Abstract:
A hollow element assembly has a base and a lid. The base has a wall that at least partly defines a recess, and the lid is locatable on the base so as to further bound the recess. Location of the lid on the base is achieved by bringing an edge of the wall into abutting contact with a corresponding contacting surface on the lid. At least one of the edge of the wall and the contacting surface of the lid has a channel running there along, such that when the lid is located on the base, a welding conduit is provided that follows the edge of the wall. At least one of the base and the lid further has an inlet aperture arranged to deliver molten welding material to the welding conduit from a region external to the hollow element assembly, so as to weld the base and the lid together, to provide a hollow element.

Description:
Technical Field 
       [0001]    The invention relates to hollow element assemblies for assembly into hollow elements, in particular for assembly into hollow elements for housing electronic components and/or for use in medical devices, and a method and apparatus for the manufacture thereof. 
       BACKGROUND 
       [0002]    It is known to prepare two-part hollow elements through an injection moulding process. For example, GB2360243, which is hereby incorporated by reference, describes an injection moulding apparatus for hollow parts that has first and second co-operating dies. 
         [0003]    Each die has a male die core and a female die recess. The dies are rotatable relative to each other so that they can be moved between first and second configurations. In the first configuration, the male die core of the first die is received by the female die recess of the second die, while the male die core of the second die is received by the female die recess of the first die. Thus, each male die core/female die recess pair defines a mould whose shape corresponds to one part of the hollow element assembly. Molten material is injected into each mould to form the parts. 
         [0004]    In the second configuration, the female die recesses of the first and second dies are aligned, thus bringing the two parts of the hollow element assembly together, such that they may be joined, e.g. by a collar weld. 
         [0005]    It is desirable to improve this process to provide a cosmetically acceptable join having good mechanical integrity. 
       STATEMENT OF INVENTION 
       [0006]    Therefore, at its most general, the present invention may provide a multi-component hollow element assembly that may be joined to form a hollow element in which the weld is provided in an internal region of the element. 
         [0007]    As a result, it may be possible to provide a hollow element in which the weld is not visible at an external surface. Thus, a cosmetically acceptable hollow element is provided in which only a join-line corresponding to the abutting contact of two adjacent components is visible externally. 
         [0008]    In a first aspect, the present invention may provide a hollow element assembly for assembly into a hollow element, the hollow element assembly comprising a base and a lid, the base having a wall that at least partly defines a recess, the lid being locatable on the base so as to further bound the recess,
       the hollow element assembly being arranged such that the lid is locatable on the base through the process of bringing an edge of the wall into abutting contact with a corresponding contacting surface on the lid,   wherein at least one of the edge of the wall and the contacting surface of the lid has a channel running therealong, such that when the lid is located on the base, a welding conduit is provided that follows the edge of the wall,   at least one of the base and the lid further having an inlet aperture arranged to deliver molten welding material to the welding conduit from a region external to the hollow element assembly, so as to weld the base and the lid together, to provide a hollow element.       
 
         [0012]    As a consequence of the configuration of the lid and the base, positioning of the lid on the base results in the formation of an internal welding conduit that is situated within the abutting surfaces of the base and the lid. Thus, it may be possible to deliver welding material to the welding conduit in such a way that the welding material is not visible on the external surface of the resultant hollow element. That is, an internal weld may be formed. An internal weld generally has a greater contact surface with the lid and the base than is the case with an external weld (e.g. a collar weld). As a result, the strength of an internal weld may often be greater than that of an external weld. 
         [0013]    The terms “lid” and “base” merely refer to the typical functions of the two components of the hollow assembly. They do not imply any fixed orientation of the assembly, or the resultant hollow element. 
         [0014]    Typically, the hollow element assembly further comprises an outlet aperture that is spaced from the inlet aperture and arranged to allow excess welding material to exit the welding conduit. 
         [0015]    Typically, the inlet and outlet apertures are both located on the same part of the hollow element assembly e.g. the base. In general, the inlet and outlet apertures are located opposite each other. 
