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PWL#077 - Hermetic Seal Laser Welding, Selecting Carbide for Hardfacing, New Consumable Process Tape
January 04, 2010
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PWL#077 - Hermetic Seal Laser Welding, Selecting Carbide for Hardfacing, New Consumable Process Tape for Spot Welding, Direct Manufacturing Process with EBW, Interview with Leonard Mills, Monitoring Structures, Production Failures and more...

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January 2010 - Practical Welding Letter - Issue No. 77


TABLE of CONTENTS

1 - Introduction

2 - Article - Hermetic Seal Laser Welding

3 - How to do it well: Selecting Carbide for Hardfacing

4 - Consumable Process Tape for Spot Welding

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Direct Manufacturing Process with EBW

8 - Site Updating: Monitoring Structures, Production Failures

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Interview with Leonard Mills

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board


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1 - Introduction

Practical Welding Letter wishes to all Readers and their Families a happy and prosperous New Year in peace and good health.

The New Year starts here with this 77th Issue of Practical Welding Letter. A few articles bring quite recent information that should not escape to attentive readers who might enjoy the news for enlarging their horizons, if not for practical, immediate problem solving.

This Issue opens with an article requested by a kind reader who simply wrote he would like to read something on Hermetic Seal Laser Welding. Other readers too are invited to let us know which subjects they would like to read about.

This article summarizes a few fundamental facts and provides further links to sources adding useful information.

Then comes the answer to the question if it is worthy to switch to a cheaper carbide used for Hardfacing. One should be skeptic and doubtful before changing a process that works.

Further down is a report on a recent innovation in spot welding, successfully used already for a few years, essentially in the automotive industry. Its advantages may appeal especially for mass production.

The next article describes the use of Electron Beam Welding with special automatic setup, for building reactive metals free forms in a way reminiscent of Rapid Prototyping. The potential for considerable economy seems quite attractive.

In the Website Update we introduce two subjects that may interest you: Monitoring Structures and Production Failures.

The first item, Monitoring Structures, describes a trend in manufacturing new structures, to include sensors.

The second page, on Production Failures, could help with useful hints when unexpected welding production problems suddenly appear. Even before investigating, one should be alert to the possible causes.

A new interview with Leonard Mills is published, provided by an expert Inspector and welding Instructor who kindly shares with us his memories and comments.

The other sections can be found at their usual place. Enjoy.

Use the Contact Us form to let us have your comments and feedback. (Don't use Replay).


2 - Article - Hermetic Seal Laser Welding

A reader was so kind to send us an appreciated feedback, requesting this time an article on the subject described in the above title.

Laser sources, especially of the modern ND:YAG solid state kind with pulsing capabilities, and using fiber optics delivered beams, are successfully employed for sealing leak tight metal enclosures.

Laser welding is preferred to competing processes for its lower heat input applied locally where needed, without heating surrounding parts.

Although laser light is transmitted in air, most often the enclosures to be sealed need an inert atmosphere at their inside, to guarantee long time operation. Furthermore certain reactive materials must be shielded from oxygen and moisture, so that suitable protective environments are generally provided in closed containers to perform laser sealing.

If needed, Helium can be included in the shielding gas mixture, providing an easy way to test welded enclosures for leakage, with suitable sensors.

Depending on application requirements, the design is generally optimized to require loose fit tolerances, automatic assembly and CNC welding.

Laser welding is performed autogenously, without filler metal. However, if required for certain metals combinations that would crack without a suitable filler, the additional operation of preplacing it in the joint increases manufacturing costs.

Some indications on the metals used for enclosures can be found in the following references providing additional insight for interested readers.

Designer's Guide for Laser Hermetic Sealing
http://www.nucfil.com/laser/Design_Guideline_1.pdf

Hermetic Encapsulation
http://www.ami.ac.uk/courses/topics/0261_herm/index.html

Laser Welding
http://www.designsci.com/laser.html

Laser Welding Article
http://www.uslasercorp.com/envoy/welding.htm


3 - How to do it well: Selecting Carbide for Hardfacing

Q: We use Tungsten Carbide to hard face our steel and I recently heard from someone that Vanadium Carbide cost 30% less, you get 30% more coverage per pound. Is there any truth to this and if so is the abrasion resistance as good as tungsten carbide. Any info you have would help us a lot. Thanks.

