Abstract:
A mold for use in blow molding has a first fixture and a second fixture. The fixtures correspond to typical mold halves or portions. The first fixture includes drive means, typically in the form of pins, while the second mold fixture has drive receiving means, typically in the form of holes, to receive the pins. When the second mold fixture is in registration with the first mold fixture, the pins or other drive means are extended to lock and locate the two fixtures together. Blow molding can then be carried out without the need of the typical blow molding presses.  
     A method of blow molding involves the use of a robotic arm to move the relatively lightweight second mold fixture described above beneath a parison head to accept a parison as it is being extruded so the parison is contained within the mold cavity. After extrusion is complete the arm moves the second fixture toward the first fixture so that the fixtures can be located and locked together. A single robot using a single extrusion head can serve several mold stations depending upon cycle times.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an apparatus and method for manufacturing blow molded plastic articles and particularly to manufacturing articles without the need for typical blow molding presses or clamping systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is well-known that blow molding is effective in fabricating hollow plastic articles. Typically when molding articles in a blow molding process, a parison is extruded and the parison is accommodated in a suitable cavity in one-half of a blow mold. The more complex the shape of the article, the more complex will be the shape of the mold and the cavity in the mold. For very simple articles, the parison may be extruded to hang vertically and the mold halves may be closed around the parison moving in a horizontal direction. For other slightly more complex parts, particularly larger parts, it may be desirable to place the parison in the mold as the parison is being extruded. When the parison has been accommodated in the lower mold half, the lower mold half is then often moved in a substantially horizontal direction to a molding station. When the lower mold half, accommodating the parison, is in the molding station, a molding press is then used to move the upper mold toward the lower mold half to close the mold prior to blow molding. Substantial force is required in the blow molding press as, in many cases, the press is required to pinch the parison at either end and the resultant flow of plastic material must be accommodated by the press forces, while at the same time the press must close to bring the mating surfaces of the mold halves together. This is required so that the parison does not expand into any space between the mating surfaces of the mold halves during the blowing operation. The press is also required to withstand whatever pressures may be exerted on the mold halves tending to separate them, arising from the pressure of the blowing gas operating over the area of the mold cavity.  
           [0003]    The prior art offers several solutions for placing a molten parison in what are usually lower mold halves. For example, one solution involves introducing means for horizontally, (i.e. in an x, y plane) moving the lower mold half beneath the parison extrusion head in such a manner that the parison is dropped within the mold cavity. Molds which are used in typical blow molding are normally quite heavy and hence this solution requires significant effort to effectively and accurately move the mold half.  
           [0004]    In some prior art devices, the extrusion head is moved horizontally in an x, y plane so that as the parison is extruded, it is arranged to follow and lie in the cavity in a lower mold half. Extrusion equipment used in typical blow molding is also large and heavy to support the extrusion temperatures and pressures involved and it is costly and cumbersome to move the extrusion head, even in a horizontal plane.  
           [0005]    U.S. Pat. No. 5,030,083 to Kohno, teaches the use of a robotic hand to grasp and transport an extruded parison to a remote lower mold half having cavity and place it therein. Where a sizable parison is required, however, the swinging action of the parison induced by its movement by the robot hand can make the path the hand must follow to properly load the parison in the mold, quite complex. Another significant problem is the weight and strength of the molten parison. The parison may break under its own weight during transport from the extrusion head to the mold.  
           [0006]    U.S. Pat. No. 5,464,635 to Geiger, discloses the use of a moveable premold having a shape matching the lower mold cavity. A molten parison is extruded into the premold which is moved under the extrusion head, by robotic or other means, to cause the parison, as it is extruded, to be deposited in to the premold cavity. Hence, once loaded with the parison, the premold is transported to the lower mold half and positioned thereover, with the premold and mold cavities substantially aligned. The premold includes openable doors or other similar acting structure so that by opening the structure, the parison is dropped directly into the mold cavity of the lower mold half. This system requires the design of a complex premold with means to accurately release the parison so that it accurately falls into the groove of the lower mold half.  
