Before a product is mass produced, manufacturers love to test their products and conduct market surveys. They therefore, need small batches of prototypes and sample products. One way of getting this small batches of prototype is Vacuum Casting.
Vacuum Casting, also called urethane casting involves creating a mold of the desired product and then injecting liguid plastic or metal into it, this is done under a vacuum, to prevent air from getting into the mix. Once it solidifies, the mold is taken apart and the product revealed.
This article explains what vacuum casting is all about by giving a step-by-step process. This article will also consider the various applications of vacuum casting, its advantages and disadvantages, and alternatives to vacuum casting will also be stated.
Introduction to Vacuum Casting
It seems fitting to first explain what casting is all about.
Casting
Casting is a manufacturing process where liquid material, either metal, resin or plastic is poured into the hollow space of a mold, the mould is then taken apart after the liquid material has solidified. This shows that, the result of casting will only be as good as the mould. What is this mold and what is it made from?
The Mold
For the vacuum casting process, the shape that forms the mold that holds the liquid material is usually made from silicone. This silicone mold is so important that it is one of the first steps in vacuum casting. It is flexible, heat resistant, and tear resistant. The process of making the mold will be futher explained when explainig the process of Vacuum casting.
Apart from the mold, another factor instrumental to the casting process is the vacuum. What does pouring liquid under vacuum mean and how does it work?
The Vacuum
We can agree that the word vacuum means space. However in the context of casting, a vacuum is a space where the air pressure has been significantly reduced, it is a sealed environment where air has been removed by a vacuum pump. For vacuum casting, we generally have a vacuum casting chamber.
You see, without the vacuum, air can be trapped inside the liquid material creating air bubbles and air pockets, resulting in a poor surface finish. The more disastrous effect of this is that it will create weak spots in the material, resulting in structural defects.
For vacuum casting, the most commonly used material is urethane.
Other Types of Casting Methods
Before the use of vacuum casting became widespread, other traditional means of casting had been in use. Each of them well suited for different materials and requirements. A few of them include:
Sand Casting
Here, molten metal or other liquid material is poured into a sand mould. The materials commonly used for this kind of casting is metal. E.g, Iron, aluminum, brass, etc.
Die Casting
Here a metallic mold is used. The metallic mold is called a vacuum die.The liquid material use in die casten is usually from aluminum, zinc, and magnesium. Die casting has the advantage of high precision and fast production. It is however quite expensive, this is because the die is costly to make. It is therefore not suitable for small scale production runs.
Centrifugal Casting
This is done in a centrifugal casting box, a kind of rotating mold. Liquid metal is poured into this mold as it rotates. This type of casting is used for metals like steel, iron, and bronze. It produces strong parts and is ideal for cylindrical materials like pipes. The downside to this type of casting is that it can only be used to make symmetrical shapes. It is also more expensive than Vacuum casting.
More modern ways of casting, or at least prototype manufacturing, include 3D printing and Digital Light Processing.
The Vacuum Casting Process
This heading will fully explain the entire Vacuum Casting Process, starint from the preliminary stage to the very end.
Step 1: Make the master model
The very first step is to create the silicone vacuum casting mold, this is done by creating a master mold. It is called the master moldel because it is the mold which in turn helps to form the silicone mold which then forms the final material.
The master mold is usually made by 3D printing or CNC machining. The final product will be the exact replical of the silicone mold, it is extremely important that the master moldel for the silicone mold be made with great precision and critical detailing.
Step 2: Make the Silicone mold
The master model is then placed in a mould box, and the liquid silicone is poured over it. Air bubbles are removed by placing it in a vacuum casting chamber. The silicone is left to cure, the curing usually takes 8 to 24 hours.
Once the silicone has cured, the silicone mold is then cut carefully to remove the master model, this reveals a hollow cavity which must be the exact negative of the material to be made. If properly made, the silicone mold casting can be reused to make multiple identical and perfect replicals of the original material.
The Silicone is highly detailed and heat resistant. It has a flexible texture and is sometimes transparent. the Silicone mold is then carefully joined back together leaving the hollowed cavity accessible for the urethane to go through for the final production process product.
Step 3: Casting Preparation
Before casting, the polyurethane must be mixed and prepared. Colorings may be added to get the desired color of the final material. At this time, the mixture may be vacuumed to remove air bubbles
Step 4: Pouring the polyurethane resins
The silicone mold is then placed in the vacuum chamber, and the resin is poured inside the mold. The resin must thoroughly fill and cover the entirety of the mold.
Any trapped air must be allowed to escape completely , this will prevent a defective final product.
Step 5: Trimming and Finishing
The resin must be left to cure after it has been taken from the chamber. The mould is then opened, and the finished product is removed. Excess materials must be trimmed, ad the final product may require finishing like sanding or painting.
Materials Used in Vacuum Casting
| Materials Types | Characteristics | Common Applications |
| Rigid Polyurethane (PU) Resin | Hard,tough plastic Can mimic ABS, PP or Nylon |
Enclosures, Housings, Electronic Castings, Fixtures |
| Flexible Polyurethane (PU) Resin | Rubber-like Elasticity Soft touch Varying Levels |
Glaskets, Seals, Grips Flexible Connectors |
| Transparent PU Resin | Clear or tinted , Glass-like fin Can be polished UV Stable | Light covers, lenses, display part, decorative items |
| High-Temperature PU Resin | Can wsthstand heat up to 120-150°C Thermal stale |
Automotive under-the-hoodparts, thermal test samples |
| Epoxy Resin(for casting) | Excellent chemical andheat resictance, Strongstiff, sometimes brittle | Soft touch produc, prostheticsflexible models |
Other materials used in vacuum casting are:
- ABS-Like Resins
- Glass-Filled Nylon-Like
- Elastomeric TPE-Like
- PC-Like
- Clear Resins
- High-Impact Resins
Vacuum Casting Machine
The vacuum machine helps eliminate airbubvles. It helps ensure that the resin completely covers the mold. This ensures that the the final result is precise and free from defects
Parts of a Vacuum Casting Machine
The Vacuum chamber
This is where the mold and the resin is placed. It is a chamber where the air presssure is greatly reduced to ensure airbubbles do not form during the process.
