Claims
[1] A drill comprising: a point formed with cutting edges; one or more spiral flutes; and one or more lands formed between the spiral flutes, respectively, thereby bordering the flutes, wherein a groove with a predetermined depth is formed on the top surface of each of the lands, so that fluid can be supplied to the point of the drill along the groove. [2] The drill as claimed in claim 1, wherein each of the lands has an edge area, which is formed adjacent to a corresponding one of the grooves, the edge area getting in touch with the wall of a hole while the hole is being formed in a workpiece by the drill. [3] The drill as claimed in claim 1 or 2, wherein the lead angle of the flutes is about
40-45°. [4] The drill as claimed in claim 1 or 2, wherein the point angle of the drill is about
136-145°.
[5] The drill as claimed in claim 4, wherein the point angle of the drill is about 138°.
[6] A method of manufacturing a drill comprising steps of: providing a cylindrical rod having flute lines for forming one or more flutes with a lead angle suitable for a desired use of a drill; forming one or more flutes along the flute lines; forming a groove with a predetermined depth on the top surface of each land, one or more lands being produced as the flutes are formed; and performing a thinning operation for reducing the diameter of one end of the cylindrical rod so as to form cutting edges. [7] The method as claimed in claim 6, wherein as the grooves are formed, an edge area of a small area is formed on each of the lands, the edge area getting in touch with the wall of a hole while the hole is being formed in a workpiece by the drill. [8] The method as claimed in claim 6 or 7, wherein the lead angle of the flutes is in the range of about 40°to 45°. [9] The method as claimed in claim 6 or 7, wherein the point angle of the drill formed in the thinning operation is in the range of 136°to 145°. [10] The method as claimed in claim 9, wherein the point angle of the drill is about
138°. |
Description DRILL PROVIDED WITH FLUID GUIDE MEANS
Technical Field
[1] The present invention relates to a drill, and more particularly, to a twist drill for drilling a hole, which includes one or more spiral flutes, and one or more lands formed between the flutes, respectively, thereby bordering the flutes. Background Art
[2] A drill is a tool generally used so as to drill a hole or to cut a groove in a workpiece of metal or wood. At present, twist drills are most frequently used. The twist drills include one or more spiral flutes (grooves for taking out chips), and one or more lands formed between the flutes, respectively, as mentioned above.
[3] During a drilling operation using a drill, frictional heat is generated between cutting edges of a drill and a workpiece. As a result, it is necessary to prevent an area surrounding a hole formed in the workpiece from being overheated by heat generated during the drilling operation. Specifically, if the drill is overheated by being repeatedly used, the performance or property of the drill may be changed or deteriorated. Consequently, it becomes impossible to obtain a desired hole (for example, burrs may occur on the walls or in the vicinity of the drilled hole). In this regard, in order to prevent the cutting edges of the drill from being overheated, cutting oil (or water) is supplied to the point of the drill, which is continuously in contact with the workpiece while a hole is being formed.
[4] However, the above-mentioned method of supplying cutting oil or the like to the point of the drill from the outside has several disadvantages. For example, if it is desired to form a hole in the workpiece by using a drill and the hole has a depth which is four or more times larger than the diameter of the drill, the cutting oil cannot be sufficiently supplied to the point of the drill. Consequently, the point of the drill will be overheated.
[5] In order to solve this problem, oil hole drills have been widely used since the Mid-
1980s, wherein such an oil hole drill is formed with one or more spiral oil holes through the drill body so as to allow cutting oil to be supplied to the point of the drill from the outside. The oil hole extends from the trailing end area to the point of such a drill through the drill body, wherein the trailing end area means a part to be grasped by a holder or a drill chuck of a drilling machine. The cutting oil is supplied from the trailing end area and exits from the point of the drill, thereby preventing the point of drill from being overheated. The cutting oil exiting from the point of the drill is discharged to the outside along the flutes of the drill, thereby enabling chips to be more
smoothly discharged from a hole formed in a workpiece while the hole is being drilled.
[6] Consequently, by forming oil holes through the body of a drill, it is possible to prevent the point of the drill from being overheated, to make chips more smoothly discharged from a workpiece, and to enhance lubrication. However, the drill with such an oil hole has many disadvantages as follows.
