Engraving vs EDM
Why is Engraving better than EDM (Electrical Discharge Machining)?
The value of a Marking Die is composed of:
- The Initial Cost
- Service Life
- Cost of Lost Production (rework, scrapped work, downtime)
The basic difference between an Engraved Die and one made by EDM (Electrical Discharge Machining) involves how material is removed to form characters and designs.
EDM uses a high frequency electrical discharge to erode away unwanted material, leaving the desired characters or design. Due to the EDM’s intense local heat (up to 10,000;c), the cavity surface is structurally changed to a depth up to 0.005. As this surface layer is untampered, premature failure may occur when these dies are either subjected to stress cycling; high impact or tensile stresses are encountered. These stresses remain in the finished product and can cause short die life and or failure. Obviously, the smaller the character, the greater the negative effect these stresses have on the die’s life and performance.
As the surface layer is structurally changed, so is the subsurface. The intense heat creates three layers (see fig.1). The top layer (EDM surface layer) is created when the displaced molten metal and small amounts of electrode material form spheres and is strewn over the work metal’s surface.
The middle layer is the recast layer. The EDM process has literally altered the work metal’s metallurgical structure and characteristics in the recast layer. Due to the displaced molten metal’s rapid quenching, micro cracks can form in this very hard, brittle layer. Left untreated, the affects of this layer can cause premature failure.
The annealed layer (last layer) has only been heated as opposed to melted. The power used for the cut combined with the heat sinking ability of the material regulates the depth of both the layer and that of the heat effected zone.
An Engraved Die is cut without incurring temperatures that would change the metallurgical properties of the metal and avoids creating any stresses. Being engraved, these dies will have finer detail and produce a cleaner, more precise mark. Heat-treating after the final engraving ensures the die has uniform metallurgy and will hold up under repeated use and deliver a longer service life.
The math is simple. You get the most bang for your buck with engraving.
Engraving, it’s what we’ve done at Wagner Engraving for over 90 years!