AWS New Welding Technologies The Key to Higher Productivity Controlled Short Circuit GMAW

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AWS New Welding TechnologiesThe Key to Higher
ProductivityControlled Short Circuit GMAW
Root Pass Pipe Weldling

• Jim Cuhel
• Welding Engineer
• Miller Electric Mfg. Co.

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Short Circuit Transfer
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Taking Control
Short Arc
RMD
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What 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)
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Power Density in the Necking Region
Wire
Molten Wire
Necking Region
dl
Puddle
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Short 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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Heat Input
Resistive Heating
Arc Heating Term
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How 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
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Putting This Knowledge to Use
Heat In
I2(t)ß
I(t)a
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Little 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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Duration 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
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Stick out variation video
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Constant Voltage GMAW Comparison
RMD 0.035 ER70S-6 on 8 Sch. 80
Conventional GMAW
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Establishing 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

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Joint Configuration

• Standard 75 degree included angle
• Land 0 3/32
• Root Opening 1/8

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Five 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

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Five 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

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Five 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

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Thank You

• Any Questions