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Views: 50 Author: Site Editor Publish Time: 2022-01-15 Origin: Site
CNC machining, short for computer numerical control, involves machines controlled by programmed instructions, typically in the form of G-code, directing their movements. These machines encompass various types, including milling machines, lathes, and plasma cutters. This article will explore different variants of CNC mills and lathes, as well as their combinations. Movement in CNC machines is governed by axes, primarily X, Y, and Z for linear motion, with more advanced systems incorporating rotational axes denoted by A, B, and C. CNC machines can operate in up to five axes, offering versatility in machining processes. Below are some common types of CNC machines:
CNC Lathe: Utilizing a rotating chuck, a CNC lathe spins the material while a tool maneuvers in two axes to carve cylindrical parts. Its advanced capabilities enable the creation of intricate curved surfaces, surpassing manual lathe limitations. Additionally, live tooling allows for tool movement during operation.
CNC Mill: Primarily employed for flat part production, CNC mills possess the versatility to fabricate complex shapes with advanced models offering increased degrees of freedom. Material remains stationary as the spindle, carrying the tool, traverses along three axes to sculpt into the material. In certain configurations, the spindle remains fixed while the material moves.
CNC Drill: Functioning akin to CNC mills, these machines are specialized for uni-directional cutting along the Z-axis, solely penetrating the material depthwise without lateral movement along the X and Y axes.
CNC Grinders: Equipped with grinding wheels, CNC grinders achieve superior surface finishes by precisely removing minute material layers from hardened metals. Primarily utilized for finishing operations, they excel in providing high-quality surface textures.
CNC machining operates on the principle of subtractive manufacturing, where material is gradually removed from a solid billet to shape the desired part. This process encompasses techniques such as milling, turning, grinding, and drilling. In contrast, additive manufacturing, exemplified by 3D printing, builds parts layer by layer, adding material from scratch to form the final product.
Tooling in CNC machining plays a crucial role in cutting operations. These tools, housed in tool holders, are inserted into the spindle as needed. Due to the diverse requirements of machining, a variety of tools are employed, each tailored to specific tasks. Common types of mill tools include the versatile end mill, designed for multidirectional cutting, the face mill for surface-facing operations, the thread mill for creating threads, and the slotting cutter for carving t-slots along parts. This diversity underscores the absence of a singular solution for all machining needs.
Moving beyond tooling, CNC machining offers numerous advantages and disadvantages that have propelled its widespread adoption in manufacturing. Let's explore some of these pros and cons below.
CNC machining employs a range of specialized tooling to execute precise operations on workpieces. Among these tools are:
OD Turning: Tailored for outer diameter cutting, this tooling can be solid or utilize carbide inserts for shaping.
ID Grooving & Threading: Slim and flexible, these tools reach inside parts to bore out inner diameters post-drilling and perform threading tasks.
Parting: Employed as the final step, a parting tool cleanly separates finished parts from the workpiece.
Drilling: Utilized to create longitudinal holes in the part, though additional reaming or boring may be necessary to achieve precise tolerances.
CNC machining tools come in a variety of materials, each with its own set of characteristics:
High Carbon Steel: Economical but short-lived, losing hardness around 200°C.
High-Speed Steel (HSS): More durable than carbon steel, maintaining hardness up to 600°C, enabling faster cutting speeds.
Carbide Inserts: Extremely hard with good temperature resistance (up to 900°C), though prone to fracturing if mishandled.
Ceramics: Exceptionally hard, typically used for cutting hard materials at high temperatures. Variants include alumina and silicon nitride.
Cubic Boron Nitride: Ideal for cutting hardened steels and superalloys, boasting excellent abrasion and thermal resistance.
CNC machining has slowly taken over the manufacturing industry as it is simply more efficient than using manually operated machines. Some of the pros and cons of CNC machines are listed below.
Pros | Cons |
Faster than Manual | Expensive |
No human can match the speed, precision and accuracy of a CNC machine. In high production environments, using a manual machine will simply result in financial loss. | A CNC machine is an extremely advanced piece of equipment. It is manufactured to very high tolerances and rigidity. This is to allow it to manufacture millions of parts and still produce a quality result. This quality translates directly into cost; the more advanced the machine the higher its cost. |
Reduced Production Cost | Higher Skilled Operators |
A CNC machine can essentially run non-stop if the loading and unloading of materials and parts is further automated, this means the machine can run overnight with no supervision. Also, one operator can run multiple machines, offsetting higher labour costs. | Despite needing fewer operators, a CNC machine requires highly skilled operators, which will result in a higher labour cost. |
Higher Efficiency | Higher Maintenance Costs |
A CNC machine can move from one operation to the next in a fraction of a second. Tool changes can happen very quickly as some machines have a turret with many tools pre-fitted or a tool library that loads a new tool into the spindle when needed. | Due to the complexity of CNC machines the cost of maintenance is much higher when compared to manual machines. |
Increased safety
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CNC milling machines come in two main configurations:
Vertical Machining Centre (VMC): In VMCs, the spindle remains fixed while the table moves underneath, offering rigidity and precision. However, they typically have a smaller work area. VMCs can feature 3, 4, or 5 axes for versatile machining capabilities.
Horizontal Machining Centre (HMC): HMCs have a horizontally oriented spindle, making them ideal for high-volume production. They can machine significantly more than VMCs but come at a higher cost. HMCs allow for continuous production by fixturing multiple parts on the machine bed and quickly transitioning between workpieces.
A CNC lathe operates in two axes and typically features a single chuck. Various types of CNC lathes include:
Engine Lathe: This type is a versatile lathe, with the term "engine" stemming from historical usage when lathes were powered by external engines via pulleys. An engine lathe denotes a lathe with an integrated motor, distinguishing it from earlier designs.
