Ascending vs Traditional Milling – How Do They Differ?
Geoffrey wang
??Stamping Processing/CNC Processing/Sheet Metal Processing/Laser Cutting/Precision Mould -Business Development and Project Manager of BoYi Company.??Mechanical knowledge high-quality content creator??
CNC milling stands out as a prevalent machining technique employed for crafting intricate components. When embarking on the milling process, machinists encounter a pivotal choice: opt for conventional or climb milling. Despite their apparent similarities, the crux lies in the interplay between the cutting tool’s rotation and the workpiece’s movement. This seemingly subtle distinction wields significant influence over the machined part’s outcome.
The conventional wisdom dictates that CNC operators predominantly favor Climb Milling, while their manual machining counterparts lean towards Conventional Milling. The rationale behind this division lies in the potential hazards associated with Climb Milling on manual machines due to backlash issues. However, with technological advancements and the integration of lead screws, Climb Milling has evolved into a viable alternative for CNC milling machines.
Delving deeper into each CNC milling type reveals distinct characteristics and optimal use cases. Exploring the nuances between Climb and Conventional Milling sheds light on their respective advantages and drawbacks, influencing decisions about the milling approach. Additionally, this exploration delves into practical applications, such as the production of a rough surface, illustrating how each method plays a role in achieving specific machining goals.
Milling Fundamentals
CNC milling refers to a subtractive manufacturing technique in which a rotating cutting tool is employed to eliminate material from a workpiece. This process enables the creation of intricate geometries with consistent precision and plays a pivotal role in the production of various components. The utilization of 3, 4, 5, and even 6-axis CNC mills empowers the incorporation of diverse features and elements into part geometries, all while maintaining a high level of repeatability. Modern CNC machinery has evolved to handle intricate complexities effortlessly.
In order to manufacture a component using a CNC mill, the initial step involves securing the workpiece in the machine, commonly referred to as fixturing. Once fixtured, the cutting tool progressively eliminates material from the workpiece during each pass. CNC milling machines operate in either of two ways: with a moving tool impacting a stationary part or a stationary tool impacting a moving part. In both cases, material removal occurs as the cutting tool swiftly rotates to extract chips of material, shaping the workpiece according to the desired specifications.
Differences in the movement of the cutting tool across the workpiece lead to variations in surface finishes, cutting techniques, and machine requirements. Specific CNC machines are better suited for certain components; for instance, Swiss machines excel in producing small parts with precise tolerances. Fictiv provides a diverse range of CNC options to efficiently manufacture even the most intricate components at remarkably fast speeds.
Traditional Milling
’Traditional CNC milling, also known as conventional milling, involves the cutting tool rotating in the opposite direction to the feed, creating a cutting action that goes against the feed direction. This method is commonly referred to as up milling, as the cutting tool initiates the cut from the base and moves upward through the workpiece. In many cases, manual CNC milling predominantly utilizes traditional milling techniques.
The utilization of conventional CNC milling as a longstanding machining methodology is underpinned by a multitude of advantages, contributing to its continued relevance in the manufacturing domain. Noteworthy merits associated with conventional CNC milling encompass:
Despite the array of advantages, conventional CNC milling is not without its drawbacks. Some notable limitations include:
In the context of conventional milling, the rotation of the cutting tool results in chips being expelled in the same direction as the tool movement, often leading to recutting and consequent surface quality degradation. Additionally, the method demands higher clamping forces to counteract the natural tendency of the cutting tool to lift the workpiece, especially pertinent for machines susceptible to backlash or when dealing with materials prone to tearing or chattering. Despite these limitations, conventional milling, particularly in the form of up milling, remains a preferred approach in scenarios where the advantages outweigh the drawbacks, such as applications involving manual machines or instances where minimizing backlash is critical.
Milling Methodology: Climb Milling, also known as Down Milling
Climb milling, alternatively referred to as down milling, represents a milling technique that closely resembles conventional milling, distinguished primarily by the orientation of the cutting edge concerning the workpiece. In conventional milling, the cutting tool rotates in the “up” direction, whereas in climb milling, the cutting edge rotates “down,” causing the tool to climb or pull into the workpiece. In essence, climb milling aligns the cutting direction and the cutting tool’s rotation, synergistically inducing an upward motion away from the workpiece. This results in an enhanced surface finish and diminished energy consumption. It is worth noting that on certain equipment, such as gantry routers, the spindle movement may necessitate the reversal of labels, a consideration duly highlighted by G-Wizard.
