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RSW Electrodes Life, Al-Bronze Weld to MS, Aerospace Filler Metal, Backing Bars, Processes, more...
January 02, 2007
We hope you will find this Letter interesting and useful. Let us know what you think of it.

PWL#041 - Extending Life of Copper RSW Electrodes, Welding Aluminum Bronze to Mild Steel, Filler Metal for Aerospace Applications, Backing Bars, Additional Processes, Interview with Greg Metko and more...

This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. We actively seek feedback to make it ever more useful and up to date. We encourage you to comment and to contribute your experience, if you think it may be useful to your fellow readers. Click on Contact Us (opens new page).

You are urged to pass-along this publication to your friends, if you like it, and if you want to help them. If you received this from a friend and if you like what you read, please subscribe free of charge and you will also receive a bonus book on Practical HARDNESS TESTING Made Simple.
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January 2007 - Practical Welding Letter - Issue No. 41


1 - Introduction

2 - Article: Extending Life of Copper RSW Electrodes

3 - How to do it well: welding Aluminum Bronze to Mild Steel

4 - Filler Metal for Aerospace Applications

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Backing Bars

8 - Site Updating: Additional Processes

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contribution: Interview with Greg Metko

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board

1 - Introduction

We start this New Year 2007 of PWL publication with warm wishes of good health, peace and prosperity for all our readers and their families. We plan new programs and we nurture hopes of bringing this Website, already appreciated by many visitors, to higher levels of usefulness.

You may be interested to know that by now the number of voluntary subscribers who opted-in to receive this newsletter passed 3150 individuals, about 900 of whom joined during the year 2006.

The first Article reports on progress in research intended to automate as much as possible the routine maintenance of copper electrodes used for spot welding aluminum alloys. It appears that the need is particularly felt in robotic cell set-ups for automotive production where productivity gains are actively sought for.

How to weld Aluminum-Bronze to Mild Steel is the subject of our next item, written in response to a specific question sent by one of our readers. It seems that our answer filled a pressing need.

For the Filler Metal section we deal with Aerospace Applications. Although many international Standards exist, the most known and diffused are probably those prepared by SAE as Aerospace Material Specifications. The article may help readers in search of information.

Our next Article covers the Backing Bars subject. These are powerful welding aids contributing to successful production of full penetration root passes. A kind of refractory tape used for this purpose is apparently not yet used as much as it could, perhaps because of resistance to change.

In our Page of the Month review of new website titles, we introduce a presentation of a few processes not easily groupable under a common characteristic, to provide easier ways to find what one may need.

We continue with the Contribution of an experienced weld teacher and trainer, Greg Metko, whose interview we are authorized to reprint thanks to the kindness of the original editor. We hope to be able to bring in, in time, various views of qualified welding professionals, that will enrich our knowledge and stimulate our curiosity.

Do our Comments intrigue you? See Section 13

We wish to call your attention to the Comments section of this issue where we are going to offer some original thoughts, possibly unexpected by those who asked for our help. Nonetheless, in our view, they are really important for every one.

We recommend to pause for reflection on the items discussed and then to send us your feedback. We will especially appreciate if you are going to comment from your firsthand experience on those subjects, and we will publish your entries in the next issue.

Other departments follow where they are expected. We would like to urge our readers to comment with their feedback and contributions from their practical experience to the content of this Newsletter.
Click on Contact Us or on the button of the same name from the Navigation Bar of every page of our website (

2 - Article: Extending Life of Copper RSW Electrodes

Resistance Spot Welding (RSW) is a time and production proven method, for joining sheet metal elements apt for automotive mass production, whose main advantages are:

  • Suitability to robotic manipulation
  • Absence of consumables (per weld)
  • Absence of additional parts or materials in the assembly
  • Readiness and availability
  • Relative economy of equipment

The main limitation is the continued need of tip maintenance due to rapid and progressive deterioration of electrode surface quality. This is particularly true for electrodes used for welding of aluminum sheets, which require higher clamping forces and current values than corresponding joining of steel.

Electrode life is affected by aluminum pick-up, a normal occurrence with RSW. The buildup of aluminum on the electrode surface is detrimental to the process as it increases the normal resistance value at the interface and affects spot weld quality.

