Abstract:
A system and method for trepanning holes into a work piece as relative movement between the work piece and a pulsed laser occurs. As a cylindrical work piece rotates for example, a position controlled pulse laser fires a first series of timed pulses. During each subsequent rotation of said work piece another series of pulses is fired such that the periphery of a row of identical holes is cut into the cylindrical work piece.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to laser cutting of holes, and more particularly to apparatus and methods to trepan a plurality of holes into a cylindrical work surface. 
     It is common practice to use computer targeted lasers to drill holes into metal surfaces. Lasers are particularly useful in drilling holes into alloys of metal that are particularly tough to machine. One application is in aircraft turbine engines where multiple small diameter holes must be drilled, often at an angle, into tough alloy material. 
     U.S. Pat. No. 6,130,405 shows one prior art method of drilling holes using a laser. In the method of this patent the work piece is continuously rotated and a computer controlled laser punches holes into the work piece. Laser pulses are timed with the rotation of the work piece such that a row of spaced holes are created. U.S. Pat. No. 6,130,405 is limited to creating holes having a diameter equal to the diameter of the laser beam. This technique is useful in creating holes having a diameter in the range of 0.01 to 0.03 inches. However many of the holes required are going to have a larger diameter than is possible to cut with this method. 
     Another prior art example of laser cutting holes in a cylindrical work piece is U.S. Pat. No. 4,952,789 to Suttie. In the Suttie device, a laser L is used to cut a plurality of holes in a cylindrical work surface. Again, the diameter of the holes laser drilled in the work piece is determined by the diameter of the laser beam used for drilling. 
     U.S. Pat. No. 5,223,692 to Lozier et al. discloses a method of laser trepanning that can be used to cut a hole in a work piece having a diameter larger then the diameter of the laser beam. While the method of Lozier can be used to cut a larger diameter hole, it is very slow to use in applications where 100 or more holes can be spaced out in a row around a cylindrical work piece. 
     As can be seen, there is a need for an improved method and system of drilling holes in a cylindrical work surface using a laser. There is a need for a system and method that will allow for rapid cutting of holes having a diameter larger then the diameter of the laser beam used to cut the holes. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, there is continuous movement between a work piece and a pulsed laser that sequentially trepans a plurality of holes arranged around the work piece. Each hole to be cut in the work piece is larger then the diameter of the laser beam, and requires a sequence of laser pulses targeted at its periphery to complete the hole. 
     In another aspect of the invention, a first series of small trepan cuts are made into the work piece, the laser is then targeted to the next trepan position and a second series of trepan cuts are made. The cuts in the first and second series of cuts are connected to form a portion of the periphery of a series of holes to be cut. Targeting to the next trepan position is done while the work piece continues to rotate from the last hole in the row back to the first hole in the row. 
     In a further aspect of the invention, a sensor detects that the cylindrical work piece is properly positioned relative to said laser prior to each laser pulse. 
     In a still further aspect of the invention, a programmable controller is used in a method to set the characteristics of the series of holes to be cut into the cylindrical work piece. Programmable steps include setting the hole angle, hole diameter, and number of holes to be cut. A hole can be cut normal to the surface of the cylindrical work piece, or a hole can be cut at an angle to the normal. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of the system in use on a piece part; 
     FIG. 2 shows enlarged view of a portion of the piece part and; 
     FIG. 3 shows the process flow chart. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     In laser drilling a row of holes into a cylindrical work piece it is desirable to be able to drill the holes as rapidly as possible to minimize the time required to manufacture the work piece. 
     Referring now to the Figures, FIG. 1 shows a view, of the laser cutting system  10  in use on a cylindrical work piece  100 . The cylindrical work piece  100  can be constantly rotated on table  12  as indicated by arrow R. As the cylindrical work piece  100  rotates, the laser power supply  14  can send a laser pulse  16  of laser energy through laser lens  20  when laser shutter  18  is open. A number of partially cut holes,  101 ,  102 , can be formed in a row evenly spaced around the periphery of the cylindrical work piece  100 . Although holes are normally evenly spaced, gaps in this even spacing can be created simply by holding the shutter  18  closed to block some pulses to stop the cutting of some of the holes. The position of the laser lens  20  relative to the cylindrical work piece  100  can be controlled by a computer controller  22 . In addition to rotation, the table  12  can move up and down and to the left and right to control the trepan position of the laser lens  20  relative to the piece part  100 . The controller  22  receives feedback from position sensor  24 . Drive  26  can control the rotation of the table  12  as well as controlling the trepan position through control  22 . 