           [0007]    In our co-pending application, we have provided an alternative solution. The alternate solution provided in our co-pending application involves the use of a relatively lightweight lower mold half the lightweight lower mold half comprises a cavity into which the parison is extruded. A robotic arm or other manipulation means is used to move the lightweight lower mold half into a suitable position so that as the parison is extruded from the extrusion head, the lower mold half may be moved so that the parison is extruded directly into place in the mold cavity. Once the extrusion process is completed, the parison is cut and the lightweight lower mold half together with the parison located therein, is then moved to a molding station. At the molding station, the lightweight lower mold half is placed in a lower mold half support. The lower mold half support provides the weight and substance as well as physical support for the lower mold half so that it may be used in a typical mold press or clamp to blow mold parts. The disclosure of our co-pending application is incorporated herein in its entirety by reference.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with this invention, a mold assembly comprises a first mold fixture. The first mold fixture includes a first mold cavity. The mold assembly includes a second mold fixture. The second mold fixture includes a second mold cavity. The first and second mold cavities define a complete mold for blow molding a parison. The first mold fixture includes drive means and the second mold fixture includes drive receiving means. The drive means of the first mold fixture and the drive receiving means of the second mold fixture are adapted to locate and lock the second mold fixture against the first mold fixture with the first and second mold cavities in registration to form the complete mold.  
           [0009]    In accordance with another aspect of the invention, a process for blow molding parts comprises the use of a first mold fixture and a second mold fixture. The first mold fixture includes a first mold cavity and the second mold fixture includes a second mold cavity. The first and second cavities define a complete mold for blow molding a parison. The first mold fixture includes drive means and the second mold fixture includes drive receiving means. The drive means of the first mold fixture and the drive receiving means of the second mold fixture are adapted to locate and lock the second mold fixture against the first mold fixture with the first and second cavities in registration to form a complete mold. The process further comprises the steps of extruding a parison from an extrusion head. A parison is extruded from the extrusion head. While the parison is being extruded, the second mold fixture is moved so that the parison is extruded to lie within the second mold cavity. The second mold fixture is moved by manipulation means to receive the parison as it is extruded. Manipulation means are also used to translate the second mold fixture from adjacent to the extrusion head to adjacent the first mold fixture so that the second mold fixture is substantially in registry with the first mold fixture. The drive means of the first mold fixture are then extended and are received within the drive receiving means of the second mold fixture. The receipt of the drive means within the drive receiving means locates and locks the first and second mold fixtures in registry to form a complete mold. The process involves blow molding the parison within the first and second fixtures without the need for any outside clamping force. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings.  
         [0011]    The drawings show a preferred embodiment of the present invention in which:  
         [0012]    [0012]FIG. 1 is cross-sectional view through a mold assembly;  
         [0013]    [0013]FIG. 2 is a perspective exploded view of the mold assembly of FIG. 1;  
         [0014]    [0014]FIG. 3 is a perspective view of one of the components of the mold assembly of FIG. 1 showing the component ready for manipulation;  
         [0015]    [0015]FIG. 4 is an enlarged vertical section of a portion of the mold assembly of FIG. 1;  
         [0016]    [0016]FIG. 5 is a plan view showing a multi-stage manufacturing process using plurality of mold assemblies of the type illustrated in FIG. 1, and  
         [0017]    [0017]FIG. 6 is a vertical partial sectional view similar to FIG. 1 showing an alternate embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    With respect to FIGS. 1 and 2, the mold assembly  10  includes a first mold fixture  12  and a second mold fixture  14 .  
         [0019]    The first mold fixture  12  comprises a first mold cavity  22 . The first mold cavity  22  is defined in the mold fixture surface  24 . The first mold fixture  12  further comprises a pair of substantially downwardly depending surfaces  26  and  28 . The surfaces  24 ,  26  and  28  define therebetween a receiving recess indicated generally as  30 .  
