Spiral end mill and method of manufacturing the same

Abstract: A spiral end mill which can approximate the shape of a corner of a work surface to that of a sharp corner and attain stable working accuracy for a long time and a method of manufacturing the same are provided. A negative relief face (6) is provided with a circular land (3b) having a width (H) which is different from the width (h) of a circular land (3a) provided along the outer periphery of an insert portion, to be continuous with the circular land (3a).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a spiral end mill and a method of manufacturing the same, and more specifically, it relates to a spiral end mill comprising a hard sintered compact which is arranged on its insert portion and a negative relief face having a chamfer for reducing the angle of an axial rake which is provided on the forward end of the insert portion, and a method of manufacturing the same. Description of the Background Art A spiral end mill made of cemented carbide or high-speed steel, which may be coated with a ceramic material on its surface, is employed in general. However, such a material is so insufficient in wear resistance that it is difficult to maintain stable working accuracy over a long time. Particularly in case of stage working for working bottom and side surfaces at the same time, a tool corner portion is extremely worn in the conventional tool material to consequently reduce the tool life when the radius (R) of the corner portion is defined to be not more than 0.2 mm, for example. Therefore, employment of a spiral end mill having an insert portion made of a hard sintered compact which is excellent in wear resistance is proposed. In case of the spiral end mill, its sharpness is improved as the helix angle is increased, while the wedge angle of a front edge is disadvantageously reduced and sharpened. In this specification of the present application, the term "wedge angle" is defined as follows. "Wedge Angle" = 90° - ("Helix Angle" + "Relief Angle") When a spiral end mill having an insert portion made of a hard sintered compact which is less tougher than with the conventional material is set at a high helix angle of 15 to 45°, for example, the front edge is easily chipped. In order to prevent the front edge from chipping in this case, there is proposed provision of a negative relief face having a chamfer of at least 0.1 mm in width, for example, for reducing the helix angle by approximating an axial rake to 0°, for example. The width and angle of the negative relief face are set in response to the cutting conditions etc. When such a negative relief face is provided, however, the tool diameter is reduced in a portion subjected to front return if no circular land is formed on the peripheral cutting edge. When stage working is performed, therefore, the shape of the cutting edge is transferred to the work surface to damage the shape of a corner portion of the work surface, leading to inconvenience in such application that a shape which is close to that of a sharp corner (a shape having a sharp angle shown in Fig. 9) is required to the corner portion. When a peripheral flank of an end mill is worked, this peripheral flank is not driven into a cutting edge but a cylindrical ground surface is left between the cutting edge and the peripheral flank. The term "circular land" indicates this cylindrical ground surface. In order to prevent the aforementioned inconvenience, a circular land 3 may be provided to cover a negative relief face 6, as shown in Fig. 11. A hard sintered compact 1 forming an insert portion is bonded to a surface of a tool body 2. Fig. 11 is a schematic diagram as viewed from the side of a peripheral flank 4. In such a structure, however, the circular land 3 must have a width h of at least Wtanδ mm, assuming that W represents the width of the negative relief face 6 and δ represents the helix angle. When the width h of the circular land 3 is increased in order to cover the negative relief face 6, friction between the circular land 3 and a working surface is so increased that slanting degree or the like is caused on a side surface of a work surface, leading to such new inconvenience that excellent cutting performance cannot be attained. When a circular land 3 having a width h which is smaller than the width Wtanδ of the negative relief face 6 is provided in an ordinary method as shown in Fig. 12 considering that the cutting resistance is reduced as the width h of the circular land 3 provided on the peripheral cutting edge portion is reduced, on the other hand, the circular land 3 is disadvantageously broken by a width T on the front return part 6. If no circular land 3 is formed on the negative relief face 6, the tool diameter is reduced in this negative relief face 6 as hereinabove described. Consequently, it is difficult to approximate the shape of the corner of the work surface to that of a sharp corner. When no negative relief face is provided for approximating the shape of the corner of the work surface to that of a sharp corner, however, the front edge may be chipped as hereinabove described. When stage working is performed by a spiral end mill having an insert portion made of a hard sintered compact which is excellent in wear resistance with a high helix angle, it is difficult to approximate the shape of the corner