“Must Have” Multi-Axis Control Options

When you’re doing multi-axis machining, things can get complicated pretty quickly. And this can involve a lot of time-consuming and tedious operator intervention. The CNC control options I’ll discuss here make multi-axis machining operations much more user-friendly by allowing your machine tool to automatically determine where it should be – and stay on path. They also provide a universal platform so you don’t need to reset programs – they’re automatically shared amongst operations. And perhaps best of all, these functionalities are not part-specific or machine-specific – just set one and you’re done.

Okuma’s OSP-P300M control, which comes standard with every MU series CNC machine, provides features that do all kinds of work for you, whether you’re performing 3 axis machining, 3+2 machining, 4 axis machining or full 5 axes. It’s worth it to check this list and see what you might be missing.

The Usual Go-To: Inverse Time Feed

Inverse time feed (Okuma G93) is the most commonly used control feature for doing multi-axis simultaneous cutting. In this mode the feed rates are specified in cutting time instead of cutting feed rate (IPM or IPR). This is a calculated value based on the axis motion of the rotary and linear axes. When using inverse time feed there must be a feed rate command on each and every line, and also the rotational centers must be known and compensated for when creating cutting programs. This process is part-specific, so you need to know a lot about the machine configuration to run it. Plus, the program is machine-specific due to variations of rotational centers. While inverse time feed is a “known entity” for many CNC machine operators, it can be a cumbersome way to go, though your CAM system requirements may make this your option of choice.

The following options provide a more streamlined and dynamic process, which translates across parts and across machines. They not only simplify processes, but also automatically account for variances in part requirements and machine configurations.

Tool Center Point Control

This function (Okuma G169 H_ ) controls the movement of each axis by adding the tool length offset amount (which determines how the tool center point moves along the workpiece through the tool path), as specified by the axis movement commands. It also controls the feed rate of each axis so that the tool center point moves along the part at the specified feed rate (Okuma G94). With this function the rotational centers are stored via parameter and therefore do not need to be considered when creating the cutting program. This makes the program universal for similarly configured Okuma machines.

Tool Posture Compensation

Tool Posture Compensation is now part of Tool Center Point Control. With the expansion of 5-axis machining there may be areas in the CAM program output (errors due to linear approximation) that make the tool posture move radically. This means that smooth cutting is difficult to maintain, and results in long cycle times and rough surface finishes. Tool Posture Compensation (Okuma G445) enables minor axis inversions to be filtered while using TCPC via either parameter setting or G-code.

Fixture Offset Function

This function is a must for 3+2 machining. It allows you to set one work coordinate, and then all the others will be calculated by the CNC control. One and done…what you get is a simplified part program.

Super-NURBS RT (Rotary Table)

This function is a must for today’s high-speed, high-accuracy machining. Super-NURBS RT is for simultaneous machining (though not limited to), and can be used for 2D, 2.5D and 3D high-speed machining.

Super-NURBS permits the machining of free form curves at the most stable feed rate possible. Super-NURBS is divided into two functions: Progress Shape Reconstruction which reconstructs and adjusts high order curves, and Progress Shape Adaptive Control, which controls the feed rate according to high order curves. While using Shape Reconstruction the control judges the series of G1 moves and reconstructs them to obtain the machining shape and feed rate. Shape Adaptive Control calculates the interpolated points with high accuracy and density and reconstructs the shape. Super-NURBS now performs adaptive control of feed rates and minimizes not only acceleration but also jerk (acceleration change rate), allowing the axes to move smoothly without vibration.

One of the things we hear frequently from Okuma users is that the machine tools work intuitively with the operator to get the job done in the simplest, most error-free way possible. Take advantage of these “must have” control options and you’ll see what they mean.

Are you using any of these control options? Comment below and share your experiences. And feel free to contact us or your distributor if you’d like to learn more about streamlining your multi-axis machining processes.

Ron Raniszewski is Senior Applications Engineer, Okuma America Corporation.