1. Field of the Invention
The present invention relates to a cutting tool, in particular to a cutting tool mounted for rotary drive with a coolant and lubricant supply.
2. Description of the Related Art
Such cutting tools are known in prior art. For example, DE 10 2010 046 044 A1, which is regarded as most obvious prior art, discloses a reamer as a cutting tool mounted for rotary drive according to the preamble to claim 1. This reamer exhibits an axially centrally running coolant/lubricant supply duct, as well as at least one cutting edge on the periphery. The axially centrally running coolant/lubricant supply duct is sealed with a coolant screw. The coolant screw exhibits two leveled areas on the screw shank, by which the coolant/lubricant can flow toward the face end of the reamer. At least one (radially running) groove, but usually several grooves, leading to the corresponding cutting edges are milled into the reamer at the face of the reamer. The screw head sitting at the face end of the reamer serves as a cover, which together with the groove forms a radially running duct, which diverts the coolant/lubricant out of the axially centrally running coolant/lubricant supply duct. Coolant/lubricant is to be applied to the periphery of the reamer in proximity to the cutting edge(s) by way of the radially running coolant/lubricant duct, thereby cooling and lubricating the cutting edge(s) and work piece.
As was revealed in simulations and tests, however, the problem that arises for a configuration according to this prior art is that the coolant/lubricant is not distributed over the entire periphery uniformly enough. In extreme cases, this might lead to several cutting edges in the cutting tool not being cooled, and others being excessively cooled. This results in an elevated wear on the tools on the one hand, and, in particular during high-precision machining, less of an ability to control the thermal expansion of the tool and work piece on the other, thereby elevating the production tolerances.
Therefore, the object of the invention is to improve prior art with an eye toward achieving a uniform cooling of the work piece.
This object is achieved with cutting tools as described herein.
The invention provides a cutting tool, in particular a reamer, with a distributor screw that exhibits a flow section having a cross section with a lower diameter in the flowing direction of the coolant and/or lubricant in the area between the flight lands and head, which forms an axially extending annular space around the entire flow section with an axial bore in the cutting part of the tool.
The coolant/lubricant flowing in through axial grooves between the flight lands can be distributed In this annular space, and drain away uniformly on all sides of the cutting tool. As a result, even given a smaller passage for coolant/lubricant than in prior art through the axial grooves along the coolant screw, the coolant/lubricant can be sufficiently distributed in the flow section, so that enough coolant/lubricant is available over 360° of the entire periphery. Several axial grooves are optimally formed in the thread between the distributor screw and cutting tool. However, as a result of the improved distribution of the coolant/lubricant in the annular space, the coolant/lubricant can in principle be distributed in all cutting edges homogeneously enough even through a single axial groove or a comparable opening with a low cross sectional area, for example a leveled portion of a male thread of a distributor screw between the axially centrally running coolant/lubricant supply duct and the annular space.
Even though reference is made above to a “distributor screw” and “flight lands”, let it be noted that the connection between the axially central coolant/lubricant supply duct and the screw head and shank of the distributor screw above the thread of the distributor screw which together with the coolant/lubricant supply duct forms the annular space according to the invention can also be established without a screw thread, for example through procedures such as soldering, adhesive bonding or injection. The only critical factor is the ability to guide coolant/lubricant from the coolant/lubricant supply duct by the attachment (the “flight lands”) of the distributor screw and into the annular space, and there divert it in a radial direction along the face of the cutting tool and allow it to exit through a gap between the distributor screw and face of the cutting tool.
Another advantage to the invention apart from that of a uniform coolant/lubricant distribution is that no additional radial grooves have to be milled into the face of the cutting tool. The bottom side of the screw head can also have a conventional flat design, without exhibiting any grooves.
