Thermal and magnetic arc blow

Date 09-24-2009 00:04

Just a small help. Magnetic arc blows are neutralized by changing the welding current from DC to AC. If this isn't possible, try changing the position of the earth clamp in several places until you find the best one.
Giovanni S. Crisi
Sao Paulo - Brazil

By ssbn727 (*****)

Date 09-24-2009 02:02 Edited 09-24-2009 02:10

Hi 2008642!

First off, "Weldcome" to the AWS forum!!! :) :) :)

Now as far as your query is concerned, even though you provided some information with regards to your set up , there are still some unanswered questions that come to mind...

1.) Why is your CFH rate @ 45 to 50? Also, are you using a dual stage regulator/flowmeter as opposed to a single stage configuration?

2.) You mentioned that you are welding a 400 series stainless but you didn't mention specifically which grade and this is important because, as you already might know that "400 series" stainless can include both ferritic as well as martensitic stainless steel and unless you list a specific grade, we cannot just assume what you're welding together based on the filler metal grade you did specifically list so, please include this information. Also what is the thickness of the base members? I'm thinking not so thick because you're using a 98-2 mix instead of a 99-1 mix which is preferable to use on thicker base metals due to less possibility of undercut as well as other factors, and that's another reason why it's important to know the thickness of the base/parent metal. Also, if your heat input is too high and your travel speed insufficient then there is a possibility of thermal arc blow occurring in your set up when welding provided that everything else is correct.

3.) What is your CTWD (Contact Tip to Work Distance) and, contact tip set back, electrode extension and nozzle standoff distance? What size gas cup/nozzle are you using in your setup?

4.) Where is, and what type of work attachment do have on your set up?

5.) What are your cleaning/prep procedures for the base metal? What is the Joint configuration? What step(s) do you take to insure that the filler metal is protected from contamination?

6.) If you're using pulse spray @ 24 V and 300 A, what is your peak and background settings as well as you dwell timing, pulse frequency and while we're asking, what type of power source are you using in your configuration and what are the polarity settings for both torches and finally, are you using only one power source or two separate power sources?

7.) Do you use any other spool of a different type of filler wire such as another grade of metal other than the 439Ti MCAW grade you are using in the setup you're using?

8.) What type of liner/conduit are you using for your MIG gun/torch as well as the rest of the components along the wire path from the spool to the contact tip?

9.) "Several people assumed it was the gas, but both robots are split off the gas line." Now, when you mentioned the fact that both robots are split off the gas line, what exactly do you mean when you say this? Are you saying that you're only using one regulator/flowmeter for both GMAW torch/guns and split via a "Y" valve connection?

10.) What is your travel speed? When you mention your parameter settings @ 24V and 300A, are these your closed circuit output readings or your power source settings with an open circuit prior to welding? If you have this info, do you happen to know what are your Kilojoules per minute, hour or whatever you used to determine your heat input?

11.) Are the MIG gun/torches always six inches apart throughout the welding sequence? And what are the metal cored Filler metal Mfgr's recommendations for your application even if it's in the semi automatic mode only? And what is the total length of the joint?

I ask these questions to narrow down the possibilities of is causing this condition of porosity to occur on an intermittent basis throughout the length of the joint

My final question which could lead you towards narrowing down the cause and effect of you problem is to point you towards Lincoln Electric's " The Procedure Handbook of Arc Welding." I have the 14th edition but, I believe the 12th and 13th editions have this information available also... If you look at page 3.2-1 through 3.2-5 you'll be able to read the descriptions for Magnetic arc blow, thermal arc blow, and Arc blow with multiple arcs.

Arc blow with multiple arcs could be, or not be your problem but, since I do not know all of the specifics involving your set up, I can only describe what this means...
When two arcs are close to each other, their magnetic fields react to cause arc blow on both arcs. Multiple arcs are often used to increase the welding speed of the submerged arc welding process, and usually the arcs are less than one inch apart. When two arcs are close and are of opposite polarities the magnetic fields between the arcs add to each other. The strong field between the arcs causes the arcs to blow away from each other...

