JP2010162677A5 - - Google Patents

Description

In recent years, miniaturization of home appliances and machine products has been remarkable, and electronic parts and semiconductor-related parts have become more precise and complicated. For example, in the connector-related mold and has become necessary to cut with a cutting end mill of HRC60 to the processing of ultra-El high hardness steel (e.g. JIS SKD11 heat-treated). In recent years, for example, the thickness of mobile phones has been decreasing year by year, and the structure of the ribs has been changed in order to give the frame strength even if it is thin. In other words, a mold material that is harder than before has been required for press processing of fine ribs, and a small-diameter end mill with a blade diameter of 3 mm or less is particularly required for cutting because of the need for fine processing. Yes. However, the above-described machining of a hard steel material with a cutting tool has a problem with tool wear, and it is difficult to perform high-efficiency and high-precision machining for a long time. For this reason, electrical discharge machining with extremely low machining efficiency is still often employed.

That is, the present invention is a small-diameter CBN ball end mill having a blade diameter of 3 mm or less and an arcuate radius Rmm forming a blade portion and an outer peripheral blade made of CBN, the rake face of the ball blade and the outer peripheral blade The outer peripheral edge rake face of R / 5 or more in length is formed in the same plane, the outer peripheral edge is formed by right-handed left-handed twist, and the axial rake of the ball blade is in the range of −25 ° to −5 °. Therefore, the small-diameter CBN ball end mill is characterized in that the ridgeline of the ball blade is formed in an inverted S shape when viewed from the tip direction of the blade edge . Here, R means the radius of the ball blade.

In particular, the present invention realizes a long neck small-diameter CBN ball end mill due to the above-mentioned feature of the tool shape. That is, another invention of the present invention is a small-diameter CBN characterized in that the blade diameter D is 3 mm or less and the ratio L / D of the neck length L to the blade diameter D is 5 or more. It is a ball end mill.

Further, the present invention is characterized in that the axial rake of the ball blade is set in the range of −25 ° to −5 ° . This improves the chipping resistance against the resistance applied in the axial direction, and the tool which is the biggest problem of the conventional small-diameter CBN ball end mill even in the case of non-uniform machining in the previous process of the finishing process. This has the effect of preventing the drop of CBN particles, chipping and chipping, and instability of cutting caused by vibration and insufficient strength.

In the small-diameter CBN ball end mill of the present invention, the outer peripheral blade is formed by a right blade left-handed twist. Due to this effect, the end mill is applied with a force in the direction of being pulled toward the main spindle side of the machine tool, so that the holding rigidity of the cutting tool is increased and the vibration toward the workpiece side can be reduced. In addition, the rigidity of the cutting edge increases, and there is an effect of suppressing chipping. In particular, in the case of a long neck where L / D is 5 or more and vibration is likely to occur, the blade part is often hit by the workpiece, but the axial rake of the ball blade is -25 ° or more and -5 ° or less. By making it into this range , since the rigidity of the blade part itself can be increased, damage such as chipping and chipping can be made difficult to occur.

When a steel material is cut using a CBN sintered body, a mist-like coolant is often used for cooling the cutting edge. The reason why the coolant is used in the form of mist is that CBN tends to drop off and wear easily when it is rapidly cooled. Since the mist-like coolant is sprayed in the atmosphere in the form of a mist, the coolant also flows along the air flow. Especially in the small-diameter CBN tool that is used by increasing the number of revolutions during cutting, the right-handed right-handed shape of the right blade as well as the mist-like coolant flows to the shank side together with the air around the blade edge. Difficult to spread on the cutting edge. As in the present invention, by setting the axial rake of the ball blade in the range of −25 ° or more and −5 ° or less as the shape of the right blade left-handed twist, the mist coolant can be efficiently spread to the tip of the blade portion. it can. Thereby, the cooling effect of the cutting edge can be enhanced to further increase the tool life, and the surface roughness quality of the machined surface can be improved by enhancing the lubricity.

