Vertical-up or -down in robotic welding?

Vertical-up or -down in robotic welding?

We have a weldment that incorporates 0.375-in.-diameter steel rods and a 0.060-in.-thick sheet metal stamping of 1018 CR material. Each weld is the same, 0.75 in. long with a 0.25- in. fillet, perhaps including weaving. The assembly is fixtured and welded robotically using GMAW with CO2 gas and repeated 100 to 300 times.

We utilize vertical welding, but which is a better progression, down or up?

Richard P.

Vertical-up and vertical-down welding are significantly different from one another in the technique used and the resulting finish weld. This is the reason welding codes consider this change in progression an essential variable and require additional testing when changing from one to the other.

From your description, I would have to conclude that of all the possible positions (flat, horizontal, vertical, and overhead), this is an ideal candidate for welding vertical-down. Your greatest concern in this application is going to be burn-through on the 0.060-in. sheet metal. Welding vertical-up will be difficult, if not impossible, in this configuration because of the low travel speed and high heat input. Welding vertical-up with GMAW typically requires a weave technique to carry the puddle and give you the proper bead profile. GMAW vertical-up is a deep-penetrating technique, and this characteristic is going to lead to consistent burn-through.

GMAW vertical-down, on the other hand, tends to lack penetration and side-wall fusion. These characteristics are undesirable in most applications, but given that you are using a fully automated system, tight control of wire feed speed (WFS), voltage, travel speed, and bead placement should allow you to counteract these characteristics and control your finish weld quality.

I’ve had a lot of success setting up similar applications in what I call the 45-degree vertical-down position. The key is using a slight drag angle (10-15 degrees) and keeping the arc on the leading edge of the puddle at all times. This is a little easier to do at a 45-degree incline than at straight 90 degrees.

If possible, consider a mix shielding gas (minimum 85 percent argon/maximum15 percent CO2) as opposed to the straight CO2 you are using today. This should reduce chances of burn-through and reduce weld spatter considerably. A 0.035-diameter solid electrode should work well in this application.
You stated the weld size was 0.25 in. Talk to the engineering team and your customer about reducing the weld size to 0.19 or even 0.125, which will help increase travel speed, ensure penetration into the root, and reduce cost. Large welds with no root penetration or side-wall fusion are of little benefit to your customers.

Do I need a welding procedure specification?

Question
Do I need a welding procedure specification (WPS) for my company when it is just me and all I do is on-site portable welding of a wide range of items?

Steven B-

Answer

Whether your company requires a WPS depends on the customers you serve. For example, if your company is hired to fabricate your neighborhood association’s new flagpole, using your skills and best judgment would most likely be acceptable. On the other hand, if you are contracted to fabricate steel supports for a new government facility in your hometown, a little more paperwork probably is involved.

Review all the documentation from your clients in detail. Ask questions if you are unsure. A common statement found in contract documents is "All welding shall meet the requirements of the latest revision of AWS D1.1, D1.2, D1.5, ASME B31.1, B31.3, API 1104 ..." This statement indicates written weld procedures and documentation are required that show your welders and welding process meet the code requirements. You need to know, before you strike an arc ... before you bid the job, if there are specific code requirements.

Does your company need (as opposed to require) written WPSs? Yes!
Without a clearly documented and followed process, it is difficult to communicate details of your welding to your customers. With a clearly defined WPS, everyone involved knows what is to take place. Should something go wrong, say that new flagpole drops on top of the neighborhood association president’s new MINI Cooper, you'll be able to show the insurance investigators that you are a professional and the failure was clearly not caused by an uncontrolled weld process.

In your company name you use the term Certified. To be a certified welder requires testing, typically to a nationally recognized standard. This is monitored by a third party, often a professional organization such as the American Welding Society (AWS) or a governing agency like the state department of transportation, and administered at an accredited test facility. These organizations would most likely require your work be completed per a qualified WPS to maintain your welder qualifications.

PWC
It's Good to be Me!

Look Inside >>  May/June 2009

Good Call!

We have is a stiffener bar (continuity connection) in a column that calls for (AWS D1.1) BTC-P4 for the flanges and fillet welds both sides in the web. The stiffeners were field welded. After assembling 35 connections we discovered no fillet weld on the bottom side in the web. Problem is we can't weld the bottom side of the stiffener now because of clearance. What are our options? Could we add more than the required 1/4” fillet on top of stiffener to satisfy the inspector? He is not offering any solutions. He just wants the requirements to be met, fillet weld both sides. If you can help, it will be greatly appreciated.
Thank you,
Brian N.