If the arcs are of the same polarity the magnetic fields between the arcs oppose each other. This results in a weaker field between the arcs, causing the arcs to blow towards each other. Now this may or may not be what is going on with your configuration but, I thought it was relevant enough to point this out to you also even though you're not using SAW and instead are using MCAW instead with a CV set up.

Thermal Arc Blow:
The physics of the electric arc reqires a hot spot on both the electrode and plate (base/parent metal) to maintain a continuous flow of current in the arc stream. As the electrode is advanced along the work, the arc will tend to lag behind. This natural lag of the arc is caused by the reluctance of the arc to move to the colder plate. The space between the end of the electrode and the hot surface of the molten crater is ionized and therefore, is a more conductive path than from the electrode to the colder plate.

When the welding is done manually, the small amount of "thermal back blow" due to the arc lag is not detrimental, but it may become a problem with the higher speeds of automatic welding, or when the thermal back blow is added to magnetic back blow. Both of these descriptions can be found on page 3.2-3 in the Procedure Handbook of Arc Welding published by the James F. Lincoln Foundation.

You also mentioned this: "(we use a house gas mix of 98%argon 2% Oxygen)" What steps do you take to insure the quality of gas you're using with respect to contamination and purity levels as well as safeguards to prevent moisture from encroaching the stored gases or during the mixing of the two gases, and are they mixed just prior to entering the pathway towards the regulator/flowmeter then towards the gun/torch nozzle or are the gases mixed and stored for some period of time prior to the start of welding?

I ask this because, I was reading my AWS Welding Handbook ninth edition vol. 2 Welding processes part one and I went to page 194, table 4.21 and it mentions this:

Possible Causes and Remedies for Porosity
Possible cause .1: Inadequate shielding gas coverage Corrective Actions: Optimize the gas flow, increase gas flow to displace all air from the weld zone. Decrease excessive gas flow to avoid turbulence and the entrapment of air in the weld zone. Eliminate any leaks in the gas line. (you did that already) Eliminate drafts ( from fans, open drafts etc.) blowing into the welding arc. Eliminate frozen or clogged regulators when using CO2 which doe not pertain to you. Reduce travel speed. Reduce nozzle to workpiece distance. Hold gun at end of the weld until molten metal solidifies.

Possible cause .2: Gas contamination.   Corrective action: Use welding grade shielding gas.

Possible cause .3: Electrode Contamination.   Corrective action: Use only clean and dry electrode (filler wire spool)

Possible cause .4: Workpiece Contamination.   Corrective Action: Remove all grease, oil, moisture, rust, paint and dirt from workpiece surface beofre welding. use a more highly deoxidizing elecrode.

Possible cause .5: Arc voltage too high.   Corrective action: Reduce voltage.

Possible cause .6: Excessive contact tip to work distance.   Coirrective action: Reduce electrode extension.

Then I went to the troubleshooting section for process related problems encountered in GMAW (even though the process you're using is MCAW) found on page 197, Table 4.26.
As I was reading, I noticed that porosity in the weld could also be found in Tables 4.24 and 4.25 as well so, I decided to list all of them here...

We'll start with Table 4.24, Troubleshooting Electrical problems encountered in GMAW: Problem: "Porosity in weld" Possible cause: "Loose or broken wires to gas solenoid valve" Remedy: "Repair or Replace."

Now I'll go to Table 4.25, Troubleshooting Mechanical Problems encountered in GMAW: Problem: "Porosity in the weld bead" Possible cause: Failed gas valve solenoid, Gas cylinder valve closed (possible that one of the "Y" connection valves is closed or not fully open?), Insufficient shielding gas flow (I personally do not think it is applicable with 45-50 cfh), Leaks in gas supply lines (including the gun).

Finally, I look at Table 4.26, Troubleshooting Process Related Problems encountered in GMAW: Problem: "Heavily oxidized weld deposit" Possible cause" Weld joint area dirty, Improper gun/torch angle, Excessive nozzle to workpiece distance, Air drafts, Contact tube not centered in the gas nozzle distance." then I look down to the next problem and I find this: Problem: "Porosity in the weld bead" Possible cause: Dirty base material, Excessive wire feed speed, Moisture in shielding gas, Contaminated electrode (Filler wire spool).

