3D printing processes for lost-wax casting are increasingly becoming the preferred choice for artisans, engineers, and industrial manufacturers. Using 3D printers and PolyCast , users can test designs, reduce costly manufacturing processes, and shorten lead times. A better understanding of 3D printing processes helps avoid early design errors and yields more perfect finished products under the same conditions.
Part 1: 3D Printing with PolyCast
PolyCast is a filament specifically designed for lost-wax casting, capable of almost complete melting within the mold cavity with less than 0.003% residual ash. (The automatic printing parameters for PolyCast can also be selected using Cura LulzBot Edition on the LulzBot 3D printer .)
． Determine the directionality of printing based on the prototype requirements. Fewer supporting structures result in a more aesthetically pleasing surface and shorter printing time.
Using minimum fill (i.e., 10%) and wall thickness (2-3) for 3D printing can promote complete melting of the prototype within the cavity.
• Add shrinkage compensation to the STL file to reduce dimensional errors between the molten and solid states of the metal. This can be achieved by modifying the model dimensions using a metal/alloy-related compensation coefficient, typically between 1.007 and 1.030. (For example, if the compensation coefficient for steel is 1.025-1.030 and the metal part is 1 meter in size, then the size of the printed pattern should be 1.025-1.030 meters.)
A layer height of 0.1-0.2 mm is an ideal setting, which also helps with print resolution and post-processing.
PolyCast readily absorbs moisture, so it is recommended to store the cable in a dry environment (relative humidity not exceeding 20%), such as a dehumidifier box.
The key to lost-wax casting is a smooth surface. Coating and spray polishing are two recommended methods. It is suggested to first use 800-grit sandpaper to remove initial surface marks or seams and remove dust from the object.
1) Coating and polishing:
Use thin thread to suspend objects.
Immerse the printed object in isopropyl alcohol for 5-10 seconds, and increase the number of times as needed to achieve a better polishing effect.
Allow the item to dry for 20-30 minutes during this period, then determine whether the above steps need to be repeated.
2) Spray polishing:
• Use Polymaker 's Polysher alcohol polisher. The machine automatically performs alcohol spray polishing for 20-40 minutes while maintaining dimensional accuracy.
After completing the above steps, place the item in a 40°C dryer for about 1 hour to ensure complete solvent evaporation and surface hardening, or let it air dry overnight.
The wax tree structure can fix the casting and ensure that the metal flows smoothly and evenly into the part. The wax rod or gate will form a channel for the metal flow.
Minimize the curvature in the gate to reduce the impact of slowed metal flow on the parts.
Use a small torch on the final part to remove scorch marks or holes in the wax tree.
After the 3D printed prototype evaporates during the melting process, the ceramic shell becomes the mold for casting the metal.
The molding process involves repeatedly dipping the wax tree into ceramic slurry and silicon dioxide, and it is necessary to ensure that the coating is applied evenly and gaps are minimized in both steps.
At least 5 layers should be applied, and 7-9 layers are recommended for complex objects to prevent damage to the mold shell during the casting process.
Before repeating this step, it is crucial to allow each coating to dry completely. Once the shell reaches the desired thickness (approximately 9.525 mm on average), it can be melted.
Part 5: Complete Melting
Sintering or hardening the ceramic shell and burning away the internal 3D printing material to form a mold cavity.
Place the above-mentioned objects into the kiln with the opening facing down, and heat to about 1100-1200℃ for about 40-60 minutes.
(Note: The exact time and temperature depend on the type of kiln used and the metal parts being produced.)
After the 3D printing material is completely melted, allow the membrane cavity to cool completely.
Part Six: Forging
The membrane cavity is preheated in preparation for the injection of molten metal.
If any molten ash or debris remains in the membrane cavity, it must be thoroughly cleaned.
The mold cavity is placed in a kiln to preheat for pouring metal; the temperature is generally between 550-1100°C.
The metal flow passes through the gate and enters the mold cavity, allowing the mold and casting to cool and shrink at the same rate, forming a part that meets dimensional accuracy.
Allow the metal to cool and solidify completely; the curing time will vary depending on the material and the thickness of the object.
The metal parts are removed from the ceramic shell and then precision machined.
After the casting has completely cooled, remove the mold from the metal part, or use other tools such as pneumatic jacks or high-pressure water jets.
Remove the gate by sawing, cutting, grinding, or using a plasma cutter.
Part 8: Post-processing of Metal Parts
The appearance of the finished product depends on the materials used and the purpose of the parts. For some materials, the patina effect will be treated or retained, while some metal parts only need a layer of anti-corrosion protective coating.
For bronze parts, a layer of potassium sulfide is applied; after baking in another oven, a layer of ferric iron is added, and finally a protective agent is applied to keep the surface shiny.
For steel products, especially functional parts, only one layer of protective agent is needed.
3D printers are more economical than those costing millions, making them suitable for companies of almost all sizes to reduce costs and accelerate innovation. SanDiMa will continue to share all the latest news and technical tutorials related to 3D printing . Follow our fan page for the latest information and free events. We also offer printing services and industrial-grade 3D printers for any needs.
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More finished metal casting products: Check out these metal parts! A comprehensive collection of 3D printing castings!
Related resources: https://www.lulzbot.com/learn/tutorials/3d-print-patterns-investment-casting?pk_campaign=newsletter_feb19&pk_medium=email&pk_source=phplist&pk_content=polycast