Medical parts’ porous moulds and liquid silicone rubber (LSR) moulds require extremely high standards in CNC manufacturing, due to their precision, surface quality, and complex structures. The main required technologies are as follows:

🔧 CNC Technologies for Porous Moulds

High-precision micro-machining: Porous structures may have micron-level hole sizes, requiring micro-tools or EDM assistance.
High-speed milling: Reduces tool load, improves surface quality, and avoids burrs on hole walls.
5-axis CNC machining: Enables multi-angle cutting of complex porous geometries, avoiding errors from multiple setups.
EDM / Micro-EDM: Suitable for tiny deep holes and irregular shapes where conventional tools cannot reach.
Polishing and surface finishing: Ensures smooth hole walls to prevent residue in medical applications.

🔧 CNC Technologies for LSR Moulds

Precision cavity machining: Achieve ultra-high surface finish (Ra < 0.2 μm) to ensure smooth LSR moulding surfaces.
Thermal control features: Accurate machining of heating/cooling channels for temperature regulation.
Hard steel machining: Capable of hard milling stainless steel or hardened steels.
5-axis and deep cavity machining: Suitable for complex curved surfaces and deep cavities without interference.
Mould alignment accuracy: Achieve micron-level mould fitting to prevent silicone leakage.

一、整體製程流程 | Overall Process Flow (Recommended)

Design Stage (DFM): Confirm hole diameter, tolerance, depth/aspect ratio, venting, and internal surface accessibility.
Rough Machining (conventional milling): Remove most of the stock material.
Micro-milling: Machine fine geometries, sharp corners, and cavity details.
Micro-hole / Deep-hole EDM (hole-drill EDM / micro-EDM): Used when hole diameters are extremely small or materials are too hard.
Deburring & Internal Finishing: If necessary, apply AFM or ultrasonic polishing.
Precision Polishing: Hand polishing, diamond film, ultrasonic, electro-polishing, or mirror-EDM texturing to achieve required Ra.
Inspection: Optical profilometer, white light interferometry, CMM, or microscope measurement.
Cleaning: DI-water rinsing, drying, and packaging (medical parts require cleanroom/no oil).

二、微細銑削（Micro-milling） | Micro-milling

Principle & Application
Uses ultra-small diameter end mills to directly cut micro features and cavities. Suitable for high shape freedom and high surface quality when hole size is within tool capability.

Tools & Equipment

Micro end mills: 0.05–3 mm, typically ultra-fine grain carbide.
High-speed spindle: tens of thousands RPM to maintain cutting speed.
High-rigidity machine, low-vibration fixtures, minimized tool overhang.
High-precision holders/chucks for minimal runout and dimensional stability.

Machining Strategy / Parameters

Small depth of cut, shallow step-over, multiple roughing–semi-finishing–finishing passes.
High feed per tooth with trochoidal paths and climb milling.
Cooling/lubrication: MQL or light coolant, avoid tool vibration.

Surface Quality & Limits

Achievable sub-micron Ra, but affected by runout and tool wear.
For <0.08–0.1 mm diameters or high aspect ratios, micro-EDM is preferred.

三、微細 EDM（Micro-EDM） | Micro Electrical Discharge Machining

Principle & Application
Removes material through electrical discharges. Suitable for ultra-small deep holes, non-standard shapes, or features inaccessible to cutting tools. Works only with conductive materials.

Tools & Equipment

Micro-electrodes: copper/tungsten, as small as 10–20 μm diameter.
Precision servo control to maintain discharge gap.
Stable power supply for controlled pulse energy.
Rigid machine structure to ensure discharge stability.

Machining Strategy / Parameters

Low-energy pulses to remove material at micron scale.
Slow feed with segmented machining to avoid short circuits.
Ideal for high aspect ratio holes, fine micro-features, and medical implant moulds.

Surface Quality & Limits

Achievable Ra <0.1 μm, burr-free.
Lower efficiency than milling, restricted to conductive materials.

四、拋光與表面處理 | Polishing & Surface Finishing

Purpose
Remove burrs, eliminate EDM recast, reduce Ra, and ensure fluid/biocompatibility—especially critical for medical parts.

Common Methods

Manual/Mechanical Polishing: oil stones, diamond wheels, felt wheels.
Mirror EDM / mirror-EDM texturing.
Ultrasonic Polishing: effective for deep cavities and micro holes.
Abrasive Flow Machining (AFM / Extrude Honing): high-viscosity abrasive fluid removes EDM recast uniformly.
Electrochemical Polishing / Chemical Etching: remove micron-level surface layer and stress concentration.

Surface Roughness Targets

High-grade LSR molds: Ra ≤ 0.2 μm.
Standard molds: Ra 0.4–1.0 μm.

五、檢測與量測 | Metrology

Common Instruments / Methods

White-light interferometer / 3D optical profiler: non-contact measurement of micron/sub-micron surface roughness and topology.
Optical microscope / vision measurement system: magnified inspection of hole openings, diameters, and defects.
CMM (contact measurement): measure overall geometry and tolerances; limited for micro holes or thin-walled parts.
Specialized micro-probes / non-contact fiber probes: scan inner diameters of tiny holes.

Practical Notes

Micro-holes and internal surfaces require 100–400x magnification or interferometer checks for Ra and residual particles.
Include measurement steps in process validation (IQ/OQ/PQ), especially critical for medical parts.

六、常見問題與實務建議 | Common Issues & Practical

Issue	Possible Cause	Solution / Recommendation
Tool breakage / chipping	Excessive tool overhang, cutting depth too large, insufficient rigidity	Reduce tool overhang, lower cutting depth, use shorter/more rigid holders, increase spindle rigidity
Vibration / chatter affecting surface	Fixture rigidity insufficient, unbalanced tool	Improve fixture rigidity, balance tools, use vibration-avoidance tool paths, reduce cutting parameters
EDM recast / white layer	Rough discharge or improper parameters	Use fine discharge parameters, follow with AFM / ultrasonic / chemical polishing
Internal holes cannot be polished	Poor accessibility for deep/narrow holes	Use AFM, ultrasonic fluid polishing, or design demountable mold sections
Cleaning / residual oil or polishing paste	Inadequate cleaning	Ultrasonic cleaning + DI water rinse + drying / sterilization, establish clean verification procedure
Dimensional instability (flash / sealing issues)	Low mold alignment accuracy or poor thermal control	Increase mold alignment precision, control mold temperature, check surface roughness and tolerance

Practical Recommendations

Micro-hole ≥0.1 mm with aspect ratio <3–5: use micro-milling; hole <0.08–0.1 mm or high aspect ratio: micro-EDM recommended.
Surface roughness targets: LSR/mirror areas Ra ≤0.2 μm; standard molds Ra 0.4–1.0 μm.
Inspection items: hole diameter, position, tolerance, Ra, burrs, EDM recast, cleanliness.

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