Abstract:
A method involves creating a recess in a surface of a part so the recess is adjacent a portion of the part, thereafter forming a coating on the surface of the part with a portion of the coating being disposed in the recess, and thereafter removing material of the portion of the part with a tool. According to a different aspect, an apparatus includes a recess-forming section that forms a recess in a surface of a part so the recess is adjacent a portion of the part, a coating section that forms a coating on the surface of the part with a portion of the coating disposed in the recess, and a material-removing section that subsequently removes material of the portion of the part with a tool.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to techniques for cutting a part with a coating thereon and, more particularly, to techniques for cutting the part while avoiding undesirable damage to the coating. 
     BACKGROUND 
     There is often a need to cut a part that includes a substrate with a coating thereon. One example is an optical component having a substrate such as a lens, with a coating on one or both side surfaces of the lens. The coating may be an antireflective (AR) coating, a filter coating that passes some wavelengths and reflects other wavelengths, or a protective coating that helps avoid scratches or other physical damage to the substrate. Sometimes the substrate can be cut before it is coated, but this is not always possible, and in some cases it is not cost-effective to cut the substrate and then coat it. Consequently, it is sometimes necessary to cut the part at a point in time after the coating has been applied to the substrate. 
     A common problem is that the coating is often mechanically tougher than the substrate, and will tend to hold together and pull away from the substrate, rather than remain bonded to the substrate and be cut apart. For example, where a hole is to be drilled through a part, the drill first makes contact with the coating. The drill exerts not only a downward force on the coating, but also a twisting force. In some cases, the coating will hold together despite the force, and an irregular portion significantly larger than the intended hole will be pulled off the substrate. Alternatively, when a coating is cut with a saw, the coating will be pulled sideways where the saw contacts the coating, and irregular portions of the coating can be pulled off the substrate. Sometimes the damage is sufficiently significant that the part must be scrapped, thereby reducing the effective yield of the manufacturing process, and increasing the average cost per completed part. Consequently, while existing cutting techniques have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is diagrammatic sectional view showing a conventional optical component that includes a substrate with a coating on one side thereof. 
         FIG. 2  is diagrammatic view, partially in section, showing an apparatus that embodies aspects of the invention, and that includes a diamond point turning (DPT) machine, and the substrate of  FIG. 1  before formation of the coating. 
         FIG. 3  is a diagrammatic view, partly in section, showing a coating machine, a cutting machine, and also the substrate of  FIG. 2  with the coating formed thereon. 
         FIG. 4  is a diagrammatic sectional side view of the optical component, after the cutting machine of  FIG. 3  has made a cut that has the effect of splitting the optical component into two physically separate portions. 
         FIG. 5  is a diagrammatic view, partly in section, that is similar to  FIG. 2  but that relates to a different way of cutting the optical component. 
         FIG. 6  is a diagrammatic view, partly in section, showing the substrate of  FIG. 5  with the coating thereon, and also showing the cutting machine. 
         FIG. 7  is a diagrammatic sectional side view showing the optical component of  FIG. 6  after the cutting machine has cut the substrate in a manner that has the effect of splitting the optical component into two physically separate portions. 
         FIG. 8  is a diagrammatic view, partly in section, that is similar to  FIG. 2 , but that relates to yet another type of cut that can be made in the substrate. 
         FIG. 9  is a diagrammatic view, partly in section, showing the substrate of  FIG. 8  with the coating thereon, and also showing a drilling machine. 
         FIG. 10  is a diagrammatic sectional side view of the optical component of  FIG. 8 , after a hole has been drilled therethrough by the drilling machine. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is diagrammatic sectional view showing a conventional optical component  11 . The drawings do not show all subject matter to scale, and in fact some characteristics are intentionally shown without proper scale for increased clarity. 
     The optical component  11  has an optical axis  17 , a substrate  18 , and a coating  19  on one side surface of the substrate  18 . The substrate  18  is an optical lens made of a refractory material. The coating  19  may be any of a variety of different types of coatings that are known in the art, including but not limited to an antireflective (AR) coating, a filter coating that passes selected wavelengths and reflects other wavelengths, or a protective coating that is made of a material harder than the material of the lens  18 , and that helps avoid scratches or other physical damage to the lens  18 . The coating may be a single layer of one material, or may include multiple layers made of different materials. 
     During fabrication of the optical component  11 , at a point in time after the coating  19  has been applied to the lens  18 , the fabrication process may require that the lens  18  be cut, which also means that the coating  19  thereon must be cut. As one example, assume that the optical component  11  is to have a final diameter  26 , such that a cut needs to be made along a cylindrical path  31  that is concentric to the axis  17 . In other words, the annular portion of the component  11  that is disposed radially outwardly of the cylindrical path  31  will be cut off and discarded. 
