Features and benefits of vacuum casting - Prototype Projects

Vacuum casting is an established prototyping technology that has been around longer than 3D printing, so it might not seem as high-tech or glamorous as additive manufacturing. Nevertheless, vacuum casting in polyurethane resin remains a valuable option for producing high-quality prototypes. Here at Prototype Projects, we have in-house vacuum casting, five different 3D printing technologies, CNC machining, laser cutting and traditional modelmaking, so we can provide independent advice about which technology – or combination of technologies – is best for your project.

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We have a separate page describing the vacuum casting process and our capabilities but this article focuses on the features and benefits of vacuum casting, a most versatile prototyping technology.

Wide choice of material grades

All of our vacuum castings are produced in polyurethane resins. This may sound limiting in terms of the material properties of the finished part but, in fact, the opposite is true. Polyurethane resins are available in a wide choice of grades to simulate materials ranging from glass-filled nylon through to soft elastomers – and everything in between. Polyurethane is also available in water clear grades.

Excellent material properties

The material properties you need will depend on your application. Polyurethane resin material properties vary considerably from one grade to the next but, in general, polyurethane is isotropic, non-porous, water resistant, heat resistant, UV-stable and some grades are fire retardant.

Almost unlimited colours

We can mix colours in-house or, if you need a specific shade, our supplier can colour-match a physical sample, RAL number or Pantone colour code. As mentioned above, clear grades are also available.

Any surface finish can be produced

Vacuum cast parts are typically produced for prototyping parts that will, ultimately, be injection moulded. Any surface finish required for an injection moulded part can also be produced on vacuum cast parts, including high gloss, satin, spark eroded and textured.

A cost-effective process

Compared with 3D printing or CNC machining, the vacuum casting process contains more steps. However, the silicone rubber moulds can typically be used 20 to 25 times (sometimes far more), so the cost per part can be very reasonable.

Excellent part-to-part consistency

The casting process is very tightly controlled, mould wear is almost non-existent and minimal hand-finishing is required. All of this means there is virtually no part-to-part variation, which can be highly beneficial where multiple parts are required for assembling with other parts and/or testing. If the mould reaches the end of its life and a new one is required, another master pattern will need to be 3D printed. Using the SLA process, the accuracy of the master pattern is excellent, so castings from moulds made from different masters should be indistinguishable.

Complex geometries can be cast

We usually 3D print the master pattern using one of our SLA machines, which enables the production of accurate, highly detailed parts with complex geometries. The mould is produced by pouring liquid silicone resin around the master pattern, resulting in a perfect mould-to-pattern fit and, therefore, accurate replication when the polyurethane parts are cast. Vacuum casting enables complex features to be produced, including snap fits, thin walls, living hinges, undercuts and similar features. There is also no need for draft angles, which can help to speed the prototyping process.

Choice of finishing options

Elsewhere we have said polyurethane resin is available in an almost unlimited range of shades for self-coloured parts, but additional finishes can also be applied. These include blackout/EMI/RFI coatings on internal surfaces, and vacuum metallisation. Painting suitability depends on the resin grade, so talk to us first if this is necessary.

Minimal shrinkage

Shrinkage depends on the part geometry and the process parameters but, generally, shrinkage (ie the difference between the master pattern and the cast part) is approximately 0.15 per cent. This is less than for injection moulded ABS or glass-filled Nylon 6/6, and an order of magnitude less than injection moulded Acetal, polypropylene or thermoplastic elastomers. This helps to ensure vacuum cast parts are as accurate as possible, which is important for visual prototypes and absolutely vital when the parts are for functional testing.

Wide range of sizes can be moulded

Our vacuum casting facilities give us the capability to cast very small parts up to a maximum weight of g. The maximum mould size is 450 x 470 x 400 mm. This is similar to the build envelope of our SLA machines, so we can vacuum cast almost anything that we can 3D print.

Multiple options for threaded holes

Sometimes customers prefer to assemble prototypes using screws rather than production technologies such as bonding or snap fits. Threaded fasteners enable the prototypes to be disassembled, inspected, modified and reassembled as required. Vacuum cast prototype parts can incorporate blind holes for subsequent tapping, plain bosses for drilling and tapping, or threaded inserts can be insert moulded or installed after casting. If in doubt about the best option, talk to us as early as possible.

Volume production

‘Volume’ is a relative term and the number of parts that can be cast from a mould depends on the part geometry, surface finish, grade of polyurethane resin and the skill of the operative. Typically, we expect a mould to produce 20 to 25 parts, though up to 100 can be moulded in some cases. If more parts are required, we can manufacture a new mould. A single mould is usually sufficient for prototyping requirements, but we also have customers for whom we vacuum cast low-volume production parts.

