Tool temperature control

A tool element assembly (100) has a tool element (102) with a tool surface (110) and a control surface (112) opposite the tool surface. A thermal control structure (104) is provided defining a flow chamber (103) partially bounded by the control surface, and having an inlet (148) and an outlet (121) which control chamber diverges towards the control surface.

The present invention is concerned with a tool element assembly for controlling the temperature of a tool face. More specifically, the present invention is concerned with the provision of an assembly which provides an independently controllable fluid chamber to control the temperature of a zone of a tool face whilst minimising influence from adjacent zones.

Manufacturing tools or patterns are well known in the art for forming workpieces constructed from metal, plastic or composite materials. In particular, the applicant's prior published patent application, WO02/064308, discloses a system whereby a reconfigurable series of tool pins, or elements, can be raised or lowered and subsequently machined to the desired profile of the workpiece.

It is desirable during forming of a workpiece on such a tool to be able to control the temperature of the tool, for example, if “out-of-autoclave” composite curing is desired. In addition, it is also desirable to be able to independently control different areas of the tool face and thereby influence the material properties of the workpiece across the surface of the tool. For example the user may want to form a workpiece being stiff in one area, but flexible in another (e.g. for a film hinge).

The applicant's prior applications published as WO2006/067447 and WO2011/015823 discuss the potential for supplying heating or cooling fluid into individual tool pins to selectively heat and/or cool them. A problem with such a system is that the pins are formed from bulky metal blocks with channels formed therein and are therefore of a high thermal inertia (meaning that they take time to heat and/or cool). Furthermore each pin either contacts, or is very close to the adjacent pins across a significant area (meaning that the heating/cooling of one pin will affect adjacent pins, which is undesirable).

Accordingly, it is an aim of the present invention to provide an improved tool element assembly.

According to a first aspect of the invention there is provided a tool element assembly comprising: a tool element having a tool surface, and a control surface opposite the tool surface, a thermal control structure defining a fluid chamber partially bounded by the control surface, and having an inlet and an outlet, in which the fluid chamber diverges towards the control surface.

Advantageously, the use of the structure defining a fluid flow chamber bounded by the control surface allows the operator to flood the chamber with a fluid of appropriate temperature. Because of the high contact area with the control surface of the element, and the flow of fluid thereover, the system has a low thermal inertia which enables rapid changes in temperature thereby allowing greater control over the manufacturing process.

Further, the divergent nature of the chamber allows adjacent chambers to be thermally isolated. Because of the divergent nature of the chambers, adjacent chambers can be formed with a large space therebetween. Therefore each zone will be influenced by adjacent zones by a lesser extent than in the prior art.

By “divergent” we mean increasing in cross sectional area approaching the control surface. For example, step changes in cross sectional area may occur. Such divergence need not be gradual (e.g., tapered), although this is preferable. Plural inputs may be provided which diverge towards the control surface.

Preferably the inlet is positioned closer towards the control surface than the outlet. This minimises contact of the incoming fluid with the fluid in the chamber, preventing undesirable heating and/or cooling.

In order to achieve this, the inlet may be defined by a pipe extending into the flow chamber. In this way, the outlet may be formed proximate the entry point of the pipe.

The pipe may axially adjustable relative to the control surface.

Preferably the pipe is directed towards the control surface. This provides an impinging jet for maximum heat transfer to the control surface.

Preferably the structure defines a load path for supporting the tool element. This allows the loads on the tool during the manufacturing operation to be reacted. Preferably the load path diverges towards the tool element to support the tool element proximate its periphery. This allows the fluid to access the control surface of the tool uninhibited.

Preferably the thermal control structure comprises at least one plate defining the flow chamber. A plate like structure is light, inexpensive and has a high thermal agility. The plates may be constructed from an insulating material.

Preferably the load path comprises a load beam in contact with the at least one plate. The plates can thereby be supported in position with no additional structure.

Preferably the inlet is directed towards a target position on the control surface, and the tool element has a thickness tapering away from the target position. This mitigates hot cold spots from occurring in the centre of the element—the area which is exposed to the highest heat transfer coefficient from the impinging jet of fluid is made thicker to intentionally slow its change in temperature to match the surrounding parts of the element which experience lower heat transfer coefficients.

