Abstract:
Apparatus for machining workpiece made of an explosive material, the apparatus including: a drive system and a cutting tool assembly for cutting a workpiece made of an explosive material; an elongate member carried by, and projecting along an axis from, the drive system for holding the workpiece at a machining location while being rotated about the axis by the drive system; and a first shield element interposed between the machining location and the drive system for protecting the drive system against damage in the event of explosion of the workpiece.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/108,864, filed Nov. 17, 1998. 
    
    
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     TATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT The invention was made by, or under contract with, an agency of the U.S. Government, specifically, the U.S. Department of the Army (Picatinny Arsenal)/DAAE 30-97-C-1040. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the machining of explosive materials. 
     In a number of industrial and scientific fields, it is necessary to machine explosive materials, such as those employed for weapon warheads and rocket propellants. In the course of development of a new explosive material, it is necessary to machine the material in a laboratory setting in order to determine whether the material can be safely machined in an industrial manufacturing facility. In accordance with standard safety practices, such experimental machining is carried out under automated or remote control in an enclosure from which personnel are evacuated prior to a machining operation so that there will be no danger of injury or fatalities. 
     However, the experimental machining apparatus itself is of necessity in proximity to the material being machined and will be subject to destruction, or at least costly damage, in the event of an explosion. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to prevent or minimize damage to machining apparatus in the event of explosion of material being machined. 
     A more specific object of the invention is to prevent physical damage to the machining equipment due to explosion shock waves. 
     Another specific object of the invention is to prevent the machining apparatus from experiencing damage caused by dust resulting from an explosion of material being worked on. 
     The above and other objects are achieved, according to the present invention, by an apparatus for machining workpiece made of an explosive material, the apparatus comprising: a drive system and a cutting tool assembly for cutting a workpiece made of an explosive material; an elongate member carried by, and projecting along an axis from, the drive system for holding the workpiece at a machining location while being rotated about the axis by said drive system; and a first shield element interposed between the machining location and the drive system for protecting the drive system against damage in the event of explosion of the workpiece. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a top plan view of one preferred embodiment of apparatus according to the present invention, with several cover components removed. 
     FIG. 2 is a side elevational view of the embodiment shown in FIG.  1 . 
     FIG. 3 is a cross-sectional view along line  3 — 3  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 illustrate one preferred embodiment of machining apparatus according to the invention. 
     The illustrated apparatus includes a machine, such as a programmable lathe, having a drive motor  2 , which may be a variable speed motor, coupled via a gear set  4  to a shaft  6  that is mounted in rotary bearings  8  for rotation about a longitudinal axis  10 . Shaft  6  has an output end that is provided with a chuck, or collet, that may preferably be a quick change collet. 
     The machine further includes a linear actuator  20 , which may be driven by a servomotor. Actuator  20  includes a rod  22  having a free end coupled to a cutting tool assembly. The cutting tool assembly includes a support composed of two slide members  24  and  26  and a connecting plate  28  connected between members  24  and  26 . Each of members  24  and  26  is guided by a respective one of two stationary, horizontally extending rails  30  and  32 . Plate  28  is coupled to rod  22 . In addition, plate  28  carries a tool holder  34  which is constructed in a known manner to carry a cutting tool  36 . 
     All of the components described thus far are conventional in the art and are mounted on a work bench, or table,  40  having a table top  42  which directly supports all of the components of the machining apparatus. 
     Collet  12  is constructed, as is also conventional in the art, to receive and grip an elongate workpiece support member  50 , such as an arbor, or shaft, having a free end to which is secured a workpiece  52 . If desired, workpiece  52  may be supported on the free end of elongate member  50  via a conical nylon collar  54  that offers a larger connection surface with workpiece  52 . According to one common practice in this art, collar  54  may be simply bonded, by any suitable cement, to both the free end of member  50  and to workpiece  52 . 
     In accordance with one feature of the present invention, elongate member  50  is intentionally made of a material which will be easily fractured or disintegrated if workpiece  52  should explode. In addition, it is desirable that elongate member  50  be made of an inexpensive material so that its replacement will not be costly. In accordance with the preferred embodiments of the invention, these results are achieved by making elongate member  50  of wood. Thus, member  50  can be constituted by a commercially available wooden dowel having an appropriate diameter, e.g., 1 inch. In this case, after machining of workpiece  52  has been completed, it can be removed for further machining or use by simply sawing through elongate member  50  or collar  54 . 
