Preface
This manual is intended for product designers, makers, and small-to-medium enterprises. It details the full manufacturing process of CNC prototypes (metal/plastic materials), covering tool preparation, step-by-step operations, parameter settings, and troubleshooting. Following this manual ensures the production of qualified prototypes with a precision of within ±0.01mm.
Practical Manual for CNC Prototype Manufacturing

I. Preparations: Tool, Material, and File Verification

1.1 List of Essential Tools and Equipment

Category
Specific Tools/Equipment
Specification Requirements
Purpose
Machining Equipment
3-axis/5-axis CNC Milling Machines (Recommended Models: Haas TM-1, Taiquan T-V856)
Positioning accuracy ±0.005mm, spindle speed ≥12,000 rpm
Core machining equipment
Clamping Tools
Precision Vises (e.g., Schunk KSP+), Vacuum Chucks
Clamping force ≥5,000N, repeat positioning error ≤0.002mm
Secure materials to prevent vibration during machining
Cutting Tools
Carbide End Mills (TiAlN Coated)
Diameter 1-12mm (commonly used: 2mm, 4mm, 6mm)
Milling contours, drilling holes, slotting
Inspection Tools
Digital Calipers (Accuracy 0.001mm), Coordinate Measuring Machine (CMM)
Range 0-300mm (calipers), measurement accuracy ±0.003mm (CMM)
Dimensional verification
Auxiliary Tools
Coolant System, Deburring Tools, Sandpaper (400#/800#)
Cooling pressure ≥5bar, sandpaper grit matching materials
Cooling, deburring

1.2 Material Selection and Pretreatment

Select materials based on prototype purposes, and complete pretreatment in advance:
Material Type
Recommended Grade
Application Scenarios (Prototype Function)
Pretreatment Steps
Metals
Aluminum Alloy 6061-T6, Titanium Alloy TC4
Strength testing, assembly verification (e.g., drone frames)
1. Cut into blanks 5-10mm larger than the design size; 2. Remove surface oxide layer with sandpaper
Engineering Plastics
ABS (Acrylonitrile-Butadiene-Styrene), PC (Polycarbonate)
Appearance simulation, lightweight testing (e.g., headphone housings)
1. Cut into regular blocks/sheets; 2. Wipe with alcohol to remove surface oil stains
Composite Materials
Carbon Fiber-Reinforced PC (CF-PC)
High-strength, lightweight needs (e.g., robot arms)
1. Cut along fiber direction (to avoid fiber breakage); 2. Apply protective film to prevent scratches

1.3 Design File Preparation and Verification

Provide files that meet CNC machining standards to avoid design flaws:
  1. File Format: Prioritize STEP/IGS (universal formats compatible with all CNC software); avoid STL (significant precision loss).
  1. Design Specifications:
    • Minimum Wall Thickness: ≥0.5mm for metals, ≥1mm for plastics (to prevent machining breakage);
    • Fillets/Chamfers: All sharp corners require R0.2-R0.5 fillets (to avoid tool chipping);
    • Hole Depth Limit: Blind hole depth ≤4×hole diameter (e.g., ≤16mm for φ4mm holes, to prevent drill breakage).
  1. File Verification: Open the model in UG/NX software, run the “Geometry Check” function, and fix issues such as overlapping faces and non-closed edges.

II. Core Steps: Step-by-Step Operation for CNC Prototype Manufacturing

2.1 Step 1: Design File Import and Programming (Critical Link)

Use programming software (e.g., Mastercam, UG) to convert 3D models into G-code recognizable by the machine:
  1. Import Model: Open the programming software, import the STEP file, and confirm the model coordinate system (default: model bottom surface as Z-axis zero point).
  1. Set Machining Strategies:
Machining Requirement
Recommended Strategy
Parameter Settings (Taking Aluminum Alloy 6061-T6 as Example)
Rough Milling (Material Removal)
Pocketing
Spindle speed 8,000 rpm, feed rate 1,500 mm/min, cutting depth 1mm
Finish Milling (Detail Refinement)
Contouring
Spindle speed 12,000 rpm, feed rate 800 mm/min, cutting depth 0.2mm
Drilling (φ4mm Hole)
Drilling Cycle
Spindle speed 5,000 rpm, feed rate 50 mm/min, peck drilling depth 2mm
  1. Simulation and Verification: Run the “Machining Simulation” function to check for tool path collisions (focus on the distance between the tool, fixture, and machine table). Generate G-code and save it to a USB drive.

