A rotary cutting tool with improved chatter supression performance

Abstract

The present invention proposes a rotary cutting tool (10) comprising a shank portion (11) and a cutting portion (12) extending from the shank portion (11) to a cutting tip (13), the cutting portion (12) having a length of cut, and a plurality of blades (20, 30) separated by flutes (40) extending along the length of cut; wherein each blade of the plurality of blades comprising a rake surface (21, 31), a flank surface (22, 32), and a cutting edge (23, 33) formed at an intersection of the rake surface (21, 31) and flank surface (22, 32), wherein plurality of blades (20, 30) comprises a first type blade (20) having a wavy rake surface (21) with a wave pattern (50).

Description

[0001] A ROTARY CUTTING TOOL WITH IMPROVED CHATTER SUPRESSION PERFORMANCE

[0002] Technical Field of the Invention

[0003] The present invention relates to rotary cutting tool according to the preamble of claim 1.

[0004] Background of the Invention

[0005] Rotary cutting tools, such as end mills, typically have a cylindrical configuration that includes a shank portion and a cutting portion. The cutting portion contains a plurality of helically disposed cutting blades that extend from a first end of the cutting portion adjacent the shank portion, toward the opposite end of the cutting portion. Improving process stability is one of the objects in milling operations. Instability in machining operations cause poor surface finish and quality problems reducing productivity, increasing cost and material waste. The proposed rotary cutting tool can be used in milling operations as a solution to increase stability and improve productivity.

[0006] A prior art publication in the technical field of the invention may be referred to as EP2398615 (Bl), which discloses a rotary cutting tool with a longitudinal axis includes a shank portion, a cutting portion defining a length of cut.

[0007] A prior art publication in the technical field of the invention may be referred to as US9327353 (B2), which discloses a roughing and semi-finishing end mill having serrated and non-serrated cutting teeth.

[0008] Summary of the Invention

[0009] An object of the present invention is to provide a rotary cutting tool increased stability which improves productivity in milling operations.

[0010] The present invention proposes a rotary cutting tool comprising a shank portion and a cutting portion extending from the shank portion to a cutting tip, the cutting portion having a length of cut, and a plurality of blades separated by flutes extending along the length of cut; wherein each blade of the plurality of blades comprising a rake surface, a flank surface, and a cutting edge formed at an intersection of the rake surface and the flank surface, wherein plurality of blades comprises a first type blade having a wavy rake surface provided with a wave pattern having a wave length and an amplitude. Substantial part of the wavy rake surface is provided with a wave pattern. The wave pattern begins at a distance from the cutting tip for at least one of the first type blades. The distance may be different for two first type blades. In another embodiment of the present invention, the wave pattern of the one of the first type blades begins from the cutting tip. Therefore, manufacturing process of the first type blade is made easier. The geometry of the waves can be periodic (e.g. sinusoidal), non-periodic, or a combination of the two. Plurality of blades further comprises at least one second type blade having a smooth rake surface, wherein the second type blade is adjacent to the first type blade. Therefore, the rotary cutting tool provides a robust performance against changes in spindle speed and natural frequencies. Besides, the production cost of the rotary cutting tool is decreased while the performance of axial depth of cut is increased.

[0011] In an embodiment of the present invention, the plurality of blades is in a repetitive arrangement such that the first type blade is alternated with the second type blade and the second type blade is alternated with the first type blade. Therefore, fluctuation range of a pitch angle is increased and thus, chatter frequencies are suppressed effectively.

[0012] In another embodiment of the present invention, the wave pattern is sinusoidal in shape. Therefore, manufacturing the first type blade is made easier.

[0013] In another embodiment of the present invention, the wave length and the amplitude are the same for each first type blade of plurality of first type blades. In another embodiment of the present invention, the wave length and the amplitude of at least one first type blade are different from the wave length and the amplitude of another first type blade of plurality of first type blades. The wave amplitude has a strong effect on cutting dynamics behavior and each wave amplitude is effective at a specific spindle speed range. Having the ability to disrupt the regeneration mechanism, higher values of wave amplitude result in higher stability limits at the conditions where the ratio between natural frequency and spindle speed is low. However, the manufacturing of high wave amplitudes on edges is hindered by dimensional limitations. Therefore, these rotary cutting tools lose their effectiveness at situation where the ratio between natural frequency and spindle speed is very low. As the edge wavelength in the rotary cutting tools increases, the number of delays introduced to the system decreases. Therefore, the effectiveness of crest-cut tools reduces and the stability limit approaches to those of a standard endmill. On the other hand, higher wavelengths provide a wider range of the producible wave amplitudes in manufacturing of these tools. Therefore, the wavelength should be selected as small as possible, so that it enough to manufacture desired wave amplitude.

[0014] Brief description of the figures

[0015] The accompanying drawings are given solely for the purpose of exemplifying the invention whose advantages over prior art were outlined above and will be explained in detail hereinafter:

[0016] Fig. 1 is a perspective view of the rotary cutting tool in the state of the art.

