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PWL#040 - Error Proof Assembly Design, Steel to Aluminum, Weld Cracking, Fiber Optics and more...
November 30, 2006
We hope you will find this Letter interesting and useful.
Let us know what you think of it.

Error Proof Assembly Design, Joining Steel to Aluminum, Filler Metal for Limiting Weld Cracking in Low Carbon Steel, Fiber Optics Sensor Technology, Interview with Ed Craig, Economics of Welding 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).

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December 2006 - Practical Welding Letter - Issue No. 40


TABLE of CONTENTS

1 - Introduction

2 - Article: Design for Error Proof Assembly

3 - How to do it well: Joining Steel to Aluminum

4 - Filler Metal for limiting Weld Cracking in Low Carbon Steel

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Fiber Optics Sensor Technology

8 - Site Updating: Economics of Welding

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contribution: Interview with Edward F. Craig

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board


1 - Introduction

This new issue of Practical Welding Letter for December 2006, opens with some recommendations to designers, urging them to think ahead. They should introduce physical features in the components to prevent their incorrect assembling when building up a complex structure.
Expensive layout time may also be saved by machining bevels or slots to indicate the location of welds.

An old problem came up recently again when a correspondent asked how to weld successfully steel to aluminum. It is possible by cold welding and by a few other techniques, but fusion welding should be avoided as improper to this dissimilar material combination.

For those readers who may have met weld cracking problems with thick plates of carbon steel welded by the Flux Cored Arc Welding process, we point out the results of an investigation published recently indicating the culprit in excessive amount of boron in the filler wires.

Fiber optics may seem a far away subject unlikely to interest welders.
In fact it is not so. More and more fiber optic sensor panels are being embedded in welded structures, buildings, bridges etc., for monitoring in real time their state of stress and strain.

This rapidly developing technology becomes therefore a necessary tool to check design and to predict in advance the approaching of dangerous conditions.

The subject of our Website Page of the Month is Economics of Welding
a matter possibly not so familiar to technically trained welders.
It is important though, especially to those running or wishing to start their own shop.

We are pleased to be able to present the interview with Edward F. Craig who generously agreed to share his views with our audience. He is a world renowned expert, especially in Gas Metal Arc Welding, whose contributions were essential in solving manufacturing problems in very important companies all over the world.

Other departments appear as usual in their place. We would like to urge our readers to comment with their feedback and contibutions on the content of this Newsletter. Click on Contact Us.


2 - Article: Design for Error Proof Assembly

Welded items are generally assembled by arranging together different simpler elements in a certain order, tack welding and then proceeding with the final joining process. It is evident that if several elements are similar in shape and dimensions, errors can occur in assembling whereby costly mistakes can be made.

Not only improper and useless welding may have been performed, with unrecoverable expenditure of energy, work time and consumables, but additional work must be spent to get back some of the parts in their useful shape, to limit the value of unserviceable material to be scrapped.

If fixtures are used, to assist in establishing the correct mutual positioning of the simpler parts, it will help having special features designed and performed in the assembling tool that will not permit to find the location for any but for the correct part.

This kind of assembly is called self-inspectable, because if it could be performed, it must be correct as it is the only possible configuration by design.

Marking element sides with letters or numbers to be matched at assembly may be useful, but building physical hindrances like tabs that must be inserted in slots to set the parts in place are much surer means for avoiding mistakes.

In the assembly drawing every element is identified by a part number, as are the single welds, numbered in the order of execution in the Weld Map. However it is recommended to establish in the procedure inspection stops, where somebody else than the welder is charged with the task of making sure that minor elements or welds were not forgotten, while there is still time and opportunity to correct the oversight.

To set up correct and consistent root openings, special standoff protrusions may be machined in the elements, so that only alignment is to be taken care of.

To relieve the welder from time consuming layout, slots can be machined in the parts to indicate the exact emplacement of welds, or weld length and spacing may be made evident by the contour of the machined component itself.

