Sizing Solutions- Using TIG welding to size up a palladium ring

The purpose of this article is to familiarize the reader with a different way of sizing a ring up.The traditional method would be to cut the shank and insert the proper amount of sizing stock. The TIG process enables the user to fuse molten metal on top of the shank to build it up in thickness, which in turn is flattened to increase the size of the ring. Instead of putting metal in, metal is put on. It is common when finishing a casting to hammer the remainder of the sprue gate to gain proper ring. This is the same technique applied to a finished ring. The additional metal is determined by the incremental increase of size needed. This article gives a step-by-step illustration of sizing a 950 Tru-Pd ring from Hoover and Strong Inc. with a TIG welder.

Before beginning I feel a brief explanation of TIG welding will be interesting to readers that are not familiar with TIG welding. GTAW is the industrial anagram given to Gas Tungsten Arc Welding, the type of welding process commonly known as Tungsten Inert Gas welding (TIG). This type of welding has been around since the 1940’s. It was patented by chief of research V.H.Pavlecka and engineer Russ Meredith of Northrup Aircraft, Inc. (patent number 2274631, 24 February 1942) and named Heliarc® welding. It is use widely in many industries to join many different types of metal. The jewelery industry uses automated machine TIG welding for production of precious metal tubing. In this manufacturing process the TIG torch is fixed to a machine head, which continuously welds the tubing seam as it is drawn from flat stock into tubing. The way I am using the torch is similar to the pipe fitter or metal fabricator. The torch is held like a gas torch and moved over the work in much the same way. The TIG torch is either air-cooled or water-cooled. The two types of torches are much the same size. The difference is that one has extra tubing for circulating the coolant. In my daily work I do not need to make long duration welds that would cause the torch to over heat, so I use an air-cooled torch. I have two that I do jewelry work with, the Weldcraft WP-9 and the micro WP-50.

The WP-9 is very common and is rated for welding of 125 amps. I have used this torch for short duration welds of 200 amps. Weldcraft does not recommend exceeding amperage limitation of the torch. The WP-50 has a 50-amp limit. The advantage is the compact head on the torch. It is small enough to fit inside a ring when necessary. (Figure 1).

My power supply is an inverter type machine. Shop current is converted from AC to DC and maximizes output amperage. I have an ITW Miller Dynasty 200 DX.(Figure 2).

The machine can operate in several modes. I use the machine in spot welding mode when I want it to perform similar to a capacitor discharge welder. There is several jewelry oriented welding machines on the market that produce this sort of weld. They are known as pulse welders. My machine has a pulsing mode, which is different from the spot mode. In pulsing mode the machine does not produce a burst of energy.The term pulsing refers to the machines circuitry changing the amperage within the arc during a continuous connection of the arc. The pulser produces an effect similar to a gas torch that is alternately on and off the work in order to control the temperature of the work. The TIG machine has a large range in which the arc can be controlled, which can be adjusted to various metals and tasks. My Dynasty can be set to run a sequence of amperage settings, much like commands are programmed into a computer. The program can be stored if many welds needing the same sequence will be done. This is how machines are set up to weld particular parts. I can also use the machine in straight DC mode, in which any variation of the amperage is controlled instantly by the foot control.Finally I have the ability to weld with alternating current. This is known as AC mode. I have not found an advantage to this mode as yet. AC welding has a great advantage in welding aluminum, and is used when precise aluminum welds are needed. The most common form of aluminum welding is MIG welding.While welding I protect my eyes with an electronic automatic shade.

The shade is integrated in a full helmet (Figure 3); which protects all exposed areas of my face. The shade can be set to a wide variation of shade settings. I do not need different helmets for gold and platinum as I can simple increase the shade setting for the higher protection needed. The shade is solar powered and the arc provides the radiation needed to keep it charged. I use TIG welding gloves to protect my hands from radiation and burns.(Figure 4)

The biggest advantage to the process is the inert gas atmosphere that covers the molten metal during the welding process. This is especially important in the case of palladium which is know to absorb atmospheric gas at greater rates than other precious metals. Hydrogen being absorbed by the molten palladium is one of the main reasons for product defects. By covering the melted metal with a stream of inert gas, hydrogen and other gases are unable to be absorbed by the molten metal. It is this feature that makes TIG a good choice for the fabrication and repair of palladium jewelry. Another advantage is the ability to precisely control the amount of energy inputted into the work. This control allows the operator to hold the work within a temperature range desired. A piece of palladium can be brought to an annealing temperature and held with out melting. The same piece of metal can rapidly be brought to melting point, fusing a joint with the same setting used for annealing on the machine. The machine is set to work within an input range and controlled with a foot control much like the flex-shaft control. I find an advantage to heating the joint on each side prior to making a weld. As is the case with gas torch welding, molten metal is attracted to the hottest area. As the operator prepares to fuse the metal, amperage is increased via the foot control and the arc is held over the point were fusion is wanted.

In the sizing example this article is concerned with, no joint is fused at all. Because the base material and the added metal are both molten, a re-crystallization of the base and added material form a solid single mass. This is similar to adding additional wax to a model.

The first step is to determine how much larger the ring needs to be. Then place the ring on a mandrel nice and snug to prevent unwanted arcing from marring the inside of the ring.

A piece of 950 Tru-Pd wire is used as filler to form a soft lump on the shank (figure 5). In this photo I have run a bead of metal down one half of the band (figure7). I’ll use this metal as a source to draw from as I carefully pull metal to the side of the ring.

It’s important that the transitional area of the build up be gradual to prevent over lapping of the weld edge onto the shank (figure 8), during the process of stretching the ring. I have found that Hoover 950Tru-Pd is more fluid than other alloys, which makes this step easier to accomplish.

In this image a small portion of the sidewall of the band has melted toward the center (figure 9). I won’t worry about this because the width of the ring will widen during compression of the lump of added TruPd. Note the gradual transition to the left and right of the additional metal.

Hammer or alternatively use a stone set style ring stretcher to flatten out and work harden the lump of metal. Check the size regularly during this process until the lump is level with the shank or the proper size has been obtained. (Figure 10) The inside of the shank is undisturbed during the process.

After I file and emery the ring I finish as usual for a perfect sizing increase. This ring was increased two and one half sizes. This method can be used on all of the Hoover alloys. It is especially good on Platinum and TruPd for an absolute invisible ring sizing.(Figure 11)

Illustrations by Kevin Shane Lindsey. February, 2009

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