Full Penetration - Integral Backing Strip - V-Groove Weld

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dgoddard
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Full Penetration - Integral Backing Strip - V-Groove Weld

Post by dgoddard »

Is there a welding engineering in the house ????
Weld_Prep.jpg
The Problem is to find the proper parameters to weld the above configuration with a root pass followed by one or more filling passes with a MIG welder..

What is not negotiable is:
-- the general configuration of the weld.
-- there is no gap at the root of the weld
-- the root pass must burn into the backing lip
-- the thickness of the parts
-- the thickness of the backing lip
-- the available equipment
-- the material is 1018 cold rolled

What could be adjusted.
-- the 15 and 60 degree angles of the weld (but the object is to minimize weld distortion by minimizing the size of the weld deposit)
-- the thickness of the .020 - 060 dimension (which is to maintain secure alignment of the parts)

The available equipment:
-- Hobart 187 MIG welder
-- Wire ER70S-6 (most probably)
-- Wire diameter 0.030 (most probably)

What must be figured out:
-- The settings for the welder

Inside the cover of the welder are wire feed rate settings and voltages settings for various metal thicknesses, However:
-- these appear to be roughly based on making fillet welds between two pieces of the given thickness.
-- the feed and voltage settings use arbitrary numbers rather than actual voltages and feed rates (i.e. arbitrary numbers instead of volts or in/min).
-- the actual feed rate for a giving feed setting varies depending on the voltage setting (more voltage = faster feed at the same feed setting).
-- there is a chart which can be used to roughly estimate the amperages based on the voltage settings.

The objective in making the root pass first to assure good fusion at the root has been achieved and to allow the possibly of dye penetrant inspection of the root pass before proceeding.

Please comment and suggest an approach to achieving the objective.
Last edited by dgoddard on Thu Mar 10, 2011 9:03 pm, edited 1 time in total.
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Russ Hanscom
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by Russ Hanscom »

Not sure even a welding engineer could give you all of the settings first pass (pun not intended).

I suggest you set up a few test pieces. Pick a middle of the range setting to start, make a weld and reviewe the results; then adjust as necessary.
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by hammermill »

insufiscient data no wire size or type selected
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dgoddard
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by dgoddard »

hammermill wrote:insufiscient data no wire size or type selected
See update edit of original post
However I am open to suggestions
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dgoddard
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by dgoddard »

Russ Hanscom wrote:... I suggest you set up a few test pieces. Pick a middle of the range setting to start, make a weld and reviewe the results; then adjust as necessary.
Well that is what approach I was planning for, however it would be nice to get any available suggestions from those more accomplished and experienced than I am. It could save me from making lots and lots of tests if I had some suggested starting parameters in whatever form I could get them. I am checking welding books for whatever I can find to enhance penetration with a small bead in order to make the root pass. I figure that the rest of the groove will be easily filled in a single pass.

When Hobart put the recommendations in the manual and on the underside of the machine cover, they did not say much about what kind of weld was being made, just some stuff about the thickness and the wire size and alloy plus their recommended settings. Their tech people were not much more help but more or less confirmed that the settings were for fillet welds. At least one of their techs was unaware of such a thing as a backing strip weld with zero root gap. We used to specify them all the time and they are a standard feature in the industry where I worked and are covered by the ASME boiler and pressure vessel code Subsection NG 3350. My objective in following those guidelines is to maximize the weld strength and minimize its fatigue sensitivity. and that particular subsection is very well suited to materials and weld filler that are essentially of equal strength. Any enhanced properties of the weld wire should only get me that much more margin.
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fonzy
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by fonzy »

Just a comment... "Integral Backing strip" The designer seems to describe that the 1/4 " plate is setting on top of the 5/16" plate in such a way that the 5/16" plate serves as the back up strip [the last 1/16" of the 5/16" plate is the backing strip] and will be engulfed by the first or root bead, or as a single pass weld.
Take some 5/16' & 1/4" plate, bevel it and make some mock up tests. The designer did not state any procedures, so it is up to you to come up with what ever works.
This is not to any welding code, right...just commercial quality-liquid tight
Is this a tank, A pipe joint, an ocean liner?
We are talking light 1018 plate here, a lot of lee way, and easy for MIG welding. It also depends on the position of the weld?? That is all left out how can anyone help you with it? I am pretty sure I can weld that all in 1 pass with MIG, after a trial bead or two. If the root bead is critical 2 passes, to take more care on the root.
Your mock up tests will get you in the ball park for parameters...voltage/amperage/wire speed all depend on the welding machine, welding speed/welder's skill & experience.
Last edited by fonzy on Sun Mar 13, 2011 10:22 am, edited 1 time in total.
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dgoddard
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by dgoddard »