Another invention of the present invention is a small-diameter CBN ball end mill having a blade diameter of 3 mm or less and an arcuate radius Rmm forming a blade portion and an outer peripheral blade made of CBN, The outer peripheral edge rake face of R / 5 or more of the outer peripheral edge length is formed in the same plane, the outer peripheral edge is formed by right-handed left-handed twist, and the axial rake of the ball edge is −25 ° to −5 ° in the range of less, further around the tip of the ball cutting edge 20% of the total length of the ball cutting edge includes a range radial rake of -10 ° or 0 ° or less, the length of the whole ball blade The radial rake of the outer peripheral side ball blade exceeding 20% is a small-diameter CBN ball end mill characterized in that the minus angle gradually increases until reaching the outer peripheral blade in the range of −25 ° to −12 ° . Here, the range of 20% of the total length of the ball blade includes the range where the radial rake is -10 ° or more and 0 ° or less. The angle where the radial rake is −10 ° or more and 0 ° or less is This means that it is surely in the range of 20% of the total length of the ball blade with the tip of the tip as the center. For example, the radial rake is −15 ° at the position of 10% of the entire length of the ball blade, and the radial rake is −5 ° at the position of 15%. The conditions of this axial rake and radial rake are effective when a long-necked tool having an L / D of 5 or more is used. That is, for example, the above-described radial rake conditions ensure the biting property in the vicinity of the tip of the ball blade and ensure the strength on the outer peripheral side of the tool of the ball blade, so that the small diameter CBN combines both cutting performance and strength. It becomes a ball end mill.

The small-diameter CBN ball end mill of the present invention can spread the mist coolant to the tip of the blade portion by setting the axial rake of the ball blade to be in the range of −25 ° to −5 ° as the shape of the right-handed left-handed twist. As a result, the cooling effect of the cutting edge is enhanced to further extend the tool life, and the surface roughness quality of the work surface of the workpiece can be improved by improving the lubricity. That is, high-precision machining for a long time can be realized stably even in rib groove machining and deep corner machining, and the present invention is effective for cost reduction such as precision component machining mainly targeted.

FIG. 4B shows an axial rake of the small diameter CBN ball end mill of the present invention. The present invention is characterized in that the axial rake 13 of the ball blade 5 of the ball end mill is in the range of −25 ° to −5 ° . As a result, the outer peripheral blade 6 is formed with a right-handed left-handed twist. However, due to this effect, the end mill is applied with a force in the direction of being pulled toward the main spindle side of the machine tool. Vibration can be reduced. Further, since the axial rake 13 of the ball blade 5 of the ball end mill is in the range of −25 ° to −5 ° , the rigidity of the ball blade 5 is increased and chipping can be suppressed. Here, if the axial rake 13 of the ball blade 5 is larger in the positive direction than −5 °, the rigidity of the ball blade 5 is insufficient, the strength of the CBN sintered material is not obtained, and the CBN particles fall off. Will cause chipping, and if the axial rake 13 is larger than −25 ° in the negative direction, the rigidity of the ball blade 5 will increase, but the resistance will increase, and conversely, the drop of the CBN particles will proceed, resulting in a large defect. It will be connected. In particular, in the case of a long neck end mill with a small diameter such that the ratio of the neck length L to the blade diameter D is 5 times or more, if the cutting resistance increases, it will affect the occurrence of tilting and vibration. By making the axial rake 13 of 5 within a range of −25 ° or more and −5 ° or less , stable processing can be performed.

As shown in FIG. 8 (a), the conventional right end twisted ball end mill is a view of the ridgeline of the ball blade 5 as viewed from the tip direction of the blade tip, and has an S shape. On the other hand, the small-diameter CBN ball end mill of the present invention has a right-handed left-handed twist, and the axial rake 13 of the ball-shaped blade 5 is in the range of −25 ° to −5 ° , and is shown in FIG. Thus, the ridgeline of the ball blade 5 is a view seen from the tip direction of the blade tip, and has an inverted S shape. Thereby, since the radial rake 14 near the tip of the ball blade 5 can be set to a negative rake angle smaller than that of the conventional S-shape, the cutting resistance can be lowered and further stable machining can be performed.

FIG. 9 is a diagram for explaining the entire length of the ball blade and the angular range of the radial rake condition in the CBN ball end mill of the present invention. The radial rake 14 represented in FIGS. 10 and 11 is centered on the tip 17 of the ball blade 17 in FIG. The radial rake 14 includes a range of −10 ° to 0 ° , and the radial rake 14 of the outer peripheral side ball blade 5 exceeding the 20% range 16 has a range of −25 ° to −12 ° to the outer peripheral blade 6. The minus angle is gradually increasing. Here, the length 15 of the entire ball blade indicates a ball blade length of −90 ° to 90 ° in the front view. In other words, it refers to the range of the curve CC ′ in FIG. As a result, the sharpness near the tip of the ball blade 5 can be improved, and even when the neck length L is long, vibration can be suppressed and stable machining can be performed, and the rigidity of the ball blade 5 near the outer periphery can be improved. As a result, chipping and chipping can be suppressed. A black circle point O in the figure indicates the center point of the radius R.

