Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Patent
1998-04-16
2000-02-01
King, Roy V.
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
4272497, 427237, 427238, 427239, 427902, 427904, B05D 306, B05D 722, C23C 1626
Patent
active
060200367
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of forming a hard carbon film over an inner surface of a guide bush for supporting a rod-like workpiece for rotation and axial sliding at a position near a cutting tool (cutter), mounted on an automatic lathe, the inner surface coming in sliding contact with the workpiece.
BACKGROUND TECHNOLOGY
Guide bushes mounted on the column of an automatic lathe to hold a rod-like workpiece rotatably at a position near a cutting tool are classified into a rotary type and a stationary type. The rotary guide bush rotates together with a workpiece and holds the workpiece for axial sliding while the stationary guide bush remains stationary and holds a workpiece for rotation and axial sliding without rotating itself.
The guide bush of either type has a taper outer surface, a portion provided with slits for affording elasticity to the portion, a threaded portion for mounting the guide bush on the column, and an inner surface for holding a workpiece. The inner surface constantly in sliding contact with the workpiece is susceptible to wear and, particularly, the inner surface of the stationary guide bush undergoes intense wear.
A guide bush proposed in, for example, JP-A No. 4-141303 has an inner surface, coming in sliding contact with a workpiece making sliding and rotative movement, securely attached with a superhard alloy or a ceramic material by brazing or the like.
When the inner surface of a guide bush is attached with a superhard alloy or a ceramic material excellent in wear resistance and heat resistance, the wear of the inner surface of the guide bush can be reduced to some extent.
However, when the workpiece is subjected to heavy machining on an automatic lathe, in which the depth of cut is large and the cutting speed is high, the workpiece is damaged or seizure occurs due to a decrease in a clearance in the radial direction between the guide bush and the workpiece even if the inner surface of the gude bush is attached with the superhard alloy or the ceramic material because the superhard alloy and the ceramic material have a comparatively large coefficient of friction and a low thermal conductivity. Therefore, it has been difficult to increase the depth of cut and cutting speed.
The stationary guide bush has advantages in that a workpiece can be accurately machined in a high roundness because the workpiece can be held such that its axis has no runout, less noise is generated, and the construction of the automatic lathe may be made simpler and compact.
However, the inner surface of the stationary guide bush is worn far more rapidly than that of the rotary guide bush and hence, it has been difficult to increase further the depth of cut and the cutting speed when the stationary guide bush is employed.
For solving such problems, a proposal has been made to provide a guide bush wherein wear resistance of an inner surface thereof, in sliding contact with a workpiece, is dramatically enhanced by forming a hard carbon film over the inner surface, enabling an automatic lathe to machine a workpiece with an increased depth of cut and at a higher cutting speed without damaging the workpiece or causing seizure between the guide bush and the workpiece.
The hard carbon film is formed of hydrogenated amorphous carbon having properties closely resembling those of diamond. Therefore, the hydrogenated amorphous carbon is also called diamond like carbon (DLC).
The hard carbon film (DLC film) has high hardness (not lower than Vickers 3000 Hv), excellent wear resistance, a small coefficient of friction (about 1/8 that of a superhard alloy), and excellent corrosion resistance.
For example, a plasma CVD process as described hereinafter is available as a method of forming the hard carbon film over the inner surface of the guide bush.
More specifically, in carrying out the process, a vacuum vessel is evacuated so as to reach a degree of vacuum not higher than 3.times.10.sup.-5 torr (such a pressure as reached initially is referred hereinafter as "an initially reached pressure") a
REFERENCES:
patent: 4746538 (1988-05-01), Mackowski
patent: 5521351 (1996-05-01), Mahoney
patent: 5879763 (1999-03-01), Sugiyama et al.
Koike Ryota
Miya Yukio
Sekine Toshiichi
Sugiyama Osamu
Toida Takashi
Citizen Watch Co. Ltd.
King Roy V.
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