MoldMaking Technology

NOV 2018

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Page 16 of 51 15 Simple and easy-to-use workholding can be equipped in most machine tools. These poor flushing conditions result in an increased con- centration of conductive particles that linger within the spark gap rather than being flushed away. These conductive particles continue to spark with each pulse, wearing the EDM wire more quickly than it would under better circumstances. Add to this the loose metal powder that uniquely coats and •ills •D-printed parts, and the operator has even more conductive materials that are not flushed away within these hollow spaces. All of this causes increased wire breaks when cutting additive parts. Operators can avoid wire breaks by strategizing their choice of wire. Most shops rely heavily on standard, •.• •-inch brass wire, so the goal in troubleshooting is to improve wire breaks over this benchmark. For this type of application, operators can switch to •.• €-inch wire. The larger diameter provides additional strength that keeps the temperature of the wire core low. Others users may switch to steel-core wire, which is much less likely to break under these conditions. However, it is not compatible with most wire-choppers on the market and is more dif•icult to recycle. Before buying new wire, however, it may be more cost- effective to explore solutions on the machine control itself. On Japanese controls, the key settings for this case are MAO set- tings, which more broadly have to do with ON time, OFF time and the sensitivity of adaptive circuits. Increasing the sensitiv- ity of adaptive circuits enables operators to adjust to more conservative settings on most of the newer EDM models when the cutting environment is not ideal. One example is when the wire opens a pocket of trapped powder. Likewise, increasing the OFF time opens more opportu- nity for the swarf and other debris to clear between electrical pulses. Additional speed can be regained by increasing the ON time, which means that the EDM model will have both longer pulses and longer gaps between pulses. Because adaptive cir- cuits treat ON and OFF time differently, a more sensitive cir- cuit will continue to be conservative even when ON and OFF time are both increased. In broader strokes, the goal is to make the spark environment more conservative while recovering the speed where that is possible. Machine-Tool Specifications Additionally, many shops would bene•it from reviewing machine speci•ications in regard to the type of work that they do. Shops that plan to take on more additive work may want to consider machinery that is suited more speci•ically for this application, as the requirements of an additive part can be quite different than other processes. Often, wire-EDM work on an addi- tive part is limited to the removal of supports or of a baseplate, meaning that the goal is no longer •ine •inishing or extreme precision but capacity, cutting speed and reliability under unfavorable conditions. This change has put equipment manufacturers in a some- what dif•icult predicament, as they design around very dif- ferent speci•ications than those that the additive market demands. As additive applications continue to grow in size at a fairly rapid pace, the Z height required to machine these parts with EDM also continues to increase. And yet, while this application does not necessarily require an extreme surface •inish and micron accuracy, the only machines This connector mold is ready for wire cutoff. Operators can avoid wire breaks by strategizing their choice of wire.

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