Suitable for many phases in product development

We have already shown that vacuum casting is an incredibly versatile process. As a result, it is used at virtually every stage in a product development project where multiple parts are needed. This includes concept development, visual and functional prototypes, handling trials, performance testing (eg airflow), assembly system concept development, assembly line trials and marketing – such as for exhibitions, presentations to backers, focus groups and promotional photography.

The ultimate prototyping technology?

Vacuum casting is not the fastest prototyping technology because of the multiple steps involved and the cure time for the silicone mould and individual castings. However, vacuum cast parts can typically have the same level of detail as high-quality SLA 3D printed parts yet but with a wider choice of material properties. In addition, if the prototype has particular functional requirements, CNC machined parts can be overmoulded by vacuum casting with polyurethane. The resultant parts benefit from the strength, stiffness and accuracy of CNC machined metal parts, as well as the complex surfaces and detailed design features associated with 3D printing. The piece part cost remains very reasonable and, although the timescales are longer than for 3D printing, it is far quicker and more cost-effective than injection moulding with soft tooling.

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Are you looking for high-precision parts with exceptional detail and accuracy? Vacuum casting fits the bill perfectly.

As a cornerstone of the manufacturing industry, vacuum casting produces high-quality parts for small and medium batch production.

Whether you’re an experienced engineer, a budding designer, or simply curious about manufacturing processes, this article highlights everything you need to know about vacuum casting.

What is Vacuum Casting and How Does it Work? 

Vacuum casting is a manufacturing process that leverages a vacuum chamber to produce high-quality, detailed parts with exceptional surface finish and dimensional accuracy.

This versatile process is ideal for casting various materials, including plastics, rubber, and other composites. Often employed for prototype projects, small-scale production runs, and low-volume production, vacuum casting stands out for its ability to create intricate designs with precision and efficiency.

Vacuum casting, or urethane casting, involves using a vacuum to draw liquid materials into a mold. The result? Highly detailed, precise components with a fast turnaround.

The vacuum casting process begins with creating a master model, typically using high-precision techniques such as 3D printing or CNC machining. This model is then surrounded by liquid silicone to create a mold, which is then placed inside a vacuum chamber.

Once the silicone hardens, the master model is removed, leaving a perfect silicone mold ready for casting. The mold cavity, created from the master model, is essential for replicating high-quality prototypes. The mold then goes into a vacuum casting machine. The casting material then fills every crevice of the mold, replicating the intricate details of the design. The final part is removed following a curing period, and the mold can be reused to replicate the process.

The mold lasts approximately 30 parts before a new one is needed, making vacuum casting ideal for small to medium-sized production batches.

Unlike traditional injection molding, which uses metal molds, vacuum casting works with soft silicone molds, allowing for more flexibility and cost-effectiveness in prototype production.

Benefits of Vacuum Casting

So, why choose vacuum casting for your project?

First, vacuum casting provides a virtually unmatched level of detail and accuracy, making it an excellent choice for intricate designs that other manufacturing processes might struggle to reproduce.

Vacuum casting is also known for its speed and efficiency. Because the silicone molds can be reused, a series of identical parts can be produced in a relatively short period. This makes vacuum casting an ideal choice for rapid prototyping or small-scale production.

Another significant advantage is the variety of materials available. Vacuum casting offers various choices to suit specific requirements, from different polyurethane resins that mimic the properties of materials like ABS, polycarbonate, or rubber. Additionally, when mixed with color pigments and deaerated in a vacuum, vacuum casting resins ensure better flow and filling of the mould, making the casting process more effective and efficient.

For more information, please visit What is Vacuum casting.

Furthermore, vacuum casting is more cost-effective for small series production than other manufacturing methods. Silicone vacuum casting, in particular, offers lower costs and flexibility in design changes compared to injection molding. It eliminates the need for expensive tooling and machinery, making it a go-to solution for businesses looking to minimize costs while maintaining high-quality results.

Applications of Vacuum Casting

Vacuum casting boasts a broad reach, finding uses in diverse industries thanks to its versatility and high precision.

In the automotive industry, vacuum casting allows designers and engineers to quickly produce prototypes for new car parts, interior components, or small series parts for special vehicles. The accuracy and speed of vacuum casting help accelerate the design and testing phases, enabling faster product development and launch. Additionally, polyurethane casting is used to create complex parts with high detail, making it ideal for producing high-quality prototypes and components.

The medical device industry also relies heavily on vacuum casting. The process’s ability to precisely reproduce intricate designs is vital in producing surgical tools, diagnostic equipment, and other healthcare devices. Furthermore, the range of biocompatible materials available for vacuum casting is a significant advantage in this field. Using 3D-printed master patterns enhances the accuracy and aesthetic quality of the final vacuum-cast products, making it a cutting-edge alternative for rapid prototyping.

