mech1641 - w2008 lecture 10 - welded joints i

7/30/2019 MECH1641 - W2008 Lecture 10 - Welded Joints I

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MECH1641 Machine Design II

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Lecture 10: Welded Joints I Direct Shear

Welding Processes

Weldments

Groove Welds and Fillet

Welds

Welded Joints & Symbols

Groove Welds and Fillet

Welds

Direct Shear due to Parallel

& Transverse Loading


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Objectives

After this lecture and associated homework, you willbe able to:

Describe and distinguish between SMAW,GMAW, GTAW, FCAW, and SAW.

Distinguish between the five different types ofwelded joints.

Interpret and use basic welding symbols.

Identify the important dimensions of groove and

fillet welds.Calculate shear stress in loaded weldments, anduse the associated concepts to design welded

joints for direct shear loading.


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Arc Welding Processes

Common arc welding processes include:

SMAW (Shielded Metal Arc

Welding, a.k.a. stick welding.)

GMAW (Gas Metal Arc

Welding, a.k.a. MIG welding.)

GTAW (Gas Tungsten Arc

welding, a.k.a. TIG welding.)

FCAW (Flux-Cored ArcWelding, similar to MIG.)

SAW (Submerged Arc

Welding, similar to MIG.)


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SMAW


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SMAW


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The SMAW Welding Circuit


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GMAW


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GMAW


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GTAW


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GTAW


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C


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FCAW

MECH1641 M hi D i II


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SAW



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SAW



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Review

What is SMAW?

9 Shielded Metal Arc Welding, also known as stick

welding.

What is GMAW?

9 Gas Metal Arc Welding, also known as MIG welding.

What is FCAW?

9 Flux Cored Arc Welding.



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Review

What is SAW?

9 Submerged Arc Welding.

In SAW, what is the arc submerged in?

9 Flux. (SAW is notunder-water welding.)

Which arc welding processes use a wire as the weldingelectrode? (SMAW, GMAW, GTAW, FCAW, SAW)

9 GMAW, FCAW, SAW.

9 TIG filler metal is in the form of 3-ft rod for manual, and

spooled wire for automated TIG.

9SMAW uses flux-coated rods, or electrodes, about 14 inlong.



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Review

Which arc welding processes can be done by robots or

other machines? (SMAW, GMAW, GTAW, FCAW, SAW)

9All of them except SMAW. Stick welding is virtuallyalways manual process.

Which arc welding processes can be done with or without

filler metal?

9 GTAW. All of the others use a consumable electrode,

which melts in the arc and becomes part of the

solidified weld.



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Review

Which arc welding processes do not required shielding

gas? (SMAW, GMAW, GTAW, FCAW, SAW)

9 SMAW, FCAW and SAW all get their shielding from the

flux. GMAW and GTAW use bottled shielding gas.

Which arc welding processes is best for small precisionwelds of exotic metals?

9 GTAW.

Which arc welding processes is best for automated, high

speed, high deposition-rate welding on a horizontal joint?

9 SAW.



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Weldments

Welded assemblies are called weldments.

Load-bearing weldments are most commonly made

from carbon steel, but may also be stainless steel,

aluminum, cast iron, and other alloys.

Weldments used in construction, bridges and

pressure vessels are subject to appropriate welding

codes.



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Weldability of Common Metals

G Good. X not used. F fair.



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The Five Basic Joints



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Juvinall Figure 11.6 (p. 453)

Representative butt joint groove welds: (a) open square double-groove weld, (b)single vee groove weld, (c) double vee groove weld, (d) single-bevel groove weld.

Groove Welds



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Juvinall Figure 11.6 (p. 453)Representative butt joint groove welds: (a) open square double-groove weld, (b) single vee

groove weld, (c) double vee groove weld, (d) single-bevel groove weld.

Fillet Welds



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Identify the Weld Type

Fillet Welds (all around)

Fillet Weld (all around)

Groove Weld



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Welding Symbols: General Notes

The r ef er ence lineis always hor izont al.

The t ailis only used when supplement ar y process inf or mat ion is

included.

The ar r ow point s t o t he j oint .

I t ems below t he r ef er ence line indicat e welding on t he arrowsideof t he j oint .

I t ems above t he r ef er ence line indicat e welding on t he ot hersideof t he j oint .



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ArrowSide and OtherSide

other sidearrow side other sidearrow side

other sidearrow side

other sidearrow side



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Fillet Weld Symbol Review



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Fillet Weld Size

The sizeof a f illet weld means t he leg.

I .e., not t he t hroat , f ace, or anyt hing else.

0.25"

0.5"

Most commonly, t he legsar e equal and only onedimension is needed.

I f t he legs ar e meant t o

be unequal, bot h legsmust be specif ied.

Not e t he f illet weldsymbol always slopes t o

t he r ight, regar dless oft he act ual weldor ient at ion.



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Groove Weld Symbols

Squar e Gr oove Weld

Squar e Gr oove Weld



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Groove Weld Symbols

V Gr oove Weld

Double V Gr oove Weld



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Weld-All-Around Symbol

1/4

or



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Weld Length and Pitch

1/4 2-4



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Examples: Intermittent Fillet Welds



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Examples: Intermittent Fillet Welds



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Weld Symbol Summary



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Activity Problems 1 4

Complete the weld symbols for the welds shown.