The purpose of these and similar measures are to improve efficiency so that work time is employed productively while mistakes in assembly are eliminated.

Please let us have your comments on this article by clicking on Contact Us. Pertinent comments will be published in the next issue of PWL.


3 - How to do it well: Joining Steel to Aluminum

Q: How is Steel welded to Aluminum?

A: A similar question was formulated involving Stainless Steel. See Frequently Asked Questions.

One should remind that the same obstacles already mentioned there hinder the proper formation of successful fusion welding of such dissimilar metals. These are: widely different melting temperatures, no mutual solubility in molten state, discrepancy in thermal conductivity and in thermal expansion that cause stresses and cracks.

Furthermore during fusion welding, but also during heating to some low temperature like 200 0C (400 0F) melting phases and several brittle intermetallic phases are generated that compromise the integrity of the weld.

If confronted with a similar problem, short of selecting a different material for one of the components, so that the combination be more favorable, one should explore which alternative process is suitable for the application.

Solid state processes like Explosion-, Friction-, Magnetic Pulse-, Ultrasonic-welding, Roll bonding and High Temperature Diffusion joining avoid fusion by definition. Obviously not all of them can be suitable for a given application, because of the specific limitations of each one of them.

Other than those, High Energy like Electron- and Laser-beam welding could sometimes be applied as they are able to concentrate their energy in a very tiny spot limiting their influence in heat, location and time duration.

Finally, if the joint configuration can be adapted to process requirements, brazing, soldering or adhesive bonding might provide a suitable solution.

Please let us have your comments on this article by clicking on Contact Us. Pertinent comments will be published in the next issue of PWL.


4 - Filler Metal for limiting Weld Cracking in Low Carbon Steel

A recent article of the Welding Journal points out an unsuspected source of weld cracking in low carbon steel. The problem was found while erecting one structure and repairing another one, made of ASTM Steel A36 plates ranging in thickness from 32 to 35 mm (1.25 to 1.375 in.).

Welds were performed by Flux Cored Arc Welding (FCAW) in horizontal position using E71T-1 Cored Wire of 1.32 mm diameter (0.052 in.).

Cracking found in the structures was transversal and detected when the weld was still hot. This is not typical of hydrogen-induced cracking (from moisture), that is generally longitudinal, delayed and occurring after the weld cools down.

Testing showed increased hardness in the weld. The authors of the investigation suspected that boron, which is known to increase hardenability of low carbon steels and is used as a microalloying element to improve strength, could cause hardness changes.

Boron content is not specified in the accepted specification for FCA Welding wires AWS A5.20. In the investigation boron analysis of the cracked welded materal was performed. It was found that a boron content in excess of 0.006% in the filler metal was associated with cracked specimens, while the flux cored wires used in field repairs that did not crack, contained boron in lower quantity.

The authors concluded that the maximum boron content in carbon steel flux cored welding wire should be limited to 0.003% and transmitted this recommendation both to wire manufacturers and to the AWS standards writing committee members.

The article, titled "Weld Cracking linked to Wires containing Boron" was published in the November 2006 issue of the Welding Journal at page 28. Interested readers are urged to seek the original publication.

Please let us have your comments on this article by clicking on Contact Us. Pertinent comments will be published in the next issue of PWL.


5 - Online Press: recent Welding related Articles

From The Fabricator:
As advised in issue 39 of PWL, you will find my article on
Promising welding innovations
http://www.thefabricator.com/LaserWelding/LaserWelding_Article.cfm?ID=1485
Make sure to follow the links (see print with different color).

Joining GMAW and GTAW
http://www.thefabricator.com/ArcWelding/ArcWelding_Article.cfm?ID=1492

From AWS
Improved Assessment of Pipeline Integrity
http://www.aws.org/itrends/2006/10/it1006-18.pdf

Understanding AC GTAW Balance Control
http://files.aws.org/wj/2006/11/wj200611/wj1106-64.pdf

From TWI: The complete Issue 3 - May 2006 (in pdf format) of
Welding and Cutting Magazine (56 pages)
http://www.twi.co.uk/j32k/protected/pdfs/wjsnews_may2006.pdf
(may require no cost registration)


6 - Terms and Definitions Reminder

Accelerating Potential is the potential between cathode and anode that imparts speed to electrons in a beam in vacuum.

