Mold Maintenance & Repair

OCT 2013

Mold Maintenance & Repair

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the requisite training needs to be made with regard to three factors: (1) quality of repair needed, so that you can match the equipment to the expectation; (2) quantity of repair work anticipated to help calculate an roi (check your history for a baseline); and, (3) the option of outsourcing weld repairs. Keep in mind that with outsourcing comes the headache of logistics. For example, scheduling, availability, transportation, additional downtime, lost production etc. on the other hand, outsourcing allows you access to the knowledge, skills and expertise of a specialist. Resistance Welding in terms of initial investment, resistance welding though not the cheapest is still at the low end of the scale. This type of equipment is available from a variety of vendors from polishing suppliers to mold component suppliers. not to be dismissive of this technology, it is probably the most limited in terms of efcacy. resistance welding is basically a spot welding process. To accomplish a repair you perform a series of over-lapping spot welds and then if necessary go over the area several times layering to get an adequate build-up. its advantages include its lower cost to purchase, it can be used for very small repair areas and the basic operation of the equipment can be learned in a few minutes. However like any new skill or equipment, it takes does take time to master, and this equipment—though simple and straightforward—is no exception. With things that are simple to understand and operate the learning is often what not to do. To maximize the efectiveness of resistance welding, don't rush, take your time to clean the workpiece, the electrode and the fller material; take time to carefully position the fller material and electrode; take time to learn the discipline of removing your foot from the pedal before taking the electrode of the workpiece. speaking from experience, lifting the electrode while the system is energized can result in a crater blasted into your workpiece that is 10 times the size of the original repair you were attempting. due at least in part to the fact that there is no shielding gas to create a clean atmosphere for the weld, porosity and contamination in the weld is a concern. Another drawback is that weld penetration is minimal at best. There are three types of media with this process: (1) sheet stock, (2) wire stock and (3) powder. All of them—once the repair is polished—have a tendency to leave a repair with plenty of inclusions (for example, cavities, holes, voids, etc.). This is rarely acceptable for a surface that forms the molded part; although sometimes it will pass, if it is on the core side of the part. Again, patience, cleanliness and attention to technique can mitigate these dangers. This option is quick, and sometimes an acceptable band-aid repair until something better can be done. TiG Welding Tig (tungsten inert gas) welding is also a reasonably inexpensive option, but unlike resistance welding, Tig welding ofers signifcant penetration and includes an Argon gas shield that provides a clean environment within which the weld can take place. The result is what can be referred to as homogenous weld. The Tig arc melts the base metal and fller rod is added to the pool. The resultant repair is all one piece of metal. sure there is a possibility of inclusions due to contaminants (or sub-standard base metal), but these are the exception not the rule. The down side of repairs made with this process is the HAZ (Heat afected Zone). The most obvious efect is seen when the repair is brought back down to fush and the sink around the weld becomes apparent. The amount (depth) of the sink is minimal and in some cases can be blended adequately. Again, speaking as an end user not a metallurgist, i'll borrow a phrase from an engineer i once worked with: "i know more than i understand" about how heat afects the steel being welded. You have a small area that gets heated to several thousand degrees and two inches away the steel may be only a couple hundred degrees. This range of heat afects the hardness and characOctober 2013 15

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