Step-by-Step Process for Plastic Injection Molding Prototype Models

Creating a plastic injection molding prototype is a critical step in product development—it lets you test design feasibility, validate performance, and avoid costly mistakes in mass production. Unlike mass-produced parts, prototypes prioritize speed, cost-efficiency, y adaptabilidad, while still following core injection molding principles. Below is a complete, actionable breakdown of the prototype development process, from material pick to final application.

1. Material Selection for Prototypes

Choosing the right material is the first (and often make-or-break) step for prototypes. The goal is to balance propiedades de los materiales with prototype goals—whether you’re testing durability, apariencia, o costo. Here’s how to navigate key choices:

Pro Tip: Prioritize rentabilidad for early-stage prototypes—opt for common resins like PP or ABS instead of high-end materials like PEEK. For supplier selection, choose vendors who offer small batch sizes (1-5 kilos) to avoid waste. Also, check densidad (affects part weight) y tasa de flujo (ensures the resin fills small prototype mold cavities easily).

2. Design Considerations for Prototype Success

Prototype design should be “mold-friendly” to speed up production and reduce defects. Even small design tweaks can save days of rework. Here’s a checklist of critical factors:

Core Design Elements & Consejos

• Part Design: Keep it simple—avoid overcomplicating with unnecessary features (p.ej., intricate logos) in early prototypes. Focus on testing the part’s core function.
• Wall Thickness: Aim for 1-3 milímetros (uniform across the part). Thinner walls (<1 milímetros) cause short shots; thicker walls (>3 mm) lead to sink marks. Use gradual transitions if thickness must change.
• Draft Angles: Add 1-3 degrees to all vertical surfaces. This lets the prototype eject smoothly from the mold—no more stuck parts or scratches.
• Ribs & Bosses: Ribs (for stiffness) should be 0.5x the wall thickness; bosses (for screws) should have a diameter 2x the screw size. Add fillets (radius = 0.5 milímetros) to avoid stress cracks.
• Undercuts: Minimize them! Undercuts (p.ej., side grooves) require complex mold slides, which increase prototype cost and lead time. Si es necesario, use temporary solutions like post-machining.
• Tolerancias: Loosen tolerances for early prototypes (±0.1 mm is enough for fit tests). Tolerancias estrictas (<±0,05 milímetros) add cost and slow production.

Design Validation Tools

Before finalizing the design:

1. Usar CAD Modelling (p.ej., SolidWorks, Fusión 360) to create 3D models—share these with your mold maker to avoid miscommunication.
2. Run Mold Flow Simulation (p.ej., Autodesk Moldflow) to test resin flow. This catches issues like air traps or uneven filling early.
3. For high-stress parts (p.ej., soportes automotrices), usar Análisis de elementos finitos (FEA) to test strength—this avoids building prototypes that fail under load.

3. Mold Preparation for Prototypes

Prototype molds (called “soft tools”) are simpler and cheaper than mass-production molds. They’re often made from aluminum (instead of steel) to speed up machining. Here’s the key process:

Mold Components & Preparation Steps

Mold Making Process

1. Mold Machining: Use CNC milling for simple shapes; usar electroerosión (Mecanizado por descarga eléctrica) only for fine details (p.ej., pequeños agujeros). Aluminum machines 5x faster than steel—perfect for quick prototypes.
2. Mold Polishing: Polish cavities to a #4 finalizar (mate) for functional prototypes. High-gloss finishes (#8) are only needed for appearance tests.
3. Mold Assembly: Assemble components loosely first—test fit with a dummy resin (p.ej., wax) to ensure alignment. Tighten screws only after test fitting.
4. Mold Testing: Run 5-10 test shots with scrap resin. Check for leaks, misalignment, or stuck parts—fix issues before running the actual prototype batch.

