Do you mean this conclusion Larry?

KEYHOLE DOUBLE-SIDED ARC WELDING
PROCESS FOR DEEP NARROW PENETRATION
Y. M. Zhang and S. B. Zhang
Welding Research and Development Laboratory Center for Robotics and Manufacturing Systems and
Department of Electrical Engineering. University of Kentucky, Lexington, Kentucky 40506

"CONCLUSIONS
The proposed keyhole DSAW process is capable of achieving deep narrow penetration on thick
plates. In particular, 9.5 mm (3/8 inch) and 12.7 mm (1/2 inch) thick stainless steel plates have been
fully penetrated using the keyhole DSAW with relatively small amperage, less than 70A.

Also, as observed from in the experiments, the keyhole DSAW process is robust with respect to variations in
heat input, thus welding conditions.

Preliminary analysis suggests that the presence of the arc in the keyhole which results in a heat compensation mechanism is the key to achieving such deep narrow penetration.

However, to truly understand the principles of the process such as the penetration
mechanism and the conditions for keyhole mode, further research is needed.

In addition, efforts should also be directed to practical issues such as welding speed improvement, power supply development, and torch alignment."

http://docs.google.com/viewer?a=v&q=cache:pXaMOsX2OWQJ:citeseerx.ist.psu.edu/viewdoc/download%3Fdoi%3D10.1.1.33.7308%26rep%3Drep1%26type%3Dpdf+DSAW+on+Stainless+up+to+3/8%22&hl=en&gl=us&pid=bl&srcid=ADGEESgHUDraht11Z_E37y7XMZ1GyPYPYQZB0sx2kYF5ARUcqOjstQwqZ3U4Y9T-dMWueeMWVfQ5MBbq81ronGknjwqO29hh9jkOYYIdEF44k4WVC9ZUuMcn_bh0lmp4Ro8jeatgtEWt&sig=AHIEtbT-7tn6tUZI6rT31VgmKic8M36cXA

Or, is it this one?

FINAL REPORT
A PRELIMINARY STUDY OF DOUBLE-SIDED ARC WELDING PROCESS IN SHIP STRUCTURE MANUFACTURING
Sponsor: National Shipbuilding Research Program
Sponsoring Committee: SP-7 Welding Panel
Project Period: Jul 2001-Feburary 2003
Project Value: $91,706
Prepared by
YuMing Zhang, Associate Professor (Principal Investigator)
Bret Losch, Graduate Research Assistant
University of Kentucky Manufacturing Center College of Engineering
Lexington, KY 40506
Phone: 859/257-6262 Ext. 223 FAX: 859/323-1035 Email: ymzhang@engr.uky.edu
Key Personnel: Yu Ming Zhang, University of Kentucky (Principal Investigator)
John Matthews, Electric Boat (Co-Principal Investigator, January 2002-February 2003)
Warren Mayott, Electric Boat (Co-Principal Investigator July-December 2001)
Lee Kvidahl, SP-7 Committee Chair (Project Technical Administrator)
February 28, 2003 For Public Release:

5. CONCLUSIONS AND FUTURE WORK
5.1 CHARACTERISTICS OF DSAW
·  Concentrated arc: Observation shows that the diameter of the plasma arc beam in DSAW is
less than 1/3 of that in conventional PAW. The energy density is thus 10 times of that of
conventional PAW. Analysis shows that the unique current direction in DSAW generates an
concentrating electromagnetic force which is responsible for the improvement of the energy
beam density.

Deep narrow penetration: The concentrated arc improves the capability of the arc to penetrate
the workpiece without generating a wide weld pool. The resultant weld pool is thus narrow
and along the thickness like a laser weld pool, although it is wider than that of laser.

Penetration capability: The deep narrow penetration makes DSAW be capable of penetrating
½ in. thick plates using 70 A in a single pass. It is suspected that thicker plates, possible up
to ¾ in., can be penetrated in a single pass on square butt joint.

Symmetric weld shape and minimal angular distortion: The symmetrical heating and small
heat input associated with the DSAW, because of the deep narrow penetration capability,
generate symmetrical weld pool shape and minimize the distortion.

5.2 ADVANTAGES
Robustness with respect to manufacturing conditions: The process is controlled using the
pulse keyhole method so that the welding parameters are automatically adjusted to establish
the keyhole when the manufacturing conditions such as the gap vary.

Single-pass process: Plates up to ½ in. thick plate can be welded in a single pass without joint
preparation on square butt joint in a single pass. This single-pass process also produces the
desired positive reinforcement on both sides of the weld.