Preferably the control surface has features defined thereon to increase its surface area. This increases the thermal agility of the element.

The features may be protrusions. The protrusions may be reactive to a fluid flow thereon to move relative to the control surface. Alternatively the protrusions may be reactive to temperature to move relative to the control surface.

According to a second aspect of the invention there is provided a tool element assembly comprising:a tool element having a tool surface, and a control surface opposite the tool surface,a thermal control structure defining a fluid chamber partially bounded by the control surface,in which the control structure is constructed from one or more panels.

By “panels” we mean thin walled sections of material, for example in which the aspect ratio of thickness to minimum length is at least 20:1. Beneficially, using thin panels of heat resistant material provides the best thermal agility for the system (because very little thermal energy is stored by the panels).

In other words, the invention utilises a thin walled enclosure which is supported by a skeletal structure.

Preferably the control structure comprises at least one support member arranged to form a load path for loads incident on the tool element.

One or more baffles may be positioned within the fluid chamber arranged to control the course of flowing fluid within the chamber. The baffle position may be adjustable.

Preferably at least one baffle is positioned within the fluid chamber to define a flow path diverging towards the tool element.

According to a third aspect of the invention there is provided a tool comprising a plurality of element assemblies according to the first or second aspect, in which the tool elements of the tool element assemblies tessellate to define a tool face.

According to a fourth aspect of the invention there is provided a method of manufacturing a workpiece comprising the steps of:providing a tool element assembly according to the first or second aspect, providing an opposing tool element,forming a workpiece between the tool element and the opposing tool element.

Turning toFIG. 1, the tool element100comprises a tool block102, a support structure104, a thermal control assembly106and a support rod108.

The tool block102is a generally plate-like structure having a tool surface110on a first side and a temperature control surface112opposite the tool surface110. The tool block102is generally rectangular in shape and has a downwardly extending side walls114surrounding the periphery of the tool block102and extending away from the tool surface110. The projection of the side walls114from the temperature control surface112forms a tool block cavity116. The temperature control surface112is contoured such that the tool block cavity116is shallower in the centre of the tool block102than at the sides proximate the side walls114. In other words, for a flat tool surface110, the tool block102is thicker in the middle of the tool block102than at the edges proximate the side walls114. The thickness tapers towards the periphery of the tool block102.

A thermocouple (not shown) is positioned within the tool block102in order to measure the temperature of the block102(preferably near the tool face110). Control of the face temperature is achieved using this thermocouple.

The support structure104comprises four generally triangular plates118. The plates are arranged such that their edges touch forming a plenum103. Each plate118has a truncated lower end119such that an exhaust orifice121is formed at their base. At the centre of each of these triangular plates118is a load beam120which comprises a first attachment flange122for attachment to a relevant side wall114of the tool block102mthe first flange122extends into an elongate axial load bearing beam124terminating in a second flange126. Along the length of the beam124, a plurality of mechanical fasteners128secure it to the relevant triangular plate118. The plates118extend to meet the side walls114of the tool block102, but stop short such that an area of the sidewalls114forms a part the plenum103for reasons described below.

Each of the four load beams120attaches to a collar130via mechanical fasteners132. The collar130is generally cylindrical, having a central through bore134.

A pair of support bars136are attached to the collar130and terminate in a support flange138. It will be noted that the second support bar136is provided but is not visible inFIG. 1.

The support rod108extends downwardly from the support flange138.

The thermal control assembly106comprises an electrical resistive air heater140having a heater component and a temperature sensor. The heater component is controlled by a power supply142and the temperature of the heater140is measured by a control line144. Air is supplied to the heater140through an air line146connected to an air pump or pressurised air source and is heated. A hot air output from the heater140enters a hot air tube148which extends through the collar130and is fastened thereto, in this instance by the fasteners132which pass all the way through the assembly of the collar130, two of the second flanges126of the load beams120and the hot air tube148. The heater140is controllable to provide the required fluid temperature, and may be deactivated completely to provide a cooling (ambient temperature) air flow.

The hot air tube148extends towards the tool block102and is directed to the central point of the temperature control surface112such that fluid passed therethrough impinges on that surface.