A: While it is essentially a good thing to try to improve processes and reduce expenses, one has to be very cautious before changing processes working satisfactorily. In particular one has to be extremely skeptic when someone (not better defined, could have hidden interests?) throws in an idea whose reckless adoption might cause much damage.

There is more to Hardfacing than the carbide powder used. The abrasion resistance of the final application depends much on the type of thermal spray process, on actual spraying parameters, on hardness but also on adhesion and on the type of materials your equipment is called to work on.

Tungsten carbide is called the ultimate in abrasion resistant qualities. If you are interested in comparing two different carbide powders, you should set up an experimental study for your specific applications and draw conclusions from practical results.


4 - Consumable Process Tape for Spot Welding

Delta Spot is a quite interesting resistance spot welding new development from the Fronius Company, the Austrian manufacturer and technology developer working especially for the automotive industry. They introduced unique equipment making use of a process tape interposed between each resistance welding electrode and the work.

After each spot weld, both process tapes are advanced automatically to a clean surface new position. The result is that the electrodes are protected from contamination and need not frequent redressing, while sparks and weld spatter are eliminated.

Besides increasing electrode durability, especially for aluminum, the interposed process tapes improve electric contact, add resistance and consequently heat even with reduced current, and weld quality results consistent for much longer series of spots when compared to regular processes.

It is also affirmed that the shunt effect is drastically minimized, contributing to additional reduction in current requirements.

Although not explained completely in the commercial publications, it appears that much thought must be given to tape materials and coatings, whose adroit selection helps customize the heat balance for any different application.

Practical results show that instead of a limited nugget where the sheets contact each other, a thicker molten cylinder or barrel is obtained, easily covering almost all the combined sheet thickness.

Experimental applications of this new spot welding method to three sheets of different steels, all galvanized but with different processes, produced satisfactory results.

Additional advantages permitted by this innovation are the welding of two steel sheets with a conductive polymer sheet interposed for noise abatement, and the production of spot welds on narrow flanges (required for weight reduction) without expulsion of molten metal.

Special concave shape of electrode, called expo electrodes, reduce indentation to the minimum, required in certain applications for aesthetic reasons. The automotive industry in several countries has already adopted Delta Spot for mass production.

One amazing result, considered impossible till not long ago, is the production of direct steel-aluminum spot welds. This was the consequence of selecting suitable different process tapes against the two base materials, to produce targeted heat input in the joint location.

A short presentation of the process is available online in the following publication.

Delta Spot - A Novel Resistance Spot Welding Process (Presentation, 34 slides)
http://www.cesol.es/17Jornadas/conferencias/Praesentation_DVS_Dresden_EN_UK.pdf

See in the next section the link to a short video on applications.


5 - Online Press: recent Welding related Articles

Miller Electric PowerClick
Miller.

Delta Spot (video)
http://sama-community.ning.com/video/delta-spot-1

Welding of austenitic stainless steel
http://www.twi.co.uk/content/jk103.html

Inspector Responsibilities
http://files.aws.org/itrends/2009/10/it200910/it1009-14.pdf

Correcting Thin-Plate Distortion in Shipbuilding
http://files.aws.org/wj/2010/01/wj201001/wj0110-30.pdf


6 - Terms and Definitions Reminder

Base Metal Zone is the portion of base metal non affected by the heat of a nearby (adjacent) weld, braze, solder or thermal cut.

Carbon Electrode is a consumable carbon or graphite rod non filler electrode used to establish an arc between itself and the workpiece for welding or cutting.

Double Square Groove Weld is a weld in a square groove joint welded from both sides.

Edge Preparation is the cleaning, plating or shaping of the joint edges by suitable means.

Face Bend Test is the bend test of a welded specimen where the weld face is on the convex surface. The bend radius is specified for the opposed side of the specimen.

Gas Metal Arc Cutting is an arc cutting process using the arc maintained between a continuously fed consumable wire electrode and the workpiece, under gas shielding.

Incomplete Joint Penetration is present when the weld does not extend through the whole thickness.

Root Reinforcement is the additional weld material extending beyond the joint thickness, at the side opposite that from which welding was done.


