Powder injection molding (PIM), including metal injection molding (MIM) and ceramic injection molding (CIM), is an advanced molding technology that can produce a large number of shape components from powder. This process uses injection molding technology to produce a large number of small and complex parts with high accuracy. The optimal application weight is usually less than 100 grams.
PIM mixes metal particles or ceramic powder with a resin binder to form raw materials that can be processed by plastic processing equipment. The raw material is heated in a screw feed barrel, injected into a mold cavity in liquid form under pressure, cooled in the cavity, and then sprayed. Next, the resin binder material is removed, and the molded product is sintered to form a final product. During the binder removal phase, resin removal can have a significant impact on the mechanical properties of the sintered part.
PIM material injection is usually accompanied by spraying and separation of powder and binder materials. The mixture of powder and binder material may separate due to the strong shearing effects that occur during the feed. Separation of powder and binder materials can lead to uneven distribution of the powder in the molded part. Since the binding material was finally removed, appearance defects occurred in areas with a low powder concentration. To accurately predict the flow rate, a wall slip model is enabled when performing a powder injection molding simulation.
The powder injection molding process can be used to predict black lines in parts with low raw material powder concentrations. This simulation requires a model with a 3D mesh. The use of a suspension equilibrium model (SBM) solves the problem of separation of powder and binder materials. SBM predicts changes in powder concentration due to convection and shear. To determine areas where the powder volume is abnormally small, check the powder volume concentration results.
The Powder Concentration Module uses a suspension equilibrium model (SBM) to predict the effect of powder separation.
In this model, the gradient of particle normal stress is considered as the driving force for particle motion. As a result, powder separation due to shearing and convection of powder concentration from upstream to downstream can be considered.
Although SBM models fluids and particles in two stages, the complete Navier-Stokes equation solves only mixtures or suspensions of fluids and particles. An additional particle phase mass balance equation similar to the transport equation is used.
The powder volume concentration results showed a dense portion of the powder in the molded product. Therefore, you can check whether the distribution in the raw material is uneven.
This result is produced by the powder injection molding process.
Fill + Pressure holding
The powder volume concentration results show how the powder is distributed throughout the part. You can use this result to predict black lines. Black line is one of the most common defects in powder injection molding. Black lines appear when the powder and binder in the raw materials are unevenly distributed and the powder concentration is relatively low, but they cannot be visually confirmed until the sintered molded product.
Powder volume concentration results
The result should be uniform color throughout the part. If the powder concentration in your area is low, consider the following:
Change process settings.
Change the shape of the molded product.