Injection Molding vs. Vacuum Casting

Find out which technology is best for strength, speed, and costs.

Selecting the proper manufacturing method is like solving a puzzle. When you solve that puzzle, you build better parts and save money producing them.

Two methods stand out among the many available options: injection molding and vacuum casting. These manufacturing techniques offer unique advantages you must carefully weigh to bring your creations to life.

The Injection Molding Process

1. Mold Design and Fabrication: Using precision machining techniques, create a mold with two halves – the cavity and the core.

2. Material Preparation and Injection: Melting thermoplastic material within an extruder and putting it into the mold under high pressure.

3. Cooling and Solidification: The molten material cools and solidifies within the mold through controlled cooling channels.

4. Mold Opening and Part Ejection: Opening the mold and ejecting the finished part using ejector pins or mechanisms.

The main advantages of injection molding are:

High Production Efficiency and Speed: Injection molding enables high-volume production with fast cycle times. Once the molds are created and set up, the injection molding process can quickly produce large quantities of parts.

Superior Strength and Durability of Parts: Injection molded parts exhibit excellent mechanical properties, including strength, durability, and dimensional stability. The high-pressure injection ensures uniform material distribution, resulting in parts with consistent and reliable performance.

Wide Range of Material Options: Injection molding offers a vast selection of materials, including engineering-grade plastics such as ABS, polypropylene, polycarbonate, and nylon. These materials provide properties such as high strength, heat resistance, chemical inertness, and electrical conductivity. Additionally, specialized materials like elastomers and thermosetting plastics are readily available for specific applications.

The Vacuum Casting Process

Vacuum casting involves the following steps: 

1. Master Pattern Creation: Creating a master pattern using 3D printing or CNC machining as a basis for the silicone mold.

2. Mold Preparation: Liquid silicone rubber is poured over the master pattern and cured to create a flexible and durable silicone mold.

3. Mold Assembly and Vacuum Chamber: Assembling the silicone mold and placing it inside a vacuum chamber to remove air bubbles.

4. Casting Material and Vacuum Casting: Mixing and pouring a two-component polyurethane resin into the mold cavity under vacuum for proper filling.

5. Curing and Demolding: The curing process solidifies the material so that it takes on the shape of the mold. Once cured, the mold is opened, and the finished part is carefully removed.

The main advantages of vacuum casting are:

Cost-Effectiveness for Low-Volume Production: Vacuum casting eliminates the need for expensive metal molds used in injection molding. Instead, it utilizes silicone molds, reducing initial tooling costs. This makes vacuum casting cost-effective for producing small to medium quantities of parts or prototypes without the high upfront investment. However, these molds are typically only usable for about 30 parts before a new one needs to be used.

Design Flexibility for Complex Geometries and Overmolding: Vacuum casting allows for intricate and complex part designs, including undercuts, internal features, or overmolding. Using silicone molds enables the replication of fine details and complex geometries, providing design freedom for creative and innovative projects.

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Tooling Costs

Injection Molding – Higher Tooling Costs and Initial Investment: Injection molding requires the creation of molds, which can be costly, especially for complex geometries or multiple cavities. The initial investment includes mold design, engineering, and precision machining. However, once the molds are created, they can be used repeatedly, reducing the cost per part over time.

Vacuum Casting – Reduced Tooling Costs: Vacuum casting typically uses silicone molds, which are less expensive than the metal molds used in injection molding. This reduces the initial tooling costs, making it a cost-effective solution for low-volume production.

Production Costs

Injection Molding- Production Costs for Different Volume Requirements: Injection molding materials are often more cost-effective for high-volume production runs due to economies of scale. The cost per part decreases as the production quantities increase.

Vacuum Casting- Affordable Production for Small to Medium Quantities: Vacuum casting suits small to medium production quantities. It offers cost advantages when producing limited quantities, but the molds are only usable for about 30 parts before they need to be replaced.

Production Speed

Injection Molding – Cycle Times and Overall Production Times: Injection molding has shorter cycles due to the high-pressure injection process and efficient cooling systems. This results in faster production rates and shorter overall production times than vacuum casting. However, it may not be as time-efficient for low-volume production runs due to the initial setup and mold fabrication processes.

Vacuum Casting – Longer Production Times, Shorter Setup: Vacuum casting generally has longer production times than injection molding. However, the initial setup time is often quicker.

Strength and Material Options

Injection Molding – Strength and Material Suitability: Injection molded parts benefit from higher material density and uniformity, resulting in superior strength and structural integrity. The high-pressure injection ensures consistent material distribution, eliminating weak points or variations. Injection molding offers various material options, including engineering-grade plastics with specific properties suitable for multiple applications.

Vacuum Casting—Material Limitations and Reduced Strength: Vacuum casting materials often have lower strength properties than materials used in injection molding. The casting resins used in vacuum casting are typically weaker than engineering-grade plastics. However, advancements in materials are expanding the range of options available for vacuum casting, providing improved strength characteristics.

Getting Started

Injection molding is ideal for high-volume production, with its efficiency, strength, and extensive material options. It provides reliable solutions for automotive, consumer goods, and other industries.

On the other hand, vacuum casting shines in low-volume production, offering cost-effectiveness and design flexibility for intricate, tailored creations. It thrives in prototypes and small-batch production.

Want to get started with injection molding or vacuum casting? Need some expert consultation on what manufacturing technology is right for you? Try out the MakerVerse platform and start your project today. We’re ready to help.