7 - Article - Direct Manufacturing Process with EBW

Readers may recall having read in this publication an article titled "Huge Savings in repairing expensive Scrap Parts". It appeared in section 2 of Issue 43 of Practical Welding Letter for March 2007.
Click on PWL#043 to read it again.

It describes the use of Laser power beams to fuse precisely deposited metal powders for Near Net Shape freeform fabrication. The above technique was developed essentially for the repair of delicate objects like airfoils and labyrinth seals of gas turbine engines.

As remarked in the above article the current equipment used is in the power range from 0.4 to 3 kW. It appears that the same concept, inspired by recent achievements realized with the techniques of Rapid Prototyping, was brought to a higher level with the development of Electron Beam Welding equipment of up to 42kW power.

Laser applied to weld shining reflective surfaces of the metals cannot compete in efficiency with EBW: electrons are not reflected away, all their energy is absorbed.

Electron Beam Welding is performed preferably under high vacuum. This characteristic fits perfectly with the requirements of reactive materials like aluminum and titanium. For speedier freeform fabrication, the metal is fed as a continuous wire, precisely at the focal point of the electron beam.

A suitable CNC table permits to weld the material drop by drop, layer by layer, to build complex items, right from their computer aided design (CAD) data.

The studies reported hereafter show that correct metallurgical structures and acceptable mechanical properties were obtained in aluminum and in titanium alloys.

The main advantages of the technique described are reduced production and material costs, reduced development and lead times, and improved performance relative to traditional manufacturing methods.

One of the possible most convenient applications is that of attaching, by the above technique, short appendages like bosses or flanges (to be built in place), to simple shape forgings or castings.

The forecast savings are remarkable both in material and in machining time. Besides that, increased flexibility should also be considered, permitting to change details and modify applications quite easily, even at an advanced design stage.

A short article describing this development, titled:

Electron Beam Free Form Fabrication (EBF3)
was published in AMS AM&P issue 167 of November-December 2009 at page 45:
Click on ASM

At the bottom of that page there is a link to a Nasa page, wherefrom a captioned video of the Author, Ms. Taminger’s seminar on this topic can be reached.

Electron Beam Freeform Fabrication
for Cost Effective Near-Net Shape Manufacturing (10 pages)
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013538_2008013396.pdf


8 - Site Updating: Monitoring Structures, Production Failures

In the Pages of this Month we introduce Monitoring Structures and Production Failures.

The first item, Monitoring Structures, is dealt with in a page that describes a trend of increasing applications, in the future, of local sensors of different types to follow the behavior of structures along their service life, and to be alerted in time of impending stability problems.
Click on Monitoring Structures to read this page.

The second page, on Production Failures, could provide useful hints when unexpected welding production problems appear all of a sudden, disrupting the regular supply of manufactured goods. Every case is different, but the approach to find the underlying causes of mishaps is largely the same.
Click on Production Failures for reading it.

Check regularly for new pages in the Web Site Map or subscribe to the RSS feed using the instructions given in every page (www.welding-advisers.com) under the Navigation Bar.

For finding what you look for, you may use the Google Search Box which appears in almost every page of the website. More often that not there is some reference to your subject either in the website or in the collection of Practical Welding Letters.

And if you do not find what you need you can always Contact Us using the usual form.


9 - Short Items

9.1 - Solution Heat Treatment consists in heating an alloy to a suitable temperature and keeping it there long enough to diffuse constituents into solid solution, and then quenching fast enough to hold the constituents in solution.

9.2 - Spalling is the separation of flakes from a surface, like that occurring with rolling elements of bearings or gears because of subsurface fatigue or that of a surface coating.

9.3 - True Stress is that calculated by dividing the amount of the applied force by the actual cross sectional area of the specimen.

9.4 - Tumbling is a surface treatment of castings or forgings, enclosed in a rotating barrel partially filled with abrasive material, to remove fins or scale. Same as Barrel Finishing.

9.5 - Ultimate Tensile Strength (UTS) is the maximum stress sustained by a specimen in a tensile test.

9.6 - Vacuum Induction Melting (VIM) is a process used for refining molten metals, heated by induction in a vacuum chamber.


