JPH0375306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a polishing surface plate used for lapping, and in particular to a polishing surface plate suitable for obtaining an extremely smooth finished surface with surface roughness on the order of several tens of angstroms. It is useful, for example, for finishing the gap forming surface of a ferrite magnetic head for video use.

Structure of conventional example and its problems As is well known, lapping processing consists of a surface plate 1 made of soft metal or non-metallic material, as shown in Fig. 9;
Fine abrasive grains 12 are supplied between the surface plate and the surface of the workpiece 8 that is pressed by force F, and the surface plate 1 and the workpiece 8 are moved relative to each other to be covered by the abrasive grains 12. This process removes minute amounts of chips from the surface of the workpiece, resulting in an extremely smooth and highly accurate finished surface.

In recent years, this lapping process has been used to finish the gap surfaces of VTR magnetic heads, which require extremely high processing precision.

The magnetic gap width of the magnetic head for VTR is 0.3μ.
m to 0.5 μm, and the allowable dimensional tolerance is approximately ±0.02 μm (200 Å).

Therefore, in order to stably achieve this dimensional tolerance accuracy, the finished surface roughness of the surface forming the magnetic gap surface must have an accuracy of at least one-tenth of the dimensional tolerance. In other words, in terms of surface roughness, an extremely smooth finished surface is required, with a surface roughness of 0.002 μmRz (20 Å).

In addition, when machining the gap surface, it is required that there is almost no formation of a damaged layer due to the machining.

The reason for this is that the gap of the magnetic head is formed by a non-magnetic thin film, such as glass, interposed between a pair of bonded magnetic materials. That is, the thickness of this nonmagnetic thin film becomes the gap width.

However, when ferrite is used as the magnetic material, the magnetic properties are significantly reduced in the process-affected layer that occurs when machining the gap-forming surface. Therefore, the depth of this process-affected layer is substantially equal to the gap width. This is because it becomes a factor that increases the

According to experiments conducted by the inventor of the present application, the depth of this process-affected layer reaches approximately 0.2 μm in lapping processing using 3.0 μm diamond abrasive grains. This value cannot be ignored considering the magnetic gap width of a video magnetic head, which is 0.3 μm to 0.5 μm.

Conventionally, as a polishing surface plate used for machining the gap surface of a magnetic head for VTR, for example,
Publication No. 59764, Utility Model Publication No. 18694, 1986, Utility Model Application No. 18694, 1987-
There is a type proposed in No. 113496 etc. in which grooves 20 to 23 are formed as shown in Figs. 10 and 11.
It is stated that it is effective in improving polishing efficiency and reducing polishing scratches by discharging polishing debris.

However, according to the experiments of the present inventor, it is impossible to achieve the finished surface accuracy required for the magnetic gap surface of the magnetic head with any polishing surface plate.

Specifically, even if ferrite, which is a magnetic head material, is lapped using diamond abrasive grains with an average grain size of 1 μm, the final surface roughness is only 60.
It was about Å to 100 Å, and it was not possible to stably process the gap surface with sufficient accuracy.

Purpose of the Invention In view of the above-mentioned viewpoints, the present invention aims to provide a polishing surface plate device that is capable of processing extremely smooth surfaces, and is particularly suitable for use in lap processing of ferrite materials used in video magnetic heads. It is useful.

Structure of the Invention The present invention is characterized by forming deep grooves with a large distance between the grooves, shallow grooves with a small distance between the grooves and an inclined wall surface, and slopes of the shallow grooves on the polishing surface of a conventionally flat surface plate. This is an inverted V-shaped mountain formed into a spiral shape. An inverted V-shaped mountain is one that is machined using a tool trajectory that does not form a flat portion at the top of the mountain.

According to the above configuration, the abrasive grains are held at the top of the mountain for a certain period of time in a state where a part of the abrasive grains is buried in the surface plate, and the workpiece is cut little by little. Since the abrasive grains that fall off from the top fall into the shallow grooves adjacent to the peaks, they do not participate in the processing of the workpiece.

That is, in the present invention, on the surface plate for a certain time,
Since the workpiece is processed only by the abrasive grains that are held buried, stable and highly accurate processing can be achieved compared to the conventional method.

In this way, the abrasive grains repeatedly sink into the surface plate and fall off, while the abrasive grains as a whole move along the spiral groove and are removed from the surface plate. In particular, most of the abrasive grains that have fallen into the deep grooves flow along the grooves and are removed from the surface plate.

