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PWL#075 - Sinter Brazing and Resonant Acoustic Inspection, Brazing Flux Removal, Active Solder
November 02, 2009
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PWL#075 - Sinter Brazing and Resonant Acoustic Inspection, Brazing Flux Removal, Active Solder Joining, Submerged Arc Welding Case History, Interview with Charles Hyatt, Shot Peening, Joining Aluminum Metal Matrix Composites and more...

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November 2009 - Practical Welding Letter - Issue No. 75


TABLE of CONTENTS
1 - Introduction

2 - Article - Sinter Brazing and Resonant Acoustic Inspection

3 - How to do it well: Brazing Flux Removal

4 - Filler Metals for Active Solder Joining

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Submerged Arc Welding Case History

8 - Site Updating: Shot Peening, Joining Aluminum Metal Matrix Components

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Interview with Charles Hyatt

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board


(Sponsored Links)


1 - Introduction

Here we are with our 75th Issue! of Practical Welding Letter. It seems incredible, is not it?, but month after month new issues were published, some more interesting, some less, but anyhow there has been a continuing effort trying to reach our audience with new content, letting readers gain some insight and some welding information.

It appears that at least some readers value the Letters, according to the feedback received. More active participation would be highly appreciated, and here and there we get a few contributions that provide different points of view or relate interesting experiences.

The first article hereafter reports on a recent practical applications combining two known processes, sintering and brazing, realized together in the same thermal cycle. This particular use permits greatly simplifying the complexity of dies for producing Powder Metallurgy compacts.

It is therefore an economic manufacturing method suitable for mass production. But the real gain comes from the implementation of automatic inspection, as explained. Readers are urged to see for themselves all the details in the original publication indicated.

Following a reader's question, we recall some of the principles to be kept in mind for easy removal of brazing flux: essentially it is an operation not to be delayed, for maximum efficiency.

Then there is an article devoted to a new class of brazing materials and methods, widely applied quite recently for specialized electronic devices, but suitable to give appreciable benefits in a wide range of applications, if only one thinks "out of the box". All should know what is in Active Solder Joining, that makes it so successful.

A kind reader sent a short note on an application of SAW that saved them many work hours and made welders available for other tasks. Many of the readers could possibly relate on their gains obtained by daring to apply something new.

The new Pages of the Month added to the website (www.welding-advisers.com) deal with Shot Peening, which is a simple (in principle) cold work procedure that can save parts likely to fail by fatigue, and with joining methods applicable to Aluminum Metal Matrix Composites.

We have a new Interview submitted by a kind reader. There is much to learn from the experience of those who dedicated their professional life to welding activities. We remind to all readers who promised their participation but did not yet realize it, that we look forward to get their story.

Other sections are where they should be, even in this 75th Issue event. Your feedback is always welcome. Please don't use REPLY. Use the Contact Us form instead.


2 - Article - Sinter Brazing and Resonant Acoustic Inspection

Sinter brazing is a common process used to assemble powder metal parts produced by Powder Metallurgy. It is an economic process that permits to perform at the same time, within the same thermal cycle sintering of the pressed preforms and brazing, to assemble two or more part as needed in a brazed assembly.

Splitting a given P/M part in a number of simpler components, substantially simplifies the production of the dies needed for compacting the powders. The technique of sinter brazing consists in assembling the components in their green state (that is before sintering), interposing brazing filler metal at the joint locations as required, and heating the prepared assembly in a controlled atmosphere furnace to fuse the brazing alloy and to sinter the powders in the same heat cycle.

Several defects could possibly crop up both in the sintered bodies and/or in the brazed joint in case the preparation or the processing parameters are occasionally at fault. As this is essentially a mass production operation where the produced parts need to be inspected individually before being supplied, an automatic inspecting and sorting inspection process is sought, capable of separating the defective parts for further disposition.

A short description of the Resonant Acoustic Method was provided (11) in issue 38 of PWL for October 2006. To perform the inspection, the item is given a reproducible impact blow, and its acoustic response spectrum, collected with a microphone, is analyzed per frequencies and amplitude.

The part's mechanical resonances amplify the broadband input energy at its specific resonance frequencies, clearly indicated as peaks in the recorded spectrum.

By collecting a number of good parts spectra one can easily find the differences exhibited by deviating parts as shifted resonant frequencies or amplitudes.

This technique has been demonstrated to be reliable and easy to apply for screening mass produced sinter brazed parts. An article reviewing this inspection method was published in the October 2009 issue of The Welding Journal at page 48. Interested readers are urged to seek it.


3 - How to do it well: Brazing Flux Removal

Q - Ran into an horrendous problem removing brazing flux - is there a process that would reduce the level of aggravation and labor? The metals involved were German silver and a stainless that is extremely tough. The object was to braze a guard to the blade.