10 - Explorations: beyond the Welder

Nature's Images of the year
http://www.nature.com/news/specials/2009/gallery/index.html

Nature News 2009
http://www.nature.com/news/2009/091223/full/462962a.htm

How Much Atmospheric Carbon Dioxide Is Safe?
http://www.scientificamerican.com/article.cfm?id=climate-numerology

Gaming for Profits: Real Money from Virtual Worlds
http://www.scientificamerican.com/article.cfm?id=real-money-from-virtual-worlds

Chinese Gold Farmers in MMORPGs (video)
http://www.youtube.com/watch?v=rEegohRPsqg


11 - Contributions: Interview with Leonard Mills

Q: What did appeal to you when you first considered welding as your Career?
A: I was fascinated with the way metal flowed together when welding.

Q: How did you start your welding Career?
A: I joined the apprenticeship of the United Association of Plumbers and Pipefitters of the U.S.A. and Canada.

Q: Did you plan to achieve definite Career milestones in a given timeframe?
A: My biggest driving drive was to be able to weld all the metals that could be welded.

Q: In which field of welding are you active?
A: Welding Inspection, welding pipe, writing welding procedures, and Instructing welders.

Q: Which were your major achievements during your Career in welding?
A: My proudest moment is when I was called welding instructor.

Q: Which challenges did you find hard to overcome?
A: The hardest thing is to delete the statement "It can't be done".

Q: What did help you in persisting and overcoming the difficulties?
A: You are only limited by your capabilities.

Q: Which is the most important lesson you would like to transmit to young welders?
A: As you have shown in your own studies, the field of metallurgy is the most exciting science I know of because the more you know the more you find you need to know.

Q: Which goals should a young welder aim to reach?
A: I deal with the 18-30 year old's every day and as they are informed of the professional roles in welding that are interesting, thought provoking, and rewarding, a welding career is, they do join the numbers to push the welding industries.


Thanks to Leonard Mills for having submitted this note. One can feel the pride and the satisfaction for having served all his professional life in an important industry.
We congratulate him on his achievements.
Readers who offered to write their interview but did not yet send it to us, are reminded to do it now.


12 - Testimonials On Wed Dec 02 18:35:56 2009, the following message was submitted to
Welding Advisers

Name: Josh Warn
E-mail Address: removed for security
Country: United States
Introduce Your Organization: Ironworkers Local 25
Describe Your Responsibility: steel erection/welding foreman
Questions and Feedback : I appreciate this site. The answers are more straightforward than the ones I have tried to get from the sites of the welding equipment manufacturers.[...]


From: Kerekes, Erika
to Welding Advisers
Date: 03 Dec 2009, 11:28:12 AM
Subject: welding safety

Elia - thank you so much for the valuable information. I posted the response on your behalf, with a link to your website.
[...]
Again, thank you so much for the response.

Best,
Erika


13 - Correspondence: a few Comments

13.1 - I already advised in the comments of the November issue of PWL that I don't like to receive comments from unspecified contributors. Now again, other readers, under Anonymous disguising, sent comments to notes appearing as contributed publications.

It is unacceptable to me that autors or commentators hide their name and affiliation. Therefore such comments are systematically deleted.

13.2 - All kinds of questions appear in my correspondence. Generally I like them as they challenge my capability to provide a concise useful answer. Sometimes I get unanswerable questions that would need volumes to be treated thoroughly.

Readers should provide a few lines of background to let me understand the reason for their questions. Knowing the context eases the task of providing useful answers.


14 - Bulletin Board

14.1 - The Japan Int'l Welding Show 2010
April 21-24, 2010 - Tokyo Big Sight, Tokyo, Japan
Organized by the Japan Welding Engineering Society and Sampo Publications.
www.weldingshow.jp/english

14.2 - AWS Detroit Sheet Metal Welding Conf. XIV
May 11-14, 2010 - VisTaTech Center, Livonia (Detroit), Michigan, USA
www.awsdetroit.org

14.3 - Try the SBI! 2.0 Video Tour
http://videotour.sitesell.com/Quark.html


Important Announcement

For assembling at no cost your own Encyclopedia Online,
a rich collection of valuable information from expert Internet Sources, on
Materials, Volume 1,
and Metals Welding, Volume 2,
is now available.
See our New Page on Metals Knowledge.

Click on the following image to watch the SBI! TV Show!

SBI TV Show

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