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MIM Process Series Part 6: Sintering

Sintering is the final step in the MIM process. During this blog series, we’ve been through feedstockcompoundingmolding, and debinding. This final blog post in the series will explain how a part goes from being “brown” to being complete.

The parts that have been debinded are placed on ceramic trays. These trays are made specifically so that minimal movement occurs during sintering. It is then placed into a high temperature furnace. The “brown parts” are heated slowly in the furnace and any remaining binder is evaporated. Once this is complete, the part is heated to a temperature high enough to fuse the particles in the part together. This process shrinks the part by about 20% (depending on the materials used for the part) and transforms the “brown part” into a dense solid part. The furnaces are allowed to cool, and then the parts can be removed and are considered final. The sintering process takes anywhere from 15-20 hours. Any additional steps would be part of the finishing process, such as machining operations or surface coating.

Types of Furnaces

There are two kinds of furnaces that are available for MIM production: continuous furnaces and batch furnaces. Continuous furnaces can debind and sinter in the same step. The temperatures reach near melting temperature of the base metal, and these furnaces are only ideal for high volume manufacturing. The batch furnaces also reach temperatures near the melting temperature of the base metal but have a much shorter process time then continuous furnaces. These furnaces run under vacuum and during the process a flow gas is pumped through the furnace – these gases can be nitrogen, argon or hydrogen. There is also supporting equipment for this furnace, including a hydrogen generator, a nitrogen generator, and a back up emergency power generator for cooling the vessel in times of a power failure.

Issues During Sintering

There are issues that can occur during sintering, which is why the design step of our business is so critical. Without our engineers looking at all of the potential defects or issues, there could be problems with the final part. These problems include not taking into consideration gravity or friction. The resulting part can be warped. There are options that our engineers use to minimize this. Some of these options include spacers, adding a support rib to the part, and coining. There can also be sag issues with a part. Using special setters that support the pieces most likely to sag upright can solve this issue. Parts can also be set in a special ceramic tray, or they can include a runner.

Now that you have read all of my blogs on the MIM process, what are your questions? Is there anything that I didn’t go over that you would like to know more about? If so, please comment below or fill out a “recommend a topic” form. I’d love to hear your recommendations for future blog topics, as well as any comments you have about my most recent blog series, MIM 101.

For more information, contact our team of engineers today!

You may also be interested in:

MIM Series Part 1

MIM Series Part 2 – Feedstock

MIM Series Part 3 – Compounding

MIM Series Part 4 – Molding

MIM Series Part 5 - Debinding

 

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Last updated 12.12.2019