Patent Application
20140356081
The invention pertains to a rotary cutting tool. More particularly, the invention relates to a solid end mill having a double positive end geometry (i.e., positive axial and radial rakes on both the leading and trailing edges) that enables the end mill to perform a ramp operation at an extremely high ramp angle.
At its most basic, milling is the meeting of a rotating tool with a clamped and stationary workpiece, as opposed to turning where the tool is stationary and the work material rotates. Actually, the workpiece has feed motion imparted from the machine tool. The meeting of the rotary motion of the cutter and the cutting edge of the tools produces fluctuating cutting forces: vibration, heat, and, if all goes well, chips.
Milling machines may have either vertical or horizontal spindle orientation, and typically, face milling cuts flat surfaces, but multi-axis CNC machines make it possible to include three-dimensional movements. That said, there are four basic categories of milling: face milling, periphery milling, slot milling, and specialty applications.
Face milling is used for creating a flat surface (face) on the workpiece. The cutting plane is usually perpendicular to the axis of rotation and the cutters most often feature a single row of inserts, designed with a wide range of cutting geometries, inserts, lead angles, and mounting adaptations. Surface finish requirements are an important input to determine the best tool type. Typically, face milling is performed by tools offering a lead angle for long tool life and reduced chance of breakout when exiting the workpiece.
Periphery milling generates a primary surface parallel to the spindle rotation. A secondary surface is sometimes produced. The cutting plane is usually parallel to the axis of rotation. Periphery milling cutters can be high-speed steel, solid carbide, or indexable-insert-based. Insert-based cutters may include one or more rows of inserts and may produce a simultaneous face-milling operation.
Slot milling is used for producing a slot or channel in the workpiece. There are two primary types of slot milling cutters: disk mills and end mills. Disk mills can be high-speed steel, brazed carbide, and indexable-insert-based. They are typically used in operations perpendicular to the spindle rotation.
End mills used for slot-milling operations are similar to the tools used in periphery milling. The slot being generated is parallel to the spindle rotation. However, because of full engagement in the periphery, poor chip formation, and evacuation, end mills are not a first choice for slotting operations.
While very versatile, end mills are the least stable of all milling cutters due to the smaller tool diameter and greater length. The diameter is the weakest portion of the tool because of the high tangential forces directed across it.
Specialty applications include Z-axis plunge milling, ramping, helical and circular interpolation, trochoidal, and others.
Z-axis plunge milling is commonly used for removing large amounts of workpiece material. Cutting forces are directed into the cutter axially for higher metal-removal rates with long reach capability. The cutting plane is perpendicular to the axis of rotation.
Ramping creates an angled surface on the workpiece or is used at the point of entry for making a pocket (pocketing). Compared to plunging, ramp milling may be less productive depending on conditions. This is also a common application requirement for pocket milling from a solid workpiece.
Helical and circular interpolation is commonly used for creating a cylindrical surface on the workpiece, or for creating entry points for later applications. This application does not necessarily require an existing hole, depending on the type of tool chosen.
Trochoidal milling is an application that typically produces a slot in difficult-to-machine materials. It uses a combination of periphery milling and circular interpolation in the X and Y planes.
In milling, ramping has gradually grown more significant. The speed and precise interpolation of modern CNC machines make it possible for a small tool to mill out a much larger hole or pocket in a relatively short time. Ramping is an important element of doing this. Either the tool ramps from one level of passes to the next within the feature, or else it follows a helical path at a continuous angle all the way down to the feature's depth.
Limitations on the ability to ramp generally result from the tool.
Many end mills that are able to ramp were not necessarily designed to emphasize this type of cutting. When the tool is designed with ramping in mind, various features change.
A tool that has the capability to ramp at a steeper angle reaches the bottom of the feature sooner, potentially reducing machining time. Thus, it would be desirable to design an end mill that is capable of an extremely high ramp angle (i.e., greater than ten (10) degrees) during ramping.
The problem of designing an end mill that is capable of an extremely high ramp angle (i.e., at least ten (10) degrees) is solved by providing an end mill having a cutting tip with a double positive geometry (i.e., both positive axial and radial rakes on both the leading and trailing edges) when the trailing face contacts the work during a ramp operation without contacting the work at the center of the end mill.
In one aspect of the invention, a rotary cutting tool with a longitudinal axis comprises a shank portion; a cutting portion extending from the shank portion to a cutting tip, the cutting portion having a length of cut, and a plurality of blades separated by flutes extending along the length of cut, each of the blades including a leading face, a trailing face, a land surface extending between the leading face and the trailing face, and a cutting edge at the intersection between the leading face and the land surface, the cutting tip comprising a corner radius, a first portion proximate an outer diameter of the rotary cutting tool, a third portion proximate the central axis, and a second portion between the first and third portions, wherein the trailing face contacts a work during a ramp operation in such a way that the first, second and third portions of the cutting tip have a double positive geometry, thereby enabling the rotary cutting tool to perform the ramp operation with a ramp angle of at least ten degrees.