In conclusion, I would have to say that you need to go over each and every one of the possible causes to either rule them out or single one of them out to find the root cause of this problem you're having and if non of these turn out to be the problem then, I would look towards the possibility of adjusting your electrical parameters and requalification of the WPS to meet the tolerances in the essential variables found in the code you're working t which you didn't mention either.

If you find that none of this is helpful, then the possible cause can be Magnetic arc blow and you can find that on page 3.2-1 thru 3.2-3 in "The Procedure Handbook of Arc Welding." You can also find Magnetic arc Blow in "The AWS Welding Handbook, Vol. 1, Welding Technology" on pages 48 and 49.

Hopefully this will help you narrow down the possible cause of your problem. ;)

Respectfully,
Henry

By 2008642 (*)

Date 09-24-2009 05:52

Thank you Henry. This is the info I've gathered.
1.) We run CFH at this rate due to the higher rate of travel speed.
2.)The flange is 409 SS Ni, and the shell is 409 SS, the shell is .074" thick and the flange is .485" thick
3.) CTWD 5/8", the tip sticks out of the nozzle 1/4" for clearance reasons, electrode extension/ stickout after welding is 3/8" and the nozzle stand off distance, which I assume is the disctance from the end of the nozzle to the workpiece is a little over 3/4". The nozzle is a tough gun 401-48-50 which reduces to .55". We use this for clearance reasons.
4.)When you say work attachment I assume your talking about how we ground to the machine. We use a rotoground to ground through the positioner and have several shunt straps at various positions on the fixtures.
5.)We don't have any set procedures for cleaning parts. However, the operators know to clean off the parts if any dirt, grease, debris are on the part. Our parts typically come precleaned.
6.)Pulse spray- 27.3 Vpk, 14.5Vbk, 370Apk, 75Abk, PW 1.9 PPS 175, the power source is a Miller Axcess 450 DI using reverse polarity for both torches and we are using two seperate power sources for each robot.
7.)The only wire we can use according to the print is 439 TI
8.)We are using a tough gun torch lead with a tough gun 1/16"-5/64" liner, tough gun defuser, 1/16" tip and a 401-48-50 nozzle.
9.)When I say both robots are split off the same line I mean that there is one gas line ran to the machine and just before it gets to the regulators it splits and each robot has its own seperate regulator.
10.) The travel speed is set to 52 IPM, which I know is fast, but you know how important production is. The open circuit parameters are 24V and 240 the closed circuit parameters are 20-21V and 280. However, do you have any info on figuring heat input? If so I would appreciate it.
11.) Torches stay at a constant 6 inches apart during the cycle.

I hope this helps some I appreciate your help.

By aevald

Date 09-24-2009 07:28

Hello 2008642, on point 3. of your description of parameters and details you listed a 1/4" contact tip stick-out. In my experiences with this sort of condition and the flowrates that you have also listed, that is a pretty good recipe for turbulence or a venturi effect at the arc. As the gas flows past the end of the contact tip it will create a low pressure area that could cause excess turbulence or draw atmosphere into the arc zone due to a venturi effect. If at all possible, you should consider alternatives to reduce this distance and possibly play with the flow rates as well. Are there any other contact tip/gas nozzle combinations available for your torches that would still allow for resolving the clearance issues that you mentioned? Maybe even some photos of your set-up might give others on the forum the necessary information to provide you with additional suggestions and possible resolutions to your problems. I realize in many instances these sorts of things can be proprietary, yet if allowed, pictures really are worth a thousand words. Just a bit more for your consideration. Best regards, Allan

By ssbn727 (*****)

Date 09-24-2009 10:58

Have you read this article below yet?

http://www.infosolda.com.br/download/16DEE.pdf

Here is where the article originated from:

http://www.esab.com.cn/cn/cn/news/upload/Svetsaren_1_2000-2.pdf

Here is another article which may or may not be of interest towards your application:

http://www.esab.com/global/en/products/upload/Consumables.pdf

Are you sure you're using an .062 diameter wire? And not an .052 or an .045 instead? I ask this because this is the product sheet for "Arcaloy" 439Ti from ESAB even though you didn't mention which brand you're using. However if you look at the tabs where it says: "Part No." and open it, ESAB only offers .045 and up to .052 diameter wire in a variety of packaging options such as: 600, 500, 250, 44 and 33 lb packages. Which one of the packages do you use?

