Abstract:
To prevent stereo lithography (SLA) support structures for parts fabricated in an SLA apparatus from interfering with features in the parts, a structural shield such as a dome may be place around the feature and then discarded at the conclusion of the SLA process.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     A hearing instrument for insertion into the user&#39;s ear canal may be manufactured by fabricating the hearing instrument shell using stereo lithography (SLA), one of the processes mentioned in U.S. Patent Application Publication No. 2002/0196954 A1, published Dec. 26, 2002 and titled, “Modeling and fabrication of three-dimensional irregular surfaces for hearing instruments,” incorporated here by reference. When using SLA, a part is constructed layer by layer. Since the raw material is a liquid bath, a means of supporting the initial layers is required to prevent the piece from floating away. 
     Typically, a support structure is created along with the part and then later discarded (e.g., during a finishing process such as tumbling). One such support structure comprises a plurality of thin columns, perhaps braced together. When the part is finished, it is lifted out of the structure and the bath, and the support structure is discarded. 
     Some hearing instrument shells have receiver holes with finely detailed features. Since the receiver hole is located on the tip of the shell, it is one of the first items formed during the SLA process. Further, as the support structures are created simultaneously with the shell, these structures may extend into openings on the bottom of the shell, such as the receiver hole. Once the part is finished, extensive machining may be required to remove the support from the receiver hole and restore the hole structure. 
     The entry of the support structure into the receiver hole can be prevented by shielding the receiver hole with a structure such as a dome having a thin shell. Once the part is completed, the dome can be removed without harming the part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevation view of a hearing instrument in an ear canal and comprising a tip having a receiver hole and a vent hole; 
         FIGS. 2 and 3  are perspective views of the tip of the hearing instrument shell, illustrating the receiver hole and the vent hole; 
         FIG. 4  is a drawing of the tip of the hearing instrument shell as it is fabricated and the accompanying support structures; 
         FIG. 5  is a partial cross-sectional view of the tip of the hearing instrument shell, illustrating a protective dome covering the receiver hole; 
         FIG. 6  is a drawing of the shell tip, having a protective dome covering the receiver hole, as it is fabricated, with the accompanying support structures not shown; and 
         FIGS. 7 and 8  are drawings of the shell tip, having a protective dome, as it is fabricated and the accompanying support structures. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     A hearing instrument  10  comprising a shell  20  and a faceplate  30  is shown in the user&#39;s ear canal  12  in  FIG. 1 . The shell  20  has a shell tip  40  comprising apertures such as a receiver hole  42  and an optional vent hole  44 . The receiver hole  42  and the optional vent hole  44  are shown again in perspective views of the hearing instrument shell tip  40  in  FIGS. 2 and 3 . Although the shell tip  40  is shown with a flat surface in  FIGS. 2 and 3 . (and In the subsequent figures), it may be rounded or assume some other shape. 
     An apparatus  100  for fabricating the hearing instrument shell  20  using stereo lithography (SLA) is shown in schematic representation in  FIG. 4  with a portion of the shell tip  40 . The figure also shows support structure elements  110 . Although these support structure elements  110  are illustrated as thin, rectangular columns in the figure, they may assume the shape determined by the particular SLA process employed. 
     Since the support structure elements  110  are designed to extend to a solid surface, they will enter openings in the underside of the device being fabricated. For example, in  FIG. 4 , they extend into the receiver hole  42  and the vent hole  44 . After the part has been completed, the portions of the support structure elements  110  remaining in the receiver hole  42  and the vent hole  44  must be removed. Further, if the receiver hole  42  has a shape other than a simple round hole, the hole must be restored to the desired configuration. For example, the receiver hole may have a keyway slot that has been obscured or otherwise altered by a support structure element  110 . A machining operation may be required to restore that feature. 
     To prevent the intrusion of a support structure element  110  into the receiver hole  42  (or the vent hole  44 ), a protective structural shield may be built around or in front of the hole  42 ,  44 . One such structure is a dome  120  with a thin shell, as shown in the cross-sectional view of the hearing instrument shell tip  40  in  FIG. 5  and again in  FIG. 6 . The dome  120  has a drain hole  122  that permits excess material, in liquid form, to drain from the dome  120  when the completed part is removed from the SLA apparatus  100 . Although the figures show a dome-shaped structure covering the receiver hole  42 , other shapes could be used as well. 
     The thickness of the dome  120  is selected to facilitate its removal from the hearing instrument shell  20  during the finishing phase. For example, where the hearing instrument shell  20  has a thickness of 0.6-1.0 mm, the dome  120  may have a thickness of 0.1-0.2 mm. 
     In  FIG. 7 , the SLA apparatus  100  is again shown with a hearing instrument shell tip  40  having a dome  120  covering the receiver hole  42 . As illustrated, the dome  120  prevents the support structure elements  110  from entering the receiver hole  42 . In  FIG. 8 , an additional dome  130  covers the optional vent hole  44 , similarly preventing the support structure elements  110  from entering the hole  44 . 
     After the hearing instrument shell  20  is completed, it will undergo a finishing process such as tumbling. During that process, the domes  120 ,  130  and any support structure elements  110  that remain are removed.