The need for periodic and frequent dressing of electrode surface to control quality of welds, disrupts the normal production flow and adds to expenses.

Research at the University of Warwick, UK, in conjunction with Innoval Technology, resulted in studies on the use of coordinated robot movements to perform electrode buffing operations in dead time between each component welding.

The key of the success was probably a particular abrasive wheel that was found capable of removing effectively the aluminum build-up from electrode surface.

If the surface deterioration is too advanced, then buffing alone is not sufficient: the electrode needs dressing with chip removal by a cutter to create a fresh electrode face.

Monitoring of electrical signals from the weld controller helps in directing the robot to the required action. This phase of the research requires further work to detect and measure electrode damage in order to trigger the robotic action needed, be it either buffing or dressing operation.

On this subject see also the following online publication:

Joining Processes for Low-Carbon Automotive Applications

Please let us have your comments on this article by clicking on Contact Us, or use the Contact Us button from the NavBar in any page of our website

3 - How to do it well: welding Aluminum Bronze to Mild Steel

Q: - Can we weld Aluminum Bronze to Mild Steel A36? If yes what should be the electrodes?
Note: This is an actual question sent to us by one of our readers.

A: - Yes, Aluminum Bronzes are weldable to carbon steels using SMAW (Shielded Metal Arc Welding), GTAW (Gas Tungsten Arc Welding)(with Alternating Current stabilized by High Frequency) and GMAW (Gas Metal Arc Welding)(with Direct Current Electrode Positive).

One should note that aluminum in these bronzes forms tenacious oxides that must be removed before welding. This is probably the most pressing concern that should worry whoever considers to perform this welding. Shielding gas, or fluxing by electrode cover are used for preventing their formation while welding.

For the first process, electrodes ECuAl-A2 can be used with preheat from 150 to 200 0C (300 to 390 0F) for sections thicker than 6 mm (1/4").

ANSI/AWS A5.6-84 (R2000)
Specification for Covered Copper and Copper Alloy Arc Welding Electrodes
24 pages
Click to Order.

For the other processes above, rods or wires ERCuAl-A2 are used. For repair welding of aluminum bronze casting with highly stressed cross sections, ERCuAl-A3 may be preferred because it has less tendency to crack.

ANSI/AWS A5.7-84(R2000)
Specification for Copper and Copper Alloy Bare Welding Rods and Electrodes
18 pages
Click to Order.

4 - Filler Metal for Aerospace Applications

In aerospace applications one finds light metals (Aluminum, Magnesium, Beryllium, Lithium) for structural construction, tough steels for demanding assemblies (pylons, wing hinges, undercarriages) and heat resistant materials (Nickel, Cobalt, ceramics) for propulsion systems.

You may meet occasionally SAE Aerospace Materials Specifications (AMS), even outside the USA. European Specifications are used in Europe. Materials described by these specifications are intended for aerospace use. As such their quality is controlled and traceable, their properties are tested and documented by binding documents. As long as the materials are identified, they can be used with confidence for critical applications.

If you do not know what AMS documents are and where they come from, here is a brief introduction.

The Society of Automotive Engineers (SAE) has a long record of having provided to the whole world some of the finest specifications concerning Materials, Processes and nondestructive testing methods.

In their Home page > About SAE ( they state:
"The Society of Automotive Engineers has more than 90,000 members - engineers, business executives, educators, and students from more than 97 countries - who share information and exchange ideas for advancing the engineering of mobility systems. SAE is your one-stop resource for standards development, events, and technical information and expertise used in designing, building, maintaining, and operating self-propelled vehicles for use on land or sea, in air or space."

A nice presentation explaining the activities of SAE, (and then going on to deal with Friction Stir Welding Standardization) can be found in the first ten frames of a document downloadable at: stirweld_pf/showFile/100011/d20040615142645 /Yes/FSW+Stds+.ppt

In another page on SAE Aerospace Technical Committees
the different Divisions are outlined and the Committees are reported.