Also there are other tabs in the link to the type of wire you are currently using such as: Depositions/parameters, Properties, Features, Classifications, etc. If you look at the product data sheet found in the link above the tabs and on the right side just below where it says "Find Nearest Dealer" click it you open up a link to the .pdf "Product Data Sheet" Once there you will notice that the suggested parameters are for using only .045 diameter wire, and nothing for the .052 diameter wire which is what I believe you are using although it would be best to double check to make sure. ;)

Here is a link to another grade of filler that may or may not be more suitable for your application which is limited to .045 diameter 33 & 600 lb. packages:

http://products.esabna.com/EN/home/filler_metals_catalog/filler_metals_product_detail/q/display_id.id4367f2a95d2735.20265908/category_id.842/path.filler_metals_cored_wire_stainless_steel_gasshielded_metal_core_arcaloy_18crcb_no_aws_class

They also have available these MCAW wires:

http://products.esabna.com/EN/home/filler_metals_catalog/filler_metals_product_detail/q/display_id.id4367f2a95cf902.04400132/category_id.1468/path.filler_metals_cored_wire_stainless_steel_gasshielded_metal_core_arcaloy_409ti_ec409

http://products.esabna.com/EN/home/filler_metals_catalog/filler_metals_product_detail/q/display_id.id4367f2a95d0fe3.28192647/category_id.1467/path.filler_metals_cored_wire_stainless_steel_gasshielded_metal_core_arcaloy_409nb_ec409nb

I included these other filler wires because you didn't include the specific chemical composition of the base/ parent metals of 409Ni stainless and the 409 stainless and as you already know the compositions may vary somewhat from different producers especially if your material is coming from China.

Now I believe you can call ESAB at their 1-800-372-2123 North American Technical support number to get some recommendations on what the suggested parameters would be for .052 diameter wire which shouldn't be too much different since we're only talking a difference of seven thousandths of an inch in diameter between the two sizes. I would also ask them if the flow rate is adequate or not for your application... Finally, I don't know exactly how your business end of the gun/torch assembly is configured but, have you ever considered a sort of trailing shield to connect to the back of the torch so you could use less gas flow rate while ensuring the coverage of the still solidifying weld that's being left behind in hurry due to your travel speed?

Now if you're using a different mfg. such as Select Arc instead hten they do offer larger diameter wires than ESAB does for your application, I would encourage you to read page 85 of the .pdf catalogue below as well as page 60 and 61 also:

http://www.select-arc.com/pdfs/master_select-arc_catalog.pdf

Page 85 in the catalogue will give you suggested parameters as well as optimal parameters for different diameters, and show you some relevant charts regarding deposition rates and Wire feed speed vs current charts as well.

There are no such cleaning procedures with respect to preparing the parts for welding at all???? I find that rather troublesome at the very least especially if you have your parts made somewhere else, and you only assume that they are pre-cleaned when they arrive at the welding cells... I think there needs to be some sort of validation component in your quality assurance system to verify the cleanliness of the two different thicknesses found in both parts. Now if the parts are made or completed in-house (such as drilling holes into the flanges as an example or preparing the joint surfaces for welding by some sort of metal removal whether it be grinding, milling or turning etc.) then there needs to be a mechanism to verify that pre-cleaning did actually take place prior to the parts reaching the robot cell.

You also didn't mention how you are making sure that your gas mix is being monitored for consistency (consistent ratio) and purity with respect to contamination due to the possibility moisture entrapment coming from the source... are you using a gas mixer? if you are, what is the set up consist of? And have you studied the entire supply line from the start of the mixing location to the gas mix at the business end of the gun/torch itself Including the condition of the gas solenoid valve? I mean just because you're getting gas flowing out of both torches doesn't tell you what is the exact proportion of the gas mix without analyzing it at the business end of the system... You need to verify that your gas mix is indeed 98% Argon -2% Oxygen coming out of the nozzle in order to eliminate the possibility of inconsistent gas quality!

