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Effective Welding Heat Input

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Many weld properties are dependent on welding heat input.   Quenched and tempered (Q&T) steels achieve optimum strength and impact properties through heat treatment. When Q&T steels are welded the area adjacent to the weld deposit is heated almost to the melting point of steel. Mechanical properties are particularly changed and mostly degraded as this area experiences temperature to about 1300 degrees F. 

These structural changes in the material are sufficient that a chemical etch will alter the appearance of this zone from almost melting to about 1300 degrees F.   This is called the Heat Affected Zone or HAZ.  The line that demarks the plate that reached the 1300 degree F point is referred to as the outer etching boundary.


Maximum allowable "Heat Input" is often specified in welding codes.  A simple (Volts x Amps)/ Travel approach is used to define this parameter but does not consider the more complex issues such as arc efficiency, effects of oscillation or how to handle multiple wire processes.   In addition issues arise about how to measure short circuiting MIG or Pulsed MIG amps and volts.  With these processes there are wide variations in both parameters at frequencies of 200 cycles per second or more.


Two examples are presented which show how employing a weld cooling rate approach developed by Professor Mel Adams was used to show that  "Effective Heat Input" can be easily determined.

One example shows how this "Effective Heat Input" approach was used when surfacing an HY-80 Navy vessel using a Plasma Hot Wire process .  How this 50% arc efficiency process and the effects of oscillation were defined.  Another defines Oscillated MIG and Multiwire Submerged Arc Processes were handled.


Professor Adams developed this simple method of defining "Effective Heat Input."  It is easy to apply with simple weld cross sections and easy to measure parameters. Paraphrasing Professor Adams conclusions: “Equations were developed that are considered particularly accurate for calculating temperatures between two known reference locations such as the fusion boundary and the characteristic etching boundary; in this circumstance there is no need to know knowledge of the arc energy is required.”

“Characteristic etching boundaries in H-80 and T-1 steels are associated with specific peak temperatures regardless of cooling rate, preheat, arc energy or geometry.”


A report is available that presents full details on how this information was used and how to apply the approach to handle other process variations as would occur with Hybrid MIG, Tandem MIG etc.

Click ICON for PDF Download of "Effective Weld Heat Input"


The welding industry is lacking in effective means of accurately measuring amps and volts.  Without accurate measurements calculating "Heat Input" is not possible.  An example is shown where voltage measurements can be easily changed just by altering the location of the voltage pick-up leads relative to the power cables.  Methods of improving this situation are also shown in the above referenced report.

Having Variations in Chary Impact Test Results? 

We did also.  We found out why the same weldment achieved 45 ft-lbs and 7 ft-lbs in the same deposit!  Want to know why?

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