Continuing our series of electrical discharge machining articles (extracts from our EDM machining guide, ‘The EDM Handbook’), this section looks at the technical challenges towards running a success electrical discharge machining company.

Di-Spark: The Electrical Discharge Machining Company

Di-Spark Ltd in terms of an ‘Electrical Discharge Machining company‘ supply precision EDM machining (spark & wire electrical discharge machining services).

Di-Spark are an electrical discharge machining company supplying clean cut wire erosion & spark erosion machining services to high technology industries such as Formula 1, Oil & Gas, Medical, Aerospace, Satellite, Defence & Energy Markets.

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KEYS FOR SUCCESSFUL ELECTRICAL DISCHARGE MACHINING COMPANY

There are many factors that must be considered to ensure successful EDM.

9.1 ELECTRICAL DISCHARGE MACHINING COMPANY: MACHINING TIPS

The following recommendations are guidelines only. The single best source of cutting technology is from the application engineers employed by the machine tool builder.

For Speed: EDM is always a compromise between speed, electrode wear and machining stability. If the kerf, electrode wear, and surface finish are satisfactory and flushing is adequate, the metal removal rate of an EDM operation can be increased by slowly decreasing the off-time, until machining becomes erratic, and then quickly returning to the last stable setting.

For Wear: Wear is not a serious consideration for wire EDM because the wire is constantly renewed from the spool. For spark EDM, leaving a minimal amount of stock material for finishing can help keep electrode wear to a minimum.

For Finish: In EDM, producing a good surface finish can be time consuming. Careful planning and preparation is often required. For both wire erosion and spark erosion machines, careful selection of the current and frequencies used and the amount of material left to remove is paramount. Whether skim cutting with a wire or orbiting with a solid electrode, the amount of material removed should be only slightly more than the maximum crater depth left by the previous cut.

When producing parts requiring minimal recast or a mirror finish, metal removal is not the main consideration, as this is the duty of the roughing and semi-finishing operations. At this point, the part should only be a few microns away from its finished dimensions and the only requirement is to change the surface finish, actually removing very little material. Using low power, very high frequencies, and the minimal amount of offset for each cut is the best strategy.

Fine finishing on manual spark erosion machines is more difficult because of the inability to orbit the electrode. Most jobs on manual machines need to be finished using several electrode passes. The problems associated with this method are:- the time required for each finishing pass, uneven electrode wear, and the time and support equipment used to make or redress multiple electrodes. The very small volume of material remaining for finishing (usually 0.100 mm to 0.250 mm per side) cannot accept very much current. In addition, while using finishing settings, excessive wear on the leading edges of the electrode can occur because it must cut the entire Z-depth in order to finish the sidewalls. The worn electrode must be redressed or replaced by a new one to remove the material left by the first finisher. In many cases, several dressings and passes must be made before the electrode removes the sidewall taper and corner radii to the drawing requirements.

The speed and performance of finishing operations on manual spark erosion machines can be greatly improved at a relatively low cost, by adding an auxiliary orbiting device to the head. While an orbiting device will not make a manual machine into a CNC machine, it will help improve speeds, finishes, flushing, and reduce electrode corner wear.

9.2 ELECTRICAL DISCHARGE MACHINING COMPANY: ELECTRODE MOTION

For manual spark EDM applications multiple electrodes – roughers and finishers – are required. All electrodes must be manufactured undersized to allow for the spark gap, relying heavily on the technology supplied by the machine tool manufacturer. Tables within the manuals of the machine should provide spark gap information based upon electrode material, work-piece material, amperage, and finish desired. With this information, the spark gap can be determined for both roughing and finishing electrodes.

Sparking using orbiting technique offers the following advantages;

1. Reduced machining time.

A much larger surface area of the electrode can be presented to the work-piece allowing the use of high currents and frequencies this will result in a substantially faster metal removal rate.

2. Reduced, Uniform electrode wear

Machining with faces of the electrode ensures uniform electrode wear instead of requiring only the leading edges of the electrode to do all of the work.

3. Reduction in the number of electrodes required

The finished sizes produced by an electrode can be varied using orbiting thus reducing the reliance on dedicated roughing and finishing electrodes. Theoretically a single electrode can be used as both a rougher and a finisher.

4. Improved surface finishes

Improved surface finishes due to electrode motion can be achieved.

5. Improved accuracy

Orbiting provides the ability to precisely control sizes mechanically instead of hoping that the spark gap produced during single axis machining is the same as the electrode undersize.

6. Reduced scrap

Electrode motion improves flushing the debris from the work-piece reducing the risk of arcing and the increased control over accuracy ensures consistent, predictable results.

7. Reduced operator involvement

There is a reduction in direct labour costs and support equipment involvement because fewer electrodes are required, also polishing or benching of the work-piece is reduced or eliminated due to the improved surface finishes.

9.3 PLANNING: SUCCESS AS AN ELECTRICAL DISCHARGE MACHINING COMPANY

The most successful EDM jobs are the ones utilising careful planning from the start. The concept of designing around flushing is the most prudent. An experienced EDM machinist will study the detail and visually determine where and how the electrode and work-piece is to be flushed. Conditions such as surface area, corners, side draft, turbulence, cavitation, gas evacuation, and secondary discharge need to be considered. To the inexperienced EDM machinist, this may seem overwhelming, but all these things become second nature with training and experience.

Each style of flushing has its own properties and applications, and choosing the correct one is not always a straightforward proposition. Many times, the most logical choice is not practical, i.e., slots or other details that are too deep or too narrow to drill flushing holes in the electrodes. So, just like other choices in EDM, a compromise must be made, usually opting for the next best method.

Many times, reasons such as, “it’s too much trouble”, or “there’s not enough time”, are given for not adequately planning a job. Also EDM often becomes the process of last resort when the job cannot be completed any other way. EDM machining with the best possible flushing conditions will always optimise the process. Failure to provide good flushing conditions in order to save money or time will always prove to be a false economy. 

Contact Di-Spark: The Electrical Discharge Machining Company