Abstract:
A machining apparatus is provided. The machining apparatus includes a discharge machining head assembly and a slide assembly supporting the head assembly. The machining apparatus also includes an electromagnet configured to support the slide assembly in a position on a work piece to machine an area. The slide assembly permits linear displacement of the head assembly generally parallel to the supporting work piece surface.

Description:
TECHNICAL FIELD 
     The disclosed apparatus relates to a machining apparatus and method for use in a confined space. More specifically, the disclosed apparatus relates to a machining apparatus that uses either an electrochemical discharge machining technique or an electro-discharge machining technique. 
     BACKGROUND OF THE INVENTION 
     Electrochemical machining (ECM) and Electro-discharge machining (EDM) are two techniques used in industry for the machining of metals. In EDM, a DC voltage is applied to a drill electrode and the work piece is eroded by a spark formation in a gap between the drill electrode and the work piece. A dielectric liquid is usually forced into the gap between the electrode and the work piece. 
     In ECM, a drill electrode is placed in proximity to the work piece and an electric potential is placed across the drill electrode and the work piece. Electrolyte is forced into the gap between the electrode and the work piece, and work material is removed by electro-chemical action. 
     Commercially available EDM drilling machines, as opposed to EDM machining machines, may use water as the working fluid. In some cases, a non-conductive de-ionized water may be used, however, in some cases tap water may be used wherein the conductivity depends on the mineral content of the tap water. The EDM drilling process is not exactly the same as the EDM machining process. The EDM machining process uses a non-conductive dielectric, whereas in EDM drilling, a semi-conductive fluid may be used EDM machining has some similarity with ECM (Electro-Chemical Machining), which uses highly conductive electrolyte. The metal removal process is partly spark erosion and partly electro-chemical. Therefore, commercial EDM drilling machine uses a process in between that can be called an Electro-chemical Discharge Machining (ECDM). 
     Typically, for both ECDM and EDM, the drill electrode is hollow and the machining liquid (either the dielectric liquid or the electrolyte, depending upon the application) flows internally along the electrode, issuing through a hole, slot, or some other like aperture at the working face of the electrode. In ECDM, bubbles resulting from electrolytic dissolution cause a non-conducting region between the electrode and material, subsequently leading to an electrical discharge owing to a high electrical voltage applied to this non-conducting region. 
     Unfortunately, currently available ECDM and EDM tools are large, cumbersome, and have an inability to be used in confined spaces. Currently available ECDM tools and EDM tools are configured for use on work pieces that must be installed in a drilling machine such that the EDM or ECDM drill electrode is moved down towards the work piece, much in the same way as a drill is moved down in a drill press. Additionally, ECDM and EDM currently only drill holes around 6 mm in diameter, when a larger diameter drill hole may be needed to efficiently drill out certain hardware such as pins and screws. 
     As stated above, currently available EDM and ECDM tools are impossible or very difficult to use in confined spaces. An example of a confined space is the space around the rotor blades attached to a rotor of a turbomachine. Turbomachines include, but are not limited to: steam turbines, compressors, and gas turbines. Rotor blades often need to be removed from the rotor of a turbomachine. Such blade removal may be required, for example, to allow inspection, refurbishment or cleaning of the blades during scheduled maintenance or after a required shutdown of the turbomachine. A rotor for a turbomachine, such as a steam or gas turbine, typically has several rows of blades arranged along its periphery. Each row of blades comprises a circumferential array of blades spaced equally about the circumference of the rotor. Typically, each blade has a root portion by which it is retained in the rotor. Various blade root shapes have been utilized, such as firtree, dove-tail, etc. At assembly, the blade roots are axially slid into correspondingly shaped grooves formed in the rotor circumference. A locking device, such as a pin, is typically used to prevent the blade root from sliding out of the groove. During operation of the turbomachine, the pins may seize in their respective holes. Once these pins have seized, they are very difficult and time consuming to remove by using such known means as hammering or mechanical drilling. Part of the difficulty in removing these pins and tabs is that space is very limited between the hubs of a turbomachine rotor, thus making it very awkward if not impossible to drill out the pins and tabs. Additionally, the blades extend around a 360 degree interior of the turbo machine casing, making it difficult to position cumbersome tools to drill out all the pins. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An embodiment of the disclosed machining apparatus relates to a discharge machining head assembly; and an electromagnet configured to support the head assembly in a position to machine an area. 
