GB2467784A

GB2467784A - Forming a curved sheet from plastics or composite material

Info

Publication number: GB2467784A
Application number: GB0902537A
Authority: GB
Inventors: John Gould
Original assignee: FORMTEXX Ltd V; TEXXUS Ltd
Current assignee: V-FORMTEXX LIMITED
Priority date: 2009-02-17
Filing date: 2009-02-17
Publication date: 2010-08-18
Also published as: GB0902537D0

Abstract

A method and a cell are provided for forming a curved sheet. The method comprises the steps of (a) configuring a first array of pins 100 to have a profile designed to form a curved sheet from a flat sheet received thereon, (b) configuring a second array of pins 142 to transport a flat sheet into contact with the first array of pins 100, (c) forming a curved sheet having the profile of the first array of pins 100 from the flat sheet by covering with a diaphragm 144 to seal around the first array of pins 100 and evacuating the first array of pins 100, reconfiguring the second array of pins 142 to have a profile conforming to the curved sheet, and using the second array of pins 142 to move the curved sheet out of contact with the first array of pins 100. A cell 120 having the said arrays 100, 142, with the second array of pins 142 adjustable to accommodate a flat sheet profile and a curved sheet profile, a diaphragm 144 and a vacuum assembly 146, is provided. A third array of pins 152 may support the curved sheet whilst it is cut to size in a trimming station 150. The configuration of the pin arrays may be controlled automatically based on digital data representing the curved shape to be formed.

Description

IMPROVEMENTS IN OR RELATING TO THE CREATION OF CURVED FORMS

The present invention relates to a method and apparatus for multi-point forming and, in particular, to a method and apparatus for multi-point forming of plastics parts.

There is an increasing demand from building and marine architects, façade designers and fabricators to produce buildings and marine hulls formed from curved panels in a variety of materials. These structures are characterised by the use of asymmetrical, non-repeating curved surfaces. Some of the surfaces may even include compound curves.

The fabrication of panels for such projects using standard single use thermoforming moulds is very time consuming and very wasteful of materials as each mould can only be used for one panel and must then be destroyed. This is not only wasteful of resources, but also makes some projects prohibitively expensive.

In order to reduce the wastage of time and resources inherent in single use moulds, multi-point forming techniques have been used to prepare a series of different moulds sequentially using the same pins, reformatted for each new mould. Whilst this allows the mould to be effectively reused, there is still a disconnect between the shape data and the element groups used for the multi-point forming.

The present invention has been created in order to overcome some or all of the drawbacks identified with regard to the known state of the art.

According to the present invention there is provided a method of forming a curved sheet from a plastics or composite material, the method comprising the steps of: configuring a first pin array to have a profile aligned with the curved sheet to be formed; configuring a second pin array to transport a flat sheet into contact with the first pin array; forming a curved sheet from the flat sheet by covering the flat sheet with a diaphragm that is configured to form a seal around the first pin array and evacuating the first pin array; wherein the curved sheet has the profile of the first pin array; reconfiguring the second pin array to have a profile aligned with the curved sheet, and using the second pin array to move the curved sheet out of contact with the first pin array.

The first pin array acts like a reconfigurable mould which can be reused. This reduces the wastage of resources inherent in the use of standard moulding techniques, where an individual mould has to be prepared for each sheet that has a unique shape and must then be discarded after use.

The second pin array, when it is reconfigured to have the profile of the curved sheet, protects newly formed curved sheet that may be delicate when newly formed.

Moving them using a pin array that is closely configured to the shape of the sheet allows the sheet to be moved more quickly after forming, thereby speeding up the forming process.

The configuration of the first and second pin arrays may be controlled automatically based on digital data representing the curved shape to be formed. The digital data originates from the CAD data prepared by the architect showing the shape of the object to be fabricated. This data is digitally manipulated to provide instructions to a series of actuators provided on each of the pins within the first and second pin arrays. The actuators move the pins from their datum position so that the profile of each of the pin arrays is aligned with profile of the curved sheet to be created. In this way, the array is formed directly from the CAD data of the shape to be formed without this data being taken out of the digital realm and interpreted by a skilled operative.