of the work surface to that of a sharp corner while attaining excellent cutting performance, as hereinabove described. SUMMARY OF THE INVENTION An object of the present invention is to provide a spiral end mill which can approximate the shape of a corner of a work surface to that of a sharp corner while attaining excellent cutting performance. Another object of the present invention is to provide a method of manufacturing a spiral end mill which can readily form a spiral end mill capable of approximating the shape of a corner of a work surface to that of a sharp corner. The present invention notes the following point: With increase in difficulty in cutting of workpieces and sophistication of application, a spiral end mill which is made of a hard material mainly composed of diamond or CBN is strongly required. Particularly with sophistication of application, tool accuracy allowing no small steps shown in Figs. 7 and 8 is required in recent years. In particular, it has recently been proved that even an extremely small step exerts a remarkable influence on the performance of the product in a mold or a fluid carrier to which accuracy is required. Thus, the present invention has been proposed in order to solve the problems. According to a first aspect of the present invention, a spiral end mill comprises a hard sintered compact which is arranged on its insert portion and a negative relief face having a chamfer for reducing the angle of an axial rake being provided on the forward end of said insert portion, said spiral end mill comprising: a first circular land portion being provided along an outer peripheral portion of said insert portion excluding said negative relief face to have a substantially constant first width ; and a second round portion , having a substantially constant second width , being provided on an outer peripheral portion of said negative relief face of said insert portion to be continuous with said first circular land portion, a helix angle of a line being defined by said second round portion and a peripheral flank being smaller than that of said first circular land portion. Preferably, the width (W) of the negative relief face may be set in the range of at least 0.05 mm and not more than 0.5 mm. In this spiral end mill according to the first aspect of the present invention, the second circular land portion defining a line having a helix angle which is smaller than that of the first circular land portion with the peripheral flank is formed on the outer peripheral portion of the negative relief face of the insert portion to be continuous with the first round portion which is provided along the outer peripheral portion of the insert portion excluding the negative relief face, whereby the negative relief face is prevented from reduction of the tool diameter. Thus, a corner of a work surface is finished in a shape which is close to that of a sharp corner. When the width (W) of the negative relief face is set in the range of at least 0.05 mm and not more than 0.5 mm, initial chipping in cutting is prevented and no cutting noise is increased. According to a second aspect of the present invention, a method of manufacturing a spiral end mill comprises the step of changing the widths of circular lands which are formed on an outer peripheral portion of an insert portion excluding a negative relief face and that of the negative relief face at the time of working a relief angle on the outer periphery of the insert portion by changing helix angles between the outer peripheral portion of the insert portion excluding the negative relief face and that of the negative relief face. Preferably, the width (W) of the negative relief face may be set in the range of at least 0.05 mm and not more than 0.5 mm. In this method of manufacturing a spiral end mill according to the second aspect of the present invention, the widths of the circular lands which are formed on the outer peripheral portion of the insert portion excluding the negative relief face and that of the negative relief face are changed at the time of working a relief angle on the outer periphery of the insert portion by changing the helix angles between the outer peripheral portion of the insert portion excluding the negative relief face and that of the negative relief face, whereby the circular land portions of the outer peripheral portion excluding the negative relief face and that of the negative relief face are readily formed with different widths. Further, the work surface can be more excellently finished when the width (W) of the negative relief face is set in the range of at least 0.05 mm and not more than 0.5 mm. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side elevational view showing a basic shape of a spiral end mill having an insert portion made of a hard sintered compact; Fig. 2 is a front elevational view of the spiral end mill shown in Fig. 1; Fig. 3 is a schematic diagram showing a tool profile model according to comparative example provided with no negative relief face, having a peripheral cutting edge portion formed in a sharp corner; Fig. 4 is a schematic diagram showing a tool profile model according to comparative example provided with a negative relief face but with no circular land; Figs. 5A and 5B are schematic diagrams showing tool profile models according to embodiments of the present invention having negative relief faces and circular lands provided on the outer peripheries of insert portions and the negative relief faces; Fig. 6 is a perspective view for illustrating a cutting step of a spiral end mill having an insert portion made of a hard sintered compact; Fig. 7 is a sectional view showing the shape of a work surface cut by the tool profile model according to comparative example shown in Fig. 4 or 12; Fig. 8 is a partially enlarged view of a corner portion 100 of the work surface shown in Fig. 7; Fig. 9 is a sectional view showing the shape of a work surface cut by the inventive tool profile model shown in Fig. 5A or 5B; Fig. 10 is a partially enlarged view of a corner portion 200 of the work surface shown in Fig. 9; Fig. 11 is a schematic diagram showing a tool profile model according to comparative example provided with a negative relief face while leaving a circular land with a large width for covering the negative relief face; Fig. 12 is a schematic diagram showing a tool profile model according to comparative example provided with a negative relief face while leaving a circular land, which is broken on the negative relief face due to its constant width; Fig. 13 illustrates the cutting performance of spiral end mills obtained in Example 3 with widths H and W shown on the axes of ordinates and abscissas respectively; and Figs. 14A and 14B are schematic diagrams showing tool profile models according to other embodiments of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 1 and 2, a hard sintered compact 1 is bonded to an insert portion of a tool body 2. When a spiral end mill having such an insert portion of the hard sintered compact 1 is set at a high helix angle δ (see Fig. 11) of 15 to 45°, for example, the forefront wedge angle  is reduced and the edge angle is sharpened, as shown in Fig. 3. When the insert portion is made of the hard sintered compact 1, therefore, a negative relief face 6 which is chamfered for setting or approximating an axial rake at or to 0°, for example, is generally provided on the forefront portion as shown in Fig. 4, in order to prevent the forefront edge from chipping. When such a negative relief face 6 is provided, however, the tool diameter is disadvantageously reduced on this negative relief face 6 and hence the shape of a corner of a work surface cannot be approximated to that of a sharp corner as described above. In order to eliminate this inconvenience, a circular land 3b having a width H which is larger than a width h of a circular land 3a provided on an outer peripheral portion of an insert portion consisting of a hard sintered compact 1 is provided on a negative relief face 6 to be continuous with the circular land 3a according to the present invention, as shown in each of Figs. 5A and 5B. Due to such provision of the circular land 3b which is obtained by changing the width h of the circular land 3a provided on the outer peripheral portion to the width H on the negative relief face 6, the circular lands 3a and 3b remain on the overall region of the insert portion. It is possible to provide the circular lands 3a and 3b according to the present invention shown in each of Figs. 5A and 5B by changing a helix angle from the negative relief face 6 (part A) toward the peripheral cutting edge portion (part B) in each of Figs. 5A and 5B when a radial relief β (see Fig. 2) generally having an angle of 5 to 30° is subjected to lead working. Namely, the part A is lead-worked at a helix angle which is identical to or close to a front return axial rake angle, while the part B is lead-worked at a helix angle along the cutting edge, similarly to an ordinary spiral end mill. The width h of the circular land 3a is preferably not more than 0.15 mm and at least 0.01 mm. If the width h exceeds 0.15 mm, the cutting resistance is increased and the cutting face is waved to cause extreme difficulty in manufacturing of the tool. More preferably, the width h of the circular land 3a is not more than 0.1 mm, in order to reduce the cutting resistance. The circular lands 3a and 3b according to the present invention may be shaped as shown in Figs. 14A and 14B, in place of the shapes shown in Figs. 5A and 5B. Description is now made on results of a test for actual cutting shown in Fig. 6 with tools shown in Figs. 3, 4, 5A, 5B, 11 and 12. The shapes of the tools shown in Figs. 3 to 5B, 11 and 12 are first described. In the tool according to comparative example shown in Fig. 3, the peripheral cutting edge was formed in a sharp corner, with no provision of a negative relief face on the forward end. The term "sharp corner" indicates a cutting edge which is formed by driving a flank into the cutting edge and rounding up the same while leaving no negative relief face in working. In the tool according to comparative example shown in Fig. 4, the peripheral cutting edge was formed in a sharp corner, while providing the negative relief face 6 on the forward end by a width W of 0.2 mm. In the tool according to the embodiment of the present invention shown in Fig. 5A, the negative relief face 6 was provided on the forward end by a width W of 0.2 mm, while the circular lands 3a and 3b having widths h and H of 0.02 mm and 0.1 mm were provided on the peripheral cutting edge portion and the outer periphery of the negative relief face 6 respectively. In the tool according