     Another embodiment of the disclosed apparatus for machining relates to a discharge machining head assembly; and a head assembly adaptor plate coupled to the discharge machining head assembly. 
     In addition, an embodiment of the disclosed apparatus for machining relates to a discharge machining head assembly; a sliding assembly coupled to the discharge machining head assembly; and a sliding assembly adaptor plate coupled to the sliding assembly. 
     Also, an embodiment of the disclosed apparatus for guiding a drill electrode relates to a bushing; an insulated annulus located in the bushing; and a bushing holder coupled to the bushing. 
     An embodiment of the disclosed method relates to attaching a machining tool to a surface; positioning a drill electrode to a work piece; and drilling the work piece with the machining tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the figures, which are exemplary embodiments, and wherein like elements are numbered alike: 
         FIG. 1  depicts a view of the disclosed apparatus and part of a steam turbine rotor; 
         FIG. 2  depicts a perspective view of the disclosed apparatus; 
         FIG. 3  depicts a perspective view of a head assembly from the disclosed apparatus; and 
         FIG. 4  depicts a guide bushing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A detailed description of several embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to  FIGS. 1 through 4 . 
     DISCHARGE MACHINING 
       FIG. 1  shows a non-limiting example of a confined space where a portable and small ECDM or EDM apparatus would be useful. A side view of part of a rotor  10  from a turbomachine is shown. In this example the rotor  10  is a steam turbine rotor with a L- 1  stage hub  14  and a L- 0  stage hub  18 . Although  FIG. 1  shows the space between two hubs of a rotor, this is only one of many possible uses of such an apparatus in confined spaces. Attached to the L- 1  stage hub  14  is a disclosed apparatus  22 . The disclosed apparatus  22  is attached to the hub  14  via an electromagnet  26 . The electromagnet  26  allows the apparatus  22  to be positioned in a variety of orientations with respect to a work piece, in contrast to commercially available ECDM and EDM tools, which are oriented to vertically drill in a downward direction into a work piece. The disclosed apparatus  22  may be positioned using the electromagnet such that the apparatus may machine downward vertically, upward vertically, at a horizontal, or any angle in between.  FIG. 1  shows how the non-traditional discharge machining apparatus  22  may be positioned in the constricted space between two hubs  14 ,  18  in order to drill out a rotor blade pin (not shown) located on the L- 1  stage hub  14 . 
       FIG. 2  shows a perspective view of the disclosed apparatus  22  and which can be quickly and accurately positioned to operate in a constricted space with 5 axes of adjustment. 5 axes of adjustment means that an apparatus may be adjusted about 3 linear axes and 2 rotational axes. The head assembly  30  is shown at the top of the apparatus  22 , and will be discussed in more detail with respect to  FIG. 3 . The electromagnet  26  is coupled to a slide assembly  28  via a slide assembly adaptor plate  31 . A first manual slide  34  is coupled to the slide assembly adaptor plate  31 . The first manual slide  34  allows an operator to position the head assembly  30  after the disclosed apparatus  22  has been attached to a surface, such as the hub  14 , via the electromagnet  26 . A second manual slide  38  is operatively coupled to the first manual slide  34  and may be configured to provide perpendicular translation of the head assembly  30  with respect to the first manual slide  34 . The second slide  38  is operatively coupled to a mini tilt and swivel vice  42 . The slide assembly  28  comprises: the first manual slide  34 ; the second manual slide  38 ; and the mini tilt and swivel vice  42 . The mini tilt and swivel vice  42  allows for rotation of the head assembly  30  in both directions illustrated by the curved arrow  46 . The mini tilt and swivel vice  42  allows for rotation of the head assembly  30  in the direction of the curved arrow  46 . The mini tilt and swivel vice  42  also allows for a angular tilting of the head assembly  30 , this angular tilting is represented by the arrow  50 . Although manual slides and mini tilt and swivel vices are discussed in this embodiment, it should be understood that any mechanism that allows for the positioning of the head assembly  30  relative to a surface or area to be drilled would be equivalents that may be used in various embodiments of the disclosed apparatus. 