         [0016]    Typically, both the edge of the wall and the contacting surface of the lid have a channel running therealong, such that abutting contact between the edge of the wall and the contacting surface of the lid results in merging of the two channels to provide a single welding conduit. 
         [0017]    In certain embodiments, the edge of the wall and the contacting surface of the lid are additionally configured to provide an interlocking arrangement that is preferably situated inwardly of the welding conduit (that is, located between the welding conduit and the recess). Typically such an interlocking arrangement comprises a protrusion provided on one of the wall edge and the contacting surface, and a corresponding depression provided on the other of the wall edge and the contacting surface. 
         [0018]    For example, the contacting surface of the lid may have a triangular-shaped ridge extending therealong. The edge of the wall may have a corresponding V-shaped trough for engaging with the triangular-shaped ridge. 
         [0019]    This interlocking arrangement may help to prevent overspill of welding material from the welding channel into the recess. Furthermore, it may help to prevent distortion of the internal surface of the recess during the welding process, and may also assist with positioning the lid on the base. 
         [0020]    The lid and the base may be formed from the same or different materials. Suitable materials include: polycarbonate, polycarbonate/ABS blend, nylon 12 or 35% glass-filled, high temperature nylon, although it will be appreciated by the skilled man that any other material of suitable properties may be used. Typically, the materials used are polymeric. 
         [0021]    In a second aspect, the present invention may provide an apparatus for manufacturing a hollow element assembly according to the first aspect of the invention and for joining the hollow element assembly to form a hollow element, the apparatus comprising first and second dies,
       the first and second dies having respective die faces that are positioned facing each other, the first and second dies being movable across each other and additionally towards and away from each other,   the first and second dies each having at least one female die cavity and at least one male die core,   the apparatus further having fluid delivery means for delivering fluid to at least one of the first and second die faces,   wherein, in a first configuration, the female die cavity in the first die receives the male die core of the second die to define a first mould, and the female die cavity in the second die receives the male die core of the first die, to define a second mould, the first and second moulds being adapted to receive fluid from the fluid delivery means, to create moulded parts; and   wherein, in a second configuration, the female die cavities of the first and second dies are aligned with each other to define a third mould that is adapted to receive fluid from the fluid delivery means, to join the moulded parts.       
 
         [0027]    The apparatus is configured for the manufacture of a hollow element assembly according to the first aspect of the invention. Thus, the first mould has the shape of one of the components of the hollow element assembly e.g. the lid, while the second mould has the shape of the other component of the hollow element assembly, e.g. the base. 
         [0028]    Typically, the first die has a fixed position, while the second die is movable. The apparatus may be configured to allow the first and second dies to move across each other along a rotational path or a linear path. Movement along a linear path is preferred. 
         [0029]    In general, movement of the dies is achieved through hydraulically-powered means. 
         [0030]    Typically, the fluid delivery means comprise a single injection device in fluid communication with both the male die core and the female die recess of one of the dies (e.g. a die that is fixed in position). Thus, molten material may be supplied to the first and second moulds from the single injection device. In this case, the apparatus may be generally known as a “single shot” machine. “Multi shot” machines having separate fluid injection devices for delivering fluid to the different moulds may also be used, but are less preferred (of course, in the case that different materials are used for the different components of the hollow element assembly, a “multi shot” machine will be required). 
         [0031]    The apparatus may be arranged such that when it is placed in the second configuration, a further fluid flow path may be provided to place the single injection device (or, as the case may be, one of the fluid injection devices of a “multi shot” machine) in fluid communication with the inlet aperture of the hollow element assembly, when it is located inside the third mould. This feature allows fluid for the welding process to be delivered to the inlet aperture of the hollow element assembly, without the need for an additional injection device. 