The consumer electronics industry is another sector that extensively uses vacuum casting. Vacuum casting offers precision and fine detailing that are instrumental in an industry where aesthetics and form factors are as crucial as functionality.

In the aerospace industry, vacuum casting is used to create lightweight, durable components and prototypes. Due to the industry’s stringent standards, the precision and high-quality finish achieved through vacuum casting are critical.

Beyond traditional industries, vacuum casting is also a popular choice in the gaming industry, where it creates detailed figurines, game pieces, and collectibles.

How Much Does Vacuum Casting Cost?

The short answer is, “it depends.”

If you want to do vacuum casting in-house, an industrial-grade machine can cost thousands of euros—but that doesn’t include the tools you’ll need to make the master model. This is why injection molding services, such as the one offered by MakerVerse, are so popular.

If you’re starting from scratch with no existing prototype, you’ll need to factor in the cost of 3D printing or CNC machining a master model. This master model is vital for the creation of silicone molds. It might seem like a hefty upfront cost, but when you consider the high-quality replications it enables, it becomes a worthy investment. Small molds can cost less than 100 euros. Additionally, injection mould tools, typically made from steel or aluminum, can significantly increase the initial costs but are essential for traditional injection moulding processes.

Another crucial cost consideration in vacuum casting is the materials used. Higher quality, specialized materials usually cost more but offer superior results. Materials that mimic the properties of ABS, polycarbonate, or polypropylene can vary in price, affecting the final cost.

The production volume also impacts the overall cost. Vacuum casting is typically used for low to medium-volume production, as silicone molds have a lifespan of about 30 casts. While this may limit long-term use, it provides an economical solution for smaller production runs and prototyping.

If you’re producing just a few pieces or need a small production run, vacuum casting can be more cost-effective than alternatives like injection molding.

Materials Used in Vacuum Casting

Polyurethane resins are the most commonly used materials in vacuum casting thanks to their ability to mimic a range of plastics with different properties.

ABS-like resins are often chosen for their robustness and high-impact resistance, mimicking the properties of ABS plastic. This makes them an excellent choice for functional parts and enclosures.

Transparent resins are another popular choice in vacuum casting, especially when optical clarity is a requirement. These resins can be used to create clear, glass-like parts or tinted to achieve various colors and levels of transparency.

For projects that require heat-resistant parts, high-temperature resins are the go-to material. They can withstand elevated temperatures, making them perfect for heat-composed components.

Flexible resins offer elasticity and are used when the part requires to be bent or flexed during its operation.

Silicones are frequently chosen in vacuum casting for their flexibility and biocompatibility, making them suitable for medical or food industry parts.

Design Considerations for Vacuum Casting

Designing for vacuum casting involves several considerations. The process’s high accuracy favors parts with complex geometries and intricate details.

However, undercuts, overhangs, and very thin walls may require special attention or modifications.

Always consider the properties of the selected material and the lifespan of the silicone mold, as these can impact the design and production run.

Vacuum Casting vs Injection Molding vs 3D printing

So, which of the many manufacturing processes is suitable for you? That’s a complex question that depends on the needs of your project. However, there are some quick rules of thumb to guide you in the right direction.

Vacuum casting is a low-to-medium-volume production method for high-quality, intricate parts. Compared to injection moulding, vacuum casting uses silicone moulds, making it ideal for detailed designs. Injection moulding uses hard metal moulds suitable for high-volume production and consistent surface finishes. Check this guide for an in-depth look at injection molding vs. vacuum casting.

However, if you’re looking at larger production volumes or if your design is relatively simple, alternatives like injection molding might be more economical.

Similarly, 3D printing may be better for one-off prototypes or highly customizable parts. For high-quality metal parts, vacuum investment casting offers precision and durability, making it a preferred choice in various industries.

Your project’s requirements should guide your decision, and you should consider factors like production volume, part complexity, material properties, and timeline.

Getting Started with Vacuum Casting

Vacuum casting is a versatile, cost-effective method for producing intricate parts and prototypes. Its ability to mimic various materials and provide a quick turnaround makes it an attractive choice for multiple industries.

However, as with any manufacturing process, it’s vital to consider your project’s specifics. By understanding the ins and outs of vacuum casting, you can make an informed decision that brings your project to life most effectively.

If you want to get started with vacuum casting or know what manufacturing process is best for you, we’re here to help. Once you upload a part on the MakerVerse platform, our experts will contact you to provide the guidance you need to see your project through.

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