The step of forming the curved sheet may include the steps of covering the flat sheet with a diaphragm that is configured to form a seal around the first pin array and evacuating the first pin array.

When the first pin array is evacuated the seal formed by the diaphragm forces the flat sheet to deform so that the profile of the sheet matches the profile of the first array of pins, thereby forming a curved sheet.

The method may further comprise the step of heating the flat sheet before transporting the flat sheet into contact with the first pin array. The flat sheet will be more malleable when it has been heated and therefore it can be more easily formed into a curved sheet.

The method may further comprise the step of cooling the curved sheet before it is moved out of contact with the first array of pins. The cooling of the curved sheet ensures that the sheet is sufficiently resilient that it will not deform when it is removed from the first array of pins.

The method may further comprise the steps of: configuring a third pin array to have a profile aligned with the curved sheet; using the second pin array to transport the curved sheet into contact with the third pin array and trimming the curved sheet.

The provision of a third pin array that has a profile that is aligned with the curved sheet enables the curved sheet to be supported and held securely whilst the sheet is cut to size. This enables the curved sheet to have a different shape from the flat sheet.

The trimming of the curved sheet comprises a trimming tool following a path that defines the desired profile of the curved sheet. The trimming of the curved sheet uses a trimming tool that follows a path in order to maximise the flexibility of the method as a whole in that the path of the trimming tool is not constrained and therefore the sheet can be cut to any shape. This is a contrast to a cutting tool that acts like a stamp and cuts the shape as a whole in one action.

The choice of trimming tool will be dictated by the choice of the material from which the sheet is fabricated and the thickness of that sheet. The trimming tool may be a laser or, alternatively a water jet, mechanical milling machine or electron beam.

The method may further comprise checking for conflicts between a path of the trimming tool and the position of the pins in the third pin array and, if a conflict is detected, retracting the pin or pins that are subject of the conflict. The conflict checking and resolution ensures that the trimming tool has complete freedom of movement to cut the curved sheet to any shape that is required.

Furthermore, according to the present invention there is provided a manufacturing cell for fabricating curved sheets, the cell comprising: a first array of pins that can be configured to have a profile aligned with the curved sheet to be formed; a second array of pins that can be configured firstly to interface with a flat sheet and secondly to have a profile aligned with the curved sheet and a diaphragm and a vacuum assembly.

The diaphragm preferably takes the form of a resilient frame and a flexible portion within the frame. The frame is preferably sized so that it can cover the first pin array in its entirety. In use, the frame forms a seal around the first pin array so that the vacuum assembly can form a partial vacuum around the first pin array and thereby cause the flat sheet to deform to match the profile of the first pin array thereby forming a curved sheet. When the frame is providing a seal, the flexible portion holds the flat sheet in close contact with the first pin array. The flexible portion may be elastic and may be formed of rubber.

The second array of pins may have a lower density that the first array of pins. The first array of pins is used to form the curved sheet and therefore they must be sufficiently closely packed that they form a substantially continuous surface. There must not be sufficient space between the pins for the sheet to deform between the pins and leave a witness mark identifying the edge of the pins.

In contrast, the second array of pins needs only to be of a sufficient density to hold the sheet and to move it through the manufacturing cell. The density of the second array of pins may therefore be 1110th of the density of the first array. For example, if the material to be pressed is 2mm thick, then 25 pins/rn2 may be provided.

Alternatively, if the material is in the region of 50mm thick then only 9 -16 pins/m2 may be required. If the material is considerably thinner, for example 0.75mm to 1.5mm then a higher density of pins, up to 36 pins /m2 would be required.

The pins of the second array may be provided with suction pads for holding the sheet securely without marking the sheet.

The cell may further comprise a heater for heating the flat sheet. When the flat sheet has been heated it becomes more malleable so it is easier to cause the deformation required to form the curved sheet.

The cell may further comprise at least one further heater. Depending on the material that is chosen, it may take a considerable length of time to heat the flat sheet. If the time taken to heat the flat sheet exceeds the time taken to form the curved sheet, the pin arrays will be idle unless more than one heater is provided. A number of different flat sheets can be heated simultaneously and introduced to the first array of pins sequentially.

