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The airbag is a core component of automotive passive safety. The inflator must generate high-pressure gas within tens of milliseconds after receiving a collision signal to rapidly deploy the airbag. This process imposes extremely stringent requirements on the strength, pressure resistance, and dimensional accuracy of the metal parts. A top-five global automotive safety system supplier needed three MIM parts for its new-generation micro-inflator: the sleeve, the filter support, and the igniter base.
The sleeve is the main pressure-bearing part of the inflator, with a wall thickness of 1.2mm, an inner diameter of 12mm, and internal stepped holes and annular grooves. The filter support is a complex mesh structure requiring uniform porosity and no burrs. The igniter base needs a precision threaded interface, and the fit clearance with the igniter tube must be ≤ 0.02mm. The customer required that all parts must withstand an impact pressure of 30MPa within a temperature range of -40°C to 85°C without any cracks or permanent deformation, and each part must have full traceability.
After receiving the drawings, Fangchi's Automotive Business Unit first conducted a feasibility analysis. The material selected was low-alloy steel Fe-2Ni, which can achieve a sintered density of over 7.6 g/cm³, a tensile strength exceeding 600MPa, and good low-temperature impact toughness. The feedstock used a self-developed formula of carbonyl iron powder + 2% nickel powder, and after mixing, the injection flowability index (MFI) reached 450g/10min, suitable for filling the thin-walled sleeve.
For the mold, the sleeve used a one-cavity, four-impression layout with the gate located on the bottom flange face, using a ring-type submarine gate for material entry, ensuring the melt filled sequentially from one end to the other to avoid internal air trapping. The filter support used a one-cavity, two-impression layout and was designed with a slider ejection mechanism to ensure the fine pins in the mesh area were not broken during mold opening. All molds were equipped with mold temperature controllers and a hot runner temperature monitoring system.
Debinding used an oxalic acid catalytic debinding process, with the debinding time calculated as 6-8 hours based on the part wall thickness. After catalytic debinding, the parts appeared off-white with no surface cracks. Sintering was carried out in a continuous mesh belt furnace at a maximum temperature of 1280°C with a 90-minute hold time, in an atmosphere of 75% hydrogen + 25% nitrogen, with a dew point of -55°C. After sintering, the dimensional shrinkage rate of the parts was controlled at 1.170 ± 0.002, and the density spot checks all fell between 7.62-7.65 g/cm³, far exceeding the customer's lower limit requirement of 7.6 g/cm³.
To meet the traceability requirements of the automotive industry, Fangchi implemented laser marking on each part, with the marking content including the production date, batch number, furnace number, and machine number. All inspection data — including CMM dimensions, hardness, density, and metallographic photos — were uploaded to the Kingdee ERP system, allowing the customer to access quality reports for any batch online via an authorized account.
Over the two years of mass production, Fangchi has supplied a total of over 12 million pieces to this customer, with zero batch quality incidents or customer complaints. The customer's quality director wrote in the annual audit report: 'Fangchi's MIM parts are superior in dimensional stability to similar European suppliers, and the traceability system is very complete. They are our most reliable Chinese partner.'
