Mold Maintenance & Repair

OCT 2016

Mold Maintenance & Repair

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October 2016 15 heats up to a couple thousand degrees Fahren- heit, which can cause distortion and damage to small molds and inserts during welding. Experience is the most critical component to micro-TIG welding success. It is very difficult to become a proficient micro-TIG welder with no welding background, because the operator has to learn the basic steps, such as starting an arc, before he or she can progress. One becomes a micro-TIG welder by becoming a proficient TIG welder first then moving to a special mold-weld- ing microscope for practice. However, learning to weld under a microscope takes time, as the welder gradually learns about depth of field and positioning. Consultants are available who can help train already-established TIG welders in the fundamentals of micro-TIG welding. Laser welding. The laser welding process begins with lining up the weld area in the crosshairs of the microscope. When the laser is engaged, a weld puddle will form in the center of the crosshairs. At this point, filler is added. Instead of using an arc generated from a welding torch, laser welding uses a wavelength of light. The laser beam is generated from a fixed point, typically an extension or arm at- tached to the machine's power base (see Figure 3). The laser can be a neodymium yttrium aluminum garnet (Nd:YAG) type that disperses a pulsed light at a wavelength of 1,064 millinewton (mn). A microscope is also attached to the arm and allows the operator to see ex- treme detail, similar to a micro-TIG microscope. The laser creates a pulsed microscopic weld puddle that allows pinpoint weld deposits of a couple of thousandths of an inch. When the laser pulses, a weld puddle is formed that can be seen under the microscope. When the laser is not pulsing, a weld puddle does not form, allowing the workpiece to stay cool. This is why laser welding has a low heat displacement, which is critical for minimizing any welding sink or distortion. The duration and size of this pulse can be adjusted. There are some drawbacks to laser welding. For example, this process is very specialized. In my welding shop, it is used for very small re- pairs. Plus, it can be time-consuming, depending on what is being repaired. Most often, my laser welding projects involve repairing shut-off areas (see Figure 4). Most professional mold weld shops are skilled in both processes, and designate laser welding or TIG welding depending on the job and cus- tomer preference. Many times, both processes are used on the same job. For example, the speed of TIG welding can be used to repair a large area and then the low-heat capabil- ities of a laser welder can be used to fix any distor- tion around the weld. Buying a Laser Welder There is a trend today towards mold builders adding or expanding their mold repair capabilities to serve their customers bet- ter, and having access to both TIG and laser welding technologies is key. Here FIGURE 2: A micro-TIG operator uses the microscope to create small and large weld buildups.

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