Abstract:
An injection molding system for the formation of molded articles with reduced crystallinity comprising a laser cutoff subsystem for the removal of an elongated vestige or sprue from the molded article.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to copending application, entitled “Method and Apparatus for Cutting Plastics Using Lasers”, filed contemporaneously herewith and incorporated herein by reference and Provisional Patent Application serial No. 60/267,859 filed Feb. 9, 2001, also incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to injection molding systems and apparatus for the production of molded articles. More particularly, the invention relates to systems and apparatus specifically adapted for injection molding articles of substantially amorphous polyethylene terephthalate and similar materials, whereby the gate vestige is removed by a laser cutting system which produces a molded article with reduce crystallization.  
           [0004]    2. Summary of the Prior Art  
           [0005]    The use of polyethylene terephthalate (hereinafter referred to as “PET”) and similar materials as the materials of choice in the formation of numerous injection molded articles is well known in the art. For example, in the bottle and container industry, the blow molding of injection molded PET preforms has gained wide acceptance, and is experiencing strong growth. Among the reasons for this is the fact that PET and similar materials offer a wide range of desirable properties. Specifically, PET materials generally evidence high strength, good clarity, and low gas permeation characteristics. Further, PET materials are comparatively easy to recycle. Accordingly, they are desirable for use in retail packaging applications.  
           [0006]    PET and similar materials, however, present molders with significant processing problems. These problems may be at least partially explained by the fact that these materials are considered to be what is known in the art as “crystallizable” materials. By this it is meant that the randomly oriented polymer chains of the amorphous phase of the material may be caused to form a highly ordered, crystalline structure in a controllable manner. This may be accomplished either by mechanical stretching of the material so as to cause an ordered orientation of its molecules and the formation of stress induced crystals, or by controlling the temperature of the material over time in a manner which induces crystal formation and growth. More particularly, as the temperature of the material is increased from the ambient, the material passes through a number of states. Specifically, the material in its so-called “glassy” (or rigid) state at ambient temperature upon heating will sequentially pass through a glass transition temperature range, a crystallization temperature range, and a crystal melting temperature range, before it reaches its molten state.  
           [0007]    In the glassy state, existing crystals in the material are stable, and additional crystals cannot form because the molecules are too sluggish. This is to say that the molecules of the material lack the requisite energy to move about sufficiently to induce the creation of the intermolecular bonds necessary for crystal formation. In the glass transition temperature range (which for PET is typically between about 175.degree. F. and about 185.degree. F.), the material transforms from its glassy state to a rubbery state.  
           [0008]    In the rubbery state, crystals tend to form and grow. The rate of this crystal formation and growth is both time and temperature dependent. More particularly, the rate of crystal formation and growth follows a substantially parabolic curve on a temperature versus time graph. It, therefore, will be recognized by those skilled in the art that for PET materials the rate of crystal formation and growth typically increases with temperature from about 185.degree. F. up to about 350.degree. F., and thereafter decreases to substantially zero at about 480.degree. F. Further, the extent of crystal formation and growth depends significantly upon the length of time during which the material is permitted to reside at any given temperature within its crystallization temperature range.  
           [0009]    The crystal melting temperature range for PET extends between about 480° F. and about 490° F. Above about 490° F., the material exists in its molten state.  
           [0010]    It is to be understood that the foregoing is a generalization of the crystallization properties of PET and similar materials. Variations in the properties of the particular material under consideration (such as its intrinsic viscosity, its diethylene glycol content, its water content and/or its comonomer or other additive content) may alter the melting point of the material, the crystallization behavior of the material, or both.  
           [0011]    Furthermore, the breakdown product acetaldehyde is known to be generated in significant amounts whenever PET material is in a molten state. It is also well understood that slight changes in the melt temperature will significantly effect the rate of acetaldehyde generation. Since acetaldehyde is a potent flavorant, its presence in the melt material must be minimized during the injection molding of food or drink containers (or preforms therefor). If this is not done, detectable changes in the flavor or aroma of foods packaged in such articles (or in containers made from such preforms) may be induced. Heretofore, acetaldehyde minimization has been accomplished by maintaining the melt temperature as low as possible, while still allowing substantially clear articles (or preforms therefor) to be formed by so-called “runnerless” injection molding apparatus.  
