CNC machining has changed the world of manufacturing. While milling machines — devices that use rotary cutters to cut material away from an unshaped “workpiece” — have existed since the nineteenth century, the emergence of CNC (computer numerical control) technology in the mid-twentieth century has made machining much faster and more accurate.
Today’s CNC machines, which use computers to control the movement of the cutter and/or table, are highly advanced pieces of equipment that allow manufacturers to create complex parts with extremely low tolerances.
However, with all the different CNC machining options out there, it can be difficult to know where to start. Different parts require different machining processes depending on their shape, size, quantity and end purpose, so choosing the right CNC process is rarely a straightforward task.
One of the biggest questions for companies using CNC machines concerns the number of axes offered by the machine. 3-axis, 4-axis and 5-axis machines are all frequently used, but what is the practical difference between them? And more importantly, which should you use for your part?
What are the CNC machine “axes”?
Getting your head around the multiple “axes” of machining can be confusing — and for good reason.
The concept is confusing because, intuitively, it seems that three axes could cover all possible shapes. By having a cutter that can move along the X, Y and Z axes (side to side, back and forth, up and down), a machine should be able to cut a workpiece at any point on its surface. By manually reorienting the workpiece on the table at certain intervals (creating a new “set-up”), the machine operator can also allow the cutting tool access to any side of the workpiece.
But while many CNC machines use only three axes, and while the kind of three-axis CNC machining described above can be sufficient for many projects, there are other axes to be exploited too.
These extra axes are the result of rotation around one or two of the X, Y and Z axes, taking account of not just position, but orientation as well. In practical terms, these axes can be exploited by either rotating the cutting tool or tilting the table holding the workpiece.
Why are 4-axis and 5-axis CNC machines useful?
Having a CNC machine with these extra axes presents many advantages. Since they can cut the workpiece from different angles, 4-axis and 5-axis machines can complete a part in a shorter timeframe, with less of a need for multiple set-ups. This has the knock-on benefit of eliminating incorrect alignment — a risk every time the workpiece has to be manually reoriented for a new set-up.
Another related benefit of multi-axis machining is how it eliminates the need for complex fixtures, generally needed to hold parts in place on 3-axis machines.
From a client’s perspective, however, the biggest advantage of 4-axis and 5-axis CNC machining is how it can produce extremely complex shapes to a very high standard. With the extra axes, the machine can move in new arcs and angles with greater reach and flexibility. This ultimately results in the ability to create a wide range of unusual geometries.
Additionally, by having a machine that can orient its cutter at any angle, the job can be programmed to cut the workpiece in the most efficient manner — coming at an angle that will provide optimal cutting speed and chip removal, resulting in a higher quality of the finished part.
The arrangement is also ideal for producing contoured surfaces. With a 3-axis machine, a curved edge requires multiple small cuts which can take a long time to carry out and which rarely leave the perfect finish. But with a multi-axis machine, gradual rotation — adjustment of the fourth or fifth axis — can produce near-perfect contours with a smooth finish.
5-axis machining or 3+2?: A Short Guide to Finding the Right Fit
When it comes to cutting tools, one of the main considerations you have to make is in choosing how many axes are appropriate for your workflow. You can settle for a 3-axis system for relatively simple jobs, but for more complex parts you may need an upgrade. That’s where 5-axis and 3+2 axis machines come in.
While 5-axis machining is somewhat of a perennial favorite, 3+2 also has its own particular place and serves up some distinct advantages. 3+2 or 5-axis indexed (or any of its various alternatives titles) is a form of machining that has found popularity among mold shops and companies with less complex print requirements.
So let’s take a closer look:
The core differences between the two technologies come down to angling and continuous versus indexed machining. This means that 3+2 machining or 5-axis “indexed” machining does not maintain continuous contact of the cutting tool and work piece through all rotational axes. Contrary to this mode of machining, simultaneous or true 5-axis machining uses the machine tool’s three linear axes (X, Y and Z) and two rotational axes (A and B) at the same time, resulting in more complex contour surface machining.
