Abstract:
A mould assembly ( 60 ) and a method of use in injection moulding of a part having a functional cavity therein. The mould assembly has a recess ( 72 ) to receive a hollow tubular insert ( 48 ) intended to be placed in the mould assembly before the injection of a mouldable material into the cavity and to remain in the part after moulding. A gas supply arrangement supplies pressurised gas to the hollow tubular insert at a selected stage during the injection process whereby to form the functional cavity in the part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority of provisional application Ser. No. 60/528,421, filed Dec. 10, 2003. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates generally to gas assisted injection moulding and more particularly to gas assisted injection moulding to produce moulded parts with functional cavities.  
       BACKGROUND OF THE INVENTION  
       [0003]     Gas assisted injection moulding is a thermoplastic moulding process in which an inert gas is injected into a mouldable material after the moulded material enters a mould. The gas does not mix with the mouldable material but is intended to remain in the middle of the thicker sections of the moulding. By controlling the gas pressure, the quantity of mouldable material injected into mould and the rate of gas flow, a hollow portion can be formed within the moulded part. The gas pressure compensates for the tendency of the mouldable material to shrink at the thicker parts of the moulding, preventing warping and reducing stress. Gas pressure can be relieved before opening the mould.  
         [0004]     It has been proposed in the past that the introduction of pressurised gas into the mould may be through the same nozzle that introduces the mouldable material in the part. In the production of some parts it is desirable to induce the pressurised gas at a different location as that of which the mouldable material is introduced. In the past, a gas pin has been used for this purpose, however, this is not applicable where it is desired to produce a functional cavity.  
         [0005]     By the term “functional cavity” in this specification it is generally intended to mean a cavity which is formed in an injection moulded part which in the finished product is used for a defined or useful purpose. The defined or useful purpose may be for instance to enable the joining of two ducts or tubes retained in the mould and extending into the mould cavity and moulded into a part to provide a fluid connection between them within the functional cavity. The functional cavity, for instance, may be used to mix two fluid flows or to enable fluid flow from one duct to another within the moulded part.  
       SUMMARY OF THE INVENTION  
       [0006]     In one form therefore, the invention is said to reside in a mould assembly for use in injection moulding of a part having a functional cavity therein, the mould assembly comprising at least a first mould portion and a second mould portion which when joined together define a cavity for moulding the part, at least one of the first and second mould portions having an opening therein for allowing injection of a mouldable material into the cavity, a recess in at least one of the first and second portions, the recess being to receive a hollow tubular insert intended to be placed in the mould assembly before the injection of a mouldable material into the cavity and to remain in the part after moulding and a fluid supply arrangement to supply pressurised fluid to the hollow tubular insert during the injection process whereby to form the functional cavity in the part.  
         [0007]     Preferably the pressurised fluid is a gas.  
         [0008]     It will be seen therefore that a cavity is formed in the part by injection of gas through the hollow insert during moulding and hence after the moulded part has been completed, access to the cavity formed in the mould can be possible through the hollow insert. Where a moulded part has more than one insert then the functional cavity can act as a flow joiner between a first and second hollow insert.  
         [0009]     In a preferred embodiment the mouldable material can be a resilient material and hence a pump and or suction device can be formed. Manipulation of the finished part will enable fluids to be drawn into and expelled from the functional cavity through the hollow tubular insert. For other applications the mouldable material may be any appropriate moulding material.  
         [0010]     In the process of injecting mouldable material into the cavity, in one preferred arrangement, a less than complete volume of mouldable material to fill the cavity may be injected and during the injection process, gas at a selected pressure may be injected through the hollow tubular insert substantially into the centre of the desired cavity.  
         [0011]     The volume of injected material, the time of injection and the pressure of injection as well as the volume, pressure, temperature and timing of gas injection may be selected to give desirable properties and dimensions to the finished product and the functional cavity.  
