Mistakes happen. A workpiece is machined incorrectly. Accidents happen. A workpiece is nicked, chipped, cracked, or damaged. Wear happens. Critical work-piece surfaces lose size and fail to perform properly. Whatever the cause, the result is that material isn't where it needs to be. Often, these unwelcome situations mean an expensive workpiece must be scrapped or remade, usually resulting in production delays, added costs, or missed deliveries.
Micro-precision welding is emerging as a technique for repairing damaged, worn, or mismade workpieces. This technique allows small amounts of metal to be applied to workpiece surfaces without causing significant thermal changes to the parent material. Filler wires as fine as 0.005 inch can be used, for example. Newly built-up surfaces, as thin as 0.002-0.003 inch, can be subsequently ground or machined to restore like-new conditions to the workpiece. Very small components can be welded together or to larger workpieces as well.
A new micro-precision welding workstation from Jordan Precision Welding (Conneautville, Pennsylvania) makes it possible for shops to adopt this technology. The workstation is designed as a free-standing setup which provides everything needed for successfully performing this technique. Only the welding power supply must be supplied by the user (standard TIG welding power supplies such as those offered by Lincoln, Hobart or Miller are acceptable).
As the name implies, micro-precision welding involves materials and tools so small that magnification is required. The Jordan workstation addresses this issue by providing readily adjustable components that make it easy to see the work while keeping hands free to manipulate the welding tools.
For example, a 20× stereo microscope is mounted on a rack-and-pinion height stand that can be raised or lowered with the turn of a knob. Two 250-watt halogen quartz lights mounted on either side of the microscope light the work area. Light-sensitive lenses protect the operator from "flash" while allowing complete visibility of the workpiece. These lenses darken instantly and automatically when the first arc is struck, so hands-free operation is not impaired. Toolholders, air hookups, and electrical outlets are located within convenient reach.
Two hotplates are provided because proper heating of workpieces is essential to successful micro welding. Doug Jordan, developer of the workstation, explains: "Welding is a thermal process that can cause unwanted changes to the properties of a material. In steel, for example, carbon particles can migrate from the parent material to the weld zone, causing the material added by welding to be surrounded by material that has become significantly softer." The way to avoid this, he says, is to make sure the difference between the temperature of the workpiece and the temperature of the weld is minimized. This means heating the workpieces sufficiently before welding and then welding with very low amperage to deposit new material at the lowest effective temperature.
The hotplates will heat workpieces from 100 to 1,000 degrees Fahrenheit and allow the operator to weld right on the plates themselves. After welding is completed, a workpiece can be reheated to stabilize the entire workpiece. By allowing the workpiece to cool slowly on the hotplate, thermal changes can be minimized. In many cases, no further heat treating or stress relieving is necessary, allowing repaired parts to be returned to service immediately.
According to Mr. Jordan, facilitating good welding techniques is the main advantage that his workstation represents. "The design of this workstation is based on insights into how the welding process works when applied in situations requiring micro-precision work."
Welding with 0.5 amp power settings, for example, reduces chances that the specified hardness of the workpiece or its grain structure will be affected. Likewise, the insulated copper work surface supplied with the workstation helps preheated workpieces hold their temperature while providing excellent electrical conductivity for clean starts on intricate work. The manual that accompanies the workstation offers guidelines for choosing settings, working with various workpiece materials, following effective preheat and post-heat strategies, and so on.
A few examples of micro-precision welding demonstrate its usefulness. Certain surfaces on a stamping die made of D2 die steel (58-60 Rc) were wearing ahead of the rest of the tool, causing it to be returned for regrinding after only 20,000 cycles. Rather than rebuild the entire tool, the user elected to have the trouble spots ground down and built up with M2 steel (65-66 Rc) using the micro welding process. After regrinding the new surfaces, the die was returned to service. Turnaround was less than 24 hours. The tool subsequently completed 100,000 cycles before regrinding.
Micro-precision welding was also used to repair a mold that had been damaged, allowing flash approximately 0.003 inch in diameter and 0.001 inch thick to form on the molded part. The damaged area was welded and remachined, eliminating the unwanted flash. Welded portions of the die did not require plating or other treatment, with no effect on mold release.
In another case, an engineering change to a mold required a gate on a runner to be relocated. The original gate was filled up with micro-precision welding. No further machining was required.