       FIG. 3  shows a close up perspective view of an embodiment of the head assembly  30 . In this document the term “discharge machining” shall refer to both EDM and ECDM when used with respect to the head assembly  30 . A head assembly adaptor plate  54  is used for coupling the head assembly to the mini tilt and swivel vice  42  shown in  FIG. 2 . Fixedly coupled to the head assembly adaptor plate  54  is a servo-controlled drill slide  58 . Fixedly coupled to the servo-controlled drill slide  58  is a manual positioning slide with lock in drill direction  62 . The manual position slide  62 , the first manual slide  34 , the second manual slide  38 , and the mini tilt and swivel vise  42  provide the  5  axes of adjustment for the disclosed apparatus. Fixedly coupled to the manual position slide  62  is a spindle bearing block and manifold  66 . Rotateably coupled to the spindle bearing block and manifold  66  is a drill spindle  68 . The drill spindle  68  may be adapted from a commercially available straight shank collet chuck. Fixedly coupled to the drill spindle  68  is a drill electrode  70 . Currently available EDM and ECDM tools drill holes that are about 6 mm, which may not be large enough to drill out various hardware such as pins and screws. In one embodiment of the disclosed apparatus, the drill electrode  70  is sized to drill holes of around 12 mm. In one ECDM embodiment, the spindle bearing block and manifold  66  contains electrolyte, (common tap water can be used in this case), and the manifold is in fluid communication with the drill spindle  68 . The drill spindle  68  is in fluid communication with the drill electrode  70  which is hollow. The manifold  66  supplies the drill electrode with the necessary electrolyte for the ECDM process. In another embodiment, the head assembly may be configured for an EDM process, and the manifold in that case would contain a dielectric, which would be supplied to the hollow drill electrode  70 . Coupled to the drill spindle  68  is an electric brush holder  74 . The brush holder  74  provides a voltage to the drill spindle  68  and drill electrode  70 . An electrical power supply, not shown, will be in communication with the brush holder  74  when the apparatus  22  is in operation. When the drill electrode  70  is sized for drilling holes of about 12 mm, the use of the brush holder  74  allows for a greater amount of current to reach the electrode. Attached to the spindle bearing block and manifold for electrolyte  66  is a spindle motor  78 . The spindle motor  78  transmits power to rotate the drill spindle  68  and the attached drill electrode  70  via a transmission means  82 . The transmission means  82  may be, but is not limited to, a pulley and belt system, a gear system or a direct coupling. Fixedly coupled to the head assembly adaptor plate  54  is a servomotor  86  that transmits translational movement to the servo-controlled drill slide  58  via a transmission means  90 . The transmission means  90  may be, but is not limited to, a pulley and belt system, a gear system or a direct coupling. The servomotor  86  receives a signal proportional to the current supplied to the drill electrode  70 . Based on the current signal, the servomotor will move the servo-controlled drill slide  58 . The servo-controlled drill slide  58  will back-out the drill electrode  70  from the work piece if a short circuit condition between the drill electrode  70  and work piece is indicated by the current signal. This backing-out protects the drill electrode  70  from being welded to the work piece. 
