Abstract:
A multi-layered tool for forming a working having an active thermal layer disposed between two layers of the tool which is independently controllable to add or subtract thermal energy to or from the tool.

Description:
BACKGROUND 
       [0001]    The present invention is concerned with the management of temperature of a mould tool. More specifically the present invention is concerned with management of the temperature of a mould tool which utilises fluid heating and cooling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]    An example tool for forming a workpiece in accordance with the present invention will now be described with reference to the appended drawings in which: 
           [0003]      FIG. 1  is a temperature profile of a known layered mould tool. 
           [0004]      FIG. 2   a  is a schematic view of a first embodiment of a mould tool assembly in accordance with the present invention; 
           [0005]      FIG. 2   b  is a temperature profile of a the mould tool assembly of  FIG. 2   a;    
           [0006]      FIG. 3  is a schematic view of a second embodiment of a mould tool assembly in accordance with the present invention; 
           [0007]      FIG. 4  is a schematic view of a third embodiment of a mould tool assembly in accordance with the present invention; 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Fluid heating of layered mould tools is known, in particular from the applicant&#39;s earlier application published as WO 2013/021195. In this document, fluid-based heating of the back of the mould tool face in order to control the curing properties of the workpiece is discussed, whilst the control circuitry and delicate componentry of the mould tool is protected from excessive temperatures through the tool&#39;s layered structure. 
         [0009]    Heat management can be characterized in the three axes of the mould tool: X, Y and Z, (X and Y in the lateral direction, and Z in the vertical direction). Mould tools may be designed so that the predominant direction for heat transfer is towards the mould face (i.e. +Z), to mitigate heat losses in the −Z direction. However, if the mould tool is employed on a long duration temperature cycle, the inevitable conduction of heat throughout the tool is unavoidable and problematic. 
         [0010]    Such tools also need to be thermally agile-that is to be able to be heated and cooled quickly to provide the necessary control. Therefore a light tool with low thermal mass is desirable. However, given the necessary mechanical properties of a mould tool, e.g. stiffness to support loading without deflection, strength and hardness to withstand repeated loading etc. it is desirable to make the tools bulky, and therefore thermal energy management within a mould tool is a challenge. Fluid channels and electrical components also need to be provided, making the tools more bulky. Providing a stiff, strong mould tool with the necessary functionality and which is thermally agile is desirable. 
         [0011]    Zone control of tool temperature is also known, in particular from the applicant&#39;s earlier application published as WO 2011/048365. In this document, heating and cooling means are independently associated with each tool “pixel” -which may be defined as described below. 
         [0012]    In one embodiment of WO 2011/048365 each heated/cooled tool pixel has an independent in-line heater/cooler associated therewith, comprising an internal channel in each tool pixel below the tool surface through which a heating/cooling fluid is passed. The pixels are arranged to tessellate to form the tool surface at their upper surface. 
         [0013]    In WO 2013/021195, a first layer provides the mould tool face, and is heated by impingement of an in-line air heater. A second layer sits beneath the first layer, and provides exhaust channels for the used fluid. A third layer sits beneath the second layer and holds the heater unit, with the control electronics. Each in-line air heater has a tube which extends from the heater in the third layer, through the second (exhaust) layer to the first layer. As such, fluid is passed through the heater, passed through the second layer (in the sealed tube) and is impinged on the back face of the first layer. The used fluid then escapes downwardly through the second (exhaust) layer. 
         [0014]      FIG. 1  is a temperature profile of a known layered mould tool (such as that disclosed in WO 2013/021195). The profile shows a period of operation starting at time t, with two temperature cycles completed by time t_ 5 . The first layer temperature is indicated by line  102 . The first layer is repeatedly heated to 150° C. (at times t_ 1  and t_ 3 ) and cooled to 50° C. (at times t_ 2  and t_ 4 ) by turning the heater off (and impinging ambient air on the back of the tool) during the forming of a part in a sequence of heating phases and cooling phases. The temperature profile of the exhaust layer  104 , positioned directly under the first layer undergoes a similar heating and cooling cycle by conduction from the first layer, and partially from the in-line air tubes, and its temperature profile lags behind the first layer with reduced magnitudes of temperature. The temperature profile of the third layer  106  of the tool is even lower in magnitude, and again lags behind. 
