Oct. 07, 2024
CNC machines, or Computer Numerical Control machines, exhibit a diverse range of designs and functions, yet a commonality among them is their functionality and reliance on axes. The axis count varies between two to five, with configurations that include linear and rotary axes. The number of axes plays a vital role in determining what a CNC machine is capable of – whether it be the intricate nature of the fabrication process or the dimensions of the parts it can handle, as well as the machine's overall precision.
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This article delves into linear and rotary axes, fundamental concepts that familiarize us with various CNC machine axis configurations seen across different machinery. In addition to this exploration, we will analyze the types of CNC machines based on their axes and assess whether machines with a higher axis count offer superior performance.
The Cartesian Coordinate System, a prevalent reference framework in mathematics and engineering fields such as CAD and manufacturing, is foundational in understanding CNC machinery. Defined by three orthogonal axes intersecting at a zero point, these axes represent the linear capabilities of CNC machines. The linear axes consist of the following:
The X axis allows movement from left to right, parallel to the cutting tool.
The Y axis enables front-to-back movement, perpendicular to the cutting tool.
The Z axis facilitates vertical movement from top to bottom, also perpendicular to the cutting tool.
While familiarity with the linear axes is typically drawn from mathematical concepts, machining introduces an additional set of axes known as rotary axes – namely, the A, B, and C axes. These rotary axes augment the machine's capabilities by facilitating the cutting tool's access to more sides of a workpiece and enhancing fabrication efficiency. This is accomplished by permitting the part to rotate, altering its orientation in relation to the tool.
The relationship between rotary and linear axes becomes clearer through the following movements:
The A axis denotes rotation around the X axis, also referred to as the tilt axis.
The B axis indicates rotation about the Y axis.
The C axis signifies rotation around the Z axis.
Conceptually, rotary axes are linked to the rotational motion around linear axes via a rotary table, allowing the cutting tool to access different angles and enabling features to be machined on additional sides of a part.
Understanding a CNC machine's axis serves to represent the direction and plane through which a feature on a workpiece can be machined. It is essential to note that "side" can refer to internal surfaces aligned parallel to the exterior faces of a shape, not simply the external surfaces themselves.
A CNC machine designated as a 2-axis machine can engage with features on only two sides of a workpiece simultaneously. This generally involves movements along two linear axes. Conversely, a 3-axis machine operates similarly but can interact with three sides of the workpiece at the same time, allowing for length (X), width (Y), and depth (Z) corrections through its movement capabilities.
Implementing rotary axes results in the emergence of 4-axis and 5-axis CNC machines, termed multi-axis machines. Following this principle, a 4-axis machine can manage work on four sides at once, while a 5-axis machine allows manipulation across five sides. The versatility of multi-axis machines—in contrast to their 2-axis and 3-axis counterparts—comes from their ability to reposition both linearly and rotationally, showcasing greater adaptability and broader access to various surfaces.
The designation "2-axis CNC machine" indicates that its operations traverse along two axes. Depending on the machine type and the orientation of the operational work envelope, these axes typically comprise either the X and Y axes, X and Z axes, or Y and Z axes.
CNC lathe machines and turning centers predominantly fit into this classification, executing movements mainly along the X and Z axes. For example, within this system, the chuck manipulates the workpiece while rotating around the Z axis, whereas the cutting tool translates along both the X and Z axes.
The movements performed by the cutting tool relate the X axis to inward or outward functions, while the Z-axis pertains to longitudinal movements, enabling the classification of such machines as 2-axis CNC machines.
Several leading manufacturers, including Haas with the ST-series and Knuth with the Forceturn series, offer high-performing CNC lathe machines and turning centers. Additional examples among 2-axis machines include some compact vertical milling and high-precision grinding machines.
Commonly found in CNC milling configurations, 3-axis CNC machines secure the workpiece via a vise anchored to a moving table. This table traverses along the X and Y axes while the milling or drilling tool operates along the Z axis. The combined movements permit the simultaneous removal of material across the workpiece's length, width, and depth.
This configuration is well suited for producing simple parts with minimal features; however, it also accommodates more complex items although potentially incurring longer machining times compared to multi-axis machines.
Commercial examples of 3-axis CNC machines include units like the EC-ZT, VF-1, and VF-2SS from Haas Automation, Knuth's BO 90 CNC and BO T CNC 110 series, Huron's VX8, and Okuma's GENOS M series.
