achieved - Joint design is often simple
68
Limitation of adhesion:
Joints are general,g not as strong - adhesive must be compatible with material being joint - -service temperatures are limited - Cleanliness and surface preparation important - Curing time can limit production rate - Inspection of bonded joint is difficult

Manufacturing (12 decks)

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