Referring to
Historically, the sharp edge was ground free-hand with a pencil grinder. Later, tooling was developed, as shown in field repair document FRD-2003-1002 from GE Energy Services, the disclosure of which is incorporated herein by this reference, and as schematically illustrated in
Referring to
A more robust assembly is provided according to example embodiments of the invention by offsetting the drive shaft of the cutting assembly with respect to the center axis of the bar in which it is housed, whereby a larger sized collet and bearing can be accommodated.
Thus, the invention may be embodied in a grinding tool comprising: a main body; a drive shaft bore defined along at least a part of the length of said main body, said drive shaft bore having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom; a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage; a drive shaft disposed to extend through said drive shaft passage of said main body; and a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate said cutter by said drive shaft.
The invention may also be embodied in a method of grinding an edge of a cooling hole of a dovetail groove, comprising: providing a tool including a main body, a drive shaft bore defined along at least a part of the length of said main body, said drive shaft bore having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom, a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage, a drive shaft disposed to extend through said drive shaft passage of said main body, and a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate the cutter by said drive shaft; securing a cutter to said cross head assembly; operatively coupling a torque motor to said drive shaft; inserting said main body into a dovetail groove so that the main body is disposed in a base portion of the dovetail groove and the cutter is disposed adjacent the edge to be ground; actuating the motor; and displacing the cutter about and along the edge to grind the same.
These and other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
As noted above, the 90° head cutting tool 20 conventionally provided for grinding the wheel cooling slot was a standard tool for 1/16″ shank cutters. While more controlled than a pencil grinder, the conventional tool assembly lacks robustness with the primary failure modes being broken shanks, looseness in the cradle due to wear, and poor surface finish.
As understood from a consideration of
As mentioned, the size of the assembly is necessarily limited by the diameter at the base of the dovetail, but the inventors recognized that a ⅛ tool could be accommodated in the required package envelope (defined by the base 18 of the dovetail groove) by offsetting the drive shaft. Moreover, exercising careful choice of bearings and assembly sequence gives strength and compactness. In this regard, in illustrated example embodiments, the cross head components load from the cutter side and are retained by a snap ring.
Furthermore, to provide better tool stiffness, reduce component parts and increase robustness of the assembly, according to example embodiments of the invention, the grinding tool has been integrated into an elongated bar, thereby eliminating a two-part grinding tool plus bar assembly previously provided. This eliminates the prior problem of looseness in the tool bar cradle due to wear. With better tool stiffness and a stronger cutter shank, the material removal process can be better controlled with reduced cutter chatter and gouging. A larger shank cutter also yields longer tool life.
Two example embodiments of the integrated grinder and bar are illustrated herein. One example embodiment 30 may be used during manufacture (bench) whereas another embodiment 130 is proposed for use in the field. In these example embodiments, the grinding tool assembly 32, which is an integration of a grinder and a bar, is the same but bearing handles 34, 134 differ. The example bench tool 30 is depicted in
As understood from
The component parts of the cutter assembly for receiving and driving the ⅛″ cutter are also larger. In this regard, not only is the collet larger, as a ⅛″ collet rather than a 1/16″ collet, but the additional space afforded by the offset of the drive shaft 48 allows the maximum size ball bearing 50 close to the cutter 42 which lowers heat generation and increases rigidity. In the illustrated example embodiment, the cutting assembly includes, from the side opposite the cutting face, a wave disk spring 54, a ball bearing 52, a standard NSK drive gear 56, a ball bearing 50 (as noted above) and a retaining snap ring 58. In this regard, careful choice is made in bearings and assembly sequence to give strength and compactness. Further in this regard, the cross head components load from the cutter side and are retained by snap ring 58, whereas in the conventional assembly, the cross head component parts are loaded from the side opposite the cutting face.
The larger cutter assembly also means a larger drive shaft 48 and hence bigger bearings 50, 52 than for a 1/16″ cutter. Bigger bearings means less heat generation which equates with less wear.
In the illustrated example embodiments, a jam nut 64 and control arm 66 are further provided at one end of the grinding tool main body. These component parts are optional for the bench tool 30 but in the illustrated embodiment, one such control arm is shown interposed between the speed reducer 38 and the main body 40. The field tool 130 is illustrated as having a control arm on either end of the grinding tool. The control arm(s) facilitate operation of the tool in both axial and rotational motion relative to the centerline M of the tool.
Attached to the distal end of the main body 40 of the bench tool 30 is a bearing handle 34 to facilitate controlled, two handed manipulation of the grinding tool assembly 32 with respect to the cooling hole being ground. In the illustrated example embodiment, the bearing handle 34 is attached to the distal end of the main body 40 by engaging and threading complimentary threaded components defined at the interface 68 thereof. The bearing handle could be integrally included as a part of the main body, but a detachable bearing handle allows the handle type to be changed as deemed necessary or desirable, and depending on whether the tool is for bench or field use. For example, an interchangeable bearing handle allows for the use of an alternate handle material, e.g., plastic, aluminum, titanium, carbon fiber, etc., to lower the overall weight of the tool and reduce ergonomic stress. The bearing handle can also optionally be knurled as at 76 in
As illustrated in
Thus it will be understood that the tool described herein is an electrically driven, right angle drive grinder utilizing e.g. a ⅛″ collet size for rigidity. The packaging has been optimized for access to confined spaces. It can be used with fluted cutters and burrs. It is applicable to both OEM (original equipment manufacture) and field use (assembled rotor) to produce a smooth, continuous blend of turbine wheel air cooing slots. With higher tool stiffness and a stronger cutter shank, the material removal process can be better controlled with reduced cutter chatter and gouging. A larger shank cutter also yields longer tool life.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.