Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Lost PLA casting (also known as lost-PLA investment casting) is a hybrid technique that combines 3D printing with traditional investment casting. You create a disposable pattern using PLA filament, encase it in a refractory material (investment), burn out the PLA to leave a cavity, and pour molten metal into the mold. This method is ideal for producing small to medium metal parts like prototypes, jewelry, or custom hardware. It's more accessible than full metal 3D printing and allows for complex geometries. Common metals include aluminum, bronze, or brass. The process can take 1-2 days, depending on burnout time.

Step-by-Step Guide

This is a standard investment casting workflow, compiled from reliable maker tutorials. Adjust for your scale and metal.

1.Design and 3D Print the Pattern

Model your part in CAD (e.g., Fusion 360). Design it hollow with thin walls (1-2mm shell thickness, 0% infill) for easier burnout—thicker walls (>2mm) can trap ash and cause defects. 

Include sprues (pouring channels), runners (main flow), and gates (entry points) in the model, or add them post-print. Print at high resolution (0.1-0.2mm layer height) with supports if needed. Sand the print smooth and fill voids with wax to prevent investment leaks. Tip: Add a 1cm base to compensate for shrinkage (~1-2% in metal). 

2.Assemble the Sprue Tree

Attach 1-4 patterns to a central wax rod (sprue) using hot wax or glue, forming a "tree." Orient parts so the sprue is the highest point to allow air escape and even filling—avoid traps for bubbles.Secure the tree to the flask base with wax. Multiple parts improve efficiency but add complexity.

3.Mix and Pour the Investment

Mix investment powder with distilled water per package ratios (e.g., 2:1 powder:water for a creamy slurry). Let it sit 2-3 minutes to "stew," then degas in a vacuum chamber for 1-2 minutes or vibrate vigorously to remove bubbles. Place the flask on a vibrating table and slowly pour investment over the tree until full (1-2" above the top). Tap to settle. Cure for 1-2 hours until hard. 

4.Burnout the PLA

Place the flask in a kiln upside-down (sprue up) on a props to allow ash drainage. Follow a gradual schedule to avoid cracks:  Ramp to 200°C, hold 2 hours (dry out water).  

Ramp to 460°C, hold 2 hours (initial PLA melt).  

Ramp to 740-800°C, hold 4-6 hours (full burnout; PLA vaporizes above 400°C).

Cool slowly to 200-500°C (casting temp, depending on metal—lower for aluminum). 

Total time: 8-12 hours. Ensure complete burnout to avoid inclusions; inspect for residue.

5.Melt the Metal

Load scrap or ingots into a preheated crucible. Heat in a furnace or with a torch until molten (cherry-red glow). Skim dross (impurities) with a graphite rod. Degass if needed (stir with a plunger). Keep molten but pour quickly to avoid oxidation. 

6.Pour the Metal

Use tongs to position the hot flask in sand for stability. Pour steadily through the sprue hole into the cavity. Fill completely and tap gently to settle. Let solidify 5-10 minutes (aluminum cools fast).

7.Cool and Demold

Quench the flask in water or sand after initial cooling to break away investment. Knock out the casting tree. Cut off sprues with a hacksaw or grinder.

8.Finish the Part

File/grind gates and rough spots. Sand progressively (80-400 grit), then polish or tumble for shine. Inspect for defects; minor porosity is common in first tries.