     In further accordance with the invention, components  2 ,  4 ,  6 ,  8 ,  10 ,  12 ,  20  and  22  are protected against damage in the event of an explosion by a series of shield elements which are each preferably in the form of steel plates. 
     These shield elements include at least a first shield element  60  that is interposed between, on the one hand, components  2 ,  4 ,  6 ,  8 ,  10 , and  12 , and on the other hand, workpiece  52 , and extends along a vertical plane. Shield element  60  is provided with a single opening through which elongate member  50  may be passed in order to be secured to collet  12 . Preferably, this opening conforms as closely as possible to the cross section of elongate member  50  and member  50  has a circular cross section. 
     In further accordance with the invention, table top  42  may also be constituted by a steel plate to which the lower end of shield element  60  is welded. 
     A second shield element  62  extends along a plane which is orthogonal to both the plane of table top  42  and the main plane of shield element  60  and is interposed between the machining location where workpiece  52  is held and slide members  24  and  26 . Element  62  is welded to element  60  and table top  42  and is provided with an elongated opening, as shown in FIG. 2, to permit passage of tool holder  34  and to permit movement of tool holder  34  and tool  36  parallel to axis  10  during a machining operation. Shield element  62  will act to protect rails  30  and  32  and members  24  and  26  against damage in the event of an explosion. 
     In order to further minimize explosion damage, in further accordance with the invention, tool holder  34  is preferably mounted on connecting plate  28  by means of between two and four shear bolts  66  which extend in a direction perpendicular to the direction in which tool holder  34  extends through the slot in shield element  62 . Shear bolts  66  are constructed, in a manner known in the art, so that if an explosion should occur, the resulting shock wave acting on tool  36  and tool holder  34  will cause these bolts to shear at the interface between tool holder  34  and connecting plate  28 . As a result, damage to plate  28 , slide members  24  and  26  and rails  30  and  32  will be prevented. 
     It may occur that member  50 , because of the material of which it is made, will have a low resistance to bending or breakage in response to machining forces applied by cutting tool  36  to workpiece  52 . In order to prevent such deformation of breakage, and improve the resulting machining accuracy, there is further provided, according to the invention, a bearing  70  containing a ball bearing assembly that includes an inner race through which member  50  extends, preferably with a friction fit. In the illustrated embodiment, bearing  70  is securely mounted to shield element  62 . However, bearing  70  could also, if desired, be mounted on table top  42 . 
     FIG. 3 shows the arrangement of bearing  70  and its relation to elongate member  50  in greater detail. This is a partly cross-sectional view taken along the line  3 — 3  of FIG.  1 . As shown, elongate member  50  fits tightly within an inner race  76  of the ball bearing assembly. This allows member  50  to be given an increased length to increase the distance between workpiece  52  and the machine components while stabilizing the rotational movement of workpiece  52 . Bearing  70  is secured to shield element  62  by screws which will be sheared in the event of an explosion. 
     In further accordance with the invention, components  2 - 12  and  20  are enclosed by a lid  74  that forms, together with an associated portion of table top  40 , a housing for those components. Three sides of lid  74  may, as illustrated, be secured to three associated sides of table top  42 , while the remaining side of lid  74  is secured to shield element  60 . Lid  74  is provided with a coupling  76  for introducing air under pressure into the region enclosed by table top  42 , shield element  60  and lid  74 . This will establish an over pressure in this region from which air can escape only via small gaps, such as those in shield element  60  around rod  22  and/or elongate member  50 . As a result, if workpiece  52  should explode, the resulting explosion debris, which can be in the form of very fine dust particles, will be incapable of entering the enclosure beneath lid  74 , due to the remaining over pressure. Therefore, such dust particles will not reach a location where they can damage any bearing surfaces of the drive system. 
     Finally, according to an optional feature of the invention, there may be provided a third shield element  78 . Shield element  78  is shown in broken lines in FIG.  1  and in solid lines in FIG.  2  and preferably extends from the upper edge of shield element  60  in a forward direction to overly slide members  24  and  26 , connecting plate  28  and tool holder  34 . In addition, shield element  78  lies in a horizontal plane and is secured, as by welding, to the upper horizontal edges of elements  60  and  62 . 
     According to preferred embodiments of the invention, shield elements  60 ,  62  and  78  and table top  42  may each be a plate made of steel, for example, a mild steel, with a thickness of the order of 2 inches. Both the nature of the steel and the thickness of the plates can be varied to satisfy the requirements associated with the explosive force that would be expected from the particular materials to be machined. 
     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 
     The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.