Patent Description:
It is a property of molten resin that it has a very large, typically <NUM> to <NUM>% volumetric shrinkage when it transacts from liquid to solid phase. That shrinkage is invariably not acceptable and hence extra material is pushed into the tool compressing the pliable thermoplastic during part of moulding process known as packing stage. However, that leads to stress in the moulded part due to flow of liquid in already solidifying resin in the mould, flow induced shear thinning and temperature rise in the flow and different rate of solidification on account of thickness and cooling rate variation leading to eventual differential shrinkage and internal stress. These stresses are the result of locally varying densities within the moulded part. The speed of light propagation is affected by the material density and its variation in moulded optical element in turn leads to different light speeds within the moulded optical element which in application can lead to poor performance for example double refraction and birefringence.

Also when the part to be moulded is thin on the outside and thick zone in the middle and material has to be injected from thin edge for example moulding of a spherical and aspherical lens the thin edge freezes off lot before central thick zone that leads to gross defects in form of sink marks as volumetric shrinkage continues in the thick zone or sometimes can lead to internal shrinkage that appears as bubbles or vacuum voids in the part making it un-fit for purpose optically or structurally as the case may be.

<CIT> discloses a method of injection moulding showing means of application of external force inside a cavity, however the disclosed arrangement suffers from high internal stress and not applicable to moulding of optical elements.

<CIT> discloses a process for the formation of large void-free thermoplastic articles. Large thermoplastic articles are injection molded, cooled to a self-supporting temperature, transferred to a vessel, the articles being maintained under fluid pressure sufficient to prevent the formation of voids on cooling to ambient temperature. It has to be waited a time to gain the "self-supporting temperature", contaminates the part and has no control over final shape post cooling and logically limited to simple non critical applications, which are not suitable to precision optical components and not suitable for overmoulding.

<CIT> discloses a method of lens moulding having intermediate cooling stations. The method has major limitation a long time has to be waited to gain the "self-supporting temperature" until the part can be handled and is able to hold its shape when transferred to the cooling stations. The method contaminates the part and has no control over final shape post cooling and fails to compensate for additional shrinkage of central thick part hence likely to suffer with high stress and risk of voids particularly for very thick lenses.

<CIT> discloses a method and apparatus for injection moulding thermoplastic polymers wherein a layer of pressurised gas is provided between at least selected moulded parts and the cooling polymer. The gas takes up shrinkage as the polymer cools and allows visual sink marks to be substantially eliminated. Furthermore, cycle times are reduced, fast cooling being permitted by urging the polymer against the outer mould and cooling the outer mould.

<CIT> discloses a method for manufacture of an overmoulded article made up of at least two parts, so arranged that moulding first part according to parameters that are adapted for fastest possible cycle time without having any regard to temperature required at interface of second part moulding, cooling first part rapidly followed by heating face of the first part by application of heat before the said first part has completely cooled to room temperature, so characterized that at end of heating there exists at least three temperature zones in the first part.

<CIT>discloses a plastic molding having high accuracy includes at least one transfer surface and at least one imperfect transfer portion <NUM> having a concave or convex shape. The mold assembly includes a cavity into which molten resin is injected, a slide cavity piece which is capable of being slid at a prescribed time so that a gap is formed between the resin and the slide cavity piece, and a vent hole for supplying a compressed gas in the cavity. A method of producing the plastic molding includes the steps of heating resin to provide a molten resin, injecting the molten resin into a cavity of a molding, applying a resin-pressure to the molten resin, cooling the resin, sliding the slide cavity piece, and opening the mold assembly.

<CIT> discloses a method and a device for manufacturing optical components, wherein a preform is produced in an injection mold and then and then finished in an embossing tool.

Various effort are made in prior art to overcome some of the challenges.

It is an object of the invention to overcome the above disadvantages. It would be desirable improvement in moulding technology capable of moulding very thick articles having varying thickness at fast production rate without defects like internal voids and is intent of the present invention.

