CNC Milling Overview: To Manufacture Custom Milled Parts
The most widely used CNC machining technique, from the automobile to the aerospace industries, is CNC milling. This is because CNC mills enable high levels of precision, reproducibility, and output rate. This page will discuss CNC mills, including all of its parts, their operation, and the numerous models that are available.
At Sungplastic, you will know more about CNC milling technology.
What is CNC Milling?
CNC milling is a sophisticated automated manufacturing process that involves controlled removal of material to create parts. This method is compatible with a wide range of materials, including metals, plastics, and wood. While CNC mills require skilled operators for setup, once programmed, they can autonomously produce parts without constant supervision. Components like engine blocks, gears, and brackets are commonly manufactured using CNC mills.
It’s important to distinguish CNC milling from CNC turning: In CNC milling, the tool moves across a stationary workpiece, while CNC turning rotates the workpiece, with a stationary tool performing the cutting.
CNC Milling Process
The CNC milling process typically follows these steps:
Design: Parts are designed using 3D CAD software while adhering to Design for Manufacturing (DFM) principles.
CAM: The CAD design is processed using Computer-Aided Manufacturing (CAM) software. CAM software converts the 3D model into a set of instructions that dictate the machine’s actions, such as tool selection, cutting speeds, coolant usage, and feature probing. This set of instructions is often referred to as G-code for CNC machining. CAM software automates much of the programming, simplifying machine tooling and table positioning based on a coordinate system.
Machining: The instructions generated by the CAM software are loaded into the CNC machine. Raw materials are secured in fixtures, and the CNC milling process commences. Once the parts are complete, they are removed from the CNC milling machine, ready for assembly, delivery to consumers, or additional post-processing steps.
Key Components of a CNC Mill
Here are the essential components that constitute a typical CNC mill:
Spindle: The CNC mill’s spindle is engineered to rotate at exceptionally high speeds while enduring substantial lateral loads without deflecting. A variable-speed motor drives the spindle, and its rotation is transmitted to the cutting tool via a tool holder.
Tool Holder: The tool holder securely clamps onto the spindle using hydraulics and is designed to hold the cutting tool in place.
Machine Bed: The machine bed serves as the foundational structure on which other machine components are mounted. It is usually constructed from cast iron or heavy steel to provide stability. The bed incorporates the X, Y, and Z-axis ways, which consist of linear guides or ball screws that control the movement of the machine’s components along these axes. Additionally, the machine bed houses the electrical and mechanical systems, including the control panel, spindle, and drive motors. The rigidity of the machine bed is critical for maintaining accuracy and precision.
Worktable: The worktable is situated atop the machine bed and provides a flat surface with slots or holes for securing workpieces using clamps. In standard CNC mills, the worktable moves in the X and Y directions, while advanced 5-axis CNC mills can rotate and pivot the bed to enable more complex machining operations.
Drive Components: Servo motors are responsible for moving the machine bed and spindle. These motors utilize linear drive elements like ball screws to convert rotational motion into precise linear motion. Linear guides ensure accurate and precise movement along the relevant axis with minimal deviations.
Coolant Tank: The coolant tank in a CNC mill stores the coolant used during machining. The coolant is delivered to the machine tool via a coolant line, although in more advanced machines, it is directly supplied to the tool through the spindle.
Controller: The controller encompasses the electrical hardware that communicates machining instructions to various electro-mechanical components of the machine, including drive motors, coolant pumps, and chip conveyors.
Interface: The interface of a CNC mill is typically a screen and keyboard attached to the machine. It enables direct machine control through the interface, and basic CNC programming can be carried out using the same interface.
Advantages of CNC Milling
CNC milling offers numerous benefits compared to traditional milling and other forms of CNC machining. Some of these advantages include:
Improved Productivity: CNC milling enhances productivity through automated and precise machining processes.
Reduced Labor Costs: Automation reduces the need for manual labor, resulting in cost savings.
Increased Safety: CNC milling minimizes direct operator involvement, improving safety in the machining process.
Higher Consistency: CNC machines consistently execute programmed instructions, ensuring uniform part quality.
Better Finish Quality: The precision of CNC milling leads to superior surface finish quality on parts.
Increased Flexibility: CNC milling machines can adapt to various tasks and part geometries.
Varieties of CNC Milling Machines
CNC machines come in a variety of configurations, with two primary styles: Vertical Machining Center (VMC) and Horizontal Machining Center (HMC). A VMC positions the spindle vertically along the Z-axis, while an HMC positions it horizontally along the Z-axis.
CNC mills can also be categorized by their degrees of freedom, which include up to 6 degrees (3 translational and 3 rotational). Greater degrees of freedom allow for more complex component production. Common multi-axis CNC machines include 3, 4, and 5-axis systems, with 5-axis CNC milling machines typically available in trunnion and gantry configurations.
Enhancements for CNC Mills
In addition to the core components of a CNC mill, various add-on equipment can significantly enhance efficiency:
Automatic Tool Changers: These devices automatically switch between different tools from a tool library during machining, eliminating the need for manual tool changes and boosting efficiency.
Robotic Arms: Robotic arms can integrate with CNC mills to perform tasks like loading raw materials, unloading finished parts, and changing workholding devices. This automation supports lights-out manufacturing and cost reduction.
Chip Conveyors: Chip conveyors remove chips from the milling process, keeping the machine clean and minimizing downtime for manual cleaning, resulting in increased machining uptime.
Varieties of CNC Milling Operations
CNC milling operations involve the removal of material by guiding a rotating tool through the raw material, reshaping it as needed. Several cutting techniques and tools are available to create specific parts, with some of the most commonly used methods outlined below:
Plain Milling: This fundamental operation creates flat surfaces parallel to the milling machine’s bed.
Face Milling: Similar to plain milling, but using a larger diameter tool and shallower cuts to produce large, flat surfaces.
Contour Milling: This technique shapes curved or contoured surfaces. Typically, a rough shape is first formed, followed by a final contour pass using a tool like a ball end mill to achieve the desired shape.
Angular Milling: Angular milling involves cutting a flat surface that is not parallel to the machine’s bed or spindle axis, often creating chamfers or beveled edges.
Side Milling: This method is employed to create flat, vertical surfaces on the side of a workpiece.
Groove or Slot Milling: Slotting entails cutting grooves within the raw material, either passing through or partially into the material.
Hole Drilling: Holes are usually drilled with specialized drills, but larger holes can be created using an end mill that spirals down into the workpiece.
Reaming: After drilling, a reamer is used to precisely size and finish the hole, often for precise alignment with locating pins.
Hole Tapping: Hole tapping occurs in pre-drilled holes, where a tap is introduced to cut or form threads at the required pitch to accommodate fastening elements like bolts.
Gang Milling: In gang milling, multiple milling cutters simultaneously engage the workpiece for efficient material removal.
Constraints of CNC Milling
Despite the widespread adoption of CNC milling, certain drawbacks exist:
Expensive Equipment: CNC mills are high-precision automated tools, making them significantly more expensive than manual machines. Their cost can only be justified when there is sufficient production volume to benefit from the automation.
Advanced Operation: Operating CNC mills requires skilled programmers and operators, and training individuals for these roles can be costly and time-consuming.
CNC Milling at Sungplastic
To ensure that a part can actually be machined, it’s imperative to adhere to fundamental DFM (Design for Manufacturing) criteria while designing a part for CNC milling. Our CNC milling specialists at Sungplastic will assist you in improving your design and ensuring that you receive the high-quality, precisely machined parts you want. Additionally, there are automated production lines, CNC milling operation systems, highly skilled designers, engineers, and laborers.
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