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Lost Resin Casting

IMG 0538Several years ago, I began experimenting with using 3D printing to produce the master models needed for investment casting. Fused Deposition Modeling (FDM) is one 3D printing process that extrudes thermoplastic in layers. One plastic, Polylactic Acid (PLA) will burn out of the mold. But the layers are large, and the resulting model and casting looks very poor.

Another form of 3D printing uses a Ultraviolet light sensitive resin. The printer uses “pictures” of each layer and the layers are extremely thin and near invisible in the resulting print and casting.

Resin 3D printing is by far the best choice. Resin designed for burn out casting is easily available. My first choices for making casting models were to use the lowest cost resins. I tried four brands, all with very limited success.

I eventually determined I didn’t have the “right stuff” in either skills, equipment or materials. So, I returned to using carved wax for casting. 3D printing for casting was put on hold.

Since then, I have obtained a new, more powerful, resin 3D printer. I made the decision to try printing casting models again, but using professional grade castable resins.

BlueCast

Sometimes, when I desire to play a serious game, I must pay the entry fee. BlueCast is an Italian producer for a product line of castable 3D printer resin. It has a reputation for high quality and one if not THE highest purchase costs.

As I said above, it’s been several years since I first desired using 3D printing to create the master (casting) models for use in investment metal casting. Investment casting is the process used in jewelry and other high detail casting commonly known as “lost wax casting” -- when the model is made from wax.

It is an all-in-one-piece molding process where an exact model is created using material that can be completely disintegrated and vaporized in a high temperature kiln firing. The model is surrounded by wet investment (plaster like material) in a steel tube called a flask. 

The high temperature kiln firing destroys (melts/vaporizes) the model and cures the investment into a hollow ceramic mold. The empty cavity the vanished (lost) model created is then filled with the hot molten metal.

The investment mold must be destroyed after the metal solidifies, to remove the cast metal duplicate of the model. The investment mold is therefore also “lost”. 

To make another part, a new model and mold must be created again, to be destroyed (lost) to the casting process. It’s how it is done. A new model and new mold every time.

Using a 3D printed model for the expendable investment master model, is a huge time benefit for making investment cast duplicates. For this reason, almost all the professional investment jewelry casting is now done using 3D printed master models. This provides a direct path from the CAD (Computer Assisted Design) drawing to finished cast item. 

A professional (commercial) caster cannot risk unpredictable or undependable processes and materials. Neither can the hobbyist.  Bluecast resins are considered reliable professional grade material and justifies the cost. I am a hobbyist caster and can produce professional grade results using the correct materials.

AS mentioned, I have experimented with lower cost castable 3D resins with mixed results, especially with the kiln burn-out of the resin material. I had some success, but the typical issue was damage to the mold interior from the resin model burn-out. Thirty hours of production time is lost from a damaged mold, unseen until after the metal was cast.

Using wax master models, my successful cast rate is 99%. Resin model success has been less than 50%

I tried all the tips and tricks to get the low-cost castable resins to burn out clean. There are a great number of variables. The requirement is consistent dependable results. Couldn’t get there from here.

Now I have a more powerful printer and “paid the piper” for the “good stuff” resin and will see if it works for my needs and my print system, an Anycubic Photon Mono SE.

Step One

The first Bluecast X5 print was a success using the printer settings published on the Bluecast website. The next step is to cast this first model and see how the burnout behaves.

Step Two

The investment cast of the first Bluecast resin model in silver is also a success! Model and mold are of course “lost”, but the tangible result is a perfectly useable silver duplicate of the resin model.

Resin (material) costs are six times higher than the bargain-brand material, but in total production time and cost, the effect on product end cost is completely justified and not an issue.

Off to a good start. I have a good feeling I have a workable system. I will be doing many more resin model investment casting projects.

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First BlueCast X5 (resin) print just finished Closer look at print on the build plate
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This n is the un-UV-cured print after clean-up. Good detailed print. UV after-curing fades out the blue color. This step is unnecessary if no sanding, filing or drilling is necessary.
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After casting and pickeling. Very good burn-out. Finished pendant. Note the fine detail.

 

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