           [0012]    Injection molded preforms adapted for subsequent blow molding into a finally desired container form should consist of mostly amorphous material. This permits the preform to be blow molded into a desired shape easily and with a minimum of reheating. It also avoids the formation of undesireable cracks or a whitish haziness in the finished article/preform caused by the presence of excessive crystallized material therein. Further, the article/preform should have an acceptable acetaldehyde level, and be free from contaminants or defects.  
           [0013]    In systems and apparatus for the “runnerless” injection molding of articles/preforms of the type alluded to above, a mold and a molten material transport means are commonly provided. The mold typically includes a first cavity extending inwardly from an outer surface of the mold to an inner end, an article formation cavity, and a gate connecting the first cavity to the article formation cavity. The gate defines an inlet orifice in the inner end of the first cavity, and an outlet orifice which opens into the article formation cavity.  
           [0014]    The means for transporting the material extends from a melt source to the vicinity of the inlet orifice of the gate. These means typically include an elongated bushing residing at least partially within the first cavity. This bushing defines an elongated, axial passageway therethrough which terminates at a discharge orifice. A “gate area”, therefore, is defined by the assembled mold and bushing between the discharge orifice of the bushing and the outlet orifice of the gate. Ideally, this gate area is the portion of the system/apparatus in which the transition of the material from the molten phase present in the “runnerless” injection apparatus to the glassy phase of the completed article occurs during the time period between sequential “shots” of material.  
           [0015]    Specifically, during the injection of a “shot” of molten material (i.e., melt), the melt flows from the discharge orifice of the bushing, through the gap between the discharge orifice of the bushing and the inlet of the gate, through the gate, and into the article formation cavity of the mold. Since the temperature of the melt is maintained above its maximum crystal melt temperature in the bushing, and the temperature of the mold is maintained well below the minimum glass transition temperature of the material, the majority of each shot cools quickly to its glassy state in the article formation cavity of mold. This results in the preform containing low crystallinity levels (i.e., an article made up of substantially amorphous PET or other similar crystallizable polymer) because the material temperature does not remain within its characteristic crystallization range for any appreciable length of time.  
           [0016]    At the end of each “shot”, however, injection pressure commonly is maintained on the melt for between about 1 to 5 seconds in order to assure that the melt is appropriately packed into the article formation cavity of the mold. Thereafter, the injection pressure on the melt is released, and the article is allowed to cool in the mold for between about 10 to 15 seconds. Subsequently, the mold is opened, the article is ejected therefrom, and the mold is reclosed. The latter steps take on the order of about 5 to 10 seconds. It will be understood, therefore, that for correct system operation the temperature of the melt material must transition in the gate area of the system/apparatus during the time interval between successive material “shots” between its molten phase temperature and its glassy (rigid) phase temperature in a controlled manner.  
           [0017]    Accordingly, thermal control of the temperature gradients in the material located in the gate area between successive “shots” of molten material is critical both to the prevention of stringing or drooling of melt material from the gate, and to the prevention of gate freeze-off. In addition, a failure to isolate the majority of the crystallized melt material formed during this transition within the vestige which extends outwardly from the completed article ejected from the mold may be detrimental not only to the efficiency of subsequent blow molding operations, but also to the quality of the final blow molded article for the reasons mentioned above.  
           [0018]    To accomplish this thermal gate control, the art has heretofore adopted two alternative approaches. In the first of these alternatives, a mechanical melt shut off mechanism is provided by what is known as a “valve gate”. In the other alternative, the axial length of the gate is increased so as to ultimately form a vestige extending outwardly from the article/preform which is substantially longer than the comparatively short vestige normally resulting from “runnerless” injection molding operations.  