The cell may further comprise a blanket that is configured to lie on the first array of pins. The provision of a blanket helps to smooth any faceting present in the first array of pins to provide a continuous surface for the flat sheet. In addition, the blanket may be configured to impart a texture to the surface of the flat sheet.

The cell may further comprise a chiller unit that is configured to cool the curved sheet in situ on the first array of pins. Because the deformation of the flat sheet to create the curved sheet takes place when the sheet has been rendered more malleable by the application of heat, the sheet has to be cooled before it is removed from the first array of pins to ensure that it retains its shape. Whilst the sheet could be allowed to cool under ambient conditions, this may occupy the first array of pins for an unacceptable length of time.

The cell may further comprise a third array of pins and a trimming tool. The third array of pins has a reduced density relative to the density of the first array of pins.

Each of the pins within the third array may also be configured to be reduced to the datum height to allow the trimming tool to trim the curved sheet without impediment.

The trimming tool may be a laser. Alternatively, the trimming tool may be a water jet, an electron beam or a mechanical milling machine. The selection of appropriate trimming tool will be dictated by the choice of material of the sheet and the thickness of the material.

The third array of pins may be provided with suction pads in order to secure the curved sheet whilst the trimming tool is active.

Each of the pins in the first, second and third arrays may comprise a stem and a head and wherein the head can tilt relative to the stem. The head may be mounted on the stem using a ball and socket joint. The ball and socket joint allows the pin head to tilt passively as it comes into contact with either the blanket or the sheet.

This tilting brings the overall surface of the first array of pins closer to a continuous surface and reduces the risk of witness marks from the edges of the pin heads.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a cross-section through a first array of pins that forms part of a manufacturing cell of the present invention; Figure 2 shows a cross-section through a second array of pins that forms part of the manufacturing cell according to the present invention; Figure 3 shows a plan view of part of a first array of pins shown in Figure 1; Figure 4 shows a perspective view of an example of a manufacturing cell according to the present invention; Figure 5 is a flow diagram showing steps in the method of operating the manufacturing cell shown in Figure 4.

Figure 1 shows a cross section through a first array 100 of pins. Although only a small number of pins 102 is shown in Figure 1, it will be understood that the array comprises considerably more pins than can be illustrated. The array 100 extends in two dimensions and may comprise in the region of 2000 pins.

Each pin 102 has a head 104 and a stem 106. The stem 106 extends substantially orthogonally from a pin bed 108 that defines a datum. Each stem 106 is provided with an actuator (not shown). The actuator may be a screw thread or a piston which may be electrically or hydraulically operable. Alternatively, the actuator may be a step motor. The actuator is configured to extend the stem 106 above the pin bed 108. Once the stem 106 has been extended, the actuator must lock the pin 102 in the extended position.

The pin head 104 is mounted on the stem 106 using a ball and socket joint. In the example shown in Figure 1, a ball 110 is provided at the end of the stem 106 adjacent the head 104. The head 104 is provided with a socket 112. The socket 112 is at least hemispherical so that the ball 110 cannot become detached from the socket 112. The range of movement of the head 104 is limited by the extent of the socket 112. As the socket 112 tends towards a sphere, the range of movement of the head becomes more limited. In other examples, not illustrated, the ball could be attached to the head and the socket could be attached to the stem.

Figure 2 shows a cross section through a second array 142 of pins. The second array of pins is similar to the first array of pins and those parts which are common to both types of pins are denoted using the same reference numerals. The heads 104 of the pins 102 of the second array 142 are provided with suction pads 143. The suction pads 143 enable the pins of the second array to be attached to the sheet without damaging it.

The heads 104 of the pins in both the first and second arrays are circular and are illustrated in plan view as shown in Figure 3. As a result of the circular shape of the heads 104, they do not tessellate with the adjacent heads 104. The extent of the gaps between the heads is not sufficient for the material of the sheet to deform between the heads. In order to ensure that the gaps between the heads are minimised, each row of heads is offset relative to the adjacent rows in order to provide a triangulated or honeycomb formation as illustrated in Figure 3. The use of a circular head is advantageous in that it ensures that the head 104 can rotate relative to the stem without coming into contact with one or more of the adjacent heads.

