8/13/2019 152145273 Welding Manual

1/17

WeldsWelds

Lecture 33Lecture 33

Engineering 473Engineering 473

Machine DesignMachine Design

8/13/2019 152145273 Welding Manual

2/17

8/13/2019 152145273 Welding Manual

3/17

Ancient Welding ProcessesAncient Welding Processes

Arc Welding Instructions for the Beginner, Lincoln Arc Welding Foundation, Fig. 6

Welding was using

in ancient (3,000years ago) times by

pouring molten

metal into a cast

located on another

metal part. Sand

casting is still used

today.

Sand Cast

8/13/2019 152145273 Welding Manual

4/17

Modern Welding ProcessesModern Welding Processes

OxyOxy--acetyleneacetylene

Gas WeldingGas Welding

Arc WeldingArc Welding

Metal Inert GasMetal Inert Gas

(MIG)(MIG)

oror

Gas Metal ArcGas Metal Arc

WeldingWelding

(GMAW)(GMAW)

Tungsten InertTungsten Inert

Gas (TIG)Gas (TIG)

ororGas TungstenGas Tungsten

Arc WeldingArc Welding

(GTAW)(GTAW)

There are many welding

processes.

The ability to produce pure

oxygen @1900 was

important to the

development of welding.

8/13/2019 152145273 Welding Manual

5/17

Arc WeldingArc Welding

Arc Welding Instructions for the Beginner, Lincoln Arc Welding Foundation, Fig. 9&13

Electric current flowing through a

high resistance air gap generates anintense arc with temperatures ranging

from 6,000 to 10,000 oF.

Arc welding is the

most commonmethod used with

structural steel

welding.

8/13/2019 152145273 Welding Manual

6/17

MIG or GMAWMIG or GMAWArgon and CO2 are

common inert gases used

in the MIG process. Amixture of 75% Argon

and 25% CO2 (C-25) is

also very common.

www.hobartbrothers.com

Small commercial

MIG welder.

Continuously fed filler wire makes MIG welding suited to high

volume, machine assisted industrial welding applications.Haynes Welding Manual, 10445(2110)

8/13/2019 152145273 Welding Manual

7/17

TIG or GTAWTIG or GTAWThe shielding gas in the TIG

process is Helium. This gives

rise to the term heli-arcwelding.

The TIG process is

considered the most

precise, most controllable,

and cleanest method of

welding.

The TIG process can be used to make welds of great strength

and quality in thin, light, and dissimilar materials.Haynes Welding Manual, 10445(2110)

8/13/2019 152145273 Welding Manual

8/17

Soldering and BrazingSoldering and Brazing

Soldering and brazing are common methods of

joining two metals.

Soldering and brazing are not welding processes

because they do not melt the parent material.

In soldering and brazing, the parent metal is heated

and the the filler metal is melted into the joint where

it cools.

Lead based filler metals are used in soldering and

brass based filler metals are used in brazing.

8/13/2019 152145273 Welding Manual

9/17

Filler MetalsFiller Metals

Filler metal rods and wires are designated

by a system established by the American

Welding Society (AWS).

AWS Designation SystemAWS Designation System

E70XX

Electrode

Minimum yield strengthof the completed weld

(ksi).

Type of process

Position of the weld

The static strength of a good weld is

often higher than the base material.

8/13/2019 152145273 Welding Manual

10/17

Residual StressesResidual Stresses The uneven heating and cooling in welding operations gives

rise to significant residual stresses in the vicinity of the weld.

The residual stresses may distort the part.

The residual stresses and discontinuities in a weld have a

significant influence on the fatigue life of a part.

The fatigue life of a weld is often less than the base material.

Residual stresses are influenced by the % carbon found inthe material being joined.

Residual stresses may be removed by annealing.

8/13/2019 152145273 Welding Manual

11/17

Butt WeldsButt Welds

t

fs

yp

N

S

LtP

Design CriteriaDesign Criteria

8/13/2019 152145273 Welding Manual

12/17

Welds Loaded in ShearWelds Loaded in Shear

Real Surface

Theoretical

Surface

Potential

Shear Failure

Planes

h

Weld Throat

Lh0.7071

Lh45cosAs

=

=

Deutschman, Fig. 17-5

Fillet Weld GeometryFillet Weld Geometry

8/13/2019 152145273 Welding Manual

13/17

Welds Loaded in ShearWelds Loaded in Shear

(Continued)(Continued)

Lh0.7071

Lh45cosAs

=

=

ytys

fs

ys

s

0.6SS

N

S

2A

P

=

Design CriteriaDesign Criteria

two shearplanes

Deutschman, Fig. 17-5

Weld Shear AreaWeld Shear Area

8/13/2019 152145273 Welding Manual

14/17

8/13/2019 152145273 Welding Manual

15/17

8/13/2019 152145273 Welding Manual

16/17

AssignmentAssignment

Read sections 9-1 through 9-3 in Shigley.

The figure shows ahorizontal steel bar, 3/8 in

thick, loaded in tension and

welded to a vertical support.

Find the load F that will

cause a shear stress in the

welds of 20 kpsi.

8/13/2019 152145273 Welding Manual

17/17

AssignmentAssignment

(Continued)(Continued)

A 5/16 in steel bar is welded toa vertical support as shown.

What is the shear stress in the

welds if the force is F=32 kip?