Apparatus and methods for forming composite parts

Abstract

An apparatus for fabricating a composite part, comprising a forming tool 100, a tooling caul 104 which has regions made from different material where the coefficient of thermal expansion (CTE) is grea

Description

Technical Field Apparatus and methods for forming composite shaped parts. In particular, the present disclosure relates to apparatus and methods utilising an improved tooling caul for manufacturing composite parts with tight and / or low tolerances. Background of the Invention In the manufacture of composite parts, such as C-channel shaped parts in the aerospace and other related industries, using tooling cauls with tight and / or low tolerances are a specific requirement. For example, tight and / or low tolerances are required on both a tool inner mold line (IML) and a caul outer mold line (OML) when manufacturing C-channel composite parts. It is found that when curing a composite C-channel shaped part that has a large length to width ratio requiring tight geometric control of features, conflicting requirements arise. For example, debulking of the flange plies makes a tooling caul composite with a coefficient of thermal expansion (CTE) higher than the composite part material desirable. The same need for the debulking of the flanges makes a semi-rigid caul desirable whereas the need for accurate location of geometry drives the need for a rigid caul. To obtain tight and / or low tolerances current methods adopt two basic approaches. The first is to address the control of geometry using rigid cauls which have the disadvantage of increasing the risk of poor consolidation and having poor laminate quality. A second approach to obtain tight tolerances is to use semi-rigid cauls which provide good laminate quality but have unacceptable geometric control. Therefore, both known methods to use tooling cauls where tight and / or low tolerances are required have specific disadvantages. There is therefore a need in manufacturing processes where tight and / or low tolerances are required for an improved tooling caul for the manufacture of composite parts in the aerospace and other related industries. A similar need also relates to manufacturing processes where tight and / or low tolerances are also required in the manufacture of frames, spars and any other similarly shaped products manufactured from composite material. It is an object of at least one aspect of the present invention to provide an improved tooling caul. Summary of the Invention According to a first aspect there is provided apparatus for fabricating a composite part comprising: a forming tool; a tooling caul which has regions made from different material where the coefficient of thermal expansion (CTE) is greater in a lower section; and wherein a cured composite part is capable of being fabricated in a gap between the forming tool and the tooling caul. Generally, there is herein described a tooling caul and apparatus for manufacturing cured composite parts with tight and / or low tolerances. The cured composite parts have improved quality of feature location along a manufactured length. Typically, the tooling caul and apparatus may achieve tolerances of the order of: about 0.1 mm to about 1.0 mm; about 0.1 mm to about 0.75 mm; about 0.25 mm to about 0.75 mm; about 1 mm; lower than about 0.5 mm; lower than about 0.25 mm or lower than about 0.1 mm. The cured composite parts may be used in aerospace construction such as for wing or fuselage parts. Typically, the coefficient of thermal expansion (CTE) of the tooling caul may be tailored to provide an improved tooling caul for manufacturing composite parts with tight and / or low tolerances. The tooling caul may comprise a main lower section and first and second upstanding leg portions. The first and second upstanding leg portions may be described as flanges. The tooling caul may have a substantially C-shaped cross-section. The tooling caul may be in the form of an extended longitudinal structure. The tooling caul may be defined as being rigid. The tooling caul may comprise a first material in a lower region of the tooling caul and a second material in the first and second upstanding leg portions. The material used in the lower region of the tooling caul may therefore be different to the material in the first and second upstanding leg portions of the tooling caul. The first material in the lower region of the tooling caul may have a higher coefficient of thermal expansion (CTE) than the second material forming the first and second upstanding leg portions. The tooling caul may also comprise non-isotropic material which has a different coefficient of thermal expansion (CTE) in different directions such as between the width and length. This provides the compaction needed on the upstanding leg portions (e.g. flanges) of the formed composite part while retaining the feature location of the composite part being formed along the length. The forming tool may have a substantially C-shaped cross-section. The forming tool may be in the form of an extended longitudinal structure. The tooling caul may fit within the forming tool. A gap may be formed between the forming tool and the tooling caul. The gap may comprise a substantially C-shaped cross-section which has an extended longitudinal structure. The composite part may be formed in the gap. The gap may be defined as the area between the tool inner-mold line (IML) width and the caul outer mould line (OML) width. Suitable sizes for the forming tool and tooling caul are typically less than about 6 or 12 inches across the flanges but have ranges up to about 30 or 60 inches across. A cured composite part may therefore be manufactured and fabricated between the forming tool and the tooling caul. During manufacture, the composite material used to form the composite part may be placed onto the forming tool. The composite material