Lecture Overheating

7/28/2019 Lecture Overheating

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To reduce or prevent Overheating on Welds:

For GTAW:

1. Reduce amperage (Current), slightly increase travel speed or shorten the arc length.

2. If applicable, use stringer passes to minimize overheating which can cause distortion.

Notes:

1. Figure 7A shows discoloration on a stainless steel weld caused by overheating, which

not only affects a material’s color, but degrades its corrosion resistance and mechanical

properties as well. Unfortunately, once this error is made, there is nothing that can be

done to fix it except for scrapping the part and starting over.

2. Figure 7B shows proper coloration of stainless.

For GMAW:

To reduce or prevent Weld Spatter

Only for GMAW Process:

Metal particles expelled during welding that do not form a part of the weld is weld spatter.Excessive spatter creates a poor weld appearance, wastes electrodes, makes slag removaldifficult, and can lead to incomplete fusion in multiple welds. Solutions are to:

1. If using Short-circuiting mode of transfer (Voltage ranging V) for welding structural thinmaterials, it is recommended to:

a. Reduce the welding current.

b. Decrease the arc voltage.

c. Shorten the amount of stick-out (Stickout to be 6-12mm).

2. Avoid using Globular mode of transfer (Low voltage and current) in welding thicker materials for Structure.

3. Recommended to used Spray arc mode of transfer for thicker Structural materials(Voltage ranging 23-35V).

Remarks:

1. Test a few welds on scrap metal to check that the voltage are set to perform accurately.



2. Voltage that is too high will create excessive spatter, additionally, can cause

undercutting, a groove melted into the workpiece that is not properly filled with weld

metal. Voltage set too low produces a narrow weld bead that lacks proper penetration

and fusion.

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1. Increase the voltage

Reduce spatter by adjusting the voltage of the machine. Voltage is closely linked tothe welding arc’s length and the heat input of the weld. Find the right balance, so theweld is being created with the correct intensity.

2. Welding Torch Angle

Positioning your welding gun with the wire in front may make a nice, smooth weld,but it shoots spatter outward. A drag angle with the wire behind, keeps spatter in theweld pool.

3. Clean the weld surface

One simple way to avoid spatter is to keep your welding surface free fromcontamination. Substances like oil may cause the welding power supply to alter themachines parameters settings – creating spatter before and after the rightadjustments are made.

Anything that oxidizes the weld pool (rust) may cause bubbles which rupture,generating even more spatter. It is advisable to clean the surface and avoid themess. Remove any build-up with an abrasive tool/brush or chemical.

4. Shielding Gas and Wire

The shielding gas and welding wire should be preventing spatter, not contributing toit. Argon gas can minimize spatter, but it can alter other aspects of the weldment.Many wires contain deoxidizing substances, which will reduce the amount of spatter.Flux cored wires are considered an excellent safeguard against spatter. Reducingthe wire feed speed can help overcome the problem of excessive spatter.

If this isn’t effective, the excessive spatter may be the result of arc blow that occurswhen magnetism in your base metal affects the quality of your arc. To combat arcblow, try welding toward your work return clamp.

5. Shelter the Welding Environment

In the battle against spatter, wind is considered an enemy. Ensure the shielding gasisn’t being affected by air flow. Another environmental problem that causes spatter,cable grounding, can be easily fixed. Make sure cabling is secure and on cleansurfaces, otherwise, you may have weld altercations.





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Figure 1 ARC LENGTH



Figure 2 – Nozzle to Work Distance (Stickout)

Figure 3 – Large Spatter Deposits

Lecture Overheating

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