Comprehensive Guide to CNC Milling Parts

1. Understanding CNC Milling Parts: Key Components and Common Types

1.1 Key Components of CNC Milling Machines: The “Critical Factor” Determining Milling Part Precision

 

• Spindle: The core component that clamps cutting tools, with a speed range typically between 8,000–15,000 rpm. High-speed spindles (e.g., above 12,000 rpm) are suitable for precision small-part processing, while low-speed, high-torque spindles are ideal for heavy metal parts.
• Servo Motor: The power source controlling the movement of milling parts along the X/Y/Z axes. High-quality motors can achieve a displacement precision of ±0.001 mm, making them essential for aerospace-grade milling parts.
• Guide Rails: Support the sliding of the worktable. Cast iron guide rails offer strong stability, while granite guide rails provide better anti-vibration performance, making them suitable for high-precision milling needs.
• Worktable: The platform for placing workpieces, which must have deformation resistance. Common materials include 45# steel or aluminum alloy, with the surface treated by quenching to enhance wear resistance.
• Tool Magazine: An automatic tool-changing device. The tool magazine capacity (16–60 tools) determines processing efficiency; large-capacity tool magazines are required for multi-variety milling part production.
• Cooling System: Prevents milling part deformation due to excessive temperature during cutting. Oil cooling is suitable for high-speed processing, while water cooling is used for heavy-duty cutting.
• Feedback System: Real-time monitors displacement through linear scales or encoders to ensure the dimensional error of milling parts is within the allowable range.
• Control System: Systems such as FANUC and Siemens; their operating smoothness and compatibility directly affect processing efficiency.

1.2 Common Types of CNC Milling Parts: Classified by Material and Application Scenario

 

• Classified by Material:
  • Aluminum Alloy Milling Parts (e.g., 6061, 2024-T6): Lightweight and corrosion-resistant, suitable for electronic equipment enclosures and automotive components. Professional manufacturers in the industry can achieve over 85% adaptability of such products in the drone and consumer electronics fields.
  • Stainless Steel Milling Parts (e.g., 304, 316): High-strength and rust-resistant, used in medical equipment and food machinery. Manufacturers need to provide full-process customization from design to processing to meet medical-grade precision requirements.
  • Titanium Alloy Milling Parts (e.g., TC4): High-temperature resistant and high-strength, suitable for the aerospace field. Manufacturers equipped with 5-axis high-precision milling equipment can achieve a processing precision of ±0.003 mm for titanium alloy parts.
  • Plastic Milling Parts (e.g., POM, PC): Insulating and low-cost, suitable for home appliance accessories. Specialized plastic processing production lines can avoid cracking and deformation during processing.
• Classified by Application Scenario:
  • Precision Structural Parts (e.g., sensor enclosures, connectors): Require a precision of ±0.005 mm and need 5-axis CNC milling equipment for processing. The 5-axis workshops of leading industry manufacturers can handle over 200 precision part orders per day.
  • Load-Bearing Parts (e.g., mechanical brackets, fixtures): Emphasize strength and stability, mostly made of 45# steel through milling. After quenching and tempering treatment, their service life can be increased by 30%.
  • Customized Accessories (e.g., non-standard screws, special-shaped interfaces): Require OEM services from manufacturers. High-quality suppliers support small-batch customization (starting from 10 pieces) with a sample lead time as short as 3 days.

2. CNC Milling Parts Selection Guide: 3 Core Dimensions + 4 Common Misunderstandings

2.1 3 Core Selection Dimensions

• Dimension 1: Match Precision to Actual Needs
  Higher precision is not always better—electronic equipment enclosures require a precision of ±0.01 mm, while mechanical brackets only need ±0.1 mm. Excessively pursuing high precision can increase costs by 30%–50%. It is recommended to select according to industry standards:
  • Aerospace: ±0.002–0.005 mm (requires 5-axis milling);
  • Automotive Manufacturing: ±0.01–0.02 mm;
  • General Machinery: ±0.05–0.1 mm.
• Dimension 2: Match Material to Usage Environment
  Prioritize 316 stainless steel for humid environments (e.g., bathroom equipment); titanium alloy or high-temperature alloys for high-temperature environments (e.g., engine components); and 6061 aluminum alloy for lightweight needs (e.g., drones). For example, 6061 aluminum alloy milling parts customized by a drone manufacturer are 40% lighter than traditional steel parts while meeting impact resistance requirements.
• Dimension 3: Match Production Capacity to Order Scale
  • Small-Batch Customization (10–100 pieces): Choose manufacturers that support “rapid prototyping” (usually providing samples within 24 hours, with prototype costs deductible from bulk order payments);
  • Large-Batch Production (1,000+ pieces): Prioritize suppliers with automated production lines (monthly capacity up to 150,000 pieces). Scale production can reduce unit costs, with bulk orders eligible for discounts of up to 20%.

2.2 4 Common Selection Misunderstandings

• Misunderstanding 1: Focusing only on “surface precision” while ignoring “stability”—some manufacturers mark precision as “single-process precision,” but errors may exceed limits during mass production. It is necessary to require suppliers to provide “batch inspection reports” (e.g., coordinate measuring reports);
• Misunderstanding 2: Ignoring “processing process compatibility”—for example, high-speed milling of stainless steel parts can easily cause tool wear. Professional manufacturers will use “low-speed, high-torque + special cooling oil” processes for stainless steel parts to reduce tool loss;
• Misunderstanding 3: Not considering “subsequent assembly needs”—the hole positions and tolerances of milling parts must match other components. It is recommended to provide assembly drawings to manufacturers; some suppliers can offer “pre-assembly testing” services;
• Misunderstanding 4: Blindly choosing low-cost suppliers—unqualified small factories may use inferior materials (e.g., non-standard aluminum alloy), leading to milling part deformation. High-quality manufacturers use raw materials that meet international standards (e.g., Southwest Aluminum 6061, Baosteel 304 stainless steel) and provide material certification.

