JPS6242728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, hard sintered bodies made by sintering diamond or high-pressure phase boron nitride have been developed and are being put into practical use. Normally, these hard sintered bodies have a structure in which a hard sintered body layer 1 is bonded to a support member 2 made of cemented carbide or the like as shown in Fig. 1, and this composite structure sintered body forms the tool body. It is used by being fixed by brazing.

These composite hard sintered bodies are used not only in brazing bits and throw-away tip types, but also in rotary cutting tools such as end mills and jig boring bits.

Now, electrical circuits such as home appliances such as televisions and electric measuring instruments are generally printed wiring, but holes for wiring in the wiring board are made using a small diameter drill made of cemented carbide.

Printed wiring boards are made of a laminated board made of resin such as epoxy and a thin layer of copper, and drilling the holes not only requires dimensional accuracy, but also the burrs at the entrance and exit of the hole, which can damage the inner surface of the hole and cause burn-in. It is required that there be no such thing.

On the other hand, as mentioned earlier, composite hard sintered bodies have recently become widely used, and diamond sintered tools in particular are often used for cutting non-ferrous alloys such as copper and aluminum, as well as plastics. The tool life is several tens to hundreds of times longer than that of conventional carbide tools. Therefore, it can be said that a diamond sintered tool is a highly desirable material for drilling holes in a printed circuit board made of a laminated material of resin and copper.

The present application was obtained as a result of various studies in order to apply a diamond sintered body as shown in FIG. 1, which has been found to be desirable as described above, to a composite minute diameter drill.

That is, the diamond sintered body is made in an ultra-high pressure container, the thickness of the diamond layer is usually 2 mm or less, and the support member underneath is usually made of cemented carbide and has a thickness of about 2 to 3 mm. When using this as a tool, it is joined to the tool body using silver solder or the like. Furthermore, since the main stress during cutting is designed to be applied almost perpendicularly to the joint surface, and the joint area is designed to be much larger than the area of the part that is actually cut, silver solder etc. Sufficient bonding strength can be obtained by bonding.

Furthermore, various drills using diamond sintered bodies were known before the present application, but the diameter of most of such drills is 10 mm or more. In the diamond sintered body, various measures have been taken to apply cutting stress perpendicularly to the bonding surface between the diamond sintered body layer and the supporting member.
A structure as shown in the figure is known.

However, it is extremely difficult to provide such a structure in a compound micro-diameter drill having a diameter of 3 mm or less, and it is difficult to apply such a method to a compound micro-diameter drill.

In order to solve such problems, the first part of the present application
The structure shown in the figure was achieved. In a compound micro-diameter drill like the one of the present invention, since cutting is performed over the entire outer circumference, the shear applied to the joint becomes very large. In order to solve this problem, it became necessary to increase the strength of the joint to more than twice the strength of the conventional joint between the diamond sintered body and the tool body. Conventional diamond sintered bodies do not have such problems at all.

The main problem is that, as mentioned above, the bonding strength of the conventional method is insufficient. To solve this problem, it is necessary to use a brazing filler metal with a high melting point, but if this is heated using the method used for ordinary cutting tools, the temperature of the diamond sintered body will exceed 700℃, making it difficult to cut the diamond. It metamorphoses into graphite, which is completely useless as a tool. This is the second problem.

Just as diamond sintered tools are generally used, this drill for drilling holes in printed circuit boards is also used as a second tool.
As shown in the figure, it is sufficient to braze and secure a diamond sintered blank to the drill cutting edge, but the problem is that the diameter of this drill is usually 3 mm or less, and most often around 1 mm, so the brazing area is very small. It is. In other words, silver solder with a melting point of about 650 to 700°C is normally used for brazing diamond sintered blanks, but the brazing strength is 20 kg/1 in terms of shear strength.
It is about ^mm2 . At this level of strength, there is a very high possibility that the diamond sintered blank will be separated from the joint due to the cutting torque during drilling. The inventors actually created a drill as shown in Figure 2 and conducted a test for drilling holes in printed circuit boards, but the blank came off after the first hole.

