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The pursuit of lightweight design in smart wearables has never stopped. In 2024, a renowned international smartwatch brand planned to launch a new series positioned as an 'ultra-light business flagship.' The watch buckle for this series was required to be made of Ti-6Al-4V titanium alloy, with the finished weight of a single piece strictly below 0.5 grams. Additionally, the buckle needed to integrate a snap-fit spring tab, a curved contact surface, and connection holes for the strap — all features to be formed in a single shot, with no welding or riveting processes allowed.
The difficulty of titanium alloy MIM is far greater than that of stainless steel. Titanium powder is extremely reactive and highly prone to oxidation and oxygen pickup during the debinding and sintering processes, leading to part embrittlement and cracking. Fangchi's feedstock R&D team specifically formulated a dedicated binder system for titanium alloy: using POM as the backbone, supplemented with a small amount of antioxidant and dispersant, to ensure the titanium powder surface was not excessively contaminated during mixing. The entire feedstock preparation process was carried out under nitrogen protection, with the mixing temperature controlled at 160-170°C to avoid prolonged exposure of the titanium powder to air.
In terms of mold design, the snap-fit spring tab of the buckle is only 0.25mm thick, with a cantilever length of 4mm. During injection, it is highly susceptible to localized degradation due to excessive shear heat. Fangchi's mold engineers installed local heating rods in the cavity area corresponding to the spring tab, raising the mold temperature in that area to 125°C — 15°C higher than other areas — thereby improving the melt flowability in the thin-wall region. A fan-shaped film gate was also adopted, with its width covering the entire length of the buckle, ensuring the melt front advanced in parallel and avoiding weld lines in the spring tab area.
Debinding is another challenge in titanium alloy MIM. Conventional nitric acid catalytic debinding generates a strongly acidic atmosphere that can corrode the titanium powder surface. Fangchi switched to oxalic acid vapor catalytic debinding, which is relatively milder, with the debinding rate controlled at approximately 1.5mm/h. This ensured the binder decomposed slowly, allowing the generated gases to escape the part smoothly without forming micro-cracks internally. After oxalic acid debinding, the parts appeared light gray with no surface oxide scale.
Sintering was carried out in a vacuum furnace with an ultimate vacuum of 10⁻³ Pa, a maximum sintering temperature of 1250°C, and a hold time of 3 hours. To further control the oxygen content, high-purity argon gas was introduced as a protective atmosphere during sintering, with a gas flow rate of 30 L/min. After sintering, the oxygen content of the titanium alloy buckle was controlled below 0.25%, with a tensile strength reaching 950 MPa and an elongation of 12%, fully meeting the usage requirements for wearable devices.
For surface treatment, Fangchi commissioned a partner certified for PVD coating on medical implants to deposit a rose-gold colored TiN film on the buckle surface, with a thickness of 1.5μm. The coating hardness exceeded HV 2000, and it passed a 500-hour artificial sweat corrosion test without peeling or discoloration.
Mass production of the buckle began in September 2024. The Anhui base handled injection molding, debinding, and sintering, while the Shanghai headquarters performed final inspection and packaging. The daily shipment volume was stable at 800,000 pieces. After over 20,000 open-close cycle tests, the elastic retention rate of the snap-fit spring tab remained above 95%. The customer awarded Fangchi an A-level supplier rating.
