Browse Prior Art Database

DATUM TARGETTING METHOD FOR CMC PART

IP.com Disclosure Number: IPCOM000248343D
Publication Date: 2016-Nov-16
Document File: 6 page(s) / 140K

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention relates to machining of ceramic matrix composite (CMC) parts. Specifically, a method for aligning an as-molded composite part in a computerized numerical control (CNC) machine and creating a datum reference is disclosed.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 01 of 6

DATUM TARGETTING METHOD FOR CMC PART

TECHNICAL FIELD

    The invention relates to machining of ceramic matrix composite (CMC) parts. Specifically, a method for aligning an as-molded composite part in a computerized numerical control (CNC) machine and creating a datum reference is disclosed.

BACKGROUND

    Lightweight fiber composites hold great promise for the aircraft industry. Fiber composites provide a significant improvement in specific strength and stiffness over conventional metal alloys. Better specific strength and stiffness translates into weight savings, which translates into fuel savings and lower operating costs.

    A recent development is making parts from a ceramic matrix composite (CMC). One CMC form is a silicon carbide matrix that weighs a third of advanced alloys but has improved fracture toughness compared to conventional ceramic materials and can perform at higher temperatures than metal. The material is going to be used to make aircraft parts such as engine shrouds, combustor liners and stator vanes among others.

    An exemplary process for making CMC parts involves taking continuous silicon carbide fibers, coating them via chemical vapor deposition to keep the fibers from bonding with the matrix; forming the coated fibers into a prepreg tape by running the fibers through a slurry compound, winding the fibers onto a drum, and drying it; laying the tape into the desired form; using an autoclave to consolidate the composite; using pyrolysis to burn off the leftover organic


Page 02 of 6

constituents, leaving a preform consisting of a porous lattice made from ceramic coated silicon carbide fibers in the shape of the desired part; and melt infiltrating the preform with molten silicon to form the fully dense silicon carbide matrix. A result of the layup and MI process is the free edges of the as-molded part are generally rough and not suitable for part datum locating.

    The part may be partially of fully machined to its required shape and tolerances at any step between forming and densifying. For example, machining of the part may occur before the melt infiltration phase, while the preform is still in its green form to reduce or eliminate the final machining operation. Also, final machining may be done after melt infiltration to meet final specifications. Machining of CMC parts may be done using a CNC machine.

    CNC machines are controlled by computer software which directs a cutting tool to move along a specified path that will cut a part to the desired dimensions. CMC parts for use in the aircraft industry generally require small tolerances and need to be accurately located by the machine based on a datum. A datum is the origin from which dimensions of part features are established.

    A common problem occurring during machining of CMC parts, especially axisymmetric parts, is that the free edges of the final as-molded part are generally rough and...