A i i P bl S l i


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Activity Problems 1 4 Solutions



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Fillet Weld Terminology

Face

Toe

Leg

Leg

Throat

Toe

Root


G W ld Th t


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Groove Weld Throat

Normally, the throatof a fillet weld is defined asthe shortest distance from the intersection of the

two plates to a line through the ends of the weld

legs.

Alternatively, for concave welds, the throat is the

shortest distance from the intersection of the two

plates to the surface of the bead.

F

hL =

yS

n

=


Fill t W ld L d Di ti


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Fillet Weld Load Direction

Parallel Loading

Transverse Loading


Fillet Weld Throat


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Fillet Weld Throat

Normally, the throatof a fillet weld is defined as the

shortest distance from the intersection of the two

plates to a line through the ends of the weld legs.

Alternatively, for concave welds, tis the shortest

distance from the intersection of the two plates to the

surface of the bead.


Fillet Weld Size


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Fillet Weld Size

0.707t h=

The sizeof a weld is given as the leg length h.

The throat is t.

The length of a weld is L.

2 2 2

22 2

2

h t t

hh t t t

= +

= = =


Weld Direct Shear Stresses


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Weld Direct Shear Stresses

Both parallel and transverse external loadsare considered to be carried by shear forceson the throat area of the weld.

The shear area is then the t x L rectanglewhere tis the weld throat and L is the weld

length.

0.707shear

F F F

A tL hL = = =


A Closer Look


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A Closer Look

Our assumption that the external

load is carried by shear forces on

the throat area is true for parallel

loads.

It is a useful, conservative

simplification for transverse loads.

0.707

F

hL =


Welding Filler Metal Strength


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Welding Filler Metal Strength

Welding electrodes (filler metal) has been standardized by the AWS.

The E60 and E70 series electrodes are designated E60xx and E70xx,where xx is a code for welding process details, and the 60 and 70mean 60 and 70 ksi tensile strength of the weld metal, respectively.

The yield strengths of the metals are shown below. The yieldstrength in shear is calculated using the Distortion energy theory, i.e.Ssy=0.577Sy.

Note that in the absence of yield strength data, you can estimate thatthe yield strength is 12 ksi less than the tensile strength for E60 anE70 electrodes.


Problem 6


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Problem 6

The welded plates shown are 12 mm thick,

made of steel with Sy=350 MPa. The 6-mm

fillet welds are 50 mm long, were made using

E6011 electrodes. What maximum load can

be carried by this joint with a safety factor of

3?

Ref. Juvinall, Sample Problem 11.1

3 3 6

6

2

Find given: 50 50 10 ; 6 6 10 ; 345 345 10 ; 30.577 0.577

0.7072 2 0.707

0.577 0.577 2 0.707Combining,

2 0.707

0.577 345 10 2 0.707 6 1

1 1

y

ys y y

y y

F L mm m h mm m S MPa Pa nS S S

nn

F Ft h

t L h L

S S h LFF

n h L n

NF

m

= = = = = = =

= = =

= = =

= =

=

3 30 50 10 128.1

1 1 3

m mF kN

=


Problem 7


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Problem 7

The welded plates shown are in thick, made

of steel with Sy=120 ksi. The in fillet welds

are 2.5 in mm long, and were made with E120xx

electrodes. What safety factor results if the

applied load is 25,000 lbf?

2

Find given: 2.5 ; 0.25 ; 120 ; 25,000

0.577 0.577

0.7072 2 0.707

0.577 0.577 2 0.707Combining,

2 0.707

120,0000.577 2 0.707 0.25 2.5

1 1 1 1

y f

ys y y

y y

f

n L in h in S ksi F lb

S S Sn

n

F Ft h

t L h L

S S h LFn

n h L F

lb in inn

in

= = = =

= = =

= = =

= =

=

12.45

25,000 fn

lb =


Problem 8


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Problem 8

A joint similar to the one from the previousquestion must carry a shear load24 kip.The welding electrode is E7018, and thetwo welds will be 4 in long. What size

welds are required to provide a safetyfactor of 2 against static yielding?

2

Find given 4 ; 70 ; 2

0.577 0.577

0.7072 2 0.707

0.577

Combining, 2 0.707 0.577 2 0.707

24,000 2 1 1 1 10.21

1 1 0.577 70,000 2 .707 4

Comment:Rou

y

ys y y

y

y

f

f

h L in S ksi n

S S S

n n

F Ft h

t L h L

S F F n

hn h L S L

lb inh h in

lb in

= = =

= = =

= = =

= =

= =

1

4nd up to a " weld.


Closing Notes & Homework


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Closing Notes & Homework

Read Juvinall, Sections 11.3-11.4.

Do problems 11.1, 11.2, 11.6, 11.7, 11.12.

Create a spreadsheet to analyze fillet weld

joints, and use it to check your answers for

problems 11.1, 11.2, 11.12.I.e., calculate Ssy, t, , n given Sy, F, L, h.

Make two versions of the spreadsheet, one for

SI, one for US units.

Test 1 (20%) is on Friday March 7.

(Rescheduled from February 22.)

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