CNC machining: Everything you need to know II

Jack Lie CNC machining expert

Specialize in CNC Milling, CNC Turning, 3D Printing, Urethane Casting, and Sheet Metal Fabrication Services.

CNC machining axis

A CNC machining axis is one of the many axes a Computer Numerical Control machine can work on.

For a better understanding, remember that a CNC machine performs different cutting operations on a workpiece based on the program created to manufacture such piece. The instructions given by the program normally include:

  • Type of operation (milling, turning, drilling, etc.)
  • Tool selection
  • Movements or route to follow in order to achieve the desired results

Therefore, a reference is needed for the last point above and here is where the CNC machining axis becomes relevant. Most machines move along the 3 axes of the XYZ plane (Vertical, Horizontal and Depth) which is the most obvious way to position the tool for simple operations. However, some operations require more complex movement, like rotation around the X axis and rotation around the Y axis which introduces axis number 4 and axis number 5 respectively.

Clearly, the more axes the CNC machine can use, the more it can achieve. This determines the type of work, the amount of detail and the locations that can be processed.

Currently, the most innovative and powerful CNC machines include 6 and even 7 axes which we will be discussing here below.

4 axis CNC machining

As it was mentioned above, 4 axis CNC machining involves rotation around the X axis, and this added axis is known as the A axis.

This makes the 4 axis CNC machining a good solution when operations are required along an arc or on the surface of a cylindrical piece. Also, 4 axis CNC machining usually allows the workpiece to rotate while in operation, making it possible to work as a milling machine and a lathe at the same time.

4 axis CNC machining can happen in one of two modes. These modes are:

  • Indexing: the operation takes place when the rotational movement on the 4th axis is stopped and secured by the machine’s braking system. This is commonly applied for gears and similar pieces, where the same operation is required along an arc or a cylinder with high precision.
  • Continuous: the operation takes place while the piece is in constant rotational motion. This is more useful for features that cover the whole surface of the cylinder, such as camshaft lobes.

Apart from the possibility to cover the rotation on the X axis, 4 axis CNC machining provides important benefits such as process speed and reduced setup, which in turns results in higher productivity and profitability.

5 axis CNC machining

Similar to the 4 axis CNC machining, the 5 axis CNC machining introduces a new rotational movement to the capabilities of the machine. In this case, the rotation takes place around the Y axis, as it was described before.

The new added axis is normally known as B axis, and together with the other 4 axes, it allows the possibility to achieve even more complex geometries with features that would not be possible to produce using manual machining resources.

For 5 axis CNC machining you can find three types of machines. They are classified depending on the arrangement of the rotational axes. These are the three types:

  1. Head-Head: this type of 5 axis CNC machine includes both rotational axes in the head that holds the tool. Therefore, the operations take place while the piece is fixed on the table and the tool moves and rotates along the 5 axes.
  2. Table-Head: as the name suggests, the rotational axes are distributed, one in the head and the other in the table. This type usually has the advantage of allowing the rotation of the workpiece on the table without limits.
  3. Table-Table: clearly, both rotational axes are found in the table. It is not the most common arrangement, and it is usually limited to a small group of applications.

5 advantages provided by the 5 axis CNC machining which can be highlighted are:

  • Reduced setup
  • High rotational precision
  • Possibility of complex geometries
  • Fast material removal
  • High-quality surface finish

6 axis CNC machining

As you can imagine now, 6 axis CNC machining means that there is a new added axis in this manufacturing process. And yes, it is another rotational axis.

This time, the rotation is added around the Z-axis, and it means a significant increase on process speed when compared to the 5 axis CNC machining. Some experts claim that 6 axis CNC machining can reduce cutting times by 75%.

Moreover, big 6 axis CNC machines make it very easy to process big workpieces smoothly and with high precision, which is why 6 axis CNC machining is the preferred solution for engine blocks and turbines production, for example.

Adding to the previous point, there are innovative 6 axis CNC machines come with one or more turrets and the possibility of automate the tool changes.

So, who would care for the previous types of machining if this sounds so perfect? Well, there is a drawback out of 6 axis CNC machining, it is highly expensive. The level of complexity make these machines costly for workshops with simple job requirements, which is why 6 axis CNC machining is only used in demanding sectors such as the aerospace industry which can justify the expenses.

7 axis CNC machining

Although we already saw that 6 axis CNC machining is a very complex configuration for manufacturing, and that it is usually limited to industries that can justify the cost, we still have one more step in CNC machining complexity, the 7 axis CNC machining.

So far, we have spoken about 6 axes, 3 linear axes and 3 rotational axes which are:

  • The X axis (vertical movement)
  • The Y axis (horizontal movement)
  • The Z axis (depth movement)
  • The A axis (rotating around the X axis)
  • The B axis (rotating around the Y axis)
  • The C axis (rotating around the Z axis)

For the 7 axis CNC machining we add a new one, which is called the E axis. This new axis allows the freedom of moving the arm of the machine in a twisting motion.

The main benefits of 7 axis CNC machining include:

  • High efficiency
  • Possibility of the achieving even the most complex and detailed geometries
  • No post-processing needed
  • The highest process speeds

However, there are some limitations too. And the biggest of them is that it is even more expensive. Again, this means that it is only used for applications that justify the high cost.

