US20130031945A1

US20130031945A1 - Metalworking machine

Info

Publication number: US20130031945A1
Application number: US13/641,876
Authority: US
Inventors: Tadahiro Ohmi
Original assignee: Tohoku University NUC
Current assignee: Tohoku University NUC
Priority date: 2010-04-20
Filing date: 2011-04-13
Publication date: 2013-02-07
Also published as: JP2011224723A; WO2011132576A1; KR20130069630A

Abstract

A metalworking machine includes a tool for machining a workpiece metal and a cooling liquid supply unit for supplying a cooling liquid to a machining portion between the tool and the workpiece metal. The cooling liquid is formed by applying a degassing treatment that removes dissolved gases from the cooling liquid, and a hydrogenation treatment that adds hydrogen to the cooling liquid.

Description

TECHNICAL FIELD

This invention relates to a metalworking machine and, in particular, relates to a metalworking machine that carries out metalworking with high precision for a short time.

BACKGROUND ART

Conventionally, as a working machine, there is known a lathe comprising a main spindle base having a main spindle, a cutter base having a machining tool, a drive mechanism that drives the cutter base to move the machining tool relative to a workpiece, and a cooling liquid supply means (nozzle) that supplies a cooling liquid to the machining tool and the workpiece (see, e.g., Patent Document 1).

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: JP-A-2007-38323

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

Herein, when using the working machine described in Patent Document 1 to cut a workpiece metal such as an iron alloy or an Al alloy precisely for a short time (i.e. at high speed), it is necessary to carry out high-speed machining by moving the tool at high speed without causing any vibration or micro-vibration.
Then, as the machining speed increases, a machining portion between the tool and the workpiece metal generates more heat and therefore, it is necessary to cool the machining portion by supplying a large amount of cooling water or cooling liquid thereto.
As a consequence, the cooling liquid is supplied to the machining portion at a pressure of about 10 kg/cm²to 30 kg/cm², but there has been a problem that if the large amount of cooling liquid is supplied at such a high pressure, vibration is excited at the machining portion to adversely affect the precision machining.
The present applicant has elucidated the cause of the excitation of vibration at the machining portion due to the supply of the cooling liquid and has obtained the following knowledge.
That is, atmospheric components (dissolved gases) are dissolved in a normal cooling liquid and, when the cooling liquid is transferred under pressure in a liquid supply pipe, a large amount of bubbles are generated.
The generated large amount of bubbles are repeatedly attached to and detached from an inner wall of the liquid supply pipe. When the bubbles are adhered to the inner wall of the liquid supply pipe, the cross-sectional area through which the cooling liquid flows decreases so that the pressure for flowing the cooling liquid increases, while, when the bubbles are released from the inner wall of the liquid supply pipe, the area through which the cooling liquid flows increases so that the pressure for flowing the cooling liquid decreases.
Since the large amount of bubbles repeat attachment to and detachment from the inner wall of the liquid supply pipe in this manner, extremely severe pressure oscillation occurs in the supply system of the cooling liquid.
Then, this oscillation is transmitted to the machining portion so that vibration is excited at the machining portion.
On the other hand, when cutting/grinding an iron alloy or the like, oil is widely used as a cooling liquid in order to prevent oxidation of the workpiece metal.
In this case, there has been a problem that when a large amount of cooling liquid is required for high-speed machining, it is necessary to dispose a large amount of waste oil and there has been a problem that it is necessary to clean a product after the machining, resulting in an increase in workload.
Therefore, this invention is intended to solve the conventional problems, that is, it is an object of this invention to provide a metalworking machine that does not require waste oil disposal or product cleaning operation while preventing oxidation of a workpiece metal and that prevents the occurrence of vibration at a machining portion even when a large amount of cooling liquid is supplied thereto, thereby achieving metalworking with high precision and at high speed.

Means for Solving the Problem

A metalworking machine of the present invention comprises a tool for machining a workpiece metal and a cooling liquid supply means for supplying a cooling liquid to a machining portion between the tool and the workpiece metal, wherein the cooling liquid is formed by applying to water a degassing treatment that removes a dissolved gas and a hydrogenation treatment that adds hydrogen, and thus, resolved the foregoing problems.

