Vacuum casting is a process to quickly and cost-effectively produce small quantities of high-quality rapid prototyping parts. So, what is the definition of the vacuum casting process? Vacuum casting is also known as urethane casting or polyurethane casting. It is a manufacturing process in which the original master sample is used to create a silicone mold, following the rubber-like, ABS-like, PP-like, and other polyurethane liquid raw materials are poured into the silicone mold to produce small batches of prototype parts under vacuum. Generally speaking, the properties and quality of vacuum-cast parts are comparable to those of injection-molded parts. The process of vacuum casting offers various end-use, rigid plastic, rubber, and silicone parts with production-level quality.
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What Exactly is Vacuum Casting?
Vacuum casting is a casting process that uses a vacuum to draw a liquid material into a silicone mold to create complex components. Elastomers such as plastic resins and liquid silicone rubber are liquid materials in vacuum casting. Because the process is performed under a vacuum, it creates high-quality bubble-free casting with a smooth surface texture and no blemishes.
Vacuum casting is also known as polyurethane casting or urethane casting. This is because it takes polyurethane resin, a type of elastomer, as the casting material. The lower production cost and higher efficiency of vacuum casting make it a more cost-effective alternative to injection molding for plastic components.
Vacuum casting is an excellent manufacturing method for batch production and other low-volume jobs. With high accuracy and repeatability, this process is ideal for applications requiring critical precise dimensions, such as consumer goods and industrial electronics. Note that vacuum casting is not appropriate for every application. For instance, it is unsuitable for casting materials hypersensitive to pressure or heat.
How does Vacuum Casting Work?
Vacuum casting is similar to conventional injection molding in that the cast material is injected into molds to generate products. The types of molds used distinguish vacuum casting from injection molding.
Molds for injection molding are made of aluminum, steel, and other materials. Silicone molds, on the other hand, are used in vacuum casting. Because silicone is less expensive and has a longer lifespan, this significantly reduces the cost of the mold. Below are the typical steps of vacuum casting.
#Step 1: Create a 3D Model of Component
The first step in making any vacuum-cast component is to create a 3D model of the component in question. This may be performed using any design software like AutoCAD, Solidworks, or CATIA. Note that the model uses the same design guidelines as injection molding molds.
Before creating the 3D model, proper calculations must be performed. Deformities in the model can impact the finished product after casting. As a result, it is critical to adhere to design guidelines and make necessary adjustments to calculations.
# Step 2: Create a Master Pattern of Mold
The mold’s master pattern is created using 3D rendering. The master pattern is the primary mold used to create the silicone molds used for casting. It is a prototype for silicone molds made of high-durability materials such as metals or other plastics.
Previously, master patterns were created using CNC or hand tools. Still, today, 3D printing, stereolithography, and other processes are used to create master patterns that are more cost-effective and precise. Texture surfaces can be done by painting or spraying sanding on the master model.
Because the silicone molds are copies of the master pattern, any deformation on the master pattern will cause the silicone molds to deform. As a result, a high level of precision is required when creating the master pattern. It is important to note that the master sample should withstand temperatures up to 40°C.
#Step 3: Produce Silicone Molds
The next step is to create silicone molds after creating the master pattern. The master pattern and a casting box are used to create silicone molds directly.
Inside the casting box, the master pattern is suspended. Cores and inserts are inserted into the master pattern. Along with the core, the casing box contains casting gates and risers for pouring molten silicone and removing the final mold.
Around the master pattern, hot, molten silicone is poured into the casting box. It flows inside the master pattern, filling the prototype mold’s crevices. For about 8-16 hours, the molten silicone is allowed to cure inside the casting box, which is kept at 40°C. Timing is subject to variation based on the dimensions of the silicone mold.
When the silicone has solidified and the curing process has been completed, the risers are removed, and the silicone mold is removed from the casting box. The process is carried out in a vacuum chamber to remove the air from the silicone and guarantee no bubbles on the surface of the mold.
# Step 4: Pour Polyurethane Resin
The polyurethane (PU) resin mixture is prepared before casting by mixing the resin with other casting components, such as pigments and other agents, and heating the resin. Depending on the product type to manufacture, various polyurethanes with varying material and structural qualities are available.
To make the resin mixture, combine the two parts of the resin in a container and heat the mixture to around 40°C. At this stage, color pigments are also mixed. It should be noted that the resin and pigments have completely mixed into a homogeneous solution before pouring the resin mixture into the molds.
When the solution is finished, it is poured into the silicone molds using a funnel to ensure uniform distribution and to prevent air bubbles from forming. When the solution has been completely poured into the mold, it is sealed and ready for casting.