           [0019]    The valve gate utilizes a pin which is axially movable in the bushing passageway. In a first retracted position, this pin allows melt material to flow through the bushing, into the gate area, and ultimately into the article formation cavity of the mold. In a second extended position, however, the distal end of the pin closes off the gate area, and thereby shuts off the flow of melt material therethrough. Specifically, the distal portion of the valve pin either may seal the inlet of the gate, or may substantially fill the volume defined by the gate so as to accomplish melt shut off.  
           [0020]    This mechanism has several advantages. Principle among these is the preclusion of the potentially detrimental presence of melt material in the gate area between successive “shots”. The absence of melt material adjacent to the gate outlet prevents stringing of melt material between the gate and the vestige. Drooling of melt material from the gate between “shots” also is prevented for the same reason. In addition, the resulting vestige (if any) is of acceptably short length, and is composed primarily of substantially amorphous material. The latter result is achieved because the vestige is substantially thermally isolated from the melt transport means upon extension of the valve pin. Consequently, the vestige (if any) cools primarily under the influence of the surrounding gate portion of the mold which, as mentioned above, is maintained well below the minimum glass transition temperature of the material.  
           [0021]    The elongated vestige alternative, on the other hand, evolved from the fact that the portion of the mold forming the gate walls in a conventional hot runner system is inadequate for controlling the crystallization of PET and similar crystallizable polymeric materials in the gate area during the time interval between successive material “shots”. More particularly, it will be understood that the metal (typically steel) forming the gate walls in a conventional hot runner system is located between the inner end of the first cavity of the mold adjacent to the inlet orifice of the gate and the portion of the article formation cavity of the mold adjacent to the outlet orifice of the gate. In such a system, the quantity and thermal conductivity properties of the metal defining the gate are not adequate to both (1) effectively withdraw heat from adjacent melt material in the article formation cavity of the mold in a manner which assures its amorphous nature in the completed article, and (2) at the same time effectively participate in the required melt material crystallization control in the gate area.  
           [0022]    Accordingly, the axial length of the gate in some cases has been increased by artisans in the field of this invention so as to provide a gate wall structure capable of performing both of the above functions simultaneously. This, in turn, has resulted in the presence of an elongated sprue, or vestige, projecting from the finished article or preform.  
           [0023]    The latter alternative has the advantage that the machine/mold designer can be relatively sure that substantially all crystallized material in the completed article/preform will be contained within the vestige. The resulting article/preform, however, may be adversely effected by the presence of the elongated vestige during the blow molding operation. Specifically, cracks may form at the vestige/article interface during the blow molding operation thereby ruining the blow molded article.  
           [0024]    It is within this approach that significant effort has been employed to produce an injection molded article with an elongated vestige, and during post-processing, remove the elongated vestige. The prior art has seen numerous attempts at employing various cutting means including mechanical cutter means and grinding. These methods have generally proved unsuccessful due to low aesthetic quality and surface imperfections that are formed during the cutting process.  
           [0025]    There exists a need for an improved injection molding system that allows for the use of an elongated sprue on a preform for reduced crystallinity that is subsequently cut off in a high speed manufacturing environment.  
         SUMMARY OF THE INVENTION  
         [0026]    The primary objective of the invention is to provide an injection molded preform made of PET or similar material exhibiting reduced crystallinity through the use of an elongated sprue.  
           [0027]    Another object of the invention is to provide a system and apparatus for removing an elongated sprue from an injection molded article by laser cutting.  
           [0028]    A further object of the invention is to provide an improved injection molded preform with an improved surface finish in the area of the cut-off elongated sprue.  
           [0029]    Still another feature of the present invention is to provide an injection molding system and apparatus that comprises an automatic recovery and recycling system of the cut-off elongated sprue material.  
           [0030]    The foregoing objects are achieved by providing an injection molding machine which comprises a plurality of preform mold cavities for the formation of molded articles therein, the mold cavities comprise an elongated vestige feature whereby substantially all crystallinity occurs within the elongated vestige. Following the molding process, the preforms are placed in a conveyor like apparatus so that the elongated vestige of each preform is passed inline with at least one laser cutting apparatus. The energy of the laser is adjusted so that the elongated vestige is severed from the preform, thereby resulting in an improved preform with improved crystalline properties and acceptable surface finish in the area of the removed elongated vestige. The cut off elongated vestige is captured by a recycling system and remelted so that waste is minimized.  