     FIG. 2 shows details of how the two partially cut holes  101 ,  102  are formed. Dashed lines  101   a  and  102   a  show the trepan path that laser lens  20  will trace out on part  100  as table  12  is moved by controller  22  in forming the partially cut holes  101  and  102 . The arrow R shows the direction of rotation of the cylindrical work piece  100 . A cut  101   d  from a laser pulse  16  has just formed a portion of the periphery of partial hole  101  and the rotation R will carry the cylindrical work piece  100  to position the next cut  102   d , shown in phantom lines, under the laser  20 . 
     FIG. 3 shows the basic steps used in controller  22 . The table  12  can be set to an angle in the set laser angle step  110 . Any angle of hole might be cut using this arrangement, though not shown it would also be possible to set an angle by moving the laser lens  20 . The system  10  can create holes  101 , 102  at any angle relative to the surface of cylindrical work piece  100  including holes angled up or down, left or right or compound angles. Next the number of holes can be set in step  120  and the diameter of the holes can be set in step  130 . The number of cuts  101   b,c,d  and  102   b,c,d  required to complete a hole  101 , 102  can be set in step  140 . A typical hole  101 , 102  might require  36  cuts depending upon the diameter of the hole  101 , 102 . Such a hole  101 , 102  would require  36  rotations of the cylindrical work piece  100  to complete all holes  101 , 102  assuming that each cut  101   b,c,d  and  102   b,c,d  pass clear through the wall thickness of cylindrical work piece  100 . If multiple pulses  16  are required for each cut  101   b,c,d  and  102   b,c,d  then this would multiply the number of rotations required. The coordinates of each trepan position on path  101  a can be calculated. Most holes  101  require just x and y coordinates, though a z component might be required for large holes  101  where focusing of the laser lens  20  might be required. Once the set up steps  110 - 150  are complete the table can begin to rotate in step  160 . A first set of cuts  101   b,   102   b  can be made in the form cuts step  170  and once a set of cuts  101   b,   102   b  are completed then the table  12  can trepan through step  180  to the next cut location  101   c,   102   c  and so on. For thick walled work pieces a plurality of laser pulses  16  can be used for each trepan location; this would require more than one work piece  100  rotation per cut. Step  190  can check to see if all the programmed cuts  101   b,c,d  have been made. If not, the laser cutting system  10  can return to step  170  and perform another set of cuts. Once the holes  101 , 102  are complete, and cuts have been made through the entire path  101   a ,  102   a , then the control sequence can end and the table  12  can shut off and the completed cylindrical work piece can be removed. 
     Because the duration of the laser pulse is very short (typically about 0.5 milliseconds), the table  12  can be rotated at a constant speed in direction R without stopping the table for each pulse. The laser lens  20  can fire evenly timed pulses creating a series of evenly spaced cuts  101   b ,  102   b  around the cylindrical work piece  100 . When the cylindrical work piece  100  completes one rotation, the laser lens  20  can trepan to the next location to make cut  101   c . Once cut  101   c  is made, the cylindrical work piece  100  continues to rotate until cut  102   c  can be made. The cylindrical work piece completes another rotation, the laser lens  20  trepans to make cut  101   d . Ideally the pulse rate of the laser power supply  14  can be constant in timing with the rotation of the table  12 , however the sensor  24  must confirm that the cylindrical work piece  100  is in the correct location prior to each laser pulse  16 . FIG. 2 shows that the cut  101   d  has just been made and that the laser lens  20  can next trepan to make cut  102   d . Thus, in FIG. 1 partial holes  101  are those that have cut  101   d  and partial holes  102  do not have this cut d made yet. As the cylindrical work piece  100  continues to rotate, the laser lens  20 , controlled by controller  22 , will trace out the path  101   a  and complete each partial hole  101 , 102 . 
     It should be understood that the controller  22  could control the laser lens  20  to cut out a variety of shapes other than circles, including ellipses, rectangles, and irregular shapes, and would not be limited to a circular path as shown. Also, it should be understood that the process could be used on any rotatable part including cylinders as disclosed but also flat plates, cones, tori, spheres and others that would be obvious to one skilled in the art. While the process of this invention is most applicable to making holes in metals, it could also be used to make holes in other materials, such as plastics, paper and ceramics. Also, while the table trepans in the example shown, the process would work equally well if the laser lens  20  was moved to the trepan positions instead. Further although a laser having a circular cross sectional pulse has been described, the system would also work with a laser having a pulse with a different cross sectional shape such as square. 
     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.