Sculptures At The Micron Scale: How 5-axis CNC And Micro Electrical Discharge Machining Work Together To Overcome The Manufacturing Limits Of The End Cap Of An Endoscope

In the manufacturing of the end cover of the endoscope, the complex geometries and micrometer-level tolerance requirements specified in the design blueprint pushed traditional manufacturing techniques to their limits. When it was necessary to accommodate square CMOS sensors, multiple fiber bundles, and irregular fluid channels, with a wall thickness as thin as 0.05 millimeters, a single processing method was no longer sufficient. The modern precision manufacturing provides the answer: the integration of 5-axis CNC micro-milling and micro-electrical discharge machining (Micro-EDM) processes. This is not a simple stacking of procedures, but a precise and coordinated battle at the micrometer scale based on complementary material removal principles. This article will deeply analyze how these two cutting-edge technologies each showcase their strengths and seamlessly connect, transforming a solid metal billet into a complex-structured, precisely-sized, and flawlessly-surfaced miniature functional carrier.
I. The Visual Representation of the Manufacturing Challenges: Why Did the Traditional Processes Fail as a Collective?
Before delving into the technical details, it is necessary to clearly define the manufacturing challenges of the remote housing, as these challenges represent the limit of traditional processing methods:
The "impossible" geometric shape: Modern endoscopes strive for the highest level of functional density. The cross-section of the distal housing may be an asymmetrical "Swiss cheese", containing D-shaped sensor cavities, multiple circular or elliptical channels, and tiny grooves reserved for the wires. The spatial relationship of these features requires extremely high positional accuracy (±5 μm).
The "blow-and-touch-breakable" thin-walled structure: To accommodate all functions within the minimum outer diameter (such as Ø2.0mm), the metal "partition walls" between adjacent channels must be as thin as a cicada's wings (0.05-0.1mm). This is thinner than a regular copy paper. Any minor cutting force or clamping stress could cause it to deform or break.
The internal requirements for "absolute right angle": The installation surface of the image sensor must be absolutely flat, and the corners of the installation cavity need to be perfect right angles (sharp internal corners). Any rounded corners will cause the sensor to tilt and result in image distortion. Traditional milling ball nose cutters or end mills will inevitably produce tool radius rounded corners.
"Mirror-like" and smooth inner surface without burrs: All inner surfaces, especially those through which optical fibers and wires pass, must be as smooth as a mirror (with an extremely low Ra value) and absolutely free of burrs. Any microscopic protrusions or burrs could cut through fibers thinner than a hair, causing the equipment to fail.
"Sticky" difficult-to-machine materials: Whether it is 316L stainless steel or Ti-6Al-4V titanium alloy, they both present challenges in micro-processing. Stainless steel is prone to work hardening, while titanium alloy has poor heat conductivity and is prone to sticking to the cutting tool, posing a severe test to the tool life and processing stability.
II. 5-axis CNC Micro-milling: The Macro Shaper of Complex Three-dimensional Forms
Five-axis CNC micro-milling is the core force for constructing the main contour and most features of the part. The term "five-axis" refers to three linear axes (X, Y, Z) and two rotational axes (typically the A-axis and C-axis), which gives the tool unparalleled degrees of motion freedom.
Core advantage: One setup, multiple complex processing. This is the greatest leap of 5-axis compared to 3-axis. The tool can be tilted at an angle, approaching the workpiece from the side or even the bottom, thus enabling the processing of parts with complex curved surfaces, inclined holes, and deep cavities in a single setup. For the remote shell, this means that the external streamlined curved surface, inclined flushing channel outlet, and multiple different angles of installation surfaces can all be processed continuously, avoiding the cumulative errors caused by multiple setups and ensuring extremely high relative position accuracy between all features.
The technical backbone for achieving "micro" milling:
Ultra-high-speed spindle and micro-diameter cutting tools: The spindle speed is usually several tens of thousands to several hundred thousand revolutions per minute (RPM). Combined with hard alloy or diamond-coated milling cutters with diameters as small as 0.1mm or even smaller, extremely high cutting line speed can be achieved, while the cutting volume per tooth is extremely small, thereby minimizing cutting force and heat, which is crucial for processing thin-walled features without causing deformation.
