Question: When wire EDM machining, what is the most effective method for slug removal or detainment?
Answer: There are several different techniques for wire EDM slug removal or detainment, but these methods will vary based upon the material type and size. It is important to have a slug management plan in place before machining begins, as it is imperative to prevent damage to the machine.
- Rare Earth Magnets: These high-power magnets are a very convenient and inexpensive method to controlling most slugs on magnetic/ferrous materials. Several different sizes and power of magnets are available, and many magnets can be used to retain a slug. For wire EDM purposes, using a lower profile magnet typically prevents interference and collision issues with the machine nozzles. While magnets are effective, they do have limitations. As a general rule, once a slug becomes larger than a 50mm (2.0") cube or greater than 5kg (11 lbs.), additional support or retaining methods should be considered.
- Adhesives: On smaller parts, glue or adhesives such as Super Glue or Bond-O can be used to retain the workpiece or slug. This method would be reserved for smaller, lighter and more delicate part details, but a method for removing the adhesive must be determined before employing this method.
- Tape: Using tape such as duct tape can be an effective method in controlling and retaining slugs. When machining some thin material parts (part size dependent), it might be necessary to apply tape mid-process, as thin materials can sag under their own weight, which will cause inaccuracies to the final part. If tape is applied mid-process, it is important to disable Automatic Wire Break recovery, as the machine could potentially crash or disturb the machine setup if the tape is placed near the program path.
- Clamps: These are simple C-clamps or Kant-Twist clamps that are used to retain a slug from dropping. While effective, these clamps do hang below the table level, so extreme care should be taken to ensure that the machine does not crash into these clamps during operation or when moving the machine to extract the slug.
- Top Straps: Top straps are a flat bar of steel bolted to the slug before final cutoff and dropping of the slug. This method requires preplanning, as one or more tapped holes should be machined into the slug prior to wire EDMing. This method is very effective on larger and heavier slugs.
- Slug Ejection Via Programmable Flushing: On certain jobs where the slugs can freely fall away for the parent block, programmable flushing can be utilized to automatically eject the slug. All Makino wire EDMs feature dual, independent flush pumps, which enable programming of different flush pressures between the upper and lower heads. Depending on requirement, slugs can be pushed down and out the bottom of the part (higher pressure on upper head—lower pressure on lower head), or slugs can be pushed up and out from the top (higher pressure on lower head—lower pressure on upper head). In either case, the use of programmable flush for automatic slug ejection is typically reserved for smaller slugs, and the lower profile HEAT or Laminar nozzle would be used.
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