CNC machined parts refer to components produced using CNC equipment. CNC machining—short for Computer Numerical Control machining—is a precise manufacturing method that has now become a widely used process in modern manufacturing.
The equipment used in CNC machining is called a CNC machine tool (or simply “CNC machine”), though regional naming conventions differ. In the Yangtze River Delta region of China, it’s often called a “machining center,” while in the Pearl River Delta region, it’s commonly referred to as a “CNC milling machine” or “computerized milling machine.”
Common Types of CNC Machines
CNC Lathe – Works by rotating the workpiece held in the chuck while the cutting tool moves along two axes to produce cylindrical parts.
CNC Milling Machine – Typically used for flat parts, but more advanced models with additional degrees of freedom can produce complex shapes. In most cases, the workpiece remains stationary while the spindle rotates the cutting tool along three axes (or four/five on advanced machines). In some designs, the spindle is fixed and the workpiece moves into the cutting path.
CNC Drilling Machine – Similar to milling machines but designed to cut along only one axis (Z-axis), with the drill bit feeding straight down into the workpiece.
CNC Grinding Machine – Uses a grinding wheel to achieve high-quality surface finishes, often as a finishing process on hardened metals to remove small amounts of material.
CNC Machining vs. Traditional Machining
Compared to conventional machining methods, CNC machining offers higher precision and flexibility, but the cost can be higher than other manufacturing processes such as injection molding, die casting, or stamping.
The main factors that affect CNC machining costs include:
1. Machining Equipment
The cost of equipment includes the purchase price, operating costs, maintenance expenses, tooling costs, and CNC system usage fees. The more expensive and complex the machine, the higher the cost per part.
Milling machines are generally more expensive than lathes due to their more complex moving components, greater setup difficulty, and ability to perform more complex machining. Therefore, where possible, design parts to be machinable on a lathe rather than requiring milling.
The cost also varies with the type of milling machine. Machines with more axes are more expensive. While 5-axis machines can produce complex geometries more quickly and accurately (reducing cycle time), they are more costly than 3-axis machines.
2. Design Costs
Design costs include CAD modeling, CAE optimization, and CAM programming. CAD/CAE costs may not always be allocated to part costs—it depends on the client-supplier arrangement. Since design costs are fixed, producing higher quantities reduces the per-unit cost.
3. Material Costs
Material cost is one of the largest components of part cost, and is determined by:
- Raw material cost – Prices vary by material type and market location. Choose materials based on functional requirements, not unnecessarily high-performance (and expensive) ones. For example, stainless steel 316 is significantly more expensive than 304.
- Material usage – Reduce waste by designing parts that require less material. In some cases, consider splitting a complex part into two simpler parts for later assembly.
- Machinability – Materials that are easier to cut (e.g., aluminum) reduce machining time and costs, while harder materials (e.g., stainless steel) require more expensive tooling and increase wear, raising costs.
4. Production Volume
Unit costs decrease significantly as production volume increases due to shared design and setup costs. Programming and machine setup are typically one-time tasks for a batch.
5. Special Requirements
Tighter tolerances increase machining difficulty and scrap rates, raising costs. Higher surface finish requirements may require additional processes such as grinding, which also adds cost.
Post-processing (e.g., heat treatment, anodizing, plating) can improve performance or appearance but also increases costs. Applying different surface finishes to different areas of the same part significantly increases cost—uniform finishes are more economical.
6. Structural Design Factors
The complexity of a part directly impacts cost. Complex geometries often require advanced machinery, more setups, longer machining times, and stricter inspections. Key design considerations include:
(1) Avoid Thin Walls
Thin walls are fragile, prone to vibration and deformation, and require slow cutting speeds. For metal parts, wall thickness should be >0.8 mm; for plastic parts, >1.5 mm.
(2) Avoid Non-Machinable Features
For example, perfect 90° internal corners cannot be milled directly because end mills have a cylindrical shape, resulting in filleted corners. If sharp corners are required, EDM (Electrical Discharge Machining) is necessary, which is more expensive. Where possible, design with internal radii instead.
(3) Use Larger Internal Corner Radii
Small radii require smaller tools and slower speeds, increasing machining time and cost. A general rule: the corner radius (R) should be at least 1/3 of the cavity depth (D), and ideally 1.3× the tool radius.
(4) Limit Cavity Depth
Deep cavities require more time and present tool deflection and chip removal challenges. As a rule, cavity depth should be no more than four times the cavity width.
(5) Minimize Complex Curved Surfaces
Curved surfaces require smaller tools and slower machining. Where possible, replace rounded edges with chamfers to save time and cost.
(6) Limit Thread Length
Threads longer than three times the hole diameter rarely increase strength but do increase machining time. For blind holes, leave a relief area equal to at least half the diameter at the bottom.
(7) Design Holes to Standard Sizes
Using standard drill sizes is faster and cheaper than milling custom hole diameters. Recommended depth is ≤10× the drill diameter.
(8) Minimize Setups
Design parts so all features can be machined in as few setups as possible to reduce handling, repositioning, and the need for custom fixtures.
(9) Avoid Unnecessary Text or Engraving
Engraving text increases machining time. If text is required, consider screen printing or laser marking, and use simple sans-serif fonts of at least 20 pt size.
Conclusion
By optimizing structural design with cost-efficiency in mind—avoiding unnecessary complexity, selecting appropriate materials, and reducing setup and processing time—you can significantly lower CNC machining costs without sacrificing function or quality.
If you want, I can also turn this into a more concise, client-facing version that’s easier for non-engineers to read while still keeping the technical depth. That would be suitable for blogs, brochures, or customer education.
Do you want me to prepare that polished version?