Turret Lathe: This lathe facilitates rapid production by preloading all necessary tools into the turret before machining, allowing for quick tool changes.
Tool Room Lathe: Ideal for precise, low-volume work, this lathe specializes in crafting tools and dies, offering exceptional versatility.
Speed Lathe: Suited for light-duty tasks, this lathe features a straightforward setup with a headstock, tailstock, and tool post.
CNC Turning Centers: Highly advanced, these lathes boast extensive capabilities such as milling, turret tool posts, and dual spindles. They come in both vertical and horizontal configurations, with horizontal lathes facilitating chip removal via a conveyor and vertical lathes utilizing gravity to secure parts in the chuck. Horizontal lathes are more conducive to automation, and the choice between vertical and horizontal depends on the specific application.
Materials CNC machines can process a diverse range of materials, from aluminum to high-performance superalloys like Inconel. Each material presents unique challenges and demands tailored tooling, cutting speeds, and feeds.
Aluminum Aluminum, being relatively soft, poses the risk of gumming up cutting tools due to its low melting point. Employing harder aluminum grades can enhance machinability.
Carbon Steel The machinability of carbon steel varies widely across its numerous grades, influenced by factors such as cold work, chemical composition, and microstructure. Elements like lead and tin can boost cutting speed by lubricating actions, while sulfur reduces chip strain hardening.
Titanium Titanium's diverse alloys each pose distinct challenges. Continuous tool engagement is ideal to prevent rubbing, heat buildup, work hardening, and tool wear. While pure titanium behaves similarly to aluminum, its alloys are generally harder, leading to heat buildup and tool wear. Lower RPM and higher chip loads can mitigate tool wear by reducing temperatures.
Superalloys Engineered for exceptional strength at high temperatures, superalloys present formidable machining difficulties, necessitating high-powered machines. These materials quickly work-harden, complicating subsequent machining operations. Lower cutting speeds are typically advised for superalloys.
Copper Machining copper poses challenges due to its malleability, which causes it to flow around tools rather than being cleanly cut. It finds primary use in electrical and heat exchanger components requiring high conductivity and heat transfer coefficients. High speeds and feeds are effective with pure copper, while copper alloys offer improved machinability.
Plastics Plastics exist in numerous forms, ranging from thermosetting to thermoplastic varieties, with a wide spectrum of hardness and mechanical properties. Rigid plastics are conducive to machining and can maintain tolerances, whereas softer variants tend to deform around cutting tools, leading to out-of-spec parts. Heat accumulation at the cutting edge is common due to plastic's insulating properties, risking melting if not managed carefully.
Despite the versatility and capabilities of CNC machines, there are inherent risks involved in their operation. Below are some of the most prevalent mistakes made in CNC machining.
CNC Crashes - CNC machines lack cognitive abilities; they execute commands precisely as programmed. Inaccurate programming can lead to catastrophic collisions where the cutting tool inadvertently engages with the machine itself, resulting in immediate damage. While machines are typically equipped with crash detection mechanisms, preventive measures such as software simulations can mitigate this risk. Simulating tool paths prior to executing the code helps anticipate and prevent potential collisions. However, complex 5-axis machines may require specialized software beyond standard computer-aided manufacturing (CAM) tools to accurately simulate operations.
Incorrect Speeds & Feeds - Optimal speeds and feeds are essential for achieving high-quality machined components. Inappropriate settings can accelerate tool wear and result in subpar surface finishes and dimensional inaccuracies. Given the diverse properties of materials and alloys, determining the ideal cutting parameters often involves iterative adjustments to achieve the optimal setup.
Lack of Maintenance - Similar to any intricate machinery, neglecting maintenance routines can lead to rapid deterioration of CNC machines. Regular cleaning and adherence to original equipment manufacturer (OEM) maintenance schedules are imperative to ensure operational efficiency and longevity.
CNC machining profoundly impacts industries reliant on component manufacturing, directly influencing their operational efficiency and product quality. Here's how CNC machining is pivotal in key sectors:
Aerospace - Precision and repeatability are paramount in aerospace, necessitating components like turbine blades, tooling, and combustion chambers manufactured with exceptional accuracy. CNC machining facilitates the production of such intricate parts crucial for aircraft and rocket engines.
Automotive and Machine Building - The automotive sector relies on CNC machining for fabricating high-precision moulds for casting engine blocks and machining parts like pistons. Gantry-style machines play a pivotal role in sculpting clay moulds utilized during the car design phase.
Military - The military demands components with stringent tolerances and precision, from missile parts to gun barrels. CNC machining ensures the accuracy and reliability of machined parts crucial for military applications.
Medical - Advanced medical implants often feature intricate, organic shapes and are crafted from specialized alloys. CNC machines are indispensable in crafting these complex components, as manual methods cannot achieve the required precision and intricacy.
Energy - The energy industry encompasses a broad spectrum of engineering, including steam turbines and cutting-edge technologies like fusion. CNC machining is instrumental in fabricating precision blades for steam turbines and crafting complex shapes of advanced materials used in plasma containment chambers for fusion research and development.
As technological advancement accelerates, there's speculation about additive manufacturing surpassing CNC machining. However, a more probable scenario involves the integration of multiple technologies into hybrid manufacturing centers. These hybrids leverage the strengths of both subtractive and additive approaches, enhancing overall capabilities. Early versions of such machines are already in existence.
Moreover, the ongoing automation trend in the fourth industrial revolution will lead to highly automated systems capable of self-diagnosis, optimization, and operation with minimal human involvement. This automation enables the customization of products to meet individual consumer needs, facilitated by the flexibility offered by CNC machines.