A thick thermoplastic article having varying thicknesses is injection moulded according to the present invention by including two stages of injection of a material filling stage and a packing stage, cooled for a predetermined time by a first cooling at least including duration of filling stage and packing stage at end of which a first runner is blocked and further cooling by a second cooling under application of external force, characterized in that application of the external force deforms adaptively at least one surface of the first part said first surface causing higher displacement at a first region having a lower density and a lower strength compared to a displacement at a second region having a higher density and a higher strength and advantageously the application of force adapts to change the location of the first region and the second region that may arise as the first part continues to solidify ensuring that the rate of displacement in the first region is higher than that in the second region reducing difference between a maximum and a minimum thickness of the first part producing the first part advantageously free of internal voids having uniform density and reduced internal stress.

The method for moulding of a thermoplastic article is defined by the appended claims.

It has to be noted here that cooling the first part, a first cooling comprising total duration of the first filling stage and the first packing stage and optionally a small time increment of few seconds so configured that end of the first cooling the first part was not allowed enough time necessary to fully solidify and has at least two regions defined by its structural strength and/or density: first region having lower structural strength and/or lower density generally associated with thickest portion of the first part and second region having higher structural strength and/or higher density generally associated with thinnest portion of the first part. After end of first packing stage the first runner is blocked and means of block include but not limited to freezing the first runner for example by application of CO<NUM> cooling solidifying it or by way of activation of blocking means in a simple form a pin is activated by application of force blocking off the first runner completely, subsequent to blocking of the first runner and end of the first cooling further cooling to solidification second cooling is continued under application of external force so characterized that application of the external force deforms adaptively at least one surface of the first part say the first surface causing higher displacement at first region compared to displacement at second region and advantageously the application of force adapts to redistribution of the first region and the second region that may arise as the first part continues to solidify ensuring rate of displacement in the first region is higher than that in the second region reducing difference between maximum and minimum thickness of the first part producing the first part advantageously free of internal voids having uniform density and reduced internal stress.

Advantageously the first moulding tool and second moulding tool are integrated in one and located on a moulding machine having suitable means of directing melt to either the first melt passage or the second melt passage or both and in non limiting case the first resin and the second resin are the same.

The method according to any one of previous discussion wherein the cooling under application of external load after the packing phase is carried out at a location outside the injection moulding machine, wherein the process of second cooling or the fourth cooling is carried out away from the moulding machine may comprise the steps of:.

The cooling under application of external force may be carried out inside tool inserts so configured that they form a sealed gas tight volume between say the first surface and corresponding face of the tool insert when closed wherein a small gap first gap is developed as the first part starts to shrink on solidification and uniform force on substantially entirety of the first Surface is applied by application of high pressure gas advantageously combined with cooling by flowing low temperature gas including but not limited to high pressure nitrogen gas so configured that it preferably flows over entire the first surface and exits in a controlled manner via a back pressure mechanism.

Method according to any one of the preceding discussion, wherein cooling under application of external force is carried out in tool inserts configured with having a elastically flexing membrane The first flexing membrane having a first and second opposing face fixed to a corresponding side of the at least one of the first core, the first cavity, the second core, the second cavity, making hermetically tight connection at its periphery defining a closed space therein, wherein the first opposing face is advantageously in full contact with say the first surface and fluidic pressure is applied on the second opposing face and the first flexing membrane continues to deform on application of the pressure transmitting force on to the first surface advantageously application of force is combined with passing heat exchange fluid under pressure having entry and exit points so configured that it is directed to flow substantially over entire second opposing face, whilst maintaining pressure thus providing cooling of the first part under force.

