Cutting tool for machining plastics

Abstract

A cutting tool (1) for machining plastics comprises a tool shank (2) for arrangement in a tool holder, and a hollow cylinder (3) contiguous to the tool shank (2) and comprising at least one front opening (4) for accommodating a cutting element, and additionally at least one inner coolant outlet (6a) on the hollow cylinder (3).

Description

[0001] Cutting tool for machining plastic

[0002] The invention relates to a cutting tool for machining plastic according to the independent claim.

[0003] The invention lies in the technical field of tools for machining processes, in particular drills for producing holes in plastic, such as carbon fiber reinforced plastic.

[0004] The production of holes in plastic, especially in carbon fiber reinforced plastic, represents an important task in new developments, especially in road or air transport or in mechanical and plant engineering, where resource-saving requirements are placed on design and construction.

[0005] Such drills are already known from US 5 451 128 A and US 4 500 234 A. When drilling large holes in carbon fiber reinforced plastic, particular attention is paid to avoiding delamination and fiber protrusions at the hole exit and to reliably maintain the overall hole tolerances with regard to diameter, shape, and surface.

[0006] This problem is already addressed in European Patent Application No. 21206884.5, which shows a cutting tool for machining plastic, comprising a tool shank for placement in a tool holder, which has a hollow cylinder adjoining the tool shank with cutting elements on the end faces, on which a channel for a coolant is arranged. This design has proven particularly advantageous with regard to delamination during the machining of plastic.

[0007] One problem with machining plastics with such crown-type drills is that severed material residues remain in the hollow cylinder, which must be removed before the drill is repositioned. This usually requires stopping the drill, which is particularly disadvantageous in industrial manufacturing processes.

[0008] The invention has the object of providing a cutting tool which overcomes the disadvantages of the prior art and enables easy removal of material residues generated during drilling, for example when machining plastic.

[0009] The object is achieved by a cutting tool for machining plastic having the features of independent claim 1. Advantageous embodiments form the subject matter of the associated subclaims.

[0010] The invention comprises a cutting tool for machining plastic, comprising a tool shank for arrangement in a tool holder and a hollow cylinder adjoining the tool shank. The hollow cylinder comprises at least one opening arranged on the end face for receiving a cutting element, as well as at least one internal coolant outlet on the hollow cylinder. The internal coolant outlet allows for the flushing out of material residues generated internally during drilling. In this way, an axial force for detaching material residues can be generated on the internal material residue even while the cutting tool is rotating. The escaping coolant advantageously creates an overpressure in the chamber of the core drill.This pressurized cooling medium causes the material plug to be automatically ejected when the last fiber layer is cut through in fiber-reinforced plastics, which would otherwise remain within the hollow cylinder in the tool or even become jammed.

[0011] A particularly advantageous aspect provides that the hollow cylinder comprises at least one external coolant outlet and, alternatively or additionally, at least one front-end coolant outlet. The external coolant outlet enables the cooling medium to be discharged between the outer wall of the hollow cylinder and the component to be machined. This reduces heating and fraying on the component, especially when machining fiber-reinforced plastics. The front-end coolant outlet is advantageously formed on the front edge section of the hollow cylinder. For example, a section of the opening for the cutting element can serve as the front-end coolant outlet.

[0012] A further advantageous aspect provides that the at least one external coolant outlet comprises an opening arranged in the (outer) lateral surface of the hollow cylinder. This allows the coolant to be distributed evenly over the outer surface of the hollow cylinder.

[0013] Particularly preferably, the at least one internal coolant outlet comprises an opening arranged in the bottom surface of the hollow cylinder. From this opening, the coolant can be discharged under pressure toward any remaining material.

[0014] Particularly preferably, the at least one internal coolant outlet, the at least one external coolant outlet, and the at least one front-end coolant outlet are connected via a common supply channel in the tool shank. The coolant is introduced through the shank of the tool. Further branches of the coolant channels are located on the inside of the base body. The balance of the amount of coolant that exits directly at the cutting edges and on the inside of the core drill can be determined by the diameter of the hollow-drilled screws. This balance defines the cooling effect and the ejection force.

[0015] Furthermore, it is preferred if a cutting element with a cutting surface is arranged in the at least one opening arranged on the end face. According to one example, three or more cutting elements are provided.

[0016] Advantageously, the cutting surfaces are arranged at an angle a to the radial connection between a hollow cylinder's central axis and the cutting element's central axis. The cutting edges not only have a positive rake angle, but are also turned inward by the angle a. This results in an overlap of the rake angle (drill) and the radial side rake angle (milling cutter). This combination generates an inward and upward cutting force in the drilling tool, which prevents delamination.

[0017] It is further preferred if the cutting element has a wedge step with a larger rake angle than the cutting surface. The wedge step is part of the cutting edge, but has a second, significantly larger rake angle. It serves to cleanly separate protruding fibers that were not severed during the breakthrough of the cutting edges.

[0018] Particularly preferably, the hollow cylinder includes a guide rail (on the outside). Three or more guide rails are particularly advantageous for guiding the tool through the workpiece.

[0019] In the following, the invention is explained in more detail using an embodiment shown in the drawings.

[0020] They show:

[0021] Fig. 1 is a perspective view of a cutting tool according to the invention for machining plastic, with an enlarged detail of the cutting element; Fig. 2 is a perspective view of the paths of the internal cooling channels;

[0022] Fig. 3 is a front plan view of the illustration in Fig. 2;

[0023] Fig. 4 is a front plan view of the cutting tool of Fig. 1 with a bushing; and

[0024] Fig. 5 perspective view of the socket from Fig. 4.

