Despite decades of effort, custom and practice dictates that stopping the machine and manually removing slugs is still the norm. But the developments from GF Machining Solutions for its latest wire-cut machines now provide a reliable answer.
This system, called Automatic Slug Management (ASM), ensures manufacturers are able to run EDM machines in true, lights-out style and benefit from reduced cycle times with no operator intervention.
Left to their own devices, slugs will fall onto the lower head of an EDM machine. This can cause a crash or trigger alerts that cause the machine to stop. To help prevent this, CAM programs include ‘tabs’ to keep the slug connected to the workpiece during machining operations. Once completed, operators remove the tabs and slugs.
Such manual intervention prevents true unmanned operation from being realised. At best, manufacturers can achieve rough cutting of parts overnight - but will need to wait until operators are available to remove the slugs and to run trim and finishing passes.
With Automatic Slug Management, manufacturers can machine parts (roughing and finishing) overnight. The system is particularly well suited to die-stamping applications and other small cavity operations.
The process begins with a complete roughing pass, leaving no welds or tabs. Instead, the GF Machining Solutions’ wire EDM machines‘ lower head catches the slug before it can fall into the tank. A device retro-fitted to the upper head is lowered and blows high pressure air over the slug, which creates suction and pulls the slug from the part.
The slug is the deposited away from the machining zone by the upper head (moving along the U-and V-axes). ASM is slower than the manual alternative, but the fact that it requires no human intervention, means manufacturers can load machines at night with raw material and return the next morning to completed parts.
Because suction is used, an obvious limitation is the slug’s size and weight. In these instances, it is possible to remove slugs using a pocketing strategy, where EDM wire is used like a milling cutter to machine the slug away.
Applications involving/producing heavy slugs and large cavities are more likely to adopt ASW (Automatic Slug Welding) as the process of choice. Although ASW doesn’t enable true uninterrupted, lights-out operations to occur, it does significantly reduce cycle times.
ASW makes use of an unwelcome EDM condition when using brass wire: the creation of a brass residual build-up that could re-attach the slug to the workpiece.
The slug welding process uses G-code commands to manipulate brass accumulation. It prevents top-to-bottom welds from occurring but does enable welds between the surface of the workpiece and the slug. The end result is a slug that can be (gently) knocked out of the workpiece with a hammer. (The brass residue that remains does not interfere with or compromise skimming passes or other finishing operations).
Although ASW does not facilitate true lights out automation, it does eliminate the need to cut slug tabs and does shorten EDM process times.
ASM and ASW, available on GF Machining Solutions’ latest wire EDM machines, are, along with automatic threading and rethreading, SMART consumables’ technology and remote monitoring, helping manufacturers fully automate their EDM processes.