The first part and/or the overmoulded second part according to any of preceding discussion in non-limiting case comprises a central generally bulbous area surrounded by planar thick area at its periphery and the first flexing membrane is mounted on a movable piston contacting the bulbous area and piston having two ends, first end in contact with the planar thick area and another end connected to means of actuation of the piston, the piston is integrated within corresponding side of at least one of the first core, the first cavity, the second core, the second cavity, and cooling under application of external force is carried out by advancing the piston applying force on the planar thick area and the first flexing membrane provides flexible contact with the bulbous area maintaining force as its size and shape is changing relative to the planar flat area as it solidifies and by way of example only piston is advanced by application of hydraulic pressure and application of force to the first flexing membrane is by way of example only application of hydraulic or pneumatic pressure advantageously the piston is provided with internal means of heat exchange through which heat exchange medium is circulated and advancement of piston and application of force to the first flexing membrane is either sequential or simultaneously and pressure exerted on to the first part by the piston and by the first flexing membrane is independently controlled improving upon compression injection moulding process reducing stress in moulded article.

The second cooling and/or fourth cooling under application of force may be carried out by at least one of the following steps:.

Method according to above, wherein the travel of the first insert and the second insert continues until it reaches its individual travel stops so configured that at end of travel the first chamber volume is reduced to second volume which closely matches that of the first part when fully solidified and the first end of the first insert and the first end of the second insert generally coincide with final shape of the solidified the first part, when cooled to predetermined ejection temperature producing the first part or the overmoulded second part having uniform density and free of internal voids and minimal stress.

The method may comprise at least one of the following steps:.

The moulding tool assembly may be provided with means of ejecting moulded part contained therein and in cooperation with the transfer station eject the part and the injection moulding machine moving half including its slide and means of ejection are eliminated reducing required floor space and cost of the injection moulding machine.

The method may comprises for example moulding n1 numbers of Part1 followed by n2 numbers of Part2 followed by n3 numbers of Part3 and back to n1 numbers of the Part1 and so on wherein which when assembled together make up a Group <NUM> and the number of tool sets for moulding of the Part1 and the Part2 and the Part3 are so arranged that the production runs in a continuous fashion without the moulding machine waiting for any of the tool sets whilst any of the Part1 Part2 and Part3 are undergoing cooling under application of external force at the holding facility whilst fully contained within tool set it was moulded within, further comprising that the other groups say Group <NUM> and Group <NUM> and so on can be moulded in fully flexible manner as demanded of production schedule for example moulding of m1 numbers of Group <NUM> is followed by moulding of m2 numbers of Group <NUM> followed by m3 numbers of Group <NUM> and back to m1 numbers of Group <NUM> and so on wherein n1, n2, n3, m1, m2 and m3 are positive integers and fully automated production sequence is made possible by computerised scheduling program and automation, furthermore some of the part <NUM>, the part2, the part3, the Group <NUM>, the Group2 and the Group3 and so on may optionally undergo further processing including but not limited to preparing for Overmoulding, trimming, painting, marking, laser inscription, embossing, gluing, assembly and packaging operation and the further processing advantageously is taking place outside the injection moulding machine whilst injection moulding machine continues with moulding operation without any delay. It would be a good example of an overmoulded clear component that the first shot is laser inscribed with part serial number and/or any unique identifier which once overmoulded is encapsulated providing value added information that is tamper proof and protects against possible fraud. This also opens up possibility to for example emboss or coin some design features on surface of first shot and once overmoulded they are encapsulated providing a whole new way of designing and enhancing performance of two shot moulded parts. Another example could be moulding components of an air register louvers for automotive air-conditioning system and all sub components including some overmoulding are produced in sequence such that there is no in process inventory is maintained and desired air registers for example from right, front left, centre right, centre left and so on are produced sequentially eliminating in process inventory and entire car set is produced and packaged together without any cost penalty of such flexible production arrangement.

Some other salient beneficial features of the invention described above are:
Total tooling cost is substantially reduced for example the tool inserts for first shot can be made at low cost by investment casting including cast cooling channels, machined aluminum alloy, and may have very low precision.