Nanometer-level servo and dynamic accuracy: The linear and rotational axes of the machine tool need to have nanometer-level positioning resolution and extremely high dynamic response characteristics. When processing complex curved surfaces, all axes need to move synchronously, smoothly, and at high speed. Any slight lag or vibration will leave marks on the workpiece surface.
Intelligent tool path and vibration suppression: CAM software needs to generate optimized tool paths to avoid sharp turns and sudden feed changes. Advanced machines are also equipped with vibration suppression systems that can monitor and counteract the vibrations generated during processing, which is crucial for achieving high-quality surfaces and extending the lifespan of the tools.
The manifestation of process limits: Although the 5-axis micro-milling is powerful, it is fundamentally a "force" processing. When the following situations occur, its physical limits are exposed:
The true internal sharp corners: As long as a rotating milling cutter is used, round corners caused by the tool radius will be unavoidable.
Microscopic holes or grooves with an extremely large depth-to-diameter ratio: The slender cutting tools lack rigidity and are prone to bending deformation, resulting in hole deviation or inconsistent groove width.
Work hardening and tool wear: When processing stainless steel and titanium alloys, the tool wears out relatively quickly. The worn-out tool will intensify the work hardening process and affect the dimensional accuracy.
III. Micro-EDM (Micro Electrical Discharge Machining): Non-contact Microscopic Etching Art
When milling reaches its physical limit, micro-electrical discharge machining comes into play. This is a non-contact processing method that uses the high temperature generated by pulsed discharge to melt and vaporize local materials. It mainly includes wire electrical discharge machining (Wire EDM) and sinker discharge machining (Sinker EDM).
Working principle: A pulsed voltage is applied between the tool electrode (copper, tungsten, etc.) and the workpiece (conductive metal). When the two are brought close to each other within a range of a few micrometers to several tens of micrometers, the insulating working fluid (usually deionized water or oil) is broken down, resulting in an instantaneous spark discharge. The center temperature of the discharge channel can reach over 10,000°C, causing the local metal material to melt or even vaporize. The explosive force throws the molten material into the working fluid and then washes it away.
The "special forces" that have overcome the challenges of milling:
Achieving perfect sharp corners and clean edges: By using forming electrodes (sink box EDM), any shape can be precisely replicated, including absolute right angles, acute angles, and complex two-dimensional contours. It is commonly used to remove internal rounded corners left by milling, creating perfect right-angle mounting seats for sensors.
Stress-free processing of ultra-thin features: Due to the absence of mechanical cutting force, electrical discharge machining can easily produce ribs, walls and narrow grooves as thin as 0.05mm or even thinner without causing deformation of the workpiece. This is crucial for processing ultra-thin metal partitions that separate various chambers.
Processing high-hardness and difficult-to-machine materials: The ability of electrical discharge machining only depends on the conductivity of the material, and has nothing to do with its hardness, strength, or toughness. Therefore, it can easily machine hardened materials after quenching, without introducing mechanical stress or causing the material to harden.
Achieve excellent surface quality: By using advanced machining parameters (low current, high frequency), a surface with an extremely low Ra value (<0.1μm) can be obtained, without any directional tool marks. The recast layer (white layer) generated by the discharge is very thin and can be removed through subsequent electrolytic polishing.
Self-limitations: The material removal rate is relatively slow; it can only process conductive materials; the electrodes are prone to wear and require compensation; for large-scale material removal, the efficiency is much lower than that of milling.
IV. The Wisdom of Process Integration: A Synergistic Manufacturing Process of 1 + 1 > 2
Top manufacturers do not use these two processes independently. Instead, they conduct intelligent process planning based on the design features of the parts to achieve complementary advantages. A typical remote housing manufacturing process is as follows:
5-axis CNC micro-milling (for rough machining and main body finishing):
Initial processing: Utilize relatively large-sized cutting tools to quickly remove most of the excess material, thereby forming the basic outline of the part.
Semi-finishing: Use smaller cutting tools to leave uniform allowances for the subsequent finishing process.
