Micron-sized metal powder (typically 5-15μm particle size) and thermoplastic binders (paraffin wax, polyoxymethylene, polyethylene, etc.) are fed into an internal mixer in precise proportions. The mixture is heated and mixed at 150-180°C, ensuring the powder particles are uniformly coated by the binder to form a paste-like compound with good fluidity. The compounded material is then extruded and pelletized by a pelletizer to produce cylindrical feedstock pellets with a diameter of 2-3mm and a length of 3-5mm. The pelletizing process removes air bubbles trapped during mixing, ensuring uniform feedstock density. Fangchi is equipped with professional internal mixers and supporting pelletizing lines, with a daily processing capacity of 600kg.

Feedstock pellets are added to the injection molding machine hopper, heated to 170-200°C to a molten state, and then injected into a precision mold cavity via a screw plunger. The mold temperature is controlled between 90-130°C, and the melt rapidly cools and solidifies within the cavity, forming a green part that matches the shape of the mold cavity. The key to the injection molding process lies in controlling parameters such as temperature, pressure, and speed to avoid defects like short shots, flash, weld lines, and warpage. Fangchi can produce micro to small precision parts weighing less than 100 grams. Taking a phone Type-C shell as an example, the single injection cycle per machine is approximately 15 seconds, with a daily output of 900,000 pieces.

The purpose of debinding is to remove most of the binder from the green part, forming an interconnected pore network within the part in preparation for subsequent sintering. Fangchi utilizes a catalytic debinding process, where the green parts are placed in a debinding furnace, heated to 110-130°C, and exposed to nitric acid or oxalic acid vapor as a catalyst. This causes the polyoxymethylene-based binder to decompose into formaldehyde gas, which is then exhausted from the furnace. No liquid phase is formed during the debinding process, so the parts do not deform and maintain good dimensional accuracy. Debinding time is determined by the part's wall thickness, typically ranging from 4 to 8 hours. After debinding, the parts appear grayish-white, with the volume unchanged but the weight reduced by approximately 30-40%. These are called brown parts. Fangchi is equipped with 6 debinding furnaces from Xingshuoshuo and Sibaerui, with a daily processing capacity of 1.44 million pieces (based on Type-C shells).

The brown parts undergo densification sintering in a high-temperature sintering furnace. The furnace temperature is raised to 1200-1350°C and held for 1-4 hours. At high temperatures, metal atoms diffuse and migrate, causing the pores between powder particles to gradually close. The part volume shrinks by approximately 15-20%, ultimately achieving over 97% of theoretical density. Sintering is carried out in a vacuum or protective atmosphere (hydrogen, argon, nitrogen) to prevent metal oxidation. After sintering, the parts exhibit a metallic luster and excellent mechanical properties.

Sintered parts are already close to the final shape, but post-processing may be required based on customer requirements:

- Dimensional Finishing: Using CNC lathes and milling machines for minor cutting operations on threaded holes and high-precision mating surfaces to achieve ±0.005mm accuracy.

- Heat Treatment: Performing solution treatment and aging on precipitation-hardening stainless steels such as 17-4PH to enhance hardness and strength.

- Surface Treatment: Including polishing, sandblasting, electroplating, PVD coating, passivation, etc., to improve appearance, corrosion resistance, or wear resistance.

- Assembly: Assembling multiple MIM parts with other components into sub-assemblies.

100% of all finished products undergo full dimensional inspection and visual inspection. Fangchi is equipped with 5 CCD optical inspection devices that simultaneously measure over 12 critical dimensions at an inspection speed of 700 parts per hour, automatically rejecting parts that fall outside tolerance. Samples are also taken from each batch for performance testing, including hardness, density, salt spray, and insertion/withdrawal life tests. Products that pass inspection are cleaned, packaged, and labeled according to customer requirements, and shipped with an outgoing inspection report. Quality data for each batch is uploaded to the MES system, supporting full traceability throughout the process.