Computer Numerical Control (or CNC) machining combines the efficiency of computer programming with the accuracy of lathe machines. The programmed software controls the movement of tools and other machines, automating the manufacturing process and keeping the design consistent.
Modern multi-axis CNC milling machines come with a wide range of features that add value and functionality. However, these are only useful if the machine can move seamlessly along its axes. Moreover, these axes are primarily responsible for maintaining accuracy in forming the feed. Thus, they are essentially the life and blood of any milling machine. Let’s take a look at the functions and capabilities of various multi-axis CNC milling machines.
3-axis CNC machining
3-axis CNC machining evolved from rotary filing. Here, the workpiece occupies a stationary position while the cutting tool moves along the X, Y and Z axes. The X axis is together with the rotary table, the Y axis is toward the front/back of the table and the spindle falling from the top to the bottom marks the Z axis. It is ideal for simple tasks that do not require intricate detail or depth. As such, it is one of the most preferred techniques for making mechanical parts for automation. You also use it for cutting sharp edges, boring, milling slots, tapping and drilling holes. 3-axis machining has the following limitations:
- It operates in a complex programming environment;
The initial capital investment and installation costs are high;
It requires highly skilled professionals to operate and maintain the machine.
4-axis CNC machining
The 4-axis CNC functions much the same as its 3-axis counterpart. The feed is in a stationary position and the cutting tool works to remove the excess material and form the desired part. As the name implies, 4-axis machining includes an additional axis in addition to the usual X, Y and Z planes. This additional motion is present in the form of rotation along the X axis, which forms the fourth plane – the A axis (horizontal). However, cutting can also take place along the B axis (vertical). But since horizontal machining is considered more productive than vertical machining, the former is more common. This milling technique is useful for cutting holes, cutting along an arc or cutting out cutouts, especially on the sides or around a cylinder. It is also useful for high-quality precision engraving, milling and drilling. Limitations:
The biggest limitation of the 4-axis milling machine is the Geneva mechanism. Although the Geneva mechanism is quite common because of its simplicity, reliability and precision, it allows the 4th axis only in principle. However, in practice, it does not support continuous machining since it has a fixed set of stops. Therefore, operators can only use the machine as a pure indexer. Other disadvantages include:
- Rapid wear of the worm gear mechanism, especially during heavy use;
- The problem of backlash can affect accuracy and machine durability.
5-axis CNC machining
The 5-axis CNC milling machine marks the pinnacle of innovation in 21st century machining. It has greater competence than 3- and 4-axis milling machines and is a precise, high-speed powerhouse for micro-machining. In this setup, the X, Y and Z axes are similar to a 3-axis machine layout. The table then rotates along the A-axis, just like the 4-axis. However, the 5-axis machine includes the rotary motion at the joint of the table, followed by rotation along the C axis, which defines the fifth motion. With 5-axis machining, the operator can simultaneously touch five different sides (or more!) Of a part, depending on the complexity of the design. As a result, the tool is highly capable of producing highly accurate products and parts. Therefore, it should come as no surprise that it is widely used in medical technology, research and development, architecture, military, automotive and even creative arts. It is also used in drilling holes at compound angles. Limitations:
Although the 5-axis CNC machine is excellent in terms of speed and accuracy, it has the following problems:
- CAD/CAM programming for 5-axis machines can be extremely complicated, especially if you imagine the spatial trajectory.
- Because 5-axis milling machines are not yet very common, their purchase and maintenance is quite an investment. Similarly, tooling solutions are equally expensive.
- It takes a highly skilled CNC machine operator you can trust with your 5-axis beauty.
7-axis CNC machining
The 7-axis CNC milling machine can make long, slim and heavily detailed parts. The 7-axes involved are the usual right-to-left, top-to-bottom, back-to-front, followed by axes defined by tool rotation, part rotation, tool head rotation, and movement for clamping, re-tensioning, or part removal. This high degree of movement gives greater accuracy to the final product without the need for post-machining processes.
9-axis CNC machining
The 9-axis CNC combines lathe and 5-axis machining. This allows the part to be turned and milled along several planes in one setup, providing sharp accuracy. One of the biggest advantages of a 9-axis CNC is the elimination of secondary fixtures and manual loading. The 9-axis CNC is highly capable to the point where it can complete a fully finished part in a single operation!
12-axis CNC machining
If 9-axis CNC machining is the whole package, then its 12-axis counterpart is an absolute beast! 12-axis CNC machines typically include two heads that allow movement along the X, Y, Z, A, B and C axes. This configuration doubles productivity and accuracy while reducing production time by half!
Final Thoughts
CNC machining remains relevant and effective to this day. It serves various production-intensive industries and maintains product quality, precision and standardization. As machines gain more axes of motion, they will only get better with each iteration. So while they can be a significant investment, they also promise long-term service in return!