Finishing process: Utilizing ultra-fine micro-diameter milling cutters and high rotational speeds, with extremely small cutting depths, the final contours and most of the curved surfaces are processed to meet the main requirements for dimensions and surface finish. The 5-axis linkage comes into play at this stage to complete the smooth processing of complex curved surfaces.
Micro electrical discharge machining (for toughening and edge finishing):
Wire cutting EDM: It can be used for cutting materials, or for machining certain irregular external contours that cannot be reached by a milling cutter.
Box EDM: This is a crucial step for achieving internal sharp corners and ultra-thin features.
Electrode fabrication: Firstly, based on the 3D model, precise processing (even micro-electrical discharge machining) is used to create the formed electrodes made of copper or graphite. The accuracy of the electrodes directly determines the accuracy of the workpiece.
Electrical Discharge Machining: Precisely position the electrode at the specific area of the workpiece that needs to be machined (such as the corner of the sensor cavity), and perform electrical discharge etching. By using multiple electrodes (coarse cutting, fine cutting) or changing the electrical parameters, gradually shape perfect right angles and achieve the specified surface finish.
Processing ultra-thin walls: For walls as thin as 0.05mm, special thin sheet electrodes are used. Fine discharge is carried out simultaneously or sequentially from both sides, precisely controlling the amount of etching to form the final thin wall structure.
Post-processing and ultimate purification:
Deburring and polishing: Although EDM produces no burrs, the machined edges may still have microscopic burrs. Final processing can be carried out using a gentle abrasive flow, magnetic polishing, or chemical polishing.
Electrolytic polishing: The workpiece is immersed in the electrolyte as the anode. Through electrochemical dissolution, the microscopic protrusions on the surface are selectively removed, resulting in a mirror-like smooth surface. At the same time, the thin layer of re-machined layer generated by EDM is also removed.
Multi-level ultrasonic cleaning: The parts are cleaned in multiple ultrasonic tanks with different frequencies and solvents, thoroughly removing all micrometer and sub-micrometer metal particles, oil stains and processing fluid residues, achieving medical-grade cleanliness.
Micron-level measurement verification:
Using a coordinate measuring machine (CMM) equipped with ultra-fine probes, the key dimensions, positional accuracy and form and position tolerances are measured.
Using high-resolution optical vision systems or white light interferometers, the surface roughness, contours, and microscopic defects that are invisible to the naked eye can be detected.
All the data were compared with the CAD model, and a full-size inspection report was generated to ensure that each feature met the tolerance range of ±5 μm.
V. The Role of the Manufacturer: From Equipment Owner to Process Integration Expert
Having advanced 5-axis machine tools and electrical discharge machines is just the ticket. The real core competitiveness lies in:
Process planning and simulation capabilities: Before the actual machining, through CAM and machining simulation software, the entire machining process is simulated in advance to optimize the tool path, select electrode strategies, and predict possible interferences or overcuts, achieving "getting it right the first time".
Thermal management and process stability control: The entire processing environment requires strict temperature and humidity control. For micro-metric processing, the thermal expansion of the machine tool itself, as well as the influence of the operator's body temperature, must all be taken into account. Standard configurations include constant-temperature workshops, machine tool preheating, and on-line temperature compensation.
Cross-process benchmarking uniformity: Ensure that from milling to EDM and finally to the final inspection, the workpiece has a unified and precise coordinate system throughout the entire process. This relies on precise fixture design and accurate machine tool alignment systems.
Conclusion: The manufacturing of the end cap of the endoscope is the pinnacle of precision processing technology. The combination of 5-axis CNC micro-milling and micro-electrical discharge machining represents the current highest level of subtractive manufacturing at the micrometer scale. The former precisely shapes the macroscopic form through "force" control, while the latter overcomes extreme features through "electricity" micro-etching. This process integration not only resolves the contradiction between complex geometric shapes and ultimate precision, but also maximizes the potential of high-performance difficult-to-machine materials. For manufacturers who can master and proficiently apply this collaborative manufacturing strategy, what they deliver is not merely a part, but a miniature engineering platform that integrates optics, fluidics, and mechanics perfectly. It is the fundamental guarantee for promoting minimally invasive surgical instruments to continuously evolve towards smaller, smarter, and more powerful directions.