Five-axis machines are complex, and machinists need to be skilled to work with them. However, the machine’s application is really what drives its complexity.
There are two general application categories for five-axis machining: machining complex 3D shapes and conventional machining of tilted surfaces. In both cases, the difficulties related to creating five-axis programs have been simplified over the years. Additionally, the two categories have little in common. A machinist will be able to master the five-axis technology with less difficulty because he or she has to learn only one specific application.
Like any CNC machining center, a five-axis machine has three linear axes. The layout for these axes will be the same as any three-axis VMC or HMC. For a vertical viewed from the front, left/right is X, fore/aft is Y and up/down is Z.
Unlike three-axis machining centers, five-axis machining centers have two additional rotary axes. For a VMC, the A axis is the rotary axis with a center line parallel to the X axis. The rotary axis parallel to the Y axis is the B axis. (This is the most common configuration for a vertical.)
Rotary axes can take one of two basic forms. One style incorporates rotary tables. The first rotary table is mounted to the machine table and the second is mounted to the first. The workpiece can be tilted in two directions.
With the second style of five-axis machining center, the rotary axes are incorporated into the machine’s headstock and spindle. The spindle and cutting tool can be tilted in each rotary axis. This method enables the workpiece to remain stationary, which is beneficial for machining large parts.
With either style, the axis conventions remain the same. When viewing a vertical machine from the front (while X/Y is left/right), workpiece/cutting tool tilt clockwise/counter clockwise is the B axis. When viewing the machine from the right side, workpiece/cutting tool tilt clockwise/counter clockwise is the A axis.
Machining Complex 3D Shapes
For this application, the two rotary axes are used to keep the cutting tool at, or close to, 90 degrees to the surface being machined.
In the early days of five-axis machining, programming a machine for 3D work was a daunting challenge. CAD and CAM systems were in their infancy—and didn’t talk to each other very well. The programmer almost always had to define the workpiece geometry in the CAM system before the machining process could be started, and glitches were common.
Today, CAD and CAM systems communicate very well. The design engineer’s 3D drawing can be directly imported in the CAD system. Once imported, the programmer’s task is relatively easy. Choices in machining methods are numerous, and the programmer can command the CAM system to progress from roughing the workpiece to finishing it with successively smaller cutting tools. The problem related to shape violation has been all but overcome, meaning the CNC program developed by today’s CAM systems will almost always appropriately machine the workpiece.
Admittedly, I have over-simplified the process of five-axis programming for 3D work, but I believe most experienced five-axis programmers would agree—improvements in CAM systems have simplified the task of programming five-axis machining for 3D work.
Conventional Machining of Tilted Surfaces
The second application category for five-axis machining is simply an extension of what is commonly done with three-axis machining centers. That is, a machine used for this application will perform common operations such as drilling, tapping, reaming, boring and milling. However, the workpiece surfaces are not always square with the machine’s three linear axes. While this application is much simpler than 3D work, it can still be challenging to determine program coordinates for surfaces that are not square with the linear axes.
Programming for this application has also been simplified over the years. While CAM systems can definitely help, most manufactures that specialize in making controls for five-axis machines can also provide a feature that makes it possible, even for a manual programmer, to program basic machining operations for angular surfaces.
Fanuc calls this feature 3D coordinate conversion. Like the standard plane selection commands (G17, G18 and G19), this feature enables the programmer to define a plane for machining—and the plane can be tilted at any angle along either or both rotary axes. Once the angular plane is defined, simple programming features, such as canned cycles and cutter radius compensation, can be used to machine the surface.
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