Abstract:
A miniature machine tool for micro-machining is capable of performing on a workpiece at least one conventional mechanical machining operation and another micro-machining operation such as electrochemical machining (ECM), electro deposit machining (EDM), micro-milling or micro-turning or micro-drilling. The machine tool includes a holder in which the workpiece is clamped during all successive machining operations so that the machining operations may be performed in succession without intervening reclamping of the workpiece. This increases dimensional accuracy when micro-machining high-precision components.

Description:
BACKGROUND OF THE INVENTION 
     a) Field of the Invention 
     This invention relates to a new or improved compound fabrication process and apparatus therefor, and in particular to the development of a miniature machine tool for manufacture of micro, high precision components. 
     b) Description of the Prior Art 
     In general, conventional machine tools are used to manufacture micro components. Usually the manufacture of such micro components requires multiple machining processes such as micro Electrode Discharge Machining (EDM), micro Electro Chemical Machining (ECM), micro milling, micro turning and micro drilling. Therefore to manufacture a simple part may entail use of more than one machine, depending on the geometry of the workpiece. For example to machine a micron sized hole in a workpiece one may have to first machine an electrode using turning, milling or other processes. The machined electrode will have to be placed in the spindle of an EDM machine to machine the micron-sized hole. During this process, if the electrode is not properly aligned on the spindle with respect to the workpiece there is a possibility of producing an inaccurate hole because of the set-up and machine errors. The prior art does not address the problem of combining multiple processes on a single set-up, but is confined to simple single process machines such as those disclosed in U.S. Pat. No. 3,998,127, U.S. Pat. No. 5,439,431, U.S. Pat. No. 4,706,371, U.S. Pat. No. 4,646,422, U.S. Pat. No. 5,117,552. 
     The above mentioned references do not cover any method or means for combining conventional processes such as milling, turning, etc. with non-conventional processes such as Electrode Discharge Machining or Electro Chemical Machining. Therefore when conventional and non-conventional processes must be applied in succession there arises the possibility of inaccuracies in alignment of workpieces due to the fact that they have to be repositioned for conventional and non-conventional machining. These problems are particularly acute in the case of micro machining where the dimensional tolerances are very small. To minimize such inaccuracies, the present inventors have appreciated that it would be desirable to perform multiple manufacturing or fabrication processes in a single machine and thus avoid the manufacturing inaccuracies which are inherent in multi-stage processing operations. 
     SUMMARY OF THE INVENTION 
     The objective of the invention is to provide an improved fabrication process and apparatus through which multiple manufacturing steps can be performed on a single platform without re-gripping of the workpiece so that very significant improvements can achieved in terms of the dimensional accuracy of the workpiece being produced. 
     The invention provides a miniature machine tool for performing on a workpiece at least one conventional mechanical machining operation and at least another machining operation selected from electrochemical machining (ECM) and electro deposit machining (EDM); said machine tool including a holder in which said workpiece is clamped during said machining operations; wherein said machine tool is configured to perform said machining operations in succession without intervening reclamping of the workpiece. 
     For example the machine can be a micro scale universal milling machine in which various conventional forming operations such as turning, milling, drilling, shaping polishing and grinding can be performed as is known, and wherein it is also possible to perform non-conventional machining processes such as Electro Discharge Machining and Electro Chemical Machining. For example the machine tool can be used to manufacture an electrode by known mechanical material removing processes and then used carry out a micro Electro Discharge Machining operation with the electrode. The equipment can also be used to carry out Electro Chemical Machining operations on milled or turned workpieces, or to perform electro discharge manufacturing on workpieces to improve surface finish and accuracy. No machine in the prior art has the capability to perform all the above listed steps on a workpiece. 
     A preferred apparatus for carrying out the invention comprises a miniature universal milling machine having a machine frame formed by a gantry structure having two spaced vertical pillars connected at their upper ends by a crosshead beam which supports a carriage on which tooling such as a universal milling head can be adjusted horizontally and vertically. A machine bed positioned in a lower part is arranged to be adjustable in a horizontal plane and also vertically. The machine is capable of supporting various driven spindles which can carry tools for performing milling, drilling, grinding etc. operations. 
     The invention also provides a method of fabricating a workpiece in a miniature machine tool as described above, the method comprising the steps of: providing a workpiece blank and clamping said workpiece blank in said holder; performing a first conventional mechanical machining operation on said workpiece blank; and without re-gripping of said workpiece blank performing a second machining operation therewith, said second machining operation being selected from ECM and EDM. 