Brian,
Thank goodness for “on-the-ball” inspectors. The inspectors’ part in this construction project is to monitor the fabrication and erection. Should issues arise, he is to bring them to the attention of those who need to know. Speaking from past experience that can be a thankless job.
The inspector on your site is insisting the welding completed meets the requirements of the jobs documentation. When things go wrong and an inspector raises the “red flag”, it is often the case that those on the ground will look to him and ask, “What should we do?”
The inspectors’ first response should be “Contact the Engineer and come up with a documented solution”.
Often, when we start to brain-storm solutions on the job site, we don’t have all the facts or we may not understand all the requirements, to make the call. Example: Your suggestion for missing weld on one side of the joint was to increase weld size on the opposite side. There may be times when this is an acceptable solution, but if the engineers concern is the stress riser created from the missing fillet (which is often the case in today’s building construction) that oversized fillet would be of little benefit. And better to bring the issue into the light for engineering analysis now, than to find out after the concrete has set, that the fix was unacceptable.
Inspectors may or may not have the engineering back ground to make this call, but it is the engineer responsible for the project that should come up with an acceptable solution.
Brian contacted me by email to let me know that the solution to his welding issue was to backup, disassemble each connection, and add the original required ¼” fillet weld. Good call!

Look Inside >>  March/April 2009

What are the negative effects of whipping or weaving?

“We Mig weld carbon steel materials 1/8” thick and greater. Our Welders use a whipping technique that you have described as a bad work habit. What are the negative effects of whipping or weaving?

Whipping and Weaving.
As with many welding techniques, there is a time and place for everything. Watch most robotic applications and you’ll see a constant weaving motion (side to side). Observe as a Fitter puts a 6010 root pass in a pipe and you’ll notice a distinct whipping action (fore and aft). This movement is perfectly acceptable for these applications. The robot uses the motion to find its way. The Pipe Fitter uses the “fast freeze” characteristic to burn away the land and place the root perfectly at each whip.

In production GMA (Mig) welding those same techniques can have negative affects on your finished product. Weaving with the Mig process is a common technique when welding vertical up. It can be difficult to carry the puddle up without the weave technique. A slight weave is common when Mig welding in other positions, but slight should be defined as 2-1/2 x the electrode (wire) diameter. With an 0.035 diameter wire that is about 1/8” of movement. Exceeding that can lead to overlap, undercut and other undesired conditions. Multiple stringer passes should be considered when additional bead width is needed.

As for whipping when Mig welding… There are times when whipping is used to bridge a gap, but often the Welder would be far better off turning the welder down to a short circuit transfer and applying that root. Again, a slight whip is common but slight in this case should be defined as 1-1/2 x the wire diameter. If the key to quality Mig welding is keeping the arc on the leading edge of the puddle, then the whip technique goes against that.

When a whip is excessive weld throats can be undersized and weld spatter is increased. Each time the Welder backs the arc up away from the leading edge the wire is driven into the molten metal and spatter increases. This will require removal and increases the cost of your product.
Good technique is important to improving weld quality. The internet is loaded with great resources for improving our welding skills. Check out this Mig Handbook for additional information. (http://www.esabna.com/EUWeb/MIG_handbook/592mig1_1.htm)

Certified Welders

My younger brother is the Service Manager for a “High-End” import car dealership on the west coast. He received a recall notice concerning Receiver Hitches on Cross-Over SUVs. Welds on the hitch could not be verified as being completed correctly therefore they would need to be removed and re-welded. The Recall Notice stated, “All welding shall be completed by an AWS Certified Welder.”
Joe’s question to me, “What does that mean? Where do I find an AWS Certified Welder?”
Not all welders are AWS Certified Welders. Certified welders are tested at an accredited test facility and their records need to be strictly maintained within AWS QC7-93 guide lines. QC7 is the AWS “Standard for AWS Certified Welders”.
So where does Joe go to find a certified welder? My first suggestion was to contact the nearest “Accredited Test Facility”. The AWS maintains a list, online, at http://files.aws.org/certification/docs/auto/atf_listing.pdf The closest facility for Joe was in Tacoma, WA.
With a little help knowing where to look and the right questions to ask, Joe was able to get the 40 SUV’s on his lot repaired so his sales team could feel confident and start moving them.
If you want to know how you can become “Certified” log on to http://www.aws.org/w/a/certification/index.html There are AWS certification programs for Welders, Inspectors, Supervisors and more. Certification can open doors, present opportunities (like Joe’s) and put you out front in a tough job market.