The method further comprises the step of providing in the first set or the second set at least one auxiliary melt chamber flowably communicating with the first chamber or the second chamber and the auxiliary melt chamber is fitted with means of applying pressure on the melt contained therein and advantageously fitted with means of application of heat on the melt contained therein comprising steps of:.

This leads to increase in part weight and helps reduce risk of uncontrolled warpage or shrinkage induced vacuum bubbles on the inside of moulded part.

The method may further include a thermoset part and/or combination of thermoplastic and thermoset, wherein the thermoset part is cured by application of heat and thermoplastic part is formed by removal of heat and advantageously produces an overmoulded part that is combination of both the thermoset and the thermoplastic, by way of example the thermoset part is liquid silicone rubber or a vulcanizing rubber and the moulding machine is provided with means of injection of the liquid silicone rubber or placement of vulcanizing rubber preform.

Method of moulding according to any of preceding claims whilst transporting the first kit or the second kit to the intermediate holding facility means of cooling under application of force is activated during transit and means of cooling and application of force is advantageously included in the tool set and/or provided by the transport system.

The first packing stage or the second packing stage according any one of preceding claims are either omitted completely or reduced by <NUM> % or more advantageously by <NUM>%.

The method also makes it possible to have varying parting line and line of draw in each moulding as only limitation is overall size of insert and receiving pocket in the tool body. This is a big improvement over traditional injection moulding where the entire tool assembly is opened at its parting line limiting what is possible for multiple parts having varying parting line and line of draw without drastic increase in tool complexity.

Since it is possible to mould only one component at a time despite having a very large tool, the machine tonnage can be reduced and accordingly simple low cost machine is deployed reducing total cost of ownership.

It will be also understood that where the word "comprise", and variations such as "comprises" and "comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.

In order that the invention may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention with reference to the accompanying drawings, wherein:.

Reference is made to <FIG>, showing an isometric view, a plan view, a location of section plane and a corresponding section view. <FIG> shows a first cavity <NUM>, a first core <NUM> and cross section through basic moulding setup wherein cooling channels <NUM>, moulded article <NUM> having its shape defined by tool surfaces <NUM> and <NUM>. Liquefied polymer is injected in the cavity from a machine output at <NUM>, passes through sprue <NUM> that leads to runner <NUM> having two ends, one end <NUM> connects to the part being moulded and another end <NUM> connects to material coming in. There is also shown an auxiliary melt chamber <NUM> and means of pushing on the melt contained therein <NUM>. Coolant is passed through the cooling channels <NUM> and after predetermined cooling time. The core is pulled away from the cavity. Now the solidified moulded part can be ejected along with the sprue and runner. The runner <NUM> and the sprue <NUM> are discarded for example by use of automatic cutting device not shown that may be integrated in the tool.

Reference is made to <FIG> showing an isometric view, a plan view, a location of a section plane and a corresponding section view. <FIG> shows a moulded first shot part being cooled in a cooling station defined by two halves <NUM> and <NUM>. Initially the moulded article has a volume equal to combined volume <NUM> and <NUM>, wherein reference numeral <NUM> is a visualisation of reduction in volume of the moulded part at the end of cooling and reference numeral <NUM> is volume of the moulded part at end of cooling. The gas, typically nitrogen, is compressed to pressure as high as <NUM> bar or more and chilled to low as -<NUM>. As it passes over the part surface it removes heat from it solidifying it. On cooling the moulded article shrinks to the volume <NUM> and the volume reduction is shown as an indicative visualisation purpose only by volume <NUM>. It is specifically noted here that shrinkage <NUM> in thickest portion having end of cooling maximum thickness <NUM> is higher than that at shrinkage near the edges <NUM>, where end of cooling thickness <NUM> is substantially less compared to thickness at <NUM>. Entry of chilled inert gas under pressure is from <NUM> and its passage over the moulded part shown by arrows <NUM> and it exits through <NUM> via pressure regulator (not shown) that ensures predetermined back pressure as the gas flows out cooling and pressing on the part and pushing inwards the first surface <NUM> from starting position <NUM>. Seal <NUM> prevents loss of pressure and leak of gas. A portion of moulding <NUM> has a portion <NUM> surrounding entire extremities of the component that seals off against seal <NUM> preventing the gas under pressure going to other face <NUM> of the component. In case of very thick parts and very short cooling time before transferring the part to the cooling station the part has substantial amount of liquid polymer inside with thin skin akin to a gel capsule and advantageously the arrangement for cooling is reversed, wherein refernce24 is at bottom and <NUM> is on top such that part is free to rest on surface <NUM> against gravity when transferred into the tool half <NUM> and during pressing the part is supported against gravity and the forces of compression by surface <NUM> and force is applied gradually so as not to deform and rupture the skin abruptly.