         [0020]    The first mold fixture  12  further comprises drive means  40 . The drive means  40  include four piston-pin assemblies as shown in FIG. 2. The four piston-pin assemblies, are located so as to extend pins  46  outwardly from the walls  26  and  28  so that upon extension of the pins, the pins project into the recess  30 . Upon withdrawal of the pins, the recess  30  is unencumbered. Two of the drive means  40  are shown more clearly in FIG. 1. The drive means  40  include a piston  42  and a pin  46 . The piston  42  is moveable within a cylinder  48 .  
         [0021]    In FIG. 1, the pins  46  are illustrated in the extended position, that is, projecting from the walls  26  and  28  so as to project into the receiving recess  30 . The pistons  42  are movable within the chambers  48  by any suitable pressure means. This can be hydraulic or pneumatic so that the piston can be moved, both left and right as shown in FIG. 1, to either extend or retract the pins  46  from the receiving recess  30 . The connections for the operating fluid have not been illustrated in FIG. 1. Conventional piston, pin and cylinder assemblies can be used for this purpose.  
         [0022]    The second mold fixture  14  is illustrated in FIGS. 2 and 3. The second fixture  14  includes a second mold cavity  60 . The mold cavity  60  is defined in the mold fixture surface  62 .  
         [0023]    The second mold fixture  14  comprises four drive receiving means  66 , two of which are visible in FIGS. 2 and 3. In the preferred embodiment the drive receiving means  66  comprise a bore  70  having an axis  72 .  
         [0024]    The drive receiving means  66  are located so as to receive each of the pins  46  of the drive means  40  of the first mold fixture.  
         [0025]    The second mold fixture  14  further comprises a gripper receiving means  80  as shown in FIG. 3. The gripper receiving means may be in the form of a projecting plate or handle. The gripper receiving means is intended to cooperate with the gripper  82  of robot arm  84 . Any suitable type of gripper  82  and gripper receiving means  80  may be utilized to facilitate manipulation of the second mold fixture  14  as described more fully below.  
         [0026]    The second mold fixture includes side surface  64 , which is visible in FIG. 3 and an opposite surface  65 .  
         [0027]    As illustrated in FIGS. 1, 2 and  3 , the second mold fixture  14  is a comparatively smaller structure than the first mold fixture  12 . In use, the second mold fixture, being comparatively lighter than first mold fixture  12 , may be relatively easily manipulated. Accordingly, in use, a manipulator in the of robotic arm  84 , is used to manipulate the second mold fixture  14  beneath an extrusion head. As a parison is extruded from an extrusion head, the parison can be received within the second mold cavity  60 . When the extrusion process is complete, the parison is cut and then lies within the second mold cavity  60 . The robotic arm  84  then translates the second mold fixture  14  and moves it into a position within the receiving recess  30  of first mold fixture  12 . The robotic arm can move the second fixture  14  until such time as the mold fixture surface  62  is adjacent to the mold fixture surface  24 , and in contact therewith. When the mold fixture surface  62  of the second mold fixture is in contact with the mold fixture surface  24  of the first mold fixture, side surface  64  of second mold fixture  14  will be closely adjacent to the depending surface  28  of first mold fixture  12 . In addition, side surface  65  of second mold fixture  14  will be adjacent depending surface  26  of first mold fixture  12 . When second mold fixture  14  is positioned within the receiving recess  30 , of first mold fixture  12 , each of the drive receiving means  66  will be aligned with and adjacent to the respective drive means  40  of first fixture  12 . When the first and second molds are in registry, then the drive means  40  are operated to cause the pins  46  to project into the recess  30 . As the pins are extended into the recess  30 , they will engage with the bores  70  of the respective drive receiving means  66 . The pins  46  and the bore  70  are sized so that the bore closely accommodates the diameter of the pin  46 . This close fit ensures the two fixtures remain in a relative locked position so that the two mold fixtures do not move relatively when the blowing pressure develops. To facilitate entry of the pin  46  into the bore  70 , the tip of the pin  46  may be provided with a part conical entry portion  47  as shown in FIG. 4. The axis  49  of the pin  46 , may substantially align with the axis  72  of the bore  70 . Thus, the extension of the pins  46  into the bores  70  accomplishes the function of closely locating the second fixture  14  with respect to first fixture  12  and also serves to lock the location of second fixture  14  with respect to first fixture  12 .  