may then be heated with the resultant cured composite part being formed. The shape of the formed composite part may be determined by the shape of the gap formed between the forming tool and the tooling caul. The formed composite part may comprise a main lower section and a first and second upstanding leg portion (e.g. flanges). The formed composite part may have a substantially C- shaped cross-section. The formed composite part may be in the form of an extended longitudinal structure. The composite part may be formed between the tool inner-mold line (IML) width and the caul outer mould line (OML) width. The tooling caul may comprise a main lower section and a first and second upstanding leg portion which extends over and covers the composite part being formed. The main lower section may be in the form of a web. The formed composite part may be formed from a range of materials including any one one of or combination of the following: Fiberglass; thermoplastics; Carbon / Epoxy; Carbon / BMI such as unidirectional Carbon / BMI (i.e. thermosetting bismaleimide resins); and Fiberglass / Epoxy. The formed composite part may be manufactured in a range of shapes and sizes including: straight; curved or following a contour as required. The tooling caul may therefore comprise a first material in the main lower section and a second material in the first and second upstanding leg portions. For the manufacture of composite parts with tight tolerances (i.e. low tolerances) this has been found to provide improved manufacturing of composite parts with tight tolerances. The first material in the main lower section of the tooling caul may have a higher coefficient of thermal expansion (CTE) material than the second material in the first and second upstanding leg portions (e.g. flanges). The higher coefficient of thermal expansion (CTE) material in the main lower section of the tooling caul may be deposited in a thick layer forming, for example, the full depth of the tooling caul in the central region and may then taperout in reducing depth towards the first and second upstanding leg portions. The amount of the higher coefficient of thermal expansion (CTE) material may therefore be at a maximum in the centre of the main lower section of the tooling caul and at a minimum at the intersection to the first and second upstanding leg portions. Extending away from a central portion of the main lower section there may therefore be a gradual reduction in the amount and depth of the first material with higher thermal expansion (CTE). At the intersection to the first and second upstanding leg portions there may be either very little or none of the first material with higher thermal expansion (CTE). Suitable examples of the higher coefficient of thermal expansion (CTE) material may be selected from fibreglass or any other type of fibreglass based material. Correct material selection may lead to a CTE that is: about 10% to about 100% greater than the material in the flange areas; about 25% to about 100% greater than the material in the flange areas; or about 50% to about 100% greater than the material in the flange areas. The first and second upstanding leg portions of the tooling caul may also comprise non-isotropic material. The first and second upstanding leg portions may therefore comprise any one of or combination of non-isotropic materials: Carbon / BMI (i.e. thermosetting bismaleimide resins) such as unidirectional Carbon / BMI; fibreglass; thermoplastic; sheet molding compound; and Carbon / Epoxy such as unidirectional Carbon / Epoxy. The tooling caul may therefore be manufactured from non-isotropic material with differing coefficient of thermal expansion (CTE) between the width and length. This has been found to provide the compaction needed on the first and second upstanding leg portions (e.g. flanges) of the formed composite part while retaining the feature location of the formed composite part along the length. An alternative approach may be to tailor the layup of the tooling caul along the main lower section to have a higher coefficient of thermal expansion (CTE) than in the first and second upstanding leg portions which extends over and covers the composite part being formed. This is achievable due to the difference in CTE between the 0 degrees orientation and the 90 degrees orientation. According to a second aspect there is a tooling caul which has regions made from different material where the coefficient of thermal expansion (CTE) is greater in a main lower section. The tooling caul may be as defined in the first aspect. Material selection may lead to a CTE that is: about 10% to about 100% greater than the material in flange areas; about 25% to about 100% greater than the material in flange areas; or about 50% to about 100% greater than the material in flange areas. According to a third aspect there is a method of fabricating a composite part comprising: providing a forming tool; providing a tooling caul which has regions made from different material where the coefficient of thermal expansion (CTE) is greater in a main lower section; and wherein a cured composite part is fabricated in a gap between the forming tool and the tooling caul. The tooling caul may be as defined in the first and second aspects. Description of the Figures Embodiments of the disclosure will now be described, by way of example only, with reference to the following Figures in which: Figure 1 is a sectional illustration of a tooling caul according to the prior art; Figure 2 is a sectional illustration of a tooling caul according to an embodiment; and Figure 3 is a schematic representation of a manufacturing process for a composite part according to an embodiment. Detailed Description There is herein described a tooling caul and apparatus for manufacturing composite parts with tight and / or low tolerances with improved quality of feature location of composite parts formed