         [0015]    It will be noted that during the heating phases of the tool, due to the delta in temperature between the first and second layers, some thermal energy flows into the second and third layers by conduction. Similarly, during cooling, thermal energy flows back to the first layer. Both effects are undesirable as they reduce the effectiveness of heating and cooling of the tool, and make it less agile. Cycle times are adversely affected as a result. 
         [0016]    Furthermore, the third layer usually has a temperature “ceiling” above which the delicate electronics stored therein may be damaged. This ceiling is at risk of breach if the mould temperatures are high. 
         [0017]    One solution proposed in the prior art is to provide insulating material of e.g. mica between the layers. In reality, this has a negative effect over many cycles, as the insulating material heats up and acts to reduce the agility of the tool. 
         [0018]    It is an aim of the present invention is to increase the thermal agility of a mould tool to allow greater control of the mould face and reduce cycle times for producing parts. 
         [0019]    According to a first aspect of the invention there is provided a mould tool assembly comprising: 
         [0020]    a mould layer comprising a mould face and a temperature control surface opposite the mould face; 
         [0021]    a temperature control assembly comprising a fluid conduit arranged to direct heating and/or cooling fluid to the temperature control face; 
         [0022]    a further layer supporting the mould layer in use; 
         [0023]    an active thermal layer disposed between the mould layer and further layer, which active thermal layer comprises a fluid chamber configured to be heated and/or cooled independently of the mould layer. 
         [0024]    Advantageously, the active thermal layer allows greater control of the mould tool to effect temperature variation of the tool face of a mould tool according to specific regimes relating to the component to be formed. The active thermal layer allows thermal decoupling of the layers. During cooling, the active thermal layer can be set at a lower temperature, to help “pull” the overall mould tool temperature down. Conversely, during heating, the active thermal layer can be set at a higher required temperature, to help “pull” the overall mould tool temperature up. In another temperature profile, the active thermal layer can be used to set certain parts of the mould tool to particular temperatures, in a “pre-heat” or “pre-cool” fashion. 
         [0025]    An intermediate layer may be provided, the intermediate layer positioned between the mould layer and the further layer. As such, the active thermal layer may be positioned between the intermediate layer and the further layer, or between the intermediate layer and the mould layer. 
         [0026]    Preferably the assembly comprises a second temperature control assembly configured to selectively heat and/or cool the active thermal layer. The second temperature control assembly may comprise a fluid conduit for connection to a pressurised source of fluid, and a heater configured to be selectively switched to provide a heating flow or cooling flow of the fluid. 
         [0027]    This arrangement allows delivery of fluid to the active thermal layer to provide temperature control of the active thermal layer, the exhaust port allowing fluid pressure to be managed. The use of fluid to supply the active thermal layer enables the requisite repeatability of the extreme temperature cycles. 
         [0028]    By supplying the active thermal layer with an independent heater assembly to the mould tool first layer, the two layers may be set to different thermal regimes. Furthermore, a different fluid may be used within the second heater assembly compared to the first heater assembly, for example nitrogen, which provides alternate thermic properties. 
         [0029]    The active thermal layer may define a further temperature control surface on a side of the fluid chamber furthest from the further layer. The fluid outlet of the fluid conduit of the second temperature control assembly is directed towards the second temperature control surface. This arrangement allows maximisation of the conduction of the thermal energy according to the demands of the tool surface, and minimisation of the conduction of the thermal energy towards the third layer. 
         [0030]    The active thermal layer may define a further temperature control surface in a region of one or more of the walls of the fluid chamber. The arrangement allows for localised increases in the surface area of the walls of the fluid chamber to provide varying thermal energy paths as is necessary. 