The Mixing and Degassing Unit
Not all Vacuum machines have this componets. This component acts as a mixer, combining trhe resin and the hardener. It also at the same time removes any air trapped in the resin.
The resin feeding system
This introduces the resin into the mold
Heating chamber
This is used to cure the resin. It ensures that the resin fully solidifies
Control panel
This is where the operator controls the timing, vacuum pressure and other details. The Vacuum CAsting Machine could be Manual, Semi-Automatic or Fully automatic
Applications of Vacuum Casting
Vacuum casting is a versatile technology with several applications across various sectors. The process’s capacity to produce delicate and accurate components makes it an excellent alternative for achieving high-quality products.
Here is a list of the applications of Vacuum casting across the various industries where they are used:
Medical implants:
Vacuum casting is frequently utilized in the medical industry to produce complex parts and components, including implants and prostheses.
Automotive industry:
Vacuum casting has the ability make parts that require precision and accuracy. It is used in the automation industry to make parts like intake manifolds, exhaust systems, and body panels
Food Industry:
Vacuum casting is used in the food industry to make packaging and presentation components. The required dimensional accuracy of some of these components can only be achieved through vacuum casting.
Aerospace components:
Vacuum casting can be used to create precise aerospace components. Components like air ducts, fuel systems, and even some elements of the aircraft exteriors are manufactured by the Vacuum casting process.
| Industry | Application Areas | Examples |
| Automotive | Prototyping, Customcomponents, Interior/exterior | Dashboards, gear knobs, headlampenses, brackets |
| Consumer Electronics | Enclosures, Functional testing Low-volume production |
Remote control shells, headphonescasings, smart wearables |
| Medical Devices | Prototyping of devices Ergonomic testing | Hearing aids, grips, soft shellsfor monitors |
| Industrial Equipment | Functional testing of parts Short-run end-use parts |
Control panel covers, gearhousing models |
| Aerospace | Fit and assembly trials Lightweight parts |
Panel switches, duct models Non-structuralcomponents |
| Architecture | Concept models Scale mock-ups |
Scale building models, interiordesign prototypes |
| Toys & Figurines | Form and fit prototypes Design validation |
Blender casings, coffee makerbuttons, knobs |
Advantages of Vacuum Casting
The vacuum casting technique has a wide range of applications in several sectors. This production approach has various advantages over other methods of prototyping and manufacturing.
Flexibility
The Vacuum casting process, is quite flexible. The process allows for a variety of design elements, from intricate details like ribs, undercuts, and embossed logos to more complex design geometries. The silicone molds are also ,reusable making it also cost-effective
High design accuracy
Vacuum casting is perfect for materials with precise and intricate details. It captures even the minutest surface texture. By this, the technique is perfect to produce multiple, identical replicas. Furthermore, the surface of the finished products from vacuum casting is quite smooth, reducing or even eradicating the need for additional post-production and other manufacturing processes
Fast production
It is perfect for industries producing small batches of products. This is because the manufacturing process is fast. The molds can be made within a few hours and the products can be cured quickly.
Low cost of Machinery
Silicone molds, which is the main part in the process, are less expensive to build than metallic molds. Silicone molds are prepared for a few hundred dollars, whereas molds for injection molding or metal casting can cost thousands.
Versatility
Vacuum casting allows for the use of different Polyurethane resins. some of them include; Rubber plastic, glass and a few metal.
Disadvantages of Vacuum Casting
The silicone mode has a short life span, meaning it canot be reused for too many times, otherwise degradation in precision and detail begins to occur and it will reduce the quality of the final product.
Vacuum casting is not suitable for mass production
The silicone molding process works best with just one kind of material – polyurethane resins. It is therefore not suitable for molding hard industrial materials.
| ADVANTAGES | DISADVANTAGES |
| High Accuracyand Fine Detail | Limited MouldLifespan |
| Smooth Surface Finish | Time-Consumingfor Large Volumes |
| Bubble-Free Parts | Limited Material Strength |
| Cost-Effective for Small Batches | Heat and UVSensitivity |
| Fast Turnaround | Manual Labour andSkill Required |
| Material Versatility | Size Limitations |
| Flexible Silicone Moulds | Highly flexible; cancast complex shapesand undercuts |
Vacuum Casting vs. Other Manufacturing Techniques
Here, a comparison between vacuum casting and other manufacturing technique will be done, a special highlight will be done to the process, the cost and the quality of work
Vacuum Casting vs. Injection Molding
Injection molding is a process where molten material usually plastic, is injected into a mold under high pressure. It is then cooled down to form a solid material. The mold used in this type of manufacturing is usually a metal mold.
The injection molding process includes:
Heat and melt the plastic pellets
Inject the melted plastic into a metal mold
wait for it to solidify
open and eject the finished product
Injection molding is more suited for mass production as against vacuum casting. The image below describes the differences between THe Vacuum Casting and the Injection molding manufacturing process.
Vacuum Casting vs. 3D Printing
3D printing is also known as additive manufacturing. A digital image of the material to be printed is first created, the printer then prints the digital file layer by layer. This manufacturing process is extremely fast.
However, the machine can be slow in making multiple copies. This means it is also not suitable for mass production. 3D printing is perfect to make materials with complex geometry and require a great dimensional accuracy