If you do not do what I have suggested, then you cannot present your argument of the possibility of thermal arc blow being the culprit without eliminating the possibility of inconsistent gas quality at the nozzle.

Now with respect to heat input or heat flow in welding, if you have access to the Welding handbook of the AWS Vol. 1 titled Welding Technology, I would refer you to Chapter 3 titled: "Heat Flow in Welding" starting on page 666 through to page 86 with page 87 showing references to the chapter contents. Pages 74 through 86 should be able to lead you where you can decide which of the heat input formulas are suitable for your application by looking first at Table 3.1 on page 67 titled: "Guide to Mathematical Symbols."

If you scroll down to each definition, you will find which equation best suits your concerns with respect to net energy input, heat transfer efficiency, solidification time, time interval between onset and completion of freezing, Rate of surface heat generation, heat of fusion, weld travel speed, thermal conductivity of the metal, volumetric specific heat, and other definitions if you choose to find solutions for. From what I can see, equations 3.6 through 3.8 will be helpful for you to determine your heat input and other similar variables also.

Here's a .pdf article by Walter Sperko of the ASME regarding the exploration of temper bead welding which will give you three ways to measure Heat Input if you read pages 4 & 5 in the .pdf:

http://www.sperkoengineering.com/html/articles/Exploring%20Temper%20Bead.pdf

Here's another excellent article on distortion written by the famous Omer W. Blodgett, Senior Design Consultant form Lincoln Electric:

http://weldingmag.com/blodgett/wdf_71186/

Here are a list of more articles by Omer Blodgett which a ton of excellent basic fundamental design considerations that need to be applied when using sound engineering practices with respect to welding design:

http://weldingmag.com/blodgett/

Here are some more articles on welding ferritic stainless steels:

http://weldingmag.com/searchresults/?terms=ferritic+stainless+steels&rp=

Here is the 12th edition of the procedure handbook of Arcwelding by Lincoln Electric:

http://www.scribd.com/doc/9328867/The-Procedure-Handbook-Of-Arc-Welding

Look at page 38 in this .pdf for a heat input formula:

http://www.most.gov.mm/techuni/media/ME02022_36_83.pdf

Another excellent article on heat input:

http://eagar.mit.edu/EagarPapers/Eagar019.pdf

This one is very good on basic fundamentals:

http://www.prest-o-sales.com/other_links/gases/PDF/ShieldingGases/Manuals/GMAW%20of%20Carbon%20Steel.pdf

Here are some more articles regarding both 409NI and 409 Stainless steel:

http://www.aksteel.com/pdf/markets_products/stainless/ferritic/409_Ni_Data_Bulletin.pdf

http://www.aksteel.it/cataloghi/download/409%20ultra%20form%20bulletin.pdf

Here's a very good article from the Welding Research Council:

http://files.aws.org/wj/supplement/12-2000-BALMFORTH-s.pdf

Here's another gem:

http://www.msm.cam.ac.uk/phase-trans/2005/LINK/183.pdf

Look at this book preview and go to Chapter 4 "Wrought ferritic Stainless steels on page 241 and read through to page 244 you might find some of the info interesting:

http://www.flipkart.com/alloy-digest-sourcebook-davis-stainless/0871706490-58w3fu0uab#previewbook

Another very good article written back in 2002 from the University of Pittsburgh covering many different metallurgical aspects regarding 409 type ferritic stainless steels by Robert Nooning from the Department of Materials Science and Engineering.

http://etd.library.pitt.edu/ETD/available/etd-12162002-233833/unrestricted/nooningrg_12_2002_etd.pdf

I would also look at page seven of this book in .pdf form produced by the American Iron and Steel Institute and distributed by the Nickel Development Institute:

http://www.ssina.com/view_a_file/weldingbook.pdf

Here is the Home page for the SSINA (Stainless Steel Institute of North America):

http://www.ssina.com/index2.html

I'm done for now so, go figure it out with all the info I provided you with because I'm not getting paid for this so, take care of your problem with the knowledge base I provided you with. ;) ;) ;) Enjoy the reading!!! :) :) :)