Now, there are various types of brazing materials, and there is also brazing material that has even higher brazing strength than silver brazing. However, brazing materials with high strength generally have a high melting point, which poses a problem. In other words, diamond is a thermodynamically unstable substance under normal pressure, and if the temperature is raised under normal pressure, diamond will transform into graphite. Particularly in diamond sintered bodies, this graphitization begins to occur when the temperature exceeds 700°C due to reaction with the bonding metal used in the sintered bodies. Therefore, the brazing material used must be
It must have a melting point of 700℃ or less.

The present invention improves such conventional methods and provides a long-life and stable composite micro-diameter drill.

That is, the present invention is a composite micro-diameter drill in which a diamond sintered body containing 70% by volume or more of diamond is fixed to the cutting edge, in which the diamond sintered blank at the cutting edge and the drill body are joined by electron beam welding. This is a composite micro-diameter drill characterized by the following.

As is well known, electron beam welding is a process in which an electron beam is emitted in a vacuum, the beam is irradiated onto the welding part, and the welding part is heated and melted by the energy of the electron beam.

Since the diameter of the irradiation beam at this time can be narrowed down to 0.5 mm or less, almost only the welded part can be heated spot-wise. Moreover, since the energy density of the electron beam is extremely high, welding can be performed in a very short time. Furthermore, in electron beam welding, the parts to be welded are welded together directly or by inserting a filler such as a Ni thin plate between the parts, but in any case, the parts to be welded are melted and joined together, so the joint strength is almost the same as that of the welded parts. You can get the strength of it. In other words, if electron beam welding is used, high-strength joining can be achieved without substantially increasing the temperature of the hard sintered body.

This will be explained below using examples.

FIG. 3 shows an embodiment based on the present invention.

A diamond sintered blank (1+2) was bonded to the tip of a drill body 3 made of cemented carbide at a bonding surface 11 using an electron beam. After this, it was ground into the shape of a φ1 mm drill, and then a printed circuit board drilling test was performed.

Drill rotation speed is 60,000 rpm, feed is 0.05mm/rev
When drilling holes in three stacked printed circuit boards under the following conditions, a drill made of carbide K10 equivalent alloy of the same shape began to produce considerable burrs after 3000 hits, whereas the diamond sintered blank of the present invention After 100,000 hits, the composite micro-diameter drill with the material fixed to the cutting edge was able to drill holes almost the same as a carbide drill.

In other words, the composite micro-diameter drill obtained in the present application has a lifespan approximately 30 times longer than that of conventional drills made of cemented carbide, and its effects are extremely significant.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of a diamond sintered blank that serves as a cutting edge in the present invention, and FIG. 2 is a front view of a composite micro drill showing an embodiment of the present invention.
FIG. 3 is a front view of a conventional drill, and FIG. 4 is a drawing seen from the cutting edge side. 1: hard sintered compact layer, 2: support member, 3: drill body, 11: joint surface.

Claims (1)

[Scope of Claims] 1. In a composite micro-diameter drill with a diameter of 3 mm or less in which a diamond sintered body containing 70% by volume or more of diamond is fixed to the cutting edge, the diamond sintered blank at the cutting edge and the drill body are bonded together by electron beam welding. A composite minute diameter drill characterized by being joined via a filler almost perpendicular to the axis of the drill body. 2 The drill diameter of the composite minute diameter drill is 1 mm in diameter.
Claim 1 characterized in that:
Composite minute diameter drill as described in section. 3. In a composite micro-diameter drill with a diameter of 3 mm or less in which a diamond sintered body containing 70% by volume or more of diamond is fixed to the cutting edge, the diamond sintered blank at the cutting edge and the drill body are attached almost to the axis of the drill body by electron beam welding. A method for manufacturing a composite minute diameter drill, which is characterized by being vertically joined via a filler and then processed into a drill shape.