Composite materials may require cutting at different stages during the manufacturing process of a component. Firstly, the dry fiber or prepreg will be cut to an approximate shape and size prior to laying-up in the mold as a preform. Net-edge trimming of the preform may then be performed to reduce post-curing machining operations, or the component may be machined after curing to achieve the finished part geometry.

Cutting of Raw Material

A variety of different methods can be used to cut uncured composite materials. The most well established is the use of an automated ply cutting table. This consists of a ‘moving bed’ with a cutting gantry that runs above the bed. The gantry houses either an ultrasonic cutter or a ‘powered wheel’ cut. The ply shapes are pre-programed into the ply cutting table and when needed, the roll of material advances along the table to the cutting zone, where a drag knife, or ultrasonic cutter are present and able to perform the cut.
 
Trimming of Preform Laminates
 
“Net-edge trimming” of shaped preform laminates (parts that have been laid-up and contoured to shape, but not yet cured) is a new technique that has been developed to reduce the amount of scrap trimmed from a part after the part has been cured. The final geometry of the part is cut-out by ultrasonic blade.
 
Advantages

Reduces the amount of post-curing machining operations required, in some cases the part can be used as-is. The waste fiber can potentially be recycled without the need to extract the fiber from cured resin.

Trimming of Cured Parts

Trimming of cured parts is a standard step in composite part manufacture to achieve final-part geometry and for any hole drilling/cut-outs required. Various cutting techniques are available: rotary cutter (machining) and waterjet are the most common, whilst laser trimming is currently in developmental stages for composite materials. The techniques can be used either on standard robotic arms or multi-axis CNC machines.
 

  Rotary Cutter Waterjet     Laser
Advantages Similar process and equipment to traditional metal trimming

No direct tool wear

Reduced heating due to water acting as coolant

Speed of operation

Very high degree of accuracy

Other machining operations possible, e.g. etching

Disadvantages

Tool damage requires repairing regularly

Heat generated can cause damage to laminate (delamination is typical)

The process is relatively slow for complex parts, due to the need for the cutting head to be reorientated as the cut progresses

May have to trim twice to achieve desired tolerance

Complex geometries not possible

Requires pilot hole to be drilled if not starting from edge of part

Machinery consumables (such as nozzles)

Can cause delamination and damage during cutting

Developmental technique - no large-scale industrial experience

The composite material experiences a ‘#heat affected zone’, which is difficult to characterize