         [0031]    Preferably the fluid chamber comprises a plurality of interconnected chambers. This arrangement, which may be dendritic in form, allows support for load paths whilst facilitating intelligent routing to the flow for maximising heating and cooling. 
         [0032]    The assembly defines a Z axis generally normal to the mould layer, in which the second temperature control assembly may be arranged to direct flow normal to the Z axis. In this case, the second temperature control assembly may be at least partly positioned exterior the tool. This arrangement allows the active thermal layer to be incorporated into existing “layered” tool designs, without the need to re-organise the arrangement of the first heater assembly. 
         [0033]    Alternatively, the second temperature control assembly inlet may be positioned within the further layer. Advantageously this arrangement prevents the need for additional scaffolding to support the second heater assembly components external to the mould tool. 
         [0034]    The fluid chamber of the active layer has a first wall adjacent the mould layer, and a second wall adjacent the further layer and at least a region of one of said first or second walls may comprise features increasing the surface area of the first or second wall over the other of the first or second wall. This allows the tool to be tailored specifically to increase heat transfer to and from the mould layer, according to the demands of the workpiece. For example, if the tool is to undergo a long duration heat cycle, the main design driver may be to prevent heating of the sensitive utilities. As such, a greater surface area on the first wall adjacent the mould layer encourages more heat transfer towards the mould layer and less towards the utilities. Alternatively, if the tool is to undergo a very short duration heat cycle, the main design driver may be to effect changes in mould surface temperature as quickly as possible, As such, by increasing the surface area of both walls of the active layer, the active layer can have a greater overall effect on the mould tool temperature. 
         [0035]    The tool may further comprise a sensor arranged to detect a temperature of the active thermal layer and/or a sensor arranged to detect ambient temperature exterior of the tool. 
         [0036]    A control system may be provided and configured to maintain the temperature of the active thermal layer at a predetermined set point. 
         [0037]    Preferably the first and third layers may be configured such that flow of fluid from the first fluid chamber into the further layer is prohibited. This prevents heat passing to the further layer by convection. 
         [0038]    The intermediate layer may be an exhaust flow layer for the mould layer heating flow. In this case a flow conduit may be provided from an outlet of the exhaust flow layer to the active thermal layer. Use of pre-heated fluid can save energy. 
         [0039]    The flow conduit may be configured to provide flow past the periphery of the mould layer to reduce the temperature difference between the mould layer and the local environment. 
         [0040]    The further layer may be a utilities layer comprising electronics for the first temperature control assembly. The further layer may be a utilities layer comprising electronics for the second temperature control assembly. In either case, the active thermal layer can protect the further layer. 
         [0041]    According to a second aspect of the invention there is provided a method of manufacturing a workpiece comprising the steps of providing a tool according to the first aspect and forming a workpiece using the tool. 
         [0042]    Referring to  FIG. 2   a , a mould tool assembly  100  comprises a first layer  102 , an second layer  104 , a third layer  106 , a support assembly  108  and an active thermal layer  160 . 
         [0043]    The first layer  102  comprises a tool face  110 . The tool face  110  defines the shape of a workpiece to be formed, and in use may be associated with an opposing tool (not shown). On the opposite side of the tool face  110 , a temperature control surface  112  is defined, having ridges to increase its overall surface area for better conductive heat transfer. 
         [0044]    The first layer  102  comprises a peripheral wall  114  so as to define an enclosed volume. The first layer  102  defines a number of discrete fluid chambers  118  which are bound by a part of the temperature control surface  112  at a first end and open at a second end  116 . The chambers  118  are separated by chamber walls  120  which extend from the temperature control surface  112  to the second ends  116 . As such, the first layer  102  defines a type of honeycomb structure comprising a number of discrete celllike chambers  118 . 