[7] Specifically, in order to manufacture such an oil hole drill, a cylindrical steel rod is prepared through sintering, wherein one or more oil holes are formed through the cylindrical steel rod while the cylindrical steel rod is sintered. Herein, each of the oil holes is formed in a spiral shape with a predetermined lead angle corresponding to the twist angle of the drill and extends through the entire length of the cylindrical steel rod. Then, on the outer circumferential surface of the cylindrical steel rod, one or more spiral flutes are formed through grinding, wherein each of the spiral flutes has a predetermined lead angle or flute angle. At this time, because the cylindrical steel rod has already formed with the spiral oil holes extending through the steel rod and having a predetermined lead angle, the oil holes may burst while the flutes are formed unless the spiral flutes are formed with the same lead angle as the spiral oil holes and substantially in parallel to the oil holes. As such, expensive steel rods may be thrown away.
[8] As a result, the lead angle or flute angle of the flutes of the oil hole drill is determined depending on the lead angle of the oil holes, wherein the lead angle of the oil holes is determined when the oil holes are formed through the cylindrical steel rod while sintering the cylindrical steel rod. However, it is technically difficult to form various drills with oil holes having different lead angles by sintering respective cylindrical steel rods for use in fabricating such drills. Accordingly, as compared to a conventional drill free of oil holes, the oil hole drill has a disadvantage in that the lead angle of flutes should be fixed. As a result, existing oil hole drills typically have a fixed flute angle (lead angle) of 28°or 30°.
[9] Furthermore, since the oil holes are formed in a cylindrical rod material used for fabricating such an oil hole drill while sintering the rod material, the rod material used for fabricating such an oil hole drill is considerably expensive as compared to a material used for fabricating a conventional drill free of oil holes four to ten times. In other words, the price of such a drill is considerably increased. In addition, since the oil holes are formed through the drill body, it is difficult to form such oil holes if a drill has a small diameter (for example, D3 or less). Further, even if oil holes are formed, the rigidity of the drill itself is very poor due to the oil holes. As a result, smooth cutting action cannot be achieved and the drill is easy to fracture. Accordingly, a small diameter drill is not formed with oil holes, whereby cutting oil is directly supplied to the point thereof from the outside so as to prevent the drill from being overheated.
However, the above-mentioned problems still occur in such a small diameter drill.
[10] Meanwhile, if a drill is repeatedly used for drilling one or more holes in a workpiece, burrs may be generated on the wall or in the vicinity of a drilled hole in the workpiece. Specifically, when drilling a hole in a workpiece, a drill is subject to high cutting load at the point and lands thereof. If the drill is repeatedly subject to such high cutting load as the drill is continuously used for forming holes in a workpiece, the performance of the drill is deteriorated, and burrs are consequently generated on the wall or in the vicinity of any hole drilled by the drill. It is known that the burrs are generated as the vicinity of a drilled hole is plastically deformed and pushed due to the feeding of the drill, and that the rotating speed, the feed, and the tip angle of the drill affect the generation of burrs. Furthermore, the performance of the drill deteriorated due to the overheating also affects the generation of burrs as described above. Due to the burrs, it is typically performed a separate process, i.e., a finishing process for removing the burrs. In particular, if such an intentional burr removal process is not perfectly performed, a critical defect may occur in the workpiece due to the remaining burrs.
Disclosure of Invention Technical Problem
[11] Accordingly, the present invention has been made to solve the problems occurring in the prior art. An object of the present invention is to provide a drill capable of achieving smooth cooling, chip discharging, and lubrication effects, even if no oil hole is provided.
[12] Another object of the present invention is to provide a drill, which can provide the same effects as an oil hole drill, and the flute angle of which can be variously determined as desired because no oil hole may be provided.
[13] Still another object of the present invention is to provide a drill capable of providing a desired effect even if it has a diameter which is too small for oil holes to be formed through the body of the drill.
[14] Another object of the present invention is to provide a drill, which has a structure allowing fluid such as cutting oil to be stably supplied to the point of the drill.