         [0032]    Typically, one of the male die cores or the female die cavities comprises one or more pins that are positioned to create an inlet aperture (and optionally an outlet aperture) in one of the moulded parts of the hollow element assembly of the first aspect of the invention. Preferably, the one or more pins extend from one of the male die cores. 
         [0033]    The apparatus may further comprise a pressure sensor that is adapted to receive molten material exiting an outlet aperture of a hollow element assembly when it is housed in the third mould. Such a pressure sensor may provide a signal that welding of the hollow element assembly is complete. The pressure sensor may also assist in determining the integrity of the weld, which may be particularly advantageous in this case, since the integrity of internal welds is generally difficult or impossible to determine through visual inspection. 
         [0034]    In a third aspect, the present invention may provide a method of manufacture of a hollow element assembly according to the first aspect of the invention and of joining the hollow element assembly to form a hollow element, the method comprising the steps of:
       1. providing an apparatus according to the second aspect of the invention;   2. placing the apparatus in the first position, such that the female die cavity in the first die receives the male die core of the second die, to define a first mould, and the female die cavity in the second die receives the male die core of the first die, to define a second mould;   3. supplying molten material to the first and second moulds via the fluid delivery means to create moulded parts;   4. moving the first and second dies away from each other and subsequently across each other to the second position;   5. contacting the first and second dies, whereby the female die cavities, each containing a moulded part, are aligned with each other to define a third mould that houses the hollow element assembly formed from the moulded parts; and   6. actuating the fluid delivery means to deliver molten material to the welding conduit of the hollow element assembly and bond the base and lid of the assembly together, to provide a hollow element.       
 
         [0041]    This method is for the manufacture of a hollow element assembly according to the first aspect of the invention. Thus, the first mould has the shape of one of the components of the hollow element assembly e.g. the lid, while the second mould has the shape of the other component of the hollow element assembly, e.g. the base. 
         [0042]    Often, the method comprises the further step, between steps 4 and 5, of placing an object (e.g. an electronic device) or a filler material between the lid and base of the hollow element assembly. 
         [0043]    Typically, the molten material delivered to the welding conduit is the same as is used to form one or other of the lid or the base of the hollow element assembly according to the first aspect of the invention. In the case that different materials are used to form the lid and the base, the molten material delivered to the welding conduit typically corresponds to the softer one of the materials used to form the lid and the base. 
         [0044]    Preferably, the steps of supplying molten material to the first and second moulds to create moulded parts and of delivering molten material to the welding conduit are all carried out using a single injection device provided within the fluid delivery means. Different flow paths provided within the apparatus channel the fluid to its destinations, as required. 
     
    
     
       DETAILED DESCRIPTION 
         [0045]    Embodiments of the invention will now be described in detail by way of example only, with reference to the accompanying drawings, in which: 
           [0046]      FIG. 1  is a cross-sectional schematic representation of a hollow element assembly according to an embodiment of the first aspect of the invention and illustrating a base and a lid in a spaced arrangement; 
           [0047]      FIG. 2  is a cross-sectional schematic representation of the hollow element assembly of  FIG. 1  and illustrating the base and the lid in a substantially engaged arrangement; 
           [0048]      FIG. 3  is a cross-sectional schematic representation of an apparatus according to an embodiment of the second aspect of the invention, for manufacturing a hollow element assembly according to the first aspect of the invention, the apparatus being shown in a first configuration; 
           [0049]      FIG. 4  is a second version of  FIG. 3 , showing magnified views of certain portions of the apparatus; 
           [0050]      FIG. 5  is a cross-sectional schematic representation of the apparatus of  FIGS. 3 and 4 , in a second configuration; 
       
    
    
       [0051]    Referring to  FIGS. 1 and 2  a hollow element assembly  10  comprises a base  12  and a lid  14 . 
