Abstract:
To provide a method for machining a workpiece, whereby chips are removed from the workpiece, wherein sufficient lubrication of the machining tool and sufficient cooling of the machining tool and the workpiece being machined are ensured, and chips resulting from the machining are simultaneously prevented from remaining inside recesses in the workpiece, a method comprising the following method steps is proposed:  
     introducing a lubricant in a flowable state into at least one recess of the workpiece;  
     solidifying the lubricant in the recess;  
     machining the workpiece, whereby chips are removed from the workpiece, with at least one machining tool coming into direct contact with the lubricant and being lubricated by the lubricant;  
     transforming the lubricant remaining in the recess of the workpiece into the flowable state and removing the lubricant from the workpiece.

Description:
[0001]    The present disclosure relates to the subject matter disclosed in international application PCT/EP02/06552 of Jun. 14, 2002, which is incorporated herein by reference in its entirety and for all purposes. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a method for machining a workpiece, whereby chips are removed from the workpiece.  
           [0003]    The present invention further relates to an apparatus for machining a workpiece, whereby chips are removed from the workpiece.  
           [0004]    During the machining of workpieces, whereby chips are removed from the workpiece, in particular, of workpieces for engine and transmission construction, for example, cylinder heads, crankcases or transmission housings, on transfer lines or in machining centers, very large amounts of liquid coolant are supplied to cool the workpiece and the machining tool, to lubricate the machining tool and to take away the chips removed from the workpiece during the machining.  
           [0005]    This conventional lubrication and cooling of the machining tool by external supply of large amounts of liquid coolant has the disadvantage that complicated preparation and circulation systems are required for the large quantities of coolant or coolant emulsion.  
           [0006]    Furthermore, it can happen that chips removed during machining of the workpiece are pressed by the coolant supplied under pressure into recesses in the workpiece instead of being taken away from the workpiece.  
           [0007]    The object underlying the present invention is, therefore, to provide a method for machining a workpiece, whereby chips are removed from the workpiece, wherein sufficient lubrication of the machining tool and sufficient cooling of the machining tool and the workpiece being machined are ensured, and simultaneously chips resulting from the machining are prevented from remaining inside recesses of the workpiece.  
         SUMMARY OF THE INVENTION  
         [0008]    This object is accomplished, in accordance with the invention, by a method in accordance with claim 1, comprising the following method steps:  
           [0009]    introducing a lubricant in a flowable state into at least one recess of the workpiece;  
           [0010]    solidifying the lubricant in the recess;  
           [0011]    machining the workpiece, whereby chips are removed from the workpiece, with at least one machining tool coming into direct contact with the lubricant and being lubricated by the lubricant;  
           [0012]    transforming the lubricant remaining in the recess of the workpiece into the flowable state and removing the lubricant from the workpiece.  
           [0013]    Therefore, with the inventive solution the lubrication of the machining tool is carried out by a lubricant which has already been introduced into the workpiece before the machining with chip removal, which has solidified in the workpiece and which comes into direct contact with the machining tool during the machining with chip removal, in order to lubricate the machining tool.  
           [0014]    The lubricant simultaneously absorbs heat generated during the machining of the workpiece with chip removal, so that the machining tool and the workpiece are cooled.  
           [0015]    Therefore, an external supply of liquid coolant during the machining of the workpiece with chip removal can be completely or at least partially dispensed with.  
           [0016]    Furthermore, it is ensured that the chips resulting from machining the workpiece are not pressed into the recess of the workpiece, as, on the one hand, the recess of the workpiece is filled with the lubricant, and, on the other hand, the chips are not subjected to an externally supplied lubricant with a pressure directed into the interior of the workpiece.  
           [0017]    A method for machining a workpiece having a cavity, whereby chips are removed from the workpiece, is known from DE 195 28 429 A1. The workpiece has openings connected to the cavity, and the openings are closed prior to the machining with chip removal by a medium which changes from the liquid to the solid phase in order to prevent machining chips from becoming deposited in the cavity of the workpiece. However, in this known method the medium introduced into the workpiece prior to the machining with chip removal does not come into contact with the machining tool, so that this medium cannot bring about either lubrication or sufficient cooling of the machining tool.  
           [0018]    Therefore, with this known method large quantities of liquid coolant have to be supplied during the machining with chip removal, in order to lubricate and cool the machining tool.  