Flash is the material that is expelled or squeezed out of a weld joint that forms around the weld under the process pressure.

Interface is the boundary between any two faces or surfaces like those of filler brazing and base material.

Liquidus is the lowest melting temperature at which a metal or an alloy is completely liquid.

Microetch test is a metallographic examination under a microscope at high magnification of a mounted specimen that is ground, polished and etched.

Prequalified Welding Procedure Specification (PWPS) does not require qualification testing, having been approved and therefore being acceptable for a particular code or specification, to whose stipulated conditions it complies with.

Root Surface is the exposed surface of a weld opposite to the side from which a groove weld was performed.

Weld reinforcement is the excess metal deposited in a weld, over and above the amount required to fill it to design requirements.


7 - Article - Fiber Optic Sensor Technology

While we are talking, huge progress is made with fiber optic sensor technology. Imagine that in the near future very large systems will be available, capable of monitoring the status of large structures such as buildings, bridges, dams, aircraft, spacecraft, highways and factories.

At present working prototypes of small sections of real structures are already tested under load to determine multiaxial strains and validate design. They can be used to determine the health condition of a structure after a major accident. The sensitivity of fiber optic sensors is high enough to detect individuals jogging on a suitably instrumented bridge.

Special sensors attached to a part processed in an autoclave can monitor internal temperature, strain, and degree of cure. With proper feedback instrumentation the signals can be used to control the process, improving yield and quality.

Fiber optic sensors embedded into or attached to materials can perform the following tasks:

  1. in manufacturing they enhance process control systems,
  2. they improve nondestructive evaluation of manufactured parts,
  3. they enhance environmental control systems,
  4. they help assess health and damage of structures during their lifetime.

Fiber optic sensors are now available for measuring quantitative data relative to linear and angular position and displacement, rotation, acceleration, electric and magnetic field measurement, temperature, pressure, acoustics, vibration, strain, humidity, viscosity, chemical measurements and many other physical properties.

Compared to electronic sensors, the advantages of fiber optic sensors include their ability to be lightweight, of very small size, passive, low power, resistant to electromagnetic interference, of high sensitivity, wide bandwidth and environmental ruggedness, high temperature capability and multiplexing potential.

Essentially the physical interaction of the environment with optical fibers embedded in a structure influences the properties of a laser light transmitted through them. Dedicated monitoring systems can then deduct by automated analysis the effect of dynamic and other forces on the structure.

As fiber optic is increasingly used for communication and data transmission, it is conceivable that future merging of sensors in very large systems will enable the capacity of monitoring the status of buildings, bridges, highways and factories over wide areas.

Also monitoring of volcanic activity, earthquakes, hurricanes and tornadoes could be readily integrated into very wide networks of sensors for the purpose of managing emergency response to disaster.

See the following articles at the given addresses:

Overview of Optical Sensors (40 pages) see
http://www.bluerr.com/papers/Overview_of_FOS2.pdf

Progress on Multidimensional Strain Field Measurements
using Fiber Optic Grating Sensors (9 pages)
http://www.bluerr.com/papers/BRR-2000_Sensors_Expo_Anaheim_p203.pdf

Fiber Optic Sensors
http://www.rp-photonics.com/fiber_optic_sensors.html

Please let us have your comments on this article by clicking on Contact Us. Pertinent comments will be published in the next issue of PWL.


8 - Site Updating: Economics of Welding

We are glad to present the new Page of the Month in our Website, this time dealing with the subject of Welding Economics. It represents a pertinent introduction to two older pages one on Starting a Welding shop and another one on Cost Estimate.

