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Posted on Jul 10, 2020
Computer numerical control, usually called CNC, refers to a system in which the cutter head moves along a predetermined path to complete various tasks (such as drilling, cutting, printing, or milling).
In the manufacturer's community, the term "CNC" is often used to indicate CNC milling, that is, the process with the spindle as the tool head. However, it is worth noting that CNC can be used not only for milling, but also for more uses.
For the purpose of this article, CNC milling is a cutting tool that systematically removes material to produce the final geometry. In this subtraction process, the computer converts the CAD design to coordinates, and then converts it into a cutting tool to remove material and display the instructions of the final object.
Five-axis CNC milling machines are simply advanced variants of ordinary milling machines in which the cutting tool moves along five different axes simultaneously. Only thanks to this freedom of movement can complex geometries be created. Ordinary 3-axis CNC machines, popular among enthusiasts, simply cannot move the cutting spindle in any way that will create, for example, partial cavities and overhangs without manually adjusting the material midway through the process.
Typical materials for CNC milling:
● carbon fiber
● wood (artistic and design applications)
Due to the ability to manufacture complex parts from strong, durable materials, the 5-axis CNC is a common production and prototype solution in the aviation industry that requires complex parts with exceptional strength.
Mathematical readers in the audience may wonder where exactly the two additional axes come from. After all, the Cartesian coordinate system has only 3 axes: X, Y and Z. But it's really very simple: a 5-axis CNC adds one additional "axis" of rotation around each of the X and Y axes.
The diagram above shows six axes. Rotation around the vertical Z axis exists on some machines, but in fact 6-axis CNC milling machines are a rare breed because the sixth axis brings little benefit.
:: See products: 5 Axis Machining Centers
There are two mechanical ways in which CNC milling machines can achieve 5-axis efficiency:
rotate the tool head
move the table (and material block)
Machines with a swivel head, as the name implies, can maneuver the tool head around a block of material to get into tight spaces at different angles. One of the advantages of this method is that you can machine a larger, heavier workpiece because the block of material remains stationary throughout the process.
On the other hand, CNC mill that moves the object on the table, also called pin, achieve an additional two axes of freedom by turning the table on which the material is placed. The advantages of this approach are speed and stability, although objects that are too large or heavy cannot be rotated in this way.
But 5-axis CNC mill has some complications, especially when milling things. For example, there is a clear distinction between the two approaches used to achieve 5-axis cutting capabilities: the continuous method and the 3 + 2 axis method. The names give definitions, somehow.
The continuous 5-axis CNC system requires continuous adjustment of the cutting tool in all 5 axes to keep the tip optimally perpendicular to the cutting surface. In contrast, the 3 + 2 method locks the element at an angle determined by the rotation axes around X and Y, while the tool head moves in 3 axes to cut the part.
:: Read more: Why You Need 5 Axis Machining Centers?
Perhaps you are wondering what are the main advantages of continuous CNC? Speed. No need to interrupt cutting to change the orientation of parts multiple times during the process, continuous 5-axis CNC mill is faster. It is worth noting, however, that the constantly moving tool head requires more moving parts (higher wear) and advanced collision detection. Thus, it’s more complicated mechanically and programmatically to execute successfully.
This raises an important issue in the 5-axis world: collisions. With heavy cutting tools and pieces of material flying at high speed all over the place, it is very important to make sure that nothing collides. But teaching the machine how to track where everything is in 3D space proves to be a great software challenge.
Speaking of software challenges, converting a 3D design from a CAD software file to a physical tool path is also a big engineering feat. Only some of the most advanced software tools are able to provide really smooth results in the real world.
It's not difficult to see the similarities between 5-axis milling and 3D printing, so you may wonder how these two processes compare. The short answer is: 3D printing and CNC are additions, not substitutes, in which CNC is used for the strongest and hardest parts.
The obvious difference is that the 5-axis CNC system is mainly found in industrial applications. 3D printing is also present in this world in the form of SLS machines that use a laser for the additional production of an object from a large powder bath. Although both are able to work with professional-quality materials such as aluminum, one problem with SLS 3D printing is performance.
Here’s the short version:
Industrial 3D printing can have longer lead times.
CNC milling can reduce raw material consumption for most order sizes.
In the SLS 3D printing process, the entire volume of the print chamber must be filled with powder to produce one part, regardless of its size. Not all unused powders can be reused, because the entire chamber containing the powder must be heated during printing. As a result, print jobs should be queued and stacked systematically to maximize the volume of powder used in each cycle and reduce unused space, as some of that unused powder will simply be wasted.
CNC milling generally has no such restrictions: as long as a block of material is delivered roughly the size of the finished model, the excess will be broken off to get the final geometry, no matter how large or small the model is. Not much material is wasted, provided that the original block of material is similar in size to the final part. In addition, for some CNC materials, such as aluminum, the cut material can even be collected and recycled.
Although not as widely used as SLS, electron beam melting (EBM), another industrial 3D printing method, uses less material. This is because it does not require filling a certain volume, it basically "fires" building material during its creation.
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