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Endoscopic linear cutters are indispensable tools in modern minimally invasive surgery, widely used in procedures such as lung lobectomy and gastrointestinal anastomosis. One of their core components is the cartridge — a complex metal part integrating multiple precision tooth slots and pusher plate slide rails. A leading domestic minimally invasive surgical instrument company aimed to launch a new powered stapler, requiring the cartridge's tooth height consistency to reach ±0.005mm, the surface roughness of the pusher plate slide rails to be Ra ≤ 0.4μm, and the cutting blade to be sharp enough to cleanly cut through muscle tissue and blood vessel bundles without tearing.
Traditional precision casting or CNC machining could not simultaneously meet the requirements for complex shapes and high precision, so the client turned to the MIM process. After Fangchi's Medical Business Unit took on the project, they first analyzed the greatest manufacturing challenge of the part: the cartridge is approximately 35mm long, 12mm wide, and 8mm high, with as many as 24 tooth slots, each measuring only 0.6×0.4mm, 0.8mm deep, with an R0.1mm fillet at the bottom of each slot. Relying on machining for these micro-features would take over 20 minutes per cartridge, making the cost prohibitively high.
Fangchi's mold design team used high-precision micro-EDM technology to form the electrodes for all 24 tooth slots in a single setup, then proceeded to EDM the cavity one by one. The entire mold cavity machining cycle took 320 hours, using 3mm thick tungsten-copper alloy as the electrode material. The mold was designed with a one-cavity, four-impression structure and featured insert-type tooth slot modules, allowing individual worn tooth slot inserts to be replaced during subsequent maintenance without scrapping the entire mold set.
Injection molding used 316L stainless steel feedstock with a POM-based catalytic debinding binder system. To ensure the tooth slots were completely filled without air bubbles, the injection speed was controlled in multiple stages: starting with a low speed to fill up to 50% of the volume, then a medium speed to fill up to 90%, and finally a high-speed burst to complete the remaining 10% of the thin-wall area. The mold temperature was controlled at 115-120°C, with an injection pressure of 140MPa. After debinding and sintering, trial samples were observed under a microscope; all 24 tooth slots were fully formed, the fillets at the slot bottoms were clear, and there were no burrs.
The cutting blade assembly was another critical part. The blade is 32mm long, 0.4mm thick, with a 15° cutting edge angle, requiring the edge straightness to be ≤ 0.01mm and the edge to be free of nicks. The MIM process formed the blade body in one shot. After sintering, a diamond grinding wheel was used for secondary fine grinding of the cutting edge, ensuring sharpness met the medical blade standard.
For quality control, Fangchi introduced a Keyence ultra-depth 3D microscope to perform 100% automatic measurement of the depth, width, and position of each tooth slot on every cartridge. The measurement data was compared against the acceptance criteria, and parts with deviations exceeding ±0.008mm were automatically rejected. Additionally, 10 pieces from each batch were randomly selected for pusher plate insertion force testing, ensuring the slide rail friction resistance was between 0.5-1.0N.
After over a year of development and validation, the stapler obtained NMPA Class III medical device registration in 2024. As the sole MIM supplier for the cartridge assembly, Fangchi supplies over 3 million sets annually. The client's R&D director commented: 'Fangchi helped us solve an industry challenge — manufacturing high-precision cartridges in volume using MIM, enabling our stapler to be the first among domestic counterparts to achieve cutting quality comparable to imported brands.'
