Gear cutting – milling – or planing – Milling – Process
Patent
1995-06-23
1997-06-24
Briggs, William R.
Gear cutting, milling, or planing
Milling
Process
408 1R, 451 28, B23C 300
Patent
active
056412525
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF TEE INVENTION
1. Field of the Invention
The present invention relates to a cutting tool and method for producing a hole in a workpiece consisting of a fibre-reinforced composite material, the central axis of which passes through a predetermined point on the surface of the workpiece and is oriented in a certain determined direction in relation to the longitudinal directions of the fibres in the immediate vicinity of the point.
2. Description of the Related Art
Polymer composite materials have been generally known since the 1950's. These materials are composed of a protective and binding polymer, either a thermoplastic or a thermosetting plastic, usually referred to as the matrix, together with fibres (e.g. glass, carbon or amide fibres), which may be regarded as a reinforcing material. The fibres may be continuous and oriented in specific directions, or they may be relatively short and arranged at random in the matrix. Composites with continuous and oriented fibres give products with mechanical properties superior to those of conventional polymer and metallic materials, especially as far as their weight-related strength and rigidity are concerned. Composites with shorter fibres find an application where rather less demanding properties are called for. One factor obstructing the wider use of composite materials is the absence of effective methods of cutting machining. The physical and chemical properties of the composite materials mean that known machining methods cannot generally be applied with successful results.
Products consisting of composite material often contain holes for various purposes. These holes may be required, for instance, to permit the laying of service lines, assembly or inspection. Bolt holes are a particularly important category of hole. Structures for practical applications are often constructed from components joined together to produce a finished product. The purpose of the joint is to transfer the load from one structural element to another. One common form of jointing is the bolted connection, in which the load is transferred by either shearing loads or tensile loads in the bolt. The strength of a bolted connection is influenced to a considerable degree by the quality and precision of the hole. Reference may be made to three particular problem areas when producing holes in polymer composite materials:
When machining laminated composite materials, there is a risk of the layers separating (delaminating) because of the low interlaminar strength. Extensive delamination damage can jeopardize the strength of the laminate.
The heat generated during machining can cause the matrix to soften and block the tool, making further machining impossible. In order to achieve good hole quality, it is accordingly necessary to provide effective cooling of the tool/hole edge, and for the material removed by cutting (chips, splinters and grinding dust) to be removed continuously from the hole.
The cutting machining of the fibre composites causes severe wear of the tool because of the good wear characteristics of the fibre materials. This leads to high wear costs, especially when producing holes with a requirement for high precision.
The methods used to produce holes in composite laminates are traditional boring, milling, sawing and grinding. The problem associated with these hole-forming methods as they are applied at the present time is that they are not sufficiently effective for various reasons from a technical/economic point of view.
High wear costs are a general problem associated with cutting machining where high precision is required. Great care must be taken when boring to ensure that delamination damage is avoided on both the entry and exit sides. Special cutters are required in order to achieve the stipulated hole quality, and special procedures must be formulated. In order to avoid extensive delamination damage on the exit side of the laminate, local lateral pressure must be applied around the edge of the hole. Another previously disclosed method of protecting the exit side from
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Backlund Jan
Eriksson Ingvar
Zackrisson Leif
Briggs William R.
Novator AB
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