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84 Cards in this Set

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Joining
Welding, brazing, soldering or adhesive bonding; permant joint between parts
Assembly

mechanical methods of fastening parts together; could allow for dissassembly

Fusion Welding

Metal is melted to join parts together


-Arc Welding


-Resistance Welding


-Oxyfuel Gas Welding

Arc Welding
a pool of molten material is formed near an electrode tip

Resistance Welding
uses friction or resistance to melt the metal and form a weld
Solid State Welding
uses pressure sometimes with low heat to weld with no melting
Consumable Arc Welding
electrodes made of a filler material are consumed during the process
Non-consumable Arc Welding
electrodes are not consumed and a filler material must be added separately
Arc Shielding

Protecting the arc from the surrounding air to prevent property degradation


-Sheilding Gases


-Flux

Flux

a substance that prevents the formation of oxides and other contaminants, or dissolves them

Shielded Metal Arc Welding (SMAW)

uses a consumable electrode consisting of a filler metal rod coated with chemicals that provide flux and shielding

Gas Metal Arc Welding (GMAW)
uses a consumable bear metal wire as electrode with shielding by flooding arc with a gas
Flux Cored Arc Welding
core provides ingredients for shielding but outside gas can also be used.
Types of Resistance Welding

Seam Welding


Roll Welding


Explosive Welding


Friction Welding

Brazing
filler metal is melted and distributed by capillary action between faying surfaces (Tm>450C)
Soldering
filler metal is melted and distributed by capillary action between faying surfaces (Tm<450C)
Sheet Metal Working

Forming and related operations performed on metal sheets, strips, and coils; also called pressworking because these operations are performed on presses

Flow Curve For Plastic Region

Stress=K(strain)^n s=KE^n


k=strength coefficient


n=strain hardening coefficient

Average Flow Stress

Relationship of K and n as T increases
K and n decrease as T increases
Cold Working

Performed at <0.3 Tm


-Better Surface Finish, accuracy, and shape


-Grain flow can cause desirable properties in product

Warm Working

0.3Tm


-Lower forces and power than cold working


-No need for annealing

T_recrystallization
about 1/2 Tm, the temperature at which a melted metal reforms crystals
Hot Working

Deformation at temperatures above T_recrystallization


-allows for substantial plastic deformation


-low strength


-low strain hardening

Friction in Metal Forming

Is undesirable because:


-Metal flow is reduced


-Forces and power are increased


-Tools wear faster

Metalworking lubricants

reduce the harmful effects of friction


-better surface finish


-remove heat from tooling

Forging
Deformation process in which work is compressed between two dies
Hot/Warm Forging advantages
reduction in strength and increase in ductility
Cold Forging advantage
increased strength due to strain hardening
Impact Forging
uses a forge hammer, applies an impact force
Press Forging
applies a gradual force
Open Die Forging
work is compressed between two flat dies, allowing metal to flow laterally
Impression Die Forging

die contains cavity or impression that is imparted to workpart


-Metal flow is constrained so that a flash is created

Flashless Forging (Closed die forging)
workpart is completely constrained in die
True strain
E=ln(h0/h)
Barreling
Occurs in open die forging with friction
Importance of the Flash
As flash forms, friction resists continued metal flow into gap, constraining metal to fill die cavity
Flash
formed by metal that flows beyond die cavity into small gap between die plates
Steps of Impression Die Forging
1)Redistribute metal for more uniform deformation2)Achieve desired metallurgical structure3)Bring the part to final geometry
Advantages of Impression Die Forging

High production rates


Greater Strength


Favorable Grain Orientation

Upset Forging

formas a head on a bolt or similar hardware item
Swaging

-rotating dies that hammer a workpiece radially inward to taper as the piece is fed into the dies


-used to reduce diameter of tube or solid rod stock

Radial Forging
Workpiece rotates while dies remain in a fixed orientation as they hammer the work
Rolling