Possessing four operational axes, 4-axis CNC machines boast capabilities akin to 3-axis systems, but with the added function of rotational movement around one of the existing linear axes. This feature typically comes via a 4th-axis rotary indexing table or a swivel head that can rotate around a designated axis.
Rotary indexing tables include built-in systems with motors to facilitate movement around a fixed axis, allowing for new surface exposure for machining – a process denoted as indexing. Parts affixed to fixtures on these tables rotate according to CNC programming generated by CAM software, enhancing versatility.
Notably, rotary tables come in various configurations, including right-hand, left-hand, or bottom types, accommodating various sizes and styles of parts. Not all 4-axis machines utilize rotary tables; some employ swivel heads paired with stationary tables, enabling tilt rather than full rotation.
5-axis CNC machines integrate a total of five axes, which encompass the three principal linear axes (X, Y, and Z) in addition to two rotary axes (A, B, or C). This amalgamation results in various types of 5-axis machines based on their mechanics:
Swivel-rotate-style 5-axis CNC machine
Trunnion-style 5-axis CNC machine
These machines include a swivel head enabling tilt around the B-axis, complemented by a rotary table functioning on the A or C axis, allowing for a 360-degree rotation. This configuration proves advantageous for machining heavy parts while minimizing tool interference concerns.
Examples of such machines encompass the Hurco VMX60SRTi and VMX42SRTi.
Trunnion-style machines incorporate dual-axis rotary tables, enabling the part’s orientation to adapt to the cutting tool, thereby exposing up to five sides of a component for machining. While these machines allow extensive rotations, streamlined performance can be curtailed due to potential interference and weight limitations.
Noteworthy examples include Hurco’s VC500i and VCX600iXP models, along with Haas’ VR and UMC series.
Machines classified as multi-axis typically feature an axis count exceeding three, meaning they include up to two rotary axes alongside the primary three linear axes. Correspondingly, the advantages of multi-axis machines over traditional two or three-axis machines include:
Reduction in setup instances, enabling tools to access more facets of the part.
Pare down cycle time significantly, enhancing overall throughput.
Higher precision, thereby minimizing human error by lessening loading instances and setups.
Despite their advantages, multi-axis CNC machines come with some drawbacks to consider:
Increased acquisition costs compared to traditional CNC systems.
Higher potential for collisions between machine components during operation, particularly in trunnion-style setups.
While expense is often a deciding factor, ensuring safety measures to prevent interference during machining processes is also paramount. Inspections after setup or utilizing extended tooling can improve outcomes and mitigate risks of collisions.
The question arises – are higher CNC machine axis counts superior? Haas Automation conducted a study comparing machining identical parts with 3-axis and 5-axis machines to highlight differences. The resulting insights indicated that the 5-axis configurations reduced machining time by 26.6%. Furthermore, fewer setups were required with the 5-axis machine compared to the 3-axis system, leading to lower instances of human error.
Additionally, due to the constant need for tool changes with 3-axis machines, longer cycle times were noted as compared to the 5-axis counterpart, which performed all requisite operations in fewer setups and significantly curtailed manual intervention.
When selecting a CNC machine, various facets such as cost, functionality, part complexity, and future plans must be taken into account.
The expense associated with different CNC systems varies widely. While 5-axis machines tend to cost more due to additional accessories, even high-performing 2-axis CNC turning centers may exhibit hefty price tags, rendering cost not always the only determinant in choice.
Despite 5-axis machines proving advantageous for complex machining operations, they may not suit all tasks, necessitating assessment of intended machine functions when determining the axis requirement.
Machined part complexity directly correlates with necessary operations and tools. When intricate features span multiple sides, continuous part orientation changes can be deemed critical. A 3-axis system could prompt time-consuming setups while a 5-axis system would minimize this, enhancing accuracy significantly.
Consider future objectives for your machine shop. Should expansion or increased operational efficiency be your goals, selecting a machine adaptable for upgrades is prudent, such as introducing fourth and fifth-axis capabilities later on.
Each CNC machine's design incorporates distinct axis counts, contributing to its capabilities, influenced by linear (X, Y, Z) or rotary (A, B, C) components. While some machines are limited to factory settings, accessory options exist to expand capabilities further. It’s clear that the number of axes within a CNC machine greatly impacts functionality, making it a vital consideration for specific applications, driven by operational objectives, complexity, and other pivotal elements.
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