In a preferred embodiment, the annular space is cylindrical. A cylindrical annular space can be easily fabricated by having the distributor screw exhibit a shank that has a lower diameter than the nominal thread diameter of the distributor screw, similarly to an expansion screw, and/or by having the face end of the coolant/lubricant supply duct exhibit a larger diameter than the nominal thread diameter of the distributor screw. Accordingly, in cases where no screw connection is used, the cylindrical annular space can be generated by a bore in the cutting tool, which forms the coolant/lubricant supply duct, and a shank of the distributor screw between the seat of the distributor screw in the coolant/lubricant supply duct and the head of the distributor screw. Simply boring a hole in the cutting tool and turning the shank of the distributor screw only involve very minor requirements from a manufacturing standpoint, and can be done with a high precision at a comparatively low cost.
In another preferred embodiment, the annular space tapers in the flowing direction. As the coolant/lubricant enters into the annular space through the axially running coolant/lubricant supply duct and axial grooves, it is slightly depressurized during entry into an annular space that tapers in the flowing direction, and accelerated again as it continues to move through the annular space, as a result of which it becomes more uniformly distributed in the flow section. At the outlet from the flow section and during diversion through the head of the distributor screw, the provided gap is the smallest, and the flow rate thus the highest. As a result, the coolant/lubricant is optimally convened toward the periphery of the cutting tool, and hence to the cutting edges of the cutting part. For example, the taper can measure 1° to 5°, preferably 3° opposite the axial direction of the cutting part.
The distributor is preferably attached in the coolant/lubricant supply duct in such a way that the distributor head exhibits a predefined distance from the face end of the coolant/lubricant supply duct. This firmly sets the outlet gap for the coolant/lubricant. For example, the distance can be defined by way of a stop that the screwed in distributor screw hits. In principle, such a stop can also be given a variable design, e.g., so that varyingly dense coolants/lubricants can be optimally used; however, a fixed stop is preferred, wherein the thickness of the outlet gap can be adjusted via the length of the distributor screw.
It is especially preferred that the side of the distributor screw remote from the head exhibit an outer cone, which abuts against an inner cone formed in front of the threaded bore in the flowing direction of the coolant/lubricant in order to center and fix the axial position of the distributor screw relative to the cutting part. This inner cone then serves as the stop. The advantage to this embodiment is that two cones (inner and outer cone) achieve a linear or surface contact over the entire periphery, even given existing production tolerances, e.g., differing cone angles. This prevents the screwed in distributor screw from tilting in the cutting part, so that the outlet gap remains the same size throughout. This prevents coolant/lubricant from exiting in unequal amounts in different directions. As a consequence, all cutting edges of the cutting tool are uniformly cooled.
It is further preferred that the flow surface on the back side of the head lie at a defined axial distance to the face of the cutting part. Just as in the most obvious prior art outlined above, the invention does also allow the incorporation of additional grooves either into the bottom side of the screw head or into the face of the cutting part, but this is not necessary if instead a defined distance or outlet gap is present all around between the back side of the screw head and face of the cutting tool. The mentioned outlet gap can be uniformly configured all around, and cover the face of the cutting tool like an umbrella or mushroom. In addition, the outlet gap must not be shaped in such a way that the bottom side of the distributor screw runs parallel to the front surface of the cutting tool, but rather can also bend toward or away from the latter, so that the outlet gap influences the exit of coolant/lubricant toward the cutting edges not just because of the defined axial distance between these surfaces, but also due to the inclination of the surfaces relative to each other. For example, an expansion can lead to an elevated acceleration of the coolant/lubricant, which then is guided similarly to a Laval nozzle (except for the diversion at the distributor head). If the bottom side of the distributor head and front surface of the cutting tool converge, this can have the effect of lengthening the tapering annular space discussed above in terms of flow. The described uniform configuration yields more easily fabricated, smooth surfaces on the distributor screw and on the cutting tool, and a more uniform distribution of coolant/lubricant is also achieved.
However, if a stricter control of the coolant/lubricant flow is to be achieved for specific reasons, it is also possible to provide grooves between the distributor screw and front surface of the cutting part, similarly to known prior art, which can be furnished in the front surface of the cutting part, on the rear side of the distributor head or in both parts. In this case as well, the annular space according to the invention provided “upstream” from the grooves results in a uniform supply of coolant/lubricant to all cutting edges, even given a low number of axial grooves. This effectively avoids the disadvantages to prior art mentioned at the outset.