2.2 Step 2: Material Clamping and Alignment (Precision-Critical)

  1. Clean the Worktable: Wipe the CNC machine table with alcohol to remove iron chips and oil stains, preventing clamping deviation.
  1. Clamp Materials:
    • Metals: Secure with a precision vise, ensuring the material’s bottom surface is flush with the worktable (use a 0.1mm copper sheet for leveling if needed). Control the vise clamping force between 3,000-5,000N (excessive force causes material deformation).
    • Plastics: Secure with a vacuum chuck (reserve a 10mm adsorption area on the material edge). Maintain a vacuum level ≥-0.08MPa.
  1. Machine Alignment:
    • X/Y Axis Zero Positioning with Edge Finder (Accuracy ±0.001mm): Mount the edge finder on the spindle, manually move the spindle to touch the material edge, record coordinates, and set as zero.
    • Z Axis Zero Positioning with Z-Setter: Place the setter on the material surface, lower the spindle until the setter alarms, and record the Z-axis coordinate (subtract the setter height, e.g., 10mm).

2.3 Step 3: Test Cutting Verification (Avoid Mass Scrap)

Test cutting is mandatory before formal machining to verify parameters and dimensions:
  1. Load Program: Insert the USB drive into the machine, call the G-code, and confirm the program number matches the machining path.
  1. Manual Override Adjustment: Set “feed rate override” and “spindle speed override” to 50%, then manually start the program.
  1. Test Cutting Observation:
    • First 30 Seconds: Focus on whether the tool moves along the path (no collisions) and if the coolant system sprays normally (full coverage of the cutting area for metal machining).
    • Pause After 10mm of Cutting: Use calipers to measure the test-cut area dimensions (e.g., contour size, hole diameter). If the error exceeds ±0.02mm, adjust programming parameters (e.g., reduce feed rate by 10%-20%, adjust cutting depth).

2.4 Step 4: Formal Machining (Real-Time Monitoring)

After qualified test cutting, proceed to formal machining:
  1. Restore Overrides: Set “feed rate override” and “spindle speed override” to 100%, and start automatic machining mode.
  1. Real-Time Monitoring Key Points:
    • Listen for Sounds: Normal machining produces a steady “rustling sound”; a “sharp squeal” indicates tool wear or excessive feed rate—pause immediately.
    • Check Vibration: Spindle vibration amplitude should be ≤0.01mm (measure with a dial indicator close to the spindle). Excessive vibration requires checking tool tightness.
    • Monitor Temperature: Spindle temperature ≤60℃ during metal machining (measure with an infrared thermometer). If exceeded, reduce spindle speed or increase coolant flow.
  1. Post-Machining: After the machine stops automatically, turn off the spindle and coolant system, then manually move the spindle to a safe position (away from the material).

2.5 Step 5: Post-Processing (Enhance Prototype Quality)

Select post-processing methods based on material type to meet prototype requirements:
Material Type
Post-Processing Steps
Tools & Parameters
Quality Standards
Metals
1. Deburring: Remove edge burrs with a deburring tool; 2. Polishing: Sand the surface with 400# sandpaper, then refine with 800# sandpaper; 3. Rust Prevention: Anodize aluminum alloys (thickness 5-10μm)
Deburring tool angle 30°, anodizing temperature 20-25℃
Surface roughness Ra ≤0.8μm, no sharp burrs
Plastics
1. Deburring: Soften burrs with a heat gun (50-60℃) then scrape off; 2. Painting: Spray matte paint (thickness 20-30μm)
Heat gun speed level 2, painting distance 30cm
No runs or color differences; adhesion reaches Grade 5B (no peeling in cross-cut test)
Composite Materials
1. Deburring: Sand with carbon fiber-specific sandpaper (1000#); 2. Edge Sealing: Seal fiber cuts with epoxy resin
Sand along fiber direction, resin layer thickness 0.1mm
No exposed fibers, smooth edges without burrs

