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How 4- and 5-axis CNCs produce complex parts

CNC machining has transformed manufacturing. While milling machines—devices that use rotating cutters to cut material from an unformed "workpiece"—have been around since the 19th century, the advent of CNC (Computer Numerical Control) technology in the mid-20th century made machining faster and more accurate of.

Today's CNC machines, which use a computer to control the movement of the tool and/or table, are highly advanced devices 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 final purpose, so choosing the right CNC process is rarely a simple task.

One of the biggest issues facing companies using CNC machines is the number of axes the machine offers. 3-axis, 4-axis, 5-axis machines are all commonly used, but what is the practical difference between them? More importantly, which should you use?

What is the "axis" of a CNC machine tool?

It can be confusing to wrap your mind around the multiple "axes" of machining - and for good reason.

This concept is confusing because, intuitively, the three axes seem to cover all possible shapes. The machine should be able to cut the workpiece at any point on its surface by using a tool that can move along the X, Y and Z axes (left and right, back and forth, up and down). Machine operators can also allow the cutting tool to approach either side of the workpiece by manually reorienting the workpiece on the table at regular intervals (creating a new "setup").

However, while many CNC machines only use three axes, and the aforementioned three-axis CNC machining is sufficient for many projects, there are other axes that can be developed.

These extra axes are the result of rotations around one or both of the X, Y, and Z axes, taking into account not only the position but also the orientation. In fact, these axes can be utilized by rotating the cutting tool or tilting the table holding the workpiece.

Having a CNC machine with these extra axes has many advantages. Because they can cut the workpiece from different angles, 4-axis and 5-axis machines can complete a part in less time without multiple setups. This has the knock-on advantage of eliminating incorrect alignment - a risk every time the workpiece has to be manually re-adjusted for a new setup.

Another related benefit of multi-axis machining is how it eliminates the need for complex fixtures, often required to hold parts in place on 3-axis machines.

However, from the customer's point of view, the biggest advantage of the 4-axis sum is its ability to produce extremely complex shapes to a very high standard. With additional axes, the machine can move in new arcs and angles with greater range and flexibility. This eventually led to the ability to create a variety of unusual geometric shapes.

Additionally, by having a machine that can position the cutter at any angle, the job can be programmed to cut the workpiece in the most efficient way - entering at an angle that provides the best cutting speed and chip removal, resulting in a higher quality workpiece completed part.

This arrangement is also ideal for producing contoured surfaces. For 3-axis machines, curved edges require multiple small cuts, which can take a long time to complete and rarely leave a perfect finish. But with multi-axis machines, gradual rotation—adjusting the fourth or fifth axis—can produce near-perfect contours and smooth surfaces.

5-axis machining or 3+2: a short guide to finding the right fit

When it comes to cutting tools, one of the main factors you must consider is choosing the number of axes that is right for your workflow. For relatively simple jobs you can use a 3-axis system, but for more complex parts you may need to upgrade. This is where 5-axis and 3+2-axis machines come in.

While 5-axis machining has been the most popular to some extent, 3+2 is also unique and offers some distinct advantages. 3+2 or 5-axis indexing (or its various alternatives) is a popular form of machining in mold shops and companies with less complex printing requirements.

Workflow Differences

The core differences between the two technologies boil down to angular machining and continuous versus indexed machining. This means that 3+2 machining or 5-axis "indexing" machining does not maintain continuous tool and workpiece contact through all axes of rotation. In contrast to this type of machining, simultaneous or true 5-axis machining uses the machine's three linear axes (X, Y, and Z) and two rotary axes (A and B) simultaneously, resulting in more complex contoured surface machining.

In terms of codes, 3+2 machining usually also uses less complex G codes. Many 5-axis machining software vendors include provisions for 3+2 machining. However, 3+2 machining simplifies tool movement because it is effectively a three-axis machine, without the "twist and turn" of the spindle head to steer the tool.

What users may want to keep in mind is that they should evaluate the CAM software for collision avoidance and program simulation capabilities. Still, one of the reasons 3+2 has become so popular is the abundance of programming utilities available, so it shouldn't be a hindrance.

Five Axis and 3+2 Similarities

In terms of common advantages, they both bring dimensional stability due to fewer setups and improved surface finish with shorter tooling. The 3+2 process uses the same 3-axis control for the milling process, but the table can be reoriented and rotated in two additional directions. As a result, the machined object can be machined from all sides, reducing the need for setup and reducing overall costs. Shorter cycle times also reduce operating costs for both technologies.

As anyone can guess, using a single setup to process all five aspects of a part requires less preparation and benefits from shorter lead times while operating with greater precision and without removing your objects from Transfer from one device to another.

Special application

5-axis machining may provide a more complex end product overall, but 3+2-axis stands out in some ways. 3+2 axis machining is ideal for parts that do not require extreme contour control, such as jigs, fixtures, housings and other such components. If you need to manufacture designs with extremely fine features, true 5-axis machining may be best for you.

Because 5-axis machining provides higher quality and finishing, it is especially useful for automotive, aerospace or medical parts. In short, tighter tolerances and more complex geometries are better for 5-axis machining. However, this is not the end of the discussion. As mentioned, 3+2 axis machining has some obvious benefits that could make it more popular.

On the one hand, it is cheaper than 5-axis machining. Common applications for 3+2 operations include roughing and other aggressive high-speed machining techniques. The short tool length also enables undercutting on cavities and steep walls, a capability ideal for mold making and other workpiece applications involving curved or angled tubular shapes. Compared to traditional 3-axis machining, 3+2 machining uses a shorter rigid cutting tool that can be tilted toward the work surface for faster feeds and speeds. . It also embodies many of the advantages of 5-axis machining, but without the higher price tag, although 5-axis machines have come a long way in terms of price over the past few years.

In some cases, both techniques can be used simultaneously. For example, 3+2 machining might work for roughing operations, followed by five-axis simultaneous machining for finishing operations. Since 3+2 allows for shorter tool lengths, it is suitable for more aggressive high-speed machining techniques such as these.

3+2-axis machines are also effective for residual machining in many cases.

At the same time, the 3+2 system and setup should not be considered a substitute for 5-axis simultaneous machining. Certain geometries absolutely require a 5-axis system, such as flat end mills for machining sharp corners in pockets. Since 3+2 machining typically uses a ball nose end mill similar to 3-axis machining, this setup can be degraded. Various other cutting modes using cutting tools with cones, lollipops, or other special geometries may require a full five-axis motion for accurate results.

5-axis and 3+2-axis machining has a place in manufacturing. Simply choose the method that best suits your workflow, investment level and end product.

Which process is right for me?

Because 4-axis and 5-axis machines can produce highly complex parts, they are often favored by customers in high-budget, high-risk industries such as aerospace. However, not every job requires a multi-axis setup.

If cost is the number one priority, 3-axis machining may be the best choice. 3-axis machines are less expensive to purchase and require less skill to operate, so 3-axis machining of parts tends to be less expensive than a more advanced process. Even regardless of cost, it is sometimes best to leave extremely simple shapes to 3-axis machines.

When neither criterion applies, decision-making gets trickier. This is why it is usually best to consult a CNC machining expert for advice on the type of machine suitable for a given job.

Xiehe is one of the leading CNC machining companies in China and one of the select companies that can offer 4-axis and 5-axis machining in addition to the more common 3-axis variety.