Turning toFIG. 2, parts of the tool element100ofFIG. 1can be seen in more detail. As shown by arrows A, fluid passed through the hot air tube148and impinges on the tool block102. The fluid direction moves through 90 degrees to be generally parallel to the control surface112and impinges again, this time on the side walls114before circulating back down past the triangular plates118and the load beams120to exhaust at a gap121between each of the load beams120proximate the collar130. The second impingement on the sidewalls114also helps heat transfer from the fluid to the tool block102.

Because the heat transfer coefficient between the fluid from the hot air tube148and the tool block102will be higher proximate the area where the jet impinges, the increased thickness of the tool block102at its central position mitigates this effect with respect to the temperature of the tool surface110. Conversely, the areas more towards the side walls114, which will not receive the same amount of thermal power, are thinner and, as such, the temperature at the tool surface110is made more consistent.

Turning toFIG. 3a, a tool160is shown comprising two opposing tool elements100,162. The correct orientation is shown inFIG. 3a—specifically the tool block102is generally horizontal and upward-facing. A tool block162of the tool160is generally horizontal and downward facing, so a workpiece cavity164is defined between the tool elements100,162.

In use, as the plenum103of the tool element100fills, the warmest air will naturally rise towards the tool block102. As such, heating of the tool block102takes place.

Because the tool element162is inverted, the warm air will not tend towards the tool block162(rather it will rise in the opposite direction). The ability of the fluid to alter the temperature of the element162depends on many factors (such as the speed of he impinging air, as well as its temperature, and therefore buoyancy in the surrounding air). In order to account for this, in the embodiment ofFIG. 3a, the tubes148,166are axially adjustable. This functionality is provided with an adjustable clamp mechanism (not shown). This allows the system performance and temperature distribution across the blocks102,162to be varied as required.

Turning toFIG. 3b, a tool150is shown comprising three tool elements100,100′ and100″. As can be seen, each of the support rods108,108′,108″ can be moved

axially relative to a support structure10such that the tool surface110can be varied in height and machined to the desired profile.

When the manufacturing process begins, the opposing mould tool pressing on the workpiece will cause a pressure to be applied to the tool surface110in direction P. Due to the presence of the load beams120, this applied load is transferred to the collar130through the support bar136into the support flange138and into the support rods108. Thus a load can be successfully reacted without any need to pass through the more fragile heating equipment.

In addition, the provision of the triangular plates118forming divergent plenums ensures that the separate chambers are kept out of thermal contact and, as such, adjacent temperatures cannot significantly affect each other. Therefore, each zone can be controlled independently providing that the area below the tool surface is sufficiently vented in order to remove the air therein.

Turning toFIG. 4a, a tool element200in accordance with the present invention comprise a tool block202having an undulating control surface204. The increased surface are of the control surface204increases heat transfer to or from the working fluid to the tool block.

Turning toFIG. 4b, a tool element300in accordance with the present invention comprise a tool block302having a control surface304with deformable ribs306. The ribs306are mounted to the control surface and able to move between a stowed position as shown on the left ofFIG. 4bin which they lie substantially flat against the surface304and a deployed position as shown on the right ofFIG. 4bin which they stand proud of the control surface304.

Movement of the ribs306occurs by virtue of the motion of the heating/cooling fluid moving from the centre to the perimeter of the tool block302, as shown by arrow A.

Fluid is pumped towards the tool block302when the temperature of the block is to be changed. Under these conditions maximum heat transfer between the fluid and the

block302is desirable. The deployed ribs306ensure that the surface area of contact between the fluid and the block302is maximised. Furthermore, the presence of the deployed ribs306in the flow of fluid disrupts the fluid flow, increasing turbulence which also increases the heat transfer coefficient between the fluid and the block302.

Alternatively, when the temperature of the block302is to remain constant, the flow of fluid can be lessened or stopped. The movement of the ribs306to the stowed position lowers the contact area between the fluid and the block302thus reducing any conduction therebetween.

Turning toFIG. 4c, a tool element400comprises a tool block402. The tool block402has a control surface404which comprises undulations per the element200, with the exception that a high conductivity coating406such as copper or gold is provided on the control surface404. This acts to increase the conduction between the fluid and the tool block402.