Effect of the Invention

According to this invention, since a cooling liquid that is supplied to a machining portion is subjected to a degassing treatment that removes a dissolved gas, it is prevented that bubbles are generated in a liquid supply pipe when the cooling liquid is transferred under pressure in the liquid supply pipe, and therefore, it is possible to avoid the occurrence of pressure oscillation in the supply system of the cooling liquid and thus to prevent this oscillation from being transmitted to a machining portion between a tool and a workpiece metal, thereby achieving metalworking with high precision and at high speed.
Since the dissolved gas is removed by applying the degassing treatment to water, it is possible to easily dissolve hydrogen in the degassed water.
By applying a hydrogenation treatment to the cooling liquid that is supplied to the machining portion, it is possible to lower the oxidation-reduction potential of the cooling liquid and thus to prevent oxidation of the workpiece metal and, when the liquid supply pipe is made of a metal, it is possible to prevent oxidation of the liquid supply pipe.
By applying the degassing treatment to the water to remove the dissolved gas, particularly an oxygen gas, as described above, the cooling liquid can have a reducing property with the addition of only a small amount of hydrogen.
The cooling liquid is mainly composed of at least the water and, therefore, it is possible to avoid the workload for waste oil disposal or product cleaning operation which is required when oil is employed as a cooling liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a metalworking machine according to an embodiment of this invention.

FIG. 2 is a schematic diagram mainly showing a cooling liquid supply means and a cooling water producing means.

FIG. 3 is a graph comparing vibration acceleration levels between pure water and gas-saturated water.

FIG. 4 is a graph showing relationships between the dissolved hydrogen concentration and the oxidation-reduction potential.

FIG. 5A is an explanatory diagram for explaining an oscillation state in a liquid supply pipe in a machine stopped state.

FIG. 5B is an explanatory diagram for explaining an oscillation state in a liquid supply pipe when water added with hydrogen less than a saturated solubility is used.

FIG. 5C is an explanatory diagram for explaining an oscillation state in a liquid supply pipe when water added with hydrogen not less than a saturated solubility is used.

MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, a metalworking machine 100 according to an embodiment of this invention will be described with reference to the drawings.

