Negative tapered endmill for machining critical holes

Abstract

The present invention aims to keep only the effective edge of the milling tool on the ID face of the hole The unused part of the cutting edge has a clearance to avoid contact to the ID face of the hole. Said geometry will allow the endmill to machine the hole directly to the finish dimension with finish machining qualities, making additional finishing operations redundant.

Description

[0001] Description

[0002] NEGATIVE TAPERED ENDMILL FOR MACHINING CRITICAL HOLES

[0003] Field of the Invention

[0004] The present invention is a resharpenable endmill design that prevents the machining laden complications in critical hole milling operations.

[0005] Background of the Invention

[0006] In the context of machining, rotating cutting tools are usually made out of hard material such as silicon carbide and used to shape the workpiece by removing material with shear deformation. Generally, these tools are driven by CNC controlled machine tool. Machine tool drives the cutting tool by the means of rotating the cutting tool in it’s own axis and positions the cutting tool on the workpiece with a pre-determined tool path.

[0007] Tool path is defined as the movement of the cutting tool in a machining area and / or on the workpiece.

[0008] Machining a hole can be described as removing cylindrical shaped material from the work part by using a rotating cutting tool such as a drill or an endmill.

[0009] Sizing or finishing a hole can be described as removing a layer of material in the previously opened, undersize hole surface to meet the final geometric qualities such as diameter, cylindricity etc. This operation usually performed with high tolerance endmills, reamers, hones or grinding wheels.

[0010] Drill tools are designed to be driven directly into the surface to open a hole. Theoretically, drills can be used to enlarge previously opened holes too. Expected hole diameter after drilling is equal to the drill tools diameter. Generally, drills are the least precise to meet a targeted hole diameter.In the prior art, the invention numbered KR20060109536 (A) and titled "Endmill Having Unequally Disposed Leading Edge" relates an endmill having an unequally disposed leading edge is provided to prevent amplification of vibration generated when the endmill makes contact with a cut material. In an endmill, the division angles between the bottom surface and a plurality of blades are differently set. The helix angles of the blades are changed as they go toward the rear side. The division angles of symmetric blades are identically set. The division angles of adjacent blades are differently set. According to the endmill, amplification of vibration generated when the endmill makes contact with a cut material is prevented. The end mill can precisely cut the cut material.

[0011] In the prior art, the invention numbered JP2023050938 (A) and titled “Endmill Specification Setting Method, Processing Condition Setting Method and Processing Method Using The Same” relates To provide an endmill specification setting method which can effectively use a wide and stable region in which a spindle rotation number larger than a spindle rotation number at a peak of a stable pocket is set. An endmill specification setting method has: a primary function acquisition step for acquiring an axial cutting depth of a peak of a first stable pocket SP1 of an endmill and a workpiece and a spindle rotation number n, and a primary function F1 which passes a point in which the axial cutting depth and the spindle rotation number n are set at zero; an a-order function acquisition step for acquiring an a-order function (a is larger than 1) Fa which is obtained by expressing the axial cutting depth for avoiding chatter vibration with respect to the spindle rotation number n in a region of the spindle rotation number n which is larger than the peak of the first stable pocket SP1 with respect to the endmill and the workpiece; and a blade number decision step for deciding a blade number N at which the axial cutting depth obtained from the a-order function Fa becomes larger than the axial cutting depth obtained from the primary function.

[0012] Endmills can be used with multiple different methods to machine a hole.

[0013] • First option is plunging milling, which, the endmill is directly driven into the surface like a drill tool. Plunge milling a hole with an endmill is same as machining with a drill tool and expected hole diameter after plunge milling is equal to the endmillsdiameter. This method can be used for sizing a hole, usually with using a high tolerance endmill.

[0014] • Second option is helical machining, which, the endmill is driven into the surface with a helix movement. In the helical machining option, machined hole diameter is greater than the endmills diameter and can be adjusted by changing the helical tool paths helix radius (pitch diameter). Also, this method can be used for sizing a hole. Usually tight tolerances can be met with this method providing that it is machined with a precise CNC controlled milling machine.

[0015] • Another option is spiral milling, which, positions an endmill into previously opened hole without removing any material and starts cutting to enlarge the hole with a spiral movement. This method can only be used for sizing.

