My next novice production welding question...

By kozak Date 04-23-2012 17:26

We are manufacuring cap clevises (clevii?) and tang mounts for air cylinders. An example would be the cap clevis mount below,

http://www.google.com/imgres?q=pneumatic+cylinder+mp1+mount&um=1&hl=en&biw=1408&bih=703&tbm=isch&tbnid=fcIj-EUXJL4-kM:&imgrefurl=http://www.motioncontrolsllc.com/k_series_datasheet.htm&docid=PV5TLeuNDyaL2M&imgurl=http://www.motioncontrolsllc.com/images/k-series-cylinders/cylinder_mountings/MP1.jpg&w=533&h=242&ei=so-VT-eJFcWJtwf89vi1Cw&zoom=1&iact=hc&vpx=1028&vpy=74&dur=4060&hovh=151&hovw=333&tx=295&ty=93&sig=115336598018578543078&page=1&tbnh=101&tbnw=222&start=0&ndsp=16&ved=1t:429,r:4,s:0,i:75

We reached out to a welding expert and he said that we probably shouldn't be welding pieces that thick with a MIG and spool gun, we should be using TIG. However I can't imagine that everyone is manufacturing these thick components with TIG, I believe that it would simply take to long.

By 803056

Date 04-23-2012 18:08

Depending on the alloys, I would most definately use GMAW, but make sure you are using spray transfer. You can consider introducing some helium to increase the heat input, but if you are using preheat you can be degrading the mechanical properites. The heat treatable alloys can overage if they are held at temperature for to long a period of time. I suggest increasing the wire feed (amperage) and used blowers (not compressed shop air) to hasten cooling between weld beads.

You should weld aluminum as hot and as quickly as you can without allowing the interpass temperature to climb progressively higher with each weld bead. Interpass cooling is essential to minimize the degradation of the mechanical properties.

Whether you use a spool gun or a push/pull gun is going to make little difference in weld quality. It will make a difference in the fatigue of the welder using the heavier spool gun over an extended period of time.

Also, use the forehand (push) technique when welding the aluminum. This is about the only time I recommend using the push technique when welding with GMAW.

Best regards - Al

By kozak Date 04-23-2012 18:53

I should state that on our prep sheets we state thast preheat is only about 200º F. Also how do I know if my welder is setup for spray transfer. As for alloys I believe that we are using 6061-T6, and we do not do any post weld heat treating or stress relieving.

By eekpod

Date 04-23-2012 19:25

You really need a CWI and or at least a copy of D1.2 the structural welding code Aluminum. It will give you guidelines to help you determine some of your questions.
I agree GTAW is not a timely process to do what you making, the GMAW sounds like the way to go.
Do you have any WPS's to know how to set the machine up? It sounds like you don't, again a CWI would help with that.
From memory I don't think there is any pre-heat for alum, something like enough to remove surface moisture, but maybe that the stainless code, I don't memorize this stuff.
Good luck

By kozak Date 04-25-2012 13:11

Thanks for the help guys, we are working with a weld inspection company to get our WPS and other qualified forms off the ground. I'm just trying to work from the other end to understand the task I have been given. Also we do have copies of D1.1, 1.2, and 1.6 and I have been trying to familiarize myself with them as we go along. So as I read in D1.2 we need to write our weld procedure then make the fillet weld test pieces using our weld procedure. Do we need to perform all the weld orientations or just the ones we plan on doing (1F,2F,3F) from section 3.4.1.3? We also need to make the coupons to the thickest materials that we will weld, do we need to make any test samples with any dissimilar sizes because we do weld dissimilar sizes too?

By 803056

Date 04-23-2012 19:44 Edited 04-25-2012 16:01

Sorry to hear you are welding 6061-T6. Of all the heat treatable aluminum alloys it suffers the most when it comes to the degradation of the base metal properties. The tensile strength drops by about 40% (from 42 ksi to 24 ksi) as soon as you strike an arc and that is if you do everything properly.

As "eekpod" mentioned, if you do not have a qualified WPS you should consider qualifying a WPS so you know what you have. The qualification process gives you an opportunity to work out any bugs in your system. I also agree with "eekpod" that AWS D1.2 is a very useful resource if you are welding aluminum, but it is a code, not a reference. It doesn't explain why you do this or that. For that information there are other references available that are very useful.

If you need to develop WPS for your production work you might consider hiring a consultant that is a SCWI and has verifiable experience welding aluminum. The ability to develop WPSs and qualify welding procedures is one of the job skills of the SCWI as defined by AWS B5.1, whereas it is nice if a CWI has that capablity, but it isn't a skill that is expected of every CWI.

One of my friends defines aluminum as "almost a metal" because of some of its unique properties. It doesn't behave like carbon steel when it is welded or heat treated. If you hire someone to help you develop WPS and to qualify the WPS, hire someone that has a good amount of experience welding aluminum. Remember "it ain't steel".

Best regards - Al