S. K. Gupta,
B.E., C.E., FIE.,
FIIW., MISNT., MAE., MITD.
PARTS OF THE ARTICLE (Each part will be published in different WeldFab Tech Times Issues.)
INTRODUCTION
Welding is used extensively as a major process in fabrication and manufacturing products ranging from Nano components to massive steel structures. Since the inception of shielded arc welding process in 1907, a proliferation of welding processes and related technologies have been developed now covering a wide range of materials, products and applications in practice.
At present, SMAW, GMAW,FCAW, GTAW, SAW, PAW, FSW, EBW , Resistance Welding etc are considered to be the basic processes, based on which specialized branch processes have been developed and effectively applied.
It is imperative to mention here that along with the process, development, manufacture and application of welding equipment and consumables have multiplied astronomically.
In order to keep up the Quality Standards of the Process and products a large number of Destructive, Nondestructive, Analytical and Statistical Process Control Techniques are in regular practice.
International Standards, Codes and Specifications in conjunction of different National Specifications have been formulated on every aspects of Process, Equipment, Consumables, Operators, Operation and Products.
All the above mentioned areas covering Welding have generated vast number of Information in the form of Data and also continuing to generate equal volume of it every period of time. It is not possible for any individual or even any manufacturing organization to store, access, retrieve and apply useful data to the best advantage. But, individually if we can identify our needs, store methodically and systematically welding data used in industries, updating these to the current standards and use Computer Software as the Welding Management System benefits will show all round Production – Operation Management especially where Welding is used as the main Manufacturing Process.
PARTS OF THE ARTICLE
In the process of writing and compiling the Data for the Article it is observed that it has become a bit lengthy. Dividing the Article into FIVE Parts will be more appropriate and as such the following Parts will constitute the Article.
Part – I deals with the Framework of Data Based Management system outlined very briefly.
Part – II deals with the Materials used in fabrication and related data.
Part – III provides details of the Data content to formation of WPS,PQR and WPQ.
Part – IV deals with the data on Welding Processes, Equipment and Consumables.
Part – V illustrates and explains how the Welding Management Software works.
WELDING DATA MANAGEMENT. PART – IV B – GMAW
GAS METAL ARC WELDING PROCESS
GMAW PROCESS
GMAW Circuit
This is the basic equipment used for a typical GMAW, semiautomatic setup. Included are:
- A welding machine which provides welding power
- A wire feeder which controls the supply of wire to the gun
- A supply of electrode wire
- A welding gun, which directs the electrode wire into the joint
- A shielding gas cylinder, which provides a supply of shielding gas to the arc area.
The reason for the term “circuit” is that there is an electrical circuit from the welding machine through the electrode lead to the wire feeder, from the wire feeder to the gun via an electrode lead, through the gun to the wire, then to the arc, through the arc to the workpiece, and back to the welding machine via the work lead.
Welding Machine
With the many types of welding machines available, certain considerations must me made in order to fit them right machine to the job:
- Mode of transfer needed? (Short circuit, Globular Transfer, Spray Arc Transfer)
- Output needed? (Voltage and Amperage)
- Duty cycle needed? (How often must the machine cool down?)
- Multi−process capability needed? (Changeable for constant voltage and constant
amperage)
- Remote control needed? (Voltage can be adjusted some distance away from the machine)
- Portability needed?
- Primary power available? (115V, 230V, 380V)
Power Supply
Almost all GMAW welding is done with direct current (DC) reverse polarity. The primary source is normally either 230 V or 460 V AC current input power, which is changed by a rectifier unit to secondary circuit DC. The power source should be a constant voltage welding machine (CV). This contrasts with SMAW welding which use constant current (CC) power supplies.
A GMAW welding power supply provides a relatively constant voltage to the arc during welding. This voltage determines the arc length dependent to the current (amperage) being used. The welding current output depends on the wire−feed−speed, while the voltage output is adjusted by a voltage regulator.
When there is a sudden change in wire feed speed, or a momentary change in arc length, the power supply abruptly increases or decreases the current depending on the arc length change.
A 450mpi is a high performance constant voltage (CV) and constant current (CC) inverter power source designed to provide multi-process welding capabilities with dependability and ease of use.
The power source should operate on a 60% duty cycle with a load of 450 amperes at 34 V dc (with 3-phase input). Duty cycle is defined as the ratio of operating time to total time. Ratings are based on a 10- minute cycle. The 60% duty cycle rating means that the
450 ampere, 34 volt rated load can be applied for a total of 6 minutes and shut off for a total of 4 minutes in a 10- minute period. If the welding current (or voltage) is reduced, the duty cycle increases. Conversely, if the welding current (or voltage) is increased, the duty cycle will decrease.
TABLE – I. RATED OUTPUT OF A POWER SOURCE
| 100% Duty Cycle | (3 phase input) | 300 A | @ 32 V dc |
| 100% Duty Cycle | (1 phase input) | 225 A | @ 29 V dc |
| 60% Duty cycle | (3 phase input) | 450 A | @ 34 V dc |
| Open-circuit Voltage (max) 70 V dc | |||
TABLE – II. Operational Features of Conventional GMAW Power Sources
| Type of power
source |
How to adjust
amperage and voltage |
Operational feature |
| 1. Thyristor type
|
(a) Welding current and arc voltage can be adjusted by controlling the knobs of the remote controller.
(b) Many brands use only the A-V individual control, but some can also facilitate the -V automatic control by shifting the switch. (c) Many models for high welding currents facilitate the crater treatment control.
|
a) The remote controller facilitates continuous, non-tapped adjustment of welding current and arc voltage.
(b) Welding current and arc voltage can be changed while the arc is generated. (c) Welding parameters can be set and changed by external electrical signals. This feature is suitable for automatic welding in uses of customized
|
| Tapped transformer
type |
(a) Arc voltage can be adjusted by controlling the tap of the power source.
(b) Welding current can be adjusted by controlling the adjusting knob. (c) Many models use the A-V individual control, and some |
(a) Tapped adjustment of arc voltage is an easier operation.
(b) Fine adjustment of arc voltage depends on the number of taps. (c) Welding parameters cannot be changed by external electrical signals and by the tap and knob while the arc is generated. |
| 3. Sliding transformer
type |
a) With many models using the A-V automatic control, welding current can be adjusted by controlling the lever of the power source.
(b) Some models facilitate individual adjustment of welding current and arc voltage by using the lever for voltage and the knob for current of the power source. |
a) Turning the lever facilitates
continuous adjustment of the output. (b) It is difficult to change welding parameters by external electrical signals. This is why most of the power sources are not equipped with a remote controller |
FIG. II,. WIRE FEEDER
- This is the spool of wire that feeds the welder. The wire 1. Wire being fed through the rollers comes off the spool, is pushed through the feeder and 2. Tensioning adjustment travels out to the welding torch.
- These are the rollers that pull the wire off the spool and send it out to the welding torch
FIG. III. GMAW GUN
(1) Torch handle,
(2) Molded phenolic dielectric (shown in white) and threaded metal nut insert (yellow),
(3) Shielding gas diffuser,
(4) Contact tip,
(5) Nozzle output face
FIG. IV WELDING TORCH
TABLE – III GUN NOZZLE SIZE & GAS FLOW
TABLE – VII, GAS MIX. & WELD PARAMETERS
TABLE – IX. GAS MIX, WELD PARAMETERS FOR CARBON STEEL AND STAINLESS STEELS