To read the new page click on Welding Economics.
You will find from there direct links to the other two pages mentioned above.

We also rewrote and edited our Site Map
in a way we feel makes it easier for you, our reader, to look for and find what you may be looking for.

In my spare time I wrote also a page on a different subject. It is about the attitude one should have when in search for a job. The need for a new job may come at any time but it may be most painful when approaching retirement.

I think that the story of how I prepared for retirement may have some interest for other people. You will find this page at Create your New Job. Good luck.

We plan to introduce quite soon a new page pointing to online available Resources which may be of help when dealing with some subjects in depth. We hope it will be ready for the next regular issue.


9 - Short Items

9.1 - Acicular Ferrite is a highly substructured nonequiaxed ferrite formed upon continuous cooling by a (mixed diffusion and shear mode) transformation that begins at a temperature slightly higher than the transformation temperature range for upper bainite.

9.2 - Bauxite is the most important ore (source) of aluminum, alumina abrasives, and alumina-base refractories. It is a mineral composed largely of hydrates of alumina.

9.3 - Fiber Optic Sensors (known also as Optical Fiber Sensors) are devices capable of sensing changes in some property, temperature, mechanical strain, vibrations, pressure, acceleration, or concentrations of chemical species, through the physical interaction with them of the surrounding medium.

Light from a laser sent through an optical fiber that undergoes physical action, is subjected to fine parameter changes detectable by suitable monitors that translate these changes into quantified values of the property being measured.

9.4 - Grain Growth is an increase in the average size of the grains in polycrystalline material, usually as a result of heating at elevated temperature. Very large grain size may impair the room properties of certain materials.

9.5 - Low-cycle Fatigue occurs at relatively small numbers of cycles (less than 104 cycles). Low-cycle fatigue may be accompanied by some plastic, or permanent, deformation. Conditions promoting its appearance in any component may limit drastically its usefulness.

9.6 - Pearlite is a microstructure consisting in a metastable lamellar aggregate of ferrite and cementite in steel resulting from the transformation of austenite at temperatures above the bainite range.
Its metallographic appearance is readily identified.


10 - Explorations: beyond the Welder

Steve Jobs Stanford Commencement Speech 2005
http://www.youtube.com/watch?v=D1R-jKKp3NA

PODCAST: November 15, 2006: Science Talk
http://podcast.sciam.com/weekly/sa_podcast_061115.mp3

SBI Video
http://ilovesbi.sitesell.com/Quark.html

Ballbots
http://www.msl.ri.cmu.edu/projects/ballbot/

Romantic Oregon Coast Vacations
http://romantic-oregon-coast.com


11 - Contribution: Interview with Edward F. Craig

We are grateful to Mr. Edward F. Craig, who agreed to this interview, and thrilled at the opportunity to present his thoughts on a range of questions, to interested readers who, we hope, will appreciate them.

He is a world renowned welding expert and author of instructive books and teaching aids on welding.

Among his books we notice:

"A Management & Engineering Guide to MIG Welding Quality-Cost-Training"

"Manual MIG and Flux Cored Optimum Weld Parameter Selection"

"Teach Yourself. "Robots" and Manual MIG Weld Process Controls"

Video: "Manual MIG and Robot MIG Weld Parameters and Weld Process Controls Made Simple".

Website: www.weldreality.com

PWL: Hi Ed,
Thank you for having agreed to release this interview.

Q - How would you describe your most important competence and expertise?
A - For more than three decades I have focused on the simplification of weld process controls. I like to believe that both the MIG and flux cored weld process are black and white, with no grey.

These processes offer narrow weld parameter ranges that are suited to either the metal thickness or specific weld. There are optimum parameters and optimum technique for each weld so therefore weld personnel don't have to play around with weld controls to attain optimum welds.

My books and website focus on the removal of the welding mystery and welding salesmanship that is evident throughout the global weld industry.