fonzy wrote:Just a comment... "Integral Backing strip" The designer seems to describe that the 1/4 " plate is setting on top of the 5/16" plate in such that the 5/16 serves as the back up strip [the last 1/16" if the 5/16" plate is the backing strip] and will be engulfed buy the first pass or root bead, or as a single pass weld
Exactly! Fonzy, you definitely grasp the point of my question.
-- Additionally, the zero root gap allows the parts to be self-aligning and aids in accurate clamping.
-- The part is made so that where the weld is, that the part is over-length. This allows the end where the the weld will be finished to be used for tacking the parts and also allows for the end where the weld stopped to be machined off, thereby removing the flaw in the weld that often occurs there.
-- Also, provided that the penetration of the root pass is all the way through the 1/16 depth of the step, any lack of width of the fusion zone of the root pass will only leave a flaw that is parallel to the plate and not into the thickness of the welded parts. This is better for both strength and fatigue issues.
fonzy wrote:The designer did not state any procedures, so it is up to you to come up with what ever works.
And that is exactly why I posted the question. In my previous experience doing design to NG3550, my design would have been passed off to a welding engineer who would have specified the parameters such as the welding process, the electrode alloy, The welding current current and other parameters before the work was passed off to a skilled welder to perform the actual weld. In this case I get to be all three Designer - Weld Engineer - Welder, so I am looking for all the advice I can get. (Fortunately in the company where I worked, good communication was encouraged between all those personel so that they could provide feedback to each other so that we could make welds of adequate strength quickly and cost effectively. Listening to each other really helps!)
fonzy wrote: We are talking light 1018 plate here, a lot of lee way, and easy for MIG welding. It also depends on the position of the weld??
The weld will be made in the horizontal position, fortunately the easiest of all.
fonzy wrote: I am pretty sure I can weld that all in 1 pass with MIG, after a trial bead or two. If the root bead is critical 2 passes, to take more care on the root.
The reason for doing it in two passes (Root and Final) is that if the root pass can be inspected prior to finishing the weld, the weld can be classified per NG3350 as type 2 and even with only a visual inspection would have a quality factor of .5 and a fatigue factor of 2. If the inspection is upgraded to root and final dye penetrant then the quality factor increases to .9
fonzy wrote:Your mock up tests will get you in the ball park for parameters...voltage/amperage/wire speed all depend on the welder's skill & experience.
Well since the skill and experience factors could definitly be higher, I am trying for the best weld configuration. The problem is that the recommended feed and voltage settings from the MIG welder manual are all based on simple fillet welds. and the objective here would be to lay down a root pass that has good penetration.
So:
-- If the feed and voltage settings are used for .060 material fillet welding, will the penetration be enough to reach the backing lip?
-- If the voltage is increased, the amperage should be increased and will that not help the penetration? However will that not also consume the wire too fast.
-- From what I read, penetration is increased in MIG welding by keeping the arc short. Is that likely to be appropriate in this case.
-- From what I read, bead size is kept small by keeping the welding tip closer to perpendicular. Is that also the correct approach to a small, deep penetrating, bead?
-- From what I read, having too much stick out tends to overheat the wire between the copper welding tip and the bead, which causes reduced current and melts off the wire faster, but I am going to have to use a bit more "stick out" to reach the bottom of the weld prep. That seems counterproductive.

I figure that if I can get some of you more experienced guys to suggest a starting point, particularly for making a penetrating root pass, I won't have to make near so many test pieces before I get it right. I am just trying to dispel some of my ignorance before wasting a lot of mockups, time and weld wire.
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fonzy
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by fonzy »

Please see my edited/added comment posted earlier,above :mrgreen:

Say...if this is code work I'm out a here...I'm just a machinist- :roll: welder. You need to be taking this up with your code organization's web site!

Seriously, AWS / ASME have huge sites with lotsa help!
Last edited by fonzy on Sun Mar 13, 2011 11:01 am, edited 1 time in total.
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by dgoddard »

fonzy wrote:... This is not to any welding code, right...just commercial quality-liquid tight
Right, and I reference NG3550 because that is where I have most of my design experience. It is the only code I am familiar with that addresses Strength, Fatigue resistance, Joint shape, weld type, and inspection. It was basically developed for 300 series stainless steels where the weld filler metal is not particularly superior to the parent metal (and therefore not very forgiving of bad weld design). And amazingly they got it packed into only 5 pages. The only part that seems a little puzzling is that the strength factor (0 to 1) represents how much the strength of the weld is to be trusted (.9 = 90 % of the parent material strength) while the fatigue factor represents how many more cycles of fatigue must be assumed to be applied to the weld for it to perform as well as the parent material ( A fatigue factor of 2.5 means that if you have to show that the parent material will not fail in 400,000 cycles of a particular loading that you must show that the weld will not fail in 1,000,000 cycles of the same loading). So a high quality factor is good and a low fatigue factor is good.

I would recommend the ASME Boiler and Pressure Vessel code Subsection NG3550 as a good study for anybody who really wants to understand the strengths of welds. It is 5 pages long (2 pages of text, 2 pages of diagrams, 1 page as a table) and a bit heavy duty reading but very readable nevertheless for anyone who wants to study it. But I suggest that you familiarize yourself with the diagrams and tables first so that they are easier to refer to when you read the text, and remember it was written for the parts that go inside a nuclear reactor to support the nuclear core (otherwise the joint diagrams might be a little confusing at first).
fonzy wrote:Is this a tank, A pipe joint, an ocean liner?.
Actually it is the receiver for a rifle action, The Chicopee, upgraded to a larger caliber than the original design was intended for.
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by fonzy »

fonzy wrote:Is this a tank, A pipe joint, an ocean liner?.
dgoddard wrote:Actually it is the receiver for a rifle action, The Chicopee, upgraded to a larger caliber than the original design was intended for.
Oh oh boom booms, I'm out of here for sure...too deep for me...next!
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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by GlennW »

It screams TIG

At least TIG the first pass if you really feel MIG is the answer
Glenn

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Re: Full Penetration - Integral Backing Strip - V-Groove Wel

Post by dgoddard »

Glenn Wegman wrote:It screams TIG At least TIG the first pass if you really feel MIG is the answer
Indeed it does scream TIG, however MIG is all I have to work with so I am trying to figure out how best to do that. I have my mock up of the weld made to experiment with. I made it with about .025-.030 at the bottom of the groove to be fused through to the backing lip.

The wire feed rate and voltage settings for the MIG welder to make Fillet Welds, are given for material thicknesses of:
.024
.036
.048
.060
.125
.188
.250
.313.

So to make just a root pass in what is essentially a V-groove weld in 1/4 inch material and achieve plenty of penetration which of those do you think is closest. and how should it be modified if at all.
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