Question & Answer

What are the two joint types most commonly used in brazing?

Under what circumstances would brazing or soldering be preferred over welding?

What is the technical difference between brazing and soldering?

How do brazing and soldering differ from the solid-state welding processes?

How do brazing and soldering differ from the fusion-welding processes?

An electron-beam welding operation uses the following process parameters: accelerating voltage =

25 kV, beam current = 100 milliamp, and the circular area on which the beam is focused has a

diameter = 0.020 in. If the heat transfer factor = 90%, determine the average power density in the

area in Btu/sec in².

An electron-beam welding operation will join two pieces of steel plate together. The plates are 1.00

in thick. The unit melting energy is 125 Btu/in3. The diameter of the work area focus of the beam is

0.060 in, hence the width of the weld will be 0.060 in. The accelerating voltage is 30 kV and the

beam current is 35 milliamp. The heat transfer factor is 0.70 and the melting factor is 0.55. If the

beam moves at a speed of 50 in/min, will the beam penetrate the full thickness of the plates?

An electron-beam welding operation is to be accomplished to butt weld two sheet-metal parts that

are 3.0 mm thick. The unit melting energy = 5.0 J/mm³. The weld joint is to be 0.35 mm wide, so

that the cross section of the fused metal is 0.35 mm by 3.0 mm. If accelerating voltage = 25 kV,

beam current = 30 milliamp, heat transfer factor f1 = 0.85, and melting factor f2 = 0.75, determine

the travel speed at which this weld can be made along the seam

The voltage in an EBW operation is 45 kV. The beam current is 60 milliamp. The electron beam is

focused on a circular area that is 0.25 mm in diameter. The heat transfer factor is 0.87. Calculate the

average power density in the area in watt/mm²

An oxyacetylene torch supplies 8.5 ft³ of acetylene per hour and an equal volume rate of oxygen for

an OAW operation on 1/4 in steel. Heat generated by combustion is transferred to the work surface

with a heat transfer factor of 0.3. If 80% of the heat from the flame is concentrated in a circular area

on the work surface whose diameter = 0.40 in, find: (a) rate of heat liberated during combustion, (b)

rate of heat transferred to the work surface, and (c) average power density in the circular area.

Suppose in Example 30.3 in the text that the fuel used in the welding operation is MAPP instead of

acetylene, and the proportion of heat concentrated in the 9 mm circle is 60% instead of 75 %.

Compute (a) rate of heat liberated during combustion, (b) rate of heat transferred to the work

surface, and (c) average power density in the circular area.

An experimental power source for spot welding is designed to deliver current as a ramp function of

time: I = 100,000 t, where I = amp and t = sec. At the end of the power-on time, the current is

stopped abruptly. The sheet metal being spot welded is low carbon steel whose unit melting energy

= 10 J/mm³. The resistance R = 85 micro-ohms. The desired weld nugget diameter = 4 mm and

thickness = 2 mm (assume a disc-shaped nugget). It is assumed that 1/4 of the energy generated

from the power source will be used to form the weld nugget. Determine the power-on time the

current must be applied in order to perform this spot-welding operation.

Resistance projection welding is used to simultaneously weld two thin, steel plates together at four

locations. One of the pieces of steel plate is preformed with projections that have a diameter of 0.25

in and a height of 0.20 in. The duration of current flow during the weld is 0.30 sec and all four

projections are welded simultaneously. The plate steel has a unit melting energy of 140 Btu/in3 and

a resistance between plates of 90.0 micro-ohms. Experience has shown that 55% of the heat is

dissipated by the metal and 45% melts the weld nugget. Assume the volume of the nuggets will be

twice the volume of the projections because metal from both plates is melted. How much current is

required for the process?

Suppose in the previous problem that a roll spot-welding operation is performed instead of seam

welding. The interface resistance increases to 100 micro-ohms, and the center-to-center separation

between weld nuggets is 25 mm. Given the conditions from the previous problem, with the changes

noted here, determine (a) the proportion of energy generated that goes into the formation of each

weld nugget, and (b) the rotational speed of the electrode wheels. (c) At this higher rotational speed,

how much does the wheel move during the current on-time, and might this have the effect of

elongating the weld nugget (making it elliptical rather than round)?

A resistance seam-welding operation is performed on two pieces of 2.5-mm-thick austenitic

stainless steel to fabricate a container. The weld current in the operation is 10,000 amps, the weld

duration = 0.3 sec, and the resistance at the interface is 75 micro-ohms. Continuous motion welding

is used, with 200-mm-diameter electrode wheels. The individual weld nuggets formed in this

RSEW operation have diameter = 6 mm and thickness = 3 mm (assume the weld nuggets are

disc-shaped). These weld nuggets must be contiguous to form a sealed seam. The power unit

driving the process requires an off-time between spot welds of 1.0 s. Given these conditions,

determine (a) the unit melting energy of stainless steel using the methods of the previous chapter,

(b) the proportion of energy generated that goes into the formation of each weld nugget, and (c) the

rotational speed of the electrode wheels

A resistance spot-welding operation is performed on two pieces of 0.040 in thick sheet steel (low

carbon). The unit melting energy for steel = 150 Btu/in³. Process parameters are: current = 9500 A

and time duration = 0.17 sec. This results in a weld nugget of diameter = 0.19 in and thickness =

0.060 in. Assume the resistance = 100 micro-ohms. Determine (a) the average power density in the

interface area defined by the weld nugget, and (b) the proportion of energy generated that went into

formation of the weld nugget.

