C6 Corvette LS7 Engine - What's this five-axis stuff, anyway?

by Hib Halverson
© May 2013
No use without permission, All Rights Reserved

Five-sided machining, also known as "3+2", is the process of setting up a part one time and machining five sides using a 5-axis, Computer Numerical Control (CNC) machining center instead of machining the part one side at a time using a conventional 3-axis machining center.

In the machine tool world, there are three primary axis: X, Y and Z, with the Z-axis parallel to the tool spindle. Three-axis CNC machining is a machine tool's ability to move the workpiece along those three different axes–left-or-right, forward-or-back, up-or-down–simultaneously.

Five-axis CNC machining is a machine tool's ability to move the workpiece–an LS7 cylinder head for example–along those three primary axes, as well as rotating about two additional axes. A five-axis machine's table not only can move along the Y-axis but it also can rotate around that axis. The table has a head which can rotate perpendicular to the plane of the table. Additionally, a five-axis machining center can move its table in all five directions at once, if necessary.

The chief benefit of five-axis machining is the ability to machine complex shapes, such as intake ports or combustion chambers, in a single set-up which shortens setup time and increases productivity. Additionally, the feature-to-feature accuracy is improved because the same "zero", or datum reference frame, is used throughout the manufacturing process.

Other advantages of five axis machining are, since simultaneous movement is allowed along the X and Y axis, shorter and more rigid tools may be used which the reduce vibration which occurs when machining deep pockets or contoured features with three-axis machines. Also, higher cutting tool speeds may be used which reduces the load on the cutting tool.

In short, GM decision to use a five-axis, CNC'ed head on the LS7 contributed to extracting the highest performance possible from a production cylinder head.