Objectives
After studying this chapter, you will be able to:
• Name four power supply specifications to which
the welding machine must conform.
• Describe the effects of adjusting open circuit
voltage, arc voltage, slope, and inductance power
supply controls.
• List nine typical maintenance guidelines.
• Discuss both major and auxiliary controls of wire
feeders.
• Discuss maintenance of the wire feed system.
• Tell how to maintain cables and guns.
Setting up the equipment correctly for the GMAW
process is essential. Proper set-up not only guarantees
intended performance standards, but also ensures that
welding work can be done safely without equipment
malfunctions.
Power Supplies
Power supplies are specially designed machines that
produce welding current for melting the welding
electrode at a low voltage. The equipment must be able to
control the operation in the areas of:
• Input voltage (primary voltage).
• Open circuit voltage.
• Output ratings and performance.
• Duty cycle.
The National Electrical Manufacturers’ Association
(NEMA) has established specification EW-1 Electric
Welding Apparatus for control of these areas.
Power Supply Specifications
Each power supply is designed for specific purposes.
Therefore, limitations are established for the proper
operation of the machine. The specification areas for
machines using utility power include:
• Primary power type, voltages, and cycles. This
includes alternating current single- or three-phase
power at 110, 208, 230, or 460 volts and generally
60 hertz (cycles).
• Primary power fusing. The fuse sizes are
specified on the machine and in the instruction
manual for the individual machine. These limits
should never be exceeded.
• Rated welding amperes. The rated welding
amperes are specified by the machine’s manu-
facturer. These amounts of current should not be
exceeded, since the cooling system cannot carry
away the excessive heat generated in the
machine.
• Duty cycle. All welding power supplies are
designed to operate for a specific time period at a
specific load. The design considerations include:
A. Size of internal wiring.
B. Type of internal components.
C. Insulation of internal components.
D. Amount of cooling required.
The duty cycles range from 20% to 100%. They may
be made to a company specification or the NEMA EW-1
specification. This specification establishes that each 10
percentage points represents one minute of operation in a
ten-minute period. Figure 3-1 shows the cycle and time
period for a NEMA-rated machine.
For example, the duty cycle might rate a 150 ampere
welder with a 30% duty cycle to weld at 150 amperes for
three minutes. The machine then has to idle for seven
minutes. This allows internal components to cool
properly before resuming welding.
Machines that are not made to NEMA specifications
have various duty cycles and time periods. The duty cycle
and time periods should be listed on the machine or in the
instruction manual. Never exceed the equipment
manufacturer’s duty cycle requirements; doing so will
cause failure of the machine components.
Equipment Set-up
and Control
3 3 3
CHAPTER
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