The Aerospace Materials Division is the seventh listed.
It is formed by the following:

  • Metals Group
  • NonDestructive Testing Group
  • Non-Metals Group

A few of the materials specified by this kind of documents were already discussed in PWL#010 in the context of filler metals for heat resisting alloys.

If the application is not aerospace, there is no obligation to use SAE AMS materials, but it may be easier and expedient to procure them this way.

You can find a list (incomplete) of SAE Aerospace Materials Specifications referring to welding and brazing materials in the following commercial page:

Additional products meeting AMS for corrosion and heat resistant materials can be found in the following commercial page:

If you are given an AMS specification number and need to know which material it describes, go to the following supplier of technical information at:

Print in the search window the number you have (AMS XXXX) and click on the arrow or Enter: a short description of the Specification will appear, with the full official designation, the latest revision available and the issue date.

As an example (not related to welding), to understand the general layout of the document (as described in frame no. 10 of the presentation above), you can see AMS 5726C (pdf format) at /Analysis/References/AMS/AMS%205726.pdf

The status of a material meeting the requirements of SAE AMS is documented by the original manufacturer. If documentation is missing or lost, such a status cannot be reinstated even by repeating all the tests. Such material can then be used only for ground applications, including test pieces if needed.

5 - Online Press: recent Welding related Articles

From AWS:
What Caused those Cracks? /it0706-22.pdf

From the Fabricator:
Which filler wire is best for welding 6061-T6 aluminum?

From Lincoln Electric:
Increasing Productivity with a FCAW Wire

From TWI:
Gas Shielded Consumables /jk85.html

The complete Issue 4 - July 2006 (in pdf format) of
Welding and Cutting Magazine (52 pages)
(may require no cost registration)

6 - Terms and Definitions Reminder

Actual Throat is the effective distance between the root and the face of a fillet weld.

Cutting tip of an oxyfuel gas cutting torch is the outermost detachable part including the nozzle through which the gases get out and burn.

Double Bevel Groove weld is a joint where welding is performed from both sides. One of the plates has a double bevel edge shape, abutting the other one that has a straight (square) edge.

Electrode Extension also called "stick out" is the length of filler wire between the contact tip end and the arc, in GMAW, FCAW and SAW.

Ferrite Number (FN) is an arbitrary, standardized value based on magnetic properties, designating the ferrite content of an austenitic stainless steel weld metal. This value directly replaces percent ferrite or volume percent ferrite and is determined by the magnetic test described in AWS A4.2M/A4.2:1997, "Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Ferritic-Austenitic Stainless Steel Weld Metal".

Ground Connection is the electrical contact established for safety between the welding machine frame and the ground.

Pulsed-mode Power welding is performed using a power source designed to cycle between low (maintenance) and high (welding) current with pulses of selectable, definite time lengths.

Shielding Gas provides a protective atmosphere displacing air to avoid oxidation and contamination of molten metal during welding.

7 - Article - Backing Bars

Backing serves the purpose of supporting and shielding the root side of a joint. It may be a metal, in which case it may or may not become partially fused and part of the joint. Or it may be a refractory material or a flux.

Accomplished and skilled welders are able to perform consistent root welds with smooth underbead, full control of penetration and without objectionable oxidation even without backing.

In cases where such a level of welders skill cannot be completely relied upon, the use of backing bars is recommended. Full penetration of welds is then assured by providing a physical barrier to contain the molten metal in the joint while avoiding its dripping away.

In certain cases the backing bar, of the same material as the welded one, may become a part of the structure and remain in place. However, if the structure is designed to stand fatigue stressing, backing should be removed because it can be described as a notch or a preferential path for initiation and propagation of cracks. It may also reduce the section, objectionably, if fluids should pass unobstructed.

A backing weld can be used in a single groove weld joint. If possible, that is if there is access to weld from the back side, the backing weld is deposited first. It can then be ground or gouged from the face side to obtain sound metal on which further passes can be welded.

Consumable backing bars of compatible material are used for welding the root pass of pipes or tubes. They are tack welded to one side at least. They help to assure alignment before welding of the separate tube elements with a consistent gap, they melt completely contributing to full weld penetration, they do not reduce the section of passage of fluids.