The cutting ability of abrasive grains decreases as the workpiece is machined, but as time passes, abrasive grains are gradually removed from the surface plate along the grooves. Abrasive grains with reduced cutting ability can be effectively removed from the surface plate.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings.

The structure of an embodiment of the polishing surface plate of the present invention is shown in FIG. Fig. 1a is a plan view of the same embodiment, Fig. 1b is a sectional view taken along line A-O-A ₁ , Fig. 1c is Fig. 1b.
It is an enlarged detailed view of the G part of.

The material of the polishing surface plate 1 is tin, and on the surface of the surface plate,
A deep spiral groove 2 with a large distance between the grooves (in Fig. 1a, the diagonal lines are applied for distinction) and a shallow spiral groove 3 with a small distance between the grooves (in Fig. 1a, a single line) ) and an inverted V-shaped peak 4 are formed spirally around the central axis of the polishing surface plate 1.

As shown in FIG. 3C, the inverted V-shaped peak 4 is formed by the sloped wall surfaces 3a and 3b of the groove 3.

In this example, the specific dimensions of the shallow spiral groove 3 and the inverted V-shaped peak 4 are D=20 μm, W
=W ₁ =100 μm. Further, as shown in the figure, the tops of the peaks 4 are processed to be sharp so that no flat portions occur. Figure 2 shows measurement data of the shape of the top of the mountain.

Moreover, the deep groove 2 is a rectangular groove with a width of 1.5 mm and a depth of 1.0 mm.

First, the method for forming the grooves 2 and 3 will be briefly explained. The detailed processing method will be described later.

First, using a cutting tool whose tip shape is similar to the groove 3 shown in FIG. Then, a deep spiral groove 2 with a large distance between the grooves is further formed on the flat surface where the shallow groove 3 has been formed.

In this way, a surface plate with the shape shown in Figure 1 is obtained, but in actual machining, a large deep spiral groove is formed, taking into account the processing of cutting waste during groove machining and the burrs generated on the cut surface. 2 is machined first, and then a small shallow groove 3 is machined.

Note that, as is clear from this description, the groove 2 is a continuous spiral groove, and the groove 3 is cut by the groove 2.

Next, processing of ferrite chips for a VTR magnetic head using the polishing surface plate of this embodiment will be described in detail.

The magnetic head of a VTR consists of a pair of rectangular parallelepiped ferrite chips, their faces facing each other, and a non-magnetic thin film such as glass with a well-controlled film thickness sandwiched between the two faces to form a so-called gapped bar. Manufactured by cutting to a predetermined width.

In this case, since the above-mentioned joint surface is a gap forming surface, it is required to have an extremely high level of mirror finishing as described above.

Therefore, in order to obtain such a gap forming surface, the following processing was performed using the polishing surface plate of this embodiment.

Note that the gap surface of the ferrite chip has already been pre-processed to a surface roughness of approximately 200 Å prior to the following processing.

FIGS. 3a and 3b are a plan view and a front view, respectively, of a polishing machine using the polishing surface plate of this embodiment.

As shown in the front view of FIG. 3b, the polishing surface plate 1 of this embodiment is mounted on the turntable 6 of the polishing machine 5, with the surface on which grooves 2, 3 and peaks 4 (not shown) are formed facing upward. It is fixed by a set screw 7 toward the direction.

Then, on this surface of the polishing surface plate 1, a disk-shaped polishing jig 9 with a ferrite chip 8 stuck thereon as a workpiece is placed so that the ferrite chip 8 faces the surface plate 1. As a result, ferrite chip 8
is pressed against the surface plate by the polishing jig 9's own weight.

In this state, a certain proportion (in this case
At the same time, the turntable 6 moves the polishing plate 1 in the direction of arrow c.
Rotate in the direction of As the surface plate rotates, the polishing liquid is spread over the entire surface of the surface plate in which the grooves are formed.

As shown in FIG. 3a, the polishing jig 9 is guided on its outer peripheral surface by a stopper 14 having a rotating roller 13 so as to be rotatable in a fixed position. Therefore, when the polishing surface plate 1 rotates in the direction of arrow c, the polishing jig 9 is at the position guided by the stopper 14.
It will rotate in the direction of arrow e.

Between the polishing surface plate 1 and the polishing jig 9 where relative movement has occurred in this manner, a polishing liquid 10 containing abrasive particles is placed between the polishing surface plate 1 and the polishing jig 9.
flows in, and the ferrite chips 8 are processed by the abrasive grains in the polishing liquid 10.