       
    
    
     BREIF DESCRIPTION OF THE DRAWINGS  
       [0031]    [0031]FIG. 1 is a simplified isometric view of an injection molding machine in accordance with the present invention;  
         [0032]    [0032]FIG. 2 is an isometric view of the underside of the shuttle table in accordance with the present invention;  
         [0033]    [0033]FIG. 3 is an enlarged isometric view of the laser cutting station with an array of preforms;  
         [0034]    [0034]FIG. 4 is a partial detail view of the laser cutting station;  
         [0035]    [0035]FIG. 5 is a detailed cross-sectional view of a typical preform  
         [0036]    [0036]FIG. 6 is a top plan view of the laser system layout.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]    Referring first to FIG. 5 which shows a blank  108 , also termed preform, of a substantially amorphous thermoplastic material, preferably PET, having a mouth portion  122 , a substantially conical portion  124  extending from the mouth portion, a substantially cylindrical portion  126 , and a region of material  128  which, when forming the blank  108  into a container, forms the bottom of the container. The blank  108  has a central cavity  130  with a substantially cylindrical upper portion  132  and a substantially cylindrical lower portion  134 , whose circumference is smaller than that of the upper portion  132 . The transition between the upper and lower portions  132 ,  134  of the central cavity is a substantially conical transition portion  136 . The cylindrical lower portion  134  is closed at its bottom, which is bulging outwards and comprises an elongated vestige or sprue  109 . It is this elongated vestige  109  that will be severed from the preform  108  because it exhibits high crystallinity.  
         [0038]    The preform  108  thus serves as starting material in the making of a blow-molded container for example a reusable bottle for beverages.  
         [0039]    The mouth portion  122  has a threaded portion  138  and an annular gripping portion  140 . The material forming the mouth portion  122  is designated A in FIG. 5. The conical portion  124  encloses the substantially cylindrical upper portion  132  of the central cavity of the blank  108 . The cone of the conical portion  124  results from an increase of the thickness of this portion towards the bottom of the blank  108 . The material of the blank  108  forming the conical portion  124  is designated B in FIG. 5.  
         [0040]    The proximal part, with respect to the bottom of the blank  108 , of the substantially cylindrical upper portion  132  of the cavity  130  is defined by a wall having a substantially uniform wall thickness in all parts of the cylindrical portion  126 . The region of the substantially cylindrical portion is marked C in FIG. 5.  
         [0041]    The region of material  128 , which after reshaping of the blank  108  is intended to constitute the bottom of the container, has an increased wall thickness in the region of the transition portion  136  of the cavity of the blank  108 , and maintains this wall thickness substantially throughout the entire region of the substantially cylindrical lower portion  134  of the cavity. The wall thickness of the blank  108  thereafter decreases in the closed bottom of the blank to have its minimum thickness in a central region of material  142  in the bottom of the blank  108 . Reference D indicates the material of the blank  108  which in the resulting container is reshaped to form part of the bottom of the container, while reference E indicates the material of the blank  108  which substantially retains its shape when forming the container.  
         [0042]    Referring now to FIG. 1, an injection molding system  10  according to the present invention is generally shown. The injection molding system  10  is comprised of an injection molding machine  12 , a transport subsystem  14 , a pick and place robot  16 , a laser cutting station  18  and an inspection station (not shown). All of these subsystems work together to form a high speed manufacturing process for the production of injection molded articles, for example PET preforms  108 .  
         [0043]    In the preferred embodiment, the injection molding machine  12  is an index type machine with a rotary turret  36  for the production of PET preforms  108 . As one skilled in the art will recognize however, any type injection molding machine may easily be adapted for use with the present invention.  
         [0044]    Injection molding machine  10  generally includes a rotary turret  36  with a plurality of movable mold halves  37   a   37   d,  a stationary mold half and platen  34  and injection unit  32 , all positioned on base  30 .  