Reference is made to <FIG>, showing an isometric view, a plan view, a location of section plane and a corresponding section view. Figure shows means of mechanical pressing an article <NUM>, a cavity <NUM> and a core <NUM>. Initially the moulded article has a volume equal to the combined volume <NUM>, which is a visualisation of a reduction in volume at the end of cooling and <NUM> which is volume at end of cooling core <NUM> is pushed under controlled pressure towards the other half <NUM> and reduction in volume is visualised by <NUM>. It is specifically noted here that shrinkage <NUM> in thickest portion <NUM> is more compared to shrinkage near the edges <NUM>, where thickness <NUM> is substantially less compared to thickness at <NUM>. It should be understood here that as the core <NUM> is moved towards support tool <NUM> initially in contact with the moulded first part that has to be visualised as combined <NUM> and <NUM> as one piece and contact is made only at the thickest portion <NUM>. As the pressing movement continues in a time and/or force controlled manner it adaptively spreads contact area, where force is applied on the first part towards areas having lesser thickness and at end of travel the initial profile <NUM> of first part is changed to <NUM> and at that time the core <NUM> has substantially full contact and the profile <NUM> and profile <NUM> are almost identical. This is key difference compared to many prior art executions, where pressing tool has full contact with part being pressed to begin with and cannot compensate for extra shrinkage in thickest part and in effect would lose contact with the part as extra shrinkage continues in thickest portion of the part or apply excessive load into thinnest part that would have solidified way before the thickest portion and essentially damage the thinnest part in process of application of continued load. In case of a very thick part and very short cooling time before transferring the part to the cooling station the part has substantial amount of liquid polymer inside with thin skin akin to a gel capsule and advantageously the arrangement for cooling is reversed wherein <NUM> is at bottom and <NUM> is on top such that part is free to rest inside tool <NUM> against gravity when transferred into the tool half <NUM> and during pressing the part is supported against gravity and the forces of compression by surface <NUM> of core <NUM> is applied gradually so as not to deform and rupture the skin abruptly.

Reference is made to <FIG> section f-f, wherein said figures show an isometric view, a plan view, a location of a section plane and a corresponding section view. <FIG> shows a first set made up of a core <NUM> and a cavity <NUM>. Advantageously the tool assembly is mounted in a vertical moulding machine having cavity <NUM> at the bottom and core <NUM> on top. As the moulded part <NUM> starts to solidify its volume decreases and a small gap starts to open up at tool surface <NUM>. Through a non-return valve <NUM> high pressure gas is introduced that spreads across the surface of the part <NUM> as shown by arrows <NUM>. As shrinkage increases the entire volume left behind <NUM> by shrinking part <NUM> is occupied by gas under pressure that continues to isostatically press on entire surface <NUM> thus improving part density and its uniformity and reduce possibility of internal voids that may form on solidification without external pressure. Cooling efficiency is further improved by allowing gas to flow across part surface <NUM> and escape through openings <NUM>, generally along portion of part having lowest thickness, through a pressure regulating valve such that flow and pressure both are maintained. The flow of gas in such a case is chilled to very low temperature, typically inert gas for example Nitrogen at -<NUM>. Pressure of gas is decided by force required to overcome shrinkage induced internal voids and typically is of the order of <NUM> bar. However, in yet another embodiment of the invention the pressure may be increased to as high as <NUM> to <NUM> bar raising glass transition temperature of polymer out which part <NUM> was moulded leading to compression induced solidification. That leads to part solidification at higher temperature yet producing part having minimum stress that is normally produced by process of solidification. The gas under pressure is prevented from flowing across to other face of the part <NUM> by means of feature <NUM> moulded in the part that acts as a seal. This part may be now transferred to over moulding tool as applicable.