-Pull the work into the gap between workpart and rolls


-Squeeze to reduce the cross section of the work

Flat Rolling
Used to reduce thickness of a rectangular cross section
Shape Rolling
Square cross section is formed into shape such as an I beam

Hot Rolling
can achieve significant deformation
Cold Rolling
produces sheet and plate stock
Draft

Amount of thickness reduction


d=t0-tf

Reduction

draft expressed as a fraction of starting stock thickness


r=d/t0

Shape Rolling

Work is deformed into a contoured cross section rather than a flat


-accomplished by passing work through rolls that have the reverse of desired shape

Thread Rolling
Uses rolling dies to put grooves in screws and bolts
Ring Rolling

a thick walled ring is compressed, causing the diameter of the ring to enlarge


-hot wok for large rings, cold work for small rings

Extrusion
Compression forming process where metal is forced to flow through a die opening to produce cross-sectional shape (toothpaste)
Direct Extrusion

Ram approaches die opening, a small portion of billet remains that cannot be forced through the die; called the butt and must be separated afterwards


-Can use a mandrel to produce hollow or semi hollow shapes

Indirect Extrusion
A ram forces itself through a stationary work billet, forming a desired shape and cross section
Hot Extrusion
reduces strength and increases ductility of the metal, permitting more size reductions and complex shapes; heated above T_recrysal

Cold Extrusion
Used to produce discrete parts

Extrusion Ratio/Reduction Ratio


True Strain of Extrusion

rx=A0/Af


e=ln(rx)=ln(A0/Af)

Wire and Bar Drawing
Work is pulled through die in drawing rather than pushed as in extrusion

Area Reduction in drawing


True Drawing Strain

r=(A0-Af)/A0


E=ln(1/1-r)

Practical Drawing Force

F=AfSd


Sd is the exit stress

Bar Drawing
Single-draft operation: the stock us pulled through one die opening

Wire Drawing


Continuous drawing machines consisting of multiple draw dies


Back Relief Exit Zone
provided with a back relief angle of about 30 degrees
Sheet Drawing
Sheet metal forming to make cup shaped, box shaped or other complex-curved, hollow-shaped parts
Clearance in Drawing
c=1.1t
Drawing Ratio

DR=Db/Dp


Db=blank diameter


Dp=Punch Diamter


DR<2.0

Drawing Reduction
r=(Db-Dp)/Db
Punch and Die
Tooling to perform cutting bending and drawing
Stamping Press
machine tool that performs most sheet metal operations

Stampings
Sheet metal products
Blanking
sheet metal cutting to separate a piece from surrounding stock
Punching
Similar to blanking except on a smaller scale, piece is not used, but the outer piece is
Clearance in Sheet Metal Cutting

Range between 4-8%


c=at


a=allowance, t=thickness of stock

Cutting Forces

F=StL


S=Shear Strength, L =length of edge

Sheet Metal Bending
Metal on inside of a neutral plane is compressed while metal on outside is stretched
Bend Allowance Formula

Ab=2pi(alpha/360)(R+(K_ba)(t)


alpha=bend angle


Kba=factor to estimate stretching (.33 if R<2t, .5 if R>2t)

Springback

When bending pressure is removed, elastic energy remains in bent part, causing it to recover partially toward its original shape


SB=(alpha-alphab)/alphab


alpha b=bent angle, alpha=springback angle

Bending Force

F=(KTSwt^2)/D


TS=tensile strength, w=width, K=1.33/.33 for v/edge bending

Roll Bending
Large Metal Sheets and Plates are formed into curved sections using rolls
Welding Defects
1. Cracks, 2. Cavities, 3. Solid Inclusions, 4. Incomplete fusion, 5. imperfect shape or contour of cross section
Relationship of K to stress and strain
lnK=ln(sigma)-nln(epsilon)
Drawing Defects
1. Wrinkling, 2. Tearing, 3. Earing, 4. Surface Scratches