[0016] Both drills and endmills are very efficient at removing material but the disadvantages are poorer surface qualities, higher disruptive effect to the material structure and cause higher residual stress compared to finish methods.

[0017] Surface texture and / or surface quality can be described as the workpiece surface’s smoothness and measured by inspecting micro deviations from nominal surface geometry.

[0018] Anything from atomic bonds of the elemental components to the crystalline structure of metals, variety of factors effect to the materials performance and in this document’s context, it is described as material structure.

[0019] Residual stress is the stress on a workpiece in a free state (with the absence of external loading) in a stable temperature (no thermal gradient) left after machining the workpiece. Also in high speed machining, machining forces may create excessive heat, disrupting the mechanical properties of the work material around the machined area. This means machining critical holes has to be restrictive in terms of cutting speeds.

[0020] This present inventions main subject is helical milling a hole.Scratches, tooling marks, chatter marks, rebonded material etc. can be specified as surface defect. Surface defect on a machined hole surface can make the hole prone to creep and fatigue related failures.

[0021] Both high cutting forces and high heat levels on the machined surface may cause irregularity of the work materials structure. This irregularity usually effects the mechanical performance negatively.

[0022] While helical machining a hole, machining forces will deflect the endmill towards the centerline of the machined hole. This deflection of the endmill causes side cutting edges of the endmill to get into contact with the inner surface of the hole. This unwanted contact may cause visual flaws, disruption of material structure or machining laden residual stress in the machined hole surface.

[0023] While helical machining a hole with a diameter close to the endmills diameter, helical tool path radius (pitch diameter) is very small and the endmill removes the material by auguring chips from the work part. This type of machining causes the removed chips get into contact with the inner surface of the hole. The contact of removed chips usually scours or rebonds to the inner surface of the hole, leading various types of visual defects, disruption to the material structure and higher residual stress on the inner surface of the hole.

[0024] Holes with very low design safety margin are specified with the lowest tolerance for machining related complications and are described as critical holes. Also critical holes usually has a tight geometric tolerances by design.

[0025] Critical holes are traditionally generated by performing multiple operations with gradual stock removal. Thus, eliminating visual defects, residual stress and similar factors that reduces the performance of the material which the work part consists of.

[0026] Finishing can be described as using less aggressive methods to increase the machined hole diameter. Reaming, honing and jig-grinding operations can be classified as finish operations. Finish methods are a lot gentle on the work part compared to drilling or millingbut incapable at generating a hole and relatively inefficient at removing material by their design.

[0027] Gradual stock removal is being implemented by utilizing at least one finish operation after machining the hole. Conventionally, hole is machined undersized (smaller in diameter) to leave some extra material in the hole surface. This undersize hole machining operation is called in-process machining. After in-process machining, a gentler finish operation is used to remove the extra material to meet the finish geometric qualities of the hole.

[0028] Summary of the Invention

[0029] The present invention aims to keep only the effective edge of the milling tool on the ID face of the hole. The unused part of the cutting edge has a clearance to avoid contact to the ID face of the hole. Said geometry will allow the endmill to machine the hole directly to the finish dimension with finish machining qualities, making additional finishing operations redundant. Additionally, the tip of the endmill is a resharpenable geometry hence exponentially increasing the milling tools economic life.

[0030] The Industrial Applicability of the Invention

[0031] Negative tapered endmill (1) provides reliable machining of holes, meets tight tolerances with minimum disruption to the workpiece material. All sorts of holes with high requirements can be machined. Also it can be implemented to the manufacturing processes of critical rotating components of aircraft engines and industrial gas turbines etc.

[0032] Description of the Figures

[0033] Fig 1: Helical movement of the milling tool in a hole.

[0034] Fig 2: Section of the tool design.Fig 3: Tool deflection and cutting sections.

[0035] Description of the References

[0036] 1: Negative tapered endmill

[0037] 1a: Tool length

[0038] 1b: Cutting length

[0039] 1c: Shank length

[0040] 1d: Root diameter

[0041] 1e: Tip diameter / effective diameter / cutting diameter

[0042] 1f: Rotation axis of the tool

[0043] 1g: Tip cutting area

[0044] 1h: Side cutting area

[0045] 1i: Effective cutting area of the tool while helical hole machining 1 i1 : Effective cutting area of the side

[0046] 1 i2: Effective cutting area of the tip

[0047] 1j: Tool deflection

[0048] 2: Machined part

[0049] 3: Helical tool path

[0050] 3a: Helix diameter

[0051] 3b: Helix pitch

[0052] 4: Hole feature

[0053] 4a: Centerline of the hole featureDetailed Description of the Invention

[0054] The present invention is a milling tool (1) with negative tapered side cutting area (1h) and resharpenable tip cutting area (1g).

