Practical Use of Heat Input calculation

[Dave Barker]

Hi

New to the forum and hope you can help!

Have been tasked with using heat input as calculated in BS EN 1011-1 2009 clause 8.7 to maintain control of manual production MIG welding process.

We have validated (lab tested samples) welding procedures for various combinations of steel sections being welded (all the same material spec.) which detail current voltage and welding speeds (wire feed and traverse) but have been asked to use heat input calculation to give the welding teams flexibility in the settings they use...

Clearly can not expect them to re-calculate every time they wish to adjust a setting, so hoping to establish a range-possibly a table they can work from? Any experience in such an arrangement?

many thanks

 

[rikrobson]

Doing a quick google, Q is Voltage x Current / velocity x 0.0008 kJ/mm

I presume the velocity is the speed of the weld as its multi process and would ignore the wire feed speed.

just put this in excel make a wee chart for them

 

[Dave Barker]

Doing a quick google, Q is Voltage x Current / velocity x 0.0008 kJ/mm

I presume the velocity is the speed of the weld as its multi process and would ignore the wire feed speed.

just put this in excel make a wee chart for them

Hi and thanks. Can use the calc OK. Was wondering if there was a simple table or similar that the shop can refer to whenever they need to make a small adjustment to the settings.

 

[TechnicAl]

The idea of doing Welding Procedures is NOT to change the settings.......I assume you have done the tests at specific settings. If you want to be "flexible" do another set at the limit of what you want to use.
The spec you are working to may have set tolerances on the settings and set restrictions on the size of plate you can weld using those settings. If you do the tests on say 10mm the spec may allow down to 5 and up to 20mm.

 

[rikrobson]

looks like all you'll be able to change is the travel speed if you vary the current. the voltage will vary and depend on the machine you are using. how are they measuring travel speed?
if the current goes up you need to travel faster. Youll need to calculat that based on the machines you are using and then just make a table in excel, print it out and stick it on the wall

 

[Dave Barker]

My understanding is that we are allowed to vary speed, current and voltage, as long as we hit the heat input which was validated. But this would mean either doing the calc each time (not practical) or as stated, only vary two settings and create a table to refer to. Is there a tolerance which can be applied or do we have to hit the exact heat input that was validated???

 

[Dave Barker]

The idea of doing Welding Procedures is NOT to change the settings.......I assume you have done the tests at specific settings. If you want to be "flexible" do another set at the limit of what you want to use.
The spec you are working to may have set tolerances on the settings and set restrictions on the size of plate you can weld using those settings. If you do the tests on say 10mm the spec may allow down to 5 and up to 20mm.

Only concern is the cost and time to validate each set of settings. We have to use an external lab to carry out hardness checks and etching.

 

[rikrobson]

the current in a mig is dependent on the voltage. you are actually changing the voltage and the current is a result of ohms law. then the machine will give constant voltage. the wire areclength etc will determine the resistsance and hence the current. I've a current display on my welder and it is seldom reading a single figure
not that you can realy see it with the mask on but when you look at the dispaly you're not look at the wed pool and i'm probablt waving it around a bit and not welding correctly. but thats the point. unless you keep everything constant its going to wander.

 

[TechnicAl]

On a constant voltage set you set 2 parameters, the Wire Feed Speed and the Voltage. The current is variable depending on the settings and the stick out (the distance between the contact tip and the workpiece). So what you end up with is constant volatge and variable current (which means variable penetration).

Changing these settings will change the Heat Inout. The old way is VAT/ run out length........these days they apply a factor.........so changing the heat input will result in a "different" weld............is that an acceptable weld?......really only you can answer that

You are doing these measurements to reduce the variables and therefore reduce the chances of failure...........again only you know the acceptable tolerances but if the **** hits the fan you need to be prepared with the facts

 

[Mid Wales welder]

Was it Intertek who did your procedures? On your WPQR you should have min/max heat input values that you are covered for. One way you can work out the heat input is amps x volts divided by travel speed (mm/sec) x1000 x the k factor for MAG 0.8. If this is within your range then it's fine, so just work out your highest and lowest setting. You should be working to WPS's that are written to your procedures anyway.

 

[Richard.]

It's very important to alter the last part of the calc as stated above the process Factor.
Mig/mag .8
Mma . 8
Fcaw ..8
GTAW .6
Saw 1.

 

[Dave Barker]

Thank you all for the help. Will dig a little deeper.