Title: Answering the 3 Questions Behind 5-axis
Course: Multi-Axis Machining Operations (ATE CENTRAL) > Section: Day 4 - 5 Hours (Total: 20 Hours)

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INTRODUCTION

What? Why? and How?

One of the greatest sculptors in the history of the world was Michelangelo. He was one of the first artists to be recognized as something special in his lifetime and worked for the famous de Medici family, the Catholic Church, and accepted many commissions from other dignitaries of the day. He dominated his time as a primary artist in the Renaissance.

How does this fit with CNC machining? It is said that Michelangelo could visualize the finished sculpture as he gazed at a block of stone. A block of marble and a block of metal are much the same thing when it comes to CNC machining. Just like Michelangelo, those who build and design items to be cut on the CNC machine can create something special out of nothing. Art or functional part, each created item is a demonstration of the skill of the designer.

What are the 5 Axis in 5-Axis?

Descarte was the one who first started to describe motion and movement in 3-dimensional space. He described that movement using 3 numbers, represented by the variables X, Y, and Z. These are 3 of the 5 relevant axis so important to 5-axis machining. When we add orientation to these three points, we have our 4th axis. This is the rotational axis around X. If we visualize this as a plane, we can describe the way that a plane banks while in the air, turning from side to side.

As we continue the visualization of the plane in space, the pitch of the plane describes that 5th axis. This is the rotational axis around Y.

There are two different conventions for axis-labelling: horizontal plane, and the vertical plane. The X- and Y-axis reside in the horizontal plane, while the z-axis resides in the vertical plane. In a horizontal machining center, the Z- and Y-axis are reversed. The specific configuration of the machine determines which rotational axis is used. See the diagram below:

A trunnion-style machine operates with an A-axis (this has the rotation around the X-axis) and a C-axis (rotating around the Z-axis). A swivel-style rotate machine operates with a B-axis (rotating around the Y-axis) and a C-axis (rotating around the Z-axis).

In a trunnion-style machine, the table is the item that moves. In a swivel-style rotate machine, the spindle is the item that moves.

How Many Axis are Necessary?

Some machining centers talk about seven, nine, or all the way up to eleven axis. It's kind of hard to envision how eleven axis could work. These numbers come into play when you have multiple spindles and multiple turrets. A top turret could have 4 axis and the lower turret could have 2. The opposing spindles could have 2 axis each as well. A machine like this could have about 9 axis easily.

The number of axis required depends on what you are making. The geometry of the object in question will dictate the most efficient machine for the application. Another aspect under consideration is the needs of the machine shop and the size of the object being machined.

5 ≠ 2+3

Five-axis is not necessarily the same as 2+3 axis machining. True 5-axis machining involves constant adjustment of the cutting tool along all five axis to keep the tip in the right perpendicular spot to the part.

In 3+2 axis machining, it involves a 3-axis program that has the cutting tool or part locked at an angle determined by two-rotational axis. There can also be a type of machining that involves the reorientation of the toolbit along the rotational axis between the cuts made by the machine. This is also counted as 3+2 machining.

True 5-axis machining speeds up the process, sometimes by a great deal. The cutting is done faster as there are less adjustments necessary between the object being machined and changing out the toolbits. This is the advantage of true 5-axis machining. This also means that the parts of the machine wear out faster because the machine is in operation for a larger total number of hours in the same time period. Something else to be aware of that is more complicated by 5-axis machining, is the part crash issue. With more moving parts, it is even more important to have correct toolpaths to ensure that there are no impacts within the machine that are not intended.

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SOURCES

Engineering.com

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