     Typically the conventional mechanical machining operation will be performed on the workpiece first followed by the second machining operation involving ECM or EDM, but in principle the order of these operations could be reversed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The invention will further be described, by way of example only, with reference to the accompanying drawings wherein: 
         FIG. 1  is a somewhat schematic front elevation of a miniature machine tool equipped for carrying out the method of the present invention; 
         FIG. 2  is a right side elevation of the machine tool of  FIG. 1 ; 
         FIG. 3  is a front elevation of the machine tool illustrating a different tooling configuration; 
         FIG. 4  is a right side elevation corresponding to  FIG. 3 ; 
         FIG. 5  illustrates three further tooling configurations which can be used in the machine tool; 
         FIGS. 6 ,  7 ,  8  and  9  are schematic views illustrating mechanical machining operations that can be performed in the machine tool of  FIGS. 1  to  4 ; and 
         FIGS. 10 ,  11  and  12  are schematic views illustrating two-stage compound machining operations that can be performed; and 
         FIGS. 13 ,  14  and  15  are views illustrating the manufacture of a component through a series of successive two-stage compound machining operations. 
         FIG. 16  illustrates the wire EDM attachment that can be used in the machine tool of  FIGS. 1  to  4 . 
         FIGS. 17 and 18  illustrate the operation of the numerical control system and how it is integrated to the machine. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , a machine tool  10  in accordance with the invention comprises a base frame  12  upon which is supported a pair of beds  14 ,  16  each of which is independently moveable under a controlled drive system (not shown) to move in the fore-and-aft direction of the machine tool as indicated by the arrow  18  in FIG.  2 . Each of the beds  14  and  16  as will be more fully explained hereafter forms one component of a machining station for carrying out operations on workpieces. 
     Rigidly attached to the base frame  12  are a pair of laterally spaced vertical pillars  20  the upper ends of which are rigidly connected to opposite ends of a horizontal crossbeam  22  which spans the width of the base frame as seen in FIG.  1 . 
     In known manner, the crossbeam provides a horizontal guide for movement of a carriage  24  thereon, this carriage in turn providing guidance for vertical movement of a linear slide  26  therein. The linear slide in turn provides a mounting for various tooling or work gripping components such as the indexing head  28  shown in  FIGS. 1 and 2 . 
     The basic machine tool configuration described above is not disclosed in any detail since it is well understood by those skilled in the art. It will be seen that the indexing head  28  accommodates four replaceable tooling or gripper sets  30  extending at angular intervals of 90° thereon. 
     In known manner the machine tool includes drive means selectively engageable to apply a powered drive for rotation of a selected one of the tooling sets/grippers  30  when it is desired to perform a mechanical machining process on a workpiece. As is known in such machine tools, the mechanical machining process can be selected from drilling, milling, shaping, turning, grinding, and polishing. 
     In the machine tool as illustrated in  FIG. 3 , the indexing head  28  is replaced by a drill head  32 , and depending upon the requirements it could equally well be replaced by the components shown in  FIG. 5  namely (a) a milling head  34 , (b) a polishing head  36 , or (c) a grinding head  38 . 
       FIG. 1  shows the machine tool  10  configured to perform in succession a turning operation and an EDM or ECM operation. In this set-up the downwardly directed tool holder  30  is configured to grip an electrode workpiece  64  in a power driven rotatable holder  40  to be machined by turning, metal removal being performed by a cutting tool  41  held in a tool mount  42  carried on the bed  16 . By suitable manipulation of the relative positions of the electrode workpiece  64  and the tool mount  42 , a required turning operation can be performed on the electrode workpiece  64  as it is rotated by the holder  40 . Thereafter, while still engaged within the holder  40 , the electrode workpiece  64  can be transferred to the location of a tank  44  (carried on the left hand bed  14  as seen in  FIG. 1 ) for the performance therein of an EDM or an ECM operation. The workpiece to be machined by EDM or ECM is placed in the tank  44  and the electrode workpiece  64  is used for machining the workpiece in tank  44 . Separate tanks are used for EDM and ECM operations. For EDM operation, the tank  44  is filled with dielectric medium whereas for ECM operations the ECM tank  44  will be filled with electrolyte. The use of two different delivery systems avoids the possibility of cross contamination. 