         [0028]    When the second fixture  14  has been locked and located with respect to first fixture  12  as explained above, then the first mold cavity  22  will be in registry with the second mold cavity  60  to form a complete mold cavity. The blow pin assembly which is preferrably part of first mold fixture  12  is then positioned so that the blow pin may be extended to pierce the parison so that a blowing gas may then be delivered to the interior of the parison. This expands the parison so that the parison will assume the configuration of the complete mold cavity comprised of first mold cavity  22  and second mold cavity  60 .  
         [0029]    Because the drive means  40  extend into the drive receiving means  66  of the second mold portion  14 , the second mold portion cannot move relative to the first mold fixture  12  so as to separate surfaces  24  and  62 . Thus, there is no need to use a molding press or other clamping pressure. Rather, the complete mold remains intact simply because of the interreaction of the drive means  40  with the drive receiving means  66 .  
         [0030]    As shown in FIG. 4, the fit of pin  46  within bore  70  is a close fit. Where a cylindrical pin and a cylindrical bore  70  are used as shown in FIG. 4, the tolerances of the pin  46  and bore  70  will have to be carefully controlled so as to ensure that there is no unacceptable separation between the surface  62  of the second mold fixture  14  and surface  24  of the first mold fixture. If desired, the axis  72  and  49  need not be parallel to surfaces  24  and  62 . The angled pins would help to limit any unwanted relative movement.  
         [0031]    In many cases the robot arm will have sufficient strength so as to move the second mold fixture containing the parison against the first mold fixture and to create enough force between the first and second mold fixtures to effect at least a preliminary air tight seal of the parison. The configuration of the mold cavities and the capacity of the robot arm are selected, where possible, to accomplish this parison seal.  
         [0032]    Depending upon the size of the product to be blow molded and the blowing pressures to be used, it may be desirable in some circumstances that the locate and lock structure comprising the drive means  40  and drive receiving means  66  acts to force mold fixture surface  62  against mold fixture surface  24 . In such a case, it is desirable to use something other than a cylindrical pin received in a cylindrical bore. Various force developing structures may be incorporated into one or other or both of the drive means and the drive receiving means. In general, the mold assembly may incorporate a camming surface which together with a follower structure generates the desired sealing force. For example, tapered pins and holes can be used. Also, wedge shaped surfaces can be provided.  
         [0033]    Alternatively, one or more of any type of commercially available force applying mechanisms can be added to mold fixture  12  that can serve to force mold fixture surfaces  62  and  24  together to compress and pinch the parison as the process requires. An example is shown in FIG. 6 at  80 . In this case, the drive means  40  is in the form of a pivoting arm  82  and the drive receiving means is the surface  84  of second mold fixture  14 . The force applying mechanism  80  is affixed to first mold fixture  12 .  
         [0034]    The amount of pressure that would be developed between the surfaces  62  of the second mold fixture  14  and surface  24  of first mold fixture  12  would be a function of the number of separate drive means used, the size of pistons and the pressures available for driving the pistons pushing the pins, wedges or levers to the engaged position. All of these factors can be varied within the scope of this invention to provide sufficient location of the second mold fixture  14  with respect to the first mold fixture  12  to ensure that the complete mold cavity remains intact, as shown in FIG. 1.  
