Abstract:
Apparatus for laser processing a foil material workpiece held to a workpiece holder by a vacuum while being processed by a laser. The foil material workpiece spans a recess in the workpiece holder and is held flat and taut across the recess. With the open space beneath the foil material workpiece defined by the recess, the laser beam can pass completely through the foil material workpiece to form a through hole or through cut in the foil material workpiece without impinging on the workpiece holder.

Description:
TECHNICAL FIELD 
     The present invention relates, in general, to laser machining and, in particular, to an apparatus and method for processing foil material with a laser. 
     BACKGROUND OF THE INVENTION 
     In laser drilling and cutting of foil-like materials, such as thin metal foils and plastic foils, the surfaces of the materials that are being processed should be flat and taut to provide a focal plane or image plane for the laser beam. Because these materials are light and flimsy, holding them properly can be difficult. 
     One way of holding these light and flimsy materials flat and taut is by the application of a vacuum through holes in a bed or workpiece holder on which these light and flimsy materials are laid. Typically, these workpiece holders are solid and present a planar surface onto which the foil material workpiece to be machined is laid and the foil material workpiece is held in place by the vacuum. 
     One common laser machining operation is drilling a blind hole in the foil material workpiece (i.e., a hole that is not a through hole that extends completely through the workpiece). For such laser machining operations, where the laser beam does not pass completely through the foil material workpiece, an arrangement that includes a bed having a planar surface on which the foil material workpiece is held is fine. If, however, a through hole or a through cut is to be formed in the foil material workpiece, the laser beam must pass completely through the foil material workpiece and can impinge on the planar surface of the workpiece holder on which the foil material workpiece is being held. When the laser beam impinges on the planar surface of the workpiece holder, small crater-like formations are developed. As a result, the surface on which the foil material workpiece is being held is no longer planar and the workpiece no longer is held flat against the workpiece holder throughout the extent of the foil material workpiece. 
     SUMMARY OF THE INVENTION 
     Accordingly, apparatus for laser processing a foil material workpiece, constructed in accordance with the present invention, includes a laser unit for developing a laser beam for processing a foil material workpiece. Also included in this apparatus is a workpiece holder that is adapted to hold a foil material workpiece and is disposed in the path of the laser beam. This workpiece holder has a recess in a first face that extends into the workpiece holder and a groove in the first face between the recess and a sidewall at the periphery of the workpiece holder. The workpiece holder also has a vacuum passage extending through the workpiece holder and opening at a first end into the groove. Apparatus for laser processing a foil material workpiece, constructed in accordance with the present invention, further includes means for applying a vacuum to a second end of the vacuum passage in the workpiece holder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
     FIG. 1 is a block diagram of a preferred embodiment of apparatus for laser processing a foil material workpiece constructed in accordance with the present invention. 
     FIG. 2A is a top view of a preferred embodiment of a workpiece holder constructed in accordance with the present invention and useful in the FIG. 1 apparatus. 
     FIG. 2B is a side view of the FIG. 2A workpiece holder. 
     FIG. 3 is a top view of another preferred embodiment of a workpiece holder constructed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, apparatus for laser processing a foil material workpiece, constructed in accordance with the present invention, includes a laser unit  10  for developing a laser beam for processing a foil material workpiece. For the embodiment of the invention being described, laser unit  10  includes a laser source  12  that emits a beam that passes through a variable beam attenuator  14 . Following variable beam attenuator  14 , the beam is weakly focused by a lens  16  to illuminate a mask  18 . Laser unit  10  further includes lenses  20  and  22  that image open apertures of mask  18  on a workpiece  24 , namely a foil material. It will be understood that laser unit can include a diffractive optical element instead of mask  18 . 
     Apparatus for laser processing a foil material workpiece, constructed in accordance with the present invention, further includes a workpiece holder  26  that is adapted to hold foil material workpiece  24  on a planar first face  27  of the workpiece holder. Workpiece holder  26  is disposed in the path of the laser beam developed by laser unit  10 . For the embodiment of the invention illustrated by the drawings, workpiece holder  26  is stepped with the smaller portion fitted within and held by a boss  28 . 
     As shown in FIGS. 2A and 2B, workpiece holder  26  has a recess  29  in first face  27  of the workpiece holder. Recess  29  extends into the workpiece holder from first face  27 . 
     In one embodiment of the present invention, recess  29  is a circular through hole that extends completely through the workpiece holder from first face  27  to a second face  31 . In a second embodiment of the present invention, recess  29  is a blind hole that extends partially through workpiece holder  26  from first face  27 . This is represented by dashed line  32  in FIG. 2B. A vent passage  33  is provided for pressure relief to equalize the pressure outside the foil material workpiece being held by the workpiece holder and the pressure inside the blind hole recess. 