       FIG. 3  shows the machine tool  10  set up to perform a micro milling operation on the workpiece. The milling tool is held in a gripper  35  that is mounted on the linear slide  26 , the workpiece then being brought into the vicinity of the milling tool  37  held in the milling head, the relative positions of the tool  37  and the workpiece W being manipulated as the workpiece is rotated to effect the desired milling operation. 
       FIG. 6  shows an alternative machining operation wherein the rotating spindle  46  carries the workpiece for machining by the tool  41 . 
       FIG. 8  shows the rotating spindle  46  carrying a grinding wheel  50  for performing a grinding operation on the stationary workpiece W. 
       FIG. 9  shows the rotating spindle  46  carrying a polishing tool  52  for performing a polishing operation on the workpiece W. 
       FIG. 10  illustrates two operations to effect hybrid machining for forming micro holes. In  FIG. 10   a  the electrode workpiece  64  held in the driven spindle  46  is machined by the turning tool  41  to produce an electrode  54 . In a subsequent step as indicated in  FIG. 10   b  the electrode  54  is then used in a micro EDM operation to produce a hole in a workpiece W. 
       FIG. 11  illustrates a milling tool  48  held in the driven spindle  46  and manipulate to cut a desired profile in an electrode  56 . The electrode is then inverted as shown in  FIG. 11   b  and used in an EDM process to shape the workpiece W. 
     As shown in  FIG. 12   a  the spindle  46  first holds an electrode  58  used in an EDM process to act upon a workpiece W. In a subsequent operation as shown in  FIG. 12   b  the workpiece is further processed in an ECM operation by an electrode  60 . 
     The hybrid machining operations described in the foregoing in relation to the apparatus shown in the drawings provide the main advantage that they enable the machining of micro components of great accuracy without changing the machine set up. For example an electrode machined by micro turning or micro milling can be further processed by micro ECM (electrical chemical machining) to improve its surface smoothness and dimensional accuracy, and this same electrode can then be used in a micro EDM operation to reconfigure functional components. In these means errors which could otherwise arise due to clamping or set up tolerances can be eliminated. 
     It will be appreciated that various other hybrid micro machining operations can be performed by combining selected operations to ensure that workpieces are produced with improved dimensional accuracy. For examples  FIGS. 13 ,  14  and  15  illustrate successive steps in a hybrid machining process for producing in a workpiece W a mould cavity configuration as shown in the right hand view of FIG.  15 . Initially, as shown in  FIG. 13  a turning tool  41  is employed to produce the desired dimensions of an electrode  64  that is rotated in the driven spindle  46 . Thereafter this electrode  64  is employed to produce in the workpiece W a preliminary cavity  61   a  corresponding to the profile of the electrode. 
     Subsequently, as shown in  FIG. 14 , without removing the electrode  64  from the spindle  46 , the lower end of the electrode is rounded as at  64   a  by the turning tool  41 , where after the spindle  46  is used to transfer the modified electrode to produce by an EDM process rounded depressions  65  providing a modified recess  61   b  in the workpiece W. 
     In a further stage as shown in  FIG. 15  the turning tool  41  is again used to reconfigure the electrode  64  to provide a small diameter extension  67 . This extension  67  is then used as shown in the right hand part of  FIG. 15  to produce by an ECM process a central hole through the workpiece W. 
     As depicted in  FIG. 16 , a portable wire EDM  100  can be attached to the spindle  46 . The wire EDM  100  is driven by a motor which makes the wire move around. The attachment can be tilted to any angle in order to produce slots of any angle. One such arrangement to produce a slot using the wire EDM attachment is shown in FIG.  16 . 
     Movements of the various components of the machine tool are driven under a program provided by a central processing unit connected to a numerically controlled system which can be designed to carry out various hybrid machining processes in predetermined combinations.  FIGS. 17 and 18  are flow-charts showing the system logic for numerically controlled machining. 
     Briefly stated, the machine tool and the processes described above deliver at least the following advantages:
     1. By virtue of the gantry structure of the micro machine tool the stability of the various components in the machine is enhanced and the dimensional accuracy of resulting workpieces is therefore improved.   2. The described system provides the capability to machine micro components using conventional and non-conventional hybrid machining processes which can include two or more of the following: micro milling; micro turning; micro EDM; micro ECM; micro polishing; and micro grinding, all performed on the same machine tool.   3. The system provides the capability of manufacturing non-cylindrical EDM and/or ECM electrodes in the single tool.   4. The system provides the capability of using EDM or ECM electrodes produced therein without changing the machine set up.   5. The system provides the capability of performing wire cut EDM using a portable attachment.