JPS58196934A - Precision oscillation cutting method for ceramics - Google Patents

Abstract

PURPOSE:To reduce cutting force in a precision oscillation cutting method for working ceramics by applying ultrasonic oscillation to a tool by applying periodical tool oscillation to a work in such a manner as to cut the work from the inside thereof toward the surface thereof. CONSTITUTION:A cutting speed (v) and an oscillation speed are composed of frequency (f) and unilateral amplitude (a) so that the locus of the movement of the blade edge of a tool 3 shows the waveform A, B, C, D. When a work further makes one revolution to get a depth (t') of cutting, the waveform is A', B', C', D'. In this case, the portion cut by a cutting edge of the tool 3 is an approximate area BB', CC', DD' EE'... indicated by oblique lines. This is not a continuous area, but divided areas to be cut fractionally. At this time, the cutting force works upon the work from the inside thereof toward the surface thereof.

Description

[Detailed Description of the Invention] Regarding ceramics, which is expected to be used as a new industrial material in many industrial fields, there is a need for the development of cutting theory and technology that can be turned freely in the same way as ordinary carbon steel.

The present invention relates to a new precision vibration turning method for ceramics that meets these demands.

The excellent properties of ceramics make them difficult-to-cut materials in cutting processes.

Hard properties mean brittleness, and the increased cutting force brought about by hard mechanical properties makes brittle ceramic workpieces more likely to break or break macroscopically, and microscopically causes microscopic cracks on the workpiece surface. will occur.

When turning ceramics, it is important to use a method that reduces the cutting force even slightly, and a method that reduces the occurrence of microcracks even slightly compared to other methods.

However, as is well known, there is no change in cutting force even when ceramics, which have excellent heat resistance, are cut at high or low temperatures.
Even if the tool shape is changed, it has no effect on ceramics. Also.

Even if the type of cutting fluid is changed, it only has a cooling effect on the cutting tool, and does not have the effect of contributing to the essential cutting mechanism and reducing the cutting force.

Here, assuming that there is no suitable method for reducing the cutting force itself, we will consider a method of increasing the rigidity, that is, the spring constant, of the ceramic workpiece on which this cutting force acts. In other words, we will consider a cutting method that minimizes deflection of ceramic workpieces even when large cutting forces are applied.

Now, let us consider the case where a round bar workpiece 1 is cut at high speed by the cutting tool 2 as shown in FIG. The cutting force waveform in the direction of back force during high-speed cutting is approximated by p;
-s” 7m) C: Horizontal viscous damping coefficient of the workpiece or crop attached to the spindle (kgf-s/n+) k: Horizontal spring constant of the workpiece attached to the lathe spindle (kgf/dragon) P, : Static cutting force component in back force direction ('9f) pt: Dynamic cutting force component in back force direction (kgf) ω: Cutting force variation angle natural frequency (rad/s): Horizontal direction of workpiece Angular natural frequency (rad/s) Here, the solution to the equation of motion in equation (1) becomes t when ω/c〉1.In other words, the time t term disappears, and the spring constant becomes static. It can be seen that the workpiece is displaced by the value X divided by the cutting force Pt.In other words, when cutting at high speed, the workpiece is displaced by the value obtained by dividing the cutting force by the workpiece's original spring constant.Now, it can be expressed as follows. Consider the case where a pulsed cutting force waveform acts on the workpiece.

The equation of motion representing the motion of the workpiece at this time is as shown in equation (2).

2) (tc: vibration of the cutting tool - net cutting time per cycle S T: Vibration period of the cutting tool S) In equation (2), when ω/>1.

becomes. In other words, the value of the workpiece's original spring constant is T/
It can be increased by lc times. What is the value of T/lc in general?
It is almost equal to the value of /4. where V is the cutting speed and PC
=2 n a f (f: frequency of the bite, a: half amplitude of the bite). The value is approximately 3 to 10 in T/lc. Therefore, the apparent spring constant can be increased by the ratio of the action time tc during which the pulse cutting force acts and the vibration period T of the cutting tool.

This effect has already been announced as a vibration cutting effect obtained by vibrating the cutting tool in the cutting direction, that is, in the principal force direction.
It is also being put into practical use. When turning ceramics, the mathematical effect shown by the solution to this equation of motion can be used in engineering, similar to the method of turning ceramics.

On the other hand, the present invention has created a new method for reducing Pl in the molecule of formula (3), that is, the cutting force itself, and further preventing the occurrence of microcracks.

In Fig. 2, when a depth of cut t' is given to the cutting tool 2 and two-dimensional cutting is performed on the workpiece 1 in the direction of the arrow at a cutting speed of 1, the principal force Pc and the back force P act in the direction shown, resulting in a resultant force. P is generated, which is - with respect to the direction of cutting speed V.
It acts in the negative direction of φ. That is, the resultant force of the cutting forces acting on the workpiece acts from the surface of the ceramic workpiece toward the inside of the workpiece, and the resultant force of the cutting forces acting on the cutting tool acts in the direction shown in the figure.