     The head assembly  30  described with respect to  FIG. 3  has been arranged to minimize its size to allow for its use in small confined spaces, such as between two hubs  14 , 18  of a turbomachine. In one embodiment, the length of the head assembly shown in  FIG. 3  is 9.6 inches, the width is 6.5 inches and the height is 5.5 inches. Thus, this embodiment of the disclosed apparatus  22  can be used in the confined space between two hubs of a turbomachine shown in  FIG. 1 , where the hubs are only 10 inches apart. This is especially useful for drilling out stator blade pins. However, the disclosed apparatus  22  may be used anywhere where ECDM or EDM would be useful, especially in small confined spaces. This head assembly  30  may also be used for on-site drilling of holes for Non Destructive Evaluation Procedure as well as Notch Cross Key removal. In another embodiment, the head assembly may be configured with smaller components to be about one half the size of the embodiment described above. 
       FIG. 4  shows another aspect of an embodiment of the disclosed apparatus. A guide bushing  94  is shown attached to a work piece, in this example hub  14 , via a bushing holder  98 . In one embodiment, the bushing holder may be any of number of commercially available magnetic bases. The guide bushing  94  guides the drill electrode  70  to a specified area on a work piece, in this example an area on a hub  14 . The guide bushing  94  has an insulated annulus  102  that can come into contact with the drill electrode  70  without short circuiting current from the drill electrode  70 . A guide bushing may be necessary when the drill electrode  70  is of such a length that the end of the drill electrode wobbles, causing an imprecise machining. 
     The disclosed apparatus  22  may be configured to couple to a multi-axis robot arm to perform ECDM or EDM in many versatile orientations, including vertical, horizontal, and angles in between. The non-traditional discharge machining apparatus  22  may couple to such a robot arm via the slide assembly adaptor plate  31  or head assembly adaptor plate  54 . 
     In one embodiment of the disclosed apparatus, the servo-motor  86  may be a Panasonic servomotor, model number MSMA042A1A. The servo-controlled drill slide  58  may be a Deltron Slides model number LS 2 - 4 . The spindle motor  78  may be a Micro-Drives motor, model number MD2230. The manual position slide with lock in drill direction  62  may be a may be a Velmex Unislide model number ZA2506A-S2 — BK-TSL. The power supplied to the disclosed apparatus may be up to a maximum input power of about 120 kVA, with a maximum working current of about 120 A and an output voltage of about 80–250V. The fluid delivery system be at a maximum pressure of about 5 MPa (725 psi). The output power may be pulsed. The disclosed apparatus has the advantage of allowing the operation of a EDM or ECDM apparatus in a confined space. Additionally, the disclosed apparatus is portable, that is, the apparatus can be moved to the work piece. The disclosed apparatus may have 5 axes of adjustment so that the axis of the drill electrode may be accurately aligned with the work piece. Misalignment may cause damage to the work piece, for example, a work piece may be a steam turbine rotor, which is a very expensive piece of equipment. The disclosed apparatus has very little to no mechanical drilling force. Relatively high drilling forces, such as those in a mechanical drill, may cause a drill to deviate from a straight path due to non-uniformity of the work-piece material or the uneven geometry of the drill, causing damage to work piece. The EDM and ECDM processes are independent of the hardness of the work-piece, therefore the drilling speed is predictable. Also, the disclosed apparatus may be attached to a surface via an electromagnet. The work piece surface can be at any angle because the disclosed apparatus can be attached to the surface via the electromagnet. In addition, the disclosed apparatus can drill holes up to about 12 mm in diameter. 
     While the embodiments of the disclosed method and apparatus have been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the embodiments of the disclosed method and apparatus. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the embodiments of the disclosed method and apparatus without departing from the essential scope thereof. Therefore, it is intended that the embodiments of the disclosed method and apparatus not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the embodiments of the disclosed method and apparatus, but that the embodiments of the disclosed method and apparatus will include all embodiments falling within the scope of the appended claims.