What are the different characteristics and requirements of different materials during CNC machining?

How does material diversity shape the rules of CNC machining?

In the field of precision manufacturing, material properties directly determine the success or failure of processing. According to the 2023 report of the International Academy of Production Engineering Sciences (CIRP), the global scrap loss caused by misjudgment of material properties in CNC processing is as high as 4.7 billion US dollars per year. From highly fluid aluminum alloys to brittle ceramics, from titanium alloys with poor thermal conductivity to easily layered carbon fibers, the processing of each material is a precise game with the laws of physics. Based on 15 years of cross-industry processing experience and combined with 200+ real case data, this article deeply analyzes the processing codes of 8 major types of materials.

Metal material processing: extreme challenges from ductility to thermal management

1. Aluminum alloy - the art of balancing speed and tool sticking

Characteristic parameters:

• Thermal conductivity: 120-220 W/(m·K)
• Hardness range: HB 60-120
• Typical grades: 6061-T6, 7075-T651

Processing pain points:

• Tool sticking: When the cutting temperature is greater than 200℃, aluminum chips melt and stick to the tool tip
• Surface finish: Soft aluminum alloy is prone to burrs

Solution:

• Tool selection:
  • 2-edge/3-edge diamond-coated end mill (front angle 15°-20°)
  • Tool tip arc radius ≥ 0.2mm to reduce chip accumulation
• Cutting parameters:
  • Speed ​​6000-15000 RPM
  • Feed 0.1-0.3mm/tooth
  • Compressed air cooling instead of emulsion (to avoid hydrogen embrittlement)

Case study:

In the processing of a drone frame, 7075-T651 aluminum alloy uses atomization cooling + 8000 RPM strategy:

• Tool life increased from 150 pieces to 620 pieces
• Surface burr height reduced from 0.15mm to 0.02mm

2. Stainless steel - a protracted battle against work hardening

Characteristic parameters:

• Work hardening index: 0.3-0.5 (austenite 304 reaches 0.52)
• Coefficient of thermal expansion: 17.3×10⁻⁶/℃ (304 stainless steel)

Processing difficulties:

• Cutting force is 25%-50% higher than carbon steel
• A hardened layer (depth 0.1-0.3mm) is produced when the cutting temperature is ＞800℃

Breakthrough strategy:

• Tool geometry optimization:
  • Large rake angle (20°-25°) reduces cutting force
  • Reinforced tool tip R angle Design (≥0.4mm)
• Parameter control:
  • Linear speed 60-120m/min (carbide tool)
  • Cutting depth > 0.1mm to avoid surface hardening
• Cooling solution:
  • High-pressure internal cooling (pressure ≥ 70bar) to penetrate the thermal barrier layer

Industry breakthrough:

A medical device company processes 316L stainless steel bone plates using titanium aluminum nitride (TiAlN) coated tools + 12% nitrate-based coolant:

• The thickness of the hardened layer is reduced from 35μm to 8μm
• The tool chipping rate is reduced by 72%

3. Titanium alloy - thermal runaway risk due to low thermal conductivity

Characteristic parameters:

• Thermal conductivity: 7-16 W/(m·K) (only 1/15 of aluminum)
• Elastic modulus: 110 GPa (prone to cause springback deformation)

Processing pitfalls:

• The temperature in the cutting zone can reach over 1000℃
• The chips are flammable (ignition point＞1200℃ but the risk of friction ignition is high)

Thermal management solution:

• Tool innovation:
  • Submicrocrystalline carbide substrate (particle size 0.4-0.6μm)
  • PVD coated TiAlSiN nanocomposite coating
• Process parameters:
  • Speed ​​limit 50-150m/min
  • Axial cutting depth ≥0.5mm (avoid surface phase change)
• Cooling revolution:
  • Liquid nitrogen cryogenic cooling (-196℃) reduces the temperature in the cutting zone
  • Carbon dioxide snow injection prevents titanium chips from burning

Aerospace case:

The processing of TC4 titanium alloy blades of an engine uses liquid nitrogen cooling + 0.8mm constant cutting depth:

• Tool life increased from 3 pieces to 22 pieces
• Surface residual compressive stress optimized from -350MPa to -850MPa

Non-metallic material processing: precise control of brittleness and delamination

1. Engineering plastics - the ultimate test of temperature sensitivity

Typical materials: PEEK, nylon 66, PTFE

Key challenges:

• Glass transition temperature (Tg) determines the processing window (such as PEEK's Tg = 143℃)
• Elastic recovery leads to pore size shrinkage (nylon 66 shrinkage can reach 0.5%-0.8%)

Processing rules:

• Temperature control:
  • Cutting zone temperature < Tg-20℃ (PEEK needs < 120℃)
  • Compressed air cooling with heat sink
• Tool design:
  • Zero rake angle/negative rake angle reduces material pulling
  • Polished cutting edge reduces friction heat
• Parameter strategy:
  • High speed (10000-24000 RPM)
  • Low feed (0.02-0.1mm/tooth)

Medical industry evidence:

When processing PEEK artificial vertebrae, use -5° rake angle milling cutter + liquid nitrogen local cooling:

• Dimensional stability is improved from ±0.1mm to ±0.02mm
• Surface crystal layer thickness <2μm

2. Carbon fiber composite material (CFRP) - prevention and repair of delamination

Structural characteristics:

• Anisotropic strength difference > 40%
• Interlaminar shear strength is only 30-50MPa

Processing restricted area:

• Axial force > 100N causes delamination
• Tool wear causes fiber pullout (burr height > 0.3mm)

Advanced technology:

• Special tools:
  • Diamond coated spiral edge drill (helix angle 35°-40°)
  • Inverted cone design (diameter reduction of 0.02-0.05mm per 100mm)
• Processing parameters:
  • Speed ​​3000-6000 RPM
  • Feed 0.01-0.03mm/tooth
• Process monitoring:
  • Acoustic emission sensor detects delamination signals in real time
  • Adaptive speed reduction of 50% to avoid damage extension

New energy vehicle case:

Ultrasonic vibration assisted drilling is used in the processing of a carbon fiber battery box:

• The delamination area at the hole outlet is reduced from 12mm² to 0.8mm²
• The tool replacement interval is extended to 800 holes

3. Ceramic materials - micro-control of brittle fracture

Typical materials: alumina (Al₂O₃), silicon carbide (SiC)

Processing difficulties:

• Low fracture toughness (Al₂O₃ only 3-4 MPa·m¹/²)
• Edge chip size > 0.1mm is scrapped

Precision strategy:

• Tool selection:
  • Diamond grinding wheel (grain size 2000# or above)
  • Laser-assisted cutting (local heating to 1200℃ softening)
• Parameter optimization:
  • Cutting depth ≤ 0.005mm
  • Feed speed 0.5-2mm/min
• Environmental control:
  • Constant temperature workshop (±0.5℃)
  • Negative pressure dust collection system (to avoid powder splashing)

Breakthrough in the semiconductor industry:

Processing aluminum nitride ceramic substrates using femtosecond laser + mechanical polishing composite process:

• Broken edge width reduced from 25μm to 3μm
• Surface roughness Ra 0.01μm

Special material processing strategies: solving industry problems

High temperature alloys - a protracted battle against high hardness

Representative materials: Inconel 718, Hastelloy X

Processing characteristics:

• Work hardening rate > 200% (hardness after cutting can reach HRC50)
• Cutting force is 2-3 times higher than ordinary steel

Efficiency enhancement scheme:

• High pressure cooling (pressure ≥ 100 bar) penetrating the cutting zone
• Variable parameter processing (speed adjustment ± 10% for every 0.5 mm cutting depth)

Magnesium alloy - risk control of flammable and explosive materials

Safety regulations:

• Cutting zone temperature is strictly <450°C (ignition point is about 500°C)
• Use a dedicated fireproof dust collection system (dust concentration <20g/m³)

Actual case: cross-industry material processing wisdom

Case 1 - Aerospace titanium-aluminum laminated structure processing

Challenge: Engine parts with alternating layers of titanium alloy + aluminum alloy (0.8mm per layer)

Innovative process:

• Dynamic switching of tool coating (TiAlN for titanium layer, DLC for aluminum layer)
• Laser online temperature measurement to adjust cooling strategy in real time

Results:

• Interlayer peeling rate reduced from 18% to 0.7%
• Processing efficiency increased by 3 times

Case 2 - Ultra-thin glass micro-hole processing

Requirement: Processing Φ0.05mm through-hole on 0.1mm thick glass

Technical solution:

• Picosecond laser pre-drilling + ultrasonic assisted chemical etching
• Real-time compensation of each hole by 3D topography instrument

Breakthrough:

• Hole taper <1°
• Broken edge diameter <2μm

Summary and Outlook: Processing Revolution Driven by Materials Science

In the next five years, the integration of materials and processing technology will present three major trends:

1. Smart materials: Adaptive processing parameter adjustment of shape memory alloys
2. Atomic-level manufacturing: Focused ion beam (FIB) to achieve nanostructure molding
3. Green processing: Zero-pollution cutting of biodegradable composite materials

Conclusion:

When we observe the interaction between the cutting edge and the material under a microscope, we see not only the peeling of metal or the deformation of plastic, but also the deep dialogue between human wisdom and the essence of matter. Every spindle rotation answers an eternal question: how to make the physical limit of the material a springboard for technological breakthroughs rather than a shackle.
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