If the backing is not to be welded in the joint and not to be left in place, it can be of a different material. Copper backing bars or rings (for tubular sections) may include passages for cooling water and/or for shielding gas used to purge the joint. When welding steel, copper backing should never be melted by occasional arc strikes, to avoid weld contamination.

Inert or refractory materials (ceramics) can be held in place by provisional means to be removed after welding has been performed. A self adhesive glass reinforced tape covered with refractory fiber placed on aluminum foil is probably the cheapest form of backing strip, usable for applications where suitable performance can be demonstrated and when the tape can be removed after welding. It seems to be adequate for most materials and for a wide range of processes.

Carbon or graphite backing bars can be used for welding copper, where there is no danger of carbon contamination of the weld.

For Submerged Arc Welding, flux can be used as a backing, pressed against the joint by means of an inflated hose within a channel fitted against the back of the joint.

Please let us have your comments on this article, possibly adding from your experience, by clicking on Contact Us, or use the Contact Us button from the NavBar in any page of our website

8 - Site Updating: Additional Processes

This time the Page of the Month is intended as an introduction to a range of different processes than cannot be easily grouped by any common characteristic.

Some are sufficiently similar to mainstream processes to be performed with slightly modified equipment, but others cater to special needs and would not be normally found in a general welding shop.

It seems however that the adaptations to be implemented for at least some of the Additional Processes discussed should be easily mastered, as sufficiently near to the welding profession.

To read the new page click on Additional Processes.

For the whole updated content of the Site click on the Site Map.

To stay updated on revisions and additions click on the Welding Blog button from the NavBar or on the following link: Welding Blog, or subscribe to the RSS feed as indicated under the NavBar in each page of the Website.

Please let us have your comments on this new page by clicking on
Contact Us, or use the Contact Us button from the NavBar in any page of our website (

9 - Short Items

9.1 - Accelerated Corrosion Test is a method designed to produce in a short time, but usually under harsher conditions, the deteriorating effects appearing under normal long-term service in a milder environment.

9.2 - Austenitic Manganese Steel is an iron base wear-resistant material containing about 1.2% C and 12% Mn. Its hardness is increasing with use and work hardening while rubbing against earth and rocks. It is used mainly for earth-moving, mining, quarrying, and heavy machinery moving materials in bulk. Also known as Hadfield steel.

9.3 - Bluing is the forming of a thin blue film of oxide for improving appearance and resistance to corrosion, resulting on the clean surface of a steel from the action of steam at some elevate temperature. May be followed by light oiling.

9.4 - Flake Graphite is graphite in the form of platelets affecting the microstructure of gray iron, that can be seen in metallographic sections.

9.5 - Normalizing is a heat treatment consisting in heating steel or ferrous alloy to a suitable temperature above the transformation range to austenitic structure and then cooling in still air to room temperature to provide definite mechanical properties.

9.6 - Springback describes the elastic recovery of metal after stressing. In forming operations it represents the difference between the shape imparted by the die and the form of the object when released. To obtain a definite profile from an elastic material it is customary to shape the die to stress the material more than necessary, in order to obtain the required form and dimension upon relaxation.

10 - Explorations: beyond the Welder

How Steel is Made start.asp?wid=0671017062835

A followup from last issue: Thoughts On
Steve Jobs's Commencement Address At Stanford University 12/saturday_rambli.html

A Robot in every Home
by Bill Gates -E7F2-99DF-31DA639D6C4BA567

A CLEVER Vehicle

Spiders Bots in Action

11 - Contribution: Interview with Greg Metko

PWL: We are indebted to Terri Ann Barry, Editor of PowerClick of Miller Electric Mfg. Co., who graciously authorized us to reprint the following interview from the last issue of their newsletter. We think that
will be of interest to at least some of our readers.

While we do not specifically endorse any of the opinions or recommendations proposed by the author, relative to the products of the firm, we think that interested readers could profit by signing up to PowerClick newsletter at

Here is the complete interview (Pictures omitted):

"Self-shielded flux cored wires meeting AWS E71T-8 requirements comprise much of the wire used for structural steel in buildings, bridges, civil construction and infrastructure applications. While popular and/or necessary for structural welds, these wires are notoriously difficult to use. Perhaps more than any other tubular electrode, these wires demand special considerations, in both technique and equipment, for obtaining good results.