#Step 5: Cure and De-mold Cast
The mold is placed in the vacuum casting machine for casting after the solution has been completely set in the mold and properly sealed. The temperature and time for casting may vary depending on the type of polyurethane used, but the process remains the same. When the casting is finished, the mold is left in the casting machine to cure – the curing process aids in retaining structural rigidity after the cast is removed from the mold.
To properly cure the cast, the casting machine is kept at around 70°C. After curing, the mold is removed from the machine, and its two halves are separated to remove the cast properly. It is critical to properly de-mold the cast and ensure that it is not damaged while being removed from the mold. Excess materials, such as gates and runners, are removed from the mold as the cast is removed.
As a result, the resin casting is complete, and the product is ready for use.
What Materials Can Be Used in Vacuum Casting?
Casting polymers are available in various hardness, surface texture combinations, and colors. You can create fully opaque, translucent, or completely transparent parts depending on your application.
Polyurethane is the most commonly used casting material in the vacuum casting process. Polyurethanes have a variety of properties, including structural rigidity, elasticity, flexibility, shock and temperature resistance, and so on. It is probably the most widely used type of casting resin applied in various fields, such as electronics, medical devices, agriculture, aerospace, automotive, etc. As a result, different polyurethanes can be used depending on the type of product being manufactured.
The following are some of the most common materials we use:
Polypropylene (PP) like (80D)
Polycarbonate (PC) like (75d)
Acrylonitrile butadiene styrene (ABS) like (83D)
Thermoplastic polyolefins (TPO or TPE-O) like
Talc-filled polypropylene like
Thermoplastic polyurethane (TPU) like
Fire-retardant (FR) PU like (78D, 80D, 85D)
High impact (85D, 88D, 80D – 90D)
Polyamide (PA) like (80D)
Acrylonitrile butadiene styrene (ABS) + high density polyethylene (HDPE) like (70D)
Elastomer like (60A, 65A, 70A, 90A, 95A)
Polyurethane (pur or pu) like (25A, 30A 40A, 50A, 60A, 70A, 80A, 84D, 85A, 90A)
The Benefits of Vacuum Casting
Vacuum casting is a very efficient manufacturing process. Complex and delicate shapes may be easily, precisely, and economically created. Let’s see some of the main advantages of this process.
- The vacuum casting technique yields parts with high dimensional precision. Vacuum-cast parts will fit together perfectly without requiring post-processing operations such as sanding or drilling.
- Multiple components from the master pattern can be used within 24 hours, reducing the product design prototyping stage and saving time and money on new product development.
- Vacuum casting can produce small batches of high-quality injection molding parts for prototypes or low-volume end-use parts for low-stress, relatively benign environments.
- Various vacuum-casting resins suit various applications, including clear, rubbery, flame retardant, food-grade, and colored resins.
- The resin type can be easily changed without retooling to test various material types for a given application or part.
- Multi-segment molds and cores can accommodate complex shapes and features.
- In-mold inserts made of aluminum or brass can also be used.
The Limitations of Vacuum Casting
While vacuum casting is an extremely effective manufacturing process, it does have certain disadvantages.
- Because the mold is soft silicone, it wears out quickly and lasts only 30 – 50 parts. Surface textures, features, and size determine tool wear. Larger parts, rough surface textures, and many proud features would reduce mold life.
- Shrinkage can cause irregular, overly thin, and thick features to deviate from normal tolerance, just like injection molding.
- Thermal expansion of the liquid and the flexible mold causes a 15% – 0.25 percent shrinkage rate. The manufacturer would generally allow and add shrinkage tolerance, but it is worth speaking with them before placing an order.
- Because the surface finish depends on the part’s post-processing, it is sometimes limited to only the outside because accessing some internal features of the pattern is difficult.
- Sharp corners and text will occasionally have rounded edges.
- Some features will also necessitate the use of plugs and cores.
- The process is not suitable for high-temperature applications.
Applications and Uses of Vacuum Casting
Vacuum casting is a versatile process that has several uses in various sectors. The process’s capacity to produce complex and precise components renders it an excellent option for high-quality outcomes.
Aerospace Components: Precise aerospace components can be manufactured using this method. Vacuum casting is commonly used to make components like air ducts, fuel systems, and even certain parts of airplane exteriors because of its greater precision, reproducibility, and ability to generate exquisite detail.
Medical Implants: In the medical business, vacuum casting is commonly utilized to produce complicated parts and components. It is suitable for the fabrication of implants and prostheses.
Automotive Industry: Automotive parts are frequently created using vacuum casting due to the process’s ability to produce highly detailed components. The greater accuracy and repeatability of silicone vacuum casting can help automobile parts, including intake manifolds, exhaust systems, and body panels.
Food Business: The process is frequently used to produce complex pieces for the food business. It can produce molds, packaging components, and other complicated forms required in food production.