         [0045]    Injection molding system  10  may be used for molding a variety of different types of articles and accordingly, is not limited for use with any particular type of article. Preforms are referred to throughout this description by way of example only.  
         [0046]    While the rotary turret  36  is shown throughout this description as rotatable on a horizontal axis, and this is the preferred embodiment, it is feasible that a similar design of a movable turret block providing the clamping action may be provided which is rotatable on a vertical axis. Accordingly, this invention is not considered limited to the horizontal axis feature.  
         [0047]    As shown in FIG. 1, rotary turret  36  is preferably longitudinally movable on base  30  via a set of bearings blocks  43  attached to the bottom of a pair of turret fittings  46 . Base  30  includes linear bearings  44  which engage bearing blocks  43  and counteract upward forces and tipping forces that may act on the turret block assembly. Rotary turret  36  is rotatable preferably by a rotational drive  41  in communication with belts and pulleys, preferably an electric servo drive motor and preferably on a horizontal axis H through arcuate sectors preferably of substantially 90.degrees. Preferably, the rotational drive is connected via a belt drive  39  to axis H for rotating the rotary turret  36 , as shown in FIG. 1, while the electric servo drive motor is preferably mounted on one of turret fittings  46  extending from base  30 .  
         [0048]    As shown in FIG. 1, rotary turret  36  includes a plurality of movable mold halves, i.e. movable mold halves  37   a - 37   d  each of which includes a plurality of mold cores  45   a - 45   d , respectively, each set having at least one mold core, adapted for engagement with a set of mold cavities  40 , each set including at least one mold cavity and located in stationary mold half and platen  34 . Preferably, four movable mold halves or faces  37   a - 37   d  are provided on rotary turret  36 , although any number supportable by the size of the rotary turret  36  can be used. Sets of mold cores  45   a - 45   d  are adapted to be rotated into horizontal and vertical alignment with sets of mold cavities  40 .  
         [0049]    Referring still to FIG. 1, rotary turret  36  includes sets of ejector pistons or stripper rings  33   a - 33   d , and a system for the operation thereof, which operate on sets of mold cores  45   a - 45   d  and strippers positioned on movable mold halves  37   a - 37   d , respectively. Accordingly, sets of ejector pistons or stripper rings  33   a - 33   d  are positioned within rotary turret  36  and parallel to sets of mold cores  45   a - 45   d  and perform the function of stripping the mold cores of finished molded articles, for example, preforms, such as those shown in FIGS. 4 and 5. Each movable mold half  37   a - 37   d  and platen  34  includes at least one ejector piston in each set  33   a - 33   d  for stripping finished articles from sets of mold cores  45   a - 45   d . For the detailed design of the ejector piston or stripper ring system for use with sets  33   a - 33   d , reference is made to U.S. Pat. No. 5,383,780, issued Jun. 24, 1995, to the assignee of the present invention, for incorporation by reference of a design of the ejector piston or stripper ring system, particularly column 4, line 29, to column 7, line 6, and FIGS.  1 - 8 . Preferably, the ejector piston or stripper ring system is actuated via the hydraulic services supplied to the rotary turret  36 , as discussed below. The hydraulically actuated ejector piston or stripper ring system actuated by on board hydraulic services is the preferred design, however, other designs may be used.  
         [0050]    Rotary turret  36  is movable backward and forward along linear bearings  44  on base  30  via piston/cylinder assemblies  38  positioned in stationary mold half and platen  34 , as shown in FIG. 1. Preferably four piston/cylinder assemblies  38 , as shown in FIG. 1 are used which are positioned in the corners of stationary mold half or platen  34 . Each piston/cylinder assembly  38  is attached to tie bars  47 , respectively, which tie bar  47  acts as the piston shaft. Accordingly, tie bars  47  extend from the piston/cylinder assemblies  38  and are connected at an opposite end to rotary turret  36 . In order to move rotary turret  36  backward and forward relative stationary mold half and platen  34 , pressurized fluid is forced into cylinders assemblies  38 . The side of the cylinder assemblies  38  in which pressurized fluid is forced against, determines the direction in which rotary turret  36  moves relative stationary mold half and platen  34 , that is, either into an open or closed position. Tie bars  47  pass through the turret fittings  46  and are attached thereto via retaining nuts.  