Greg Metko, a welding engineer with Miller Electric Mfg. Co., has spent thousands of hours training Ironworkers how to successfully weld with self-shielded flux cored wires. For the last 12 years, he has participated in the Ironworkers Instructor Training Program. This program brings together hundreds of instructors who take what they learn and pass it on to thousands of apprentices and journeymen. He is one of the experts dedicated to "training the trainers." Metko took some time out from a recent training effort to offer the following advice.

Q: Why are self-shielded T-8 wires so difficult?

A: Because they operate in a very narrow voltage range. Take a 5/64-in. diameter wire, which is pretty common. For an all-position fillet weld, its operating range is just 19 to 22 volts. If you make a weld outside of that range, the odds of the weld failing inspection are pretty good.

Q: What happens to the weld if the right voltage isn't used?

A: Excess arc voltage causes porosity, while lack of voltage causes a convex, "humped" or "ropey" bead and potentially insufficient penetration. Extremely low voltage causes "gun buck" where the wire dives through the molten weld pool and stubs on the plate.

Q: What is the most common cause of voltage variations?

A: There are lots of contributing factors, but the one I see the most during training is improper electrode stick-out. When using a flux cored welding gun, this is the distance from the end of the contact tip to the arc. With a self-shielded T-8 wire, the operator needs to maintain a stick-out of 3/4 inch. The contact tip to work distance (stick-out plus arc length) will be about 1 inch.

Q: What happens if proper stick-out isn't maintained?

A: Too little stick-out doesn't allow enough "pre-heat" time for the wire to form the proper shielding gas coverage, which leads to porosity. Too much stick-out will cause the amperage to drop outside of the proper range and the weld may have insufficient penetration. Also, long stick-outs may pre-heat the wire too long, which may change the composition of the wire.

Q: How do welders know if they're using the right voltage?

A: The weld will have little to no spatter, no porosity and a slightly convex appearance. A good way to ensure proper voltage is to use a portable wire feeder with a digital voltage display, such as the SuitCase™ X-TREME™ 12VS. It displays voltage while welding and for five seconds after you stop welding. Note that analog meters aren't very accurate compared to a digital display, and any readout back at the power source won't be accurate because long cable lengths common in field welding cause voltage drop.

Q: Other than technique, what else causes voltage problems?

A: Poor weld cables are a common culprit of excess voltage drop. Make sure your weld cables are sized properly and that the cable, clamp and all connections are in good condition.

Q: Should you use a specific type of power source for good voltage control?

A: Yes. To start, welding codes with seismic requirements (e.g., D1.1, FEMA 353) dictate using a constant voltage (CV) power source. Even if procedures don't demand it, Miller always recommends a CV welder for wire welding. This type of machine lets the operator set voltage and wire feed speed/amperage, which makes it easy to "dial-in" optimum welding parameters.

Q: Are some types of CV welders better than others for voltage control?

A: Yes. With an electric welder, primary power fluctuations can affect weld voltage. Fortunately, some inverters popular for construction work, like Miller's XMT® 350 VS, can compensate for voltage spikes and dips. They feature a technology called Auto-Line™ that maintains a steady welding output as long as the primary power remains within a 190 - 630 VAC range. With some engine drives, drawing on generator power while welding (such as using a grinder) may also affect arc voltage. Miller's Trailblazer® Series and PipePro™ engine drives are specifically designed to overcome this problem.

Q: What's the most common welding advice you give?

A: Maintain proper stick-out and use the proper gun angle. Some T-8 wires simply won't run well if you don't use a drag technique. Point the wire into the leading edge of weld puddle and angle the gun toward the direction of travel by 5 or 10 degrees. It is also critical to keep the wire directed in the molten slag pool, otherwise wire will dive into the plate, stub and create a cold spot. Some brands of wires are more forgiving to use than others, so you might want to experiment.

For good results when welding with AWS E71T-8 flux cored wires, maintain a proper stick-out (3/4 inch) and use the proper gun angle (5 to 10 degrees toward the direction of travel).