Elimination of Distortion: Symmetrical heating and weld bead shape eliminate the angular
distortion.

Single-torch operation: The modified DSAW which uses the stationary metal bar requires
only a single torch move along the weld seam like a regular arc welding.

Single-side weld: Ship hulls are normally joined together as a full penetration butt weld
which, except for very limited and controlled applications, requires welding from both sides
of the weld joint. DSAW provides an opportunity to join ship hulls from one side.

Easy set-up: The stationary metal bar requires no accurate alignment with the weld seam.
This is because that the current must form the loop and will thus automatically search for the
stationary metal bar. The back-side stationary bar can be magnetically attached to the
workpiece.

Easy fit-up and joint preparation: The gap can vary from zero to 2.5 mm. No bevels are
needed and the square butt joint can be prepared using plasma cutter. This is because the
process is controlled using a pulse keyhole method so that the input energy is automatically
adjusted based on the need for establishing the keyhole.

5.3 COMPARISON WITH LASER
Low capital investment: The equipment cost is comparable with conventional arc process.
Labor force: DSAW requires no extra personnel other than conventional arc welding
operators.

Portability: DSAW system is portable similarly as conventional arc welding systems.
Safety: DSAW creates no specific safety issues.

Appropriate heat input and cooling rate: The DSAW reduces the number of pass from
multiple in conventional GMAW to one with significantly increasing the heat input of one
pass. The cooling rate is thus similar to that in conventional GMAW which has been proved
to be capable of welding DH36. However, laser has a much higher cooling rate. Disfocusing
the laser can reduce the cooling rate but reduces the penetration capability and requires
increase of laser power.

5.4 COMPARISON WITH CONVENTIONAL GMAW
·  DSAW eliminates the distortion which is substantial in conventional GMAW.
·  DSAW reduces the number of passes to one for plates up to ½ in. thick.
·  DSAW eliminates the need for bevels.
·  DSAW eliminate the need for turnover of workpiece.

The cost of a DSAW system and its operation is comparable to that of conventional GMAW.
DSAW reduces the usage of filler metal and electricity.
DSAW improve the productivity: Although the travel speed in DSAW is lower, it requires
only a single pass. The actual speed is thus improved.

5.5 SATISFACTORY WELD PROPERTIES
Experiments in this project show that all weld properties satisfy the requirements for DH36.
The pulse keyhole control technology gguarantees that the establishment of the keyhole and
thus the required full penetration.

5.6 FUTURE WORK
In summary, this project has verified the feasibility of DSAW process for shipyard applications.
Based on the previous plan, a follow-up full-scale development proposal should be prepared for
the NSRP-ASE program. The proposed NSRP-ASE project will focus more practical issues
related to commercialization outlined below.

A commercial system is needed to demonstrate the DSAW in shipyards.
Alternative filler metals are needed. Although the amount of the filler metal used is much
smaller than that in conventional GMAW, more economic filler metal would further reduce
the overall cost of DSAW process.

Higher welding speed is desired. The current power supply used in this preliminary study
was not capable of supplying reasonable current at the voltage required by DSAW. For
higher welding speed, it is desired that a larger current can be supplied at 55 V. As
mentioned earlier in this report, it is possible to modify the software by increasing the
allowed voltage so that the power supply can supply larger currents at 55 V. Further, power
supplies have recently become available at Lincoln Electric to provide 300 A at 55 V. As a
result, the welding speed will be increased.

Experiments with other materials and thicker plates need to be explored.
The control system needs to be improved based on better understanding and modeling of the
DSAW process.

6. REFERENCES
1. Zhang, Y. M., Zhang, S. B., Jiang, M. Keyhole double-sided arc welding. Submitted to
Welding Journal, Nov. 11, 2000.
2. Zhang, Y. M., Zhang, S. B., and Jiang, M. Sensing and control of double-sided arc welding
process. Submitted to ASME Journal of Manufacturing Science and Engineering, Nov. 20, 2000.
3. Pan, C., Zhang, Y. M., and Male, A. T. Metallurgical characteristics of double-sided arc
welding. Submitted to Journal of Materials Science, Nov. 30, 2000.
4. Zhang, Y. M., Pan, C., Jiang, M. and Male, A. T., 2001. Welding of austenitic stainless
steel using double-sided arc welding process. Materials Science and Technology, accepted for
publication.

http://www.nsrp.org/Project_Information/panel.../dsaw_final_report.pdf

There's plenty more but, I'm not in the mood to go chasing all of it down tonight Larry, S o I'll just end it with these two if you don't mind.

Respectfully,
Henry