[15] Another object of the present invention is to provide a drill, which has a simple structure allowing cutting oil to be stably supplied to the point of the drill, thereby decreasing heat to be applied to the point, so that it is possible to prevent the occurrence of burrs on the wall or in the vicinity of a drilled hole of a workpiece, even if no oil hole is provided.
[16] Still yet another object of the present invention is to provide a drill capable of reducing cutting load to be applied to the drill, in particular to the lands of the drill
during a drilling operation, thereby preventing the deterioration of drill performance. Technical Solution
[17] In order to achieve the above objects, there is provided a drill including: a point formed with cutting edges; one or more spiral flutes; and one or more lands formed between the spiral flutes, respectively, thereby bordering the flutes, wherein a groove with a predetermined depth is formed on the top surface of each of the lands, so that fluid can be supplied to the point of the drill along the groove.
[18] According to another aspect of the present invention, there is provided a method of manufacturing a drill including steps of: providing a cylindrical rod having flute lines for forming one or more flutes with a lead angle suitable for a desired use; forming one or more flutes along the flute lines; forming a groove with a predetermined depth on the top surface of each land, one or more lands being produced as the flutes are formed; and performing a thinning operation for reducing the diameter of one end of the cylindrical rod so as to form cutting edges.
[19] The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings.
Advantageous Effects
[20] According to the present invention, an oil groove is formed on each of one or more lands of a drill, so that the cutting oil is smoothly supplied to the point of the drill. Accordingly, even if no oil hole is formed through the drill body through a very complicated and difficult operation such as sintering, the drill can provide the same effects as an oil hole drill. In addition, if no oil hole is formed through the drill body, it is possible to freely design a flute angle suitable for a desired use. As a result, the present invention can be applied regardless of a drill diameter. Brief Description of the Drawings
[21] FIG. 1 is a perspective view schematically showing an entire structure of a drill according to an embodiment of the present invention;
[22] FIG. 2 shows a point of a conventional drill and a point of a drill according to an embodiment of the present invention; and
[23] FIG. 3 is a partially enlarged perspective view showing a detailed structure of an oil groove. Best Mode for Carrying Out the Invention
[24] Figs. 1 to 3 show a drill 100 according to an embodiment of the present invention.
As shown, the drill 100 comprises a point 120, a main body 140, and a mounting part 160.
[25] The point 120 is formed with one or more cutting edges 122. One or more spiral
flutes 142 are formed over the entire main body 140 from the point 120. One or more lands 144 are formed between the flutes 142, respectively, so that the lands 144 border the flutes 140, respectively. The mounting part 160 is formed at the end of the drill 100 opposite to the point, wherein the mounting part 160 has a shank S and a tang T for fitting the drill to a holder (drill chuck) of a drilling machine.
[26] During the drilling operation, if the point 120 of the drill is compressed against a surface of a workpiece and rotated, the workpiece is cut by the cutting edges 122. Chips produced during the cutting are carried out to the outside through the flutes 142. While a hole is being cut by the cutting edges 122, the main body 140, which is continuous to the point 120 and is formed with the lands 144, enters the hole formed thereby. While the main body 140 of the drill enters the hole primarily formed by the cutting edges 122, the lands 144 of the drill auxiliarily cuts the wall of the primarily formed wall which gets in touch with the main body.
[27] As described above concerning the problems of the prior art, high temperature heat is generated between the point of the drill and the surface cut by the cutting edges during the drilling operation. In order to prevent the occurrence of heat, one or more oil holes are formed in a conventional drill, so that the cutting oil is supplied to the point through the oil holes. However, it is very difficult to form such oil holes through a drill body to correspond to the lead angle of the flutes of the drill, thereby increasing the manufacturing costs of such a drill.
[28] In order to solve these problems, the inventor developed a drill provided with a means capable of achieving the same action and effect as the oil holes. As clearly shown in Figs. 1 to 3, each of the lands 144 of the inventive drill 100 has a top surface which is not flat unlike a conventional drill. In other words, each of the lands is formed with an oil groove 146 with a predetermined depth on the top surface thereof, so that the grooves guide fluid such as cutting oil to the point 120 along the main body 140 of the drill 100.
