How to make a prototype mold?

Making a Prototype Mold

Prototype molds are used to test parts before committing to expensive production tooling. The best approach depends on your material, quantity, and budget.

Method 1: Silicone RTV Mold (Most Popular for Prototyping)

Best for: resins, low-temp casting, small runs (50–200 parts)

What you need

• A master pattern (3D print, machined part, or found object)

• Two-part platinum or tin-cure silicone (Shore 20–40A is common)

• Release agent (Vaseline, Mann Ease Release, or wax)

• A mold box (foam board, LEGO, or wood)

Steps

1. Prepare the master — seal it (spray lacquer or primer) and apply release agent

2. Build a mold box around it with ~1–2 cm clearance on all sides

3. Mix silicone per ratio (usually 1:1 or 10:1 by weight) and degas in a vacuum chamber if possible

4. Pour slowly over the master from a height to minimize bubbles

5. Cure — typically 4–16 hours at room temperature

6. Cut a parting line or build a two-part mold if the part has undercuts

7. Demold and cast your material (urethane resin, epoxy, etc.)

Method 2: 3D Printed Mold

Best for: small plastic parts, injection-like testing, simple geometry

• Print the mold in ABS, ASA, or resin (SLA resin gives the smoothest surface)

• Design with draft angles (1–3°), a parting line, and sprue/vent holes

• Spray with mold release before each pour

• Works well with low-pressure urethane casting or silicone parts

• Lifespan: 10–50 shots depending on material

Method 3: Machined Aluminum Prototype Mold ("Soft Tooling")

Best for: actual injection molding, 100–10,000 parts, functional testing

• Machine from 6061 or 7075 aluminum (much faster/cheaper than steel)

• Use CNC milling — can be outsourced for a few hundred to a few thousand dollars

• Add ejector pins, cooling channels, and gates

• Works in standard injection molding machines

• Lifespan: 1,000–50,000 shots (vs. millions for hardened steel)

Method 4: Epoxy or Urethane Tooling

Best for: composite layup, thermoforming, or short-run sheet metal forming

• Cast tooling epoxy over a master pattern

• Reinforced with fiberglass or aluminum powder for rigidity

• Cheap and fast — good for vacuum forming, fiberglass layup molds

Key Design Rules (All Mold Types)

Choosing the Right Method