Comparing EDM with Conventional Machining

Manufacturing engineers turn to EDM (electrical discharge machining) when milling, turning and grinding aren’t up to the task. It’s as if it’s a binary choice: if machining isn’t possible then chose EDM.

The reality is more complex. There’s a significant middle ground where EDM and conventional machining processes go head-to-head. Yes, the wire EDM cutting rate is lower than that milling or turning, but the process scores in other ways. Finished part geometry, workpiece hardness, surface finish and cost are all areas where conventional and EDM compete. Here’s a look at the advantages and limitations of EDM.

Advantages of EDM – part geometry

With EDM there are no cutting forces and neither tool nor workpiece rotate. In addition, wire EDM is done with wire typically 0.010” diameter. This all means:

  • Thin walls are possible.
  • Cut internal corners with very small radii.
  • Cut thin slots in extrusion dies with wire EDM.
  • Produce blind and high aspect ratio pockets with sinking EDM.
  • Produce non-round openings and cavities.
  • An alternative to broaching for 2D shapes like gears.

Advantages of EDM – hard materials

Material hardness has little effect on EDM wire cutting rate and doesn’t limit possible part geometries. Tungsten carbide, tool steel, Inconel and any metal harder than RC38 are all good candidates where conventional machining is slow and expensive.

A particular benefit is the ability to bring parts to their final size after heat-treatment. This takes out distortion brought about by hardening and stress-relieving.

Advantages of EDM – surface finish

Unlike conventional processes, an EDM surface has a very random texture. This is advantageous when directionality or “lay” could influence product performance. Additionally, EDM can create surface finishes as smooth as 5 RMS or around 4 micro-inches Ra. (This entails taking multiple skimming passes, for which the wire EDM cutting rate needs to be very low.)

Cost advantages of EDM

On the right job – complex 2D geometry, hard material – EDM offers cost savings over conventional processes. For example:

  • No special tooling (saves money and lead time.)
  • Skimming passes eliminate secondary finishing operations.
  • Laminate layers of material to cut multiple parts simultaneously.
  • Enables reuse of cut out slugs rather than producing chips.
  • Avoids moving a part through multiple conventional processes. The final shape is achieved in a single set up (which also improves accuracy.)

Limitations of EDM

EDM requires an electrically conductive workpiece. It will not work on wood, plastics or composites.

Material removal rates (MMR) are usually lower than for conventional processes. However, direct comparisons are difficult to make since material hardness is such a big factor. MMR is usually calculated in cubic inches per hour with 0.4 in3/hr a typical rate. Calculated this way, a narrow kerf makes the wire EDM cutting rate quite high. Also, workpiece thermal conductivity and melting point have significant impacts on EDM MMR.

Wire EDM can only cut 2D profiles, although a fourth axis to incline the wire enables conical forms and tapers.

An alternative to consider

EDM is more than just a fall-back for when conventional machining isn’t up to the task. It’s a process to consider whenever the workpiece is hard, electrically conductive, and has specific geometric challenges or surface finish requirements.

Manufacturing Locations Across National Time Zones
Manufacturing Locations Across National Time Zones
The Fathom Advanced Manufacturing Platform
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HEADQUARTERS

1050 Walnut Ridge Drive
Hartland, WI 53029
ISO 9001:2015
AS9100:2016
ITAR

ARIZONA

444 W. 21st St. Ste. 101
Tempe, AZ 85282
ISO 9001:2015
NIST800-171 Compliant
ITAR

FLORIDA

14000 N.W. 58th Court
Miami Lakes, FL 33014
ISO 9001:2015 Design Certified
ISO 13485:2016


 

CALIFORNIA

620 3rd Street
Oakland, CA 94607
ISO 9001:2015 Design Certified
NIST 800-171 Compliant
ITAR

ILLINOIS

1207 Adams Drive
McHenry, IL 60051

1401 Brummel Ave
Elk Grove, IL 60007
ISO 9001:2015 Design Certified

NEW YORK

401 W. Shore Blvd.
Newark, NY 14513
AS9100:2016
ISO 9001:2015
ITAR

1920 Slaterville Rd
Ithaca, NY 14850
ITAR

TEXAS

1801 Rowe Lane
Pflugerville, TX 78660
ISO 9001:2015
AS9100:2016

1513 Sam Bass Rd
Round Rock, TX 78681
ISO 9001:2015
ISO 13485:2016

COLORADO

7770 Washington St.
Denver, CO 80229
ISO 9001:2015
ITAR

MINNESOTA

13758 Johnson Street NE
Ham Lake, MN 55304