When developing a new machined part, it may look ideal in a 3D model, but once it enters the production phase, more manufacturing factors must be considered. Understanding the complete logic of CNC milling processes can help you precisely match machining solutions during prototyping and mass production.
What is CNC Milling?
CNC milling is a manufacturing process that uses computer-controlled programs to operate rotating cutting tools by precisely removing excess stock from metal or plastic blanks.
Unlike traditional manual milling machines, CNC milling machine centers generate machining programs via CAD/CAM software, and the numerical control system then automatically guides cutting tools, which then automatically direct the tool along the X, Y, and Z axes via a numerical control system, enabling high-precision production with consistent quality across multiple batches.
For product development projects requiring high precision, small batch sizes, and diverse product varieties, CNC milling remains one of the most commonly used manufacturing methods for producing CNC milling parts with complex geometries and tight tolerances.
CNC Milling Machines and Their Types
What is a CNC milling machine?
A CNC Milling Machine is an automated processing equipment composed of: a CNC control system, a spindle, a worktable, and an automatic tool-changing system.
Here are the main components of the machines:
- CNC controller
- Spindle
- Worktable
- Tool magazine
- Automatic tool changer
- Drive system
Types of CNC Milling Machines
- 3-Axis CNC Milling
A machine that realizes part processing through three linear axes X, Y, and Z. This machine can only allow your parts to move horizontally and cannot perform rotational movements.
- 4-Axis CNC Milling
By adding rotating A/B axes to the X/Y/Z three axes, your parts can be rotated for indexing. With a four-axis machining machine, you can reduce the number of clamping operations to achieve positioning accuracy and production efficiency.
- 5-Axis CNC Milling
The machine is suitable for manufacturing complex 3D surfaces, hubs, molds, and aviation precision parts. All irregular angle features can be processed in one setup with extremely high processing accuracy.
How does CNC Milling work?
CAD Design
Firstly, you can use CAD software to draw 2D drawings and 3D models of the parts, and mark all the technical requirements such as material, size, CNC machining tolerance, geometric dimensioning and tolerancing, surface roughness, etc.
CAM Programming
This is the process of converting CAD modeling into a language that can be understood by the milling machine. Through this step, engineers can usually set the tool specifications, cutting parameters, tool path, and feed and retraction parameters, and generate the G-code numerical control program that the machine can recognize.
Workpiece Setup
The raw materials are fixed on the machine tool worktable using flat clamps, workholding fixtures, pressure plates, and fixtures. The alignment and centering are carried out to set the workpiece coordinate system, ensuring uniform processing benchmarks.
CNC Machining
The machine tool reads the G-code program and controls the main shaft to drive the milling cutter to rotate at high speed. Various axes work in coordination to automatically complete rough machining, semi-finish machining, and finish machining throughout the process. This multi-stage process ensures the dimensional accuracy required for precision CNC machining applications. The entire operation is carried out automatically.
Inspection & Finishing
After finishing CNC milling, you can check the dimensional tolerance of the parts by using methods such as three-coordinate measurement, calipers, and micrometers. At the same time, you can perform surface finish methods such as deburring, sandblasting, anodizing, passivation, and blackening as needed.
Types of CNC Milling
Face Milling
By using the main cutting edge of the tool’s end face to remove a large amount of material, the flatness and parallelism of custom CNC milled parts can be ensured. When performing this operation, you need to pay extra attention to the flatness, surface roughness Ra, and the direction of the tool’s cutting pattern.
If you need to focus on controlling the three core indicators during actual processing- the overall flatness, the surface roughness, and the direction of the tool’s cutting pattern- avoid problems such as planar warping, chaotic cutting patterns, and local height differences. Therefore, you can mark them on the drawings.
End Milling
End Milling is one of the most widely used processing methods in CNC Milling. What you should be aware of is that if the structure is too deep or the space is too narrow, standard tools may not be able to enter the processing area.
Besides, the internal rounded corners need to take into account the radius of the tool. Therefore, for a design suitable for CNC Milling, you need to fully consider the tool movement space.
Slot Milling
The cutting tool end face can create vertical cuts to form grooves in a single pass. It can control the width, depth, and verticality of the groove. Common grooves include T-shaped grooves, keyways, and through grooves.
This machining method is mainly applied to heat sinks, guide rails, and mechanical connection parts. For example, mechanical guide rails need to control the width and position accuracy, while assembly structures need to ensure the fit clearance.
Pocket Milling
This is a method of gradually removing the internal allowances of the cavity layer by layer. The rough machining quickly removes the excess material, while the fine machining ensures the size of the cavity and the smoothness of the surface.
When performing cavity milling, you also need to pay attention to whether the tool can reach the corresponding depth, the internal radius of the corner, and the processing depth-to-width ratio.