         [0052]    The base  12  has a floor  16  and a wall  18  upstanding from the floor. The wall  18  extends around the perimeter of the floor  16 , such that the floor and the wall define a recess  20 . The wall  18  has an exposed edge  18   a  that faces away from the floor  16 . A welding channel  22  is provided in the exposed edge  18   a  of the wall  18 , the welding channel extending around the recess  20 . An inlet aperture  24  extends along the wall  18  towards exposed edge  18   a  to provide fluid communication with welding channel  22 . A corresponding outlet aperture  25  is provided opposite the location of the inlet aperture. 
         [0053]    A trough  26  extends around the recess  20 , radially inwardly of welding channel  22 . The trough  26  has a V-shaped cross-section. 
         [0054]    Lid  14  has a generally curved shape. The concave side of the lid has a contact surface  30   a  for bringing into contact with the exposed edge  18   a  of the wall  18 . The contact surface  30   a  has a further welding channel  32  that extends about the perimeter of the lid  14 . The lid further has a ridge  34  that extends around the lid, radially inwardly of the further welding channel  32 . The ridge  34  has a triangular cross-section. 
         [0055]    Referring to  FIG. 2 , the lid  14  is located on the base  12  by bringing the contact surface  30   a  into abutting contact with the edge  18   a  of the wall  18 . Ridge  34  provides a locking element for engaging with corresponding trough  26 , so as to prevent sliding along the abutting faces. The welding channel  22  and the further welding channel  32  together provide a welding conduit that is bounded on each side by the abutting surfaces of wall edge  18   a  and the lid contact surface  30   a.    
         [0056]    The lid and the base may be welded together by causing molten welding material to flow into the welding conduit via the inlet aperture  24 . The welding material then flows around the welding conduit to provide bonding between the lid and the base. Any surplus welding material exits the welding conduit along the outlet aperture  25 . A pressure transducer (not shown) detects exit of the welding material from the outlet aperture  25  and can thus provide a signal that sufficient welding material has been provided to the welding conduit. 
         [0057]    Suitable materials for the base  12  and the lid  14  include polycarbonate, polycarbonate/ABS blend, nylon 12 or 35% glass-filled, high temperature nylon although it will be appreciated by the skilled man that any other material of suitable properties may be used. The base and lid may be made from the same material or from different materials. The welding material typically corresponds to one of the materials used to make the base or lid. In the case that the base and lid are made of different materials, the welding material typically corresponds to the softer of the two materials. 
         [0058]    Referring to  FIGS. 3 and 4 , an apparatus  50  for manufacturing a hollow element assembly and welding it into a hollow element has a first, fixed die  52  and a second, movable die  54 . The second die  54  is movable towards and away from the first die  52 , as well as being movable across first die  52 , along a linear path. Movement of the second die  54  is obtained through the action of hydraulic cylinders (not shown). 
         [0059]    First and second dies  52 , 54  have respective first and second faces  52   a , 54   a , and are positioned such that the faces are opposed to each other. 
         [0060]    First die  52  has a female die cavity  56   a  and a male die core  56   b  provided at its face  52   a . Similarly, second die  54  has a female die cavity  58   a  and a male die core  58   b . First die  52  has an additional recess  56   c.    
         [0061]    The male die cores  56   b , 58   b  comprise a central generally cylindrical portion  560 , 580  that is situated within an outer ring portion  562 , 582 . The central generally cylindrical portion  560 , 580  and the outer ring portion  562 , 582  define a channel  564 , 584  extending around the cylindrical portion. 
         [0062]    The male die core  56   b  of the first die  52  additionally has a triangular shaped ridge  566  extending around the base of the channel  564 . The male die core  58   b  of the second die  54  has a V-shaped trough  586  (corresponding in shape to the triangular shaped ridge  566 ) extending around the base of the channel  584 . 
         [0063]    The shape of a radially outer portion of the male die cores  56   b , 58   b  is shown in more detail in the magnified views provided with  FIG. 4 . 
         [0064]    Pins  60   a , 60   b  are partly embedded in the second die  54  such that they extend outwardly from the face  54   a  of the die, into the ring portion  582  extending around the cylindrical portion  580  of the male die core  58   b.    