         [0035]    While the invention illustrated in FIGS. 1, 2 and  3  may be successfully utilized in a single molding station, the structure as described herein is particularly suited to a multiple stage molding system. Such a system is shown generally at  100  in FIG. 5. The molding apparatus  100  shown in FIG. 5 includes an extrusion head  102 , and a plurality of molding stations  104 ,  106  and  108 . The molding system  100  includes a robot  110  having a robotic arm  112 . The robotic arm  112  includes a gripper illustrated diagrammatically at  114 .  
         [0036]    The robot  110  may grasp a first lower mold fixture  14  and move that fixture to beneath the extruder  102 . The extruder would then operate to extrude a parison which is received within the mold cavity  60  of the first second mold fixture. With the parison in the mold cavity  60 , the second mold fixture could then be moved to the molding station  104 . At molding station  104  there would be a first mold fixture  12  similar to that illustrated in FIG. 1. The robotic arm would place the second mold fixture  14  within the first mold fixture  12  at station  104 . The drive means of the first molding station would then be operated to locate and lock the mold fixtures of station  104 . The gripper would then release and the mold arm  112  would move to station  106 . Once the robot arm leaves station  104 , the blow molding process can take place at station  104 . While that molding process occurs at station  104 , the robot can then direct its arm to station  106  where it will grasp the second mold fixture  14  for use at station  106 . The blow molding can then occur at station  106 . The robotic arm then manipulates the second mold fixture from station  106  to obtain a parison and returns it for locating and locking. While blow molding is occurring at station  106 , the robot can direct its arm to station  108  and go through another iteration of the process.  
         [0037]    Each of stations  104 ,  106  and  108  may consist of one pair of first mold fixture and second mold fixture. Alternatively, there may be extra second mold fixtures  14 . One of the issues to deal with in blow molding is cooling of the mold fixtures  12  and  14 . As mold fixture  12  is a relatively substantial structure, that structure can be cooled by known means such as fluid cooling applied through ducts. As shown in FIG. 3, the second mold fixture  14  may also have a source of cooling fluid which may be supplied through flexible hoses  69 . The fluid may flow through internal galleries  71  shown in FIG. 4 to provide cooling of the second mold fixture  14 . Sufficient length and flexibility of the cooling hoses  69  will be required to permit the robot  110  to move the respective second fixtures from the appropriate molding stations to the extrusion head and back. As an alternative, if a simpler form of second molding fixture  14  is required, the second mold fixture may not include internal cooling means and the fixtures  14  could be set aside in an ambient cooling station utilizing a fan blowing air over the fixture. In this manner, additional second fixtures  14  would be provided so as to give enough time to cool before being reused.  
         [0038]    The number of stations that could be serviced by one robot would depend on a number of factors. These would include the size of parison to be handled, the length of time for the blow molding cycle, including all necessary cooling steps and the like. While three molding stations have been shown in FIG. 5, the invention is not limited to the number of cooling stations which may be as few as one but may include as many as process times and other parameters will permit. Also, the product produced at each mold station can be the same in which case the set of first fixture and second fixture and respective mold cavities would be the same at each station. However, this is not required. A different product could be produced at different mold stations. In this latter case the sets of first and second mold fixtures and their respective cavities would be different at each station. If the different products required different parisons, then the extruder would require programming to extrude the correct parison required for the respective molding station.  
         [0039]    The mold fixtures are illustrated in FIG. 2 with the mold fixtures being generally horizontal. The second mold fixture can be moved generally vertically into the receiving recess as shown by the dotted lines. Alternatively, the second mold fixture can be moved into the receiving recess in a generally horizontal direction when the first mold fixture has open ends as shown in FIG. 2. However, there is no requirement that the first mold fixture be maintained in any particular orientation. It may be at a substantial angle to vertical and the direction of approach of the second fixture is similarly not limited. However, the two fixtures will have to be oriented or move in such a manner that the parison does not fall out of the second mold cavity before the fixtures and the two cavities are in registration.  
         [0040]    Many other changes and modifications may be made without departing from the scope of this invention which is defined in the attached claims.