After maintaining this process for 15 minutes, the supply of polishing liquid 10 is stopped, and finishing polishing liquid 1 containing no abrasive grains is removed.
1 at a certain rate (in this example, 10 milliliters/
Processing is continued for an additional 5 minutes while feeding at a rate of 50 minutes.

In addition, during this 5-minute processing, since the polishing liquid 11 containing no abrasive grains is supplied, the number of abrasive grains interposed between the ferrite chips 8 and the surface plate 1 decreases over time. It turns out.

The machining of the gap surface of ferrite chip 8 is completed after a total of 20 minutes of continuous machining, and at the end of the above 15 minutes of machining, the surface accuracy is as high as approximately 40 Å. Obtained. This is the conventional machining accuracy under the same conditions.
It is significantly larger than 60 Å to 100 Å.

After completing the above-mentioned 5 minutes of processing, the roughness of the machined surface of the ferrite chip 8 finally reaches 20 Å to 30 Å, achieving the extremely high surface precision required for the gap surface of the magnetic head. I was able to do that.

Furthermore, there was almost no process-affected layer on the machined surface, and the process was perfect for machining the gap surface of a magnetic head.

In this way, in this example, high machining accuracy,
The reason why good processing quality can be obtained is thought to be as follows.

In this embodiment, an inverted V-shaped peak 4 is formed on the surface of the surface plate, which is processed so as to minimize the formation of a flat portion at the top.

Therefore, in the lapping process using the surface plate of this embodiment, as shown in FIG.
It is believed that these abrasive grains are buried and held and are involved in processing.

Since the abrasive grains that have fallen off from the top of the mountain flow down into the shallow grooves 3, it is considered that almost no fallen abrasive grains are present between the surface plate 1 and the ferrite chips 8 that are the workpiece.

Conversely, it is thought that the abrasive grains in the grooves 2 and 3 reach the top of the peak 4 as the polishing liquid flows, are buried in the peak, and participate in the processing of the ferrite chips 8.

In this manner, in the processing shown in FIG. 3, although individual abrasive grains repeatedly sink into the top of the mountain 4 and fall off, there are Since the ferrite chips 8 are machined using abrasive grains that are always buried and held in the peak portion for a certain period of time, with almost no falling abrasive grains intervening, it is believed that high-precision machining can be stably performed.

On the other hand, in the conventional polishing surface plate shown in FIG. 5, a large number of abrasive grains 12 are embedded in the surface of the surface plate in a flat area that is sufficiently wide compared to the abrasive grain diameter, and these abrasive grains 12 are The grains come into contact with the ferrite chip.

Therefore, when the buried abrasive grains fall off from the surface plate 1, the fallen abrasive grains 12a are attached to the ferrite chips 8 and the surface plate 1.
The abrasive grains are not easily removed from between them, and the contact state between the buried abrasive grains involved in processing and the ferrite chips 8 becomes extremely unstable. Therefore, it seems that sufficient machining accuracy cannot be obtained.

In this embodiment, the two types of grooves 2 and 3 are both formed in a spiral shape. Therefore, the polishing liquid flows from the center of the surface plate toward the outside of the surface plate along this spiral groove.

As processing progresses, the abrasive grains repeatedly sink into and fall off from the surface plate as described above, and move in the direction of being discharged from the surface plate along with the flow of the polishing liquid.

In particular, regarding the abrasive grains that have fallen into deep grooves 2,
Relatively little flow into groove 3, and most of it flows into groove 2.
flows along the surface and is excluded from the surface plate.

That is, in this embodiment, abrasive grains whose sharpness has deteriorated as processing progresses can be effectively discharged out of the surface plate.

In addition, in this example, along with the usage time of the surface plate,
The top of the mountain collapses and a flat area is formed. According to the inventor's experiments, after about 8 hours of use,
A flat area of about 20 μm is formed at the top of the mountain,
The machining accuracy at that time deteriorates to about 60 Å when evaluated after completing the 15 minutes of machining.

There is a high correlation between this deterioration of processing accuracy and the cumulative usage time of the surface plate, so the actual management of the surface plate is based on the cumulative usage time, and when the cumulative usage time reaches 8 hours, The grooves formed on the surface of the surface plate are cut and removed to create a new plane, and new shallow grooves and deep grooves are formed on the plane for use.