3. CNC Milling Parts Design Tips: Improve Processing Efficiency and Product Quality

3.1 Set Tolerances Reasonably: Avoid “Over-Design”

3.2 Simplify Structures: Reduce “Complex Features”

• Avoid deep cavities (depth > 3 times the diameter): Deep cavity processing requires long tools, which are prone to vibration and precision loss. It is recommended to split deep cavities into 2 shallow cavities; a sensor customer improved processing efficiency by 50% through this optimization;
• Reduce sharp corners: Sharp corners require special tools for processing and can be replaced with rounded corners of R0.5–R1 mm to reduce tool costs and processing time;
• Unify hole diameters: Try to unify the hole diameters of the same milling part (e.g., all φ5 mm) to reduce tool changes and improve efficiency.

3.3 Consider Material Characteristics: Adapt to Processing Processes

• Aluminum Alloy: Suitable for “high-speed milling” and can be designed into thin-walled structures (minimum wall thickness 1 mm). Professional manufacturers can process aluminum alloy thin-walled parts with a minimum wall thickness of 0.8 mm without deformation;
• Stainless Steel: High hardness, so avoid “thin-walled + deep cavity” combinations; the minimum wall thickness is recommended to be ≥2 mm;
• Titanium Alloy: Poor thermal conductivity, prone to heat-induced deformation. Reserve a “processing allowance” of 0.1–0.2 mm during design; combined with “segmented processing + multiple cooling” processes, deformation can be controlled within ±0.002 mm.

4. How to Choose a Reliable CNC Milling Parts Supplier? 5 Key Evaluation Criteria

4.1 Qualification Certification: Ensure Compliance and Professionalism

 

• Quality Certifications: ISO 9001 (quality management system), ISO 13485 (medical field), AS9100 (aerospace field). Manufacturers with these three certifications can export products directly to Europe, America, Japan, South Korea, and other markets;
• Production Certifications: UL certification (material safety), CE certification (EU market access), ensuring products meet international market access requirements.

4.2 Production Capacity: Verify “Hard Strength”

• Equipment Configuration: Whether equipped with 5-axis CNC milling machines (e.g., MAZAK 5-axis machines, FANUC 3-axis machines) and high-precision testing equipment (e.g., coordinate measuring machines, roughness meters);
• Production Capacity: Whether the monthly capacity can meet order needs, and whether there is “emergency capacity” (e.g., shortening delivery cycles through two-shift production);
• Process Experience: Whether the manufacturer has served the target industry (e.g., aerospace, medical care, consumer electronics); the number of accumulated cases reflects professionalism.

4.3 Service Efficiency: Reduce Communication and Waiting Costs

• Quotation Speed: Whether supporting “online instant quotation” (generating a detailed quotation within 1 hour after uploading STP/IGS format drawings, including material, processing, and testing costs);
• Prototype Lead Time: Whether small-batch prototypes can be delivered within 3–7 days (3 days for conventional materials, 5 days for special materials);
• After-Sales Support: Whether providing “free rework for quality issues” and “real-time order tracking” (e.g., checking progress through official websites/mini-programs, and responding to quality issues within 48 hours).

4.4 Cost Transparency: Avoid “Hidden Fees”

• Quotation Inclusions: Whether including material, processing, testing, and packaging costs, and whether there are “minimum order quantity (MOQ)” requirements (high-quality suppliers have no mandatory MOQ, starting from 10 pieces, with no hidden fees);
• Bulk Discounts: Whether unit costs decrease in a stepped manner as order quantity increases (e.g., 10% discount for 1,000–5,000 pieces, 20% discount for 5,000+ pieces).

4.5 Customer Reviews: Refer to Real Feedback

5. CNC Milling Parts Frequently Asked Questions (FAQ)

1. Q: What is the processing precision of CNC milling parts?
   A: The precision of ordinary milling parts is ±0.01–0.05 mm, while precision milling parts (5-axis processing) can reach ±0.002–0.005 mm. The 5-axis processing workshops of some professional manufacturers can stably achieve a precision of ±0.003 mm, meeting aerospace-grade requirements.
2. Q: What materials are needed to customize CNC milling parts?
   A: Provide 2D drawings (marked with tolerances and materials), 3D models (e.g., STP/IGS format), and usage scenario descriptions (e.g., temperature, force conditions). Engineers from high-quality suppliers can optimize the design plan for free based on the provided materials to improve processing feasibility.
3. Q: Is the cost of small-batch customization (e.g., 50 pieces) high?
   A: The cost of small-batch production is 10%–30% higher than that of large-batch production, but manufacturers supporting “rapid prototyping + cost deduction” can reduce costs—for example, the prototype cost of 50 aluminum milling parts is 500 yuan, which can be fully deducted when placing a subsequent order of 1,000 pieces, and the bulk unit price can be as low as 15 yuan/piece.
4. Q: How to judge the quality of CNC milling parts?
   A: Check from 3 aspects: ① Appearance (no burrs or scratches, surface roughness Ra ≤ 0.8 μm); ② Dimensions (verify tolerances with calipers or coordinate measuring machines, and request inspection reports); ③ Performance (e.g., load-bearing testing, corrosion resistance testing; third-party testing can be requested if needed).

Conclusion