         [0012]     Alternatively, there may be provided, associated with the mould assembly, a further cavity apart from the mouldable material cavity with a duct extending from the main cavity to the further cavity so that a full shot of mouldable material may be placed into the mould and then when gas is injected into the mould through the hollow tubular insert, excess mouldable material may be passed through the duct from the main cavity into the further cavity. At the end of the moulding cycle the excess mouldable material that has passed into the further cavity can be separated from the moulded part and recycled.  
         [0013]     In a still further arrangement the main cavity may be filled by a full shot of mouldable material and upon injection of the pressurised gas, excess material may pass back through the opening, which is in either the first or second mould portion, back into the injection machine. For this purpose injection pressure may be removed or an injection screw rotated in reverse to allow for retraction of some of the moulded material.  
         [0014]     The pressurized gas may be air or dry nitrogen or the like.  
         [0015]     In a further form the invention may be said to reside in a process of moulding a part with a functional cavity including the steps of providing a mould assembly of the type discussed above, mounting a hollow tubular insert into the recess in the mould assembly, injecting a mouldable material through the opening into the cavity, injecting a gas under pressure through the hollow tubular insert into the cavity and allowing the mouldable material to cool before opening the mould portions to release the moulded part with the hollow tubular insert retained in the moulded part and opening into the functional cavity.  
         [0016]     The moulding process may further include the step of cooling the mould before injection of the air to form a skin on the outer surface of the moulded part. When the air is then injected the skin may prevent the cavity extending to the skin of the moulded part.  
         [0017]     Where the part to be moulded is to be formed from a resilient material, it may be desirable to carry out an initial moulding step where a hard mouldable material such as a polycarbonate may be injected into a mould in which the insert is received to form ribs around the tubular insert and then the tubular insert with the moulded portion and ribs can be placed into another mould in which the moulding of the part with the hollow tubular insert in a soft material is achieved. The ribs on the tubular insert aid adhesion of the soft outer layer. Hence the functional cavity or void formed in the moulded part could act as a pump when the moulded part is compressed and released. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0018]     This then generally describes the invention but to assist with understanding, reference will now be made to the accompanying drawings which show preferred embodiments of the invention.  
         [0000]     In the drawings:  
         [0019]      FIG. 1  shows a mould assembly according to a first embodiment of the invention;  
         [0020]      FIG. 2  shows the embodiment of  FIG. 1  with a hollow tubular insert received in the mould;  
         [0021]      FIG. 3  shows the next stage in the process with mouldable material injected in and gas also injected through the hollow tubular insert;  
         [0022]      FIG. 4  shows the finished part with a functional cavity formed in it;  
         [0023]      FIG. 5  shows the finished part of  FIG. 4  with the sides compressed to act as a pump;  
         [0024]      FIG. 6  shows a second embodiment of the invention in the form of a mould assembly in which a handle for an aspiration catheter assembly can be moulded;  
         [0025]      FIG. 7  shows the mould assembly of  FIG. 6  with a core and hollow tubular insert arrangement supported in the mould;  
         [0026]      FIG. 8  shows the arrangement of  FIG. 7  after injection of mouldable material and gas through the hollow tubular insert;  
         [0027]      FIG. 9  shows the moulded part after it has been removed from the cavity;  
         [0028]      FIG. 10  shows the finished part with a side duct mounted into the finished part;  
         [0029]      FIGS. 11A and 11B  show parts of an aspiration assembly with a hard mouldable material moulded onto the insets of the aspiration catheter as a preliminary step;  
         [0030]      FIG. 12  shows the finished product incorporating the inserts shown in  FIGS. 11A and 11B .  
         [0031]      FIG. 13  show an alternative embodiment of aspiration assembly suitable for injection moulding with an functional cavity; and  
         [0032]      FIG. 14  shows the embodiment of  FIG. 13  with part cutaway to show the functional cavity. 