         [0045]    The second layer  104  is adjacent the first layer and comprises a body  124  having a number of through bores  125  defined therein. The through bores  125  are in fluid communication with each other via internal ports  128 . The through bores proximate the periphery of the block  124  are in fluid communication with exhaust ports  130 . 
         [0046]    The third layer  106  comprises a body  132  having a series of through bores  134 . Each of the through bores  134  contains mounting apparatus for an inline air heater  150 ,  170  (as will be described below). 
         [0047]    The support assembly  108  comprises a sealing plate  136  having a plurality of blind bores  138  defined therein, a support plate  140  and a plurality of I-beams  142 . 
         [0048]    An active thermal layer  160  is provided intermediate the second and third layers and comprises a body  164  defining a single fluid chamber  162 , in fluid communication with exhaust ports  166 . The chamber  162  has a ceiling  163  comprising a plurality of ridges  165  provided to increase the surface area of the ceiling  163  to encourage conduction therethrough. A floor  167  of the chamber  162  has no such ridges and as such the active thermal layer is configured to provide a higher conduction of temperature across one surface than the opposite surface. 
         [0049]    An in-line air heater assembly  149  comprises a heater  150  into which compressed air is introduced (at an inlet end  153 ). Heated fluid then passes through a tube  152  to an outlet  154 . 
         [0050]    As will be seen in  FIG. 2 , the layers are assembled with the support assembly supporting the third layer  106  in which the heaters  150  of the assemblies  149  are mounted. The active thermal layer  160  is stacked onto the third layer  106  such that the tube  152  passes through it. The second layer  104  is staked onto the third layer, again with the tube  152  passing through. Finally the first layer  102  is stacked onto the second layer  104 . When assembled the outlet  154  of the tube section  152  impinges onto the temperature control surface  112  of the first layer  102  to heat or cool it (depending on whether the heater  150  is active). 
         [0051]    The fluid then enters the chambers  118  where it flows down into the second layer  104 , and is then exhausted to ports  130 . 
         [0052]    An active thermal layer heating assembly  169  is provided, comprising a heater  170  having an inlet  173  and a tube section  172  having an outlet  174 . The outlet  174  of the tube section  172  ejects into the chamber  162  of the active thermal layer  160 . 
         [0053]    The active thermal layer can make the tool more agile as follows. 
         [0054]    Referring to  FIG. 2   b , the first and second layers have respective characteristics  102 ,  104  as with  FIG. 1 . The prior art third layer profile  106  is shown, as well as the profile  106 ′ with the active thermal layer in place. The active thermal layer has temperature characteristic  107  which is controlled by injection of hot or cold air via the assembly  169 . 
         [0055]    As can be seen, when heating the main mould tool, the thermal layer temperature can be increased to 100 degrees to provide a boost. When cooling, the active thermal layer can be cooled to provide a heat sink at 50 degrees. It will also be noted that due to the isolation of the third layer,  106 ′ is at a generally lower temperature than  106 . Therefore the utilities such as the electronics are better protected. Conduction between the active thermal layer  160  and the third layer  106  is not as good as between the active thermal layer  160  and the second layer  104  due to the increased surface area on the ceiling  163  of the active thermal layer  160 . 
         [0056]    Turning to  FIG. 3 , a second mould tool assembly  200  similar to  FIG. 2   a  is shown with reference numerals designating similar components 100 greater. The main differences between the tool assemblies  100  and  200  is the arrangement of the inline heater assembly  269  supplying heated fluid to the active thermal layer  260  and the division of the block  264  into multiple, interconnected chambers  262 , separated by walls  268  with orifices defined therein. The inline heater  270  is arranged external to the tool  200 , with tube section  272  passing through block  264 , such that outlet  274  of tube section  272  ejects into the multiple interconnected chambers  262 . Furthermore, disposed between the active thermal layer  260  and the third layer  206  is an insulative layer  264 . 