           [0019]    A method for preventing machining residues in hollow articles to be machined by removing chips therefrom is known from DE 44 24 452 A1. Prior to the machining with chip removal, the cavities in the workpiece are filled with a foam to prevent chips or other impurities from entering and becoming lodged in the cavities during the machining. However, this foam does not come into contact with the machining tool during the machining of the workpiece with chip removal. Nor does it have any lubricating properties so that the foam introduced into the workpiece cannot bring about lubrication or sufficient cooling of the machining tool. Therefore, in the method according to DE 44 24 452 A1, too, large quantities of coolant must be supplied during the machining with chip removal.  
           [0020]    In a preferred embodiment of the method according to the invention provision is made for the lubricant to be introduced in the molten state into the recess of the workpiece.  
           [0021]    In this case, solidification of the lubricant in the recess of the workpiece takes place by cooling down the lubricant to below its solidification point.  
           [0022]    It is particularly expedient to use a lubricant whose solidification point is higher than approximately 60° C., preferably higher than approximately 65° C. It is thereby ensured that the lubricant will solidify in the workpiece when cooled down to room temperature.  
           [0023]    To achieve particularly good lubrication of the machining tool during machining of the workpiece with chip removal it is of advantage to use a lubricant which transforms from the solid to the liquid state during machining of the workpiece by the machining tool.  
           [0024]    Moreover, in this case the lubricant absorbs latent heat during transformation from the solid to the liquid state, so that, in addition to lubrication of the machining tool a particularly good cooling of the machining tool and the workpiece being machined is ensured.  
           [0025]    As lubricant it is possible to use any substance which is introducible in a flowable state into the workpiece before the machining with chip removal and which is capable of solidifying in the workpiece and has sufficient lubricating properties for the machining tool during the subsequent machining with chip removal.  
           [0026]    Provision is preferably made to use a lubricant which comprises a wax, preferably a paraffin wax.  
           [0027]    Flooding waxes such as those used in automobile manufacture for flooding vehicle body cavities exposed to corrosion for long-term protection against corrosion are particularly well suited.  
           [0028]    If the at least one recess of the workpiece has in addition to the opening for introduction of the lubricant at least one further access opening, then this further access opening is preferably closed by a closure element during introduction of the lubricant into the workpiece, so as to prevent the introduced lubricant from exiting again through this further access opening.  
           [0029]    In a preferred embodiment of the method according to the invention provision is made for the closure element to be removed again from the workpiece before machining of the workpiece with chip removal.  
           [0030]    Alternatively, provision may, however, also be made for the closure element, for example, a closure plug, to remain on the workpiece during machining of the workpiece with chip removal.  
           [0031]    In order to prevent chips from entering unmachined recesses of the workpiece during machining of the workpiece with chip removal, provision may be made for introduction of part of the lubricant, prior to machining of the workpiece with chip removal, into such a recess of the workpiece which is not machined during machining of the workpiece with chip removal.  
           [0032]    Introduction of the lubricant into the workpiece, machining of the workpiece and removal of the remaining lubricant from the workpiece can be carried out in one and the same area of an apparatus for machining the workpiece.  
           [0033]    However, in order to be able to keep to shorter cycle times in the machining of the workpieces, provision is made in a preferred embodiment of the method according to the invention for the lubricant to be introduced into the at least one recess of the workpiece in a lubricant filler station, for the workpiece to be subsequently conveyed to a machining station, for the workpiece to be subsequently machined in the machining station, whereby chips are removed from the workpiece, for the workpiece to be subsequently conveyed to a lubricant recovery station, and for the lubricant remaining in the workpiece to be subsequently removed from the workpiece in the lubricant recovery station.  
           [0034]    In order to remove the lubricant from the workpiece after the machining with chip removal, provision may, in particular, be made for the workpiece to be heated and rotated during and/or after the heating.  
           [0035]    The lubricant is made flowable again, in particular melted, by the heating of the workpiece, so that the lubricant can flow out of the recesses of the workpiece.  
           [0036]    In a preferred embodiment of the method according to the invention the workpiece is heated by being subjected to a heated fluid, preferably to heated air.  
           [0037]    A further object underlying the present invention is to provide an apparatus for machining a workpiece, whereby chips are removed from the workpiece, which makes it possible in a simple way to lubricate the machining tool and to sufficiently cool the machining tool and the workpiece being machined without chips resulting from the machining by chip removal remaining in the workpiece.  
