Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2000-01-10
2002-02-19
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069200, C427S580000
Reexamination Certificate
active
06348668
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an improvement in a method and an apparatus for performing surface treatment of a tool by interposing working fluid between an electrode and the tool and by causing discharge to occur to use the energy of the discharge so as to form a hard coating film at the tip of the tool.
BACKGROUND OF THE INVENTION
A general machining operation including a machining operation of a type using a mold has frequently used a very hard material having considerable toughness. In the foregoing case, the lifetime of the tool is excessively shortened, causing productivity to deteriorate. Therefore, if the lifetime of the tool comes to an end, the tip of the tool is again ground and modified by a machine for grinding the tool. Thus, reuse of the tool is permitted. Since the re-grinding operation causes the hardened portion of the surface of the tip to be separated or removed, a re-hardening process must be performed in order to improving the hardness of the tip.
When the process for hardening the surface of the tip of the tool is performed by chemical evaporation or physical evaporation, an excessively great cost is required. What is worse, the foregoing evaporation process must be entrusted to a special contractor. Thus, there arise problems in that a great cost and excessively long time are required to complete the process and that a long delivery times runs.
As a method and an apparatus for performing surface treatment of a tool using a discharge process, a technique disclosed in Japanese Patent Laid-Open No. 7-112329 is known. The surface treatment for a tool, which is the foregoing conventional technique, will now be described.
FIG. 8
is a diagram showing the overall structure of the apparatus for subjecting a tool to surface treatment. Referring to
FIG. 8
, reference numeral
201
represents a tool, such as an end mill or drill, which must be subject to surface treatment. Reference numeral
202
represents a green compact block obtained by molding powder of a material for forming a hard coating film. The material for forming the hard coating film is obtained by sinter-molding a material prepared by mixing powder of Co (cobalt) into W—C (tungsten-carbide). Reference numeral
203
represents a main shaft for moving the tool
201
in the vertical direction (direction Z). Reference numeral
204
represents a working tank in which the green compact block
202
is secured and which is filled with working fluid
205
. Reference numeral
206
represents an electric power source for applying voltage between the tool
201
and the green compact block
202
. Reference numeral
207
represents an interpole detecting unit for detecting bath voltage or short circuit between the tool
201
and the green compact block
202
. Reference numeral
208
represents a control unit for controlling relative movement velocity between the tool
201
and the green compact block
202
in accordance with a result of detection performed by the interpole detecting unit
207
. Reference numeral
209
represents a Z-axis drive unit for moving the main shaft
203
in the direction Z together with the tool
201
by discharge. Reference numeral
210
represents an X-axis drive unit for moving the working tank
204
in the direction X together with the green compact block
202
. Reference numeral
211
represents a Y-axis drive unit for moving the working tank
204
in the direction Y together with the green compact block
202
. Reference numeral
212
represents a rotating unit for rotating the tool
201
.
The operation of the conventional apparatus for performing surface treatment of a tool will now be described. The tool
201
held by the main shaft
203
is rotated by the rotating unit
212
. The X-axis drive unit
210
, the Y-axis drive unit
211
and the Z-axis drive unit
209
relatively move the tool
201
and the green compact block
202
so that an operation for grinding the green compact block
202
is performed. When the tool
201
is the end mill, grinding is performed in the direction of the side surfaces (that is, the directions X and Y). When the tool
201
is the drill, grinding is performed in the direction Z. At this time, voltage for performing a discharging process has been applied to a space between the tool
201
and the green compact block
202
from the electric power source
206
. Therefore, suspension of the contact between the tool
201
and the green compact block
202
owing to proceeding of the grinding work causes discharge to occur at the gap between the two elements. Powder of the hard coating film material (W—C) floats in the gap existing between the tool
201
and the green compact block
202
owing to the operation for grinding the green compact block
202
. Therefore, W—C powder is mixed into the surface of the tip of the tool
201
. Hence it follows that proper control of the feed speed of the tool
201
enables a continuous operation to be performed such that grinding and discharge are repeated. As a result, a uniform hard coating film is formed on the tip of the tool. That is, according to the foregoing disclosure, the method is disclosed with which a discharging process is performed while the block containing the material for the hard coating film is being ground so that the surface treatment of the tool is performed by the discharging process.
The foregoing method has a structure formed by combining the two contrary machining processes which are the grinding process which is performed such that the block including the material for the hard coating film and the tip of the tool are made contact with each other and the discharging process in which the block including the material for the hard coating film and the tip of the tool are free from contact. Therefore, the machining operation cannot stably be performed. Moreover, a uniform hard coating film cannot be formed on the tip of the tool. Moreover, the tip of the tool wears away by friction with the block including the material for the hard coating film during the grinding process and the tip of the tool becomes dull owing to a concentration of discharge during the discharging process. Therefore, a process is required to polish the tip of the tool on which the hard coating film has been formed.
DISCLOSURE OF THE INVENTION
To radically overcome the above-mentioned problems, an object of the present invention is to provide a method and an apparatus for performing surface treatment of a tool which are capable of automatically performing a surface treatment of a tool incorporating a main cutting edge having an arbitrary angle by using a discharging process, stably and quickly obtaining a uniform hard coating film having high hardness and exhibiting excellent adhesiveness with a low cost, automatically modifying electrodes thereof and permitting unmanned operation for a long time.
According to a first aspect of the present invention, there is provided a method of performing surface treatment of a tool, comprising the steps of: securing the first electrode to an indexing unit which indexes the angle of the first electrode; changing the first tool which is connected and secured to the main shaft which is moved vertically to a second tool or a second electrode by an automatic tool changing unit when an operation for modifying the surface of the first electrode is performed; modifying the first electrode into a predetermined shape by a machining operation which is performed by the second tool or by a discharging operation which is performed by the second electrode; changing the second tool or the second electrode connected and secured to the main shaft to the first tool by the automatic tool changing unit; indexing the first electrode to a predetermined angle of rotation by the indexing unit; causing discharge to occur while relatively moving the tip of the first tool along the surface of the first electrode such that the tip is made to be opposite to the surface of the first electrode while a predetermined distance is being maintained; and forming a hard coating film on the tip of the first tool
Goto Akihiro
Moro Toshio
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
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