In a different example, not illustrated, the heads could be hexagonal, triangular or any other suitable polygonal shape. If the shape tessellates a small gap will be provided around the entire perimeter of each of the heads to ensure that adjacent heads do not come into contact with one another.

In the example illustrated in Figure 1 the upper surface of the pin heads 104 is flat.

This helps to minimise faceting on the curved sheet. However, if a regular pattern needs to be embossed onto the surface, then each pin head 104 can be domed or pointed or provided with any other suitable profile to provide an embossed shape on the curved sheet. The provision of the profile on the pin heads 104 ensure that the embossing occurs orthogonal to the surface of the sheet at every point. It also allows the pattern to be embossed at the same time as the curved sheet is formed so that the embossing does not have to be done as a separate manufacturing step which could compromise the integrity of the material and would certainly make the manufacture process take longer.

In a further example, not illustrated, the heads of one or more of the pins in the first array may be replaced by a die configured to represent detailed shape that is to be embossed onto the curved sheet. The stems of the pins retain their functionality so that the die can be extended or retracted to conform to the profile of the curved sheet. For example the shape may be a logo or trade mark that is positioned in the same position on each of the sheets. Alternatively, the die may enable the provision of a fixing that can be used to attach adjacent sheets together after they have been formed.

The pin heads in the example shown are 50mm in diameter, although in other examples they may be between 40mm and 70mm or even up to 150mm. The size of the pin heads is dictated by the thickness of the material and the quality of finish required in the curved sheet. For example, if the cell is being used with 75mm thick material to fabricate parts that will be used in the interior of a tanker, then the thickness of the material means that faceting will not occur until the pin heads are quite large. Furthermore, because the curved sheets will not be open to close scrutiny then a small amount of faceting might be acceptable. Alternatively, if the cell is being used to 5mm thick material for the exterior of a luxury yacht then small pin heads must be used because faceting is not acceptable and the threshold head size at which faceting will occur is smaller than the threshold when dealing with thicker material.

Figure 4 shows the first array of pins illustrated in detail in Figures 1 and 3, in the context of a manufacturing cell 120. The manufacturing cell 120 has a heating region 130; a pressing region 140 and a trimming station 150. The manufacturing cell 120 is optimised for preparing curved sheets of materials including thermoplastics and composites such as filled acrylics and filled polyesters that might be used in kitchen work surfaces, for example.

In the illustrated example, the heating region 130 includes one heater 132 that is sized to accept the flat sheets that are being processed in the manufacturing cell 120. Depending on the properties of the material that is being used, it can take considerably longer to bring a flat sheet up to the correct temperature than it takes to press the sheet to form a curved sheet. In order to ensure that the efficiency of the manufacturing cell as a whole can be optimised, more than one heater can be provided so that a number of flat sheets can be heated simultaneously. Each heater 132 is configured to heat the flat sheet so that it becomes sufficiently malleable for use in the pressing region 140. The time taken to heat the flat sheet will depend on the thickness of the sheet and the thermal properties of the material from which the sheet is formed. Some materials are capable of responding to large temperature gradients whereas other materials can become brittle if heated or cooled too quickly.

The pressing region 140 includes a first array of pins 100, a second array of pins 142, a diaphragm 144 and a vacuum assembly 146. The blanket 148 is not shown on Figure 4 for the sake of clarity. The first array of pins 100 can be configured to have a profile to match the desired profile of a curved sheet to be formed using the cell. The pins 102 in the first array are closely packed as shown in Figures 1 and 3.

The first array of pins 100 includes in the region of 2000 pins, each of which has a diameter of between 2mm and 500mm, preferably between 40mm and 70mm, more preferably 50mm. The first pin array is therefore 2.5m by 5.Om. Each of the pins is configured to be capable of extending up to 1 m from the pin bed 108. The size of the pin heads and the number of pin heads can be scaled up or down depending on the application.

