composites


fi ve-axis CNC routers with a capacity of up to 20 × 30 × 5' (6.1 × 9.1 ×1.5 m). Fixturing is a challenge because the parts can’t be clamped without damag- ing them, and since they’re nonfer- rous, a magnetic table is useless. One method is to simply cover the sheet with double-sided tape and then tape it to the fi xture. Another method is to use single-sided tape to hold a sheet of plastic across the entire surface of the part and then use suction from below to hold the part to the table. The fi xtures show the operator


EC machines honeycomb on large 5-axis routers, creating contours, cut-outs, and chamfered edges. Fixturing is a challenge and tolerances can be “metalworking tight.” Here the part is being held by vacuum.


with which the fi rm can form honeycomb is another thing that sets it apart from its competition.


Machining Air and Paper The cured honeycomb that stays in- house now goes into a bandsaw that cuts it horizontally into sheets as thin as 1/16" or as thick as 6". The saw blade is high- speed steel (HSS) and produces a fi ne dust, which an overhead vacuum simply sucks up like in a woodworking shop. After this, the sheets are cut into


near-net shapes for fi nal machining and/ or assembly. In the latter case, EC may glue several pieces together and then machine the construction as a whole. Much of this cutting and gluing is done by hand, and EC employs a number of former cabinet makers, a fi ne example of repurposing traditional skills. Machining is generally used to pro- duce rather subtle contours, chamfers along the edges or cutouts. The bulk of this machining takes place on large,


where to place the near-net shape and the machines orient themselves to the fi xture. Since every edge of the part will be machined, it’s not necessary to know its precise position in the fi xture. Feed rates are comparable to many metalworking applications (e.g. 50–100


ipm [1270 × 2540 mm/min]), depending on the stability of the material, as well as its geometry. Tolerances are generally in the range of a few thousandths, but can sometimes be so tight that the entire profi le must be checked with a CMM or even a laser


Getting multiple layers of resin to safely bond requires processing the blocks through a series of curing ovens, each capable of tightly controlling humidity, air fl ow, and temperature throughout.


112 — Aerospace & Defense Manufacturing 2016


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