JP2008105113A - Shrinkage fitting type tool holder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the amount of runout of a tool attached to a shrinkage fitting type holder to 1 μm or less. <P>SOLUTION: When the tool 6 is shrinkage fitted into the shrinkage fitting type tool holder 3, an allowance being difference between the outside diameter of a shank of the tool 6 and the inside diameter of a hole formed in the tool holder 3 to fit the tool 6 into it is set to within a scope of 1-7 μm. If the allowance is within this scope and roundness and cylindricity of the shank, roundness of the hole formed in the tool holder 3, and coaxiality of the shank and the hole, are within a fixed scope, the amount of run-out of the tool 6 during rotation is suppressed to 1 μm or less so that breakage, and shortening of service life of the tool 6 caused by run-out when using the tool 6 having small diameter is thereby prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a tool holder attached to a machine tool such as a machining center, a lathe, a grinding machine, etc., and a shrink-fit type tool that fastens and fixes the tool by utilizing a difference in thermal expansion coefficient between the tool holder and the tool. Regarding the holder.

There is a shrink-fit holder as one of the tool holders used when attaching tools such as end mills to machine tools, and this shrink-fit holder is made of a material having a higher coefficient of thermal expansion than the above-mentioned tools. Drill a tool hole slightly smaller in diameter than the tool in the holder, heat it to several hundred degrees, expand the tool hole, insert the tool, cool it, and reduce the tool hole diameter. The tool is fixed by the tightening force at that time (see, for example, Patent Document 1).
JP 2002-283162 A

  This shrink-fit type holder is a tool holder having another tightening mechanism, for example, a tool holder in which a tool is inserted into a tool hole and the tool is tightened with a nut, or the tool is tightened from around a tool axis by hydraulic pressure. Compared to tool holders, etc., the amount of deflection when the tool is rotated around its axis is small (about 3 to 5 μm), and it is difficult to grip with a conventional shrink-fit holder, the diameter is about 6 mm or less Therefore, it is widely used as an indispensable tool for machining small parts with high accuracy.

  In recent years, machine parts have been further miniaturized, and accordingly, the accuracy required for machining has become more severe, and even a shake amount of about 3 to 5 μm, which has been allowed in the past, has become insufficient.

  This will be explained using a two-blade type end mill as an example. For an end mill with a diameter of 0.5 mm, the cutting conditions recommended by the tool manufacturer are 2 μm for the cutting amount per blade, so 4 μm per rotation of the end mill. For example, when the runout amount is 3 μm, one blade of the end mill cuts the workpiece 4 μm at a time, and the other blade idles without contacting the workpiece. For this reason, there is a problem that an excessive load is applied only to one of the blades, the end mill is broken, and the life is shortened.

  In other words, in order for at least both of the blades to contact the workpiece, the deflection amount must be smaller than the feed amount of the end mill during the half rotation of the end mill. The runout must be at least 2 μm or less, and the runout is preferably 1 μm or less for stable cutting with both blades.

  Until now, even with the above-described shrink-fit holder used for high-precision machining, it is difficult to suppress the deflection of the tool to 1 μm or less, and the part design is limited within the range of machining capability of this tool. There is a problem.

  Then, this invention makes it a subject to suppress the deflection of the tool attached to the shrink-fit type holder to 1 micrometer or less.

  In order to solve the above problems, the present invention uses a tool holder in which a hole having an inner diameter 1 to 7 μm smaller than the outer diameter of the shank of the tool is used, and the tool holder is heated to shrink-fit the tool into the hole. It was decided to fix it.

  According to the present invention, the amount of deflection of the tool fitted in the tool holder can be suppressed to 1 μm or less, and the blade of this tool is in stable contact with the workpiece during processing. It is possible to prevent the tool from being broken and the life of the tool from being reduced.

  The present invention relates to a shrink-fit tool holder comprising a connection portion connected to a machine tool, a manipulator holding portion that engages with a protrusion of the changer when changing a tool, and a tool holding portion that holds a tool. It is possible to employ a configuration in which a tool grip portion in which a hole for fitting a hole is formed is heated, the tool having a tightening allowance of 1 to 7 μm is inserted into the hole, and the tool is fastened and fixed by shrink fitting.

  The tightening margin refers to the difference between the outer diameter of the shank of the tool and the inner diameter of the hole formed in the tool gripping portion when the tool is removed from the tool gripping portion. Indeed, this means that the shank is gripped strongly.

  Since the quantitative relationship between the size of the interference allowance and the amount of runout has not been sufficiently investigated so far, multiple tools and shrink-fit tool holders with different interference allowances are prepared, and this quantitative relationship is detailed. Investigated. As a result, as shown in FIG. 1, it becomes clear for the first time that the amount of deflection tends to increase as the tightening margin increases. Based on this quantitative relationship, the maximum tightening margin 2 is made smaller than about 7 μm (in the figure). It can be concluded that the amount of shake can be suppressed to 1 μm or less, which is the maximum allowed by 1).

  Since this tool is gripped by a strong frictional force between the two caused by tightening of the shrink-fit tool holder, if the tightening force is reduced, the frictional force is insufficient and the tool is in use. Processing is not possible due to slippage between the two. Therefore, a tightening force that does not cause slipping is necessary, and the tightening force can be secured by setting the tightening margin to 1 μm or more.