The pins of the second array of pins 142 are similar to the pins in the first array 100 in that they can be extended from a pin bed using individual actuators and each pin 102 has a head 104 and a stem 106. However, the density of the pins 102 in the second array is considerably lower than the density of the pins in the first array 100.

The second array of pins is used for transporting the sheet between the different parts of the cell 120. The second array of pins can therefore be configured so that all of the stems are of equal length in order to allow a flat sheet to be transported from the heating region 130 into the pressing region 140. The second array of pins can then be reconfigured to have a profile that matches the desired profile of the curved sheet. The second array of pins is then used to remove the curved sheet from the first array of pins and transport it to the trimming station 150.

The first, second and/or third arrays may be divided into a plurality of modules. If all of the arrays are modular, then the cell as a whole can be reconfigured to process sheets of different shapes. For example, if 50 modules that measure 0.5m x 0.5m are provided they may either be configured to press 2.5m x 5.Om flat sheets or 1 m x 12.5m flat sheets. Alternatively, if a job requires a slightly different press area, then additional modules can be added. For example, although in some industries, the standard sheet size is 2.5m x 5.Om, thus requiring 50 0.5m x 0.5m modules, some sheet may be provided as 2.5m x 6.Om. However, rather than requiring an entirely new first array, 10 further modules can be added to the 50 used in the 2.5m x 5.Om configuration. The modular nature of the cell makes it much more adaptable.

A vacuum pump may be provided for each module. The provision of a separate pump for each module, means that each pump can be of a lower specification than a single pump that acts over the entire first array. As a result, considerably more cost effective presses with lower complexity can be used to achieve the same effect.

Each module is provided with an actuator configured to move each of the pins. The provision of a separate actuator for each of the modules speeds up the process of reconfiguring the arrays.

The modular nature of the cell also minimises the down time in the case of a fault being detected. Instead of having to take the entire cell out of service until the fault can be rectified, the single module in which the fault has been identified can be removed and replaced and the cell can then continue to function whilst the faulty module is repaired. Whilst it is not practical to remove an entire cell for repair and therefore repairs will typically have to occur in situ, with a modular system repair work can be carried out remotely with the only work carried out on the site of the cell is the exchange of a faulty module for a fresh module.

The diaphragm 144 and vacuum assembly 146 act together with the first array of pins 100 to deform a flat sheet 200 to create a curved sheet 202. The diaphragm 144 has a frame 145 and a flexible portion 147 that is located within the frame 145.

The diaphragm 144 is sized to cover the first array of pins 100 and to form a seal with the edge of the pin bed 108. The diaphragm 144 is provided so that the cell does not rely on the edges of the flat sheet 200 to form the seal. This enables the cell to be used with flat sheets that are smaller in at least one dimension than the first array of pins. Once a flat sheet 200 has been placed on the first array of pins 100, the diaphragm 144 covers the pins and the frame 145 forms a seal with the edge of the pin bed 108. The flexible portion 147 deforms to fit closely around the pins and the sheet. The vacuum assembly 146 then draws air through the pin array 100 and deforms the flat sheet 200 to form a curved sheet. If the modules of the first array are reconfigured to be a different size and/or shape, then a different diaphragm 144 needs to be provided.

In order to reduce the appearance of faceting on the curved sheet, a blanket 148 is provided on the first array of pins. The blanket 148 prevents the sheet from oozing between the pins and helps to provide a continuous geometry against which the curved sheet may be formed. In addition, if a surface texture is to be imparted to the sheet, this can be achieved by providing the texture on the blanket 148. The blanket 148 is formed from a synthetic cellular material which is gas permeable so that the vacuum assembly can suck air through the blanket 148. In other examples the blanket may be omitted and surface texturing can be provided through the use of shaped pin heads 104.

Depending on the material of the sheet, the length of time that the curved sheet takes to become sufficiently resilient to be moved from the first array of pins may be excessive. In this case a chiller 149 is provided to cool the curved sheet.