[0025] Fig. 1 shows a perspective view of an embodiment of a cutting tool 1 for machining plastic according to the invention. The lower section shows an enlarged detail of the attached cutting element 5.

[0026] The cutting tool 1 comprises a tool shank 2 for mounting in a tool holder (drill chuck). A drill bit with a hollow cylinder 3 is connected to the tool shank 2 at the front after a transition section. The section in the shape of the hollow cylinder 3 has three openings 4 on the front end (the side facing away from the tool shank) for receiving the shank of a cutting element 5.

[0027] In this preferred example, three internal coolant outlets 6a are provided on the hollow cylinder 3. The three internal coolant outlets 6a comprise openings located in the bottom surface 31 of the hollow cylinder 3 (only two are visible at this perspective angle).

[0028] The internal coolant outlet 6a allows flushing out of material residues generated inside during drilling by applying an axial force to detach material residues from the coolant while the cutting tool 1 is still rotating.

[0029] In the example shown, the hollow cylinder 3 further comprises three external coolant outlets 6c and three front-side coolant outlets 6b. All three external coolant outlets 6c have an opening arranged along the outer surface of the hollow cylinder 3.

[0030] According to the detailed illustration below, a cutting element 5 with a cutting surface 51 facing forward in the direction of rotation is arranged in the at least one opening 4 arranged on the front side. The cutting element 5 has a wedge step 52 with a larger rake angle than the cutting surface 51. It serves to cleanly separate protruding fibers that were not severed when the cutting tips broke through.

[0031] The design with interchangeable cutting elements 5 results in a chain of manufacturing tolerances. However, during machining, only very low feed rates are sometimes used. To ensure that each cutting element 5 carries a similar load, the manufacturing-related height difference of the cutting inserts can be finely adjusted using an eccentric screw 53.

[0032] In the example shown, the hollow cylinder 3 has six rectangular guide rails 7.

[0033] The guide rails 7 guide the tool within the bore. For this purpose, the guide rail diameter is smaller than or equal to the diameter of the cutting elements 5. The guide rails 7 can then be positioned axially directly behind the outer tip of the cutting elements 5.

[0034] Fig. 2 shows a detailed view of the cooling system with the corresponding channels and branches. The internal coolant outlet 6a allows for the flushing out of material residues generated within the hollow cylinder 3 during drilling. The hollow cylinder 3, shown in transparent form, comprises three external coolant outlets 6c and three front-end coolant outlets 6b.

[0035] The three internal coolant outlets 6a, the three external coolant outlets 6c and the three frontal coolant outlets 6b are connected via a common supply channel 21 in the tool shank 2 shown in transparent form.

[0036] These features are shown again in the plan view shown in Fig. 3. Fig. 4 shows the cutting tool 1 according to the embodiment of Fig. 1 in a plan view from the front, with the hollow cylinder 3 surrounded by a bushing 8. If, for certain reasons, the use of a center drill is not possible (too small a tool diameter, etc.), the tool can also be guided against an outer bushing 8.

[0037] In the example shown with the bushing 8, the guide rails 7 serve to abut and guide the hollow cylinder 3 against the inside of the bushing 8. For this purpose, the guide rail diameter is larger than the diameter of the cutting elements 5. The guide rails 7 must be set back in the axial position relative to the cutting elements 5 so far that the guide rails 7 have no contact with the workpiece when the through hole is created.

[0038] The cutting elements 5 not only have a positive rake angle, but are also turned inward by an angle a (to the radial connection between a hollow cylinder center axis 13 and the cutting element center axis 12). This results in an overlap of the rake angle (drill) and the radial side rake angle (milling cutter). This combination generates an inward and upward cutting force in the drilling tool, which prevents delamination.

[0039] In Fig. 5, the bushing 8 is shown alone, without any tools. The lateral opening 81 serves to supply a fluid or to accommodate a fastener (not shown).

Claims

Claims 1. Cutting tool (1 ) for machining plastic comprising a tool shank (2) for arrangement in a tool holder and a hollow cylinder (3) adjoining the tool shank (2) comprising at least one end-side opening (4) for receiving a cutting element (5) and at least one internal coolant outlet (6a) on the hollow cylinder (3).

2. Cutting tool (1) according to claim 1, wherein the hollow cylinder (3) comprises at least one external coolant outlet (6c) and / or at least one end-face coolant outlet (6b).

3. Cutting tool (1 ) according to one of claims 1 or 2, wherein the at least one external coolant outlet (6c) comprises an opening arranged in the outer surface of the hollow cylinder (3).

4. Cutting tool (1 ) according to one of the preceding claims, wherein the at least one internal coolant outlet (6a) comprises an opening arranged in a bottom surface (31 ) of the hollow cylinder (3).

5. Cutting tool (1 ) according to one of the preceding claims, wherein the at least one inner coolant outlet (6a), the at least one outer coolant outlet (6c) and the at least one end-face coolant outlet (6b) are connected via a common supply channel (21 ) in the tool shank (2).

6. Cutting tool (1 ) according to one of the preceding claims, wherein a cutting element (5) with a cutting surface (51 ) is arranged in the at least one end-face arranged opening (4).

7. Cutting tool (1 ) according to claim 6, wherein the cutting surface (51 ) is arranged at an angle (a) to the radial connection between a hollow cylinder central axis (13) and the cutting element central axis (12). Cutting tool (1) according to claim 6, wherein the cutting element (5) has a wedge step (52) with a rake angle that is larger than that of the cutting surface (51). Cutting tool (1) according to any of the preceding claims, wherein the hollow cylinder (3) comprises a guide rail (7).

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