         [0065]    Pin  60   a  is shown in more detail in the magnified view of  FIG. 4 . From this, it can be seen that pin  60   a  results in the formation of a corresponding inlet aperture in the base of the hollow element assembly, the inlet aperture then being in position to receive fluid from winkle gate  66 , when the apparatus is in the configuration shown in  FIG. 5 . 
         [0066]    Two valve feeds  62   a , 62   b  are provided in the first die for delivering fluid to the female die cavity  56   a  and the male die core  56   b  respectively. An alternative fluid flow path (for use in the configuration shown in  FIG. 5 ) is provided by runner  64 , situated in second die  54 , and winkle gate  66 , situated in the first die  52 . 
         [0067]    A pressure transducer  68  is in fluid communication with the female die cavity  56   a  of the first die  52 . 
         [0068]    In the configuration shown in  FIGS. 3 and 4 , the female die cavity  56   a  of the first die  52  is aligned with the male die core  58   b  of the second die  54 , to define a first mould  72 , having the shape of the base of the hollow element assembly (the shape of mould  72  as shown in  FIGS. 3 and 4  is only schematic and so does not correspond exactly to the shape of the hollow element assembly base shown in  FIGS. 1 and 2 ). The presence of outer ring  582  of male die core  58   b  results in the formation of a corresponding welding channel in the exposed edge of the wall of the base of the hollow element assembly, while the presence of the V-shaped channel  586  results in the formation of a corresponding triangular-shaped ridge. Similarly, the presence of pins  60   a , 60   b  protruding from the surface of the male die core  58   b  results in the formation of corresponding inlet and outlet apertures in the base of the hollow element assembly. 
         [0069]    The male die core  56   b  of the first die  52  is aligned with the female die cavity  58   a  of the second die  54 , to define a second mould  70 , having the shape of the lid of the hollow element assembly (the shape of mould  70  as shown in  FIGS. 3 and 4  is only schematic and so does not correspond exactly to the shape of the hollow element assembly lid shown in  FIGS. 1 and 2 ). The presence of outer ring  562  of male die core  56   b  results in the formation of a corresponding welding channel in the contacting surface of the lid of the hollow element assembly, while the presence of the triangular shaped ridge  566  results in the formation of a corresponding V-shaped trough. 
         [0070]    In the configuration shown in  FIG. 5 , the female die cavities  56   a , 58   a  of the first and second dies  52 , 54  are in alignment and male die core  58   b  of the second die  54  is received by the additional recess  56   c . Runner  64  and winkle gate  66  are in fluid communication to provide a flow path from the valve feed  62   b  on the male die core  56   b  of the first die  52  to the female die cavity  56   a.    
         [0071]    To manufacture a hollow element assembly, the two dies are initially assembled in the configuration shown in  FIGS. 3 and 4 . Molten material is introduced into valve feeds  62   a , 62   b  and flows into moulds  70 , 72 , to produce the lid and base of the hollow element assembly. 
         [0072]    The faces  52   a , 54   a  of the two dies  52 , 54  are then moved away from each other. Pressure pads (not shown) provided on the generally cylindrical portion  580  of male die core  58   b  ensure separation of the moulded part from the male die core  58   b , such that the moulded part is retained in the female die cavity  56   a  of the first die  52 . 
         [0073]    The second die  54  is moved linearly in a direction parallel to its face and brought back into contact with the first die  52  in the configuration shown in  FIG. 5 . In this configuration, the lid and base of the hollow element assembly are brought into contact. Valve feed  62   a  in fluid communication with female die cavity  56   a  is closed off. Valve feed  62   b  supplies molten material along runner  64  and winkle gate  66  to inlet aperture of the hollow element assembly. The molten material flows along the welding channel provided between the lid and base, exiting the channel at the outlet aperture. The flow of material from the outlet channel is sensed by the pressure transducer  68 , indicating that the welding cycle is complete.