The term vacuum casting commonly refers to the use of silicone molds in manufacturing. However, this process is sometimes referred to as silicone tooling or soft molding.
In some cases, ‘vacuum casting’ is used when any casting process is done under a vacuum. But for this post, we will focus on vacuum casting as it relates to the use of a master pattern, silicone molds, and casting resins in the production of parts.
Vacuum casting was developed over a half-century ago and is now well established in industrial production, especially in the manufacture of prototypes and small-series using elastomers. It is an indirect soft tooling process that has become irreplaceable and valuable to many industries, such as consumer product manufacturing, electronics, and construction.
This blog post defines vacuum casting and highlights its benefits, process steps, applications, and materials required.
What is Vacuum Casting?
Vacuum casting involves the use of a vacuum to pull liquid into silicone molds, thus making plastic or rubber parts. This process is also called urethane casting or polyurethane casting because polyurethane resin is the casting material. Because the process occurs under a vacuum, the resulting casts are bubble-free and have smooth surface textures with zero defects.
The vacuum casting process is usually used for rapid prototyping as it is a faster and more economical option than other methods, including injection molding. This process is capable of producing components with intricate details using polyurethane resins.
Used in the production of many fast-moving consumer goods and electronics, vacuum casting is excellent for producing premium quality parts in batches and small volumes within a short period. The parts created can be used for quality validation, pre-launch product testing, operation testing, designing concept models and prototypes, etc.
Advantages of Vacuum Casting
Vacuum casting offers many advantages over other molding processes. One of its main benefits is its affordability. Since it requires only one mold to create many parts, it eliminates time and material wastage. Here are other reasons for choosing vacuum casting.
Cost-Effectiveness
Vacuum casting is a cost-effective manufacturing process, especially for small-scale production and prototyping. This is true on many grounds.
Firstly, the equipment and tools required in this casting method are typically less expensive compared to other methods. This aids in reducing the overall and per-unit production costs of your project, making it an attractive investment option.
Also, molds produced from vacuum casting can be reused many times. As a result, there is less waste of silicone rubber and minimal stock preparation and setup time, making it cheaper than other rapid prototyping means, like CNC machining and 3D printing.
Another reason for its relatively low cost is that its casting materials, such as silicone and polyurethane resins, are more affordable than aluminum and steel used in other methods.
Lastly, vacuum casting uses less energy compared to injection molding and CNC machining. Hence, it helps to save energy consumption costs.
Replicate Intricate Details
Vacuum casting provides a high level of accuracy in production and reproduces parts with top-notch quality. It is capable of simulating most of the physical and intensely-detailed properties, such as texture, rigidity, and flexibility to conform to the original design intent.
Urethane casting molds can create even the most complex details on a master model, making it especially suitable for the manufacture of small and detailed components. As the operation occurs in a vacuum, air bubbles that cause deformity are easily removed.
Since molds are created using a 3D model, the quality and accuracy depend on the model. It is also easier to ensure all complex parts, including snap fits, living hinges, and undercuts are an exact replica. To ensure the best quality, the model must have a good surface finish and well-defined features.
High Efficiency
With the aid of a 3D model, the vacuum casting process can be completed within a short time, from design to finished product. Most molding methods, like injection molding, depend on tooling to manufacture components. While this is suitable for producing large amounts of parts, it is not advisable for making prototypes as they take a long time.
In vacuum casting, the silicon mold can be ready in a day and as soon as the pattern is available, 20 parts can be made successively. Vacuum casting machines can achieve continuous and quick production in comparison to CNC & injection molding.
As this process minimizes waste and does not require a lot of effort, it can also be used for large-volume production. In addition, minimal set-up time is required for this process and it can be easily automated, increasing its efficiency.
Customization
A major advantage of vacuum casting is that it is very customizable. This process can be used to make components of different colors, geometries, and shapes. and sizes.
Due to its increased flexibility compared to other casting methods, vacuum casting can be used to create parts with unique designs and features that may not be easy to produce using other methods.
Polyurethane resins used in vacuum casting have many options of grades and simulated materials to choose from, ranging from cast nylon to elastomers. These resins are also available in water-clear grades.
Vacuum-cast parts are typically prototypes and will eventually be injection molded. These prototype parts can be made with any surface finish including high gloss, satin, matte, and spark-eroded, as well as various mold textures before it is mass produced.
The Steps in the Vacuum Casting Process
Vacuum casting uses silicone molds, PU resins, and a vacuum chamber for resin casting to create superior parts or components. This process involves mold preparation, casting preparation, vacuum casting, resin infiltration, and curing and finishing.
Mold Preparation
The first step in preparing the mold is creating a high-quality and accurate master model to work with. This can be done by 3D printing or CNC machining, followed by dedicated post-processing. To achieve perfect vacuum casting parts, the master model must be of the required quality. Alternatively, an already cast model can serve as the master pattern.
Once the model is ready, the silicon mold is made using the model and a casting box. Suspended in the casting box, the master model is fitted with cores, inserts, casting gates, and risers, that aid in the pouring of molten silicon and removal of the mold.