A - You probably used a flame for brazing. Overheating should be avoided. In general flux removal should be done immediately after brazing, and the method used is generally hot water rinsing, possibly with soft brushing.

Immersing the brazed joint in water before full cooling, helps flux removal, if not objectionable for other reasons. Leaving the flux on, causes it to oxidize making it a form of glass, more difficult to remove.

Pickling solutions or chemical cleaning is available. Mechanical means are a possibility, including fiber brushing, wire brushing, blast cleaning and steam jet. Next time you may consider using a suitable stop off, to limit the area where flux is spread, heating as low as possible and removing flux immediately.


4 - Filler Metals for Active Solder Joining

Active solder joining is an emerging technology for connecting components, based on alloys endowed with active elements, that are applied using specially modified procedures to obtain the results required.

Increasingly demanding requirements of the electronic industry for better joining materials and for methods allowing improved performance at lower cost has been at the origin of the significant progress realized in the last few years in joining materials and processes.

The materials developed are included collectively in the new class of lead free active solders. The filler metals are based on various compositions of Tin and Silver or Zinc, Aluminum and Silver. The performance of the new filler solders is significantly modified by measured additions of active metals including Titanium, Cerium, Gadolinium and other Rare Earth materials.

Active elemental additions to filler metals reduce surface oxides or compounds and form fresh metal surfaces even when applied in air at low temperatures, without flux, nickel plating or pre stripping of a surface oxide layer. Wetting the surfaces of most materials, metals, ceramics and carbon composites, is normally performed without resorting to special atmospheres, by some form of mechanical agitation.

It is not only the materials but the parallel development of methods and procedures employed to put them to practical use that brings about a sort of revolution in what was known as the classic soldering practice.

Two characteristics differentiate them from normal solders. First they must be preplaced in the joints to both surfaces prior to assembly as they do not flow freely, and therefore techniques to distribute them are integrated into the processing methods. Second, they need an auxiliary mechanical action to break the shell forming around the solder, in order to wet properly the surfaces to be joined.

Mechanical agitation to affect molten filler solder and initiate wetting is accomplished by a number of methods including metal edge spatulas abrasion, wire brushing, spinning, oscillation, or ultrasonic vibration of the components.

Applications involve joining of thermal management devices, joining of electronic packages that utilize new ceramics and composite materials, joining difficult to join materials, dissimilar metals like titanium and stainless steel, intermetallics, and ceramics to metals and a number of other joining applications where adhesives or conventional solders do not perform adequately.

Thermal management is a class of applications that include heat exchangers, cold plates, heat spreaders, heat sinks and heat pipes. These devices often require that dissimilar materials be joined to provide a seal for coolants, for joining fin to plate, or attaching thermally conductive base material to devices requiring cooling such as electronic packages into enclosures. Thermal management materials include aluminum and copper as well as high conductivity ceramics such as aluminum nitride.

The requirements for thermal management device fabrication are generally that the joining materials be thermally conductive to improve the rate of heat dissipation. Active solders, with a conductivity nearly ten times better than the best filled epoxy materials, are especially suited to meet the requirements. Furthermore they are able to resist thermal cycle service stresses.

In conclusion it seems quite probable that this joining technology, being effective and easy to use, will continue to find many further practical applications, besides the quite particular ones already demonstrated up to the present time.

If it is good for NASA, it might be good also for your next application! You can ask those who develop and practice this technology, to join together your next prototype elements.

For further readings on this subject see:

Advanced Joining Technology: Simple, Strong, and Secure
http://www.sti.nasa.gov/tto/Spinoff2005/ip_5.html

Graphite Foam Heat Exchangers for Thermal Management
http://www.ornl.gov/~webworks/cppr/y2004/rpt/120437.pdf


5 - Online Press: recent Welding related Articles

Effect of Arc Welding on Aluminum Temper
http://files.aws.org/wj/2009/10/wj200910/wj1009-18.pdf

ESAB explains how to improve welding productivity
http://www.manufacturingtalk.com/news/esa/esa210.html

Understanding low-alloy steel
http://www.thefabricator.com/Consumables/Consumables_Article.cfm?ID=2291

Getting the SPA treatment
http://www.thefabricator.com/ShopStrategies/ShopStrategies_Article.cfm?ID=2305

TWI Connect - September October 2009 (8 pages)
http://www.twi.co.uk/content/consept09.pdf


6 - Terms and Definitions Reminder

Alloy Powder is prepared from a homogeneous molten alloy or from the solidification products of such an alloy.

Butting Member is a joint member that is prevented, by the other member, from movement in a direction perpendicular to its thickness dimension.