Each of the following examples in the table, examples present invention, the conventional example, shown as dividing the comparative example, form numbers regardless of the division, described a series of serial numbers.
Example 1
Example 1 is a comparison of cutting results of a right-handed left-handed torsion having the shape of the present invention with respect to a right-handed right-handed twisted blade which is a typical conventional example. Any conventional example 1 and the invention example 2, the number of blades is two blades, blade diameter 1 mm, the radius R is 0.5mm ball blade peripheral cutting edge length is 0.1mm i.e. blade length and 0.6mm This is a small diameter CBN long neck ball end mill with a neck length of 10 mm (L / D = 10) and a shank diameter of 4 mm. Conventional Example 1 was manufactured with a right-handed right-handed twist, and Example 2 of the present invention was prepared with a right-handed left-handed one. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. As shown in FIG. 12, the workpiece shape is a surface with a 1 ° gradient, the workpiece depth is 10 mm, and the bottom surface portion is formed with a plane width of 0.1 mm in order to evaluate the state of the processed surface. . In order to clarify the difference in tool performance, the cutting conditions are set such that the radial cut amount is 0.05 mm, the pitch cut amount is 0.05 mm, and the bottom cut amount is 0.05 mm. did. The rotational speed was 16000 times / min, the feed rate was 960 mm / min, mist coolant was used for cooling, and cutting was performed until the flank wear width of the tool reached 0.1 mm. The cutting results were compared based on the blade damage status, the machining surface state on the slope surface, the machining surface state on the bottom surface, and the tool life. The results are shown in Table 1.

(Example 2)
In Example 2, the number of blades is two blades, the blade diameter is 1 mm, the radius R of the ball blade is 0.5 mm, the outer blade length is 0.1 mm, that is, the blade length is 0.6 mm, and the neck length is 10 mm ( L / D = 10) Although the shank diameter is 4 mm and the right blade left-hand twist is a small diameter CBN long neck ball end mill shape, the influence due to the difference in shape between the ball blade rake face and the outer edge rake face was confirmed. In Example 5 of the present invention, the ball blade rake face and the outer peripheral edge rake face were manufactured using a method of simultaneously grinding so that the ball blade rake face and the outer peripheral edge rake face were formed on the same plane. As a comparative example, Comparative Example 3 in which the angle difference between the ball blade rake face and the outer peripheral edge rake face formed by separate processes of the ball edge rake face and the outer peripheral edge rake face was 10 °, and the ball blade rake face and the outer peripheral edge rake face. A cutting test was carried out using Comparative Example 4 in which the angle difference was as small as 3 °. The rake face of the outer peripheral cutting edge of Comparative Examples 3 and 4 was formed by the method of grinding the outer peripheral groove in the same manner as the conventional ball end mill shown in FIG. The cutting test was performed under the same cutting conditions, workpiece shape, and machining method as in Example 1, and the cutting results were evaluated by comparing the blade damage status, the machining surface condition on the gradient surface, and the tool life. The results are shown in Table 2.

Example 3
In Example 3, the influence of the axial rake of the ball blade was confirmed. Comparative Example 6, Invention Examples 7 to 11 and Comparative Example 12 were prepared by changing the axial rake of the ball blade as shown in Table 3 with the same basic tool shape as that of Invention Example 5. It used for the cutting test. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. In this test, the ball tip was evaluated by bottom cutting. The cutting conditions were an axial depth of cut of 0.05 mm, a pitch direction depth of cut of 0.05 mm, a rotational speed of 16000 times / min, a feed rate of 960 mm / min, and mist coolant was used for cooling. Evaluation was performed until the cutting distance reached 400 m. The cutting results were compared based on the state of damage to the blade and the machined surface state at the bottom. The results are shown in Table 3.

Example 4
Example 4 is an example of the present invention in which the influence of radial rake at the tip of the ball blade was confirmed. Invention Examples 13 to 17 are the same as the Invention Example 10, except that the radial rake from the tip of the ball blade to the shank side is changed to 0.02 mm as shown in Table 4. Manufactured and subjected to cutting test. From the tip of the ball blade to the place where it enters 0.02 mm on the shank side is a range corresponding to 20% of the entire length of the ball blade. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. In this test, the ball tip was evaluated by bottom cutting. The cutting conditions were an axial depth of cut of 0.05 mm, a pitch direction depth of cut of 0.05 mm, a rotational speed of 16000 times / min, a feed rate of 960 mm / min, and mist coolant was used for cooling. Evaluation was performed until the cutting distance reached 400 m. The cutting results were compared based on the blade damage status and the machined surface roughness at the bottom. The results are shown in Table 4.

