Just about everyone associated with manufacturing has heard about 5-axis CNC machines, but it's likely that relatively few of them actually understand what it means. Computer numerically controlled machines, commonly known as CNC, refers to those machine tools in which a cutting tool moves along programmed paths to accomplish any number of tasks that can include turning, drilling, boring, or cutting.
To see how far machining has come, you need to realize where it was just a few decades ago. Take the example of a manual 3-axis vertical milling machine. The table can move right or left at the direction of the operator, which signifies the "X" axis. The table can also move in and out, and that's the "Y" axis. Finally, the operator can establish the depth of the cut by moving the cutting tool head up or down, representing the "Z" axis.
A 3-axis CNC router has those same three movements; only a computer handles the conversion of a CAD design into coordinates that allow it to move in all three directions simultaneously. The instructions from the software are used by the cutting tool to remove the material and create a three-dimensional part.
CNC routers, a favorite of the woodworking industry, work under these same principles for creating cabinets and three-dimensional signs, among a host of other applications like this work of art below.
Photo Credit: Mark's Woodshop Inc.
Beyond the 3-axis CNC machine
The term "5-axis" refers to the number of directions in which a cutting tool can move. On a 5-axis machining center, the cutting tool moves across the X, Y, and Z linear axes just like any 3-axis CNC. But it also rotates on the A and B axes to approach the workpiece from any direction. As a result, you can machine five sides of a part with one setup.
CNC machines with five axes have the freedom of motion to produce some very complex geometries. Standard 3-axis CNC machines can't move the cutting tool in a manner that will create partial cavities and overhangs, for example, without re-setting the part midway through the process.
By adding an axis of rotation around the X and Y linear axes, setup times are reduced, and repeatability is practically ensured since there is no human interaction required for the additional part movement.
Well-built 5-axis machine tools can handle the machining and the complexity of a variety of components. Check out the moves on this Laguna Tools SmartShop 5-axis CNC.
The Complexities of 5-Axis Machining
CNC machines can achieve their 5-axis capability in one of two ways: they can swivel the tool head, or they can move the table and the material.
Swivel head machines maneuver the tool around the fixed block of material to machine around and through the piece and get into tight spaces from different angles. One benefit of this method is that a more massive object can be machined since the block of material remains stationary throughout the process. Take a look at the short video of the Laguna SmartShop III to see a swivel head in action. This method of 5-axis machining is often called 3+2 axis routing.
Other CNC routers can move the material on the table to get their additional two axes. By rotating the piece around one or both of the axes (usually X and Y), there is more speed and stability throughout the operation as the machine makes continuous adjustments to the cutting tool on all five axes to keep the tip perpendicular to the cutting surface. This way of machining is referred to as continuous 5-axis CNC machining.
Take notice of the difference in methods as the Smart Shop III uses a rotating axis to create the stock of a Mossberg rifle in this YouTube video.
The dangers of continuous 5-axis machining
What's the primary advantage of continuous 5-axis machining? Without a doubt, it's the speed. Since there is no need to stop cutting to reposition the part multiple times, continuous 5-axis CNC is faster. So, where does the danger come into the equation? Once again, it's the speed.
Anyone who has ever watched for the first time as a 5-axis CNC machine goes through its cycle cannot help but be thoroughly amazed by the speed of these mills. For those who cut their teeth on manual machines, the speed is frightening initially. Seeing a tool move toward the workpiece in rocket-like rapid traverse and stop within a few millimeters before starting its cut is a cringe-worthy experience.
And once it starts machining, those substantial cuts and flying chips keep you hoping that the person who did the programming was experienced and careful. Programming 5-axis machining is not a user-friendly task: it's complicated from both a mechanical and programming perspective, and expensive collisions are not all that rare.
But the benefits often outweigh the fear factor
As 5-axis technology develops, the process becomes easier to navigate. They are less complicated and safer to operate because all of the complexities have been built into the machine.
And because you can use standard length tools with continuous 5-axis cutting, the tools are more rigid, which allows for higher feed rates and longer tool life. But the most significant advantage is in the saving of labor by minimizing setups and improving quality with less human interaction.
Keep in mind, however, that these benefits come at a price. If you can't take advantage of them, your business might be better served by adding the extra axes to a quality 3-axis router to satisfy the occasional need for 5-axis machining.