4. The Injection Molding Process for Prototypes

Prototype injection molding focuses on speed and flexibility—you’ll often run small batches (10-50 regiones) and adjust parameters on the fly. Here’s how to execute it smoothly:

Key Machine Settings (for ABS Prototype Example)

Step-by-Step Molding Workflow

1. Alimentación de materiales: Load 1-2 kg of resin into the hopper (small batches reduce waste). Add a few pellets of colorant if needed.
2. Diseño de boquilla: Use a small-diameter nozzle (3-5 milímetros) to fill narrow prototype cavities. Keep the nozzle 1-2 mm from the mold to avoid leaks.
3. Injection Speed: Start at 40-60 mm/s. If the part has thin walls, increase to 70-80 mm/s to avoid short shots.
4. Packing Pressure: Aplicar 80-90% of injection pressure for 2-3 artículos de segunda clase. This fills any small gaps in the prototype.
5. Tiempo de enfriamiento: Let the mold cool for 15-25 artículos de segunda clase (aluminum cools fast!). Eject the part only when it’s cool to the touch.

Common Issue Fix: If the prototype has flash (excess resin), reduce injection pressure by 5-10 MPa. If it has short shots, increase melt temperature by 5-10°C.

5. Post-Processing and Finishing for Prototypes

Post-processing turns raw molded parts into usable prototypes. Focus on tasks that support your test goals—skip unnecessary steps to save time.

Essential vs. Optional Post-Processing

Pro Tip: For functional prototypes, skip painting/plating—focus on deburring and trimming. For appearance prototypes, usar impresión (p.ej., pad printing) for logos instead of expensive plating.

6. Applications and Uses of Injection Molding Prototypes

Prototypes are used across industries to de-risk product development. Here’s how different sectors leverage them:

Industry-Specific Uses

• Piezas automotrices: Test fit of interior components (p.ej., dashboard clips) or durability of small parts (p.ej., manijas de las puertas).
• Electrónica de Consumo: Validate the size of phone cases or the fit of charging port covers.
• Dispositivos médicos: Test the ergonomics of syringes or the compatibility of plastic parts with liquids.
• Embalaje: Check if a bottle prototype holds liquid without leaking or if a lid seals properly.
• juguetes: Test safety (p.ej., no small parts that break off) y durabilidad (p.ej., withstands dropping).
• Componentes aeroespaciales: Test lightweight parts (p.ej., plastic brackets) for strength under low pressure.

Prototype Stages in Product Development

1. Concept Prototype: Early-stage, bajo costo (p.ej., ABS parts) to test basic form.
2. Functional Prototype: Mid-stage, uses final material (p.ej., ordenador personal) to test performance.
3. Pre-Production Prototype: Late-stage, identical to mass-produced parts—used for final validation.

Yigu Technology’s View

En Yigu Tecnología, we know prototype success hinges on balancing speed, costo, and clarity of goals. For plastic injection molding prototypes, we prioritize aluminum molds (rápido, rentable) and common thermoplastics for early stages, then shift to final materials for functional tests. We integrate CAD, Mold Flow, and FEA to catch issues before molding, cutting rework time by 30%. Our focus is on delivering prototypes that solve real problems—whether it’s testing a fit, validating a design, or impressing stakeholders.

FAQs

1. Q: How long does it take to make a plastic injection molding prototype?

A: 1-2 weeks for simple prototypes (aluminum mold + ABS parts). Prototipos complejos (with undercuts or FEA testing) take 3-4 semanas.

2. Q: Can I use the same mold for prototype and mass production?

A: Rarely—prototype molds are aluminum (suave, wears out after 1,000+ shots), while mass-production molds are steel (duro, lasts 100,000+ shots). Use the prototype mold to refine the design, then make a steel mold for production.

3. Q: How much does a plastic injection molding prototype cost?

A: \(500-\)2,000 for a simple prototype (aluminum mold + 10-50 regiones). Costs rise to \(3,000-\)5,000 for complex designs (Mecanizado por electroerosión, FEA testing, or final materials like PC).