[0017] Fig. 2 is a perspective view of the rotary cutting tool, according to the present invention.

[0018] Fig. 3 is a schematic view of the rotary cutting tool.

[0019] Fig. 4a is a graphic of an unfolded view of variation of angular position of each blade along the axial height of the rotary cutting tool having one first type blade and three second type blades, according to the present invention.

[0020] Fig. 4b is a schematic view of a 3D view of variation of angular position of each blade along the axial height of the rotary cutting tool having one first type blade and three second type blades, according to the present invention.

[0021] Fig. 5a is a graphic of an unfolded view of variation of angular position of each blade along the axial height of the rotary cutting tool having two first type blades and two second type blades, according to the present invention.

[0022] Fig. 5b is a schematic view of a 3D view of variation of angular position of each blade along the axial height of the rotary cutting tool having two first type blades and two second type blades, according to the present invention.

[0023] Fig. 6 is a graphic of changing pitch angle with respect to axial position of the rotary cutting tool having two first type blades and two second type blades, according to the present invention. Fig. 7 is a graphic of changing pitch angle with respect to axial position of the rotary cutting tool having four first type blades, which is in the state of the art.

[0024] Fig. 8 is stability diagrams for the proposed rotary cutting tools and the rotary cutting tools in the state of the art for the milling of AL7075.

[0025] Fig. 9 is stability diagrams for the proposed rotary cutting tools and the rotary cutting tools in the state of the art for the milling of Ti6AL4V.

[0026] Detailed description of the figures

[0027] The present invention proposes a rotary cutting tool (10) comprising a shank portion (11) and a cutting portion (12) extending from the shank portion (11) to a cutting tip (13). The cutting portion (12) has a length of cut, and a plurality of blades (20,30) separated by flutes (40) extending along the length of cut. Each blade of the plurality of blades comprising a rake surface (21,31), a flank surface (22,32), and a cutting edge (23,33) formed at an intersection of the rake surface (21,31) and flank surface (22,32). Plurality of blades (20,30) comprises a first type blade (20) having a wavy rake surface (21). The wavy rake surface (21) is provided with a wave pattern (50). The wave pattern (50) comprises a wave length (A) and an amplitude (A). The blades (20,30) and flutes (40) of the cutting portion (12) extend helically within the cutting portion (12). The overall shape of the cutting portion (12) may be, but is not limited to, a cylindrical shape or a frustoconical shape. Referring to Fig. 2, the rotary cutting tool (10) has a total of four blades (20,30) and flutes (40). However, it will be appreciated that the invention is not limited by the number of blades (20,30) and flutes (40), and that the invention can be practiced with a fewer or a greater number of blades (20,30) and flutes (40). For example, the invention can be practiced with five blades (20,30) and flutes (40), six blades (20,30) and flutes (40), eight blades (20,30) and flutes (40), and the like. Referring to Fig. 3, the rake surface (21,31) of the rotary cutting tool (10) is the chip flowing surface. That means the chips produced due to shearing action during machining flow over the rake surface (21,31) and finally leave the cutting zone. In the Fig. 3, rake angle (60), relief angle (61) and helix angle (62) are shown. Referring to Fig. 2, first type blade (20) has a wavy rake surface (21) which is provided with a wave pattern (50) having a wave length (A) and an amplitude (A). The wave pattern (50) is defined by a series of waves, each wave having a wave length (A) and an amplitude (A). The first type blade (20) comprises wavy rake surface (21), first flank surface (22) and first cutting edge (23). Plurality of blades (20,30) further comprises at least one second type blade (30) having a smooth rake surface (31), wherein the second type blade (30) is adjacent to the first type blade (20). Therefore, pitch angles between consecutive blades (20,30) become variable along the rotary cutting tool (10) axis. The second type blade (30) comprises also second flank surface (32) and second cutting edge (33). Referring to Fig. 2, the smooth rake surface (31) extends helically within the cutting portion (12). Substantial part of the smooth rake surface (31) is not provided with any waveform or any other protrusion or recess. In the preferred embodiment of the present invention, the smooth rake surface (31) is completely smooth and not provided with any waveform or any other protrusion or recess. Referring to Fig. 4a and 4b, the rotary cutting tool (10) comprises one first type blade (20) and three second type blades (30).

