penetration

By ssbn727 (*****)

Date 03-14-2010 00:40 Edited 03-15-2010 03:03

Have you tried pulsing yet??? ;) In other words, GMAW-P??? Which specific grade and UNS number of Stainless steel according to this are you using for the bracket???

http://www.hcss.com.cn/en/image/DIN_EN%2010088-3%28995-08%29.pdf

Now this is to be welded to AISI 441 shell which is a ferritic grade of Stainless steel, yet you didn't elaborate which specific grade under DIN 10088 is the bracket... So if the two members which make up the joint are dissimilar, then E 307? may, or may not be the correct wire, or it is but your weld parameters, your work angle which should be favoring the thicker of the 2 members is not correct either...

What type of specific joint configuration are you using? Have you tried using a little more helium in the shielding gas mix than 3%?
Once again, have you tried welding the joint with pulsed spray transfer GMAW-P (Gas Metal Arc Welding-Pulse) at all??? What about "Accu-Pulse, Accu Curve, Accu Speed" or "RMD" because, that power source gives you those capabilities and more!

http://www.millerwelds.com/products/automation/auto-axcess_systems/

http://www.millerwelds.com/pdf/spec_sheets/AU8-0.pdf

Not to be disrespectful, but you have one heck of a power source to work with and from what I' have read in your post, you're not telling us anything about whether or not you're utilizing any of the advanced features that come with your power source such as the MIller Auto Axcess 450 DI... So if you could elaborate more on the specific settings you're using, then we might be able to steer you in the right direction. ;) I would also like to suggest that you contact your Miller Rep to see what they can do to help also. ;)

Respectfully,
Henry

By 2008642 (*)

Date 03-15-2010 02:32

Sorry for leaving that out. We have tried the ACCUPULSE, MIG, & the RMD (8 hr trial version that comes with the power source). We haven't tried the ACCUCURVE or ACCUSPEED as of yet. The weird thing is that when we ran some samples for cross sectioning after installing a bottle of the Argon/Helium/CO2 mix every bracket showed good penetration as well as good penetration into the shell. The next morning we came back in without any of the settings being changed we only passed on one bracket. The bracket is DIN EN 10088-2-X2CrTiNb18. I will check with the other techs to see if we have tried the ACCUSPEED, or ACCUCURVE, but to the best of my knowledge we haven't tried them as of yet.

By js55

Date 03-15-2010 13:02

I don't know what your last trimix is but those are all low energy gases. Lower penetration would be expected. So one thing to do would be to boost the energy level of the gases you use. CO2 is the likeliest choice but you have to determine if the oxidation potential can be allowed for the service. If not He is the next best choice. It is more expensive and destabilizes the arc as the volume percent increases.

By Lawrence (*****)

Date 03-16-2010 00:14

Let's look at it from another angle.

Inconsistancy in the welds you describe sound more like an inconsistant fit-up issue than a gas mix/-torch angle/- or travel speed issue..

If it works once and the fitup is good it should work consistantly.

Tell us something about your fitup/fixturing and the allowence for slop that may be in them.

By Tommyjoking (****)

Date 03-16-2010 05:12

Good call Law

By ssbn727 (*****)

Date 03-16-2010 06:48

For those of you wondering what the non-standard term "Slop" means by Lawrence... It means Tolerance, and when it comes to automated (robotic) welding, it is extremely critical, and yet if I remember correctly the OP did mention: "I've checked the fixtures to insure there isn't any movement and everything appears to be in its place." Although the OP did not mention specifically what sort of fit-up "Slop" (Tolerance) they were working to...

In fact, the only way any of us are going to get a clearer picture as to what is actually going on with this situation is for the OP (Original Poster) to show us some pictures, or even a drawing of the joint including the necessary, and pertinent dimensions involved ( is GDT being used here by any chance? ). ;) Also, is the robot that's being used achieving the repeatability that's required in order to maintain the consistency??? has the TCP been checked for accuracy recently, or this done on a fairly consistent basis? ;) Accuracy in the fixtures is critical when automating ,and equally critical is the accuracy of the parts fabricated dimensions prior to being fixtured & fit up as well as ensuring that the accuracy of the robot, or any other type of automated system is maintained also! ;)

I wouldn't rule anything out now without the OP supplying us with some more data regarding the specific joint configuration which was one of the many questions I asked in my first reply and got no response from the OP yet either. ;) Hopefully more will be revealed to us soon enough! ;)

Respectfully,
Henry

By OBEWAN

Date 03-16-2010 14:49

What is the fixture like in terms of heat sink? Is there a heat sink? Is the heat sink getting hot? I have been burned by that in the past when the tool designer did not use copper. The set-up was good but later in production things went bad.