to another embodiment of the present invention shown in Fig. 5B, the negative relief face 6 was provided on the forward end by a width W of 0.2 mm, while the circular lands 3a and 3b having widths h and H of 0.02 mm were provided on the peripheral cutting edge portion and the outer periphery of the negative relief face 6 respectively. In the tool according to comparative example shown in Fig. 11, a negative relief face 6 was provided on a forward end by a width W of 0.2 mm, and a circular land 3 having a width h of 0.3 mm was provided on a peripheral cutting edge portion. Namely, the width h of the circular land 3 was increased for covering the negative relief face 6 with the circular land 3, thereby suppressing reduction of the tool diameter. In the tool according to comparative example shown in Fig. 12, a negative relief face 6 was provided on a forward end by a width W of 0.2 mm, and a circular land 3 having a width h of 0.3 mm was provided on a peripheral cutting edge portion. The circular land 3 was broken on the negative relief face 6 due to the conventional working method. Samples of the aforementioned tools according to the present invention and four comparative examples were prepared and thereafter subjected to cutting shown in Fig. 6 under the following conditions: (Example 1) In relation to each sample, a four-flute end mill, provided with an insert portion consisting of sintered diamond, having a tool diameter of 8 mm and an insert portion helix angle of 30° was employed for cutting a workpiece of an aluminum alloy containing 10 percent by weight of Si under the following conditions: Speed of Rotation: N = 20000 rpm Feed: F = 1000 mm/min. Radial Depth of Cut: Rd = 0.05 mm Axial Depth of Cut: Ad = 0.05 mm Wall Height: 15 mm Type: wet cutting with water-miscible cutting liquid The results of cutting under the aforementioned conditions are now described. In the comparative tool shown in Fig. 3, the forward end of the insert was chipped with a cutting distance of 1 to 2 m. The comparative tool shown in Fig. 11 became unusable in an initial stage due to large side slanting degree and slanting degree. In each of the comparative tools shown in Figs. 4 and 12 and the inventive tools shown in Figs. 5A and 5B, the cutting edge was not chipped and excellent results were attained as to side slanting degree and slanting degree after working over a cutting distance of 1000 m. As shown in Figs. 7 and 8, however, a step w shown in Fig. 8 was formed in a corner portion of the aluminum alloy workpiece 5 by the front return width W in the comparative tool shown in Fig. 4. Also in the comparative tool shown in Fig. 12, the circular land 3 was broken by front return and the step w shown in Fig. 8 was formed by the width T due to reduction of the tool diameter. In the inventive tools shown in Figs. 5A and 5B, on the other hand, it was possible to obtain right-angle shapes, i.e., shapes close to those of sharp corners, in corner portions as shown in Figs. 9 and 10 respectively. The radius (R) of the corner portions remained substantially unchanged also after working over 1000 m. (Example 2) Results of evaluation of cuttability in relation to circular land widths h are now described. Samples of the inventive tool shown in each of Fig. 5A and 5B were prepared with four types of circular lands 3a having widths h of (1) 0.05 mm, (2) 0.1 mm, (3) 0.15 mm and (4) 0.2 mm, and subjected to evaluation of cutting states and side working accuracy. Workpieces were prepared from an aluminum alloy containing 5 percent by weight of Si, and cut under conditions similar to those of Example 1. Table 1 shows the results of the evaluation. Referring to Table 1, it is understood possible to attain stable cutting when the width h of the circular land 3a is not more than 0.1 mm. If side working accuracy is not much required, however, cutting is also possible with the width h of 0.15 mm at the maximum. (Example 3) Samples of the tool shown in Fig. 5A were prepared to study the widths H and W of the circular land 3b and the negative relief face 6. The samples of the tool shown in Fig. 5A were employed to work workpieces of an aluminum alloy containing 20 percent by weight of Si, and subjected to evaluation of cutting states and states of finished surfaces under conditions similar to those of Example 1, except that the widths H of the circular lands 3b were (1) 0.02 mm, (2) 0.1 mm, (3) 0.3 mm and (4) 0.5 mm while the widths W of the negative relief faces 6 were (1) 0.03 mm, (2) 0.05 mm, (3) 0.1 mm, (4) 0.2 mm, (5) 0.4 mm and (6) 0.5 mm. Fig. 13 shows the results of the cutting test with the aforementioned parameters. Referring to Fig. 13, it is understood that the tool is capable of cutting when the width H of the circular land 3b is not more than 0. 