1. Title of the invention
Method of Making Joint less Fiber Composite Bent Tubes
2. Field of invention
The present work relates to the method of manufacturing fiber epoxy composite bent tube and more particularly, to a joint less composite bent tube developed for high stiffness and high strength single.piece composite tube.
3. Use of invention
This invention relates to an improvement in the field of manufacturing advanced composite tubes intended for aerospace applications and more particularly in fabrication and processing of the composite bent tubes, In addition to the quality of the component there is a dire need to fabricate the component with less time and cost so as to improve the productivity and cost effectiveness. It is imperative that the composite manufacturer considers the latest technologies and various governing criteria involved in processing and developing state-of-the-art composite parts that satisfactorily address the diverse and complex requirements of the end user. In situations where bend tube is to be manufactured using a single tool and is to be cured in a single batch, Also this invention provides a common approach to manufacture bent tubes for any angle up to 90 deg.
4. Prior art
Only few patents are published related to the present work like EP 0213816A2, US005676780 describes method of making composite tubes and US006139038A describes about weldless bicycle frames which are fabricated from aluminium extrusions.
5. Draw backs of prior art
The following are few drawbacks in the prior patents which are published in general like
1. EP 0213816A2 describes an improved composite member and a method of making such improved composite member wound at optimized angles to produce relatively strong and flexible in bending modes and in axial modes, the scope of the invention is limited to only straight tubes and drive shafts that are useful in automobiles, helicopter rotor torsional links and couplings.
2. The patent US005676780A has described about Method of Making a Single Rear Fork Bicycle Frame, More particularly. This invention relates to legal type bicycle frames made from composite materials.
3. The Patent US006139038A describes about weldless bicycle frames which are fabricated from aluminium extrusions. However the methods disclosed in the above patents cannot be used to fabricate a composite bent tube.

6. Comparison between prior art and present invention
The existing methods of manufacturing bent tubes , which are in practice are designed based on the trial and error method and are generally applied for fabricating bent tubes in two pieces and later joining them using wet layup technique. These composite tubes does not possess enough strength at the joining area and are less efficient, The two tubes are fabricated separately and are cured in an autoclave and then the two tube ends are cut to the required angle and are joined using wet layup, this method does not ensure correct bent angle and tends to spring back after curing and hence it gets rejected. The present technique includes a new method to fabricate a joint less composite bent tube which doesn't require joining with the wet layup and ensures the structural integrity and strength. Also the present technique is developed to fabricate the joint less bent tube in a single process with the help of a newly developed tool and is used to manufacture bent tubes of any angle less than 90 deg, thereby the process time will be reduced by 30 %.
7. Aim of the invention
The aim of the invention is to develop a modified approach to manufacture single piece joint less composite bent tubes at optimum cost and time.
8. Summary of the present invention
Accordingly, it is an invention to fabricate a single piece bent tube using a modified tool that is designed for holding and curing of the bent tube. Earlier the bent tubes are fabricated in two pieces and are joined using wet layup technique and many of these tubes are rejected due to incorrect bent angle, strength and quality. Broadly stated the invention provides a modified tool and an approach to fabricate joint less bent tubes.
The new invented method comprises with the simple designed tool and holding blocks made of aluminum or any other metal on which the profile of the bent tube is machined to support the tube firmly to avoid distortions during curing process, also the tool has the drilled holes to insert the holding blocks on the top of the tool over the tube to prevent it from the transverse shrinkage, the two mandrel ends are machined and grinded to match the required angle and the prepeg layers are wound or laid at optimized angles. Each odd numbered layer wound at an angle to the longitudinal axis along the length of the mandrel in a first direction and each even numbered layer wound at an equal and opposite angle to the longitudinal axis in a second direction, the layers are oriented in a cross over relation relative to the longitudinal reference axis of the tube mandrel.

9. Brief description of drawings
Fig.1 is a schematic Top view of the tool and the supporting block arrangement to fabricate a joint less composite bent tube. The tool is made with an eurol block material for the experiment purpose and the same can be made with aluminum or any other heat conductive material.
Fig.2 shows the practical arrangement of the tool and the supporting blocks along with the laid up mandrel placed in the tool.
Fig.3 shows the schematic view of the tool with the locating holes to fit the supporting block, pins, which is used to hold the tube firmly and to avoid any distortions in the tube during curing process.
FigAshows the arrangement of two mandrels which are used in layup of layers where the prepeg layers are wound on the mandrel and after curing the mandrels are removed to obtain a hollow composite tube.
10. Statement of invention
This invention is to manufacture single piece joint less composite bent tubes at optimum cost and time.
11. Detailed description of invention
The present invention comprises of a new technique and an approach to fabricate joint less composite bent tubes that are relatively strong and provide better structural integrity as a single unit, which are used in an advanced light chopper, various techniques are available to manufacture the bent tubes in two piece method, which consumes more time and does not yield exact shape with required bent angle, also results in inferior surface finish, strength and quality.
At present the composite tubes of circular cross section are produced using a mandrel where the prepreg layers are wound in particular orientations along the longitudinal axis of the mandrel, thereafter it is cured in autoclaves and the mandrel is separated from the cured composite tube. To fabricate a angled bent tube two such cured composite tubes are joined to the required angle by cutting and matching the ends, later the two ends of the tubes are joined by applying the resin using wet layup technique, but this method doesn't ensure the structural integrity and also the required angle and hence these tubes are rejected in the assembly line.
The present invention is a modified approach of the existing process for fabricating the composite bent tubes where the two ends of the mandrels are grinded or machined to the required angle and are matched as shown the Fig. 4. There after release all is applied on the mandrel and the prepeg layers are wound on to the mandrel along the longitudinal axis of the mandrel at a particular orientation usually at 45 deg. And similarly the second layer is wound for the other end. After lay up of the required layers finally the Shrink tape is wound over the last prepeg layer to ensure the compaction of the layers during curing as the shrink tape shrinks with the temperature. The laid up mandrel is kept on the engraved tool as shown in the Fig.2 and

the supporting blocks are placed over the mandrel to avoid the distortions during curing process in autoclave due to elevated cure temperatures.
After curing the mandrels are pulled from the two directions as shown in the Fig.1, the joint less composite tube is obtained as per the required dimensions and the required angle.

Claims
What is claimed is:
1. A method for fabricating the joint less single piece composite bent tube used in aircrafts and advanced light utility choppers.
2. The method according to the claim 1.comprises of the tool and the modified mandrel arrangements to fabricate single piece joint less high strength composite tube.
3. The method as per the claiml is suited for fabricating a joint less composite bent tube of angle less than 90 deg and are made of prepeg layers only.
4. The method of fabricating as per the claim 3 is meant for lay up of prepeg layers over the mandrel and are cured in autoclaves with the tool designed specifically as per the claim 1.
5. The tool as per the claim 1 comprises of the supporting blocks and the locating pins which are ideally used to support the mandrel and can be made with any thermal conductive material.