Patent Publication Number: US-2006011290-A1

Title: Method and device for fabricating a hollow body containing at least one insert

Description:
The invention relates to a method for fabricating a hollow body containing at least one insert from two thermoplastic blanks by means of vacuum forming or thermoforming, and to a corresponding device.  
      A specific method for fabricating hollow bodies from two thermoplastic blanks by means of vacuum forming or thermoforming, also called twin sheet method, has already been known. Two thermoplastic blanks are thereby heated, vacuum-formed and subsequently bonded with their inherent heat to form a hollow body. This method is typically performed on a one-station machine, wherein two thermoplastic blanks mounted above the other are heated and processed. However, this method has the drawback that no additional components or inserts may be placed in the interior of the hollow body because said two thermoplastic blanks have to be detained airtight at a defined pitch by means of a holding system so as to prevent an uncontrolled sagging of the individual thermoplastic blanks.  
      For allowing additional components or inserts to be placed in the interior of the formed parts it would also be conceivable to apply the so-called twin sheet method in multistation machines, wherein the formed parts are fabricated successively and are completed with inserted inserts prior to their assembly. It is a drawback, however, that in such multistation machines the heated thermoplastic blanks are at first heated in a heating station and are then moved through standing air into the subsequently arranged forming station, wherein the sagging of the thermoplastic blanks cannot be controlled and influenced. In addition, also the expenditure of time for the fabrication of such formed parts is considerable, as both formed parts are formed successively.  
      The invention is accordingly based on the object to provide a method and a device of the aforementioned kind, by means of which the hollow bodies comprising at least one integrated insert can be fabricated fast and in a highly qualitative manner.  
      According to the invention this object is provided by the features relating to a method mentioned in patent claim  1  and by the features relating to a device mentioned in patent claim  9 .  
      Preferred additional embodiments of the method are described in the dependent patent claims  2  to  8 , while preferred additional embodiments of the device are mentioned in claims  10  to  13 .  
      According to the inventive embodiment of the method and the device hollow bodies can be fabricated from a thermoplastic material with at least one insert in a reliable, highly qualitative and fast manner. To this end, both formed parts are continuously and simultaneously fabricated in a single closed medium and, with the insertion of at least one insert, are bonded securely and reliably. The closable machine housing is opened merely for feeding the thermoplastic blanks and for withdrawing the finished hollow body comprising the at least one integrated insert, wherein both thermoplastic blanks for the upper formed part and for the lower formed part are preferably fed at the same time, while the feeding of the thermoplastic blanks and the withdrawal of the finished hollow body are preferably performed isochronously.  
      Both forming stations provided in the closable machine housing have in principle the same structure, wherein one forming station comprises a form tool for an upper formed part and the other forming station comprises a form tool for the lower formed part, and wherein a clamping frame associated with the respective tool halves and preferably a continuously adjustable single-plate system for the opposing edge sides of the thermoplastic blank are provided for the vacuum forming or thermoforming.  
      For joining the formed parts it is advantageously provided that one formed part is released from the clamped position in the one forming station and is moved, together with the form tool, to the other formed part still being in its clamped position in the forming station.  
      In each forming station the respective thermoplastic blanks are preferably heated on both sides prior to the forming by means of heaters, wherein the heaters are moved from their working position into an inoperative position outside the area of the form tools after the forming. By this, an extremely compact realization of the device with short movement paths for the formed parts and the finished hollow part is obtained.  
      The clamping frame provided for each forming station can preferably be moved away from all edges of the thermoplastic blank as to release the formed part, and each forming station moreover advantageously comprises a continuously adjustable window plate system which can preferably intermittently be driven apart to arrange the thermoplastic blank on the clamping frame.  
      For the sequence of the movements provided inside the device a mover is preferably provided for the lower formed part with the insert located therein, for the lowering and lifting in the area of the forming station appertaining to said formed part, as well as for a lateral shifting to the other forming station and for the lifting and lowering in the area of the other forming station.  
      According to another preferred embodiment of the device the forming station, in which both formed parts are bonded, comprises grip elements for removing the hollow body from the advanced form tool, which are movable under the clamping edge of the upper half of the formed part and which can be lifted together with the upper form tool and moved apart for the withdrawal of the hollow body to release the same after opening the associated clamping frame. This realizes an extremely simple, effective and reliable handling of the hollow body inside the closed machine housing.  