2.6 Step 6: Quality Inspection (Qualified Judgment)

Inspect against the following standards; rework if unqualified:
  1. Dimensional Inspection:
    • Critical Dimensions (e.g., assembly hole diameter, positioning pin height): Measure with CMM, error ≤±0.01mm.
    • Non-Critical Dimensions (e.g., contours): Measure with digital calipers, error ≤±0.02mm.
  1. Appearance Inspection:
    • Metal Prototypes: No scratches or dents; no anodized layer peeling.
    • Plastic Prototypes: No bubbles or sink marks; no particles on the painted surface.
  1. Functional Inspection:
    • Assembly Prototypes: Assemble with mating parts, gap ≤0.03mm (no jamming or looseness).
    • Strength Prototypes: Conduct simple load tests (e.g., apply 500N pressure to aluminum alloy prototypes with no deformation).

III. Common Issues and Solutions

Issue Phenomenon
Possible Causes
Solutions
Machined dimensions too small (e.g., φ3.98mm for designed φ4mm hole)
Tool wear, excessive feed rate
1. Replace with a new tool; 2. Reduce feed rate by 10%-20%
Obvious tool marks on surface (Ra＞1.6μm)
Low spindle speed, excessive cutting depth
1. Increase spindle speed by 2,000 rpm; 2. Reduce cutting depth to 0.1mm
Material deformation during machining (plastic bending, metal warping)
Excessive clamping force, insufficient cooling
1. Reduce clamping force by 1,000-2,000N; 2. Increase coolant flow
Tool breakage (especially for small hole machining)
Blind hole depth ＞4×diameter, no peck drilling program
1. Split deep hole machining (e.g., 10 pecks for 20mm deep holes); 2. Use extended tools (flute length ≥hole depth + 5mm)

IV. Safe Operation Specifications

  1. Personal Protection: Wear safety helmets, cut-resistant gloves, and safety goggles during machining (additional earplugs for metal machining to prevent noise damage).
  1. Equipment Maintenance: Check coolant level (must be between scale marks) and tool tightness (no looseness) before daily machining.
  1. Emergency Handling: In case of abnormalities (e.g., collisions, smoke), press the machine’s “emergency stop button” immediately, cut off power, and then inspect the fault.

V. Common CNC Machining Issues

  1. Abnormal Material Machining: When machining difficult-to-cut materials (e.g., titanium alloy), failure to use low-speed, high-cooling strategies leads to rapid tool wear and poor surface quality. For plastics, improper cutting parameters cause deformation and dimensional inaccuracies.
  1. Programming Parameter Errors: Mismatch between programming parameters and material properties (e.g., improper feed rate or cutting depth) causes cutting vibration and tool chipping, seriously affecting machining precision and efficiency.
  1. Missing Test Cutting: Skipping test cutting and proceeding directly to formal machining fails to identify programming or tool path issues in advance, leading to material waste and project delays.
  1. Inadequate Inspection: Neglecting real-time machining inspection and finished product testing may allow unqualified products to enter subsequent processes, failing to meet design and functional requirements.
  1. Speed-First Misconception: Overemphasizing machining speed while ignoring quality causes dimensional deviations and excessive surface roughness, increasing subsequent rework costs.
By following the principle of “test cutting first, then machining; prioritize inspection over speed,” strictly matching material properties with programming parameters, and enhancing inspection at all stages, these common issues can be effectively avoided, scrap rates reduced, and smooth CNC prototype manufacturing ensured.

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Author:
Dr. Benjamin Keller

Name: Dr. Benjamin Keller

Nationality: Germany

Titles: Senior Research Scientist, Industrial Technology Consultant

Work Experience and Industry Qualifications:

An expert in the CNC field from Germany, with 25 years of in – depth industry experience. He has long focused on the high – precision optimization of five – axis linkage machining technology, the intelligent upgrade of AI – driven numerical control systems, and the practical application of digital twins in machining scenarios. He is particularly good at solving machining technical problems of complex surfaces in aerospace and precision components in the medical field. He is proficient in advanced programming of G – code and M – code, and is skilled in the debugging and optimization of mainstream numerical control systems such as Fanuc and Siemens. He can build an adaptive model of cutting parameters through machine learning algorithms, use virtual simulation tools to pre – rehearse the machining process and perform error compensation. At the same time, he has the ability to integrate multi – axis machining processes and additive manufacturing technologies, which can effectively improve machining efficiency and precision consistency.

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