           [0038]    This object is accomplished, in accordance with the invention, by an apparatus in accordance with claim 13 comprising:  
           [0039]    a filler device for introducing a lubricant in a flowable state into at least one recess of the workpiece;  
           [0040]    at least one machining tool for machining the workpiece, whereby chips are removed from the workpiece, with the machining tool coming into direct contact with the lubricant during the machining and being lubricated by the lubricant; and  
           [0041]    a device for transforming the lubricant remaining in the workpiece into the flowable state and removing the lubricant from the workpiece.  
           [0042]    The advantages of the apparatus according to the invention have already been explained hereinabove in conjunction with the advantages of the method according to the invention.  
           [0043]    Further features and advantages of the invention are the subject matter of the following description and the drawings of an embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]    [0044]FIG. 1 a schematic illustration of an apparatus for machining a workpiece, whereby chips are removed from the workpiece, comprising a wax filler station, a machining station and a wax recovery station;  
         [0045]    [0045]FIG. 2 a schematic plan view of a workpiece which is to be machined in the apparatus of FIG. 1;  
         [0046]    FIGS.  3  to  8  schematic sections through a partial area of the workpiece of FIG. 2, which illustrate successive steps for machining the workpiece in the apparatus of FIG. 1;  
         [0047]    [0047]FIG. 9 a schematic illustration of the wax filler station of the apparatus of FIG. 1, before introduction of the wax into the workpiece;  
         [0048]    [0048]FIG. 10 a schematic illustration of the wax filler station of the apparatus of FIG. 1 while introducing the wax;  
         [0049]    [0049]FIG. 11 a schematic plan view of the wax recovery station of the apparatus of FIG. 1; and  
         [0050]    [0050]FIG. 12 a schematic side view of the wax recovery station of the apparatus of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]    Identical or functionally equivalent elements are designated by the same reference numerals in all Figures.  
         [0052]    An apparatus generally designated  100 , which is illustrated in FIGS. 1 and 9 to  12 , for machining a workpiece  102  shown in FIG. 2, whereby chips are removed from the workpiece, comprises, as is best seen from FIG. 1, a wax filler station  104 , a machining station  106 , and a wax recovery station  108  and also a conveyor device (not shown) for conveying the workpieces  102  along the conveying direction  110  into the apparatus  100 , through the three stations  104 ,  106  and  108  and out of the apparatus  100 .  
         [0053]    The workpieces  102  can be conveyed, for example, by hoisting beams or push rods on a roller conveyor.  
         [0054]    The workpieces  102  which are to be conveyed through the apparatus  100  and machined therein are, for example, engine blocks of an internal combustion engine (see FIG. 2) and have a plurality of recesses  112  extending through the workpiece  102  or ending in the workpiece  102 .  
         [0055]    Such recesses may, for example, be coolant openings, oil supply bores or threaded bores.  
         [0056]    Some of the recesses  112  are insulated from the other recesses; other recesses  112  communicate with one another.  
         [0057]    [0057]FIG. 3 shows a section through part of the workpiece  102  in which a first bore hole  118  opening into the bottom  114  of a hollow  116  of the workpiece  102  and a second bore hole  120  running perpendicularly into the first bore hole  118  and opening at its end remote from the first bore hole  118  into an upper face  122  of the workpiece  102  are recognizable.  
         [0058]    The workpiece  102  is conveyed by the conveyor device into the wax filler station  104  of the apparatus  100  and stopped there in a wax filling position.  
         [0059]    As is apparent from FIG. 9, the wax filler station  104  comprises at least one wax filler nozzle  124  held on a displaceable holder  126  which is displaceable by a displacement device (not shown) along the direction of the double arrow  128  between a position of rest (shown in FIG. 9) and a wax filling position (shown in FIG. 10).  
         [0060]    The wax filler nozzle  124  is connected via a flexible wax feed line  130  to a wax storage container  132  which is filled up to a level  134  with liquid wax  136 .  
         [0061]    Into the air space  138  remaining above the liquid wax  136  inside the wax storage container  132  there opens a wax supply pipe  140  via which liquid wax can be supplied to the wax storage container  132  from a wax ring line or a wax reservoir, and a compressed air line  142  via which the interior of the wax storage container  132  can be subjected to an increased air pressure in order to convey liquid wax from the wax storage container  132  through the wax feed line  130  into the wax filler nozzle  124 .  