After molten silicon is poured and it fills all the angles and holes around the pattern, it is left for about 8 to 16 hours to cure. The temperature of the casting box is kept at 40 degrees Celsius.
When it is done curing, the solidified mold is brought out of the casting box. As this process is done under vacuum conditions, there are little or no blemishes on the mold. After a while, the soft and sticky silicone mold needs to be cured again under high temperatures in an oven.
Casting Preparation
In preparing for casting, the casting material (polyurethane resin) is first heated to about 40 degrees Celsius.
Polyurethane resins are available in various types, having different structural qualities. Hence, the type used will depend on the design intent and part performance. Additionally, PP, rubber, glass-filled, and ABS materials for molding can be used.
Next, the resins and any choice of color pigments and agents are combined in specific quantities in a bowl and mixed thoroughly to form a homogenous mixture. Color pigment and agents, such as metallic powder, are added to obtain certain aesthetics or functional properties.
The resin and components are manually mixed and poured using levers and stirrers, and deaerated for a minute under vacuum conditions. Then, the mold is replaced and the pouring gates are attached to the bowl.
Vacuum Casting
The homogenous mix containing the resins, color pigment, and agents is then poured into the silicone mold via a funnel to ensure uniform distribution and also to prevent the formation of air bubbles.
After the bowl has been emptied by gravity feeding, the mold is placed in the vacuum chamber to eliminate any resistance to flow caused by air bubbles inside the mold, ensuring there are no damages to the final product.
Resin Infiltration
The resin is allowed to flow into the mold under a vacuum, ensuring uniform infiltration. Vacuum casting resins replicate a wide range of thermoplastic properties for rapid prototyping of components. When the mold cavity is filled, it is indicated by resin discharge through the risers. These risers also ensure air bubble removal from the mold cavity.
After the cavity is filled, it may be degassed again. Once the solution is completely set in the mold, the mold is properly sealed in the vacuum chamber for resin casting and it is ready for casting. The resins used will determine the temperature and time for casting, however, the process remains the same.
Curing and Finishing
After the casting is done, the mold is left in the vacuum casting machine for curing. Curing helps the part to retain its rigidity after it demolded.
For proper curing, the casting machine is maintained at a temperature of 70 degrees Celsius. Curing time will depend on the type and temperature of the resin as well as the size of the part produced. For polyurethane resins, curing takes between 20 and 40 min.
After curing, the casted part is de-molded from the silicone molds. To facilitate the process and reduce the force needed for demolding, release agents can be applied.
After demolding, the risers and any inserts are removed and any excess material is taken off from the casted part. The cured product can be painted, varnished, decorated, polished, or finished in any way to give the required look.
Materials Used in Vacuum Casting
To create effective and quality castings, it is essential to use the most appropriate casting materials. Polyurethane resin, silicone rubber, epoxy resin, PU foam, and silicone resin have the best properties required in vacuum casting.
Polyurethane Resin
Polyurethane resins are made of soft and hard phases that provide excellent flexibility and toughness. They are ideal for processes with short-run production and minimal development period. Since changes in the manufacturing process can be made quickly with minimal effort, production costs are kept low.
Like other thermoplastic materials, polyurethane resins have high performance as a result of their heat resistance, elasticity, and high e-module. PU resins can be used in vacuum casting for a wide variety of productions, including prototypes, industrial large-volume parts, hoses, and gaskets.
Having balanced physical properties with high dimensional stability, these materials are easily molded. They are most suitable for making products that require abrasion resistance and flame retardance.
Silicone Rubber
Silicone rubber is a durable and very resistant elastomer with a unique molecular structure. Its molecular structure, which comprises silicone and other molecules, is responsible for its distinct features.
As a result of its high, permanent elasticity, great release characteristics, and outstanding fidelity of reproduction, silicone rubber is the material of choice for mold making.
Some of the properties of this material include good flow and transparency, shrink-free curing at ambient temperature, provides long-term stability of the mechanical properties of cured rubber, and chemical resistance to casting resins, among others.
These properties have made silicone rubber a famous and reliable material for making molds in vacuum casting. Also, vacuum casting with silicone molds offers a high degree of freedom geometrically and provides premium-quality finishing options.
Epoxy Resin
Epoxy resin is made of epoxy and a hardener, mixed chemically. This hard resin is highly resistant to wear and tear, chemicals, and weather elements, and is capable of resisting creep under a sustained force, making it a reliable adhesive material.
Its great bonding ability, versatility, and capability to endure moderate temperatures make it attractive to the construction, manufacturing, and woodworking industries. Epoxy resin has broad applications, from being the matrix phase in several composite parts to acting as a form of surface protection.
In vacuum casting, specific epoxy resins can be used to create quality products. In this process, the resin and hardener are degassed and heated separately and stirred into vacuum tanks. Casting epoxy resins can be used to make crafts, sculptures, and jewelry.
Polyurethane Foam
Polyurethane foams are used in vacuum casting as core materials or bases for creating lightweight components with intricate designs. This material is renowned for its heat resistance, low density, manufacture of superb surface structure, and flame retardance.