      According to another embodiment of the invention the machine housing comprises at least one closable opening for feeding thermoplastic blanks and for withdrawing fabricated hollow bodies, through which preferably a charge carriage is provided for the simultaneous feeding of both thermoplastic blanks, preferably at the lower side thereof, and for the withdrawal of the hollow body, preferably at the upper side thereof. This advantageously realizes a handling with one single handling member which continuously allows an isochronous feeding and withdrawal.  
      According to another embodiment of the invention each forming station comprises a heater for the surface of the thermoplastic blank and a heater for the lower side of the thermoplastic blank, wherein each heater can be moved from a working position into an inoperative position outside the area of the form tools.  
      According to another embodiment of the invention it is additionally provided that the thermoplastic blanks for the fabrication of the halves of the formed parts are differently sized, wherein the lower formed part, in which the at least one insert is arranged, has a comparatively smaller edge than the upper formed part so as to form a grip edge for the grip elements at the edge of the upper formed part. 
    
    
      Further details, features and advantages of the invention can be inferred from the following description, in which an embodiment of the invention will be explained in more detail with reference to the attached drawings.  
       FIG. 1  shows a schematic representation of an embodiment of a device according to the invention in a position, in which both forming stations are already charged with a thermoplastic blank;  
       FIG. 2  shows a schematic representation of the device according to  FIG. 1 , wherein both thermoplastic blanks are already simultaneously formed and wherein an insert is inserted into the right formed part;  
       FIG. 3  shows a schematic representation of the device according to  FIG. 1  in a phase, in which the lower formed part with the insert affixed thereto moves from the right forming station to the left forming station after the release;  
       FIG. 4  shows a schematic representation of the device according to  FIG. 1 , wherein both formed parts are joined and bonded in the left forming station;  FIG. 5  shows a schematic representation of the device according to  FIG. 1  in a fabrication phase, in which the hollow body is lifted by grip elements for removing it from the lower tool and the lower tool is lowered;  
       FIG. 6  shows a schematic representation of the device according to  FIG. 1  in a phase, which immediately follows after the phase according to  FIG. 5 , wherein a charge carriage with two new thermoplastic blanks drives in; and  
       FIG. 7  shows a schematic representation of the device according to  FIG. 1  in a phase following  FIG. 6 , in which the thermoplastic blanks are already deposited in the forming stations and the previously fabricated hollow body comprising an integrated insert has fallen down for being transported away after the grip elements on the upper side of the charge carriage were opened. 
    
    
      The figures schematically illustrate a device  10  for fabricating a hollow body containing at least one insert from two thermoplastic blanks  11 ,  12  by means of vacuum forming or thermoforming. In  FIG. 1  the quadrangular thermoplastic blanks  11 ,  12  are each disposed in associated forming stations  15 ,  14 , wherein they are each clamped at the sides of their edges between a clamping frame  17 ,  18  and a window plate system  19 ,  20  and sag, due to their inherent weight, downwardly in the direction of a closed housing  21 . The housing  21  is closed, thus allowing the thermoplastic blanks, which become soft while being heated, to be supported in a controlled manner due to a small overpressure in the housing  21 , so that an undesired sagging of the thermoplastic blanks is avoided and the passage can purposively be kept in a predefined area.  
      Each of the forming stations  14  and  15  comprises an upper heater  23 ,  25  for the upper side of the thermoplastic blanks  11 ,  12  and a lower heater  24 ,  26  for the lower side of the thermoplastic blanks,  11 ,  12 . The upper heaters are provided with a temperature sensor  28 ,  29 . Such a temperature sensor may also be provided at the lower heater  24 ,  26 .  
      A form tool  30  for the fabrication of the upper formed half of the hollow body is illustrated in the left forming station  15  above the heater  23 . For the fabrication of the lower half of the formed part of the hollow body a form tool  31  is provided inside the housing  21  in the right forming station  14 . The lower form tool  31  is arranged on a shifting table  32  and, on said table, may be brought into a position underneath the heater  24  in the forming station  15 , as will be explained later.  