         [0062]    In the position of rest of the wax filler station  104  shown in FIG. 9 the compressed air line  142  is closed by a stop valve (not shown).  
         [0063]    The wax filler station  104  further comprises at least one closure element  144 , for example, in the form of a closure plate, which is held on a displaceable holder  146 , which is displaceable by a displacement device (not shown) along the direction of the double arrow  148  between the position of rest shown in FIG. 9 and a closed position shown in FIG. 10.  
         [0064]    After the workpiece  102  has been conveyed into the wax filler station  104  and stopped there, the wax filler nozzle  124  is moved by the displaceable holder  126  into the work position shown in FIG. 10, in which the wax filler nozzle  124  rests against an outer face of the workpiece  102  and the outlet opening of the wax filler nozzle  124  covers the hollow  116  into which the first bore hole  118  opens (see FIG. 4).  
         [0065]    Furthermore, the closure element  144  is brought by the displaceable holder  146  into the closed position shown in FIG. 10 in which the closure element  144  closes the orifice of the second bore hole  120  on the upper face  122  of the workpiece  102  (see FIG. 4).  
         [0066]    The interior of the wax storage container  132  is subsequently subjected to an increased pressure by opening the compressed air line  142 , so that liquid wax  136  passes through the wax feed line  130  and the wax filler nozzle  124  into the hollow  116 , into the first bore hole  118  and from there into the second bore hole  120  communicating with the first bore hole  118 .  
         [0067]    During this wax flooding procedure, the closure element  144  prevents liquid wax from passing out of the workpiece  102  through the orifice of the second bore hole  120 .  
         [0068]    After flooding of the first bore hole  118  and recesses in the workpiece  102  communicating therewith, the wax filler nozzle  124  is moved into a further work position on a further bore hole which is to be filled with wax, in order to also flood this further bore hole with wax.  
         [0069]    When all cavities of the workpiece  102  that are to be flooded have been filled with wax, the wax filler nozzle  124  is returned to its position of rest.  
         [0070]    Furthermore, the closure element  144  is also returned to its position of rest.  
         [0071]    Instead of successively flooding several cavities of the workpiece  102  with the same wax filler nozzle  124 , provision may also be made for the wax filler station  104  to comprise several wax filler nozzles  124  so as to able to simultaneously flood several cavities of the workpiece  102 .  
         [0072]    These several wax filler nozzles may be connected to the same wax storage container  132  or to various wax storage containers  132 .  
         [0073]    Furthermore, while the wax is being filled in it is possible for the closure element  144  to be moved from the first closed position into one or several further closed positions on the workpiece  102 , so as to close orifices of the workpiece  102  communicating with the respectively filled cavity of the workpiece  102 .  
         [0074]    It is, furthermore, possible for the wax filler station  104  to comprise several closure elements  144  which are used to close different orifices of cavities of the workpiece  102  during the wax filling procedure.  
         [0075]    Finally, provision may also be made for moving and/or rotating the workpiece  102  into different wax filling positions relative to the wax filler nozzle  124  and the closure element  144  instead of moving the wax filler nozzle  124  and the closure element  144 .  
         [0076]    After filling the liquid wax into the first bore hole  118  and the second bore hole  120 , the wax cools down to below its melting temperature and solidifies so that the solidified wax  148  remains in the workpiece  102  during subsequent transportation of the workpiece  102  out of the wax filler station  104  to the machining station  106  (see FIG. 5).  
         [0077]    After the workpiece  102  has been conveyed by the conveyor device into the machining station  106  of the apparatus  100  and stopped there in a machining position, the workpiece is machined and chips thereby removed from the workpiece by machining tools located in the machining station  106 .  
         [0078]    Such machining with chip removal may, for example, be carried out with a drilling device comprising a drill  150  which is introduced into the hollow  116  of the workpiece  102  to widen the outer section of the first bore hole  118  (see FIG. 6).  
         [0079]    The solidified wax located in the hollow  116  and in the first bore hole  118  is at least partially heated beyond its melting temperature and melted owing to the heat generated during the machining of the workpiece  102  with chip removal.  
         [0080]    The molten wax  149  comes into direct contact with the machining tool, for example, the drill  150  during the machining with chip removal, and the machining tool is thereby simultaneously lubricated and cooled by the molten wax  149 .  
         [0081]    The cooling effect of the wax is intensified by the wax absorbing latent heat during the melting.  