Reference is made to <FIG>, showing an isometric view, a plan view, a location of section plane and a corresponding section view and an enlargement detail G. <FIG> shows a first set made up of a cavity <NUM> and a core <NUM>, where in the surface <NUM> of part <NUM> is separated from the core <NUM> by a flexible membrane <NUM> which in a simplistic form is shaped like a bellow made of thin metal. As the moulding starts to shrink a tiny gap that initially develops adjacent to the bellow. Pressure is applied into space defined by surface <NUM> of the core <NUM> and underside of the bellow <NUM> and application of pressure is by a heat exchange fluid supplied through <NUM> and the same exits through <NUM>, which may be via a counterbalance valve, a pressure regulator or any such device that ensures there is predetermined pressure applied on part surface <NUM> via flexing of the said bellow. As volumetric shrinkage increases more the bellow presses against the moulded part surface increasing the gap as referred above and extra space is occupied by the heat exchange fluid similar to expanding balloon. Key advantage of this setup is that the part surface is separated by the membrane that helps to overcome potential contamination of surface and advantageously the heat exchange fluid is high pressure Nitrogen that has been dried and chilled and it takes away heat from the part very efficiently. It is also possible now to apply pressure by high pressure air or hydraulic pressure as there is no risk of contact with the part surface simplifying and potentially reducing costs. This enables cooling of the moulded article under pressure. It has to be noted that the moulding surface will carry impression of the shape and texture of the bellow which may not be acceptable in some instances and it is conceivable that this part may be overmoulded in another setup covering at least the side that was pressed by the bellow during its moulding cycle. It has to be noted that this mode of cooling is applied either in the moulding tool or external cooling arrangement. Advantageously safety interlocks are built in the tool and application of pressure is interlocked to presence of required pressure, temperature and dispensation of shot weight by the injection moulding machine in the chamber such that unintended activation of pressure in empty or partially filled chamber is avoided protecting against damage.

Reference is made to <FIG>, showing an isometric view, a plan view, a location of section plane and a corresponding section view. A similar setup as described by <FIG> with addition of a hydraulic piston <NUM> on which bellow <NUM> is mounted is shown by <FIG>. The piston has internal passages that enable application of pressure on the underside of the bellow <NUM> which in turn presses on the surface of part <NUM>. First set made up of cavity <NUM> and core <NUM> where core <NUM> in non-limiting aspect also acts as integrated hydraulic cylinder outer body containing piston <NUM>. In this instance the moulded article has two distinct zones made up of flange area <NUM> and bulbous area <NUM> in the middle. In this configuration the piston is advanced advantageously but not limited to be application of hydraulic pressure applying pressure over entire part surface and compensation for additional local shrinkage in the bulbous area is achieved maintaining cooling under application of load for part having varying thickness and ensuring the part is not allowed to develop internal bubbles or shrinkage induced vacuum bubbles advantageously producing part having uniform density. The heat removal fluid by way of example is high pressure chilled water, or high pressure chilled nitrogen enters in the tool close to the bulbous thick area <NUM> via opening at <NUM> and exits after flowing over the surface of bellow and exits via opening <NUM>. Required pressure is maintained by controlling exit of the heat exchange fluid via a counterbalance valve, a pressure regulator or any such device that ensures there is predetermined pressure applied on part surface <NUM> via flexing of the said bellow. It has to be noted that this mode of cooling is applied either in the moulding tool or external cooling arrangement. Advantageously safety interlocks are built in the tool and application of pressure is interlocked to presence of required pressure, temperature and dispensation of shot weight by the injection moulding machine in the chamber such that unintended activation of pressure in empty or partially filled chamber is avoided protecting against damage.