As a result of the cutting test, in all of Examples 13 to 17 of the present invention, the blade edge was in a worn state with a stable flank wear width of 0.1 mm or less even after being cut by 400 m, and could be continuously machined. . Therefore, the tool life was better than that of the conventional ball end mill. Comparing the processed surface roughness at the bottom surface, the processed surface roughness is satisfactory from the object of the invention, but the present invention example 15 was able to obtain the smallest processed surface roughness. In the present invention example 17, the maximum height Rz of the processed surface roughness is relatively large in this group, and when the radial rake becomes positive as in the present invention example 17, the biting property is improved, but the rigidity of the cutting edge is increased. It is thought that minute chipping of the cutting edge affects the surface roughness of the machined surface. On the other hand, when the radial rake becomes large negative as in Example 13 of the present invention, the cutting resistance received by the cutting edge is improved, which slightly affects the generation of vibration. From this result, it was confirmed that when the radial rake in the range of 20% of the entire length of the ball blade is in the range of -10 ° or more and 0 ° or less , it can be more stably processed for a long time. .

(Example 5)
In Example 18 to 23 of Example 5, the basic tool shape is the same as that of Example 15 of the present invention (therefore, the radial rake at the tip of the ball blade is −5 ° confirmed to be optimal in Example 4). A ball blade with a different radial rake on the outer peripheral blade side was manufactured and used for testing. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. As shown in FIG. 12, the workpiece shape is a surface with a 1 ° gradient, the workpiece depth is 10 mm, and the bottom surface portion is formed with a plane width of 0.1 mm in order to evaluate the state of the processed surface. . Cutting conditions were set such that the radial cutting depth was set to 0.05 mm and the pitch cutting depth was set to 0.05 mm, and the rotational speed was increased to 30000 in order to intentionally generate vibration. The test was performed using a mist-like coolant for cooling at a speed / min and a feed rate of 1250 mm / min. Cutting results were compared based on the damage status of the blade, the machined surface condition on the bottom surface, the machined surface roughness on the gradient surface, and the amount of uncut material. The results are shown in Table 5.

As a result of testing with all the tools generating slight chatter vibrations, the inventive examples 19 to 22 show stable wear in the blade damage state, and the maximum height of the surface roughness on the inclined surface is high. Rz = 1 μm or less, the processing surface state at the bottom surface portion was free of streaks and stuffiness, and the uncut amount was good at 0.015 mm or less, and extremely high-precision processing could be realized. In particular, Example 20 of the present invention was the most excellent in both the machined surface roughness and the uncut amount. The radial rake also in rigidity and biting of the plane of the cutting edges - around 20 ° is good, it was confirmed that the blade shape can be processed in a more stable, high-efficiency among present invention. In the example 18 of the present invention, the maximum height of the surface roughness was Rz = 1 μm or less, and the processed surface state at the bottom surface portion was good with stable wear without streaks or stuffiness, but within this group, The amount of uncut material was relatively large at 0.025 mm. This is considered to be because the radial rake on the outer peripheral side is large on the negative side and the cutting resistance is large. On the other hand, in the inventive examples 23 and 24, the blade damage status, the maximum height of the surface roughness, and the machined surface status at the bottom surface were all good as in the inventive examples 19-22. When the radial rake is small on the negative side, it is considered that the abrasion has progressed due to a slight decrease in the rigidity of the cutting edge, and the amount of uncut material has increased. From this result, the radial rake of the ball blade on the outer peripheral side is more preferably in the range of −25 ° to −12 ° .

Claims (4)

A small-diameter CBN ball end mill having a blade diameter of 3 mm or less and an arcuate radius Rmm forming a blade portion and an outer peripheral blade made of CBN, wherein the rake face of the ball blade and the R / 5 or more peripheral blade rake surfaces are formed in the same plane, the outer peripheral blade is formed by right-handed left-handed twist, and the axial rake of the ball blade is in the range of −25 ° to −5 °. A small-diameter CBN ball end mill, wherein the ridgeline of the ball blade is formed to have an inverted S shape when viewed from the tip direction of the blade edge . 2. The small-diameter CBN ball end mill according to claim 1, wherein the end diameter is a long-neck end mill having a blade diameter D of 3 mm or less and a ratio L / D of a tool neck length L to the blade diameter of 5 or more. Centering on the tip of the ball blade, the range of 20% of the total length of the ball blade includes the range where the radial rake is -10 ° or more and 0 ° or less, and the radial rake of the ball blade on the outer peripheral side exceeding 20% is 3. The small-diameter CBN ball end mill according to claim 1 , wherein a minus angle gradually increases until reaching the outer peripheral edge in a range of −25 ° to −12 ° . 4.   The small diameter CBN ball end mill according to any one of claims 1 to 3, wherein an interference avoidance portion with a work material is provided behind the outer peripheral blade.