Manufacture of stiffened composite structures

Details Manufacture of stiffened composite structures Manufacture of stiffened composite structures

1999-09-22

2001-07-17

Ball, Michael W. (Department: 1733)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C156S154000, C156S175000, C156S285000, C156S290000, C156S297000, C156S307700, C353S028000, C356S370000

Reexamination Certificate

active

06261395

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of and apparatus for manufacturing stiffened structures made from composite materials such as carbon fibre composites.
2. Discussion of Prior Art
In many areas of manufacturing lightweight, strong, structures are made from composite materials which are easy to form into complex three dimensional shapes. Automobile bodies and aircraft structures such as wings and intake ducts are commonly made from these materials. Often such structures are large and require stiffeners to give them added strength and rigidity and sometimes to provide attachment points to other structures.
Conventionally stiffened composite structures are made by forming the basic structure from uncured composite material using a mould tool whilst constructing the composite stiffeners separately also from uncured composite material. The separate stiffeners and moulded structure are then autoclaved to cure them and a difficult process then follows whereby the stiffeners are attached to the moulded structure. Typically the moulded structure will be held on a jig and a complex scaffolding erected around it. Extensive drilling of the structure and the stiffeners is then required and the two parts brought together for bolt and/or pin attachment. Where precise positioning of the stiffeners on the structure is required, say because the stiffened structure is to interface with another structure, this can be a very difficult procedure indeed and it can be extremely difficult to achieve the accuracy of drilling and location required because of the intrinsically variable nature of the jigs and scaffolding used.
SUMMARY OF THE INVENTION
It is an object of our invention to provide a method of producing a stiffened composite structure which is simpler and more accurate than the known methods.
According to the present invention in one aspect thereof there is provided a method of manufacturing a stiffened composite structure comprising at least the steps of:
moulding the structure around a mandrel tool;
curing the structure;
forming stiffeners from composite material including forming a plurality of tabs on the stiffener;
using a laser theodolite to locate the tabs accurately on the structure; and,
bonding the stiffeners to the structure at least via the tabs.
According to the present invention in another aspect thereof there is provided a method of manufacturing a stiffened composite structure comprising at least the steps of:
moulding the structure around a mandrel tool;
using a laser or digital camera to record the positions of desired pad locations on the structure;
bonding pads to the structure at the desired locations;
curing the pads and structure;
forming stiffeners from composite material including forming a plurality of tabs at points on the stiffener corresponding to the pads on the structure;
using a laser theodolite connected to receive the stored information of the pad locations relative to a datum point on the structure to locate the tabs accurately on the pads; and,
bonding the stiffeners to the structure at least via the tabs and pads.
It will be appreciated that bonding avoids penetrating the structure by e.g. drilling to provide bolt locations. This has advantages in terms of strength, durability, and aerodynamically clean surfaces.
Any bonding or curing steps may be achieved using an elevated temperature process, for example an autoclave may be used. Alternatively, any bonding or curing steps may be achieved using a cold processing technique. The cold processing technique may utilise electromagnetic radiation such as microwave energy, ultra-violet radiation, or may utilise electron beams, for example.
The stiffeners may be bonded to a convex surface of the structure. The stiffeners may alternatively or additionally be bonded to a concave surface of the structure.
The tabs may advantageously be left over from an injection moulding process.
Preferably the location tabs and any pads are machined off the final stiffened structure after bonding.


REFERENCES:
patent: 5381258 (1995-01-01), Bordignon et al.
patent: 5624088 (1997-04-01), Fiore
patent: 5651600 (1997-07-01), Dorsey-Palmateer
patent: 5771680 (1998-06-01), Zahedi et al.
patent: WO 96/19335 (1996-06-01), None

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