What is CNC milling?

This article examines the operation of CNC milling machines, the types of components that can be produced using milling, and the optimal design methods for maximizing CNC machining efficiency.

CNC milling is a precision machining process that integrates computer numerical control machines and a multi-point cutting tool or milling cutter. It involves securing the workpiece on a machine bed and cutting materials from a solid block to produce products made from glass, metal, plastic, wood and other specialist materials.

This guide outlines the operation of CNC milling machines, investigates the various CNC milling machine types, and offers design guidance for optimising CNC production.

How do CNC milling machines work? #

CNC milling machines are automated tools that use computer numerical control (CNC) to control the movement and operation of cutting tools. Here is a general overview of how CNC milling machines work:

1. Designing the part: The process begins with creating a digital design of the part using computer-aided design (CAD) software. The design specifies the dimensions, shape, and features of the part.
2. Programming the CNC machine: The CAD design is then converted into a set of instructions that the CNC machine can understand. This is done through computer-aided manufacturing (CAM) software. The instructions, known as G-code, contain commands for tool movements, cutting speeds, and other machining parameters.
3. Preparing the machine: The operator sets up the CNC milling machine by installing the appropriate cutting tools, workholding fixtures, and material stock. The machine's worktable or workpiece is positioned accurately.
4. Loading the program: The G-code program generated in the previous step is loaded into the CNC milling machine's control unit. The machine is now ready to execute the machining operations.
5. Executing the operations: The CNC milling machine follows the instructions in the G-code program to perform the machining operations. This typically involves the following steps:
   a. Tool movement: The machine moves the cutting tool along different axes (X, Y, and Z) to approach the workpiece from various angles. The tool can move vertically, horizontally, or diagonally based on the programmed instructions.
   b. Cutting the material: As the tool moves, it removes material from the workpiece. This can be accomplished through various cutting operations such as drilling, milling, facing, contouring, or pocketing.
   c. Tool changes: If the design requires different cutting tools or operations, the machine automatically changes the tool as programmed.
   d. Coolant and chip removal: During the cutting process, a coolant may be used to cool the cutting tool and workpiece, reducing heat and lubricating the cutting area. Chips and debris generated during machining are removed using chip conveyors or other chip evacuation systems.
   e. Quality control: Throughout the machining process, the CNC milling machine may use sensors or probes to measure and verify the accuracy and dimensions of the machined features. This ensures that the final part meets the specified requirements.
6. Finishing the process: Once all the machining operations are complete, the CNC milling machine may perform additional finishing processes such as deburring, polishing, or surface treatment to achieve the desired final appearance and quality of the part.

CNC milling machines offer precise and efficient manufacturing capabilities, allowing for the production of complex and high-quality parts across various industries.

What is the distinction between CNC milling and CNC turning? #

Although both machining processes rely on CNC systems, there are notable distinctions.

CNC turning is employed to construct a conical or cylindrical surface. The process necessitates a lathe - a machine tool that can revolve a workpiece around an axis of rotation - in order to undertake various operations, such as cutting, drilling, turning and threading. It also employs an SPTT or a single-point turning tool that stays in constant contact with the workpiece during the operation.

CNC milling is utilized to produce a level surface using a milling machine. It necessitates a multi-point cutting tool or a milling-cutter. Unlike turning, the milling procedure is reliant on intermittent cutting and multiple machine stages.

What are 3-, 4- and 5-axis milling machines? #

Let's examine the different types: 3-axis milling machines enable the cutting tool to move and subtract parts through the X, Y, and Z axes. This method of machining is widely used due to its low start-up costs and is suitable for manufacturing simple parts with uncomplicated geometry.

A 4-axis milling machine possesses all the capabilities of a 3-axis milling machine but with the added advantage of an extra axis. Additionally, it permits the workpiece to rotate for cutting around the A-axis, which is especially advantageous when sections must be cut around a cylinder or the edge of an object.

The 5-axis milling machine can move along three linear axes and rotate the machine head and tool head, combining to make five axes. This enables the creation of products with intricate geometries such as aerospace components, titanium parts, medical products and gas machine parts. As it can rotate in multiple dimensions, it eliminates the need for multiple setups and enables faster and more efficient single-step machining.

What types of parts can be manufactured using CNC milling machines? #

CNC milling machines provide operators with the capability to create intricate designs with precise tolerances, making it one of the most precise manufacturing processes to date.

