Patent Application
20130000121
1. Field of the Invention
This invention relates to machining gas turbine engine blades that are integral with a disk (BLISKS) or integrally bladed rotors (IBR's) and, more particularly, to the apparatus and methods for cutting the blades.
2. Description of Related Art
Bladed disks (BLISKS) and bladed drums (BLUMS), both of which are considered integrally bladed rotors (IBRS) are being used more often for fan, compressor stages in aircraft gas turbine engines. IBRS have a disk or a hub from which a plurality of integral blades extend substantially radially outwardly. Manufacturing IBRS is a challenging task due to the complex geometry of airfoil surfaces.
Existing methods of manufacturing IBR airfoils include flank milling, point milling, and use of grinding wheels. In a flank milling process, the periphery of an end mill, typically a tapered ball-end mill, generates the desired airfoil surface geometry through one or a few passes of the cutter. In a point milling process, a grinder makes numerous (usually hundreds) of shallow passes until the desired airfoil surface geometry is generated. These passes may be in the direction of airflow, or in the radial direction. The tool used in a point milling process is usually a tapered end-mill style cutter, small enough such that the entire diameter of the tool can fit between the airfoils of the IBR. Cutting speed is limited due to the small diameter of the tool, which restricts production efficiency.
Another method of manufacturing IBR airfoils includes successively plunging a cup-shaped cutter into the rotor for generating circular slots between the airfoils. This method is limited to either roughing in complex geometry airfoils or completely machining very simple geometry airfoils.
Accordingly, there is need for a better, faster, and less expensive cutter and method for roughing in complex geometry airfoils and more fully machining the BLISK and IBR airfoils.
A spherical cutter includes a spherically shaped body having an open end and a closed end defining a central cavity. Multipoint cutting edges are disposed along a circular rim at the open end of the body. The spherically shaped body is generally defined by a radius and an origin.
The spherical cutter may also include a shank at the closed end of the spherical cutter.
An exemplary embodiment of the spherical cutter further includes a plurality of cutting inserts including the cutting edges and the cutting inserts removably attached to the spherically shaped body along the circular rim. A plurality of support teeth are circumferentially disposed along the rim and positioned between adjacent recesses extending axially into the body. The plurality of cutting inserts are removably mounted and supported on the plurality of support teeth respectively.
Each of the support teeth may include a circumferentially facing front face and a circumferentially facing back face. The front face is configured for positioning one of the cutting inserts and the inserts are secured against the front face such as by clamps disposed in the recesses and attached to the rim by screws.
The inserts may be conically shaped with aft ends mated to the teeth and a wider forward cutting end with a circular cutting edge.
A multi-axis computer numerically controlled machine may include the spherical cutter mounted to a rotatable spindle of the machine. The machine may be operably programmed for moving the spherical cutter during cutting along a spherical surface generally defined by the radius and the origin.
A method for machining a cylindrical workpiece or blank to machine a plurality of circumferentially spaced apart integral rotor blades extending radially outwardly from a hub may include a step of machining a deep curved slot with the spherical cutter. The step of machining may include machining each of the slots along a spherical surface defined by the radius and the origin.
The step of machining may further include machining the slots with the spherical cutter mounted to a rotatable spindle of a multi-axis computer numerically controlled machine, the radius and the origin located along a rotational axis of the spindle, and moving the spherical cutter during the machining along the spherical surface generally defined by the radius and the origin by continually positioning the spindle during machining.
The foregoing aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawings where:
Illustrated in
Each blade 18 includes a concave pressure side 20 and a convex suction side 22. The blades 18 extend radially from a root 24 to a tip 26 of each blade 18. The pressure and suction sides 20, 22 extend generally axially between a leading edge 28 and trailing edge 30 of each blade 18. In the exemplary embodiment, each blade 18 has a suitable airfoil configuration which typically twists about a radial blade or stacking axis 27 extending from the blade root 24 to the blade tip 26, with varying taper and/or change in chord length CL therebetween. In the exemplary embodiment, a camber of each blade 18 also typically varies from blade root 24 to blade tip 26, with the resulting airfoil having a 3-D contour or shape.
Blank 12 is machined using a known machine, such as, but not limited to, a multi-axis CNC (computer numerically controlled) machine, of the type suitable for milling, indicated at 31 in the FIGS. The machine 31 includes a spindle 32 to which the spherical cutter 34 is mounted. The spherical cutter 34 is a rotatable machine tool designed for cutting or milling. The blank 12 is fixtured relative to the CNC machine 31 and the spindle mounted spherical cutter 34. The spindle 32 and the spherical cutter 34 are operable to move with a plurality of degrees, or axes, of movement for following 3-D machining paths through blank 12 while the spindle 32 and the spherical cutter 34 are spinning about a rotational axis 48 of the spindle 32.
Referring to
The spherical cutter 34 includes a spherically shaped body 42 having an open end 44 and a closed end 46 defining a central cavity 54. The closed end 46 of the spherical cutter 34 is mounted or attached to the spindle 32 of the multi-axis milling machine 31 for rotation of the spherical cutter 34 about the rotational axis 48. The embodiment of the spherical cutter 34 illustrated herein includes a shank 55 at the closed end 46 of the spherical cutter 34 used to mount or attach the spherical cutter 34 to the spindle 32.
Referring to
Each tooth 62 has a circumferentially facing front face 65 and a circumferentially facing back face 66 around the rim 58. The front face 65 is configured for positioning one of the cutting inserts 60. The inserts 60 are secured against the front face 65 by clamps 70 disposed in the recesses 64 and attached to the rim by screws 72. The inserts 60 illustrated herein are conically shaped with an aft end 74 mated to the tooth 62 and a wider forward cutting end 76 with a circular cutting edge 78. The clamp 70 presses against the forward cutting end 76. Other types and shapes of inserts may be used.
The cutting edges 78 may be of a replaceable carbide insert style or a carbide brazed-tip style. An inside 82 of the spherical cutter 34 has a concave shape 84 and the outside 86 has a convex shape 88. This enables a simple NC programming technique to generate and cut a deep curved slot 37 (illustrated in
Referring to
Machining of each of the slots 37 along a single spherical surface S results in a curved slot 37 at the end of the plunge as illustrated in
While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims.