Respectfully,
Henry

By waccobird (****)

Date 09-24-2009 12:16

Henry I want to thank You for your time and Knowledge base that you hand out here on the forum. I have always held the belief that one should learn daily. You and others on here make that task a lot easier, Thank You.
Sincerely
Marshall

By 2008642 (*)

Date 09-24-2009 23:59

Thank you Henry. That is a lot of info and I greatly appreciate the time you took to share all of this with me. The wire is .062" 439TI made by Select Arc in 800 lb barrels. Once again I appreciate everything you've done.

By ant Date 05-21-2010 13:45

thankyou my friend hard to get good infomation like this in Australia

By Stephan (***)

Date 09-25-2009 14:39

2008642,

entirely independent of the tremendous amount of information that has been put in here by Henry and the others.

May I humble ask: "What makes you believe that the root cause of your issues might be 'thermal arc blow'?"

Is there something special observable, e.g. some sort of interference, while both arcs are burning?

I'm just trying to figure this out a bit.

Thanks!
Stephan

By ssbn727 (*****)

Date 09-25-2009 17:38

Hi Stephan, Allan, 2008642!

I believe he's leaning towards a gas supply issue which seems to make sense as one would be able to discern after reading the symptoms which were described in his original as well as subsequent posts.

Although, I would also suggest that the thicker of the 2 parts be pre-heated prior to welding as is suggested in one of the links I provided but, do not remember which one it was at this moment... I am also still troubled as to why there is no mention of any procedure being used to verify that the parts are being pre-cleaned prior to arrival at the robot cell in order to prevent any contamination in the weld zone from residual films of grease, oils, solvents or any other possible contaminants... I believe there must be some sort of validation mechanism in place to verify this as part of there overall quality assurance system because, if in fact the gas issue has been eliminated, and there still is intermittent porosity occurring in the welds, then they would have to start all over again to troubleshoot the real root cause of the problem.

I would have to agree with Allan regarding the contact tip stick out as being a potential culprit for the intermittent porosity forming during the welding sequence...

I believe that 2008642 mentioned that the reason for such a stick out is necessary for clearance... I also agree with Allan that a different geometry incorporated into the design of a replacement nozzle should be able to mitigate the clearance issue. However, it is also mentioned that this porosity only occurs via only one of the robots as opposed to both which leads me to believe that the stick out issue may or may not be causing the porosity provided that both torches are configured exactly as the other.

SEM metallugical analysis of some sample welds will be able to confirm whether or not there may be some moisture in the gas supply so, that would be important to ascertain ASAP!
Once this is ruled out the next step, or even as they are in the process of determining whether moisture could be a culprit or not, the shielding gas mix can be checked for precise mixing ratios as well as any other possible contaminants before hand... I would rather send some samples out for SEM metallurgical analysis because, even if moisture is not the culprit, there may be the issue of pre-heating the thicker of the 2 members of the joint(.485 of an inch thick and .074 of an inch thick respectively.) that could also be causing the problem as well as the possibility of residual film contaminants on the surface of both members... In other words, a two pronged approach would be a more efficient way of determining the root cause of this problem.

As you know from experience that these sort of problems usually turn out to have m ore than one culprit that in the end are so simple to diagnose yet sometimes, the customer doesn;t stop for a moment to open their minds, calm down and tackle the problem from multiple approaches especially if time is of the essence as it is here when such an expensive investment of capital equipment lay idle because of what will most likely be a very simple solution once the proper steps are taken to diagnose and troubleshoot the problem(s) by ruling out the possible culprits simultaneously by using a variety of approaches.