Q: Do welders need to do anything special during arc starts?

A: Yes. Clip or jog the wire so that you start with the proper stick-out of 3/4 inch. When starting, hold the contact tip about the same distance away from the work as when you're welding (which is 3/4 of an inch), pull the gun trigger, wait a second or two for the arc to establish and the weld puddle to form, and then drag the gun forward. If you experience wire stubbing, start the arc about 1/4 inch closer, then move it back once it is established. If your wire feeder has a "soft start" or "run-in control," you can use those features to improve arc starts."

PWL: Thank you, Greg Metko

Please let us have your comments on this interview by clicking on Contact Us, or use the Contact Us button from the NavBar in any page of our website
Pertinent comments will be published in the next issue of PWL.

12 - Testimonials

From: Mahboob Siddiqi (e-mail address removed for security)
To: Welding Advisers
Date: 05 Dec 2006, 09:32:31 AM
Subject: Re: Alu-Bronze

Dear Elia,

Thank you very much for the information. It helped me a lot in solving a problem with a repair job. Thanks once again.

Best Regards,

Mahboob Siddiqi

From: Adam Prince (e-mail address removed for security)
To: Welding Advisers
Date: 10 Dec 2006, 05:08:37 PM
Subject: Re: warping

Thank you for the quick response. [...]
Thank you.

13 - Correspondence: a few Comments

13.1 - It is amazing! You may recall that the first article of the last issue was about Design for Error Proof Assembly.

Well: shortly afterwards I got the following letter: "I am a welder working for a company which manufactures trucks for the military. Myself, along with many other welders are responsible for welding the aluminum cabs and sub assemblies for these cabs. The company is scrapping cabs in which a welder may have improperly installed a part that was welded in wrong.[...]"

The correspondent just wanted to know if the company is justified in scrapping valuable subassemblies because of unacceptable rework in the specific type of aluminum alloy.

What did not dawn on him, on colleagues, engineers and management of that company is that assembly errors can and should be avoided at all, not by penalizing careless welders but by designing for error proof assembly!

I suggested that the welders themselves propose the best ways to eliminate those costly errors, and then that they ask the engineers to implement the needed changes.

I would like to be able to report in a future issue of PWL that all errors were abolished with substantial gains... if my correspondent cares to inform us.

13.2 - A worried correspondent sent me the following note:

"A small trucking company that specializes in hauling oversize and heavy machinery hired me to modify a trailer by splitting the frame in half, extend it by 5 feet ...[...]. He also needed me to build a 10 foot insert so that he could have 60 feet of usable deck space.[...]...when the trailer was loaded some of the welds started to break [...]. I still do not know the proper procedures for welding T-1 [...]."

Besides the answers I gave to the specific welding problems I felt I should ring a warning bell, and I wrote as follows: "[...] For demanding projects you should always request from your customer to provide drawings signed by a Certified Engineer who will relieve you from responsibility in case of failure and disaster.
See my page on Welding Liability. [...]"

This kind of warning may apply also to other readers who are not aware of the risks they are taking just to please their occasional customer...

14 - Bulletin Board

14.1 - A kind correspondent sent me the following note:

"Subject: RE: Hardness Book

I have one comment about the book. I use a Krautkramer Microdur 10 that uses an Ultrasonic contact impedance method for hardness testing.
An ASTM standard A1038 came out in 2005 addressing this type of hardness. If you do another book, it would be great if you could include this method. Thanks,

PWL: I will gladly update my Hardness Book as soon as possible for future subscribers.

14.2 - Friction Stir Welding and Processing IV Symposium and TMS Fall Meeting
Feb. 21 - March 1 - 2007 Orlando, Fla

14.3 - SAE 2007 World Congress
Apr. 16-19 - Detroit, Michigan

14.4 - SiteSell, our Website Host and faithful Mentor, has an absolutely unique perspective about business, and life.
Take a peek inside the world of SiteSell.
In the busy, noisy blogosphere, get ready for some quiet, original, and valuable thinking, not to mention unique insights into SiteSell itself. Visit


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Copyright (c) 2007, by Elia E. Levi and
All Rights Reserved

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Best wishes for a Happy New Year!

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