Now, when performing chisel work using a general chisel, it is well known that if the glasses are struck from inside the workpiece toward the surface, the resistance will be smaller and the glasses will break more easily. Taking this phenomenon as a reference, as shown in Figure 3,
It can be seen that the cutting force is reduced by sending the cutting tool 2 in the direction of the cutting speed V shown in the inclined direction.

That is, if the workpiece is repeatedly cut from the inside toward the surface of the workpiece, it is effective, especially when the workpiece is made of a brittle material such as ceramics, and the cutting force is thought to be reduced.

The cutting force P is composed of the principal force Pc and the thrust force P, and its direction has a direction angle of (+φ), which clearly means that the cutting force P acts from the inside of the workpiece toward the surface of the workpiece. Can be done.

Such a cutting method is realized by the cutting method shown in FIGS. 4(a) and 4(b).

That is, hold the cutting tool 3 with the vertical ultrasonic transducer 4 in the direction of the arrow 5.
The workpiece 1 is vibrated in the direction with a frequency f and a single amplitude a, and the workpiece 1 is rotated to give a cutting speed V.

The cutting speed y of the workpiece rotating at a constant speed and the vibration speed at which the direction changes due to the vibration of the cutting tool tip are combined, and the cutting tool tip advances in a zigzag pattern from inside the workpiece to above the workpiece, as shown in Figure 3. You will be able to repeat the cutting motion towards. This cutting tool 2Vc depth of cut (feed) t'' is applied in the direction of arrow 6 to two-dimensionally cut the end face of the pipe-shaped workpiece.

The cutting mechanism at this time will be explained with reference to FIG. The cutting speed V, the vibration speed due to the frequency f and the half amplitude a are synthesized, and the motion trajectory of the cutting tool tip is a waveform ABCD...
shows. The workpiece rotates one more time and the depth of cut (feed) t'
When given, the waveform becomes A/B/C/σ... At this time, the portions to be cut by the cutting edge of the cutting tool have approximate areas BB'Cσ, DD'E, E', etc. shown by diagonal lines. As can be seen from the figure, these areas are not cut into continuous areas as in the conventional case, but are divided into small areas and cut into small increments. That is, it is possible to form a pulsed cutting force waveform in which the cutting force is applied only for a short period of time equal to the vibration period of the cutting tool, and T/l C=2. The cutting force at this time acts from the inside of the workpiece toward the surface of the workpiece, as shown in FIG. This direction varies slightly depending on the vibration state of the cutting tool, but in all cases the direction acts from the inside of the workpiece toward the surface space. And the cutting force is reduced.

One of the characteristics of the cutting method of the present invention is to make this depth of cut (feed) tl extremely small compared to the single amplitude a of the cutting tool.

For example, if a-15 μm, then t'=0.5 to 3 μm is ideal.

In this way, the cutting force P can be reduced, and in addition, regarding the generation of microcracks, the waveform, for example, B'
Its occurrence can be concentrated on the curved part of the workpiece where σ is represented by .

These convex portions are regularly generated by the cutting method of the present invention, and have a surface roughness of approximately 3 to 4 μm.

Therefore, it is necessary to perform a lapping operation or the like to obtain a smooth finished surface.

This lapping process removes the minute protrusions caused by the occurrence of minute cracks, resulting in a smooth finished surface.

In this way, the turning method that is most suitable for performing rough turning on a base material that has the shape and surface roughness necessary for lapping work, which is characterized by machining a small amount of machining allowance and performing precision finishing, is This is achieved by the present invention.

The following conditions are required for the shape of the cutting tool used in carrying out the present invention. In FIG. 5, it is necessary to give the cutting tool clearance angle θ, which is determined from the relationship between the maximum vibration speed of the cutting tool with frequency f and half amplitude a and the cutting speed of the workpiece. That is, it is important to provide a cutting tool relief n angle of θ-tan'-1 to prevent the workpiece surface and the cutting tool relief surface from coming into contact. Here, D is the workpiece diameter and n is the workpiece rotation speed.

Now, assuming the relief angle of the cutting tool to be θ-2o°, f-20kHz
z, a = 15 μm, workpiece diameter D: 40111
When it is set to 1, it becomes 250 Orpm in n. At this time, the cutting speed r becomes 310 m/-. t'=0.5
By making a minute cut (feed) of about 1 μm, for example, a water-soluble cutting oil is supplied to cool the cutting edge while also providing lubrication.

Thus, the cutting speed in the present invention is extremely high. Further, the depth of cut (feed) is minute. Even if the feed amount of the lathe carriage is small, its rotational speed is high, so the feed rate is fast, and uniform feed can be given to the cutting tool without causing stick slip, resulting in a uniform cutting surface. It can be processed into

A specific example of the present invention will be explained with reference to FIG.

