Moldmakers using wire EDM face challenges when cutting high taper angles. Often EDM machines have the axis movement necessary to achieve the desired angle, but the physical properties of the wire and related machine technology may not be adequate.
Low tensile strength soft wire—needed to cut high tapers—is sensitive to the voltages and tension applied to it by the EDM machine during the AWF cutting cycle. If not handled properly, the result is a malformed wire tip, which is curved, preventing the wire from being able to be inserted into the wire guides. In these instances, the machine is unable to thread or re-thread the wire, so the erosion process is stopped and production time is lost.
To help solve this problem, look for EDM equipment that provides improved wire processing during the AWF cycle. Technology should include a way to precisely control the wire tension and energy used to cut the wire.
The ideal AWF situation is one where the wire heats and stretches until it breaks in two without melting. EDM machines that offer the ability to have cool air directed to the wire cut point, keeping the wire tip as cool as possible and preventing a molten tip to be produced during a thermal wire cutting process is very helpful.
To optimize the threading cutting cycle, rely on a timer to open an air solenoid to gently blow cool air onto the wire cutting electrode to keep the wire tip from heating up to a melting stage.
Accurately controlling wire tension is critical, especially with soft wire, during the cutting phase. An AWF system that includes a wire tension monitoring device enabling continuous observation is important.
And to maintain wire tension, EDM systems that include a dual AC motor and encoder wire drive system working in tandem to enable the tension motor and drive roller to communicate energy usage to the controller are very useful.
Some other useful tips for working with soft wire include: (1) use a die guide designed for large taper cutting, especially if you are going to skim cut the large tapers to improve surface finish and accuracy. These guides have a much larger support to help the wire transition thru the large angles’ (2) to ensure accuracy, use the features in the CNC that compensate for the changing position (in Z-Axis direction) so that the taper angles are precise; and , (3) if the cutting technology being used was developed for hard brass wire, the wire tension will have to be reduced on the rough cut.