Used in the production of insulation materials, multi-layer structures, and low-weight panels, PU casting foams find application in various industries, including construction, transport, leisure, and entertainment.
Polyurethane casting foam is less expensive compared to other casting materials and offers a short run time. It is highly machinable with great dimension stability, making it suitable for conditions that require an extreme degree of precision. Also, PU foams enable fast and easy demolding of the final product.
Silicone Resin
Silicone resins are polymers with low molecular weight and a branched-chain structure. They combine good heat resistance and top performance, creating a material with many benefits over the rubber.
Its thermal stability allows the resistance of up to 500 degrees Celsius for short periods, making them the most preferred option in a variety of applications, such as electrical insulation and serving as release agents.
In the vacuum casting process, silicone resins are formulated as release agents for thermoplastic or elastomeric materials like polyurethane. With a wide array of silicone resins available, formulators of release agents have many options for their production.
Applications of Vacuum Casting in Various Industries
As the world moves rapidly from traditional to modern manufacturing processes, several industries now use techniques, like vacuum casting, that minimize waste, offer high functionality, and provide consumer satisfaction.
Automotive Industry
Vacuum casting brings many benefits to the automobile industry. It ensures complete insulation and protection of automobile parts, including stators, rotors, coils, and sensors, among others. Also, it is widely used for prototyping and low-volume production in this industry.
Sophisticated manufacturers use vacuum-casted parts, such as engine covers, flooring metals, handles, and dashboards for industrial and commercial vehicle production. The parts produced from this process are lightweight, cost-effective, and can be adjusted to fit the requirements of any automobile.
Consumer Goods Industry
Vacuum casting is used in the consumer goods industry for the production of small batches of everyday items such as electronics, baby toys, household appliances, packages, and accessories. Many shelf items in supermarkets are created using vacuum casting.
Vacuum casted products are cost-effective, durable, and hygienic, which is why they are valued in this industry. They also offer a high level of flexibility, allowing various sizes, shapes, and geometries of products to be manufactured.
Accurate and complex designs required in some accessories, like custom decorative parts, are easily achieved through the vacuum casting process.
Medical Industry
The medical industry has very high standards of safety and quality that only a few molding processes can comply with. Vacuum casting is capable of providing quick prototyping and quality batch production needed to meet the needs of the medical industry.
Vacuum casting is used to produce custom prosthetics, prototypes of medical equipment, and dental implants. By creating prosthetics with precise weights, sizes, and symmetrical measurements, this casting process guarantees the best possible product solutions for improved body function.
Aerospace Industry
Vacuum casting is a famous process in the aerospace industry. As many of the alloys and superalloys used in this industry react with atmospheric oxygen or nitrogen in the air, vacuum casting is used to melt these alloys to prevent the formation of non-metallic oxides.
Vacuum casting also offers close compositional tolerances, temperature stability, decreased environmental pollution, and elimination of trace elements with high vapor pressure in production. Using this process, complex, difficult castings can be manufactured.
Architecture Design Industry
Vacuum casting is a very flexible technique that uses a vast array of materials to create prototypes and low-volume batches of different kinds of products. It is highly applicable in the architectural design industry. PU resins can be mixed with specific filler materials to give amazing finishes to well-designed products.
This casting process offers unlimited color options and a wide variety of patinas, which is of tremendous benefit to architectural design. Through excellent casting, this process can fulfill various design specifications.
Reliable Provider of Vacuum Casting Services
FOW Mould is a professional mold company that provides molding and casting services, including injection mold design, vacuum casting, vacuum investment casting, plastic parts production, and molded components production, among others.
Some of the different industries we cater to include home appliances, automobiles, baby products, furniture, crates, etc.
Experienced Experts
We have a team of injection molding and casting experts with many years of experience working in the molding industry.
In addition to their wealth of experience, our designers and professionals undergo intense training and workshops to be the best in this field and stay updated on industry trends.
We are continuously improving our injection molding and casting services to offer customers cutting-edge custom solutions that match your requirements and meet global standards.
Cost-Effective
At FOW Mould, we have a mission to provide cost-effective manufacturing solutions. From vacuum investment casting and vacuum casting to mold making and molded parts production, we provide both high-quality and affordable services.
By working with reliable raw material suppliers, we operate an efficient manufacturing process that ensures production and operating costs are minimal. This allows us to give the most competitive prices for our products and services.
Conclusion
Vacuum casting is a very efficient production process. It has many benefits, such as cost-effectiveness, the ability to replicate intricate details, and easy customization. Its low cost and quick turnaround time make it one of the best options for prototyping and batch-production projects.
It is a highly adaptive and flexible process that uses silicone molds, PU resins, and a vacuum chamber for resin casting to create effective parts, hence, it is advisable for custom jobs.
Do you have any projects for vacuum cast parts? FOW Mould provides professional vacuum casting services using qualified resins and modern vacuum casting machines. Our in-house factory has everything you need for rapid prototypes and molded components. You can contact us for more information.