     When attempting to make such a cut using conventional techniques, a common problem is that the coating  19  may suffer undesirable damage. In this regard, the coating  19  will often be made from a material that is mechanically tougher than the substrate  18 , for example where the coating is a protective coating provided to physically protect the substrate. Accordingly, when an attempt is made to cut through the coating, the coating will often tend to hold together rather than be easily cut, such that relatively large sections of the coating may be pulled off the substrate  18 . That is, a cutting operation will often cause damage to the coating that extends well beyond the specific point of impact of the cutting tool. This is even more pronounced where the entire cut is spaced inwardly from edges of the part, as opposed to a cut that begins at an edge of the part. In  FIG. 1 , this means that significant portions of the coating  19  located within the diameter  26  could be pulled off the substrate  18 . One aspect of the present invention is the provision of a technique that minimizes or avoids this type of damage. 
       FIG. 2  is diagrammatic view, partially in section, showing an apparatus  10  that embodies aspects of the invention, and that includes the lens  18  of  FIG. 1  before formation of the coating  19 , and a diamond point turning (DPT) machine  13 . The DPT machine  13  is a conventional device, and includes a DPT tool  14 . Before the substrate  18  is cut, and before the coating  19  is formed, a recess is created in the substrate where the substrate will be cut. In the specific example of  FIG. 2 , the recess is an annular groove  51  that is approximately radially aligned with the cylindrical path  31  of the intended cut. The DPT machine  13  is used to create this groove  51 . However, it would alternatively be possible to use any other suitable type of equipment to create the groove. The DPT machine  13  includes a part support and part movement section  36  that supports the optical component  11 , and that also rotates the optical component about the optical axis  17 . The DPT machine  13  also includes a tool control section  38  that effects movement of the DPT tool  14  in relation to the optical component  11 . In particular, the tool control section  38  can selectively move the tool  14  both axially and radially with respect to the axis  17 . 
       FIG. 3  is a diagrammatic view, partly in section, showing a coating machine  55  and a cutting machine  56 , and also showing the optical component  11  with the coating  19  formed thereon. More specifically, after the groove  51  is created, the coating  19  is formed on the top surface of the substrate  18  by the coating machine  55 . The coating machine  55  is conventional, and therefore not shown and described here in detail. In  FIG. 2 , the groove  51  is formed with a depth that is greater than the thickness of the coating  19 . Thus, a portion  19 A of the coating  19  is disposed in the bottom of the groove  51 , but is not in contact with the remainder of the coating  19  that is on the top surface of the substrate  18 . Alternatively, however, the groove  51  could be shallower, such that the portion  19 A of the coating  19  is in contact with the remainder of the coating, but still defines a discontinuity in the coating. The portion of the coating  19  that is within the diameter  26  has a radially-outwardly facing edge surface  58  thereon. 
     The cutting machine  56  of  FIG. 3  is conventional, and includes a part support and part movement section  61  that supports the optical component  11 , and that rotates the optical component  11  about the optical axis  17 . The cutting machine also includes a tool  62 , and a tool control section  63  that can move the cutting tool  62  in directions parallel to the axis  17  with respect to the optical component  11 . Due to the physical width of the tool  62 , the cutting operation will remove an annular portion of the optical component  11  that is disposed between the cylindrical path  31  and a further cylindrical path  71 , where the path  71  is concentric to and disposed radially outwardly of the path  31 . In  FIG. 3 , it will be noted that the tool  62  is positioned radially so that, as it is moved downwardly to make the cut, it will not engage the edge surface  58  on the portion of coating  19  within the diameter  26 . 
       FIG. 4  is a diagrammatic sectional side view of the optical component  11 , after the cutting machine  56  of  FIG. 3  has made the cut discussed above, which has the effect of splitting the optical component  11  into two physically separate portions. The resulting annular outer portion of the optical component  11  will be discarded, and the resulting central portion of the optical component within the diameter  26  will be retained and utilized. Most or all of the portion  19 A of the coating  19  disposed within the groove  51  has been stripped away during the cutting operation. But the portion of the coating  19  on the central portion of the substrate  18  has experienced no significant physical damage, especially along its edge surface  58 . 
       FIG. 5  is a diagrammatic view, partly in section, that is similar to  FIG. 2  but that relates to a different way of cutting the optical component  11 . In more detail,  FIG. 5  shows the same substrate  18  that was shown in  FIG. 2 , but in this case a cylindrical hole with a diameter  126  is to be created in the center of the substrate, in particular by making a cut along a cylindrical path  131 . The portion of the substrate  18  disposed radially inwardly of the cylindrical path  131  will be discarded, and the portion of the substrate disposed radially outwardly of the path  131  will be retained and utilized. The DPT machine  13  is used to create an annular groove  151  that is centered above the cylindrical path  131 . 
