Cutting by use of rotating axially moving tool – Tool or tool with support – Having peripherally spaced cutting edges
Patent
1996-02-02
1997-10-21
Bishop, Steven C.
Cutting by use of rotating axially moving tool
Tool or tool with support
Having peripherally spaced cutting edges
408144, B23B 5102
Patent
active
056789602
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a twist drill, especially for processing metals. Such drills normally have a cylindrical basic component which is divided into a shaft and a cutting section. Several swarf grooves are made in the surface of the cutting section which extend spirally around the central longitudinal axis of the drill or the drill core and end in the o-face which forms the drill tip. Drills for a specified drilling depth that is greater than or equal to three times the drill diameter are referred to as long drills. In other words, the minimum drilling depth in long drills is three times the diameter of the drill.
A problem with long drills is that undesirable torsional vibrations may occur because of the ratio of drill length to drill diameter. A further problem is chip removal with increasing drilling depth. During drilling, the chip which is removed in the effective range of the drill tip or the drill's major cutting edges is rolled in the swarf groove between the face, which is the swarf groove surface, on the one hand, and the interior wall of the bore hole, on the other hand, and is given a roughly spiral form. As the boring process proceeds, this chip or fragments thereof are transported in the swarf groove in the direction of the shaft end of the drill. The chip thereby robs against both the face and the interior wall of the bore hole. This friction decreases the chip removal rate and can finally cause the chips to back up. Other chips being pushed along cause a further increase in the friction forces which in turn causes a substantial increase in the cutting forces and increases heat development. This results in disproportionate wear of the drill's major cutting edges. In the extreme case, a backing up of the chips can cause the drill to break.
Automatic drills are frequently linked to an electronic monitoring system. This type of electronic monitoring system would interpret a disproportionate increase in the cutting forces as an indication of very high drill wear or chipping of the cutting edge and would stop the drill. In fact, however, the drill edge would not show any wear at all. Instead, there would be a backup of chips which could not be relieved by simply switching off the machine. For to eliminate the chip backup, the drilling tool would need to continue to run without feed in order to remove the collected chip material from the bore hole through the swarf groove.
Drilling could then resume normally.
A long drill known from DE-DA-39 27 615 solves the torsional vibration problem by expanding the drill core from the tip to the shaft. However, this impedes chip removal because the depth of the swarf groove decreases with increasing distance from the drill tip. To remedy this, the swarf grooves of the known drill were substantially widened. This is expressed in the ratio of back width or minor flank to groove width which is 0.8-0.9. However, this widened swarf groove can improve chip removal only to a limited extent because the depth of the swarf groove decreases with increasing distance from the drill tip. A round or spiral chip which is formed in the effective range of the major cutting edges of the drill and has a diameter corresponding to the swarf groove depth in the area of the drill tip would, with increasing distance from the drill tip, have increasing difficulty to fit into the swarf chamber bounded by the face and the interior wall of the bore hole. As a result, the chip would increasingly rub against the face and the interior wall of the bore hole and thus cause the chip removal rate to decrease.
Also known in prior art are twist drills the core diameter of which increases towards the shaft while their angle of twist decreases to improve chip removal in the same direction.
Based on the above, it is the object of the invention to make a twist drill in such a way as to avoid the backup of chips and to make it possible to operate the drill at high cutting rates over the entire drilling depth or cutting length without any significant torsional vibrations. To accomplish this, the inv
REFERENCES:
patent: 4744705 (1988-05-01), Imanaga
patent: 5350261 (1994-09-01), Takaya et al.
Just Werner
Muhlfriedel Dieter
Bishop Steven C.
Kennametal Hertel AG
Prizzi John J.
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