Flash Welding is a resistance welding process that produces a weld at the faying surfaces of a butt joint by a flashing action and by the application of pressure after heating is complete. Flashing occurs at high current densities as sparks between small contact points between the two abutting parts of the workpiece. Material is expelled from the joint. Weld is completed by rapid upsetting.

Gas Tungsten Arc Welding is a process that uses an arc between a tungsten electrode (nonconsumable) and the weld pool under the shielding of an inert gas.

High Frequency Resistance Welding is a group of process variations that use high frequency welding current to concentrate welding heat at the desired locations.

Mixed Zone is the weld metal consisting of a mixture of base- and filler-metal.

Nonbutting Member is a joint member that is free to move in a direction perpendicular to the thickness dimension, like in a lap joint.

Weld Bead is a deposit of weld metal produced by fusion resulting from a single pass.


7 - Article - Case History

[Note: The following contribution was kindly provided by Paul Ipolito, from New York State, Welding and Quality Engineer, and Project Manager at SPX Process Equipment. I would like to thank Paul for this informative article, and to invite all readers to send their own stories for publication: Elia Levi]

This seems like an appropriate time to share a success story regarding submerged-arc welding. We are producing 23 pieces of fluid-mixing equipment for a Central American mineral processing project.

Part of our equipment includes a 7.5 inch diameter Inconel 625 bar with a 2.5 inch thick flange welded to one end of the bar. Normally when processing a quantity of one or two of these type shafts in our shop we would use SMAW.

We allocated approximately 25 shop hours per shaft to complete the weldment. We felt there had to be a better way to expedite these parts through our shop. We decided to weld a test plate using Special Metals Inconel 625 wire (3/32" diameter) and Special Metals NT-100 submerged-arc flux.

The procedure testing went well and we started production with SAW (Submerged Arc Welding). We are now able to weld a complete shaft in 8 hours! We are also required to apply 100% UT examination to these shafts and I am pleased to report all have passed inspection with no apparent indications.

I believe that despite our best intentions, we would not have had the same UT (Ultrasound Testing) results with the SMAW (Shielded Metal Arc Welding) process. We were also able to have one welder produce the required shafts to maintain production flow. We assigned two welders who were scheduled to work on the shafts to other items associated with this project.


8 - Site Updating: Shot Peening, Joining Aluminum MMC

The Pages of this Month deal with different processes.

The first explains Shot Peening, a surface improvement process designed to introduce compressive stresses and to hinder the initiation and propagation of Fatigue Failures.

When properly applied the process is most effective. Together with other good manufacturing practices it can actually bring success and avoid failures, likely to affect parts which did not get it in the first place.

Although not new, this procedure should be kept in mind and investigated whenever confronting fatigue failures.

The second page, on Joining Aluminum MMC deals with Metal Matrix Composites that have to be joined to other elements in manufactured structures. The advantages of MMC risk to be lost if suitable precautions are not considered and applied as needed.

To remain updated on new additions to the website, readers can subscribe to the RSS feed as explained in every page of the website under the NavBar. The Site Map can be consulted for finding specific pages.

Comments and feedback are welcome. Don't use REPLY. Use the Contact Us form instead.


9 - Short Items

9.1 - Binary System represent the complete series of compositions produced by mixing a pair of components in all proportions. Applied in particular to miscible metals.

9.2 - Blanking is the operation of punching, cutting, or shearing a piece out of stock to a predetermined shape to be used in further manufacturing.

9.3 - Cementite is a hard (800 HV), brittle compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition can be altered by the presence of manganese and other carbide-forming elements. The highest Cementite contents are observed in white cast irons, used for high wear resistance applications.

9.4 - Mechanical Working consists in subjecting metals to pressure exerted by rolls, hammers, or presses in order to change the shape or mechanical properties of the metal.

9.5 - Semiconductor is a solid crystalline material whose electrical resistivity is intermediate between that of a metal conductor and an insulator, and is usually strongly temperature dependent.

9.6 - Transverse Rupture Strength (TRS) is the stress, calculated from the bending stress formula, required to break a specimen of a given dimension. The specimen is supported near its ends with a load applied midway between the fixed centerline of the supports. It is calculated from the value of the break load.


10 - Explorations: beyond the Welder

Views from Deep Space
http://www.esa.int/SPECIALS/Herschel/SEMUABGNA0G_0.html

Crash Test (video)
http://www.youtube.com/watch?v=_xwYBBpHg1I

Lunar lander
http://science.nasa.gov/headlines/y2009/15oct_lunarlander.htm?list25846

Robo-Bats May Be Next Remote Control Flyers
http://news.ncsu.edu/releases/robo-bats-may-be-next-remote-control-flyers/

Powering a Green Planet: Sustainable Energy, Made Interactive
http://www.scientificamerican.com/article.cfm?id=powering-a-green-planet&sc=WR_20091027


11 - Contributions: Interview with Charles Hyatt

Q: What did appeal to you when you first considered welding as your Career?