along a length. In particular, there is described the tailoring of the coefficient of thermal expansion (CTE) of a tooling caul either through the utilisation of different material in a lower region of the tooling caul (e.g. in a web) than what is used in the flanges or through the use of a non-isotropic material with differing coefficient of thermal expansion (CTE) in different directions such as between the width and length. The tailoring provides the compaction needed on upstanding leg portions on the tooling caul (e.g. the flanges) while retaining the feature location of the composite part being formed along the length. Figure 1 is a sectional side view of a forming tool according to the prior art generally designated 100. The forming tool 100 is used to manufacture a composite part 102 for use in the aerospace and other related industries. Figure 1 also shows a tooling caul 104 which is used in the manufacture of the composite part 102. The composite part 102 is therefore formed in a gap between the forming tool 100 and the tooling caul 104. As shown in Figure 1, the forming tool 100 is substantially C-shaped and comprises a main lower section 106 and a first and second upstanding leg portion 108,110, respectively. The first and second upstanding leg portion 108, 110 may be described as flanges. The forming tool 100 may have a long length and a shorter width. The forming tool 100 therefore forms an extended longitudinal structure with a C-shaped cross-section. Located within the forming tool 100 and the tooling caul 104, the composite part 102 may be manufactured and fabricated. During manufacture, the composite material used to form the composite part 102 is therefore initially placed onto the forming tool 100. The composite material may then be heated with the resultant composite part 102 being formed using known methods. The shape of the formed composite part 102 is determined by the shape of a gap 103 formed between the forming tool 100 and the tooling caul 104. The formed composite part 102 comprises a main lower section 112 and a first and second upstanding leg portion 114,116, respectively. Located on top of the composite part 102 being formed is the tooling caul 104. The tooling caul 104 has the same basic C-shaped structure as the forming tool 100 albeit with a slightly smaller width. The tooling caul 104 therefore sits and resides within the forming tool 100. Similar to the forming tool 100, the tooling caul 104 comprises a main lower section 118 and a first and second upstanding leg portion 124, 126 which extends over and covers the composite part 102 being formed. The leg portions 124, 126 may be described as flanges. Figure 1 shows that the forming tool 100 has a tool inner-mold line (IML) width 130 within which the composite part 102 is formed. Figure 1 also shows that the tooling caul 104 has a caul outer mould line (OML) width 140. The composite part 102 is formed between the tool inner-mold line (IML) width 130 and the caul outer mould line (OML) width 140. The formed composite part 102 is in the form of an extended longitudinal structure with a substantially C-shaped cross-section. It is found that when the forming tool 100, the composite part 102 and the tooling caul 104 all have approximately the same coefficient of thermal expansion (CTE), the gap 103 between the tool inner-mold line (IML) width 130 and the caul outer mould line (OML) width 140 at curing temperature only accounts for the thermal growth of the composite part 102. Therefore, the gap 103 between the tool inner-mold line (IML) width 130 and the caul outer mould line (OML) width 140 does not account for any bulk (e.g. additional thickness due to incomplete consolidation of the plies) left during the manufacturing process. For example, during the manufacture of composite parts for wing structures bulk (e.g. incomplete consolidation) may be left in plies forming part of a wing structure or deviation below nominal in a ply thickness. This is a specific disadvantage to manufacturing methods known in the prior art. Figure 2 is a sectional illustration of a tooling caul generally designated 204 according to an embodiment. Similar to the apparatus shown in Figure 1, there is shown a forming tool 200 which is substantially C-shaped and comprises a main lower section 206 and a first and second upstanding leg portion 208, 210, respectively (e.g. flanges). The forming tool 200 is of a rigid construction and forms an extended longitudinal structure with a C-shaped crosssection. Suitable sizes for the forming tool 200 may be as small as about 4 inches and may extend up to being about 60 inches. However, it should be noted that the forming tool 200 should not be interpreted as being limited to any particular size or shape. A composite part 202 is therefore manufactured in a gap 203 between the forming tool 200 and the tooling caul 204. During manufacture, the composite material used to form the composite part 202 is initially placed onto the forming tool 200. They composite material may then be heated with the resultant composite part 202 being formed. The shape of the formed composite part 202 is determined by the shape of the forming tool 200 and the tooling caul 204. The formed composite part 202 is in the form of an extended longitudinal structure with a C-shaped crosssection. The formed composite part 202 comprises a main lower section 212 and a first and second upstanding leg portion 214, 216, respectively (e.g. flanges). Located on top of the composite part 202 being formed is the tooling caul 204. Similar to as described before, the tooling caul 204 comprises a main lower section 218 and a first and second upstanding leg portion 224, 226 which extends over and covers the composite part 202 being formed. The main lower section 218 may be in the form of a web. Figure 2 also shows that the forming tool 200 has a tool inner-mold line (IML) width 230 within