Abstract:
A work piece support structure for waterjet cutting apparatus comprising a cutting table having a plurality of space to part slats, the table being supported in a cantilever fashion by a bar adapted to be positioned at the top of the front of the water tank of the waterjet cutting apparatus, the bar being axially rotatable relative to the tank and means to cause rotation of the bar from a first position in which the slats extend across the top of the tank to support the work piece for cutting and a second inclined position in which the slats extend upwardly to support the work piece during loading or unloading of the work piece.

Description:
INTRODUCTION  
       [0001]     This invention relates to a work piece support structure for waterjet cutting apparatus and in particular waterjet cutting with abrasives.  
       BACKGROUND OF THE INVENTION  
       [0002]     Waterjet cutting has been used for some years to cut a variety of materials such as steel, aluminium, glass, marble, plastics, rubber, cork and wood. The work piece is placed on a cutting table over a bath of water and a cutting head is accurately displaced across the work piece to complete the desired cut. The cutting action is carried out by the combination of a very high pressure jet (up to 55,000 psi) of water entrained with fine particles of abrasive material, usually sand, that causes the cutting action. The water and sand that exits the cutting head is collected beneath the work piece in a tank. The work piece is usually supported on a cutting table located in the top of the water bath. The table usually comprises a series of parallel steel slats or beams that provide spaced support for the underside of the work piece whilst defining many spaces for passage of the water and abrasive.  
         [0003]     This cutting technique is very powerful and can cut through stainless steel as thick as 100 mm or 4 inches. The cutting process can also be extremely accurate with tolerances of plus or minus 0.1 mm or 0.004 inches. The process is clean, fast and reliable.  
         [0004]     The waterjet cutting process described above has proved especially useful for the cutting of fragile materials such as glass and stone. However, there is a problem in placing the work piece onto the table in the bath of water prior to the cutting action. Great care has to be taken to position fragile material such as glass and/or stone on the cutting table.  
         [0005]     One commonly used technique is a overhead jig with a vacuum head that, through suction, attaches itself to the work piece which can then be positioned over the cutting table and lowered onto the table. The overhead jig can also include means to rotate the work piece and/or move it incrementally of the bath.  
         [0006]     However, there are certain large work pieces such as glass and stone in which additional care has to be taken in respect of the loading and unloading of the work piece and the use of a vacuum activated contact does not provide the necessary degree of support. The use of a vacuum head can also cause scratching of the glass due to pressure of the abrasive.  
         [0007]     It is these issues that have brought about the present invention.  
       SUMMARY OF THE INVENTION  
       [0008]     According to the present invention there is provided a work piece support structure for waterjet cutting apparatus comprising a cutting table having a plurality of spaced apart slats, the table being supported in a cantilever fashion by a bar adapted to be positioned at the top of the front of a water tank of the waterjet cutting apparatus, the bar being axially rotatable relative to the tank and means to cause rotation of the bar from a first position in which the slats extend across the top of the tank to support the work piece for cutting and a second inclined position in which the slats extend upwardly to support the work piece during loading or unloading of the work piece.  
         [0009]     Preferably the slats are supported on the bar by elbow shaped links that are displaceable along the bar to vary the spacing of the slats.  
         [0010]     The bar is preferably mounted in spaced apart bearing secured to the front of the tank.  
         [0011]     The means to displace the bar is preferably a hydraulic or pneumatic ram.  
         [0012]     In one embodiment the table comprises an open framework supported by side arms that are connected to the bar. The table is preferably secured to the side arms to be displaceable longitudinally of the arms from a lower position at which the work piece can be lifted onto or off the table to an operative position where the work piece is over the tank to facilitate the cutting operation.  
         [0013]     At least one hydraulic ram is preferably used to displace the framework relative to the side arms. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]     Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:  
         [0015]      FIG. 1  is a plan view of a cutting bath of waterjet cutting apparatus illustrating a work piece support table in accordance with a first embodiment;  
         [0016]      FIG. 2  is an end elevational view of the cutting bath showing the support table in an inclined position;  
         [0017]      FIG. 3  is a side elevational view of the bath showing the support table in an inclined position;  
         [0018]      FIG. 4  is a side elevational view of the bath with the support table in the lowered position;  
         [0019]      FIG. 5  is a side elevational view of the bath illustrating an alternative form of work piece support table in the inclined position;  
         [0020]      FIG. 6  is a plan view of a 500 kg cutting table with lifting mechanism;  
         [0021]      FIG. 7  is an end elevational view of the cutting table;  
         [0022]      FIG. 7A  is an enlarged view of the components within the rectangle A of  FIG. 7 ;  
         [0023]      FIG. 7B  is a side view of  FIG. 7A .  
         [0024]      FIG. 8  is a side elevational view of the table with the cutting table in the lowered position;  
         [0025]      FIG. 9  is a side elevational view of the cutting table in a inclined position; and  
         [0026]      FIG. 10  is a side elevational view of the cutting table in an inclined position with the work piece lowered. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     In the embodiment shown in FIGS.  1  to  4 , cutting table  10  is designed to accommodate a work piece of up to 120 kg. The cutting table  10  is positioned against the top  12  of a substantially rectangular cutting tank  20  that, in use, contains water. The cutting table  10  comprises an elongate bar  11  of square cross section that is mounted along the top  12  of the front  13  of the cutting tank  20  and supported thereon via bearings  15 ,  16 ,  17  at three spaced positions shown in  FIG. 2 . The bar  11  has cylindrical portions that are supported by the bearings to facilitate the capacity for the arm to axially rotate. The bar  11  is designed to support four replaceable elongate slats  21 ,  22 ,  23 ,  24  that are supported by elbow shaped holders  25 ,  26 ,  27 ,  28  to be displaceable along the length of the bar  11 . As shown in  FIG. 2 , the left hand holder  25  is fixed to the bar  11  but the other three elbow shaped holders  26 ,  27 ,  28  are designed to be displaceable along the length of the bar to vary the spacing of the slats. The slats  21 - 24  extend outwardly of the bar across the tank as shown in  FIGS. 1 and 4  in a cantilever fashion. As shown in  FIG. 4 , when in the operative position, the slats  21 - 24  extend just above the water level at the top of the tank  20  and support the work piece which is usually a flat sheet of glass or stone. The slats can have soft blocks (not shown) of rubber on which the work piece rests.  