[29] The oil grooves 146 are formed along the outer surfaces of the lands 144, respectively, so that fluid such as cutting oil can be supplied to the point along the oil grooves 146 during the drilling process, thereby lubricating and cooling the drill. In addition, the fluid supplied to the point of the drill is smoothly discharged to the outside along the oil grooves again. In other words, even though no oil hole is formed in the drill through a complicated manufacturing process, the cutting oil is smoothly supplied to the point along the oil grooves formed on the top surface of each land of the drill. As a result, even if a depth of a drilled hole is deepened as the drilling operation is continuously performed, the cutting oil can be stably supplied to the point of the drill along the oil grooves 146.
[30] As can be seen from Fig. 3, as the oil grooves 146 with a predetermined depth are
formed on the lands 144, respectively, stepped portions, i.e., small edge areas e, are formed on the lands. In other words, according to the invention, each of the lands 144 consists of an oil groove 146 and an edge area e, wherein the edge area e gets in touch with the wall of a hole while the hole is being drilled in the workpiece. Specifically, unless an oil groove is formed on each of the lands unlike as the invention, the lands entirely get in touch with the wall of a hole formed through a workpiece. As such, the top surfaces of the lands 146 get in touch with the wall of the hole while the hole is being formed, whereby high cutting load is applied to the lands. As a result, the drill performance is deteriorated as the drill is repeatedly used in drilling. However, according to the present invention, not the entire lands 146 but the edge areas e get in touch with the wall of a hole while the hole is being formed through the workpiece, whereby the contact area can be substantially reduced. As a result, the cutting load applied to the whole drill edges can be lowered, thereby suppressing the deterioration of the drill performance and remarkably increasing the durability of the drill.
[31] Furthermore, according to the present invention, since no oil hole is formed through the drill body, it is possible to freely design a flute angle. In other words, as described above, when one or more oil holes are formed through a cylindrical rod for forming a drill through sintering, the flute angle is determined depending on the oil hole formation angle (a lead angle). However, it is technically very difficult to freely or variously determine lead angles of oil holes which are formed through drill bodies through sintering. According to the present invention, because oil holes may be omitted from the drill, it is possible to freely design a flute angle, i.e., an angle between a tangent line of a flute and a longitudinal axis of the drill to be suitable for a desired use of a drill. For example, it is well-known in the art that the flute angle directly affects on the cutting performance and chip discharge ability of a drill. In other words, if the flute angle increases, the cutting performance of a drill is enhanced while the chip discharge ability is deteriorated. Therefore, if a workpiece is formed from a hard material and thus high cutting performance is required so as to process the workpiece, a drill with a large flute angle is used. However, if a workpiece is formed from a soft material and thus high cutting performance is not required, a drill with a small flute angle is used. Consequently, it is required to store various types of drills, the flute angles of which are different from each other, which means that it is necessary to variously design flute angles of drills, so that the drills can be suitably selected depending on the uses thereof. According to the present invention, since it is not required to form one or more oil holes through a drill body unlike a conventional oil hole drill, it is possible to freely and variously design the flute angle of a drill depending on the use of the drill.
[32] The inventor conducted a test so as to confirm the effect of a flute angle on the
amount of cutting oil supplied to a point of a drill depending on the flute angle of the drill. Through the test, the inventor obtained the following result: if the flute angle is in the range of about 40-45°. a large quantity of cutting oil was supplied to the point of the drill. As a result, the chips generated during the drilling process were very smoothly discharged to the outside along the flutes and burrs were less produced.
[33] Beyond the flute angle, a point angle of a drill also has an influence on the amount of the cutting oil supplied to the point of the drill. The inventor also conducted a test so as to confirm the effect of a point angle of a drill on the amount of cutting oil supplied to the point. Through the test, the inventor found that if the point angle of a drill is in the range of 136°to 145°, preferably about 138°, the amount of cutting oil to the point is increased, thereby prolonging the lifespan of the drill.