which the composite part 202 is formed. Figure 2 also shows that the tooling caul 204 has a caul outer mould line (OML) width 240. The composite part 202 is formed in a gap 203 and fits between the tool inner-mold line (IML) width 230 and the caul outer mould line (OML) width 240. The tooling caul 204 therefore fits within the forming tool 200 which results in the form and structure of the composite part 202 formed. This includes thickness and shape of composite part 202 formed. The formed composite part 202 may be manufactured in a range of shapes and sizes including any that require consolidation in directions that are restricted by features on the primary tool. The tooling caul 204 is specifically tailored for manufacturing composite parts with tight and / or low tolerances. The tooling caul 204 provides improvements for manufacturing composite parts with tight and / or tolerances such as of the order of: about 0.1 mm to about 1.0 mm; about 0.1 mm to about 0.75 mm; about 0.25 mm to about 0.75 mm; lower than about 1 mm; lower than about 0.5 mm; lower than about 0.25 mm or lower than about 0.1 mm. In particular, the tooling caul 204 has a tailored coefficient of thermal expansion (CTE). This is achieved through the utilisation of a first material in the main lower section 218 and a second material in the first and second upstanding leg portions 224, 226 of the tooling caul 204. For the manufacture of composite parts with tight tolerances (i.e. low tolerances) this has been found to provide improved manufacturing of composite parts with tight tolerances. The first material in the main lower section 218 has a higher coefficient of thermal expansion (CTE) than the second material in the first and second upstanding leg portions 224, 226. As shown in Figure 2, the tooling caul 204 has higher coefficient of thermal expansion (CTE) material 250 located in the main lower section 218 of the tooling caul 204. The main lower section 218 may be described as a web section. The second material in the first and second upstanding leg portions 224, 226 therefore has material with a lower coefficient of thermal expansion (CTE) than the first material in the main lower section 218. The higher coefficient of thermal expansion (CTE) material 250 is deposited in a thick layer forming, for example, the full depth of the tooling caul 204 in the central region and tapers out in reducing depth towards the first and second upstanding leg portions 224, 226 of the tooling caul 204. The amount of the higher coefficient of thermal expansion (CTE) material 250 is therefore at a maximum in the centre of the main lower section 218 and at a minimum at the intersection to the first and second upstanding leg portions 224, 226. Extending away from a central portion of the main lower section 218 there is a gradual reduction in the amount and depth of the thermal expansion (CTE) material 250. At the intersection to the first and second upstanding leg portions 224, 226 there is either very little or no higher coefficient of thermal expansion (CTE) material 250. Suitable examples of the higher coefficient of thermal expansion (CTE) material 250 are selected from any one of or combination of the following: fibreglass; any of several random mat materials with a compatible resin; or other material meeting the requirements. This material would have a CTE in the order of about 10% to about 100% greater, about 25% to about 100% greater or about 50% to about 100% greater than the material in the upturned flange areas. Furthermore, as shown in Figure 2, in the first and second upstanding leg portions 224, 226 of the tooling caul 204 there is a coefficient of thermal expansion (CTE) material 260 which is matched or substantially matched with the coefficient of thermal expansion of the forming tool 200 and the composite part 202. Suitable values for the coefficient of thermal expansion (CTE) material 260 in the first and second upstanding leg portions 224, 226 will be dependent on the base material and layup of the part being fabricated. The first and second upstanding leg portions 224, 226 can be made from any of several tooling materials that are acceptable for composite fabrication. The embodiment shown in Figure 2 also provides a tooling caul 204 which is made from non-isotropic material with differing coefficient of thermal expansion (CTE) between the width and length. This has been found to provide the compaction needed on the upstanding leg portions 214, 216 (e.g. flanges) of the composite part 202 while retaining the feature location of the form composite part 202 along the length of the forming tool 200 and tooling caul 204. An alternative approach is to tailor the layup of the tooling caul 204 along the main lower section 218 to have a higher coefficient of thermal expansion (CTE) in the width direction. This is achieved by placing a majority of the fibers along the length, than in the first and second upstanding leg portions 224, 226 which extends over and covers the composite part 202 being formed. Figure 3 is a schematic representation of a manufacturing process generally designated 300 according to an embodiment. The manufacturing process 300 relates to providing a tool 310 and also providing composite preform (or any other suitable material) 330 and then in a process step 340 applying the composite to the tool. A caul plate 320 is also provided in a process step 350 of applying the caul plate to the composite. There is then a heating step 360 with the formed composite part then removed in process step 370. It will be clear to those of skill in the art that the above-described embodiments are merely exemplary, and that various modifications and improvements thereto may be made without departing from the embodiments described. For example, the tooling caul may be a range of shapes and sizes. The tooling caul may also be made a range of suitable materials. 31 10 23