Reference is made to <FIG>, showing an isometric view, a plan view, a location of section plane and a corresponding section view. There are two timed section views, one at beginning of cooling and another at end of cooling. An arrangement for cooling under application of force is shown, wherein force is applied by however not limited to plurality of cylindrical cores <NUM>, <NUM>, <NUM>, <NUM> slidable telescoping within each other and outer core housing <NUM>. A lens in precompression as initially moulded shape and size <NUM> is moulded in a chamber defined by the cavity <NUM> and the combination of cores <NUM>, <NUM>, <NUM>, <NUM>. The cores are provided by mechanical support to at <NUM> taking up injection moulding load and when resting on the face <NUM> the top surfaces of the cores <NUM>, <NUM>, <NUM>, <NUM> define surface of the moulded lens on the core side. Advantageously the cores and cavity carry means of heat exchange in simple form a cooling duct <NUM> close to moulding surface through which cooling medium is passed. After a predetermined time cooling is continued under application of load by advancing the cores in simple case by application of hydraulic load via port <NUM> applying pressure in chamber <NUM> compressing on corresponding surface of the moulded lens. For simplicity any sealing against hydraulic fluid leaking is not shown. Maximum travel during advance is controlled by a travel stop <NUM> that abuts to face <NUM> of the end plate <NUM> when fully advanced, for simplicity shown only on the core <NUM>, however fixed to all moving cores. For simplicity hydraulic seals and other means of advancement of cores are not shown. Top ends of the cores forming the lens surface are shaped specifically that when fully advanced form a smooth surface <NUM>, which is also final shape of the lens <NUM> when fully compressed and solidified. It is also intent of the invention to be able to easily adjust volume of lens <NUM> by means of relative movement and positioning of end stops at <NUM> and <NUM> for each of the cores individually such that desired ratio is maintained between the volume as injected lens <NUM> and final volume of lens <NUM>. This ratio has in many cases to be worked out by trial and easy adjustment makes it possible to get ideal process parameters without excessive cost of new cores producing part having uniform density that is free of voids and other defects in a very fast production cycle. Whilst the concept is shown with cylindrical cores for a spherical lens it will be easily applicable to aspheric lenses as well. Whilst mentioned above the application of hydraulic load is acting on all the cores simultaneously, it is to be understood that separate individual control on each is possible by means including but not limited to use of servo electric motors, cam activation to name a few.

Reference is made to <FIG>, elaborating on a method described by way of <FIG> showing an isometric view, of two alternate embodiments of telescopic cores described above, only on core side of the tool for simplicity. <FIG> shows retracted condition of concentric generally cylindrical cores <NUM> as ready for moulding of the first part and <NUM> shows end of cooling under force where they generally line up defining smooth profile for end of cooling stage of the first part. Similarly at <FIG> a plurality of cores slidably grouped together <NUM>, are shows ready for moulding condition of the first part and <NUM> at end of cooling under force where again they line up to define smooth profile for end of cooling stage. Obvious benefit of the second execution according to <FIG> are that when the part is not simple shaped like a solid of revolution and may have extra thickness in a specific position and corresponding insert's initial position and travel can be independently controlled providing more control for every zone of the part. For simplicity other components of assembly are not shown.