     
    
     DETAILED DESCRIPTION  
       [0033]     Now looking more closely at the drawings and in particular the embodiment shown in FIGS.  1  to  5  it will be seen that the mould assembly generally shown as  1  comprises a first mould half  2  and a second mould half  4  which each have a recess which when the two parts of the mould are brought together form a cavity  6  in the mould assembly. An opening  7  provides a sprue and gate  8  for the injection of mouldable material into the cavity  6  and a recess  10  is formed as two semicircular recesses  12  and  14  in the mould halves to receive a hollow tubular part  16  which extends into the cavity  6 , when installed, as can be seen in  FIG. 2 . The arrangement as seen in  FIG. 2  is now ready for injection moulding as shown in  FIG. 3 . Material  23  has been injected as shown by the arrow  18  into the sprue  7  and a short time after the injection of the mouldable material, air has been injected through the hollow tubular insert as shown by arrow  20  from air supply  24  and controlled by valve  22 . By this process a hollow  21  is formed in the mouldable material  23 . The air pressure is maintained until the mouldable material is hardened.  
         [0034]     As an alternative to air, a dry gas such as nitrogen may be injected through the hollow tubular insert.  
         [0035]     The finished part  25  is then removed from the mould assembly  1  as shown in  FIG. 4 .  
         [0036]     Where the injected material is a resilient material the finished part can be flexed or manipulated to produce a pipette of the like. In  FIG. 5  the sides  27  of the moulded part  25  are compressed such as by finger pressure so that fluid within the cavity  21  can travel through the hollow tubular insert  16  which is now moulded into the part so that the part  25  for instance can act as a pipette or some other useful functional device. Hence the cavity is a useful or functional cavity within the part.  
         [0037]     It will be realised that if two hollow tubular inserts were used with suitable valve arrangements in them then the part could act, for instance, as a pump, to pump fluid from one insert to another.  
         [0038]     Another embodiment of the invention will now be discussed with respect to the moulding of a dual lumen aspiration catheter.  
         [0039]     The aspiration catheter will be initially discussed with respect to  FIG. 10  to show the various components and then the moulding of the aspiration catheter can then be discussed with respect to FIGS.  6  to  9 .  
         [0040]     The aspiration catheter shown in  FIG. 10  generally has a handle or body  40  through which passes an aspiration tube  42 . The aspiration tube  42  does not open into the cavity  44  within the handle  40  but extends to the tip  58  of a needle cannula  46  which acts as a hollow tubular insert extending into the handle  40  and opening into the cavity  44  within the handle  40 . A side tube  50  extends through an arm  52  on the handle  40  and flushing fluid  54  can be supplied through the tube  50  into the cavity  44  and then passed through the annular lumen  56  between the aspiration catheter  42  and the hollow needle  48  so that the flushing fluid can be provided at the needle tip  58  to assist with flushing material into the aspiration catheter  42  to a suitable aspiration system (not shown).  
         [0041]     It will be seen that the cavity  44  in this arrangement acts as a functional cavity because it provides a fluid flow junction between the tube  50  in the arm  52  and the needle insert  48  in particular the lumen annular  56  within the needle insert  58  which extends to the needle tip  58 .  
         [0042]     The moulding of such an assembly is carried out as shown in FIGS.  6  to  9 .  
         [0043]      FIG. 6  shows a mould assembly  60  comprising a first mould portion  62  and a second mould portion  64 . The mould halves join together on a part line  66 . Recesses within the mould portions  62  and  64  when they are joined together define the shape of the handle portion of the aspiration catheter. The region  75  defines the main body  40  and the region  74  defines the shape of the arm  52 .  
         [0044]     A sprue arrangement  68  is provided in the mould portion  64 . Recesses are provided at  70  and  72  in both mould portions  62  and  64 . The recesses  70  when the mould is joined together receive the aspiration cannula  42  and the recess  72  when the mould is joined together receive the hollow tubular needle  48  as can be seen in  FIG. 7 . The aspiration cannula  42  passes coaxially through the hollow tubular needle  48 .  
         [0045]      FIG. 7  shows the mould portion  62 . To form the hollow duct into which the side tube  50  can be inserted in the arm  52 , a void forming core  76  is placed into the region  64  of the mould with the core extending to the inner end  78  of the hollow tube insert  48 .  
