Testing the PUK 2 Precision Welder

If the thought of buying a laser welder gives the accountant in you cardiac arrest, you may have a more affordable option. The PUK 2 by Lampert Tools Inc. in Chicago is a spot welder that performs many of the same tasks that a laser welder can, such as repairing porosity and welding next to gemstones. Although it won't make as small of a weld as a laser, nor does it share a laser's machine-gun rapidity, the PUK 2 may be an affordable alternative for some small shops, as it retails for less than $4,000.

Generating single pulse welds at a rate of 1.7 seconds per pulse, the PUK 2 has 30 percent more power than its predecessor, the PUK III, making it more suitable for welding silver. The complete kit with accessories includes a control box, handpiece, auto-darkening viewing lens with light/magnifier, handpiece holder, argon regulator, spare electrodes, and an assortment of work holding/grounding devices.

PUK 2: Photo by Lyle Lenkeit

Using the PUK 2 is fairly straightforward. You start by positioning the work piece on the work table, clamping it with the alligator clip or cross-locking tweezers, or holding it with pliers. All of these devices can be connected to the control box and constitute the positive lead. The handpiece is the negative lead. Its collet holds the replaceable electrode, which should protrude several millimeters from the tip.

To make a weld, you simply touch the electrode point to the workpiece. Argon shielding gas then flows from the tip. An audible signal is heard just before the electrode automatically retracts, creating a momentary arc that makes one spot weld. Depending on the setting used, the entire process takes about 2 seconds. All viewing is done through a shaded shield, which automatically darkens when the arc is made. The degree of pressure exerted at the tip is the most critical factor in creating a good weld.

Spot Tests

To get a feel for the welding range that can be achieved with the PUK 2, we made single spot welds on a piece of 18k yellow sheet rolled out to four different thicknesses: 1 mm, 0.75 mm, 0.5 mm and 0.25 mm. The top row of welds was done with the Impulse set at 1, the bottom row with the Impulse set at 2. Three tests were done at each setting with the power set at 1, 4, and 8 (left to right).

The back side of the test piece (which reads as a mirror image of the front) is a good indicator of the weld penetration achieved, therefore indicating the effectiveness of each of the power levels. At 0.25 mm thickness, only the Impulse 1, Power 1 setting does not show through. For the 0.5 mm thickness, both Power 8 spots show through and the Impulse 2, Power 4 spot shows slightly. At 0.75 mm thickness, both Power 8 and Impulse 2, Power 4 are evidenced only by slight bumps. The back of the 1 mm section shows no sign of the welds. This would indicate that, depending on thickness, you may have to create a bevel at the joint or weld from both sides to get a complete weld.

As with any other type of welding, results vary with different materials. To demonstrate these differences, 1 mm thick pieces of sterling silver, 14k yellow gold, 18k nickel white gold, and 950 platinum were subjected to four shots at full power on the Impulse 2 setting. Not surprisingly, the silver (which is the most conductive) had the smallest spots, averaging 0.8 mm in diameter. The platinum spots averaged about 1 mm. And the spots on both of the gold samples averaged about 1.9 mm. This experiment shows that the best resultsâ€"the largest diameter of weld and pre-sumably the deepest penetrationâ€"were achieved on the gold samples. It also indicated that when working with sterling silver or platinum, you'd want to start with higher power settings for most applications.

Joining Test

When we completed the spot tests for the various metals, we proceeded to join two pieces of 1 mm 18k yellow gold sheet to test the strength of the weld. To acheive full penetration, we filed a bevel on one edge of both pieces and welded the joint using 0.4 mm filler wire. After welding, the piece was bent over a ring mandrel to a size 4 radius with no damage to the weld joint. (Note: The sheet was fully annealed; if this had been done with work-hardened material, the joint probably would have failed.

Pros and Cons

During the course of learning how to use the PUK 2 you will likely go through a substantial number of electrodes. The welded material may be deposited on the tip, sometimes necessitating replacement. Also, at times you may only get one pulse from a fresh tip, as opposed to 10 or more. This is more likely to occur when you are operating in a tight area at high power levels.

To change the electrode, you must re-move the end cap, loosen the collet, remove the old electrode, insert the new one, tighten the collet, and close the end cap. This can get time-consuming. Some type of quick-change collet would make operating the PUK infinitely more rewarding.

On the bright side, the protruding electrodes offer advantages over recessed electrodes found in some other welders. Welds can be made with virtual pinpoint accuracy in some very hard to reach areas. For example, you can weld a broken ring gallery from the underside. For those of us who don't have laser welders, this expands our range of strategies for both manufacturing and repair work.

In my opinion, the least favorable features of the PUK are the handpiece holder and the shield. The handpiece holder is adjustable to ensure a comfortable working height. When the holder is set on the high end, the handpiece can be removed quickly; however, when it's set on the low end, you cannot remove the handpiece without first resetting the holder to the high end.

The shield is also somewhat awkward to use, especially if you like to work with a visor magnifier. If you want a little more (or less) magnification than what's provided, you're out of luck. A visor-mounted filter with replaceable lenses would have been a much more user-friendly option.

Despite these minor quirks, the PUK 2 has become an invaluable tool in my shop. It can perform many of the tasks that a laser welder can at a fraction of the price.