【3D Printing Knowledge】The Eight Steps of Metal Casting: A Deep Dive into the Foundry!

The 3D printing process for investment casting is increasingly becoming the preferred choice for artisans, engineers, and industrial manufacturing. Using a 3D printer and PolyCast, users can test designs, reduce expensive production costs, and shorten lead times. The more one understands the relevant 3D printing processes, the more effectively they can avoid early design errors and achieve more perfect finished products under the same conditions.


 
PolyCast is a filament specifically designed for investment casting, burning away almost completely in the mold cavity with less than 0.003% ash residue. (In LulzBot 3D printers, Cura LulzBot Edition can also be used to select automatic printing parameters for PolyCast.)
 
．Determine print orientation based on prototype requirements; fewer support structures result in a smoother surface and shorter print time.
．Use minimal infill (i.e., 10%) and wall thickness (2-3) for 3D printing to facilitate complete burnout of the prototype in the mold cavity.
．Add shrinkage compensation to the STL file to reduce dimensional errors between molten and solid metal. This can be done by modifying the model dimensions with a compensation factor related to the metal/alloy, usually between 1.007-1.030. (For example: for steel, with a compensation factor of 1.025-1.030 and a metal part size of 1 meter, the printed pattern size should be 1.025-1.030 meters.)
 
．A layer height of 0.1-0.2 mm is an ideal setting, aiding both print resolution and post-processing.
． PolyCast is prone to absorbing moisture. It is recommended to store the filament in a dry environment (relative humidity not exceeding 20%), such as a dry box.
 
The key to investment casting is a smooth object surface. Dip polishing and spray polishing are two recommended methods. It is advisable to first use 800-grit sandpaper to remove initial surface marks or seams, and to clean any dust from the object.

1) Dip Polishing:

．Hang the object with a thin wire.
．Immerse the printed object in isopropyl alcohol for 5-10 seconds. Increase repetitions as needed for more polishing effect.
．Allow the object to dry for 20-30 minutes, then determine if the above steps need to be repeated.
 
2) Spray Polishing:

．Use Polymaker's Polysher alcohol polishing machine.
．Automatic alcohol spray polishing inside the machine for 20-40 minutes, while maintaining dimensional accuracy.
After completing the above steps, place the object in a 40°C dryer for about 1 hour to ensure complete solvent evaporation and surface hardening, or allow it to air dry overnight.
   
The wax tree structure fixes the castings and ensures that metal flows smoothly and evenly into the parts. Wax rods or sprues form channels for the metal flow.
 
．Minimize bends in the sprues to reduce the impact of metal flow deceleration on the parts.
．Use a small torch on the final part to eliminate sprue holes or wax tree imperfections.
 
After the 3D printed prototype evaporates during burnout, the ceramic shell becomes the mold for casting metal.

．The mold is created by repeatedly dipping the wax tree into ceramic slurry and silica, ensuring even coating and reduced gaps in both steps.
．At least 5 layers are required, and for complex objects, 7-9 layers are recommended to prevent damage to the mold shell during casting.
．It is crucial to allow each coating to dry completely before repeating this step. Once the shell reaches the desired thickness (average of about 9.525 mm), it is ready for burnout.
   
Sinter or harden the ceramic shell and burn out the internal 3D printed material to form the mold cavity.

．Place the aforementioned object into a kiln, mouth down, and heat to approximately 1100-1200°C for about 40-60 minutes.
(Note: The exact time and temperature depend on the type of kiln used and the metal part being produced.)
．After completely burning out the 3D printed material, allow the mold cavity to cool completely.
 
Preheat the mold cavity, ready for molten metal pouring.

．If there is any residual ash or debris from burnout in the mold cavity, it must be cleaned.
．Place the mold cavity in a kiln to preheat it for metal pouring. Temperatures generally range between 550-1100°C.
．The molten metal flows through the sprue and into the mold cavity, allowing the mold and casting to cool and shrink at the same rate, forming dimensionally accurate parts.
．Allow the metal to cool and solidify completely. Different solidification times will be required depending on the material and thickness of the object.
   
Remove metal parts from the ceramic shell and perform precision machining.

．Once the cast object 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 sprues by sawing, cutting, grinding, or using a plasma cutter.
   
The finished appearance depends on the selected material and the purpose of the part. For some materials, a patinated effect will be treated or preserved, while some metal parts only require 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 maintain the surface luster.
．For steel products, especially functional parts, only a layer of protective agent is needed.
 
The cost of 3D printers is more economical compared to machines costing millions, making them suitable for companies of all sizes to reduce costs and accelerate innovation. 3DMART will continue to share all the latest news and technical tutorials related to 3D printing. Follow our fan page for first-hand updates or free events. If you have any needs, we also offer printing services and industrial-grade 3D printers.

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More metal casting finished products: Metal parts here! A collection of 3D printed castings!
Related data: https://www.lulzbot.com/learn/tutorials/3d-print-patterns-investment-casting?pk_campaign=newsletter_feb19&pk_medium=email&pk_source=phplist&pk_content=polycast