In addition, in lapping machining performed with abrasive grains that are free in the polishing liquid, rather than with abrasive grains that are held embedded in the surface plate, in order to obtain the same degree of machining accuracy as that obtained with the surface plate of this embodiment, it is necessary to In the above processing using the surface plate of this example, the abrasive grains are held on the tin surface plate at the top of the mountain and the workpiece is processed, since the processing time is about 8 hours. It is thought that there are.

Next, the processing method of the surface plate of this embodiment, that is, the groove 2,
3. A method for forming the inverted V-shaped peak 4 will be explained.

As mentioned above, the grooves 2 and 3 are actually formed by first forming the deep spiral groove 2 with a large pitch, and then forming the shallow groove 3 with a small pitch. For convenience, the explanation will be made assuming that the processing is performed in the reverse order.

In Fig. 6, 1 is a circular surface plate made of tin, and a shallow groove 3 and a deep groove 2 are formed on the flat surface of the surface plate.
It is intended to form a

For this purpose, this surface plate 1 is attached to a lathe processing machine 15 with a mounting bolt 16, and while rotating it in the direction of arrow C, a cutting tool 17 with a V-shaped tip that gives a predetermined depth of cut B is inserted. Radial direction E of surface plate 1
move it to As a result, a spirally connected shallow groove 3 is formed on the flat surface of the surface plate.

At this time, the locus of movement of the cutting tool is such that there is no flat part at the top of the mountain in the locus of movement of the tool, as shown in Fig. Machining is not performed on the movement trajectory that creates the flat portion 18 at the top of the .

As a result, on the surface of the surface plate, as shown in Figure 6,
A shallow groove 3 and an inverted V-shaped peak 4 with a sharp top
is formed.

The movement trajectory of the tool is shown in Fig. 7a instead of Fig. 7b.
In order to achieve this, the number of rotations of the surface plate 1 and the amount of movement of the tool 17 in the radial direction E per one rotation of the surface plate 1 must be appropriately selected in relation to the depth of cut of the tool 17 and the shape of the tool tip. It's just a matter of time.

After forming shallow grooves on the flat surface over the entire surface as described above, as shown in FIG.
A spiral groove 2 with a larger pitch and deeper depth is machined.

As a result, the surface plate of this embodiment having the shape shown in FIG. 1 can be easily obtained.

We conducted experiments with various dimensions and shapes for the shallow groove 3 and the deep groove 2, but as long as the inverted V-shaped peaks were formed using a tool trajectory that did not create a flat part, good machining was achieved regardless of these dimensions and shapes. It was found that accuracy was obtained.

Effects of the Invention As described above, the present invention is capable of forming shallow grooves with small groove distances and inverted V-shaped peaks on the polishing surface plate under machining conditions such that no flat portion remains on the polishing surface of the polishing surface plate due to lathe machining. Provided spirally around the rotation axis. Similarly, by forming deep grooves with a large distance between the grooves in a spiral shape using lathe processing, it is possible to obtain a polished surface with fewer scratches and damaged layers caused by polishing.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of the polishing surface plate of the present invention, Fig. 2 is a measurement diagram of the shape of a shallow groove formed in the same embodiment, and Fig. 3 is a diagram showing the use of the polishing surface plate of the embodiment. The configuration diagram of the ferrite chip polishing machine shown in Figure 4 is shown in Figure 3.
Fig. 5 is an explanatory diagram of the polishing state in the polishing machine shown in Fig. 5.
Fig. 6 is an explanatory diagram of the method for machining shallow grooves on the surface plate of the embodiment, Fig. 7 is a detailed explanatory diagram of the tool trajectory when machining shallow grooves, and Fig. 8 is a diagram illustrating the deep groove of the embodying surface plate. An explanatory diagram of the groove machining method, Fig. 9 is an explanatory diagram of the lap machining, Fig. 10 is an external view of a conventional polishing surface plate, and Fig. 11 is an explanatory diagram of the groove processing method.
The figure is also an external view of a conventional polishing surface plate. 1... Polishing surface plate, 2, 3... Groove, 3a, 3b...
...Ditch slope, 4...Inverted V-shaped mountain.

Claims (1)

[Claims] 1. On the polishing surface of the surface plate, a deep groove with a large groove distance, a shallow groove with a small groove distance and a sloped wall surface, and an inverted V-shaped mountain formed by the slope of the shallow groove. , a polishing surface plate formed in a spiral shape.