         [0082]    The wax located in the remaining cavities of the workpiece  102 , which do not come into direct contact with the machining tool, prevents chips resulting from the machining of the workpiece  102 , whereby chips are removed from the workpiece  102 , from entering these further cavities, for example, the second bore hole  120 .  
         [0083]    A suitable wax for flooding the cavities in the workpiece  102  is, for example, comprised of paraffin waxes and long-chain hydrocarbons.  
         [0084]    Such a wax is sold, for example, by the firm of Pfinder GmbH &amp; Co., Rudolph-Diesel-Strasse 14, in 71032 Boeblingen, Germany, under the designation “Flutwachs AP 2220/1”.  
         [0085]    This flooding wax has a solidifying point of approximately 69° C. and is kept in the liquid state in the wax storage container  132  preferably at a temperature of from approximately 115° C. to approximately 120° C.  
         [0086]    After completion of the machining of the workpiece  102 , whereby chips are removed from the workpiece  102 , and removal of the machining tool from the workpiece  102 , the wax remaining in the workpiece  102  cools down again to below its solidifying temperature and solidifies (see FIG. 7).  
         [0087]    The finished workpiece  102  is conveyed by the conveyor device to the wax recovery station  108  shown in FIGS. 11 and 12 and stopped there in a work position.  
         [0088]    As is apparent from FIG. 11, the wax recovery station  108  comprises a rotary device  152  with two rotary holders  154 , which are displaceable by displacement devices (not shown) along the directions of the double arrows  156  in FIG. 11 from a position of rest (not shown) to a work position in which the respective workpiece  102  is non-rotatably held on the rotary holders  154 .  
         [0089]    At least one of the rotary holders  154  is drivable by a rotary drive  158  for continuous rotary movement about an axis of rotation  160  of the rotary device  152  in the direction of rotation indicated by arrow  162  in FIG. 12.  
         [0090]    A blow nozzle  164  is arranged above the rotary device  152  and outside the interference circle of the rotary holders  152 . The blow nozzle  164  is supplied with heated air at elevated pressure via an air supply line  166  in which an air heater  168  and a blower  170 , for example, a lateral channel compressor, are arranged.  
         [0091]    A drip pan  172  is arranged below the rotary device  152  for collecting wax dripping from the workpiece  102 .  
         [0092]    The bottom wall  174  is at an incline to an outlet opening  176  at which a wax discharge line  178  opens into the drip pan  172 .  
         [0093]    The drip pan is heatable by a heating device (not shown) in order to keep the wax dripping into it liquid.  
         [0094]    After the workpiece  102  has been deposited between the rotary holders  154 , the rotary holders  154  are driven up to the workpiece  102  so as to non-rotatably receive the workpiece  102 .  
         [0095]    The workpiece  102  is subsequently rotated by the rotary drive  158  about the axis of rotation  160  of the rotary device  152  which coincides with the longitudinal axis of the workpiece  102 .  
         [0096]    During this, air drawn in from the environment is heated by the air heater  168  to a temperature of from approximately 150° C. to approximately 200° C. and conveyed by the blower  170  to the blow nozzle  164  from whose blow slot the heated air is blown at increased speed onto the workpiece  102 .  
         [0097]    The workpiece  102  and the wax contained therein are heated up by the action of the heated blow air thereon, so that the wax liquefies and owing to gravity drips through the orifices of the cavities of the workpiece  102  respectively located underneath into the drip pan  172 .  
         [0098]    By rotating the workpiece  102  while it is being acted upon by the heated air, each orifice of the workpiece  102  is made to point at least once downwards into the drip pan  172 .  
         [0099]    The rotational speed of the rotary device  152  is selected such that each orifice remains directed for a sufficiently long time at the drip pan  172  so as to enable the wax contained in the cavity of the workpiece  102  belonging to the orifice to run out completely.  
         [0100]    The liquid wax collected in the drip pan  172  is conducted away for further use by the wax discharge line  178 , for example, returned to the wax storage container  132  of the wax filler station  104 .  
         [0101]    When all of the wax present in the workpiece  102  has been removed from the workpiece  102 , the rotational movement of the workpiece  102  about the axis of rotation  160  is stopped, and the workpiece  102  is released by moving the rotary holders  154  into their positions of rest and conveyed by the conveyor device along the direction of conveyance  110  out of the apparatus  100  for further machining or storage.