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Successful development of “solid single-crystal diamond end mill tools”

Single-flute” and “double-flute

Successful development of “solid single-crystal diamond end mill tools”

“Single-flute” and “double-flute” end mill tools capable of providing a mirror finish to carbide materials — scheduled for release in 2016 or later

Kyowa Co, Ltd., a manufacturer of precision tools and wrist watches (headquartered at Ogachi, Akita, and led by President Tsuyoshi Suzuki; hereinafter referred to as “Kyowa”) has succeeded in developing solid single-crystal diamond end mill tools capable of providing a mirror finish to carbide materials.

Single-crystal diamond eliminates the grain fall-off problem experienced with sintered compacts, and so this attractive tool material can provide a mirror finish to carbide workpieces. However, single-crystal diamond is extremely hard to work with in machining and is subject to cleavage,* which limits the lattice plane available as an end mill tool. Consequently, solid single-crystal diamond end mill tools are considerably expensive and also prone to chipping of end mill tool tips, and so have been unsuccessful in the market.
*Cleavage: a phenomenon unique to single crystals, where the material tends to split along a distinct direction of the crystal.

To solve the above problems, we have developed our own special laser processing technique and polishing technique. As a result, a “single-flute” solid single-crystal diamond end mill tool can now be manufactured in half the time, at half the cost, and with a service life 1.5 times as long.
In addition, Kyowa Co., Ltd. has also succeeded in developing “double-flute” solid single-crystal diamond end mill tools, the first in the world.

During the current year-long marketing campaign, we plan to introduce these developments to a range of high-end manufacturers who require advanced precision processing techniques involving light guide plates for LCD panels, small aspherical lenses, and Fresnel lenses.
“Single-flute” and “double-flute” solid single-crystal diamond end mill tools are scheduled for release in 2016 or later.

Test machining with single-crystal diamond tools — Pattern trimming
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– Machining on carbide 20 mm × 10 mm

Test machining environment
Work material Carbide G6 or equivalent
Cutting fluid Semi-dry
Tool used Single-crystal, single-flute diamond ball end mill (R 0.5 mm)
Machining conditions
Rotational frequency 30,000rpm
Feed speed 60mm/min
Cutting (axial/radial) 0.002mm
Machining time 4h
Roughness of machining surface Ra:0.05μm

Development of special laser processing technology

Since single-crystal diamond is extremely hard, it has been processed primarily with a combination of laser processing and polishing. Laser processing is excellent for single-crystal diamonds, but it requires a certain amount of machining allowance for two reasons: the workpiece is instantaneously raised to high temperatures, and the focal length (light focusing characteristic) makes linear processing difficult. Furthermore, the portion of single-crystal diamond raised to high temperatures is graphitized and must be removed due to its significantly lowered hardness. This involves a long time for finish polishing.
With the recent progress of laser technology, we have developed a machining technology using our processing machine built for laser applications, with the result of successfully reducing the laser machining allowance to a few micrometers. The reduced tool prices made possible by the reduced fabrication time of single-crystal diamond tools are expected to increase the use of these tools.

Development of polishing technique

By applying our patented electrolytic abrasive grain polishing* and mirror polishing techniques, we have chamfered solid, single-crystal single-flute diamond end mill tools to reduce the chipping of diamond tool tips. The result is an end mill tool ideal for superior finishing of non-ferrous metals, which will find a broad range of applications, including mirror finishing of aluminum and copper, and mirror machining of carbide.
*Electrolytic abrasive grain polishing: Powder for use as abrasive grains is diffused in a solvent of silicone oil to produce a dielectric functional fluid. This fluid is subjected to a low-frequency alternating electric field to control the placement of grains while polishing is underway. (Patent No. 3595219)

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