      The device illustrated in the figures is surrounded by a closable machine housing  22  comprising at least one non-illustrated closable opening for feeding thermoplastic blanks and for withdrawing fabricated hollow bodies.  
       FIG. 2  shows a fabrication phase, in which the heaters  23  and  26  are preferably laterally moved out of the area of the form tools, and the form tool  30  rests on the clamping frame  17 , and the form tool  31  is adjacent the clamping frame  18  from below. The thermoplastic blank  11  was formed to a formed part  11 ′ in the forming station  15 , the edges of which are positioned between the clamping frame  17  and the window plate system  19 . The thermoplastic blank  12  is formed into a lower formed part  12 ′ the surrounding edges of which are positioned between the clamping frame  18  and the window plate system  20 . In the lower formed part  12 ′ an insert  33  is affixed in a non-illustrated manner by clamping, gluing or bonding.  
       FIG. 3  shows a subsequent phase of fabrication of the hollow body, wherein the upper formed part  11 ′ still is held at the sides of its edges between the clamping frame  17  and the window plate system  19  in the forming station  15 . In the right forming station  14 , however, the clamping frame  18  was moved in an outward direction at the side of the edge after having been lifted off the edge of the lower formed part  12  on the right side so as to release the formed part  12 ′. Together with the lower form tool  31  the same then has moved downwardly and, according to  FIG. 3 , is located on the shifting table  32  on its way to the forming station  15  for being positioned underneath the upper formed part  11 ′.  
       FIG. 4  shows another fabrication phase, in which the lower formed part  12 ′ and the upper formed part  11 ′ are pressed against each other and bonded at the sides of their edges, wherein—as can be seen—the surrounding edge  34  of the upper formed part  11 ′ is broader than the surrounding edge  35  of the lower formed part  12 ′.  
      In the phase shown in  FIG. 4  the hollow body already cools down. The window plate system  19  is opened and allows the grip elements  37 ,  38  to grip the upper formed part  11 ′ from underneath a cranked-off section of the surrounding edge  34  thereof. The grip elements  37  and  38  are aligned over the circumference of the edge  34  in a distributed manner, wherein the number thereof is defined according to need. The heater  24  still shown in  FIG. 3  was preferably laterally moved out of the area of the forming station  15  prior to the upward movement of the lower form tool  31 . The grip elements  37  and  38  are coupled to the upper form tool  30  and, in the next fabrication phase and according to  FIG. 5 , move with the same in an upward direction away from the window plate system  19 , while the lower form tool  31  has moved downwardly onto the movement table  32 .  
       FIG. 6  differs from the representation according to  FIG. 5  merely in that a charge carriage  41  is schematically illustrated, which feeds new thermoplastic blanks  11  and  12  into the forming stations  14  and  15  by means of suction cups  42  provided at the underside thereof. The window plate system  20  in the forming station  14  is opened, allowing the new thermoplastic blank  12  to fall onto the clamping frame  18 , which is in the initial position as shown in  FIG. 1 . The window plate system  19  of the forming station  15  is in the closed working position according to  FIG. 1 , as to pick up the new thermoplastic blank  11  falling down from the charge carriage  41 , as is shown in  FIG. 7 .  
      According to the fabrication method illustrated in  FIG. 7  the thermoplastic blank  12  lies on clamping frame, and next the window plate system  20  is then moved into the working position shown in  FIG. 1  to clamp the formed plate blank  12  at the side of its edges.  
      The lower form tool  31  still is positioned in the area of the left forming station  15  and then subsequently moves towards the right into the forming station  14 , as is indicated in  FIG. 1 . The upper form tool  30  still is positioned above the charge carriage  41 , wherein the grip elements  37  and  38  have meanwhile however released the surrounding edge  34  of the hollow body  40  and the hollow body  40  is disposed on the upper side of the charge carriage  41  for the withdrawal thereof. After laterally driving the charge carriage  41  out, without the previously fed new thermoplastic blanks  11  and  12  and with the fabricated hollow body  40  located on the same, the fabrication of the hollow body  40  is terminated and a new fabrication cycle with the new thermoplastic blanks  11  and  12  can be started, as was described in connection with  FIG. 1  to  FIG. 7 .