A: I actually started young enough that it was like playing with fire, in a controlled atmosphere of course.

Q: How did you start your welding Career?

A: My father was a machinist by trade and he also performed maintenance on heavy equipment for a construction company that he and my uncle owned. My dad tried to teach me how to run machining equipment but I wasn't really interested in it all that much. To my fathers credit he kept introducing me to things until we got to welding. As they say the rest is history.

Q: Did you plan to achieve definite Career milestones in a given timeframe?

A: Not at first. After I had about 15 years in as a qualified welder for a chemical company I had a goal to become a CWI and then to pursue the API certifications.

Q: In which field of welding are you active?

A: Inspection and teaching at an area college.

Q: Which were your major achievements during your Career in welding?

A: The first one was becoming qualified to weld pipe with the GTAW process. Then becoming qualified on high alloy materials. After several years of practical experience I then achieved the CWI certification and the API 510, 570 and 653 certifications.

Q: Which of your achievements procured to you the highest satisfaction?

A: Probably the ability to produce acceptable welds on 100% X-ray high alloy pipe welds.

Q: Which challenges did you find hard to overcome?

A: You have to be persistent when talking to the "old timers" there is a wealth of information sitting there if you are respectful and sincere in your approach. Not that everything you always get from them is totally useful, but there will always be some little gem from them somewhere that will help.

Q: What did help you in persisting and overcoming the difficulties?

A: The desire to be the best that I could be.

Q: Which is the most important lesson you would like to transmit to young welders?

A: Anything you do, try to do it better than the last time you did it. Every weld you make, try to make it better than the last one. You obviously will reach a point where you really can't make them better but if you keep trying it keeps you sharp and occasionally opens the door to improvements in the process or procedure that you may have not thought of.

Q: Which goals should a young welder aim to reach?

First, try to be the best, become the go to person when a "tough one" comes up.

Second, never stop learning.

Q: Do you foresee interesting developments likely to change the welding profession?

A: I'm a huge fan of technology. Welding has changed (for the better) tremendously just in the past 30 or so years that I've been involved with it.

Q: How would you invite young people to consider welding as their Career?

A: We should be introducing them to it at middle school and high school levels or at the very least college. The perception of "If you don't go to school to become smart, then go learn a trade" needs to be changed to learn a trade and you will always be able to make a living and you may just enjoy the experience.


Thanks to Charles Hyatt for having shared with us his experience. We look forward to be able to publish other interviews with readers ready to send us their interesting stories.


12 - Testimonials

Date: 01 Oct 2009, 02:10:04 PM
Name: John Diehl
E-mail Address: removed for security
Country: United States

Many thanks for your kind and prompt reply.

[...]

Kindest regards, and thanks again for a superb letter -
always look forward to reading it.

John Diehl


Name: Michael Bennett
E-mail removed for security
Country: United States
Date: 08 Oct 2009, 08:59:08 AM
Subject: RE: ASTM A53

Hi Elia,

Thanks for reply. [...]
Thanks

Michael


13 - Correspondence: a few Comments

13.1 - I received comments for my page on Welding Art from an "Anonymous" reader. They were encouraging messages and expressed some appreciation for the exhibits considered. Sorry, I will not publish them until that reader exits from anonymity.

I wanted to ask the reader permission to publish name and location of the Author, but I was prevented to do so, unfortunately, by the lack of an email address. I might be wrong but I don't like this extreme shyness. On the contrary I would see it appropriate that the author stress his/her competence and experience in the field, that qualify the judgement expressed.

13.2 - A welding inspector asked if a silver brazing of Cupro Nickel to carbon steel will withstand high pressure upto 650 kg/cm2.

The welding inspection has to be commended for his worry, but the information submitted is not sufficient to verify if the design is adequate. In any case this should be an engineer's worry, not the inspector's.

Brazing joints are generally obtained by overlapping the elements to be joined for a certain length, with a capillary gap between them to be filled by the molten filler metal. Adequately designed and performing brazed joints should fail not in the brazing but in one of the base metals, wherever the strength is weaker. That obviously depends not only on the strength of the individual materials but also on the dimensions of the elements and on the type of loading.

The inspector's duty is to verify that the quality of the brazed joints produced conforms to the specified requirements, no more and no less than that.


14 - Bulletin Board

14.1 - 35th International Symposium for Testing Failure Analysis (ISTFA)
November 15-19 - San Jose, California, USA
www.aws.org

14.2 - International Electron Beam Conference
November 16-17 - Chicago
www.aws.org


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