Claims

1. Apparatus for fabricating a composite part comprising: a forming tool;5 a tooling caul which has regions made from different material where thecoefficient of thermal expansion (CTE) is greater in a main lower section; andwherein a cured composite part is capable of being fabricated in a gap between the forming tool and the tooling caul.10 2. Apparatus according to claim 1, wherein the apparatus is capable of fabricating curedcomposite parts with tight and / or low tolerances of the order of: 0.1 mm to 1.0 mm; 0.1 mm to 0.75 mm; 0.25 mm to 0.75 mm; 1 mm; lower than 0.5 mm; lower than 0.25 mm or lower than 0.1 mm.15 3. Apparatus according to any preceding claim, wherein the tooling caul comprises a mainlower section and first and second upstanding leg portions.

4. Apparatus according to any preceding claim, wherein the tooling caul has a substantially C-shaped cross-section and an extended longitudinal structure.

205. Apparatus according to any of claims 3 to 4, wherein the tooling caul comprises a first material in a lower region and a second material in the first and second upstanding leg portions and wherein the first material in the lower region of the tooling caul has a higher coefficient of thermal expansion (CTE) than the second material forming the first and25 second upstanding leg portions.

6. Apparatus according to any preceding claim, wherein the tooling caul comprises non-isotropic material which has a different coefficient of thermal expansion (CTE) in different directions.

307. Apparatus according to any preceding claim, wherein the forming tool has a substantiallyC-shaped cross-section in an extended longitudinal structure.