Implementing climb milling does not necessitate new equipment; instead, the machinist adjusts the feed direction for the workpiece. Despite its seemingly minor nature, this adjustment can significantly impact the final part’s quality.
Key Advantages of Climb Milling:
Climb cutting in milling facilitates an aggressive entry into the workpiece from the top, as the cutting tool efficiently removes a substantial material volume. The chip width progressively decreases during rotation, culminating in a gentle exit angle that contributes to superior surface quality compared to conventional milling methods. Additionally, the altered rotation minimizes recutting risks by ejecting chips away from the tool’s path and assists in pushing the workpiece into the table, subsequently reducing clamping requirements.
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Climb milling, while advantageous for its enhanced material removal rates, is not exempt from inherent challenges, which encompass the following aspects:
Pro-Tip: Mitigating backlash risks involves minimizing cutting forces by adjusting parameters such as tool size, cut depth, feed height, and spindle speed.
The pronounced entry angle of the cutting tool in climb milling, while advantageous for productivity, introduces challenges, historically addressed by conventional milling practices. Although modern machines often integrate backlash eliminators, the impact on surface quality remains a consideration.
The same forces that alleviate clamping requirements also introduce potential drawbacks. The tool’s tendency to pull into the workpiece may lead to over-material removal. Despite challenges, contemporary machine tools and CNC controls offer compensatory measures, mitigating the inherent complexities associated with climb milling.
For comprehensive guidance on designing parts conducive to CNC machining, download our Design for Manufacturing (DFM) checklist, ensuring optimal machining outcomes from the outset.
Milling Machine Precision:
Milling machines exhibit a high degree of precision, capable of achieving accuracies within a few thousandths of an inch. The precision of milling operations is contingent upon multiple factors, including the quality of the machine itself, the proficiency of the operator, and the appropriateness of the tooling employed. Regular maintenance and calibration procedures play a crucial role in maintaining and enhancing the overall accuracy of milling machines.
Comparison of Climb Milling and Conventional Milling Techniques: Climb milling and conventional milling are distinct methodologies employed in milling operations.
Climb Milling:
Climb milling entails the rotation of the cutter against the direction of the feed, leading to the tool “climbing” into the workpiece. This technique provides several advantages, including reduced tool wear, a smoother surface finish, and minimized risk of workpiece lifting. However, the implementation of climb milling necessitates meticulous consideration of factors such as backlash and control to ensure optimal results.
Determining Optimal Machining Techniques: Conventional vs. Climb Milling in Plastic Vertical CNC Milling
Selecting the appropriate milling technique is crucial in machining operations. Conventional and climb milling are both viable options, and the decision between them depends on factors such as the material being machined and the desired surface quality.
In the realm of plastic vertical CNC milling, the choice between climb and conventional milling is influenced by the material’s properties. Soft materials like aluminum exhibit favorable results with climb milling. While conventional milling is generally suitable for a broad range of materials, climb milling proves particularly effective for the following:
Conversely, hard materials such as cast iron and hot rolled steel typically benefit from conventional milling processes. However, some softer variations of steel may respond more favorably to climb milling. Conventional milling is recommended for materials prone to chatter or tearing. Climb milling, on the other hand, excels when machining workpieces with a tendency to lift, as the forces generated push the workpiece into the table.
A Pro-Tip to consider is that climb milling is the preferred choice when cutting less than half the cutter tool’s diameter. In contrast, for cutting more than 75% of the cutter tool’s diameter, conventional milling is advised due to the potential for negative rake.
Climb milling is often employed as a final pass due to its capability to enhance the surface finish of machined parts. Conventional milling primarily focuses on material removal, with climb milling utilized towards the end to achieve final dimensions with superior surface quality. Interestingly, in aerospace machining, even for harder materials like titanium, a final climb milling pass is common. This practice may initially seem counterintuitive to machinists accustomed to traditional approaches, but the consensus among industry professionals, including those at Practical Machinist, supports this strategy. This is particularly evident in thin-wall work scenarios, where the structural integrity of the walls is a concern, and minimizing tool deflection during the finish pass is crucial.
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Nick Ysidron is a mechanical engineer specializing in HVAC and IoT domains. Beyond his endeavors in designing innovative technologies for enhanced connectivity and improved air quality, Nick cherishes moments with his wife, Bridget, and son, James. Holding Bachelor’s degrees in Mechanical Engineering and Spanish from Louisiana State University, Nick’s diverse hobbies encompass outdoor activities, 3D printing, quality time with his son, and a commitment to regular reading