Reference is made to <FIG>, showing an isometric view, a plan view, a location of section plane and a corresponding section view. <FIG> shows tool halves <NUM>, <NUM>, having simplistic non-limiting embodiment by way of provision of locking tabs <NUM>, <NUM>. In a non-limiting case the locking mechanism (not shown) engages on faces <NUM> and <NUM> locking the two halves. In section E-E a schematic of moulded first part <NUM> being overmoulded on both sides with second part <NUM>, <NUM> is shown. There is provision made in the tool and on the first part (not shown) to locate the first part <NUM> in predetermined position prior to moulding in the second part such that desired gap is maintained as applicable to provide controlled thickness for second part <NUM>, <NUM>. Advantageously the first part initial shape is so configured that at end of cooling under force and associate larger shrinkage in thickest portion of the first part results in generally uniform thickness of the second part improving accuracy of the moulded first part.

Reference is made to <FIG> showing a moulding setup consisting of a mounting frame <NUM>, on which is mounted injection unit in schematic form made up of slide <NUM> on which is mounted a barrel <NUM> that produces liquefied melt, having nozzle <NUM> from where the melt is delivered into the tool <NUM>, generally through hot runner (not shown). From here the melt is delivered into the tool cavities via a runner. The tool has chambers that receives tool sets, namely a first set, made up of a first core <NUM> and a first cavity <NUM>, a second set made up of second core <NUM> and a second cavity <NUM> and melt is directed to either of them in controlled fashion. It should be understood that when more than one material is required or more throughput rate is required than possible by a single barrel, additional barrels may be mounted on to the frame and melt directed through appropriate hot runner valve gates that may be built into tool body. Inserts are removable from the tool body as sets and are held in place in precise location and connected by quick clamp mechanism, symbolically shown at <NUM>. The sets contain means of blocking runner (not shown) and clamping to each other (not shown). Once melt is directed inside a Set, the runner is blocked, set clamped and the set is released from the tool and in clamped condition moved to cooling station <NUM>, that has location to receive numerous sets <NUM> that may be of different types capable of moulding different parts including overmoulding some. The cooling station has means to connect cooling supply and pressure depending on mode of cooling under pressure defined for a given set and the connections are advantageously made by means of quick connect coupling and process of cooling under pressure is carried out automatically.

The sets may be mounted with RFID sensors that provide information to computerised control system as to what stage of the process a given set is and what cooling and/or heating needs to be applied on the set.

Claim 1:
A method for moulding of a thermoplastic article comprising the steps of:
- Injection moulding at a first moulding station, in which is mounted a first moulding tool (<NUM>, <NUM>) assembly comprising at least its shape defining elements comprising a first core (<NUM>) and a first cavity (<NUM>), which define two opposing surfaces (<NUM>, <NUM>) of a first part to be moulded and when fully closed define at a parting surface a first chamber (<NUM>, <NUM>) enclosing a fixed first volume separable, said first moulding tool assembly having internal means of heat removal (<NUM>) and further comprise a first runner (<NUM>) flowably communicating between the chamber and injection moulding machine melt passage (<NUM>),
- Closing the first core (<NUM>, <NUM>), the first cavity (<NUM>, <NUM>), the first runner (<NUM>) and means of blocking making up a first set and for the process of moulding wherein after closing the first core (<NUM>, <NUM>) and the first cavity (<NUM>, <NUM>) the first part is moulded by injecting pliable polymer first resin via the first runner (<NUM>) in the first chamber till it is completely filled as per predetermined first process parameters,
- Cooling by a first cooling step by passage of cooling medium through the internal means of heat removal (<NUM>),
- Introduction of additional material into the first chamber (<NUM>, <NUM>) flowing via the first runner (<NUM>) under second process parameters, differing form the first process parameters,
- Blocking the first runner (<NUM>) after introducing the additional material,
- Subsequent to blocking of the first runner (<NUM>) further cooling by a second cooling to solidification by combining cooling with application of external force in a cooling station (<NUM>), wherein application of the external force deforms adaptively at least one surface of the first part and wherein the process of second cooling is carried out distal from the moulding station.