I personally think that the lack of pre-heating of the thicker member which if I remember correctly is the flange, prior to welding may just be causing thermal arc blow since it is mentioned as a precaution to pre-heat parts thicker than one quarter of an inch prior to welding in one of the .pdf's I listed in one of my previous posts in this thread although, it is doubtful that this is the only culprit to the issue of producing intermittent porosity in the welds and only on one torch yet, it may very well be only one cause of this problem provided that everything else that I mentioned is ruled out also especially the verification of no residual contaminants on the surface of the parts themselves... In other words, I wouldn't in haste rule out the possibility of thermal arc blow, or shielding gas purity being at the very least, an accessory to this "crime" all together!!! ;) ;) ;) And NO! I do not watch "CSI whatever" so, please do not assume that I'm thinking along those lines. :) :) :) So 2008642, good luck and happy hunting!!! Please let us know what you found out to be the root cause(s) for your situation.

Respectfully,
Henry

By Stephan (***)

Date 09-25-2009 18:08 Edited 09-25-2009 18:32

Good points Henry!

As always!

Yes, I personally would also tend to what's been said by Allan.

The combination of the tip sticking out off the nozzle + the nozzle diameter reduction to ~ 14 mm (would be interesting to know the remaining clearance between contact tip outer- and nozzle interior diameter) + the relatively high gas flow rate of 21... 23 l/min + the relatively considerable travel speed of ~ 22 mm/s. Yes, this could eventually lead some issues to be investigated in detail.

It would be interesting to know if there are spatter generated during welding.

Anyway, you hit the nail again by saying:

Please let us know what you found out to be the root cause(s) for your situation

Thanks!
Stephan

By ssbn727 (*****)

Date 09-25-2009 21:20 Edited 09-25-2009 21:31

Hi Stephan!

I woyuld have to say that because of the high travel speed, the shielding gas flow rate is within recommendations suggested by Select -ARC who supplies the Metal Cored Filler wire electrode... However, Allan and yourself as well as myself included are correct in questioning such a long contact tip stick out from the opening of the Nozzle itself which should never be more than 1/8 of an inch maximum and too much for pulsed spray transfer!!!

No! I'm leaning towards his initial thought of the possibility of thermal arc blow as being a culprit amongst the possibility of another one being an improperly pre-cleaned part or parts, and/or some sort of contamination from the gas supply which more thna likely is the result of the venturi effect from such a long contact tip stick out, or however remote, the possibility of contamination somewhere along the gas supply route to the robot cell itself. Now if 2008642 were to preheat the flange which is over a quarter of an inch thick of 409 Ni Stainless Steel (.485") I would only ask for one to look at this link and scroll down to page seven where welding preheating is covered:

http://www.ssina.com/view_a_file/weldingbook.pdf

The book Titled "The Alloy Digest Sourcebook: Stainless Steels" in this link explains on the bottom of page 243 in the chapter covering Ferritic stainless steels on the right column which can be viewed as a preview by "Google Books" in the link below, mentions that 409Ni Stainless is a group II grade of ferritic which has better weldability than group I ferritic stainless yet, still requires both preheat as well as postweld heat treatment. I would suggest that 2008642 read both links carefully!

http://www.flipkart.com/alloy-digest-sourcebook-davis-stainless/0871706490-58w3fu0uab#previewbook

So in summary, it must be at least two culprits causing the porosity and maybe even more than two but I doubt it that it could be more than two! the only mystery in this situation is figuring out which two they actually are, and the only one who can eventually tell us this is 2008642!!! ;) So, please let us know what you come up with! ;)

Edit: One last question to 2008642... You mentioned earlier that the porosity only occurs during welding on one robot and not at both robot weld deposit locations so, is the robot that shows porosity in it's weld deposit, depositing the weld simultaneously with the second robot or is the second robot starting after the first robot which would be six inches away constantly from the first robot? This is an important question that needs to be answered. :) :) :)

Respectfully,
Henry

By 803056

Date 09-25-2009 21:27 Edited 09-25-2009 21:35

I need some edcuation here gentlemen. What the heck is "thermal arc blow"?

I know what "magnetic arc blow" is, but I have no idea what "TAB" is. I need a more detailed information than Henry gave us to help me better understand what is going on.

Best regards - Al

By ssbn727 (*****)

Date 09-25-2009 21:34 Edited 09-25-2009 21:38

Hi Al!