  From the above, the fastening allowance between the tool and the shrink-fit tool holder into which the tool is fitted needs to be in the range of 1 to 7 μm.

  Usually, in consideration of the tolerance of the outer diameter that occurs during the processing of the shank, it is preferable that the target range of the tightening margin is 4 to 7 μm in actual work.

  In addition, in order to reduce the amount of deflection of the tool fitted in the shrink-fit tool holder, it is also necessary that the roundness and cylindricity of the shank of the tool are high, specifically, roundness The cylindricity is preferably 0.6 μm or less.

  The reason for this limitation is that when the concentricity of the connecting portion and the tool gripping portion is 1 μm or less, the shank of the tool having a different cylindricity is shrink-fitted and the amount of deflection of the tool is measured. This is because it has been experimentally confirmed that the amount of shake varies within the above-mentioned range only when the amount of shake varies depending on the accuracy of the cylindricity and is within the above range.

  In addition, regarding the reason for limiting the roundness of the shank of the tool, in order to suppress the cylindricity to 0.5 μm or less, it is necessary to suppress the roundness to an accuracy of cylindricity or more in manufacturing the tool. Because there is.

  When the runout of the shank of the tool shrink-fitted into the tool holder was measured with a roundness measuring device, the maximum runout when the cylindricity was 0.5 μm, 1.0 μm, and 1.7 μm was 0.7. They were 960 micrometers, 1.496 micrometers, and 2.678 micrometers. Further, when the slew amount was measured at 15 locations for the cylindricity having the smallest maximum shake amount of 0.5 μm, the average was 0.666 μm, and the allowable 1 μm at any measurement point. It was less than the shake amount.

  In order to secure an appropriate tightening margin between the tool holder and the tool shank, the outer diameter of the shank is preferably within a tolerance h4 according to JIS standards.

  If the tolerance is within the range of h4, for example, in a tool having a diameter of 6 mm, the tolerance h4 is in the range of -3 μm to 0 μm. If the lower limit of this tolerance is set to -3 μm, the aim of tightening allowance in actual work When the thickness is set to 4 μm, a minimum tightening allowance of 1 μm can be obtained, and the necessary tightening force can be secured. If the upper limit is set to 0 μm, the allowance can be suppressed to the upper limit of 7 μm in the shrink fitting process. It is because it can do.

  Moreover, it is preferable that the roundness of the inner diameter of the hole formed in the tool gripping portion and the coaxiality of the hole and the shank are both 1 μm or less.

  The reason for this limitation is that if the concentricity is 1 μm, the shank of the tool is an ideal cylinder, and if the hole is a perfect circle, the amount of deflection when the tool is rotated becomes the maximum allowable 1 μm. This is because it is preferable to secure at least this coaxiality so as to fall within the allowable maximum range.

  An embodiment of the present invention will be described with reference to FIG. 2. This shrink-fit tool holder 3 is connected to a connection portion 4 connected to a main shaft of a machine tool and a protrusion of the changer when changing a tool. It comprises a manipulator holding part 5 and a tool gripping part 7 for gripping the tool 6. The tool gripping part 7 is heated, and the tool 6 is inserted into a hole formed in the tool gripping part 7. The part 6 is cooled and the inserted tool 6 is fixed.

  The shank of the tool 6 is provided with a stopper 8, and the insertion is maintained at a predetermined depth by the stopper 8.

  Further, when the cylindricity and roundness of the shank of the tool 6 were measured by a roundness measuring device, they were 0.513 μm and 0.197 μm, respectively, and the roundness of the hole of the tool gripping portion 7 and the connection When the coaxiality between the central axis of the portion 4 and the central axis of the hole was measured, they were 0.398 μm and 0.322 μm, respectively, and both were within the predetermined range described above. Here, the roundness means the maximum value measured at eight different locations of the shank and the hole.

  Further, the tightening allowance between the shank of the tool 6 and the shrink-fit tool holder 3 is 5 μm, and the amount of runout during tool rotation after shrink-fit is measured at 10 locations, and the average is 0.655 μm. Yes, at any measurement point, it was less than the allowable shake amount of 1 μm.

The figure which shows the relationship between the interference | tightening allowance between the tool and shrink-fit type tool holder in this invention, and run-out amount The side view which shows one Example in this invention

Explanation of symbols

3 Shrink-fit tool holder 4 Connection portion 5 Manipulator holding portion 6 Tool 7 Tool gripping portion

Claims (3)

It consists of a connection part (4) connected to the machine tool, a manipulator holding part (5) to be engaged with the protrusion of the changer when changing the tool, and a tool holding part (7) for holding the tool (6). In the shrink-fit tool holder (3),
The tool gripping part (7) in which a hole for fitting the tool (6) is formed is heated, the tool (6) having a tightening margin of 1 to 7 μm is inserted into the hole, and the tool (6) is inserted by shrink fitting. ) Is fastened and fixed.   The shrink-fit tool holder according to claim 1, wherein the roundness and cylindricity of the outer diameter of the shank of the tool are controlled to 0.6 μm or less.   The shrink-fit tool holder according to claim 1 or 2, wherein the coaxiality of the rotating shafts of the connecting part (4) and the tool gripping part (7) is controlled to 1 µm or less.

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