8. Apparatus according to any preceding claim, wherein the tooling caul fits within the 35 forming tool.31 10 239. Apparatus according to any preceding claim, wherein the gap formed between the forming tool and the tooling caul has a substantially C-shaped cross-section which has an extended longitudinal structure.5 10. Apparatus according to any preceding claim, wherein the gap formed between theforming tool and the tooling caul is defined as the area between a tool inner-mold line (IML) width and a caul outer mould line (OML) width.

11. Apparatus according to any preceding claim, wherein composite material used to form 10 the composite part is placed onto the forming tool and heated with the resultant cured composite part being formed.

12. Apparatus according to any preceding claim, wherein the formed composite part comprises a main lower section and a first and second upstanding leg portion.1513. Apparatus according to any preceding claim, wherein the formed composite part has a substantially C-shaped cross-section and an extended longitudinal structure.

14. Apparatus according to any of claims 10 to 13, wherein the composite part is formed 20 between the tool inner-mold line (IML) width and the caul outer mould line (OML) width.

15. Apparatus according to any preceding claim, wherein the tooling caul comprises a main lower section and first and second upstanding leg portions which extend over and covers the composite part being formed.2516. Apparatus according to any preceding claim, wherein the tooling caul comprises a first material in the main lower section and a second material in first and second upstanding leg portions.30 17. Apparatus according to claim 16, wherein the first material in the main lower section ofthe tooling caul has a higher coefficient of thermal expansion (CTE) material than the second material in the first and second upstanding leg portions.

18. Apparatus according to claim 17, wherein the higher coefficient of thermal expansion35 (CTE) material in the main lower section of the tooling caul is deposited in a thick layer forming the full or substantially the full depth of the tooling caul in substantially the centralregion and then tapers out in reducing depth towards the first and second upstanding leg portions.

19. Apparatus according to any of claims 16 to 18, wherein the amount of the higher 5 coefficient of thermal expansion (CTE) material is at a maximum in substantially the centre of the main lower section of the tooling caul and at a minimum at an intersection to the first and second upstanding leg portions.

20. Apparatus according to any of claims 16 to 19, wherein extending away from a central 10 portion of the main lower section there is a gradual reduction in the amount and depth of the first material with higher thermal expansion (CTE).

21. Apparatus according to any of claims 16 to 20, wherein at an intersection to the first and second upstanding leg portions there is either very little or none of the first material with15 higher thermal expansion (CTE).CO 22. Apparatus according to any preceding claim, wherein the material with the higher CM coefficient of thermal expansion (CTE) is selected from any one of or combination of theC*^) following: fibreglass; thermoplastic; sheet molding compound; unidirectional20 Carbon / Epoxy; and unidirectional Carbon / BMI (i.e. thermosetting bismaleimide resins);T— and Fiberglass / Epoxy.CO23. Apparatus according to any of claims 15 to 22, wherein the first and second upstanding leg portions of the tooling caul comprise non-isotropic materials selected from any one 25 of or combination the following: fibreglass; thermoplastic; sheet molding compound; unidirectional Carbon / Epoxy; and unidirectional Carbon / BMI.

24. Apparatus according to claim 23, wherein the non-isotropic material has differing coefficient of thermal expansion (CTE) between the width and length.

25. Apparatus according to any preceding claim, wherein a layup of the tooling caul along the main lower section has a higher coefficient of thermal expansion (CTE) than in first and second upstanding leg portions of the tooling caul which extends over and covers the composite part being formed.

26. A tooling caul which has regions made from different material where the coefficient of thermal expansion (CTE) is greater in the main lower section.

27. A tooling caul according to claim 26 which has regions made from different material where the coefficient of thermal expansion (CTE) is greater in the main lower section, wherein the different material in the main lower section has a CTE in the order of about 10% to about 100% greater, about 25% to about 100% greater or about 50% to about 5 100% greater than the material in upturned flange areas.

28. A method of fabricating a composite part comprising:providing a forming tool;providing a tooling caul which has regions made from different material where 10 the coefficient of thermal expansion (CTE) is greater in a main lower section; andwherein a cured composite part is fabricated in a gap between the forming tool and the tooling caul.1531 10 23203035

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