[0028] According to preferred embodiment of the present invention, the plurality of blades (20,30) is in a repetitive arrangement such that the first type blade (20) is alternated with the second type blade (30) and the second type blade (30) is alternated with the first type blade (20). As seen in Fig. 2, the rotary cutting tool (10) comprises two first type blades (20) and two second type blades (30). In this embodiment, each first type blade (20) is placed between two second type blades (30) and each second type blade (30) is placed between two first type blades (20). In this embodiment, referring to Fig. 5a and 5b, the pitch angle between consecutive blades (20,30) is varied along the length of cut. In Fig. 5a, A7corresponds to wavelength (A) of the j-th tooth of the respective blade (20,30), 47corresponds to the amplitude (A) of the j-th tooth respective blade (20,30), P,7corresponds to pitch angle of j-th tooth at respective tool height lj corresponds to the distance which wave pattern (50) begins from the cutting tip (13) for at least one of the first type blades (20). Therefore, rotary cutting tool (10) introduces greater fluctuation range for pitch angles. Standard crest-cut tool in the state of the art is demonstrated in Fig. 1. Standard crest-cut tool is a rotary cutting tool having only first type blades. As seen in Fig. 7 standard crest-cut tool has a fluctuation range between 78 and 96 degrees. Referring to Fig. 6, the fluctuation range is between 72 and 107 degrees when two of four blades (20,30) are first type blade (20) and the other ones are second type blades (20). Using this advantage, the number of delays introduced to the system is increased. As a result of this, the proposed rotary cutting tool (10) can suppress chatter frequencies in a much wider range of spindle speeds and natural frequencies of the system. Thus, productivity in these operations is increased significantly by using the proposed rotary cutting tool (10). Stability diagrams for the proposed rotary cutting tools and the rotary cutting tools in the state of the art for the milling of AL7075, are given in Fig. 8. The wave pattern (50) of the first type blade (20) has a wave length (A) of 20 mm and an amplitude of 1.75 mm. The rotary cutting tool (10) having the plurality of blades (20,30) in a repetitive arrangement such that the first type blade (20) is alternated with the second type blade (30) is named as "Second embodiment of the present invention". The rotary cutting tool (10) having one first type blade (20) and three second type blades (30) is named as "First embodiment of the present invention". These rotary cutting tools (10) are compared with the standard cutting tool and standard crest-cut tool. As can be seen in Fig. 8, second embodiment of the present invention has the best performance of milling of AL7075 (aluminum) at most of spindle speed. First embodiment of the present invention has the best performance when the spindle speed is between 2500 and 3000 RPM.

[0029] Similarly, stability diagrams for the proposed rotary cutting tools (10) and the rotary cutting tools in the state of the art for the milling of Ti6AL4V (titanium) are given in Fig. 9. The second embodiment of the present invention is compared with the standard cutting tool and the standard crest-cut tool. As seen in Fig. 9, the second embodiment of the present invention has the best performance at most of spindle speed. As can be deducted from the Fig. 8 and Fig. 9, stability of the rotary cutting tool (10) is increased while the manufacturing cost of the rotary cutting tool (10) is decreased. Moreover, productivity in milling operations is improved in a cost-effective way by using the proposed rotary cutting tools (10).

[0030] In another embodiment of the present invention, the wave length (A) and the amplitude (A) are the same for each first type blade (20) of plurality of first type blades (20).

[0031] In another embodiment of the present invention, the wave length (A) and the amplitude (A) of at least one first type blade (20) are different from the wave length (A) and the amplitude (A) of another first type blade (20) of plurality of first type blades (20). Therefore, fluctuation range may be increased. Reference list

[0032] 10. Rotary cutting tool

[0033] 20. First type blade

[0034] 21. Wavy rake surface 22. First flank surface

[0035] 23. First cutting edge

[0036] 30. Second type blade

[0037] 31. Smooth rake surface

[0038] 32. Second flank surface 33. Second cutting edge

[0039] 40. Flutes

[0040] 50. Wave pattern

[0041] 60. Rake angle

[0042] 61. Relief angle 62. Helix angle

[0043] A. Wave length

[0044] A. Amplitude

Claims

CLAIMS1. A rotary cutting tool (10) comprising a shank portion (11) and a cutting portion (12) extending from the shank portion (11) to a cutting tip (13), the cutting portion (12) having a length of cut, and a plurality of blades (20,30) separated by flutes (40) extending along the length of cut; wherein each blade of the plurality of blades comprising a rake surface (21,31), a flank surface (22,32), and a cutting edge (23,33) formed at an intersection of the rake surface (21,31) and flank surface (22,32), wherein plurality of blades (20,30) comprises a first type blade (20) having a wavy rake surface (21) provided with a wave pattern (50) characterized in that plurality of blades (20,30) further comprises at least one second type blade (30) having a smooth rake surface (31), wherein the second type blade (30) is adjacent to the first type blade (20).

2. The rotary cutting tool (10) according to Claim 1, wherein the plurality of blades (20,30) is in a repetitive arrangement such that the first type blade (20) is alternated with the second type blade (30) and the second type blade (30) is alternated with the first type blade (20).

3. The rotary cutting tool (10) according to Claim 1 or 2, wherein the wave pattern (50) is sinusoidal in shape.

4. The rotary cutting tool (10) according to any of the Claim 1 to 3, wherein the wave length (A) and the amplitude (A) are the same for each first type blade (20) of plurality of first type blades (20).

5. The rotary cutting tool (10) according to any of the Claim 1 to 3, wherein the wave length (A) and the amplitude (A) of at least one first type blade (20) are different from the wave length (A) and the amplitude (A) of another first type blade

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