[34] In addition, since the oil grooves 146 are formed on the top surfaces of the lands
144 instead of the oil holes, the invention can be applied irrespective of the diameter of a drill. According to the prior art, since oil holes are formed through the drill body, it is difficult to form such oil holes if a drill has a small diameter (for example, D3 or less). Furthermore, if oil holes are formed through such a drill, the rigidity of the drill itself is poor. However, the present invention can be applied to such a small diameter drill since it is not necessary to form oil holes through the drill body.
[35] In other words, it is actually impossible to form oil holes through a drill body having a small diameter such as D3 to D4 or less, as described above. Accordingly, during the drilling process using such a small diameter drill, the cutting oil should be directly supplied to the point of the drill to achieve the cooling and lubrication effects. However, if such a small diameter drill is repeatedly used for drilling, the cutting oil cannot be appropriately supplied to the point as the depth of the drilled hole is deepened. As a result, much heat is generated at the point of the drill and the burrs are generated at the wall of the drilled hole within a short time. The inventor conducted a comparison test using the inventive drills and conventional drills, each of which has a small diameter.
[36] Specifically, drilling was repeatedly performed for a workpiece made of cast iron and a workpiece made of aluminum, using the inventive drills and conventional drills free of oil grooves, wherein the diameter of all the used drills were D4. With the conventional drill, the burrs were generated on the walls or in the vicinity of drilled holes when about 200-300 holes were drilled through the workpiece of cast iron. In the case of the workpiece of aluminum, burrs were generated on the walls or in the vicinity of drilled holes when about 7,000 holes were drilled.
[37] However, with the inventive drill, burrs were generated on the walls or in the vicinity of drilled holes when about 8,000 holes were drilled through the workpiece of cast iron. In the case of the workpiece of aluminum material, burrs were generated on
the walls or in the vicinity of the drilled holes when about 20,000 holes were drilled. In other words, depending on the materials of the workpieces, the lifespan of the inventive drills was increased by about 3 times to 40 times as compared to the conventional drill.
[38] It is estimated that the above results arise from the smooth supply of the cutting oil to the point of a drill and the decrease in the cutting load applied to the drill. In other words, with the inventive drill free of oil hole, cutting oil is smoothly supplied to the point of the drill along oil grooves 146, thereby preventing the whole drill from being overheated. In addition, when drilling is performed, the lands 144 get in touch with the wall of a drilled hole. According to the present invention, the surface area of the lands is minimized due to the oil grooves and only the edge areas e get in touch with the wall of a drilled hole. As a result, the inventive drill is not overloaded in general during drilling, whereby the performance of the drill can be stably maintained for a long time without being deteriorated by overheating or excessive cutting load. Consequently, it is possible to prevent or at least reduce burrs, which are produced on the wall or at the vicinity of a drilled hole due to the deterioration of the drill performance.
[39] In the mean time, the inventive drill is manufactured by a process different from the prior art. Specifically, a conventional oil hole drill is manufactured by a process comprising steps of: preparing a sintered cylindrical rod having oil holes with a predetermined lead angle and flute lines for forming flutes with a flute angle, wherein the oil holes are spirally formed through the rod and the flute lines are formed on the circumferential surface of the rod, the flute angle corresponding to the lead angle; forming flutes along the flute lines; and performing a thinning operation so as to reduce the diameter of the tip end of the rod, thereby forming cutting edges (thinning operation).
[40] However, according to the present invention, it is not necessary to form oil holes.
Therefore, it is not required to perform a sintering process for forming the oil holes through a cylindrical rod. In other words, the inventive drill can be manufactured by a method comprising steps of: forming flute lines with a lead angle on the circumferential surface of a preform (cylindrical rod), the lead angle being determined depending on a desired use; forming flutes with the lead angle along the flute lines; forming oil grooves 146 with a predetermined depth on the top surfaces of lands 144, which are produced as the flutes are formed; and performing a thinning operation. Since it is possible to omit a relatively highly difficult operation for forming oil holes with a predetermined lead angle through a drill body, the inventive drill can be fabricated through a simplified manufacturing process.
[41] While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that
various changes in form and details may be made thereto without departing from the spirit and scope of the invention as defined by the appended claims. For example, the invention is not particularly limited to the drill types. In other words, the invention can be applied to a stepped drill or the like.
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