         [0028]     In this embodiment, the cutting table  10  is designed to be displaceable from an operative position shown in  FIG. 4  in which the slats  21 ,  22 ,  23 ,  24  extend horizontally across the tank to an inclined position shown in  FIG. 3  in which the slats  21 ,  22 ,  23 ,  24  extend upwardly out of the tank. A pneumatic ram  35  is bolted to the base  14  of the tank  20  to extend upwardly at an angle of about 45° to be in turn coupled to a lever  36  that is coupled to the bar  11  so that actuation of the pneumatic ram  35  from the position of  FIG. 4  to the position of  FIG. 3  forces the lever  36  upwardly so that the slats  21 ,  22 ,  23 ,  24  assume the inclined position shown in  FIG. 3 . In this position, the glass or stone can be carefully positioned against the slats  21 ,  22 ,  23 ,  24 , either for loading or unloading of the apparatus.  
         [0029]     The embodiment shown in  FIG. 5  is very similar to the embodiment of FIGS.  1  to  4  except that it has been designed to take a greater load, namely 300 kg. In this case the pneumatic cylinder has been replaced by a hydraulic ram  40  that is mounted against the base of the forward edge of the tank  20 . The hydraulic ram operates in a substantially vertical plane and is not inclined at 45° as the pneumatic ram of the first embodiment.  
         [0030]     The embodiment that is shown in FIGS.  6  to  10  is capable of carrying loads of 500 kg. In this embodiment, the cutting table  50  is not only driven from an operative horizontal position to an inclined position in the same manner as the previous embodiments, but the table can be displaced longitudinally to move the comparatively heavy work piece from a loading and unloading position shown in  FIG. 10  to a cutting position shown in  FIG. 9 . In this embodiment, the cutting table  50  is much sturdier than the table of the previous two embodiments and comprises a rectangular frame  51  that supports a plurality of equally spaced beams  52  that can extend across the shorter sides of the tank  20  together with a plurality of cross members  53  and two pairs of diagonal bracing struts  54 ,  55 . In this embodiment the cutting table  50  is not attached to the water tank  20  but is supported by a pair of pedestals  70 ,  71  that are bolted to the floor. A substantial hollow steel bar  58  extends across the pedestals  70 ,  71  along the length of the tank and is supported about the pedestals on flange bearings  73 ,  74  at either end so that the bar is axially rotatable. As shown in the side views, FIGS.  8  to  10 , each pedestal  70 ,  71  comprises an upstanding column  75  that supports one end of the bar  58  and an elongate base structure  76  that is bolted to the floor and attached to one end of a hydraulic cylinder  78 ,  79 . Each hydraulic cylinder  78 ,  79  is attached to a link  80  which is in turn coupled to the bar  58  so that expansion of the cylinder  78 ,  79  to the position shown in  FIGS. 9 and 10  causes the bar  58  to rotate to in turn displace the cutting table  50  to the upwardly inclined position shown in  FIGS. 9 and 10  and as the cylinders are contracted to the position shown in  FIG. 8 , the bar  58  is turned so that the cutting table  50  assumes the horizontal configuration. The degree of angular movement between the two positions is 80°.  
         [0031]     The table  50  itself is supported on either side by two side plates  81 ,  82  that are in turn coupled to the bar  58  via robust C shaped link arms  83 ,  84  that in effect mean that the table  50  is cantilevered to the bar  58  via the link arms  83 ,  84 . As shown in  FIGS. 7A and 7B  each side of the table  50  has an angled flange  85 ,  86  that supports an elongate acetal wear block  87  that rests in parallel with a lower acetal wear block  88  that is in turn supported by a stainless steel block  89  that runs parallel to the side arm  82 . In this manner the table  50  can slide on the acetal blocks  87 ,  88  longitudinally of arms  81 ,  82 . As shown in  FIG. 7B , a hydraulic ram  90 ,  91  connected at one end to the C shaped link arm  83 , or  84  is coupled to a clevis  95  extending from the top of the angled flange  85 ,  86  of the table  50 . Thus, the table  50  can be displaced by the rams  90 ,  91  to move from a lowered position shown in  FIG. 10  to an elevated position shown in  FIG. 9 .  
         [0032]     Thus, in use, a delicate but heavy work piece is first carefully positioned on the apparatus with the cutting table  50  in the inclined and lowered position shown in  FIG. 10 . The table  50  is then displaced by the hydraulic cylinders  90 ,  91  to the upper position shown in  FIG. 9  where the work piece in the operative position. The table  50  is then lowered using the rams  78 ,  79  to extend across the tank in the horizontal cutting position.  
         [0033]     This mechanism substantially improves safety and ease of handling of very large and fragile work pieces.  
         [0034]     In the embodiments described above hydraulic or pneumatic rams have been used to displace the cutting table. It is however understood that other drive means are envisaged such as linear displacement electric motors, linear actuators, servo motors or electrically driven worm and wheel drivers.