         [0051]    Services S, shown in FIG. 1, are provided to rotary turret  36  via a rotary union  31 . Accordingly, as rotary turret  36  rotates, services S are continuously supplied to the movable mold halves  37   a - 37   d . Such services S include the supply of electricity, pressurized fluid, cooling fluids, and hydraulic fluids, etc. For using these services, rotary turret  36  also includes the required circuitry and control valves (not shown) on board and movable and rotatable with the turret block.  
         [0052]    Injection unit  32 , preferably in the form of a reciprocating screw injection unit, is connected with stationary mold half and platen  34  positioned on base  30  for providing melt to the mold cores for molding. Injection unit  32  is preferably movable into and out of engagement with stationary mold half and platen  34  by means of carriage cylinders (not shown) on rollers and hardened ways, similar to as described above for use with rotary turret  36 .  
         [0053]    Still referring to FIG. 1, the transport subsystem  14  comprises an inside and outside track  48   a  and  48   b  mounted to the base  30  and running from under the rotary turret  36  to a position of easy access by the pick and place robot  16 . A motor  50  is attached to one end of the inside track  48   a  which is in communication with a shaft  54  which runs between the inside and outside track  48   a  and  48   b . Attached at each end of the shaft  54  is a pair of belts  52  which run the entire length of the tracks  48   a  and  48   b . Attached to the inside surface of each track  48   a  and  48   b  is a second pair of linear bearings  56  which interface with a plurality of bearing blocks  60  (FIG. 2) rigidly affixed to a shuttle table  58 . Each belt  52  is attached to the shuttle table  58  such that the shuttle table  58  is operatively positioned (back and forth) through the use of the motor  50  along tracks  48   a  and  48   b . In this arrangement, the shuttle table is controllably positioned beneath the rotary turret  36  to accept the molded preform  108 . Once the shuttle table  58  is filled with preforms  108 , it is operatively positioned at a far end of the tracks  48   a  and  48   b  for easy access by the pick and place robot  16 .  
         [0054]    Referring now to FIG. 2, the shuttle table  58  comprises a horizontal surface  62  with a plurality of holes  64  arranged to interface with the movable mold halves  37   a - 37   d  of the rotary turret  36 . Inserted in each hole  64  is a spacer  66  sized to accept the molded preform  108 . In the preferred embodiment, the spacers are made from a soft plastic material to minimize the scratching of the preform  108  that may occur during the handoffs from the shuttle table  58 .  
         [0055]    In the preferred embodiment, the shuttle table  58  must translate upwardly to interface with and catch the plurality of molded preforms  108  when they are released by the rotary turret  36 . To accomplish this motion, a servo-motor  68  is mounted beneath the horizontal surface  62  and in communication with a pair of ball screws  70 . Each ball screw  70  is attached to opposite ends of the horizontal surface  62  and grounded to an inside and outside support  74   a  and  74   b . A second belt  72  runs between the ball screws  70  such that the servo-motor  68  controls both ball screws  70  for raising and lowering the horizontal surface  62  of the shuttle table  58 .  
         [0056]    Once the shuttle table  58  has received a plurality of preforms  108 , the table  58  moves away from the injection molding machine  12  and aligns with the robot  16 . The robot  16  comprises a frame  80  which carries a pick-up table  84  along a trackway  82 . The pickup table  84  interfaces with the shuttle table  58  with a plurality of air operated fingers  86  which are inserted into each preform  108 . The pick up table  84  is moved under precise control in a manner similar to the way the shuttle table  58  is moved and therefore won&#39;t be further described herein. In the preferred embodiment, once the air operated fingers  86  are positioned inside the preforms  108 , air is communicated to the fingers  86 , causing them to expand and grab on the inside surface of the preforms  108 . There are myriad methods for picking up the preforms  108 , and the forgoing is just an example of one of these methods and should not be read to limit the scope of the invention.  