In another aspect of the invention, a rotary cutting tool with a longitudinal axis comprises a shank portion; a cutting portion extending from the shank portion to a cutting tip, the cutting portion having a length of cut, and a plurality of blades separated by flutes extending along the length of cut, each of the blades including a leading face, a trailing face, a land surface extending between the leading face and the trailing face, and a cutting edge at the intersection between the leading face and the land surface, the cutting tip comprising a corner radius, a first portion proximate an outer diameter of the rotary cutting tool and formed with a first dish angle with respect to a plane perpendicular to the central axis, a third portion proximate the central axis and formed with a third dish angle with respect to the plane perpendicular to the central axis, and a second portion between the first and third portions and formed with a second dish angle with respect to the plane perpendicular to the central axis, wherein the first dish angle is smaller in magnitude than the second dish angle, and wherein the second dish angle is smaller in magnitude than the third dish angle, and wherein the trailing face contacts a work during a ramp operation in such a way that the first, second and third portions of the cutting tip have a double positive geometry, thereby enabling the rotary cutting tool to perform the ramp operation with a ramp angle of at least ten degrees.
While various embodiments of the invention are illustrated, the particular embodiments shown should not be construed to limit the claims. It is anticipated that various changes and modifications may be made without departing from the scope of this invention.
Referring now to
As used herein, axial rake angle is defined as the angle between the cutter tooth face of a blade of a milling cutter or reamer and a line parallel to its axis of rotation. Radial rake angle is defined as the angle between the cutter tooth face of a blade and a radial line passing through the cutting edge in a plane perpendicular to the cutter axis. End rake angle is defined as the angle between the cutting tip at the end of a blade and a radial line passing through the cutting edge in a plane perpendicular to the cutter axis. Positive axial rake angle is defined as a rake geometry indicating that the that the cutting edge is positioned on the axial centerline of the cutter with the top surface of the cutting edge sloping back and away from the axial centerline. Positive radial rake angle is defined as a rake geometry indicating that the cutting edge is positioned on the radial centerline of the cutter with the top surface of the cutting edge sloping back and away from the radial centerline. Positive end rake angle is defined as a rake geometry indicating that the cutting tip at the end of the blade is positioned on the radial centerline of the cutter with the cutting tip sloping back and away from the radial centerline. A double positive geometry is defined as a tool orientation that uses a combination of positive axial and radial rake angles or a combination of positive axial and end rake angles. Ramp milling is defined as a combination of Z-axis movement simultaneous with X, Y, or combined axis movement. Dish angle is defined as the angle formed by the end cutting edge with respect to a plane perpendicular to the cutter axis. Helix angle is defined as the angle made by the leading face of the land with a plane containing the cutter axis. Ramp angle is defined as the angle made by the cutter when moving the cutter in both the Z-axis direction and an additional axis (X- or Y-axis) relative to the work, and is defined by the equation:
Ramp Angle=Tan/1×Z-axis feed / X/Y-axis feed (1).
High ramp angle is defined as a ramp angle of at least ten (10) degrees.
In the illustrated embodiment, the end mill 10 has a total of five (5) blades 18 and flutes 20. However, it will be appreciated that the invention is not limited by the number of blades and flutes, and that the invention can be practiced with a fewer or a greater number of blades and flutes. For example, the invention can be practiced with four (4) blades and flutes, six (6) blades and flutes, eight (8) blades and flutes, and the like.
The blades 18 and flutes 20 of the cutting portion 14 extend helically within the cutting portion 14 at a helix angle 30 of between about thirty (30) and about forty-five (45) degrees with respect to the longitudinal axis 16. In other embodiments, the blades 18 and flutes 20 are “straight flutes” that extend parallel to the longitudinal axis 16. In the illustrated embodiment, the blades 18 and flutes 20 of the cutting portion 14 extend helically within the cutting portion 14 at a helix angle 30 of about thirty-eight (38) degrees.
Referring now to
Referring now to
As shown in
Referring now to
The combination of the multiple dish angles and the double positive geometry of the first and third cutting portions 38, 42 at the cutting tip 15 enables the end mill 10 of the invention to aggressively cut the work all the way to the coolant hole, thereby providing an extremely high ramp angle capability as compared to conventional end mills. More specifically, the multiple dish angles and the double positive geometry of the cutting tip enables the end mill 10 of the invention to ramp at an extremely high ramp angle of at least ten (10) degrees in the direction of the arrow 48.
On the other hand, all three cutting portions 38, 40, 42 at the cutting tip 15 when the trailing face 24 contacts the work 100. That is, the first cutting portion 38, the second cutting portion 40 and the third cutting portion 42 of the cutting tip 15 contact the work 100 at the trailing face 24. The corner radius 36 may contact the work 100, but not the entire corner radius 36, unlike the entire corner radius 36 when the leading face 22 contacts the work 100. When the trailing edge 24 contacts the work 100, all three cutting portions 38, 40, 42 of the cutting tip 15 have both a positive axial rake angle 44 and a positive end rake angle 46 (i.e. a double positive geometry), thereby providing an end mill with high ramp angle capability.
As described above, the trailing face 24 of the end mill 10 contacts a work 100 during a ramp operation in such a way that the first, second and third portions 38, 40, 42 of the cutting tip 15 have a double positive geometry, thereby enabling the rotary cutting tool 10 to perform the ramp operation with a ramp angle 50 of at least ten degrees. As a result, the entire trailing face 24 of the end mill 10 aggressively cuts the work 100. In addition, the end mill 10 of the invention, which is a non-center cutting tool, is able to perform a plunge operation at an extremely high ramp angle, unlike conventional non-center cutting tools.
The patents and publications referred to herein are hereby incorporated by reference.
Having described presently preferred embodiments the invention may be otherwise embodied within the scope of the appended claims.
