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Comparison between binder jetting metal 3d printing and metal injection molding (MIM)

2021-12-01 11:04:11Source of article:EasyMFG

Metal injection molding(MIM) is a strong manufacturing process that is suitable for the mass production of metal parts, while binder jetting metal 3d printing provides a compelling alternative based on its unique advantages.

What is binder jetting metal 3D printing?



Binder jetting metal 3d printing adopts an array-typed printhead, slicing the CAD model into a series of two-dimensional data. Based on the 2D data, the printhead deposits binder selectively into the powder bed and bonded the powders together, finishing the green part layer by layer finally. Then put the green part into the curing furnace to get a certain strength. The curing process will take several hours. Next, pick out the cured part onto the depowdering station to remove the surplus powders. Finally, get the parts with high density and strength by sintering into the high-temperature furnace.


Advantages of binder jetting metal 3D printing


For the time being, one of the biggest advantages of binder jetting metal 3D printing is fast speed. BJ adopts an array-typed printhead, which is dozens of times more than traditional 3d printing technology, such as SLM. Because SLM builds the part from point to line, while BJ prints the part from line to surface, which is other additive manufacturing technologies struggle to compete with, so it is the only metal 3d printing that can be regarded as the only method for large scale production of metal parts.

The second advantage for BJ is a wide variety of printable powders. Basically, the powders which are not easy to oxidize at room temperature can be printed theoretically.

The third advantage is low cost, which is less than 1/5 of SLM, equivalent to traditional CNC manufacturing.

The fourth advantage is convenient processing since BJ requires no support. The unbonded powders surrounding the printed parts can support the parts.

In addition to the unique advantages of BJ, it also has the same advantages as other metal additive manufacturing methods. One is design freedom. Due to the BJ part is built layer by layer(while MIM parts are built in the mold), parts with all kinds of complicated geometries can be printed basically. This means BJ can integrate several individual parts together –Several parts can be replaced by a single part but with the same function, then assembly time can be shortened.

Another distinct advantage is that the manufacturing steps for BJ are lesser than MIM which needs molds. But BJ can directly print parts. So for a small short run, the production speed is obviously superior to MIM.

Additionally, once the mold for MIM is finished, it is not easy to adjust. So metal 3d printing can conduct multiple iterations without increasing the cost.

Based on the above advantages, binder jetting metal 3D printing is the only method that can realize the industrial mass production for metal parts. Of course, there are still some areas that BJ is not good at since post-processing is very difficult to overcome.

Due to the influence of gravity and friction, BJ is not good at processing thin-walled components, etc.


Similarities and differences between binder jetting metal 3D printing and MIM


Binder jetting metal 3D printers and MIM can both manufacture metal parts.  But there are similarities as well as differences. 

First of all, binder jetting metal 3D printing has fewer design constraints than MIM, and MIM's design needs to consider part demolding, so it limits some shapes. 

Secondly, the process is not the same.  Binder jetting metal 3D printing is made by selectively depositing binders with array nozzles (detailed above), while MIM is made by injection molding.  But the post-treatment process is the same, both need high-temperature sintering.  After sintering, the density of 3D printed parts can reach more than 98%, which is similar to MIM process.  But because MIM requires a special debinding process, it is impossible to make very thick parts. 

Generally speaking, the volume ratio of metal powders used by binder jetting metal 3d printing is about 60%, with a shrinkage ratio between 1.15~1.2.  The volume of metal 3D printed parts will shrink in the sintering process, 1.15~1.2 will shrink to 1.  Therefore, the sintering process is very important for binder injection metal 3D printing.  EasyMFG has done a lot of experimental work in the sintering process since it started to make binder jetting metal 3D printers in 2016, and has accumulated a lot of rich data, which can solve the problem in this link.


How to choose between BJ and MIM?

In most cases, the trade-off depends on yield.  For prototyping and small batches, such as tens of thousands of units, BJ is a good choice.  However, MIM is more cost-effective for mass production, such as under hundreds of thousands of units, MIM is recommended.

Besides yield being the determining factor, there are other reasons.

Due to debinding limitations, MIM cannot produce too large and thick parts.  Generally, MIM is less than 500G.  So for large size, it tends to choose BJ.

Also, complex designs tend to opt for BJ because the geometry of MIM parts is limited by demolding.

Compared with binder jetting metal 3D printing (BJ), MIM has a slightly higher surface finish and smaller roughness, so if requiring the surface roughness around1~2μ, MIM is recommended.  If the surface roughness is above 3μ, BJ is a good choice.  For high assembly accuracy, generally less than 1 μ, the late processing process needs to use CNC, MIM, or BJ both can be chosen


Use BJ as a complement to MIM

Binder jet metal 3D printing (BJ) and MIM are not two competing processes, but complementary.  In fact, BJ can be used to complement MIM.  For some small batches of more complex products, the cost of mold opening is relatively high. In this case, BJ has an obvious price advantage. 

In addition, the digital flexible manufacturing characteristics of BJ can be realized in a short period of time to produce samples and quickly achieve market validation. BJ is also a very suitable method in the process of product development.

one more MIM metal sample printed by Easy3DP-500 3d printer
One metal sample printed by Easy3DP-450 3d printer