Embodiment

First, the metalworking machine 100 according to the embodiment of this invention is a lathe and, as shown in FIGS. 1 and 2, comprises a main spindle base 110 rotatably supporting a main spindle 111 that holds a workpiece metal W, a tool base 120 provided movably with respect to the main spindle base 110 and the main spindle 111 and detachably supporting a tool 121, a cooling liquid supply means 130 for supplying a cooling liquid L to a machining portion A between the tool 121 and the workpiece metal W, and a collecting tank 140 for storing the cooling liquid L supplied to the machining portion A.
As shown in FIG. 2, the cooling liquid supply means 130 is connected to a cooling water producing means 150, which produces the cooling liquid L, through a connecting pipe 160.
The metalworking machine 100 is configured to cut the workpiece metal W using the tool 121 by attaching the workpiece metal W to the main spindle 111, attaching the tool 121 to the tool base 120, rotating the main spindle 111, and moving the tool base 120 to feed the tool 121 to the workpiece metal W.
At the time of machining to cut off an unnecessary portion of the workpiece metal W using the tool 121, the machining portion A between the tool 121 and the workpiece metal W generates heat. Accordingly, in order to ensure cooling and cutting machinability of the machining portion A, the cooling liquid supply means 130 supplies the cooling liquid L to the machining portion A between the tool 121 and the workpiece metal W.
As shown in FIG. 1, the cooling liquid supply means 130 comprises a nozzle 131 for ejecting the cooling liquid L to the machining portion A, a liquid tank 132 for storing the cooling liquid L in an airtight state, a strainer (filter) 133 provided in the liquid tank 132, a liquid supply pipe 134 for supplying the cooling liquid L to the nozzle 131 from the strainer 133, and a pump 136 driven by an electric motor 135.
As shown in FIG. 2, the cooling water producing means 150 comprises a pretreater 151 for purifying raw water through a filter or a reverse osmosis membrane, a degassing cylinder 152 for removing dissolved gases in the water purified by the pretreater 151, a moisture generator 153 for generating steam in order to adjust an external environment of the degassing cylinder 152, a gas dissolving cylinder 154 for adding hydrogen to the degassed water degassed by the degassing cylinder 152, a raw water supply pipe 155 connected to the pretreater 151 for supplying the raw water thereto, a pure water supply pipe 156 connected between the pretreater 151 and the degassing cylinder 152 for supplying pure water to the degassing cylinder 152, and a degassed water supply pipe 157 connected between the degassing cylinder 152 and the gas dissolving cylinder 154 for supplying the degassed water to the gas dissolving cylinder 154.
Hereinbelow, a specific method of producing the cooling liquid L will be described.
First, if atmospheric components (dissolved gases) are dissolved in the cooling liquid L (cooling water in this embodiment) up to the saturated solubility, a large amount of bubbles are inevitably generated when the cooling liquid L is transferred under pressure in the liquid supply pipe 134.
Accordingly, first, city water (tap water) as raw water is purified to a certain degree in the pretreater 151 using the filter, the reverse osmosis membrane, or the like.
Then, from the water purified by the pretreater 151, atmospheric components (dissolved gases) are removed in the degassing cylinder 152 using a hollow fiber membrane (not illustrated).
Herein, in the degassing cylinder 152, the external environment of the hollow fiber membrane is reduced to a pressure of 20 to 30 Torr, thereby removing a nitrogen gas (N₂) and an oxygen gas (O₂) from the water purified by the pretreater 151.
Specifically, steam is generated by catalytic reaction using a hydrogen gas (H₂) and an oxygen gas in the moisture generator 153 and then is supplied to the outside of the hollow fiber membrane, thereby causing the above-mentioned 20 to 30 Torr atmosphere to be an H₂O gas atmosphere (steam atmosphere) entirely.
When the pressure is reduced to 20 Torr to 30 Torr, dew condensation does not occur even in a 100% H₂O atmosphere.
When the water is passed through the degassing cylinder 152 in the H₂O gas atmosphere, the N₂and O₂components in the water are reduced to 1 ppb or less, respectively.
In atmospheric equilibrium, a nitrogen gas is 15 ppm and an oxygen gas is 8 ppm.
The contents of the oxygen gas and the nitrogen gas are required to be 1 ppm or less, respectively, and are more preferably 1 ppb or less, respectively.
Herein, a graph of FIG. 3 shows the results of comparing vibration acceleration levels between pure water (X1) in which the dissolved oxygen concentration is suppressed to 1 μg/L or less by applying a degassing treatment thereto, and gas-saturated water (X2) when transferred under pressure in the liquid supply pipe 134.
As is clear from this graph of FIG. 3, it has been found that when the ultrapure water subjected to the degassing treatment is used, the vibration acceleration can be suppressed to 1 Gal or less.
Then, in order to set the oxidation-reduction potential of the degassed water, in which the atmospheric components are degassed, to −0.4V to thereby eliminate oxidizability, the degassed water is introduced into the gas dissolving cylinder 154 where hydrogen is added at 0.6 to 0.8 ppm.
Specifically, hydrogen is supplied at high pressure to a hollow fiber membrane (not illustrated), thereby dissolving the hydrogen into the degassed water flowing outside the hollow fiber membrane.
The saturated solubility of hydrogen at room temperature is 1.5 ppm. Therefore, in the case of the addition of hydrogen at about 0.6 to 0.8 ppm, even if the cooling liquid L is transferred under pressure in the liquid supply pipe 134, no bubbles are generated at all in the liquid supply pipe 134.
Herein, a graph of FIG. 4 shows the relationships between the dissolved hydrogen concentration and the oxidation-reduction potential when hydrogen is dissolved in ultrapure water.
Y1 shows a case where the dissolved oxygen concentration is 0.01 mg/L (0.31×10⁻⁶mol/L), Y2 shows a case where the dissolved oxygen concentration is 3 mg/L (0.09×10⁻³mol/L), Y3 shows a case where the dissolved oxygen concentration is 10 mg/L (0.31×10⁻³mol/L), and Y4 shows a case where the dissolved oxygen concentration is 18 mg/L (0.56×10⁻⁶mol/L).
As is clear from this graph of FIG. 4, it has been found that it is possible to easily produce water having reducibility (having no oxidizability) only by controlling the gas concentration in the ultrapure water.
When the dissolved oxygen content in the water is supersaturated or saturated, the required hydrogen addition amount increases so that there arises a possibility of generation of bubbles due to hydrogen.
By degassing oxygen in the water, the water can have a reducing property with the addition of only a small amount of hydrogen, and therefore, it is possible to prevent both generation of bubbles due to oxygen gas and generation of bubbles due to hydrogen gas.
FIG. 5A is a graph measuring an oscillation state in the liquid supply pipe 134 in a machine stopped state, FIG. 5B is a graph measuring an oscillation state in the liquid supply pipe 134 when degassed water added with hydrogen less than a saturated solubility is used, and FIG. 5C is a graph measuring an oscillation state in the liquid supply pipe 134 when degassed water (hydrogen-supersaturated water) added with hydrogen not less than a saturated solubility is used.
As is clear from the graphs of FIGS. 5A to 5C, it has been found that when the degassed water is added with hydrogen less than the saturated solubility, oscillation hardly occurs in the liquid supply pipe 134.
Since the cooling liquid L is a cooling liquid that is supplied to the ultrahigh-speed machining portion A, it is effective to add degassed mineral oil or degassed oil and fat at several % (5%) to 10% in order to provide a lubricating effect.
In this embodiment thus obtained, since the cooling liquid L that is supplied to the machining portion A is subjected to the degassing treatment that removes the dissolved gases, it is prevented that bubbles are generated in the liquid supply pipe 134 when the cooling liquid L is transferred under pressure in the liquid supply pipe 134, and therefore, it is possible to avoid the occurrence of pressure oscillation in the supply system of the cooling liquid L and thus to prevent this oscillation from being transmitted to the machining portion A between the tool 121 and the workpiece metal W, thereby achieving metalworking with high precision and at high speed.
Since the dissolved gases, particularly the nitrogen gas, are removed by applying the degassing treatment to the water, it is possible to easily dissolve hydrogen in the degassed water thus obtained.
By applying the hydrogenation treatment to the cooling liquid L that is supplied to the machining portion A, it is possible to lower the oxidation-reduction potential of the cooling liquid L and thus to prevent oxidation of the workpiece metal W and, when the liquid supply pipe 134 or the connecting pipe 160 is made of a metal, it is possible to prevent oxidation of the liquid supply pipe 134 or the connecting pipe 160.
By applying the degassing treatment to the water to remove the dissolved gases, particularly the oxygen gas, the cooling liquid L can have a reducing property with the addition of only a small amount of hydrogen.
The cooling liquid L is mainly composed of at least the water and, therefore, it is possible to avoid the workload for waste oil disposal or product cleaning operation which is required when oil is employed as the cooling liquid L.
This invention is not limited to the above-mentioned embodiment and can be changed within a range not departing from the gist of the invention.
For example, in the above-mentioned embodiment, the description has been given assuming that the metalworking machine is the lathe, but this invention may also be applied to a boring machine, a milling machine, a shaping machine, a grinding machine, and so on.

