Five-axis machining is increasingly being applied to complex mold work. The technology can reduce the number of setups and/or machine tools required to produce a part,

thereby minimizing work-in-process inventory and reducing total manufacturing time.
As CNCs have become more powerful, CNC manufacturers have been able to add more five-axis features. Capabilities once found only in high-end controls are now available in mid-range products.

Most of these features have to do with making five-axis machining easier to use for shops that have little five-axis experience. Today, accessible CNC technology can deliver all of these benefits to the five-axis machining process:
Eliminate the need for qualified tooling

Allow tool offsets to be set after the part program has been posted

Support “machine anywhere” programming, so that posted programs are interchangeable from machine to machine

Improve surface finish

Support various machine configurations, so the program no longer has to account for whether the spindle pivots or the workpiece pivots. This is now accounted for by parameters at the CNC.

One example of a five-axis machining feature specifically suited to mold machining is ball-nose end mill compensation. In order to properly compensate for a ball-nose end mill as the part or the tool pivots, the CNC must be able to dynamically adjust the cutter compensation vector in X, Y and Z. (See illustration above.) Better finish is one benefit of keeping the tool’s contact point constant.

Other five-axis CNC functionality can be separated into the features related to pivoting the tool; features related to pivoting the part; and features that allow the operator to manually move the tool to a new vector.

When rotary axes pivot the tool, the tool length offset that normally affects only the Z axis now has components in X, Y and Z. In addition, tool diameter offsets that normally affect only the X and Y axes also have X, Y and Z components. And because the tool may be feeding in the rotary axes while it’s cutting, all of these offsets have to be updated dynamically to account for continuous changes in the tool’s orientation.

A CNC feature called “tool center point programming” can take of this. The feature lets the programmer define the path and speed of the center point of the tool, while leaving it to the CNC to take care of the commands in the rotary and linear axes to ensure that the tool follows this programming.

This feature makes the tool center point independent of the specific tool loaded into the machine, meaning (A) tool offsets can be input at the machine tool just as in three-axis programming, and (B) programs don’t have to be re-posted to account for tool length changes. The feature simplifies programming and posting for machines that achieve rotary-axis motion by pivoting the spindle.

Machines achieving rotary motion by pivoting the workpiece use similar functionality. Newer CNCs can compensate for this movement by dynamically adjusting fixture offsets and rotating coordinate axes to match the part’s rotary motion.

The CNC can also have an important role when the operator is jogging the machine manually. Newer CNCs allow the axis to be jogged in the direction of the tool vector . . . and allow the tool vector to be changed without the location of the tool tip changing. (See illustrations above.)

These features make a five-axis machine easier to use for 3+2 programming—the most common use of five-axis machines in mold making today. However, as new five-axis CNC features continue to evolve and gain acceptance, true five-axis mold machining is likely to become more common.