How to Boost 5-Axis Machining Results

The world of 5-axis machining opens up many new possibilities for the way we process parts. Notably, many types of 5-axis machines available today are flexible enough to allow applications to a wide variety of parts. The major difference we notice is where the rotary axes are located, either in the spindle or on the table. 5-axis machining also opens up many opportunities for decreasing processing costs. Among these are shorter setup times, reduced workholding requirements, generating more complete parts per operation, fewer requirements for custom cutting tools, and quality improvement resulting from having the ability to control the relationships of various features to each other.

Transitioning to a 5-Axis World

Along with these advantages come many new features that we must learn how to apply in our manufacturing processes. The immediate challenge is that most of these features are difficult to relate to the historic 2- and 3-axis work we’ve evolved from. Additionally, these features are usually explained in very technical terms in lengthy documents.

Compounding this problem is the fact that the translation from system to system can cause facets or low quality surfaces in the CAD data. This creates an adverse effect that results in irregular programmed angular moves when a program is posted from a CAD system. Because of this, we now see strong demand from customers for a 5-axis machine feature that addresses these undesirable moves.

Responding to Customer Demand: Tool Posture Control

Tool Posture Control is Okuma’s answer to these calls for help. It can be difficult to visualize this function from the technical explanations, so here it is in plain English. The simple purpose of this function is to:

• Shorten cycle time
• Improve the quality of the machined surface
• Compensate for fluctuation of rotary axes in the part program
• Simplify operation by accomplishing all this in the background of the CNC control with activation handled by one code

So, you may ask, what is the condition that this function can be applied to, and what’s the benefit that can be achieved? Due to the fact that the surface in the CAD data is not fluid, when the program is generated using Tool Center Point Control, an attempt is made to keep the tool normal to the surface. However this can create a lot of undesirable angular movement. Following are a couple scenarios that demonstrate how to address this by using the Tool Posture Control function.

Improving Surface Finish: How is This Possible?

The Problem: When cutting with the side of an End Mill, the tool tip is moving at a constant rate. The irregular angle moves cause the tool to travel back and forth over the same surface (much like a windshield wiper blade), causing a scarred surface.

The Improvement: The Tool Posture Control function allows limits to be set for the amount of movement. It then reads ahead in the program, projects the tool path and allows a continuous angular movement (one wipe across the windshield). One smooth pass across the surface equals a better finish.

Reducing Cycle Times: How is This Achieved?

The Problem: Using the same example as above, the “windshield wiper” effect has minimal movement at the tool tip, while at the extreme end of the wiper blade there’s a large amount of undesired movement. This movement equals actual machine travels, and is a product of the pivot distance and the tool length. For example, a desired .005-inch tool travel with 12-inch pivot length and 12-inch tool length with 5 degrees of extra movement results in 2.097 inches of machine movement. To exaggerate the problem, when the direction changes, unnecessary acceleration and deceleration time is added.

The Improvement: The Tool Posture Control function reads ahead in the program, then projects the tool path and adjusts for a continuous angular movement. This removes extra acceleration and deceleration time and also reduces much of the unnecessary machine movement. Extreme examples have reduced cycle time as much as 50%, but even less than this is significant.

By using Tool Posture Control, with just one code, quality improvements and cycle time reductions for 5-axis machining can easily be realized.

Have you faced any similar challenges when transitioning to 5-axis machining? Comment below or contact us and share your experiences.

Ed Leeson is Applications Engineer, Okuma America Corporation.