Metal injection molding (MIM) is a four-step forming process. First, the metal powders are mixed with a binder. This mixture is then injected into a mold to give it the desired shape. The last two steps consist of removing the binder and then densifying the part by sintering of the powder. The injection can lead to defects that cannot be corrected in subsequent steps. One of the most common defects is the presence of bubbles or porosities in the injected part. These porosities, always present in the final parts, have a negative impact on the mechanical properties of the part. The use of a vacuum in the mold before and throughout the injection is explored in this project in order to remove the air that would allow the formation of porosities. This process is based on a similar one used in micro injection molding of polymers and high pressure die casting of metals, but which has never been documented in MIM. To do this, an injection press was adapted, and a vacuum mold was designed and manufactured. The experiments were undertaken with a non-degassed mixture to better understand the phenomena. A vacuum affected area is visible in the parts. Its shape and its position vary depending on the mold size. This area is caused by the swelling of the bubbles under the absence of pressure. For a non-degassed mixture, an optimal sequence which consists of injecting a certain proportion of the part at atmospheric pressure and then finish the injection under vacuum eliminates a large majority of the bubbles. For a standard degassed mixture, the use of vacuum eliminated all porosities greater than 2.5 mm and reduced the total number of porosities by 48% compared to the standard process.
| Date | 15 Feb 2023 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Vincent Demers (Supervisor) |
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Coutu, M. (Author),
Demers (Supervisor),
15 Feb 2023Student thesis: Master's thesis › Master in Engineering: Mechanical Engineering