3 mm, and cutting resistance is reduced as the width H is reduced. Considering this point, it can be said that the width H of the circular land 3b is preferably set in the range of at least 0.01 mm and not more than 0.3 mm. If the width H exceeds 0.3 mm, a chatter is caused and the cutting noise is increased, while the circular land 3b is deposited to deteriorate the state of the work surface. If the width H is less than 0.01 mm, on the other hand, control is unpractically made difficult on the technique of manufacturing the tool. Therefore, the width H of the circular land 3b is preferably at least 0.01 mm and not more than 0.3 mm. As to the width W of the negative relief face 6, the tool is capable of cutting when the width W is at least 0.05 mm and not more than 0.5 mm, and this width W is preferably not more than 0.4 mm, as shown in Fig. 13. Further, the width W is preferably increased in consideration of the cutting edge strength if stable cutting is attained, and preferably at least 0.1 mm in general. In consideration of the aforementioned points, the width W of the negative relief face 6 is preferably set in the range of at least 0.05 mm and not more than 0.5 mm. Initial chipping is easily caused in cutting if the width W is less than 0.05 mm, while the cutting noise is disadvantageously increased if the width W exceeds 0.5 mm. In the spiral end mill according to the present invention, the width W is more preferably set in the range of at least 0.1 mm and not more than 0.4 mm. In the spiral end mill according to the first aspect of the present invention, the corner of the work surface can be finished in a shape which is close to that of a sharp corner by providing the first and second circular lands on the overall region of the insert portion from the outer periphery to the negative relief face, even if the negative relief face is provided on the forward end of the insert portion. Further, the hard sintered compact which is excellent in wear resistance is employed as the insert portion, whereby shape accuracy of the corner portion can be stably ensured over a long time as compared with the conventional end mill consisting of cemented carbide or high-speed steel. When the inventive spiral end mill is applied to a production line, therefore, the number of tool exchange times can be reduced and hence the production efficiency can be improved. In the method of manufacturing a spiral end mill according to the second aspect of the present invention, the circular lands can be provided on the outer peripheral portion of the insert portion excluding the negative relief face and that of the negative relief face at the time of working a relief angle in the outer periphery of the insert portion by changing the helix angles between the outer peripheral portion excluding the negative relief face and that of the negative relief face. Consequently, it is possible to readily form a spiral end mill which can approximate the shape of a corner of a work surface to that of a sharp corner. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims: A spiral end mill having a hard sintered compact being arranged on its insert portion and a negative relief face (6) having a chamfer for reducing the angle of an axial rake being provided on the forward end of said insert portion, said spiral end mill comprising: a first circular land portion (3a) being provided along an outer peripheral portion of said insert portion excluding said negative relief face to have a substantially constant first width (h); and a second round portion (3b), having a substantially constant second width (H), being provided on an outer peripheral portion of said negative relief face of said insert portion to be continuous with said first circular land portion, a helix angle of a line being defined by said second round portion and a peripheral flank being smaller than that of said first circular land portion. The spiral end mill in accordance with claim 1, wherein the width (W) of said negative relief face is set in the range of at least 0.05 mm and not more than 0.5 mm. The spiral end mill in accordance with claim 1, wherein said first width of said first circular land portion is at least 0.01 mm and not more than 0.15 mm, and said second width of said second circular land portion is at least 0.01 mm and not more than 0.30 mm. A method of manufacturing a spiral end mill according to one of the preceding claims having a hard sintered compact being arranged on its insert portion and a negative relief face (6) having a chamfer for reducing the angle of an axial rake being provided on the forward end of said insert portion, said method comprising the step of: changing the widths of circular lands being formed on an outer peripheral portion (B) of said insert portion excluding said negative relief face and an outer peripheral (A) of said negative relief face at the time of working a relief angle on the outer periphery of said insert portion by changing helix angles between said outer peripheral portion excluding said negative relief face and that of said negative relief face. The method of manufacturing a spiral end mill in accordance with claim 4, wherein the width (W) of said negative relief face is set in the range of at least 0.05 mm and not more than 0.5 mm.

Inventors: ABE MAKOTO, ABURAYA KIYOJI, KAWANISHI MAKOTO, KOHNO YUICHIRO, NAKATANI SEIJI, UEDA SHUJI, YASUHIRA NOBUO, ABE, MAKOTO, ABURAYA, KIYOJI, KAWANISHI, MAKOTO, KOHNO, YUICHIRO, NAKATANI, SEIJI, UEDA, SHUJI, YASUHIRA, NOBUO, ABE, MAKOTO, C/O ITAMI WORKS OF SUMITOMO, Kawanishi, Makoto, c/o Osaka Diamond Ind. Co., Ltd, Kohno, Yuichiro, c/o Itami Works of Sumitomo, Nakatani, Seiji, c/o Osaka Diamond Ind. Co., Ltd.
Applicants: MATSUSHITA ELECTRIC IND CO LTD, SUMITOMO ELECTRIC INDUSTRIES, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD., SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1996
Main classification: B23C5
IPC codes: B23C5