Below is a list of the products that can：

• be manufactured using this equipment: aerospace parts, including landing gear components and fuselage structures.
• Components for the automotive industry, including control panels, axles, and car molds;
• consumer electronics components, such as enclosures;
• medical components, such as surgical instruments and
• orthotics; oil and gas machine parts, including valves, rods, and
• pins; prototyping and
• modeling;
• sculptures;
• furniture; and woodworking.

CNC milling machines have the capability to cut a wide range of materials, including aluminum, bronze, copper, ceramics, plywood, various steel types, stone, wood, zinc and other engineering materials. This makes them ideal for creating prototypes during product development. These machines enable precise and quick adjustments until final approval of the end product.

While CNC milling machines offer flexibility, they have limitations concerning axis movement, prototype and drill bit size. Shape and size restrictions apply to most machines. Large CNC machines can create prototypes up to 105 feet x 21 feet,

whereas the smallest machines can only move up to 9 inches along the x-axis, 5.125 inches along the y-axis, and 6.5 inches along the z-axis. Additionally, some machines may face difficulties drilling square-edged holes in the material due to shape restrictions.

How do you create designs for CNC milling? #

There are various design factors to take into account when designing parts for CNC milling. In general, some significant recommendations from our mechanical engineering team include the following: minimize setups to speed

• up and optimize the milling process, and ensure internal corner radii are added to the parts.
• If the design allows, aim for a pocket depth of at least a quarter and ideally half of the cut depth to save costs. Instead of milling shapes, drill holes to reduce pocket depth whenever possible.
• Avoid thin walls and sections of a part, as even soft metals can deform and warp under the machining forces exerted during the milling process. Make sure that every section of the part doesn't need to be thin before creating thin sections. Done correctly, you will be able to enhance production speed, lower costs, and improve surface finishing of workpieces.
• If a feature doesn't require small size for the part to function, make it larger. Take part size into consideration: for smaller features, smaller and more delicate tools are necessary. Utilizing small tools requires more effort and time, subsequently increasing costs.
• Standardise Everything: Use standard thread sizes, standard corner radii, standard materials, and standard tolerances to save money and ensure parts arrive on time, regardless of who is making them.

Which tool or design is most effective for each type of material? #

Machining materials can be classified into three main groups: plastics, soft metals, and hard metals.

Soft metals and certain hard metals have the highest precision tolerance, making them easier to work with. However, if the material falls outside the optimal range for hardness and becomes "too hard" or "too soft," it can react unpredictably during manufacturing processes. This can significantly reduce the accuracy of cutting.

As a result, specific materials are frequently used and acknowledged as the norm within the industry. Aluminium 6061-T6 and diverse kinds of mild steel are commonly preferred among machinists due to their workability and superior qualities.

Are there any software techniques that engineers should be aware of when designing products that are easy to manufacture? #

CAD software is intended to provide easy-to-use tools that align well with the manufacture of straightforward components.

For example, the "Hole Wizard" tool enables standard-sized holes to be generated quickly, thus simplifying the process for both designers and manufacturers. Moreover, it is more straightforward to utilize the elementary "Extrude" or "Revolve" tools rather than more intricate tools such as "Lofts" or "Sweeps."

Generally, it's easier to mass-produce and manufacture a part made with simple tools than one with complex surfaces. If your part doesn't require a complex feature, avoid integrating it into your design. This will help you save money and minimise quality issues related to your design in the long run.

How can you optimize CNC milling with V1? #

To reduce costs and speed up lead times for CNC milling, it is best to focus on designing parts that are "Simple" and/or "Standard". Complex parts are not a problem when needed, but they often result in longer lead times and higher costs. To reduce costs and speed up lead times for CNC milling, it is best to focus on designing parts that are "Simple" and/or "Standard".

This means creating parts with uncomplicated features that can be manufactured using standardized tools. A straightforward component with precise tolerances, or a single intricate feature, may not pose a significant challenge if made from aluminium. However, producing such parts using plastic may appear almost insurmountable.

In summary, strive to keep your design as simple and standard as possible. While incorporating specialised materials or complex features may be necessary depending on your current product development stage, doing so will undoubtedly increase the difficulty of milling.

Our CNC milling services feature a worldwide range of 3-axis, 3+2-axis, and complete 5-axis milling centres that can create extremely precise and high-quality components. Get started on your parts today with a free, instant quote.

Frequently asked questions #