Consumer Goods: Vacuum casting can produce complicated consumer products such as toys and sporting equipment. The method may produce very accurate parts suitable for consumer usage.
Vacuum Casting vs. Injection Moulding: What are the Differences?
Generally, vacuum casting has lower tooling costs, so it works better for prototyping and short runs. Injection molding has higher startup costs but excels at high-volume production and consistency. Here is a comparison of vacuum casting and injection molding:
- The process involves pouring a liquid resin into a silicone mold and then placing the mold in a vacuum chamber to remove air bubbles. This helps ensure a good surface finish and detailed reproduction of mold details.
- It is typically used for short prototype runs or small production runs of 10-few hundred parts. It’s not ideal for high-volume production.
- Vacuum casting is an excellent choice for parts with tight tolerances and a smooth surface finish.
- Tooling costs are lower than injection molding as only a silicone mold is required, with no need for steel tooling.
- Generally slower cycle times than injection molding. Each part needs to be poured and vacuumed individually.
- Unlike injection molding, vacuum casting does not require a DFM process, allowing for project time savings.
- Thermoplastic or thermoset granules are melted and injected into a steel mold under high pressure.
- The best process for high volume, mass production part runs into the thousands or millions.
- Injection molding is best suited for parts with less stringent tolerance requirements.
- Very high initial tooling costs for machined steel molds.
- With fast cycle times. It’s an automated process that allows for high-volume output.
- A range of thermoplastic and thermoset materials are available for property requirements.
- High initial costs make it unsuitable for prototype volumes.
Vacuum Casting vs. 3D Printing: What are the Differences?
Vacuum casting and 3D printing are different manufacturing processes with their characteristics. If you prioritize speed and cost, 3D printing is probably the best choice. However, vacuum casting is the way to go if high accuracy and detail are required. Below describes their differences:
- It involves pouring liquid material like resin and plastic into a mold and using vacuum pressure to remove bubbles and help the material flow into all mold crevices.
- Typically, it uses a silicone mold created from a master pattern/part.
- Very accurate reproduction of details from the master pattern.
- It is often used for short-run production of detailed plastic or metal parts.
- It can be time-consuming, especially if you need multiple copies of your part.
- It is an additive manufacturing process where material (usually plastic filament, resin, metal powder) is deposited layer by layer to build a 3D object.
- Uses a digital file such as a CAD model or scan data to direct the printer.
- No mold or tooling is required, allowing very complex geometries to be created.
- Supports rapid prototyping and custom one-off designs.
- Resolution and accuracy are dependent on the 3D printing technology used.
- It is used more for prototyping rather than volume production.
- 3D printing is much faster than vacuum casting.
Vacuum Casting vs. CNC Machining: What are the Differences?
CNC machining and vacuum casting belong to rapid prototyping processes. Let’s take a closer look at their distinctions:
In CNC machining, the cutter on the CNC equipment cuts off extra material based on the path set by the program to produce prototypes of the desired shapes and sizes. Vacuum casting is creating simple silicone molds using master patterns and then replicating the parts.
CNC machining prototypes will have considerably higher precision than vacuum casting prototypes. The precision of CNC machining is typically between 0.02mm and 0.05mm. However, vacuum casting prototypes may be significantly distorted and shrunk because of thermal expansion and contraction; the precision is not as simple to manage, often about 0.2mm.
CNC prototypes may be made from various materials, including plastic and metal. Examples of plastic CNC prototyping materials are ABS, acrylic, PP, PC, POM, nylon, PEI, PEEK, PBT, PTFE, and other materials. On the other hand, metal CNC prototyping materials include aluminum, stainless steel, copper, steel, iron, and others. The materials utilized for vacuum casting prototypes are limited, mostly rubber, ABS, PC, PA, PP, acrylic, etc.
CNC machining necessitates step-by-step machining, whereas vacuum casting necessitates the creation of a silicone mold and replicating the component. A silicone mold can often replicate 8-15 parts, and its production rate is faster than CNC machining.
Because CNC machining prototyping must be machined step by step, and adjusting the machine takes time, the cost of the CNC prototype is normally relatively high. However, vacuum casting prototyping may be one-piece forming made using vacuum mold casting. As a result, the cost of vacuum casting will be significantly reduced.
Vacuum casting is a cost-effective, efficient, highly adaptable, and versatile manufacturing process. Compared to traditional methods such as plastic injection molding and pressure die casting, vacuum casting has a very low manufacturing cost. Because of the cost-effectiveness of manufacturing, vacuum casting is ideal for batch production and rapid prototyping jobs that require a small number of products.
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Yes, vacuum casting works well for short production runs from 10 to 10,000+ parts. It avoids the high startup costs of tooling-intensive processes like injection molding.
Vacuum casting works for visual and functional engineering prototypes ready for physical evaluations. Different resins match material properties needed for product testing.