MIM Overview

MIM, or Metal Injection Molding, is the abbreviation for Metal Injection Molding. It is a molding method in which a plasticizing mixture of metal powder and binder is injected into a model. The selected powder is mixed with a binder, and then the mixture is pelletized and injected into the desired shape.

 

The MIM process combines the flexibility of injection molding design with the strength and integrity of precision metals to achieve a cost-effective solution for extremely complex geometries.The MIM process is divided into four distinct processing steps (mixing, molding, degreasing, and sintering) to achieve the production of the part, with the need for surface treatment determined by the characteristics of the product.

 

In the process of injection molding, some abnormal phenomena are likely to occur, such as: cracks, product surface ripples, product brittle strength reduction, mold release

Difficulty, product size instability, product size instability, parts peeling and delamination, fusion marks, injection of dissatisfaction, etc., these phenomena will affect the molding die

These phenomena will affect the specific use of molding tools, so we need to find out the relevant factors and solutions.

Cracks

1. Mold is too cold, adjust the mold temperature.
2. Cooling time is too long, reduce the cooling time.
3. Plastic and metal inserts shrink differently, preheat the metal inserts.
4. Ejector device tilt imbalance, ejector cross-sectional area is small or improper distribution, adjust the ejector device or reasonable arrangement of the number of roof bars and their location.
5. The production slope is not enough, hard to demold, correctly designed demolding slope.

 

 

Ripple on the surface of the product

1. Low temperature of material, improve the temperature of material with large flick.
2. Injection pressure, material temperature is high, can reduce the injection pressure, and vice versa, increase the injection pressure.
3. Low mold temperature, increase the mold temperature or increase the injection pressure.
4. Injection speed is too slow to increase the injection speed.
5. The gate is too small, extend the gate appropriately.

 

Metal Injection Molding (MIM) is a complex manufacturing process, and like any manufacturing process, it can encounter certain problems. Here are some common issues in MIM and the best ways to address them:

 

Feedstock Issues:

 

Problem: Inconsistent feedstock properties, such as poor flowability or binder separation.

Solution: Work closely with the feedstock supplier to ensure consistent material quality. Optimize the feedstock formulation and processing parameters to improve flowability and minimize binder separation.

 

Mold Filling:

 

Problem: Incomplete filling of the mold cavity, resulting in incomplete parts or voids.

Solution: Adjust injection parameters, such as temperature, pressure, and injection speed, to optimize the flow of the feedstock. Optimize gate design and placement to ensure proper mold filling.

 

Part Shrinkage:

 

Problem: Dimensional shrinkage during the sintering process, leading to parts that do not meet the desired specifications.

Solution: Carefully control the sintering temperature, time, and atmosphere to minimize shrinkage. Consider design modifications, such as adding compensatory features or adjusting tolerances, to account for expected shrinkage.

 

Surface Defects:

 

Problem: Surface imperfections, such as warping, cracking, or roughness.

Solution: Optimize the debinding and sintering processes to minimize defects. Adjust the cooling rate during sintering to reduce warping. Implement post-processing techniques like tumbling, polishing, or coating to improve surface finish.

 

Contamination:

 

Problem: Contamination of the feedstock or molds, leading to defects in the final parts.

Solution: Ensure proper cleanliness and maintenance of equipment and molds. Implement strict quality control measures to monitor and prevent contamination throughout the manufacturing process.

 

Tooling Wear:

 

Problem: Wear and damage to the molds, leading to increased costs and decreased part quality.

Solution: Regularly inspect and maintain the molds to prevent wear. Consider using wear-resistant coatings or materials for the molds. Optimize injection parameters to reduce stress and wear on the molds.

 

Porosity:

 

Problem: Presence of pores or voids in the final parts, affecting mechanical properties and surface finish

Solution: The porosity of MIM materials is generally not greater than 5%. Selection of a specific cross-section for a MIM part is important only when considering the formation of defects. Rough and fine polishing is carried out until the residual porosity is revealed. The area percentage of porosity means the density of the part.

 

Harber is specialized in MIM and PM service for more than 15 years. We are equipped with expert engineers who understand the importance of cost management and quality. Many manufactures of MIM or PIM products employ several ways to cut down the steel part cost. At Harber, we are well aware of those techniques such as from raw material, binding method, degreasing and vacuum sintering furnaces, post-machining etc.

 

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