The trimming station 150 is provided to trim the curved sheet that is created in the pressing region 140. The trimming station 150 includes a third array 152 of pins and a trimming device 154. The third array of pins 152 is similar to the second array of pins 142 in that it has a similarly low density of pins relative to the first array and the pins are provided with suction pads 153 in order to hold the sheet in position. The entire trimming station 150 may be located in a temperature controlled environment to ensure that the extent to which the curved sheet is cooled before and during the trimming process can be closely controlled.

The trimming device 154 is a laser which travels along a path 156 around the perimeter of the sheet. A fourth array of pins 158 is provided to remove the trimmed curved sheet from the trimming station 150. The pins of the fourth array of pins are substantially the same as the pins of the second array 142. However the provision of a further array means that the second and fourth arrays can act simultaneously and independently to ensure that each region of the cell can operate at optimum capacity.

Furthermore, the provision of a dedicated array of pins that interfaces with the sheet after the trimming process ensures that no debris from the trimming process can be introduced into the pressing region 140.

The cell 120 is capable of producing sheets rapidly. For example, the time taken for an individual sheet to pass through the cell may be about 1 hour, including time for heating the sheet before it is pressed. Of course, each part of the cell may contain a different sheet at any one time so whilst a number of sheets are being heated, one may be pressed and one may be trimmed. The forming of the curved sheet from the flat sheet takes between 10 and 30 minutes, preferably 20 minutes.

Figure 5 shows a flow diagram of the steps in the method of operating the manufacturing cell described above with reference to Figure 4.

The method 300 operates in an operative free environment. This means that, when the cell is running well, there is no need for human intervention. This differs considerably from current techniques of skilled craftsmen making bespoke moulds. It also differs considerably from the semi-automated lines used by the automotive industry where a large number of operatives each complete one or more manual tasks on each vehicle that is produced. The method described herein with reference to figure 4 deskills the making of the moulds and increases the repeatability and accuracy over and above what can be expected of operatives of a production line.

The method 300 includes a data analysis phase 310; an instructing phase 320; a forming phase 330 and a quality control phase 340. The entirety of the data analysis phase 310; and at least part of the instructing phase and the quality control phase 340 may be carried out at a location that is remote from the manufacturing cell 120.

The data analysis phase 310 involves taking data relating to the overall shape of the object to be formed directly from the electronic design tool that has been used by the architect, for example CAD systems such as Microstation, Maya, 3DStudio, Catia, SolidWorks, SolidEdge, Inventor, ProEngineer, Rhyno or similar package. This object to be formed may be a building, a boat hull, a yacht or any other large and complex structure.

The data is subjected to a cut and slice analysis 312. In this step of the analysis, the data is analysed with reference to rules relating to the properties of the materials from which the object is to be made. This includes, for example, rules about the maximum extent of curvature that the material can tolerate. In addition, rules about acceptable tiling configurations are included. For example, angles close to but not exactly vertical or horizontal may be classed as aesthetically displeasing and therefore the analysis may favour tiling that is either aligned with the horizontal and vertical plane or is at a considerable angle to the horizontal. The result of the cut and slice analysis 312 is a series of virtual sheets superimposed on the object data in the position in which they will be positioned as part of the completed object.

The data is then subjected to a tiling analysis 314 in which each virtual sheet is extended to have an overlap with the adjacent sheets. This overlap effectively acts as a selvedge and can be trimmed. In this region the data is extrapolated to draw down the edges of the sheet back to the datum so that the curved sheet does not have edges that exceed the material properties and may be subject to excessive stresses during cooling.

In order to adapt the data output of the tiling analysis 314 so that it can be transmitted to the manufacturing cell, the data relating to each virtual sheet must be rotated and translated so that the virtual sheet oriented in a known position in space that can be refined as a datum. Each virtual sheet then lies as near to the horizontal as possible. This minimises the vertical excursion of the pins in the first array.

The data is then subjected to properties analysis 316. This calculates how the properties of the material will cause the shape of the curved sheet to deviate from the shape of the first pin array. In other words, the data is analysed to take spring back into account. The shape of the first pin array can then be altered to that, once the material has deformed as expected, the desired shape will be achieved.