Q - Which of your contributions to welding knowledge and practice would you consider essential?
A - The complete understanding of the unique manual/robot weld requirements necessary to produce optimum weld quality without the aid of electronic bells and whistles, three part gas mixes or special welding wires.

Q - Which of your achievements procured to you the highest satisfaction?
A - First, Working with robots, as weld perfection can be attained and Second, training weld personnel in process controls, I enjoy working with individuals who have an open mind and are willing to learn.

Q - Do you believe that modern welding Codes are important for spreading distilled welding knowledge and experience?
A - In terms of producing optimum weld quality and from a practical MIG and flux cored weld perspective, weld codes typically provide more confusion than they do weld solutions. From an inspection point of view weld codes are very important.

Q - Would you exhort the welding industry to concentrate more efforts in which directions to assure continuing progress?
A - For decades the management in the welding industry has ignored weld process expertise so today we have an industry in which workers play with the weld controls and is almost impossible to find anyone in management who can figure out the costs of a weld or is aware of the weld deposition rate potential.

Q - Which innovations do you notice having most chance of being widely adopted?
A - After two decades of product development MIG equipment manufacturers are starting to make pulsed equipment that actually provides benefits for "all" carbon steel applications. The next decade will see the elimination of traditional MIG equipment and the short circuit and spray transfer modes.

Q - Which recent trends do you remark in welding industry management?
A - Lack of process ownership, lack of welding accountability, and process ignorance.

Q - Which advice would you offer to young people just starting a welding career?
A - Look towards becoming an expert in weld process controls and look to weld automation such as controlling robots, twin wire welds, sub arc, pipe weld systems. If you don't like the weld smoke, evaluate laser welding/laser cutting or automated TIG/plasma welding.

Don't rely on weld sales advice. You will become a process expert by reading, keeping an open mind and spending the rest of your life with the weld shield down evaluating welds, consumables and equipment.

PWL: Thank You, Ed.

Please let us have your comments on this interview by clicking on Contact Us. Pertinent comments will be published in the next issue of PWL.


12 - Testimonials

From: Jeff Walker (e-mail withdrawn for security)
To: Welding Advisers
Date: 20 Nov 2006, 08:28:45 AM
Subject: Re: non magnetic

Howdy Elia,
Thanx much for your reply. [...]
Appreciate your time and honest reply.
Good days to you.
Sincerely,
Jeff


Jagdish Singh (e-mail withdrawn for security)
To: Welding Advisers
Subject: Re: PWL#039B - Corrosion, Corrosion Prevention, Corrosion Control, Cathodic Protection, SCC and more...

Thank You so much for your very informative updates Elia.
Keep up the good work.
Best Regards, Jagdish,
West Malaysia.


13 - Correspondence: a few Comments

13.1 - An unidentified subscriber who is justly worried by unsolicited e-mail, reacted to my last issue of PWL by sending me an official response by some firm specializing in discarding unwanted mail, and asking me to confirm my identity.

Please, don't load me with additional work, I do not play to such a fife. Subscribing is voluntary, if you like PWL do what you need to whitelist my sending address. Otherwise, sorry, too bad, I will not concur.

13.2 - Please consider that even if you want only to change your address to receive PWL at a new one, you should still confirm your request, because our website host is committed to counter the diffusion of unsolicited e-mail by making sure that the distributed publication is indeed requested.


14 - Bulletin Board

14.1 - NACE International Corrosion 2007 Conference & Expo.
Mar. 11 - 15, 2007 - Nashville, Tenn.
www.nace.org/c2007

14.2 - MetalForm 2007
Mar 25 - 28, 2007 - Rosemont, Ill.
www.metalform.com

14.3 - To stay informed on updated and new pages from our site, we would suggest that you bookmark for frequent visits our Blog at:
http://www.welding-advisers.com/Welding-plan-blog.html

14.4 - How I prepared for retirement may have some interest for other people, retiring and not yet. See this page at Create your New Job.


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Best wishes for the coming year 2007.
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