CNC Machining PMMA

August 02, 2025
Posted by Globo
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Why Acrylic Dominates Optical Prototyping

With 92% light transmission (surpassing polycarbonate’s 90%) and UV stability, PMMA is essential for:

Light pipes & diffusers
Transparent housings
Microfluidic devices
Automotive lenses
Key advantage: 5x higher impact strength than glass while maintaining optical clarity.

Material Selection: Cast vs. Extruded Acrylic

Property	Cast Acrylic	Extruded Acrylic
Internal Stress	Low (±0.5 MPa)	High (±8 MPa)
Machinability	Excellent (no cracking)	Prone to chipping
Tolerance Holding	±0.02mm achievable	±0.1mm typical
Cost	20-30% higher	Lower
Prototyping Tip: Always specify cast acrylic for critical optical/mechanical components to prevent stress-related failures.

Precision Machining Protocols

1. Workholding Solutions

Vacuum Fixturing: Essential for sheets >300mm² (prevents mid-cut resonance)
Custom Soft Jaws: For small batches (≤50pcs) with complex 3D geometries
Pressure-Sensitive Adhesives: Temporary mounting of thin optics (<3mm)

2. Tooling & Parameters

Operation	Tool Type	Parameters	Surface Finish
Roughing	2-Flute Carbide End Mill	18,000 RPM	0.2mm/tooth feed	Ra 3.2μm
Finishing	Diamond-Coated Router	24,000 RPM	0.05mm/tooth feed	Ra 0.8μm
Drilling	60° Point Angle Drill	6,000 RPM	Peck cycle 0.5xD	Hole ±0.05mm
Critical: Use polished/flute-free tools to eliminate machining marks.

3. Thermal Management

Pre-cool stock to 10-15°C (reduces gumming by 70%)
Air Vortex Cooling: Preferred over liquid coolants (prevents stress cracking)
Max chip load: 0.3mm to avoid recast layers

Optical-Grade Finishing Techniques

Flame Polishing
- Hydrogen torch at 1,300°C for 0.5-2 seconds
- Achieves >90% original clarity on edges
Micro-Milling
- Diamond tools with 0.1mm stepover (Ra 0.05μm achievable)
Vapor Polishing
- Dichloromethane exposure for complex internal channels

XTJ’s Advanced Acrylic Capabilities

Our ISO 9001-certified facility specializes in optical PMMA components with:

5-Axis Diamond Turning: Surface accuracy λ/4 @ 632nm
Submicron Tolerances: ±5μm on lens diameters
In-House Metrology: White-light interferometry for surface defect analysis
Recent Project: Automotive light guide (500pcs):
Achieved 92.4% light transmission
100% on-time delivery with 0.2% scrap rate

Conclusion: From Prototype to Production
CNC machining remains the fastest method for precision acrylic prototypes (24-48hr lead time). For optical applications exceeding standard tolerances, diamond tooling and cast material selection are non-negotiable.

Ready to Optimize Your Acrylic Design?
[Submit your CAD file] for a free prototype quote within 4 hours.

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