In terms of code, 3+2 machining generally uses less complex G-codes as well. Many 5-axis machining software providers include provisions for 3+2 machining. However, 3 + 2 machining simplify tool motions because it effectively is a three-axis machine without the “twists and turns” of the spindle head to maneuver the cutting tool.
What users may want to keep in mind is that they should evaluate the collision avoidance and program simulation capabilities of the CAM software. Still, one of the reasons 3+2 has been able to get so popular is the extensive available programming utilities that have cropped up, so it should not be that much of a hurdle.
In terms of common advantages, they both bring in dimensional stability due to fewer set-ups and improved surface finish using shorter tooling. The 3+2 process uses the same 3-axis control for the milling process, but the machining table can reorient and rotate in two additional directions. As a result, the machined object can be processed from all sides, decreasing the need for set ups and cutting the overall cost. The lower cycle times also reduce costs during operation for both technologies.
As anyone can guess, processing parts from all five sides using a single setup requires less preparation, and benefits from much shorter lead times while operating with better accuracy and eliminates the need to shift your objects from one piece of equipment to the other.
5-axis machining may provide more complex end products overall, but there are certain ways 3+2 axis stands out. 3+2 axis machining is great for parts without require extreme contour controls like jigs, fixtures, housings and other such components. If you need to manufacture a design with extremely fine features, true 5-axis machining may be best for you.
5-axis machining is particularly useful for automotive, aerospace or medical parts due to the improved quality and finishing it provides. Simply put, tighter tolerances and more complex geometries are more appropriate for 5-axis machining. However, this isn’t the end of the discussion. As mentioned, earlier there are some distinct benefits to 3+2 axis machining that can make it more desirable.
For one thing, it is cheaper than 5-axis machining. Common applications for 3 + 2 operations include roughing and other aggressive high-speed machining techniques. The shorter tool length also enables undercuts in cavities and steep walls, a capability well suited for moldmaking and other work-piece applications involving curves or angled tubular shapes. In comparison with conventional 3-axis machining, 3+2 machining utilizes a shorter, rigid cutting tool that can be angled toward the work surface for faster feeds and speeds. . It also embodies a lot of the advantages of 5-axis machining without the heftier price tags, although 5-axis machines have come a long way in terms of price in the past few years.
In certain cases both technologies can be used in tandem. For example, 3 + 2 machining may be applied for roughing operations, and followed up with simultaneous five-axis machining for finishing operations. Due to the shorter tool length allowed by 3 + 2, it lends itself to more aggressive high speed machining techniques such as this. 3+2 axis machines can also effectively perform rest machining in a lot of instances.
At the same time, 3+2 systems and setting should not be thought of as a substitute for simultaneous five-axis machining. There are certain geometries that absolutely require 5-axis systems, such as flat-nosed end mills for producing sharp corners in cavities. As 3+2 machining generally uses a ball-nosed end mill similar to those in 3-axis machining, this set-up can be a downgrade. Various other cutting modes using cutting tools with conic, lollipop or other special geometries may require full five-axis motion to get precise results.
Both 5-axis and 3+2 axis machining have a place within manufacturing. It’s just a matter of choosing what’s most suitable to one’s own workflow, level of investment and end product.
Which process is right for me?
Since 4-axis and 5-axis machines can produce highly complex parts, they are often favored by clients in high-budget, high-stakes industries like the aerospace sector. However, a multi-axis setup is not necessary for every job.
If cost is the number one priority, 3-axis machining is likely the best option. 3-axis machines are cheaper to purchase and require less skill to operate, so 3-axis machining of a part tends to be cheaper than one of the more advanced processes. And even if cost is no concern, extremely simple shapes are sometimes best left to 3-axis machines as well.
When neither of those criteria apply, the decision becomes trickier. And that’s why it’s often best to consult an expert in CNC machining for advice on what kind of machine is appropriate for a given job.
Prototyping specialist 3ERP is one of China’s leading CNC machining companies, and one of a select number that can offer 4-axis and 5-axis machining in addition to the more common 3-axis variety. Its HAAS CNC milling machines are some of the best available, and the company’s engineers have many years of experience in the field. 3ERP also offers a wide range of materials, including plastics like ABS, Teflon and PEEK, and metals like Aluminum, Steel and Titanium.