"Thermal Arc Blow:
The physics of the electric arc reqires a hot spot on both the electrode and plate (base/parent metal) to maintain a continuous flow of current in the arc stream. As the electrode is advanced along the work, the arc will tend to lag behind. This natural lag of the arc is caused by the reluctance of the arc to move to the colder plate. The space between the end of the electrode and the hot surface of the molten crater is ionized and therefore, is a more conductive path than from the electrode to the colder plate.

When the welding is done manually, the small amount of "thermal back blow" due to the arc lag is not detrimental, but it may become a problem with the higher speeds of automatic welding, or when the thermal back blow is added to magnetic back blow." Both of these descriptions can be found on page 3.2-3 in the Procedure Handbook of Arc Welding published by the James F. Lincoln Foundation. Magnetic arc blow can be found in page 3.2-1, 3.2-2 also in the same book.

Edit: Forgive me Al! I have the 14th Edition so, it may not be in the same pages in an earlier edition but nonetheless, it's in the "Procedure Handbook of Arc Welding"

Respectfully,
Henry

By 803056

Date 09-25-2009 21:36

Thanks Henry. I'll look it over.

Best regards - Al

By ssbn727 (*****)

Date 09-25-2009 21:52

Hi 2008642 and everyone els!

You know after watching Obama's press conference at the G-20 summit being held here in Pittsburgh, PA. I got an epiphany!!! ;) Why? because I got tired of listening to the same old jazz from a different group in name only!!! :) :) :)

What if the thermal arc blow was enough to combine with the venturi effect being formed as a result of the excess stick out of the contact tip from the bottom of the nozzle to be the cause for violently disturbing the shielding gas enough to cause the porosity, and this would lessen as the flange which is thicker than the shell would by then become hot enough to negate any further thermal arc blow form continuing and explain as to why the same condition does not occur in the welds of the second robot???

What doe you think 2008642??? Now this hypothesis can only be substantiated if and only if, all other possibilities of potential contamination to the weld are ruled out!!! ;)

So let's not jump the gun here just yet and instead methodically rule out all of the other mentioned possibilities - CAPECHE???

Respectfully,
Henry

By 2008642 (*)

Date 09-29-2009 06:35

So far this week this hasn't been much of a problem. We are starting to lean toward contaminated flanges, as you suspected. From what I've been told the flange is made from a powdered 409 SS Ni. We think that maybe the contamination was down in the flange and the heat just leached it out. If we could preheat these flanges I think it would help. I've been told that our supplier of these flanges went bankrupt and they sent us the remaining stock. So we may have just recieved a bad lot of flanges. I will continue to monitor this for the remainder of the week and keep you guys updated. I really can't tell you how much help you've been. Thanks.

By ssbn727 (*****)

Date 09-29-2009 09:27

Well, Well... There you go!!! a powdered 409Ni Stainless steel??? Well now that surely does make more sense now that you mentioned that!!! ;) Yeppres!!! I would say that you should now pre heat the remaining flanges just hot enough to encourage leeching then air cool and finally pre-clean then preheat again prior to welding in order to make sure that you've eliminated the contamination and any possible hard start by "Warming up those puppies" just enough to avoid any potential for thermal arc blow!!! :)

You should be good to go by then and, if you decide to buy from another supplier of flanges, make darn sure you know what you're getting beforehand! ;) Glad to read that you figured out the problem. :) :) :) All I did was to open your mind to some other possibilities so, please don't give me so much credit!!! ;)

Respectfully,
Henry

By 2008642 (*)

Date 10-02-2009 07:20

I have one last question. At what temperature and for how long should I preheat these parts? I discovered we do have a small furnace in our tool and die department. If the problem returns this will be the first thing I try.

By ssbn727 (*****)

Date 10-02-2009 11:59 Edited 10-02-2009 12:03

Have look in page 7 in this .pdf reference book from the Stainless Steel Institute of North America (SSNIA):

http://www.ssina.com/view_a_file/weldingbook.pdf

It recommends 300 to 450 degrees F. however, the only part you need to preheat is the Flange (.485"T) and NOT the thinner shell (.074"T) part - CAPECHE???

Respectfully,
Henry