DESCRIPTION OF SYMBOLS

- 100 metalworking machine
- 110 main spindle base
- 111 main spindle
- 120 tool base
- 121 tool
- 130 cooling liquid supply means
- 131 nozzle
- 132 liquid tank
- 133 strainer
- 134 liquid supply pipe
- 135 electric motor
- 136 pump
- 140 collecting tank
- 150 cooling water producing means
- 151 pretreater
- 152 degassing cylinder
- 153 moisture generator
- 154 gas dissolving cylinder
- 155 raw water supply pipe
- 156 pure water supply pipe
- 157 degassed water supply pipe
- 160 connecting pipe
- W workpiece metal
- L cooling liquid
- A machining portion

Claims

1. A metalworking machine comprising:

a tool for machining a workpiece metal;

a supply unit for supplying a cooling liquid to a machining portion between the tool and the workpiece metal; and

a producing unit for producing the cooling liquid by applying a degassing treatment that removes a dissolved gas from the cooling liquid and a hydrogenation treatment that adds hydrogen to the cooling liquid.

2. The metalworking machine according to claim 1, wherein

the dissolved gas comprises a nitrogen gas and an oxygen gas, and

concentrations of the nitrogen gas and the oxygen gas dissolved in degassed water after the degassing treatment are 1 ppm or less, respectively.

3. The metalworking machine according to claim 2, wherein the concentrations of the nitrogen gas and the oxygen gas after the degassing treatment are 1 ppb or less, respectively.

4. The metalworking machine according to claim 1, wherein the hydrogenation treatment is a treatment that adds the hydrogen in an amount which is less than a saturated solubility of the hydrogen and which reduces an oxidation-reduction potential of the cooling liquid to a numerical value having no oxidizability.

5. The metalworking machine according to claim 4, wherein the hydrogenation treatment is a treatment that adds the hydrogen at 0.6 to 0.8 ppm.

6. The metalworking machine according to claim 1, wherein the cooling liquid is formed by being further subjected to an oil addition treatment that adds degassed mineral oil or degassed oil and fat.

7. The metalworking machine according to claim 6, wherein the oil addition treatment is a treatment that adds the degassed mineral oil or the degassed oil and fat at 5 to 10%.