By ssbn727 (*****)

Date 03-16-2010 16:46

Hi Steve!

That is another important factor to consider also... Good point! ;) And it just reinforces what I wrote in my last post... Without ALL of the necessary data available to accurately, and comprehensively make a thorough analysis of the conditions related to the problem that the OP is experiencing, It's usually highly improbable (although not impossible) to isolate a root cause or causes for the problems or inconsistencies being encountered... So please give us some more details 2008642 and this time include every little bit of data that can be related to the set-up, the operation, and anything else that is in anyway pertinent to the project even if you think it isn't! ;) Thanks in advance!!! :) :) :)

Respectfully,
Henry

By 2008642 (*)

Date 03-18-2010 13:07

The joint is approximately an 90 degree angle(fillet weld). The converter body we are welding the brackets to has a fiberglass mat material around a substrate on the inside of the body. So the shell will have a lot more heat sink than the bracket does. We haven't had any problem getting and maintaining pentration in the bracket. I have measured 20-30 brackets and found as much as 3/4 of a mm difference between the highest and lowest measurements. The converter body is located in the same position everytime off of a O2 sensor boss. This will control the roll of the converter body. We then have hard stops to prevent the body from moving in the X or Y axis directions. The brackets are located on the converter body using pneumatic cylinders. After the body is clamped the cylinders will push the brackets to the surface of the body. There is no hard stop on this so the converter body(shell) is what stops the travel of the cylinder. The fixture is pretty robust and was built by an intergrator we have used for years and they are very good at what they do. The diameter sizing of the converter body is subject to minute variations as well. The fixture is fastened to an external positoner that rolls the part so we can get the best angles possible. I can't send pictures or drawings because some of this is proprietary information.

By SWP

Date 03-18-2010 13:55

Changes in penetration, for no apparent reason, brings to mind the issue of Marangoni fluid flow commonly seen in austenitic SS GTAW. If all your components are from the same heat of material, variable penetration due to Marangoni flow should not be an issue, but if components are coming from different heats with a variation in sulfur content from a low around 20 ppm (0.002 wt%) to a high somewhere above 60 ppm, this could contribute to variable penetration. Although most commonly seen with austenitic SS and GTAW, in theory, Marangoni flow could be a factor in GMAW. Wouldn't hurt to look at your component heats and chemisty.

By ssbn727 (*****)

Date 03-18-2010 20:26

Man O Man!!! Is that one heck of a switch regarding the change in the amount of helium and argon compared to your first post!!! :) :) :) Just out of curiosity and speaking of the penetration profile being a lot wider, was there a slightly thinner penetration profile with no significant change in the depth of penetration when you tried let's say,
a 75% Helium - 23% Argon -2% CO2 gas mix??? Or maybe with an 80%-18%-2% mix instead??? The reason why I ask this is that it might save you some extra time with the contact tips & nozzles if they start to prematurely wear out. ;)

I'm glad to read that the ACCUPULSE option worked to improve consistency by customizing the wave profile to suit your needs. ;)

Respectfully,
Henry

By 2008642 (*)

Date 03-19-2010 11:25 Edited 03-19-2010 19:02

We really didn't try any other mixes than the 95%Argon,3%Helium, and the 2% CO2, and the 90% Helium, 8% Argon, 2%CO2, and the 98% Argon, 2% Oxygen, and the 98% Argon 2% CO2. We learned from our gas supplier that when they brought the first Helium mix of 98%Argon, 3% Helium,2% CO2 that they just shot some Helium into an already mixed bottle of 98% Argon 2% CO2. We are thinking that maybe the gas was seperated and we used the biggest part of the Helium first giving us the good cross sections and then later we didn't have as much helium and caused the difference in the cross sections. Henry, you seem to have extensive knowledge in the welding trade. We had a guy from our wire supplier make the custom pulse program, but do you have any good info on making custom pulse waveforms? I understand the waveform but not 100% certain what happens when one element of the wave form is changed versus another element such as the Peak,Background, Pulse width, PPS, and the slope times. You've been a big help and I 've learned a lot from this experience. Thanks for the time you contribute to this forum. You may not see it, but it does help others.

Josh

By jwright650 (*****)

Date 03-22-2010 19:15

What type of joint are you performing this weld on? Is it like an Arc Spot weld("Puddle weld" like in AWS D1.3 - sheet steel to supporting member) or is it just a Fillet Weld or Lap Joint?

EDIT
Nevermind...I just read one of your later posts.....I'll go back to my corner and go to sleep now.