What Is MIM Melt Flow Index (MFI) and Why Is It Measured?

Melt Flow Index (MFI) is the single most commonly used quality check for MIM feedstock — yet many people outside the MIM industry have never heard of it.

What MFI measures: MFI measures how many grams of feedstock flow through a standardized capillary die in 10 minutes under a specified temperature and load. It is essentially a viscosity check — higher MFI means lower viscosity (flows more easily). The test conditions:

Parameter	Typical MIM Setting
Temperature	150-200°C (binder-dependent)
Load	2.16-10 kg (material-dependent)
Die diameter	2.095 mm (standard)
Sample preheat	4-6 minutes
Cut interval	15-60 seconds

Typical MIM MFI values:

Material / Binder System	MFI Range (g/10min)	Target
316L + POM binder	800-1500	±5% of nominal
316L + wax-polymer binder	200-600	±5%
17-4PH + POM binder	700-1300	±5%
Fe-2Ni + POM binder	900-1600	±5%
Ti6Al4V + POM binder	600-1000	±5%

Why MFI matters: A drift of just 5% in MFI corresponds to approximately 0.2-0.4% shift in sintering shrinkage. Over a 20 mm dimension, that is 0.04-0.08 mm — significant for parts held to ±0.05 mm. This is why reputable MIM manufacturers test every feedstock batch and reject any that falls outside the ±5% window. Quick Q: What is MIM Melt Flow Index?

Melt Flow Index (MFI) is a viscosity measurement for MIM feedstock — it measures how many grams of material flow through a standard die in 10 minutes at a controlled temperature. It is the primary quality check for feedstock consistency. A well-controlled MIM process maintains MFI within ±5% of the target value batch-to-batch. Deviations beyond ±10% typically result in dimensional drift in sintered parts.