In the instructing phase 320, the position of the pins in the second, third and fourth pin arrays is taken from the output of the tiling analysis 314 as this is representative of the desired shape of the curved sheet. The position of the pins in the first pin array is taken from the output of the properties analysis 316.

The quality assurance phase 340 proceeds throughout the pressing phase 330. The quality assurance phase 340 includes a first check 342 and a second check 344.

The first check involves a simple clash detection check which identifies any pins that have malfunctioned and are positioned outside an acceptable envelope followed by a detailed comparison between the data output from the tiling analysis and the actual position of the pins of the first array 100. The actual position of each of the pins can be ascertained by an optical sensor such as a camera or a laser.

Providing the output of the first check 342 is satisfactory, the pressing phase 330 will proceed. The flat sheet 200 will be heated in the heating region 130, moved by the second pin array into the pressing region 140, pressed to form a curved sheet 202.

The second array of pins will be reconfigured to match the profile of the curved sheet and then deployed to move the curved sheet to the trimming station 150.

Once the curved sheet is at the trimming station 150 it rests on the third array of pins 152. Because the third array of pins 152 is configured to match the shape of the curved sheet, there should be only one correct position for the curved sheet.

However, in order to ensure that the curved sheet 202 is correctly positioned prior to the deployment of the trimming device, the quality assurance phase includes a remote optical inspection 346 of the curved sheet. Providing that the remote optical inspection 346 confirms that the curved sheet is correctly positioned, the second array of pins is moved away and the trimming device is activated. Once the trimming process is complete, a further quality assurance operation 348 takes place to confirm that the profile of the curved sheet is correct, that the trimming has been correctly executed and also to check for the presence of any additional features added during the trimming process, for example grooves, pockets, holes or identification marks.

Claims

CLAIMS1. A method of forming a curved sheet from a plastics or composite material, the method comprising the steps of: configuring a first pin array to have a profile aligned with the curved sheet to be formed; configuring a second pin array to transport a flat sheet into contact with the first pin array; forming a curved sheet from the flat sheet by covering the flat sheet with a diaphragm that is configured to form a seal around the first pin array and evacuating the first pin array; wherein the curved sheet has the profile of the first pin array; reconfiguring the second pin array to have a profile aligned with the curved sheet, and using the second pin array to move the curved sheet out of contact with the first pin array.
2. The method according to claim 1, wherein the configuration of the first and second pin arrays is controlled automatically based on digital data representing the curved shape to be formed.
3. The method according to claim 1 or claim 2, further comprise the steps of: configuring a third pin array to have a profile aligned with the curved sheet; using the second pin array to transport the curved sheet into contact with the third pin array and trimming the curved sheet.
4. The method according to claim 3, wherein the trimming of the curved sheet comprises a trimming tool following a path that defines the desired profile of the curved sheet.
5. The method according to claim 4, further comprising checking for conflicts between a path of the trimming tool and the position of the pins in the third pin array and, if a conflict is detected, retracting the pin or pins that are subject of the conflict.
6. A manufacturing cell for fabricating curved plastics sheets, the cell comprising: a first array of pins that can be configured to have a profile aligned with the curved sheet to be formed; a second array of pins that can be configured firstly to interface with a flat sheet and secondly to have a profile aligned with the curved sheet and a diaphragm and a vacuum assembly.
7. The cell according to claim 6, wherein the second array of pins has a lower density that the first array of pins.
8. The cell according to claim 6 or claim 7, wherein the pins of the second array are provided with suction pads for holding the sheet.
9. The cell according to any one of claims 6 to 8, further comprising a heater for heating the flat sheet.
10. The cell according to claim 9, further comprising at least one further heater.
11. The cell according to any one of claims 6 to 11, further comprising a blanket that is configured to lie on the first array of pins.
12. The cell according to any one of claims 6 to 11, further comprising a chiller unit that is configured to cool the curved sheet in situ on the first array of pins.
13. The cell according to any one of claims 6 to 12, further comprising a third array of pins and a trimming tool.
14. The cell according to any one of claims 6 to 13, wherein each of the pins in the first, second and third arrays comprises a stem and a head and wherein the head can tilt relative to the stem.