     It is important that the laser beam not impinge upon workpiece holder  26  and damage the workpiece holder during laser processing of foil material workpiece  24  and, in the event that the laser beam impinges on the workpiece holder during laser processing of the foil material workpiece, the damage to the workpiece holder does not extend to beyond planar first face  27  of the workpiece holder which would result in the foil material workpiece no longer being planar and the foil material workpiece no longer being held flat throughout the extent of the foil material workpiece. 
     Workpiece holder  26  also has a groove  34  in first face  27  of the workpiece holder between recess  29  and a sidewall  36  at the periphery of the workpiece holder. For the embodiment of the invention illustrated by FIG. 2A, groove  34  is circular in shape. It is apparent that groove  34  can take other shapes, such as elliptical, square, or rectangular. 
     As shown in FIGS. 2A and 2B, workpiece holder  26  has a second circular groove  38  in first face  27  of the workpiece holder. Groove  38  also is located between recess  29  and sidewall  36  at the periphery of workpiece holder  26  and can take other shapes. 
     Workpiece holder  26  also has a vacuum passage  40  extending through the workpiece holder and opening at a first end into grooves  34  and  38  through openings  41  and  42 , shown most clearly in FIG. 2A. A second end of vacuum passage  40  opens into sidewall  36  at the periphery of workpiece holder  26 . 
     Apparatus for laser processing a foil material workpiece, constructed in accordance with the present invention, further includes means for applying a vacuum to the second end of vacuum passage  40 . As shown in FIG. 1, such means can include a vacuum source  44 , of conventional construction and operation, connected by suitable means to workpiece holder  26  at the second end of vacuum passage  40 . 
     When a vacuum is applied from vacuum source  44  through vacuum passage  40  and openings  41  and  42  to grooves  34  and  38 , portions of foil material workpiece  24  are pulled down into the grooves uniformly creating an even tension over recess  29  in the workpiece holder. The degree of tension is determined by the width of the grooves and the amount of the vacuum pressure that is applied. Having a single flat plane, the laser beam has the same focal distance across the foil material workpiece for the laser processing being performed and allows the same process performance criteria across the foil material workpiece. Workpiece holder  26  secures the foil material workpiece to the workpiece holder in a fashion that does not damage the foil material workpiece. 
     The workpiece holder  26  also includes optional grooves  43  that connect the grooves  34  and  38 . The grooves  43  allow airflow from groove  34  or  38  to groove  38  or  34  and are implemented in the workpiece holder  26  to allow the foil material to be held in place even when one of the openings  41  and  42  is blocked. In this instance, vacuum pressure from the unblocked opening is applied to both grooves  34  and  38 . One of the vacuum openings may be blocked, for example, when the foil material is pulled into the opening by the vacuum. To prevent the blocked vacuum opening from blocking the optional groove  43 , it is desirable for the groove  43  to intersect the grooves  34  and  38  at locations other than those occupied by the vacuum opening. 
     Apparatus for laser processing a foil material workpiece, constructed in accordance with the present invention, preferably includes means for imparting relative movement between workpiece holder  26  and laser unit  10 . Such means are represented in FIG. 1 by a motor  46  that, for the embodiment of the invention being described, causes workpiece holder  26  to move as the foil material workpiece is being processed by the laser unit. The present invention can be arranged to create the desired relative movement in three dimensions. It will be understood that the desired relative movement can be created by moving laser unit  10  rather than workpiece holder  26  or both the laser unit and the workpiece holder can be moved rather than only one of the two. 
     FIG. 3 shows another embodiment of a workpiece holder constructed in accordance with the present invention. This workpiece holder  50  has a rectangular recess  52  that can be a through hole or a blind hole and a first rectangular groove  54  in a face  56  of the workpiece holder between recess  52  and the sidewalls or periphery of the workpiece holder. For the embodiment of the invention illustrated by FIG. 3, groove  54  is rectangular in shape but can take other shapes. 
     As shown in FIGS. 3, workpiece holder  50  has a second rectangular groove  58  in face  56  of the workpiece holder. Groove  58  also is located between recess  52  and the periphery of workpiece holder  50  and can take other shapes. 
     Workpiece holder  50  also has a vacuum passage (not shown) extending through the workpiece holder and opening at a first end into grooves  54  and  58  through openings  60  and  62 . A second end of this vacuum passage opens into a sidewall at the periphery of workpiece holder  50 . This alternate embodiment also includes optional grooves  61  that connect the grooves  54  and  58 . As with the grooves  43 , described above, the grooves  54  and  58  allow vacuum pressure to be applied to both of the grooves  54  and  58  even when one of the openings  60  and  62  is blocked. 
     While in the foregoing there have been described preferred embodiments of the present invention, it should be understood by those skilled in the art that various modifications and changes can be made without departing from the true spirit and scope of the present invention.