1. Title of the invention
The invention relates to a detailed process to design and fabricate a more rigid and high stiffened light weight metallic co-curing layup mould to manufacture high strength composite bottom floor of an advanced light weight fixed wing aircraft.
2. Field of invention
The invention is a novel and unique method of fabricating a layup tool for co-curing composite bottom floor component of an advanced aircraft, more precisely this invention concerns the domain of fabricating light weight composite aircraft structures which is more versatile, robust, leak proof, dimensionally stable, and easy to de-mould the component.
3. Use of invention
This invention relates to an improvement in existing process of manufacturing co-cured tools intended to hand layup and to cure the bottom floor composite part in autoclave. These moulds are used in particularly for manufacturing high quality composite parts for advanced fixed wing fighter aircrafts.
4. Prior art
Patent EP3078471A1 deals with co-curing process for the joining of composite structures.
Patent US9669587 B2 deals with staged co-curing of composite structures at least a portion of an uncured first composite component.
Patent US7503368B2 deals with a method of manufacturing composite sections for aircraft fuselages and other structure.
Patent US20100124659A1 deals with the staged coTcuring of composite structures.
Patent US4167430 relates to a method of fabricating a bonded structure without vacuum bagging and autoclave curing.
5. Draw backs of prior art
The patent EP3078471A1 deals with co-curing process for joining of composite structures and is not related to the present method of fabricating the bottom floor of fixed wing aircraft.
The patent US9669587 B2 deals with staged co-curing of composite structures at least a
portion of an uncured first composite component and present method is related to first
base is cured and uncured stiffeners are bonded to base. r^ s __/-*

The Patent US7503368B2 deals with a method of manufacturing composite sections for aircraft fuselages and other structure and present method is of fabricating the bottom floor structure by using regular layup method not by filament winding.
The Patent US20100124659A1 deals with the staged Co-curing of composite structures using composite components that are cured in stages and the present method is not related to usage of cured structures.
The Patent US4167430 relates to a method of fabricating a bonded structure without vacuum bagging and autoclave curing. It is not related to present method of fabricating the bottom floor of fixed wing aircraft.
7. Aim of the invention
The aim of the invention is to design, develop a layup tool for fabrication of Co-Curing component of fixed wing fighter aircraft to achieve contour tolerances, design requirements without delamination/ compaction problems and easy to demould the part so as to meet the user requirements.

8. Summary of the present invention
The present invention is directed specifically to design and fabricate layup tool to fabricate high stiffened co-curing composite bottom floor for advanced light fighter aircraft. The major stages of this invention are:
a) Preliminary design for fabrication of tools and analyze the feasibility study.
b) After preliminary design review, the critical design review was carried and the layup tool is developed for base and stiffeners by considering all the component design requirements, compaction, delamination and demoulding issues.
c) Fabrication of layup tools and thermal survey was carried to study and understand thermal behavior of tool.
d) Application of release-all over the tool and hand layup with UB prepreg for base tool and the base tool is cued under autoclave.
e) Layup over stiffener tools and positioning the stiffeners over the cured base tool as per the design requirements.
f) Final bagging and curing in autoclave.
g) Preparation of FTT blocks and samples for FTT test,
h) Ultrasonic testing of the cured part.
i) Remove the burrs at the corner
j) Final inspection and applying epoxy primer.
9. Brief description of drawings
Fig. 1 shows the schematic diagram for Bottom Shell assembly. Fig.2 shows the arrangement of stiffeners with base. Fig.3 shows base tool with bagging facility
Fig.4. shows the stiffener tools design and assembly with base tools to meet the contour of the component.
Fig.5 shows individual stiffener tools assembly with local drafts for better compaction.
Fig.6 shows the attachment of individual stiffener tools with shear bolt assembly
Fig.7 shows the demoulding facility provided on each rib tool to avoid post curing damages
Fig.8 shows the Provision of slotted bush on base plate to avoid expansion problems in curing stage.
Fig.9 shows the position of thermocouples on tool to analyze curing conditions in Autoclave.