[0055] The negative tapered side cutting area (1h) is described as having a lower cutting edge root diameter (1d) than the tip diameter (1e). It is specified this way to have a clearance for compensating tool deflection (1j) under machining forces.

[0056] The negative tapered side cutting area (1h) is described as having a lower cutting edge root diameter (1d) than the tip diameter (1e). It is specified this way to have sweeping qualities next after the effective cutting area of the side (1 i1 ) to enhance surface texture of the machined hole (4).

[0057] The negative tapered side cutting area (1h) is described as having a lower cutting edge root diameter (1d) than the tip diameter (1e). It is specified this way to have a clearance to avoid contact with the inner face of the hole feature (4) even with deflection (1j) under machining forces. Avoiding this unwanted contact with the inner face of the hole (4) provides;

[0058] - Lower heat generation during machining,

[0059] - Lower risk of causing visual flaws

[0060] - Lower risk of disrupting material structure

[0061] - Lower the risk of causing residual stress on the hole (4) surface.

[0062] - Better surface texture

[0063] The negative tapered side cutting area (1h) is described as having a lower cutting edge root diameter (1d) than the tip diameter (1e). It is specified this way to have a clearance for easing the coolant flow to effective cutting area of the tool (1i).

[0064] The negative tapered side cutting area (1h) is described as having a lower cutting edge root diameter (1d) than the tip diameter (1e). It is specified this way to sustainably obtainan unused cutting edge in the side cutting area (1h) after the resharpening of the tool tip cutting area (1g).

[0065] Effective cutting area (1i) is the contact area of the tools (1), working (shearing) section while machining shown in Fig. 3. Effective cutting area of the tip (1 i2) and effective cutting area of the side (1 i1 ) can be separated for easy understanding.

[0066] The main target is to be able to generate conforming critical hole features (4) reliably with lower cost of machining.

[0067] This tool also allows holes (4) in confined spaces with high requirements can be machined. Due to the strict setup conditions for reaming or jig grinding, negative tapered endmill (1) allows operators and engineers to generate conforming holes (4) in odd conditions. Since the negative tapered endmill (1) is used similar to a regular endmill, giving extra effort for finicky operations redundant.

[0068] One of the cost reductions comes from the resharpenability of the tool (1) by regrinding the tip cutting area (1g).

[0069] When I after the tool (1) is resharpened by grinding the tip cutting area (1g), previously used effective cutting area of the side (1 i1 ) will also be grinded away enabling unused part of side cutting area (1h) to use. Since the largest diameter is the tip diameter (1e) and having unused effective cutting area of the side (1i1) after resharpening allows sustainable surface finish qualities even after multiple resharpening.

[0070] One of the cost reductions comes from eliminating multiple machining operation requirements, since the tool (1) has a negative tapered side cutting area (1 h), unwanted contact of the holes (4) ID face is eliminated.

[0071] Generally, endmills are more reliable at generating features with a precise location. For that reason, one of the cost reductions with negative tapered endmill (1) comes from being able to generate critical hole features (4a) more reliably compared to other tools, such as drills, hones and reamers. This decreases the risk of scrapping or rework needs of the machined part (2).As the tool (1) resharpened by regrinding the tip cutting area (1g), the tools effective tip diameter (1e) will reduce towards the root diameter (1d). This reduction will be tolerated by CNC controls tool diameter compensation function. CNC controls tool diameter compensation function tolerates the reduction of the tip diameter (1e) by enlarging the helical tool paths (3) pitch diameter with G40 / G41 codes.

Claims

CLAIMS1. An endmill design that prevents the machining laden complications in helical hole milling operations, characterized in that, it comprises an endmill (1 ) with a negative tapered side cutting area (1h) is described as having a lower cutting edge root diameter (1d) than the tip diameter (1e).

2. The negative tapered side cutting area (1h) according to claim 1, characterized in that, it provides a clearance for compensating tool deflection (1j) under machining forces.