         [0057]    Once the plurality of preforms  108  are retrieved by the pick up table  84 , the table translates to a distal location so that the preforms are aligned with a singulator  88 . The singulator  88  is a flat plate with a continuous serpentine groove  89  machined therein. The serpentine groove  89  is designed to accept a plurality of different preform sizes. Once the preforms  108  are properly seated in the groove  89  by the pick up table  84 , the air in the fingers  86  is removed and the plurality of preforms  108  are released into the groove  89 . Now the preforms  108 , which were in individual holes, have been placed into the continuous groove  89  allowing them to be easily slid in a linear fashion to be picked up by an inline, single file conveyor  90 .  
         [0058]    Referring to FIGS. 3 and 4, the preforms  108  travel down the conveyor  90  to the laser cutting station  18 . The laser cutting station  18  comprises a rotary track  92  which accepts the preforms from the conveyor  90  and spins them in a circular fashion past a plurality of laser beams  103 . The rotary track  92  comprises a circular holder  96  with a plurality of pockets to accept the preforms  108  from the conveyor  90 . The rotational speed of the rotary track  92  is matched with the linear speed of the conveyor  90  so that preforms  108  are quickly and easily transferred into the pockets of the circular holder  96 . As the rotary track  92  rotates (and before the preform aligns with the first laser beam  103 ), a segmented top plate  94  is lowered into contact with the top surface of the preform  108  and forces the bottom of the preform  108  to interface with a lower shield  98 . In this arrangement, the elongated vestige  109  is now properly aligned with the plurality of laser beams  103  as they travel around with the rotary track  92 . The elongated vestige  109  travels past each laser beam  103  in rapid succession, thereby severing the vestige  109  from the preform  108 . The now severed vestige  109  drops into a reclamation bin  112 , where the vestige  109  will be later re-melted and recycled.  
         [0059]    The shield  98  is specifically designed to both protect the main body of the preform  108  from damage by the laser and also maintain a given length of remaining vestige. Testing has shown that without the shield  98 , energy from the laser  102  can cause inadvertent damage to the body of the preform  108 . In addition, international quality inspection criteria dictate the required length of any remaining vestige. Using the shield  98  insures the laser cuts the elongated vestige  109  at the proper location.  
         [0060]    Referring to FIG. 6, the various optical components which comprise the laser cutting setup are generally shown. Two lasers  102  are each aligned such that the laser beam passes first through a splitter  106   a  and  106   b  respectively. The splitters  106   a  and  106   b  are designed to reflect half of the laser beam power at 90 degrees from the entering beam, and allow the other half of the laser beam power to continue on to a mirror  118   a  and  118   b  where the remaining laser beam power is also reflected at 90 degrees from the entering beam. In the preferred embodiment, the optimum laser cutting set up was found to be two 500W CO 2  lasers focused inline with the elongated vestige  109 . In this arrangement, four laser beams, each with approximately 250 watts of power are transmitted to a bank of focusing lenses  104   a - 104   d . Positioners  120   a - 120   d  are attached to each lens  104  and allow for minute adjustments to the focused laser beam for machine set. In the preferred embodiment, a CO2 laser operating at a predetermined pulse, for example around 100 kHz, and with a focused beam width of a predetermined diameter, for example about 0.05-0.25 mm, was found to work best.  
         [0061]    A buy product of the laser cut is a very fine dust which tends to accumulate on the outside surface of the preform. The shield  98  helps to prevent this dust from accumulating on the preform and a brush  115  is mounted in the path of the shield  98  to wipe the dust off. Alternatively, or in combination, forced air could be blown over the preforms as the cut is made, or an electrical charge could be placed on the preforms to repel the flying plastic dust.  
         [0062]    The unload conveyor  116  accepts the preforms  108  in a linear fashion after they have been cut and transfers them to an inspection station (not shown) where each preform is inspected for compliance with quality control standards.  
         [0063]    It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. For example, the exact placement and splitting of the laser beams is susceptible to myriad variations, and any such variation is fully contemplated by the present invention. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.