       FIG. 6  is a diagrammatic view, partly in section, that is similar to  FIG. 5 , but shows the substrate  18  with the coating  19  formed thereon, and also shows the cutting machine  56 . More specifically, after the groove  51  has been formed, the coating  19  is formed on the top surface of the substrate  18 . In  FIG. 2 , the groove  151  is formed with a depth that is greater than the thickness of the coating  19 . Thus, a portion  19 A of the coating  19  is disposed in the bottom of the groove  151 , but is not in contact with the remainder of the coating  19  that is on the top surface of the substrate  18 . Alternatively, however, the groove  151  could be shallower, such that the portion  19 A of the coating  19  is in contact with the remainder of the coating, but still defines a discontinuity in the coating. The portion of the coating  19  that is within the diameter  26  has a radially-inwardly facing edge surface  158  thereon. 
     Next, the tool  62  of the cutting machine  56  is used to cut the substrate  18 . Due to the physical width of the tool  62 , this cutting operation will remove a portion of the optical component  11  disposed between the cylindrical path  131  and a further cylindrical path  171  that is concentric to and disposed radially inwardly of the path  131 . The tool  62  is positioned radially so that, as it is moved downwardly to make this cut, it will not engage the edge surface  158  on the portion of coating  19  disposed radially outwardly of the path  131 . 
       FIG. 7  is a diagrammatic sectional side view showing the optical component  11  after the tool  62  has cut the substrate  18  in the manner discussed above in association with  FIG. 6 , which has the effect of splitting the optical component  11  into two physically separate portions. The central portion of the optical component  11  that is within the diameter  126  will be removed and discarded, and the annular outer portion of the optical component  11  will be retained and utilized. Most or all of the portion  19 A of the coating  19  disposed within the groove  151  has been stripped away during the cutting operation. But the annular portion of coating  19  that is on the annular outer portion of the optical component  11  has not experienced any significant damage during the cutting process, especially in the radially inner region thereof along the edge surface  158 . 
     The embodiments shown in  FIGS. 1-8  and discussed above each involve a cut that happens to follow a circular path, but this is merely exemplary. The cut could follow paths having any of a variety of other shapes, including but not limited to a straight line, or a regular polygon such as a rectangle or an octagon. Moreover, the cut does not necessarily have to follow a path, but could for example involve some other type of cut such as drilling of a hole, one example of which is discussed below. 
     In this regard,  FIG. 8  is a diagrammatic view, partly in section, that shows the uncut substrate  18  and the DPT machine  13  of  FIG. 2 , but that relates to yet another type of cut that can be made in the substrate  18 . More specifically, a hole of diameter  226  is to be made through the center of the substrate, where the diameter  226  is significantly smaller than the diameter  126  discussed above in association with  FIGS. 4-6 . In this case, rather than an annular groove, the DPT tool  14  of the machine  13  is used to create a circular recess  252  having a diameter that is slightly greater than the diameter  226 . The circular recess  252  is concentric to the optical axis  17 . In effect, the optical component  11  will be cut along a cylindrical path  231 . 
       FIG. 9  is a diagrammatic view, partly in section, showing the substrate  18  with the coating  19  formed thereon, and showing a drilling machine  256 . More specifically, after the circular recess  252  has been formed, the coating  19  is formed on the top surface of the substrate  18 . In  FIG. 2 , the recess  252  is formed with a depth that is greater than the thickness of the coating  19 . Thus, a portion  19 A of the coating  19  is disposed in the bottom of the recess  252 , but is not in contact with the remainder of the coating  19  that is on the top surface of the substrate  18 . Alternatively, however, the recess  252  could be shallower, such that the portion  19 A of the coating  19  is in contact with the remainder of the coating, but still defines a discontinuity in the coating. The portion of the coating  19  that is within the diameter  26  has a radially-inwardly facing edge surface  258  thereon. 
     The drilling machine  256  is conventional, and includes a part support section  261  that stationarily supports the optical component  11 . The drilling machine  256  also includes a tool in the form of a bit drill  262  with a diameter equal to the diameter  226 , and a tool control section  263  that can rotate the drill bit  262 , while moving the drill parallel to the axis  17 . The drill bit  262  is used to drill a hole through the substrate  18 . Since the recess  252  has a diameter that is slightly larger than the diameter of the drill bit  262 , the drill bit does not contact the edge surface  258  on the coating  19  as the drill creates the hole through substrate  18 . 
       FIG. 10  is a diagrammatic sectional side view of the optical component  11  of  FIGS. 8 and 9 , after a hole has been drilled therethrough by the drill bit  262  of the drilling machine  256 . The drilling operation has removed the portion of the optical component  11  disposed radially inwardly of the diameter  226 , leaving an annular outer portion that is retained and utilized. The portion of the coating  19  on this annular outer portion is substantially free of damage, especially in the region of the annular edge surface  258 . Most or all of the portion  19 A of the coating  19  disposed within the recess  252  has been stripped away during the cutting operation. 
     Although selected embodiments have been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.