Turning toFIG. 4d, a tool element500comprises a tool block502which has a control surface504having a central protrusion506which acts to separate and guide the airflow A parallel to the control surface504to encourage more even heat transfer with laminar flow.

Turning toFIG. 4e, a tool element600comprises a tool block602and a support structure604similar to structure104. The main difference is that bores606are formed in the structure604to permit early escape of the fluid flow A. This acts to quickly remove used fluid from the chamber to increase the thermal agility of the system.

Referring toFIG. 5, the control surface912of a tool element block902is shown. The control surface912comprises three zones: a central zone914, an intermediate zone916and an outer zone918. The general concept is that the central zone914is configured to have a low heat transfer coefficient (for conduction from the adjacent fluid), the intermediate zone916to have an intermediate heat transfer coefficient and the outer zone918to have a high heat transfer coefficient. In the embodiment ofFIG. 5, the central zone914is coated in a highly reflective material, the outer zone918in a thermally absorbent material (e.g. graphene) and the intermediate zone916in an intermediate material.

For example, the zones may be coated in different paints (the central zone914white, the intermediate zone916grey and the outer zone918black). Alternatively the zones may be coated in materials with differing properties—e.g. the outer zone918may be coated in copper or gold.

This arrangement of zones helps the tool face temperature to remain even. The heated fluid will tend to be warmer at the point at which it impinges on the tool block. The amount of thermal energy available will also be “diluted” as is spreads over the area of the tool block towards the extremities. Further, the heat transfer coefficient will be lower as the fluid moves from an impinging course at the centre to a parallel course towards the edges.

Referring toFIG. 6, a tool element1000comprises a tool block1002having a tool face1010and a control surface1012. The element1000defines baffles1060which are held in the chamber1003by brackets (not shown). The baffles are arranged to encourage a convention cell to form in the chamber1003by allowing used fluid to pass down the sides of the chamber1003without encountering newly heated air.

Turning toFIG. 7, a tool element1100is shown. The tool element1100has a tool block1102. A cuboid chamber1103is defined by panels1108and a support structure1120. As with the above embodiments, the panels1108are arranged to define the fluid chamber1103, and the support structure1120reacts loads incident on the tool face.

The left hand side ofFIG. 7shows a baffle1160which is similar to the baffles ofFIG. 6. The baffle1160forms a divergent flow area towards the block1102which encourages the heated fluid to spread more evenly. It also provides a side return path for the used fluid, which also insulates the incoming fluid, from the surrounding environment.

The right hand side ofFIG. 7shows a baffle1162which is vertical, but performs a similar function to the baffle1160in setting up a convention cell within the chamber1103.

In each of the embodiments ofFIGS. 6 and 7, the baffles1060,1160,1162form may be discrete panel sections, or may form endless loops within the chambers1003,1103.

Variations fall within the scope of the present invention. The baffles as shown inFIGS. 6 and 7may be movable, and even adjustable in use so as to optimise the flow scheme within the relevant chamber.

The support structure104does not need to define a pyramid-like structure and may be three-sided triangular, or even hemispherical. The important thing is that a separate temperature zone is defined for each of the tool elements.

The tool itself does not need to be a horizontal type tool as shown inFIG. 3, but may be a rotating mandrel in which each of the support rods108is a spoke rotating about a hub, or any other appropriate structure.

The system may be used for cooling as well as heating.

As an alternative to providing a heater integrated with the assembly, an external air supply may be provided with pre-heated or pre-cooled air.

In addition to the air, any other appropriate fluid (an alternative gas or even a liquid) may be used to affect the temperature of the tool blocks102.

The undulations ofFIG. 4amay be replaced by any feature which increases the surface area of the block202. For example static fins, ribs, corrugations, or channels may be used.

The fins306ofFIG. 4bmay be configured to react to specific temperatures rather than airflow. For example, the fins306may comprise heat sensitive elements at their base which deploy the fins at a given temperature to increase heating or cooling. Such heat sensitive elements may be constructed from a material with as high thermal expansion coefficient, whilst the fins are constructed from a highly conductive material which is configured to conduct heat to the block.

The bores shown inFIG. 4emay be formed around the periphery of the plenum chamber, and are preferably not formed in the support bars to avoid weakening thereof.