Title: AWS New Welding Technologies The Key to Higher Productivity Controlled Short Circuit GMAW
1AWS New Welding TechnologiesThe Key to Higher
ProductivityControlled Short Circuit GMAW
Root Pass Pipe Weldling
- Jim Cuhel
- Welding Engineer
- Miller Electric Mfg. Co.
2Short Circuit Transfer
3Taking Control
Short Arc
RMD
4What Is RMD?
300
250
200
Current (amps)
150
100
50
0
300
301.5
303
304.5
306
307.5
309
310.5
Time (Ms)
5Power Density in the Necking Region
Wire
Molten Wire
Necking Region
dl
Puddle
6Short Circuit Clears (standard MIG)
Detect Clearing Event
Power in Necking Region
Necking Begins
Reduce Current (hence, power)
Short Circuit Clears at Much Lower Power Level
(RMD)
Time
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8Heat Input
Resistive Heating
Arc Heating Term
9How Much Energy is Needed to Burn off the
Incoming Wire?
First we need to bring the wire temperature from
something near room temp up to the melting point
of the wire
Temperature Change
Heat Input Required to Effect Temperature Change
(where Cspecific heat of material and Mwire
Mass of the wire being heated)
Then, we need to supply sufficient energy to
cause a phase transformation from solid to liquid
(we need to melt it)
(where Hmlatent heat of fusion of material)
So, the total energy required to burn off the
incoming wire is
10Putting This Knowledge to Use
Heat In
I2(t)ß
I(t)a
11Little l
I(t)
I(t)a
Error Term
Arc Heating
S
ARC ON
ARC OFF
Little l
Jset
I2(t)ß1/2
Resistive Heating
-Jset
Jset (Heat in _at_ ½ Stickout)
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13Duration of Ball Phase is Modified Based Upon
Heat Content of Wire
Tball
Width of ball pulse is adjusted in response to
the heat input in the wire
14Stick out variation video
15Constant Voltage GMAW Comparison
RMD 0.035 ER70S-6 on 8 Sch. 80
Conventional GMAW
16Establishing Good Technique
- As with any welding process, success with RMD
process requires establishing and maintaining
good preparation and welding techniques. - The following guidelines lead to proven success
and increased productivity for welding pipe
17Joint Configuration
- Standard 75 degree included angle
- Land 0 3/32
- Root Opening 1/8
18Five Critical Items For Stainless Steels
- The techniques for welding carbon are the same
for stainless alloys - To qualify procedures for welding 300 series
stainless steel piping Without backing gas,
fabricators should do the following - 1.) Ensure a minimum 1/8 gap around the entire
circumference of the joint. This gap allows the
shielding gas to flow through to protect the
backside of the joint from oxidation
19Five Critical Items Cont.
- 2.) Clean the pipe both inside and out to remove
any contaminates or unwanted substances. Use a
wire brush to clean at least 1 in. back from the
edge of the joint - 3.) Use only a stainless steel wire with a high
silicon content, such as 316LSi or 308LSi. Higher
silicon contents helps the puddle wet out and
acts as a deoxidizer
20Five Critical Items Cont.
- 4.) For optimum performance, use a Tri-H gas
thats 90 He/ 7 ½ Ar/ 2 ½ CO2 - Alternatively, use 98 Ar/ 2 CO2
- 5.) For best results, use a tapered nozzle for
the root pass because it localizes the shielding
gas coverage. Tapered nozzles with built-in gas
diffusers provide exceptional coverage
21Thank You