The amplitude of the electrophoretic vertical vibrator 4 is expanded by an amplitude expansion horn 7, and a bending vibration system tool 3 that resonates at the natural frequency f of the electrophoretic vertical vibrator 4 is fixed to the tip of the horn with a tightening bolt 8. do. A large number of vibration nodes occur in the bending vibration system cutting tool 3.

By utilizing the positions of two of the vibration nodes, the bending vibration system cutting tool 3 is fixed to the tool rest 11 with the tightening bolt 12 via the tightening fittings 9 and 10 from both sides. On the other hand, a holder 13 is attached to the vibration node position of the horn 7, and the longitudinal vibration system horn is fixed to the tool post.

For example, f = 20kHz, a-1 stabilized in this way
Ultrasonic vibrations of 5 μm can be applied to the cross-cutting blade provided at the tip of the cutting tool 3.

Now, the first important point is the vibration direction of the cutting edge in cylindrical turning as shown in the figure. In determining this vibration direction, the vibration direction of two-dimensional high-speed cutting shown in FIGS. 4 and 5 is the basis. Therefore, in the case of three-dimensional cutting in which the transverse blade cuts in one cylindrical turning process, the angle θ between the vibration direction shown in the direction of arrow 5' and the rotation center axis of the workpiece should be smaller than the front cutting edge angle η. . That is, since the front cutting edge clearance angle does not provide the clearance angle limited in the present invention, it is necessary to provide relief so that the front cutting blade flank does not act on the cutting mechanism of the present invention. The present invention is carried out by making a cut in the direction of arrow 6' while vibrating the transverse blade from the outer periphery toward the inside of the workpiece in the direction of an angle θ smaller than this angle η. When using a diagonal cutting tool and a rounded cutting tool with equal side clearance angle and front clearance angle, the cutting method of the present invention can be carried out smoothly even if the angle θ is any angle other than zero. .

A diamond cutting tool is used to work on ceramics, which have a hardness close to that of diamond. In order to provide a large clearance angle of θ=20°, a negative rake angle of approximately 20° is provided to strengthen the cutting edge strength of the cutting tool. For an alumina oxide workpiece with a diameter of 60 m and a length of 1005 m, the rotation speed is 200 Orpm and the feed rate is 0.4 a/r.
ev, depth of cut 0.5fi, frequency 21.7 kHz
By carrying out the present invention as shown in FIG. 6 using a cutting tool that vibrates ultrasonically with an amplitude of 15 μm and a front cutting edge angle η = 22, a nose angle of 88', and a side edge angle of 70°, a ceramic workpiece can be produced. With a surface roughness of 4 to 6 μm without cutting or damage.

We succeeded in turning with a roundness accuracy of approximately 2 to 3 μm.

In this turning process, face turning or boring is performed as shown in FIGS. 7 and 8. The direction of vibration at this time is given in the direction that makes an angle θ with the feed direction of the cutting tool, and the flank surface of the cutting tool is prevented from contacting the cutting surface.
Implement the invention.

[Brief explanation of drawings]

Figure 1 is a front cross-sectional view modeling the vibration system between the cutting tool and the ceramic workpiece, Figure 2 is an explanatory diagram showing that the direction of the resultant of cutting forces in conventional cutting is directed toward the inside of the ceramic workpiece. FIG. 3 is an explanatory diagram showing that the direction of the resultant force of the cutting force decreases upward from the inside of the ceramic workpiece according to the present invention, and FIG. 4(a). (b) is a monk side view and a top view showing an embodiment of the present invention;
FIG. 5 is an explanatory diagram showing the features of a cutting mechanism according to the present invention, FIG. 6 is a top sectional view of a turning device in a specific example of the present invention, and FIG. 7 is an explanatory diagram of a face turning method according to the present invention. FIG. 8 is an explanatory diagram of the boring method according to the present invention. l...ceramic workpiece, 2,3...hide, 4...
Ultrasonic vibrator, 5.5'...vibration direction, 6.6'...feeding direction. Agent Patent Attorney Yoshi Iinuma Syllable 1 Figure 2 Figure 1 ψ Figure 3 Figure 4] Figure 5,,,□ Figure 6 Figure 7

Claims (1)

[Claims] Relief angle θ=tan-” ”, which is determined by the maximum speed of the cutting tool with frequency f and amplitude a, and the cutting speed depending on the diameter of the workpiece and the rotation speed n of the workpiece, is defined as pi n For two-dimensional cutting, give the same direction to the feed direction, and for three-dimensional cutting, give the same direction to the feed direction and make the required angle θ with the feed direction so that the vibration direction of the tool is directed toward the inside of the workpiece. The cutting tool is vibrated at a high frequency in the ultrasonic range, the cutting speed is set to a high cutting speed so that the flank of the cutting tool does not come into contact with the cutting surface, the feed rate is set to a minimum of amplitude a, and the direction of the pulsed cutting force is directed inside the workpiece. A precision vibration cutting method for ceramics that is characterized by cutting while acting in the same direction.