Electro discharge truing
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Crystec Technology Trading GmbH

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Electro discharge Truing

Grinding wheels need from time to time dressing and truing. This is done with a special dresser often consisting of a diamond tool. It is pulled over the grinding wheel in order to re-estabilish the original form of the grinding wheel, which is lost during grinding procedure over the time. The shape of the grinding wheel depends on the grinding application. Sometimes it is necessary to structure parts by grinding. For centerless grinding a concave shape is necessary in order to ensure the automatic transport of the parts through the grinding machine. The truing of the grinding wheel has to be done in order to excavate new abrasive grain to the surface. This is done by removal of the binder between the grain. A diamond dresser does dressing and truing at the same time, but the fresh grains on the surface are damaged during this operation.There is one way to avoid such a damage: electro discharge truing. Electro discharge truing is a is a precise, non-contact truing method which improves grinding accuracies while increasing productivity and quality. E-dt makes truing possible while metal-bonded diamond wheels remain on the grinder. It removes only the metal bond with no damage to the diamond grain.

electro discharge truing electro discharge truing electro discharge truing

Koyo realizes the advantages of using diamond wheels. They are non-conductive and extremely hard which makes them excellent for grinding applications with materials such as ceramics, carbide, cast iron, and sintered metal, as well as hardened steels. A diamond grain is also less expensive than cBN and has a longer life, thereby lowering tool cost.
So why aren’t diamond wheels more popular?


Koyo has the solution....... Electro discharge truing (E-dt)

Schleifrad einer Koyo Schleifmaschine mit Abrichter durch Funkenerosion

Truing (or dressing) is required to achieve highly-accurate grinding whether using cBN, diamond, or conventional aggressive wheels.  However, truing of these wheels was difficult due to the materials hardness, so these super-aggressive wheels were made with soft bonds for ease of truing or dressing the grinding face.  This resulted in a shorter life for the grinding wheel.

The diamond has a greater hardness than any other abrasive material.  It is 1.7 times harder than cBN and 3.3 times harder than conventional aggressive wheels.  A metal bond can be adopted for diamond wheels to hold the abrasive grit tightly together and to maintain the grinding face after truing.
hardness comparison

Benefits & Advantages of using E-dt:

Reduce Inventory

Down time for dressing is reduced by 1/8 to 1/5 from that of resin-bonded cBN wheels.  According to our test results on a Koyo KVD-300, it took only 15 seconds to remove 0.76” of grinding surface using with E-dt. Comparatively, the dressing time for resin-bonded cBN wheels using a WA dressing stone was 120 seconds.


Reduce Dress Frequency

The dress frequency using diamond wheels with E-dt is 3 times less than with cBN wheels.  Cycle time is decreased by 28% for sintered metal parts.  This enables dressing to be done between shifts.

Truing time

Reduce Defects

By maintaining the integrity of the grinding wheel surface after truing,  the quality of size, flatness, parallelism, roundness, cylindricity, and surface finish is dramatically improved on high-precision parts.  Using a finer grit diamond wheel, mirror-finish (0.2µm) quality can be achieved.

Grinding accuracy

E-dt Test Results:
Test results

E-dt trues accurately since there is no resistance between the dressing tool and the grinding surface.

Presently cBN wheels are dressed by using a method which fractures the cBN grit, producing a sharp edge on the tool.  In comparison, with E-dt there is no damage caused to the grinding wheel grit. This can be seen in the following pictures.

cBN dressed with WA (white aluminium oxide) stone
Diamond after Electro-discharge truing

E-dt available on the following Koyo Grinders:

Centerless: C3015F, C4520FS, 4515C, 4515CS, 4520C, KCL-50

Surface: KVD-300II, KVD-450, KVD-580, HD-3, HD-5, HD-7, HD-10, R-031, R-431, R-631, R-632

Crystec Technology Trading GmbH will be pleased to further discuss details with you.
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