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Laparoscopic surgical forceps are one of the most fundamental operating instruments in minimally invasive surgery. A good pair of forceps requires a jaw that opens and closes smoothly, provides stable gripping without damaging tissue, and can withstand repeated high-temperature and high-pressure sterilization. A European medical technology company commissioned Fangchi to develop three different jaw shapes: curved forceps, right-angle forceps, and straight grasping forceps. The core requirements were: connection hole positioning accuracy between the jaw and the shaft rod of ±0.01mm, joint clearance controlled between 0.02-0.03mm, cutting edge surface roughness Ra ≤ 0.8μm, and all edges and corners must be smooth with no sharp edges.
Fangchi adopted 17-4PH stainless steel material. After aging treatment, this material can achieve a hardness of HRC 40 or above, while also offering excellent corrosion resistance, making it suitable for steam sterilization environments. The MIM process design for the forceps jaws was divided into the following steps:
Step one, determining the mold design. Due to the significant differences in shape among the three types of forceps jaws, Fangchi created separate molds for each. The curved forceps have a bending radius of 15mm, requiring the mold to have two sliders to form the inner and outer sides of the curve respectively. To ensure a smooth arc surface, the working surfaces of the sliders underwent mirror polishing. The corners of the right-angle forceps and the anti-slip serrations of the straight grasping forceps were formed using inserts.
Step two, optimizing injection parameters. The thinnest part of the jaw's cutting edge is only 0.25mm thick, making filling difficult. Fangchi increased the injection pressure to 150MPa, used segmented control of the injection speed, and set the mold temperature to 125°C. This reduced the viscosity of the feedstock in the thin-wall area by approximately 30%, ensuring complete filling of the cutting edge. Samples were examined metallographically, and the density of the cutting edge area was consistent with the main body, with no pore aggregation.
Step three, debinding, sintering, and post-processing. Debinding used a nitric acid catalytic process, with a debinding furnace temperature of 120°C, nitric acid flow rate of 2.5L/h, and a debinding time of 5 hours. Sintering was carried out in a vacuum furnace at a maximum temperature of 1350°C with a 2-hour hold time. After sintering, the linear shrinkage rate of the forceps jaws was approximately 1.170, and the dimensional CPK reached over 1.25.
Step four, machining and surface treatment. The joint holes of the forceps jaws had a slight excess after sintering. Fangchi used high-precision small CNC machines for drilling and reaming to ensure the hole diameter tolerance of H7 (+0.012/0). The jaws were then assembled with the pivot pins, and the opening and closing torque was tested — the standard being 0.2-0.3 N·m. Afterwards, all forceps jaws underwent electrolytic passivation treatment to form a dense chromium oxide film on the surface, further enhancing corrosion resistance. Finally, a wool wheel was used for vibratory finishing to eliminate parting line marks, achieving a mirror-like smoothness of Ra ≤ 0.4μm on the entire jaw surface.
During the quality inspection phase, Fangchi used a coordinate measuring machine (CMM) to check the connection hole position, cutting edge profile, and the assembly clearance between the jaw and the shaft rod for each forceps jaw. Additionally, 5% of the samples were randomly selected for a 2000-cycle open-close fatigue test, requiring that the change in opening and closing torque not exceed ±15%. Only after all inspections were passed were the products released for shipment.
The product obtained CE certification at the end of 2023 and began mass export to Europe in early 2024. The client's procurement manager commented: 'The forceps jaws provided by Fangchi are superior in assembly precision and surface finish even to our previous German supplier, yet at only 60% of the cost.' To date, Fangchi has developed over 15 different shapes of surgical forceps jaws for this client, with an average monthly shipment of 300,000 pieces.
