The practice of using gold or silver solders to join gold in forming ornamental items has its roots going back an estimated 2800 years and probably longer. Gold-silver and gold-copper-silver alloys were used as filler metals. Though these and parallel silver alloys are termed gold or silver solders, they are by definition, brazing alloys. This is based on the definition that brazing is a welding process wherein a joint is produced by heating to a suitable temperature and using a filler metal that must have a liquidus temperature above 800°F but below that of the base metal. Therefore, in this presentation, though the term soldering may normally be used in the jewelry industry, it will be termed brazing.

Brazing is still the principle method of joining used by jewelers. Though the process requires limited capital to set up, there are drawbacks, especially in joining a high melting point material such as platinum. Perhaps the most significant drawback is the skill and training required to make reproducible, high quality brazes. There is also the damage that can be done to gem stones or the possibility of overheating and destroying the piece of jewelry as well as the cleaning that has to be done to remove firescale and flux from the jewelry after brazing.

There are many different joining and welding techniques available. Among these are friction welding, fusion welding, electron beam welding and arc welding, to name some. Many of these do not have the flexibility or adaptability to make them of interest to jewelers or platinumsmiths. A technique that theoretically gives localized, controllable high heat input was the laser. However, initially, they were very large, costly and did not have the flexibility required by the jeweler. The laser welders required significant tooling and setup time to obtain an acceptable weld. In recent years, however, laser welders have gotten smaller and more portable, to the point where they occupy less space than a jeweler's bench. They can be operated by anyone with a steady hand and a sharp eye. Their cost has come down considerably also, from several hundred thousand dollars to under $50,000. These advancements now allow lasers to be used on a wide scale in jewelry production. 

There are many seemingly obvious advantages to laser welding. First, there is very little heat generated outside the beam contact/weld area. This eliminated the need for any fluxes and leaves the piece bright and clean. The lack of heat generation also means that welding can be done very close to stones, a plus when repairing prongs. Because the pieces do no heat up to any great degree, unless rapid fire pulsing is used, the operator can hold the pieces he's joining with his hands, eliminating the need for fixturing, clamping and the like. There is no worry of melting small pieces, and several joining operations can be done without worrying about reflowing previous joints. Repairs are done with filler, when needed, of the same composition of the base alloy, eliminating the worry of color mismatch between piece and filler. Since no torch is used, there isn't the need to have compressed gases. This can be useful in small store operations where local codes may prohibit such things.

The disadvantages of laser welding are that it does take longer than traditional brazing, which can be a concern in a production environment. In addition, not all joints can be joined by laser welding. Welded joints are very different in appearance from brazed joints, which have a smooth seamless appearance due to the capillary flow and wetting of filler into the joint. Welded joints have a bulbous overlap look that can only be smoothed by grinding. If the joint is in a hard to reach area, this cleaning can be difficult if not impossible.  It is not known either, whether laser welded joints are stronger than traditionally brazed joints. This paper will attempt to answer that question.

The present study set out to compare braze and laser welded joints using the
Pt-4.8Ru alloy. It was decided to use the ASTM E290-81 standard method for semi-guided bend test for ductility of metallic materials to evaluate the joints. The semi-guided bend test is used to evaluate the quality of metals or weld as a function of ductility as evidenced by their ability to resist cracking during bending.  Additional techniques to be used in evaluating the braze or laser weld quality will include metallography of weld cross-sections, visual examination of fracture surfaces and scanning-electron-microscopy.

At this point the original article goes into a detailed account of the experimental procedures conducted.

Results
The laser weld is typified by a raised bead and a shiny appearance.  The braze is flush with the surface of the parent material but has a very dull, oxidized appearance.
Data for the 0.030 inch thick rolled strip which had been laser welded shows all samples tested passed the 1T mandrel bend test. Data for the brazed 0.030 inch thick rolled strip revealed all of the bend tests failed with the joint completely separating.

Discussion
In the course of performing the experiment, it was noted that laser welding is a longer process than traditional brazing techniques.  Initially, this would seem to be a serious downside, especially in a production environment.  However, the results of the experiments show that a laser weld is superior to a brazed joint in strength and quality (i.e., porosity). This fact might offset the longer process time.  There are several possible explanations for laser joints showing higher strength characteristics than similarly brazed ones. In the case of our platinum samples, the intense heat required to braze platinum by torch has a negative effect on the grain structure, enlarging them to a point where they compromise the strength of the metal. In addition, any small contamination in the metal along with oxidized alloying elements will congregate at the grain boundaries, further promoting failure of the joint.  It was also noted that there was very poor wetting and flow of the braze material with the base alloy. This can be attributed to poor technique, however, the high temperatures encountered does not allow the use of flux, which could alleviate the problem.  While the commercially available braze could form oxides which prevent wetting, even our experimental Pt-5Au filler material, which was used for the experiment, showed poor wetting and flow. The combination of these two conditions, enlarged grains and poor wetting, caused failure of our brazed pieces. Our laser welded butt edged pieces which failed at the larger thickness shows a need for beveling thicker pieces before welding to insure a thick enough weld bead to survive not only finishing operations, but also the mechanical stress the piece might undergo.

There may be comments on the use of the bend test in that there were many failures of the type of joints that have been used in jewelry making over the years with success. The point is that the test does not indicate whether the joining technique should be used for a specific application but it does give a relative measure of the ductility of a given joint. The bend test, along with other metallurgical techniques, certainly gives an indication of improvements that can be made by process or mechanical changes.

Conclusion
The laser welded joint of the Pt-4.8Ru alloy were more ductile than brazed joints. No special preparation is required for the welded joints at the thinner side of the material thickness used in jewelry manufacture (0.030 "). However, as the thickness increases to 0.075 inch, the 60 degree joint gave the best results.
 

V5N6

Laser Welding or Conventional Soldering
Costantino Volpe
Tiffany & Company
and
Dr. Richard D. Lanam
Engelhard-CLAL LP

This is an abbreviated version of the original work. For full technical details, please consult the original paper.