CNC machining medical devices

CNC machining medical devices requires very high precision and working with special materials, including those called biocompatible materials. This is important to comply with the most demanding standards, such as the ones established by the Food and Drug Administration or FDA in the United States of America.

Common medical devices produced by CNC machining include, but are not limited to:

  • Surgical tools
  • Hip and other type of implants
  • Monitoring devices components
  • Orthopedic devices
  • Stents
  • Catheters

Due to the level of precision required, 5 axis machining, 6 axis machining and 7 axis machining are common in this sector.

However, due to recent developments and medical requirements, surgical tools and other type of devices that are used in surgical processes must be very small, sometimes to microscopic levels and with very tight tolerances to make those surgeries as minimally invasive as possible.

Common examples of this microscopic requirements are:

  • Implantable surgical plates
  • Surgical and bone screws
  • Drills and reamers

To achieve these requirements, it is necessary to use a specialized CNC machining solution. Here is where the CNC Swiss screw machining and similar options become relevant, since they can achieve micro-machining with tolerances as tight as to the 0.0125 mm (0.0005”) range.

CNC Swiss screw machining

The first thing to mention about the CNC Swiss screw machining is that the machine is also known as Swiss lathe, which means it is a type of lathe. The main different to regular lathes is that CNC Swiss screw machining is capable of manufacturing very small parts with high level of detail and complex geometries.

Although CNC Swiss screw machining is not limited to the production of screws, it takes the name from the fact that Swiss watchmakers created these machines to manufacture very small and accurate screws for their watches.

CNC Swiss screw machining works by holding the workpiece and rotating it (like a lathe) while different tools process it from different angles, although such rotation may not be necessary for the tools to do the work.

Another difference with the standard lathe is that Swiss lathes are able to move the workpiece in the Z axis, so the tools can stay in the same position instead of moving along the piece.

The main benefits provided by CNC Swiss screw machining are:

  • Maximized efficiency
  • Highest levels of precision
  • Tightest possible tolerances, in the range of 0.0002 to 0.0005 inches
  • Continuous operation after setup. Even 24/7 operation for large runs

Common applications include:

  • Automotive industry
  • IT components
  • Agriculture small parts
  • Electronic components
  • Aerospace industry
  • Medical devices

Glass CNC machining

There are simple glass cutters that help you get clean cuts when the geometries are simple. However, there are some applications that require cutting glass in complex geometries and those are the ones using glass CNC machining.

For example, glass and other special materials are commonly used in optical components with complex geometries. This is an industry that definitely benefits from using glass CNC machining.

Glass CNC machining enables the possibility to achieve the desired results without completely breaking the glass. Common geometries that can be achieved include:

  • Specialty counterbores
  • Bevels
  • Chamfers
  • Steps
  • Slots

Apart from high precision and repeatability, glass CNC machining provides the following benefits:

  • Complex geometries are possible
  • Supervision requirements are reduced
  • Continuous operation
  • High process speed

Again, the only limitation that could be found for glass CNC machining is the cost. For example, it may not be worth the investment to produce simple spherical lenses, but it will definitely make the cut when it comes to more complex components that require high precision and tight tolerances.

Besides the optics industry, other industries benefiting from glass CNC machining include:

  • Defense and aerospace
  • Biotechnology
  • Semiconductor
  • Medical devices

Aerospace CNC machining

Aerospace CNC machining allows compliance with the highest standards found in this industry. Both special materials and very tight tolerances are required to make sure the components do not fail when in flight, so standard manufacturing process cannot cope with these demanding requirements.

It is important to highlight that aerospace CNC machining has evolved into a very advanced solution to reduce and even eliminate the risk of human error while producing high-precision components for this industry, where a simple flaw may result in disaster

Common materials processed by aerospace CNC machining are:

  • Lightweight metals such as aluminum and stainless steel
  • High-performance plastics
  • Different composites

Aerospace CNC machining is capable to deal with those materials, including when the material is naturally difficult to process or the application requires features such as thin walls or surfaces with geometries that are prone to deformation.

The main benefits obtained by the aerospace industry include:

  • Components with high-quality materials and great surface finish
  • Custom designs can be manufactured
  • Increased production speeds
  • High precision levels
  • Increased repeatability

Common components produced by aerospace CNC machining include:

  • Plane engine
  • Hydraulic manifolds
  • Transmissions
  • Fuel bodies
  • Landing gears
  • Electrical connectors
  • Housings

CNC plastic machining

It is well known that plastic has become a very popular material in different applications. As a result, different manufacturing processes have been developed to use this material, and one of them is CNC plastic machining.

CNC plastic machining is the go-to solution when the plastic component is difficult to form directly or high-precision and complex features are required.

Another important aspect of CNC plastic machining is that it achieves high-quality, mirror-like surface finishes that are not possible with other plastic manufacturing processes.

However, there are some things to consider when performing CNC plastic machining in order to achieve the desired results. Here are some:

  • Cutting tools: carbide tools are usually recommended, although high-speed steel can do the work too.
  • Cutting parameters: it is important to keep the tool moving to avoid chips from melting on the piece or the tool, so feeds are usually big and the rotation of the speed should be high.
  • Part setup: avoid high pressures to hold the part since it could break in the process. Some padding is recommended.