3. The endmill according to claim 2, characterized in that, avoiding unwanted contact with the inner face of the hole (4) provides; lower heat generation during machining, lower risk of causing visual flaws, lower risk of disrupting material structure, lower the risk of causing residual stress on the hole (4) surface, better surface texture.

4. The negative tapered side cutting area (1h) according to claim 1, characterized in that, it has a clearance for easing the coolant flow to effective cutting area of the tool (1i).

5. The negative tapered side cutting area (1h) according to claim 1, characterized in that, it is specified to have sweeping qualities next after the effective cutting area of the side (1 i1) to enhance surface texture of the machined hole (4).

6. The negative tapered side cutting area (1h) according to claim 1, characterized in that, it is specified to have a clearance to avoid contact with the inner face of the hole feature (4) even with deflection (1j) under machining forces.

7. The negative tapered side cutting area (1h) according to claim 1, characterized in that, it provides to sustainably obtain an unused cutting edge in the side cutting area (1h) after the resharpening of the tool tip cutting area (1g).

8. The endmill according to claim 1 , characterized in that, it has a geometry provides to allow the endmill to machine the hole directly to the finish dimension with finish machining qualities, making additional finishing operations redundant.

9. The endmill according to claim 1, characterized in that, after the tool (1) is resharpened by grinding the tip cutting area (1g), previously used effective cutting area of the side (1 i1 ) will also be grinded away enabling unused part of side cutting area (1h) to use.

10. The endmill according to claim 1, characterized in that, since the largest diameter is the tip diameter (1e) and having unused effective cutting area of the side (1 i1 ) after resharpening allows sustainable surface finish qualities even after multiple resharpening.

11. The endmill according to claim 1, characterized in that, to cost reduction by eliminating multiple machining operation requirements, the tool (1) has a negative tapered side cutting area (1h), unwanted contact of the holes (4) ID face is eliminated.12.An endmill design that prevents the machining laden complications in critical hole milling operations, characterized in that, it comprises an endmill (1) with negative tapered side cutting area (1h) and resharpenable tip cutting area (1g) which has the tools effective tip diameter (1e) will reduce towards the root diameter (1d) after each regrinding.

13. The tip cutting area (1g) according to claim 12, characterized in that, CNC controls tool diameter compensation function tolerates the reduction of the tip diameter (1 e) by enlarging the helical tool paths (3) pitch diameter with G40 / G41 codes.

14. The resharpenable endmill according to claim 12, characterized in that, it has a geometry provides to allow the endmill to machine the hole directly to the finish dimension with finish machining qualities, making additional finishing operations redundant.

15. The resharpenable endmill according to claim 12, characterized in that, after the tool (1) is resharpened by grinding the tip cutting area (1g), previously used effective cutting area of the side (1i1) will also be grinded away enabling unused part of side cutting area (1h) to use.

16. The resharpenable endmill according to claim 12, characterized in that, since the largest diameter is the tip diameter (1e) and having unused effective cutting area of the side (1 i1) after resharpening allows sustainable surface finish qualities even after multiple resharpening.

17. The resharpenable endmill according to claim 12, characterized in that, to cost reduction by eliminating multiple machining operation requirements, the tool (1) has a negative tapered side cutting area (1 h), unwanted contact of the holes (4) ID face is eliminated.18.A resharpenable endmill design that prevents the machining laden complications in critical hole milling operations, characterized in that, after the tool (1) is resharpened by grinding the tip cutting area (1g), previously used effective cutting area of the side (1 i1 ) will also be grinded away enabling unused part of side cutting area (1h) to use.

19. The resharpenable endmill according to claim 18, characterized in that, since the largest diameter is the tip diameter (1e) and having unused effective cutting area of the side (1 i1) after resharpening allows sustainable surface finish qualities even after multiple resharpening.

20. The resharpenable endmill according to claim 18, characterized in that, to cost reduction by eliminating multiple machining operation requirements, the tool (1) has a negative tapered side cutting area (1 h), unwanted contact of the holes (4) ID face is eliminated.

21. The resharpenable endmill according to claim 18 characterized in that, it has a geometry provides to allow the endmill to machine the hole directly to the finishdimension with finish machining qualities, making additional finishing operations redundant.

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