The unit melting energy for a certain sheet metal is 9.5 J/mm3. The thickness of each of the two

sheets to be spot welded is 3.5 mm. To achieve required strength, it is desired to form a weld nugget

that is 5.5 mm in diameter and 5.0 mm thick. The weld duration will be set at 0.3 sec. If it is

assumed that the electrical resistance between the surfaces is 140 micro-ohms, and that only

one-third of the electrical energy generated will be used to form the weld nugget (the rest being

dissipated), determine the minimum current level required in this operation.

An RSW operation is used to join two pieces of sheet steel having a unit melting energy of 130

Btu/in³. The sheet steel has a thickness of 1/8 in. The weld duration will be set at 0.25 sec with a

current of 11,000 amp. Based on the electrode diameter, the weld nugget will have a diameter of

0.30 in. Experience has shown that 40% of the supplied heat melts the nugget and the rest is

dissipated by the metal. If the electrical resistance between the surfaces is 130 micro-ohms, what is

the thickness of the weld nugget assuming it has a uniform thickness?

An RSW operation is used to make a series of spot welds between two pieces of aluminum, each

2.0 mm thick. The unit melting energy for aluminum = 2.90 J/mm3. Welding current = 6,000 amps,

and time duration = 0.15 sec. Assume that the resistance = 75 micro-ohms. The resulting weld

nugget measures 5.0 mm in diameter by 2.5 mm thick. How much of the total energy generated is

used to form the weld nugget?

A continuous weld is to be made around the circumference of a round steel tube of diameter = 6.0

ft, using a submerged arc welding operation under automatic control at a voltage of 25 volts and

current of 300 amps. The tube is slowly rotated under a stationary welding head. The heat transfer

factor for SAW is = 0.95 and the assumed melting factor = 0.7. The cross-sectional area of the weld

bead is 0.12 in2. If the unit melting energy for the steel = 150 Btu/in³, determine (a) the rotational

speed of the tube and (b) the time required to complete the weld.

A gas metal arc-welding test is performed to determine the value of melting factor f² for a certain

metal and operation. The welding voltage = 25 volts, current = 125 amps, and heat transfer factor is

assumed to be = 0.90, a typical value for GMAW. The rate at which the filler metal is added to the

weld is 0.50 in³ per minute, and measurements indicate that the final weld bead consists of 57%

filler metal and 43% base metal. The unit melting energy for the metal is known to be 75 Btu/in³.

(a) Find the melting factor. (b) What is the travel speed if the cross-sectional area of the weld bead =

0.05 in2?

A flux-cored arc-welding process is used to join two low alloy steel plates at a 90° angle using an

outside fillet weld. The steel plates are ½ in thick. The weld bead consists of 55% metal from the

electrode and the remaining 45% from the steel plates. The melting factor of the steel is 0.65 and

the heat transfer factor is 0.90. The welding current is 75 amps and the voltage is 16 volts. The

velocity of the welding head is 40 in/min. The diameter of the electrode is 0.10 in. There is a core of

flux running through the center of the electrode that has a diameter of 0.05 in and contains flux

(compounds that do not become part of the weld bead). (a) What is the cross-sectional area of the

weld bead? (b) How fast must the electrode be fed into the workpiece?

A flux-cored arc-welding operation is performed to butt weld two austenitic stainless steel plates

together. The welding voltage is 21 volts and the current is 185 amps. The cross-sectional area of

the weld seam = 75 mm² and the melting factor of the stainless steel is assumed to be 0.60. Using

tabular data and equations given in this and the preceding chapter, determine the likely value for

travel speed v in the operation.

A GTAW operation is performed on low carbon steel, whose unit melting energy is 10.3 J/mm3.

The welding voltage is 22 volts and the current is 135 amps. The heat transfer factor is 0.7 and the

melting factor is 0.65. If filler metal wire of 3.5 mm diameter is added to the operation, the final

weld bead is composed of 60% volume of filler and 40% volume base metal. If the travel speed in

the operation is 5 mm/sec, determine (a) cross-sectional area of the weld bead, and (b) the feed rate

(mm/sec) at which the filler wire must be supplied.

A shielded metal arc-welding operation is performed on steel at a voltage = 30 volts and a current =

225 amps. The heat transfer factor = 0.85 and melting factor = 0.75. The unit melting energy for

steel = 10.2 J/mm3. Determine (a) the rate of heat generation at the weld and (b) the volume rate of

metal welded.