         [0057]    Turning to  FIG. 4 , a third mould tool assembly  300  to  FIG. 2   a  is shown with reference numerals designating similar components 200 greater. Tool assembly  300  is similar to tool assembly  100  in that the inline heater  370  supplying the active thermal layer  360  is arranged with inline heater  370  mounted in the through bores  334  of the third layer  306 , with outlet  374  of the tube section  372  ejecting into the single chamber  362  of the active thermal layer  360 . However, in mould tool  300 , active thermal layer  360  is disposed between the first layer  302  and the second layer  304 . As such, tube section  372  must traverse the third layer to second layer boundary. Gasket  344  is provided between the second layer  304  and the third layer  306 . 
         [0058]    Furthermore, the single fluid chamber  362  of active thermal layer  360  has a localised central region of ceiling  363  and floor  367  comprising a plurality of ridges  365  provided to increase the surface area of the central region to encourage conduction therethrough. The outer region of the ceiling  363  and floor  367  of the chamber  362  has no such ridges and as such the active thermal layer is configured to provide a higher conduction of temperature in its centre region compared to its outer region. 
         [0059]    The passage of fluid from the first layer  302  to the second layer  304  is enabled by a series of channels disposed through the active thermal layer  360 , as indicated by arrows  380  (but not shown). 
         [0060]    Additionally, mould tool  300  has a fan  390  arranged to blow air across the active thermal layer  360  entering and exiting through ports  366 . 
         [0061]    Turning to  FIG. 5 , a mould tool assembly  400  is shown, being similar to the mould tool assembly  100  with reference numerals of similar components 300 greater. Like the tool assembly  100 , the tool assembly  400  has a first layer  402 , second (exhaust) layer  404  and a third (utilities) layer  406 . A temperature control assembly  449  directs hot or cold air to the back face  412  of the first layer  402 , opposite the mould face  410 . 
         [0062]    An active thermal layer  460  comprising a fluid chamber  462  is provided between the second and third layers  404 ,  406 . The active thermal layer  460  has an inlet  461  and an outlet  463 . 
         [0063]    A peripheral fluid chamber  1000  is provided in fluid communication with both (i) an outlet  430  of the second layer to receive exhaust air, and (ii) the inlet  461  of the active thermal layer  460 . The peripheral fluid chamber  1000  defines a channel extending so as to direct airflow  1004  from the exhaust layer  404 , to the periphery of the first part  402 , before returning past the exhaust layer  404  to the active thermal layer. 
         [0064]    The chamber  1000  comprises a baffle  1002  to direct the fluid flow in this manner. The chamber  100  also extends partially or wholly around the periphery of the first part  402  to reduce losses to the surrounding environment (on the basis that the exhaust flow is hotter than ambient air). 
         [0065]    Once the flow  1004  has entered the active thermal layer  462 , it can exit at the outlet  463 . 
         [0066]    A separate temperature control assembly  1100  is shown schematically, comprising an inline air heater which can be selectively activated an deactivated to heat or cool the air in the chamber  1000 . This can be useful to reduce still further the difference in temperature between the first layer  402  and the surroundings. The assembly  1100  can be used for heating (with the associated heater activated) or cooling (with the associated heater deactivated) per the assembly  449 . 
         [0067]    Variations of the above embodiments fall within the scope of the present invention. 
         [0068]    It will be appreciated that although the invention has been described in relation to a single tool face in many applications a tool with two tool faces will be used and that an upper tool face according to this invention may also be used in combination with a lower tool face to provide an active thermal layer for both sides of the tool. 
         [0069]    Exhaust flow from the second layer  404  may be directed to the active thermal layer  462  without the peripheral chamber  1000  (a simple conduit may be used). This will offer the advantages of using pre-heated air in the active thermal layer. Additional temperature control assemblies may be provided in the active thermal layer. 
         [0070]    The active thermal layer may be a pressurised system operated at different pressures according to the necessary heating regime. By operating the system at a higher pressure than atmospheric pressure, an additional control vector is available for the management of the tool. 
         [0071]    Active thermal layers may be positioned between both the first and second, and second and third layers.