[MIM Process] Quality Control in Powder Injection Molding – From Raw Material to Final Inspection

Introduction

Metal Injection Molding (MIM) is an advanced manufacturing process that combines the benefits of plastic injection molding and powder metallurgy. It is widely used to produce high-precision parts in industries such as electronics, automotive, medical, and telecommunications. In mass production, quality control during the injection molding stage is crucial to ensuring dimensional accuracy, density consistency, and downstream process stability during debinding and sintering.

At MIMO Metal, years of hands-on experience have shaped a comprehensive MIM process quality management system. From equipment control and material preparation to in-process monitoring and feedback, we have built a fully traceable and standardized manufacturing framework.

1. The Critical Role of Injection Molding in the MIM Process

Injection molding in the MIM process involves heating the feedstock and injecting it into the mold cavity. While similar to plastic injection in appearance, MIM demands tighter control over molding pressure, temperature, filling dynamics, and powder flow behavior.

Improper control can lead to:

• Short shots, voids, burrs, and cracks

• Uneven density and stress concentration, which can cause defects during debinding and sintering

• Poor batch consistency, resulting in lower yield and higher cost

Thus, injection molding is not only the first step in forming but also the first line of defense in ensuring overall MIM product quality.

2. Key Quality Control Measures for Injection Molding

MIMO Metal implements a "5M1E" approach (Man, Machine, Material, Method, Measurement, Environment) to achieve stability and batch consistency through standardized controls and traceable data.

2.1 Feedstock Management

• Moisture content must be below 0.05% to prevent bubbling during debinding

• Rheological curve is archived for each batch to ensure stable molding window

• Automated mixing systems prevent powder segregation and particle inconsistency

2.2 Mold Maintenance and Management

• Regular checks on clamping force, venting grooves, and slider wear

• Precision molds maintain cavity tolerances within microns to ensure dimensional repeatability

• Opening/closing pressure and timing are digitally recorded to reduce manual error

2.3 Molding Parameter Control

• Strict control of injection temperature, pressure, holding time, and cooling time within the validated window

• High-precision molding machines equipped with temperature feedback and closed-loop pressure control

• CAE simulation used for complex parts to optimize mold filling and reduce trial-and-error

2.4 Online Inspection and First-Article Validation

• First article of each mold is inspected for both dimensions and appearance

• Vision systems detect surface defects like burrs, short shots, and cracks

• Pre-debinding weight is recorded to verify completeness of part formation

3. Closed-Loop Quality Control for Process Abnormalities

Even for stable products, fluctuations in equipment or materials may cause hidden defects. To address this, MIMO Metal has developed a closed-loop quality system:

• Each injection line is equipped with real-time parameter logging

• Abnormal parts are traced through pressure/temperature curves for root cause narrowing

• On-site quality engineers are assigned to ensure rapid corrective action and rework evaluation

• Updated parameters are uploaded to the MES system to maintain live documentation of process cards

4. Standardizing Process Data and Enhancing Robustness

As MIM manufacturing evolves toward high-precision and high-volume production, quality control must transition from "experience-based" to "data-driven" management.

MIMO Metal has established a product-level process database, including molding window templates and machine setup parameters for each product, significantly improving trial efficiency and first-pass yield.

We also collaborate with clients during the DfM (Design for Manufacturability) phase to optimize wall thickness, transitions, and locking structures for better MIM molding compatibility and reduced design risk.

Conclusion: Process Control Is Key to Mass Reliability

Injection molding is the foundation of the MIM process. Its stability directly impacts the success of debinding, sintering, and final part performance. By implementing standard procedures, robust equipment controls, and real-time process data collection, MIM manufacturers can achieve greater consistency, reduce prototyping time, and lower rework costs.

As the powder metallurgy industry moves toward intelligent manufacturing and flexible production, mastering injection molding quality is the key to delivery confidence and cost competitiveness.