Phases of a MIM process

Metal Injection Molding process

PHASE 1 – Mold manufacturing

Mold manufacturing is a critical aspect of Metal Injection Molding (MIM) that requires high-strength steel molds, which are more complex and demanding compared to traditional plastic injection molds. These molds are designed with cavities shaped according to the desired part, incorporating an enlargement factor to account for material shrinkage during injection. Adhering to the design rules, available for download on our website, is crucial to ensure a stable and defect-free injection process.

The number of cavities in the mold varies depending on the part's geometry and dimensions, ranging from a single cavity to more than 10. Typically, molds for MIM feature 2 or 4 cavities, and the cycle time for each injection can range from 15 to 60 seconds, depending on the specific requirements of the part.

PHASE 2 - Feedstock

The feedstock used in Metal Injection Molding (MIM) comprises metal powder with a maximum particle size of 32 microns, with at least 80% of particles below 22 microns. This powder is mixed with binders or moldable binders, granulated, and extruded to form pellets. The binder itself is a combination of thermoplastics, waxes, polymers, and other additives.

Accurate characterization and control of the feedstock are crucial for adjusting downstream process parameters, particularly during injection and sintering stages. This meticulous control ensures the achievement of desired tolerances and repeatability in the final components. By carefully managing the feedstock, we can optimize the production process and ensure consistent and high-quality results.

PHASE 3 - Injection

The feedstock is precisely injected into a mold, taking on the shape of the desired part. Key parameters during injection include pressure, flow rate, and temperatures, both of the injection screw and the mold itself. These parameters are carefully adjusted to suit the specific geometry of the part. Our extensive manufacturing expertise is crucial in achieving defect-free parts with exceptional quality.

The resulting component, referred to as a 'green part,' undergoes an initial dimensional shrinkage as it is ejected from the mold. This shrinkage typically ranges from 0.7% to 0.9% in carbon and low alloy steels, and 0.4% in austenitic stainless steels.

PHASE 4 - Sintering

Sintering is the concluding process that involves interdiffusion bonding of metal particles through the application of temperature and gases (such as H2 or N2, depending on the alloy). This process allows the attainment of the target density, reaching 95-98% compared to the traditional sintering's 82%. Sintering can be performed in either batch furnaces, suitable for small batches or special materials, or continuous furnaces, ideal for large production batches.

At Ecrimesa Group, we possess both types of equipment, comprising three continuous lines and two batch furnaces. The positioning of the parts throughout the debinding and sintering process plays a crucial role in achieving the desired dimensional outcomes. Therefore, the meticulous definition and industrialization phase are paramount to establishing a robust and dependable process.

During the sintering phase, the second and final shrinkage occurs, resulting in the attainment of the customer's desired final dimensions. For carbon and low alloy steels, the shrinkage factor between the mold and the final part is 1.2165, while that between the green part and the final part is 1.205. As for stainless steels, the shrinkage factor between the green part and the final part is 1.166, with a corresponding factor of 1.160 between the mold and the final part.

PHASE 5 - Final-finishing operations

Following the completion of the sintering process, additional operations and treatments may be necessary to meet specific customer requirements. At Ecrimesa Group, we understand the importance of delivering fully finished parts, which is why we have an advanced heat treatment department. This allows us to provide comprehensive heat treatment services to optimize the hardness, strength, and other mechanical properties of the components.

In addition to heat treatment, we also offer our own in-house machining service. This enables us to achieve close tolerance dimensions and carry out precision machining operations to meet the exact specifications of our customers. Whether it's honing for precise surface finishes or final polishing for aesthetic or roughness requirements, our machining capabilities ensure that the parts are meticulously crafted to meet the highest standards of quality.

By offering comprehensive final-finishing operations, including heat treatment and machining services, we ensure that our customers receive fully finished parts that not only meet their technical requirements but also exhibit superior aesthetics and surface quality.

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