         [0046]     An incomplete shot of plastics material  77  is then provided through the sprue  68  (see  FIG. 6 ) until the mould is partially filled and then air is injected through the annular lumen  56  between the needle  48  and aspiration catheter  42  to form the cavity  44  in the middle of the mouldable material. After cooling, the moulded part, generally shown as  80 , is removed from the mould  60  and the core  76  is also removed. This leaves the part as shown in  FIG. 9 . The tube  50  is then pushed into the hollow aperture  82  left when the core is removed and into the cavity  44  and this enables the fluid connection via the functional cavity  44  between the tube  50  and the lumen  56  as discussed earlier.  
         [0047]     If it is desired to make the functional cavity act as a pump then before insertion of the inserts  42  and  48  into the mould, a harder plastic material may be moulded onto the insert  42  in the region  84  and onto the insert  48  in the region  86 . The mouldable material from which the handle  40  is made can then be formed from a more elastomeric material, which can give the finished part flexibility sufficient to enable it to be compressed with finger pressure to act as a pump.  
         [0048]     It will be realised that other forms of aspiration catheter assemblies can be formed such as single lumen needle systems where a junction is provided in a functional cavity between a flushing fluid entry line  50  and the aspiration cannula  42  and for this purpose the aspiration cannula  42  would have an aperture which when completed would be in the region of the functional cavity  44 .  
         [0049]      FIGS. 11A and 11B  show parts of an aspiration assembly with a hard mouldable material moulded onto the insets of the aspiration catheter as a preliminary step. In  FIG. 11A  the aspiration cannula  42  has portion of a harder mouldable material  92  such as PVC or styrene moulded onto it in a separate operation. The portion of a harder mouldable material  92  includes wings  93  which provide a greater surface area when the part is moulded into an aspiration assembly. Similarly as shown in  FIG. 11B  the needle  48  has portion of a harder mouldable material  94  such as PVC or styrene moulded onto it in a separate operation. The portion of a harder mouldable material  94  includes wings  95  which provide a greater surface area when the part is moulded into an aspiration assembly.  
         [0050]      FIG. 12  shows the finished product incorporating the inserts shown in  FIGS. 11A and 11B . It will be noted that both the added moulded parts  92  and  94  are enveloped with the mouldable material  77 . These provide a region of greater surface area and hence adhesion between the mouldable material and the inserts, which will give improved strength.  
         [0051]      FIG. 13  show an alternative embodiment of aspiration assembly suitable for injection moulding with a functional cavity and  FIG. 14  shows the embodiment of  FIG. 13  with part cutaway to show the functional cavity.  
         [0052]     The aspiration assembly  100  has a handle portion  102  with a finger grip  104 . A needle cannula  106  extends from one end of the handle  102  and a flushing fluid supply tube  108  and an aspiration cannula  110  extend from the other end of the handle. In the junction portion  112  a functional cavity  114  is formed. The aspiration cannula  110  passes through the functional cavity  114  without opening into it and extends co-axially through the lumen of the needle cannula. Both the flushing fluid supply tube  108  and the annular lumen between the needle cannula  106  and the aspiration cannula  110  open into the functional cavity  114 . Gas under pressure can be supplied through each of these to form the functional cavity. In one embodiment, gas is supplied under pressure through each of the entry points to ensure plastics material does not block either entry point.  
         [0053]     The size and shape of the functional cavity  110  can be controlled and formed by manipulating the gas pressure from both the flushing fluid supply tube  108  and annular lumen between the needle cannula  106  and the aspiration cannula  110 . The timing of the gas flow in and out also prevents the plastic forming a skin over the entry points. In this embodiment nitrogen gas at about 4-bar pressure is used. The bubble size is a balance between gas pressure and shot size.  
         [0054]     Throughout this specification, various indications have been given as to the scope of the invention but the invention is not limited to one of these but may reside in two or more of these combined together. The examples are given for illustration only and not for limitation.