It is especially preferred that the distributor head encompass a screw drive, for example a hexagon socket or hexagon head. If the distributor head is screwed into the cutting part, as described in the following embodiments, the distributor head must be provided with a screw drive.
The invention will be described below based on embodiments, drawing reference to the attached figures. The figures show:
A coolant screw according to
In comparison to the cutting tool according to
The distributor screw 1 is introduced into the bore 200 of the cutting tool 2 described above, and screwed into the thread section 210. The front outer cone 50 of the distributor screw 1 here hits the inner cone 230 in such a way as to secure the distributor screw in this location it is being screwed in. As a consequence, the outlet gap between the distributor head 40 and the face 2S of the cutting tool 2 remote from the shank portion that forms an end section of the cutting tool is determined by the difference between the length of the distributor screw 1 from the outer cone 50 of the distributor screw 1 to the distributor head 40 and the length between the face 2S and inner cone 230 of the cutting tool. In a preferred embodiment, the dimensions of the gap can range between 0.4 mm and 0.6 mm.
In an assembled state, the shank sections 30A, 30B of the distributor screw 1 and the bore 200 border the annular space, in which the coolant is uniformly distributed. Even though not depicted in the embodiment, the female thread 210 can also extend up to the face 2S; in this case, however, assembly is made somewhat more complicated by the longer screwing processes while inserting the distributor screw 1 into the cutting tool 2. In addition, coolant distribution along the smooth bore walls of the bore 200 can be improved. In particular when using an aerosol as a minimum quantity lubricant during so-called MMS lubrication, a thread longer than required might contribute to an undesired demixing of the coolant/lubricant.
In the assembled state not shown here, the outer cone surface 50 of the distributor screw 1 hits the inner cone surface 230 of the cutting tool 2 according to the embodiment. This ideally yields a surface contact, but at the very least a linear contact between the distributor screw 1 and cutting tool 2 on the cone surfaces. Due to this linear contact, which essentially runs perpendicular to the middle axis of the coolant/lubricant supply duct, the distributor screw 1 rests straightly in the cutting tool 2, while the distributor screw is prevented from tilting. As a result, the outlet gap between the distributor head 40 and face 2S of the cutting tool 2 is uniformly large all around, so that the coolant is distributed radially uniformly in all directions. Alternatively, the coolant can be additionally guided by radial grooves corresponding to the grooves 101 from prior art, which is not shown here. In this case, the outlet gap can be reduced in size by comparison to the previously described embodiment, or the distributor screw can rest flatly on the surface between the grooves.
In principle, it is also possible to provide a flat surface instead of the inner or outer cone. In such a case, however, production tolerances may cause the distributor screw 2 to tilt in the thread 210, as a result of which the outlet gap may not remain uniformly large over its entire periphery. Other shapes are also conceivable for the end of the distributor screw 1 and transition between the bore 200 and coolant/lubricant supply duct; for example, one of the surfaces could be semispherical, paraboloid or hyperboloid. It is only crucial that the distributor screw 1 be prevented from tilting relative to the cutting tool 2 to the greatest extent possible.
As also evident from
In summary, the invention provides the following:
A distributor screw 1 and cutting device 2 are created that form an annular space between a shank 30 of the distributor screw 1 and a bore 220, into which the distributor screw 1 is introduced. Coolant/lubricant supplied from a central coolant/lubricant supply duct via axial grooves 10 is uniformly distributed in the annular space, so as to be radially diverted in all directions at a distributor head 40 of the distributor screw 1, i.e., over 360°, and uniformly discharged in the direction of the cutting blades or surfaces.
Number | Date | Country | Kind |
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10 2012 216 655.6 | Sep 2012 | DE | national |
Number | Date | Country | |
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Parent | PCT/DE2013/000517 | Sep 2013 | US |
Child | 14658680 | US |