On A CNC Turning Center, One Answer Might Be 'Y'

A fourth axis, in this case a 'Y' axis, is said to come close to transforming this machining center into an almost universal metalcutting machine tool.

Case Study From: 9/1/1995 Modern Machine Shop

A fourth axis, in this case a "Y" axis, is said to come close to transforming this Mazak machining center into an almost universal metalcutting machine tool. The machine is the Mazak Integrex 50 CNC turning center incorporating the capabilities of machining centers. As is the case with many CNC turning centers on the market, the Integrex machines have three axes: Z axis, parallel with the spindle centerline for most turning and boring work; X axis, perpendicular to the spindle centerline for facing, plunge form cutting and for drilling, counterboring and so on, parallel to the Z axis, and the C axis, which is the rotary axis created by the spindle turning in continuous feed or index modes.

To mill a flat on the workpiece, there has to be simultaneous control of the C axis for rotation and the X axis for up and down (in and out of the cut). As the C axis begins to move counterclockwise, the cutting tool is at its farthest point from the centerline. Simultaneously with the C axis motion, the tool must feed into the cut, and continue to feed until it reaches the midpoint of the flat. At that point, the cutter begins to move back up until it reaches the other end of the flat, at a point equidistant from the centerline as was the starting point.

Stephen Ernst, Mazak applications engineer describes the problem. "This integration of the two axes simultaneously often generates a "flat" that is either slightly concave or slightly convex. The process with the Y axis, however, is entirely different and much simpler. Now, the C axis radially positions the part, holds that position, and then the cutting tool, feeding in the Y axis, simply mills straight across the part, generating a perfect flat. This takes a fraction of the time to program, generates a true flat and nearly always does it in less time than the C/X axes method. This ability can also be used to generate combinations of flats, such as squares (index 90 degrees on the C axis), hexagonal (index 60 degrees), and so on.

The Y axis also makes it simple to do off-center work, such as drill, bore and/or tap off-center holes. For example, on the milled flat previously described, a drill could be moved in the Y axis toward one end of the flat and then fed in the X axis to complete the hole then moved off center at the other end to repeat the operation. With ±4 inches travel (±5 inches on the model 70) the range for off center work is extensive.

Mr. Ernst and his associates are at work on a project for a customer who intends to machine camshafts in small lots. Although this is not a logical operation for a high-production cam milling machine, he plans to do it on his Integrex.

This assignment obviously requires a more complex solution than that for milling flats. This can be accomplished in two ways. In trials, Mazak has done both ways. First, in end milling, the cutting tool must always be perpendicular. So, when milling the cam contour using the C and X axes simultaneously, only a ball-nosed end will do the job; otherwise the tool would be perpendicular only on the concentric-circle portion of the cam not on the lobe. It takes about ten passes to turn the roughed blank into a "finished" shape, which then must be rough and finished ground.

The second way to generate a cam contour is to use the C, X and Y axes, simultaneously. Now users can use an end mill with indexable inserts, and the cam geometry will be generated in a single pass. The Y axis cross motion keeps the cutting tool perpendicular to the cut at all times. It is said to generate a better surface, requiring less severe grinding, and it is done in about one-tenth of the time it took with the ball-nosed tool.

The constantly perpendicular is important in other operations as well. An example would be machining a keyway along the Z axis. Using the C axis for position and the X/Z axes for machining, the cutter width must be equal to the desired width of the groove. Otherwise, if the user indexes C to make a wider groove, that new wall will be slanted, not vertical. Use the Y-axis reposition to assure perpendicularity, and all walls are straight and vertical.

Mazak managers report that customers are finding that the additional capability of the Y axis of the Integrex offers them to produce more complex parts, and complete them in a single setup. MMS

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