Contour Milling
The cutting tools follow the curve trajectory specified in the CAM drawings to perform cutting operations. They are mainly used for automotive parts, molds, and non-standard curved surface parts.
Thread Milling
This is the method of processing internal and external threads using a thread milling cutter. You can use this milling technique to machine large-sized threads. Compared to tapping, it is more suitable for high-value parts.
Advantages of CNC Milling
High Precision
High-end CNC equipment can hold tight tolerances down to ±0.005mm for ultra-precision milling parts.
Automated and Repeatable Production
The program can be written once and can be repeatedly produced in batches, with little human intervention, and the production capacity is stable.
Ability to Machine Complex Geometries
CNC Milling can directly process these complex features based on the three-dimensional CAD model, without the need to make molds.
Wide Material Compatibility
Carbon steel, stainless steel, aluminum alloy, copper, plastic, fiberglass board, etc. can all be machined. You may select any material without processing limitations.
High Consistency
The size deviation of parts in the same batch is extremely small, and the assembly of batches is highly interchangeable. Batch-to-batch consistency is improved through standardized programming, tooling, and inspection processes.
Flexible Production
If you want to produce new parts, the factory only requires replacing fixtures and importing new programs. It is suitable for small batches and multi-variety orders.
Applications of CNC Milling
Whether you are in the prototyping stage or in mass production, the CNC milling process can meet both the surface roughness and tolerance requirements. It is widely used in various applications.
Aluminum CNC milling parts
This is the most common machining material. Common aluminum materials include 6061, 6063, and 7075. You can use CNC milling to process aluminum alloy enclosures, brackets, mounting plates, frames, radiators, and other precision structural components, etc. Besides, sandblasting and anodizing are the most common surface treatment methods, which can make your products look more premium.
Stainless steel structural parts
If your parts require higher strength, corrosion resistance, and long-term stability, then stainless steel is usually the material you should consider. Common stainless steel materials include 304, 316 and 316L. You can design brackets, connectors, mounting bases, mechanical components, and various precision parts through CNC milling.
Compared with aluminum alloys, stainless steel has higher hardness and greater cutting difficulty, so it is necessary to select appropriate tools and processing parameters according to the material characteristics when machining.
Copper conductive components
You can design copper connectors, terminals, conductive components, heat dissipation structures, and other precision copper parts by considering CNC milling. For more complex copper parts, you can achieve the required structural features through different processing methods such as slot milling, cavity milling, and contour milling.
Industrial equipment assemblies
If you are developing industrial equipment, it usually contains a large number of non-standard mechanical parts, which need to be custom-machined according to the actual structure of the equipment. You can use CNC milling to process mounting plates, brackets, bases, fixtures, connection blocks, equipment housings, manifolds, and other mechanical components.
For the parts that need to be assembled with other components, you not only need to pay attention to the individual dimensions, but also ensure the machining accuracy of the hole positions, planes, and mating positions.
Medical device parts
If your product is applied to medical equipment or medical devices, the milled parts usually need to meet requirements such as dimensional accuracy, material properties, and surface quality simultaneously. Common processing materials include stainless steel, titanium alloys, and some engineering plastics. The specific materials need to be selected based on the function of your components and the actual usage environment.
Automotive components
You can process brackets, mounting bases, housings, connecting pieces, fixation components, and other functional mechanical parts in the vehicle. During the product development stage, you can also quickly obtain functional prototypes through CNC milling to verify the size, structure, and assembly effect of the parts, and then proceed to the subsequent production stage.
Aerospace precision components
If your part is used in aerospace, then factors such as dimensional accuracy, material properties, weight control, and processing consistency are usually the key points that need to be focused on. Aluminum alloys and titanium alloys are common materials. For components with complex structures in multiple directions, you can use multi-axis CNC milling service to complete processing at different angles.
FAQ
Is CNC milling good for metal parts?
Yes. It is highly suitable and is the mainstream processing method for metal precision components.
What’s the difference between CNC milling and CNC turning?
CNC milling is mainly used for processing irregular parts, while CNC turning is mainly used for machining rotational body parts such as shafts, bearing sleeves, bearing housings, circular tubes, and stepped cylindrical parts, all of which have symmetrical features around the central axis.
How much does CNC Milling cost?
The cost of CNC milling mainly consists of your design, raw material, and machining costs. If your design is complex, the factory will custom-make fixtures for unique part geometries, etc.
What materials can be CNC milled?
Aluminum, stainless steel, brass, copper, titanium, and some engineering plastics – PEEK, POM, nylon, polycarbonate, pp and so on.
Final Thoughts
With over 13 years of CNC machining experience, Yecheng supports prototype development and production manufacturing with multi-axis CNC milling, precision inspection, and customized surface finishing.
If you are looking for prototypes or production parts, contact us now, and we will review the drawings and get back to you ASAP.