10. Statement of invention
This invention specifically focuses on a unique manufacturing process of composite bottom floor to obtain zero leakage, operator friendly, no repair/rework, dimensionally accurate & stable, cost effective and efficient production tool.
11. Detailed description of invention
Composite bottom floor is manufactured using following raw materials:
i) Copper mesh (hexply 914-cu-mesh-40%).
ii) Glass prepreg (hatched area) hexply 914g-120-45%.
iii) Carbon UD prepreg (hexply / 914/34%/udl60/as4/12k/300mm).
iv) Adhesive layer
Basically bottom floor component manufacturing process carried out in two stages as per component drawing Fig.l. Base tool is to be designed to do layup for base as shown in Fig.2. To design base layup tool, provision of location for stiffener tools, demoulding facility for ribs after curing, excess layup provision and reference lines for easy layup are considered. Sufficient bagging space provided on base tool, utmost care taken for avoiding through holes for getting vacuum integrity. Space provided on layup tool for test coupon facility for NDT. Sufficient thickness for base tool is applied to avoid sagging/bending/deflection in dimensions Fig.3.
Bonding surface between top layer of base and first layer of stiffener gives the actual result in Co-curing process. To achieve good surface for top layer of base plate pressure plate / caul plate is developed. This will give better surface finish and zero undulations.
Stiffener tools are designed to make half of the rib layup in each side as shown in Fig.5. This will avoid usage shims for maintaining the rib thickness in final curing. Component stiffener thickness is 2.4mm, to achieve this each stiffener layup tools is made with a slot of thickness 1.15mm (by decreasing 0.05mm on each face). This will give more compaction between stiffeners in autoclave stage and debonding will be completely eliminated. Stiffener tools are assembled with proper shear bolt assembly and all stiffener tools are fixed to base tool with proper location pins. Marking are provided on each stiffener tool for better layup. Better stiffness provided in tools to avoid shrinkage/ loosing contour properties.
All stiffener tools are one side located with fixed pin and other side provision given for expansion of tool in curing stage. Based on the length of the component and curing temperatures elongation of tool and component is analyzed and suitable slotted bushes are provided as shown in Fig.8.
Each individual stiffener tools are designed with demoulding facility like threaded holes (To demould stiffener tools from base tool) and screw driver slots (to separate stiffener tools from one another) as shown in Fig.7.

Tool material plays a vital role in, manufacturing composite parts, a systematic study made on tool material to suit component drawing requirement. Different combinations are tried for achieving the design requirements. Finally base tool and stiffener tools are developed with the help of steel as raw material with optimized tool thickness.
Fasteners are keep on losing their strength properties while going for repeated autoclave curing's. Tool steel is used for fabricating shear bolt assemblies and considered hardness within application limits.
Due to curing of component takes place in autoclave, smooth contour is given over stiffener tools for bagging. Thermocouple positions are specified with locations to achieve repeatability behavior in the component as shown in Fig. 8. Proper engraving notes called on base plate to avoid confusion in layup stage.

Claims
What is claimed is:
1. A novel process for fabricating co-curing layup mould for manufacturing bottom floor of an advanced fixed wing aircraft in particular sections provided with a detachable stiffener tools along with the base to make provision to fabricate the bottom floor having lengthy ribs which is unique in a composite tool design.
2. The process as defined in the claim 1, said detachable stiffener tools comprised of machined steel ribs located at the two ends of the base plate to facilitate better compaction of part layers and provision for easy demoulding of component from the tool after curing, thereby to avoid the delamination's and part end damages during demoulding.
3. The process as defined in the claim 1, said the metallic base plate comprised of machined steel plate of 25 mm thick having provision of locating all the stiffener tools to maintain the stabilized contour sections and dimensional stability to meet the component design requirements.
4. The process as defined in the claim 1, said the component was fabricated with net edge layup process using UD carbon prepreg layers over the fabricated tool provided with a unique facility for flowing out the excess resin during curing process thereby to avoid the variation in rib thickness and warpages in the cured component.
5. The process as defined in the claim 1, said the co-curing layup tool is fabricated three stages where in first stage the base plate made up of mould steel is machined as the design requirements. Later the stiffener tools also of the same material of base plate to avoid the CTE variation is machined as per the design standards. Finally the machined stiffeners were located on the base plate.
6. The process as defined in the claim 1, said the base tool should be used along with a specially fabricated pressure pad made up of carbon UD prepreg to maintain the better surface finish and defined contours of the component at the end of first stage curing.
7. The curing process as claimed in the claim 6, said the stacked prepreg layers are vacuum bagged and loaded in to an autoclave where the temperature of the prepreg layers during the curing process was maintained at 175 deg.C with 7 bar pressure under 0.8 bar vacuum.