Are you looking for the most budget-friendly way to build prototypes in the current era? Experts suggest opting for vacuum casting, not only because of its cost feature but also for its flexibility due to modularity.
Vacuum casting is a casting process for elastomers that use silicone molds to make plastic and rubber components under vacuum and also draws the liquid material into the mold. It is also sometimes referred to as Urethane casting or Polyurethane casting.
Vacuum casting is known for its reliable and adaptable casting process, which is highly responsible for making prototypes and industrial parts.
Are you wondering what kind of model is required to enable this procedure? The top-quality master model is opted to meet all the requirements of the procedure. It also tends to be a complete mechanical part or a model utilized by stereolithography. This model has the ideal quality of both looks and measurements.
The vacuum casting process is extremely capable of copying the injection molding to produce complex parts in polyurethane resins and cast nylon.
Working Process of Vacuum Casting
Here are the steps involved in the working process of vacuum casting.
Step 1: Creation of a 3D part model
Like most of the manufacturing processes in the modern era, the vacuum casting process begins with the creation of 3D modeling using the stereolithography process. Vacuum casting works in a similar way which follows injection molding guidelines and requires a mold tool with a part-shaped cavity. And, Vacuum casting uses soft silicone molds for achieving better results.
In some occurrences, the part is examined with the help of 3D laser scanning and are also responsible for creating and producing 3D files.
Step 2: Building Master patterns
The master patterns, which are created from the 3D CAD or 3D part model, are manufactured using the CNC matching technique or handcrafting method.
During this stage, the customer can suggest modifications to an existing component for the casting process, and any part clean-ups is carried out at this stage. Then, the master pattern is attached with a casting gate and suspended upon the parting line in a mold.
And, some of the 3D printing techniques such as SLA or SLS are more applicable and budget-friendly as the pattern maker.
Always make sure that the patterns must be able to withstand temperatures up to 40°C. Metals used here are high tolerances in bores and critical areas. Then, the parts are custom-built manually by cleaning and form a required surface finish. By painting or spraying the master pattern, we can achieve the gloss or matt surface textures as per the customer’s requirement.
Step 3: Creating Silicone Rubber Mold
Silicone molds are created using the master patterns, and as we already know that the master patterns are fitted with casting gates, inserts, and cores which are hanged inside the vacuum mold casting box.
Then, the silicone is poured around the master pattern under the vacuum in the vacuum mold casting box. The silicone poured into the vacuum mold casting flows on all sides of the master pattern which fills every single detail.
It is allowed to cure inside the oven at around 40℃ for about 8 to 16 hours for better results. The size of the silicone mold produced depends on the time allowed to cure inside the oven. After allowing it to cure between 8 to 16 hours, the silicone rubber is dried. And, the box and risers are removed after the cure session.
Once the mold is ready, it is carefully split using a scalpel and exposes the negative shape cavity of the part. During the production process, it always makes sure to provide the accurate alignment of the 2 mold halves with the help of a wavy cut. And, the size of the mold is limited or controlled by the dimensions of the vacuum mold casting chamber.
By choosing the right vacuum mold casting, it helps in avoiding stickiness and surface defects.
Step 4: Process of mixing and pouring the Polyurethane resin
Before mixing polyurethane resin, they are preheated to about 40°C. Then, the two-component casting resin is mixed in equal proportions that include any pigment color. And, it is poured into the bowl inside the process machine. Finally, molds are returned and pouring gates are connected to the mixing and pouring bowl.
In this auto pouring process, the casting resins and the color pigments inside the bowl are stirred well. It is deaerated for 50 to 60 seconds under vacuum in the vacuum mold casting.
Then, the polyurethane resin is poured into the mold in the vacuum mold casting to avoid the air pockets and voids. It ensures to provide bubble-free molds and removes any resistance during the flow that is caused by air pockets. Probably, the filling of the tool takes place by gravity feeding alone.
Step 5: Procedure of demolding the cast part
After the casting process of the resin, the mold is placed on a heating chamber for the curing period. The casting is removed from the mold once the curing is done.
Finally, the gates and risers are removed from the vacuum mold casting and any required finishing can be carried out here.
Vacuum casting products used in the vacuum casting
The wide range of vacuum casting products chosen by the designers meets the specific and customized requirements for the mechanical, thermal, and physical properties.
Some of the vacuum casting products used in vacuum mold casting include thermoplastics, rubbers, and resins. All of these vacuum casting products have specific properties and characteristics.
- Surface texture (Gloss or Matt)
- Physical appearance.
- Transparency or Translucence.
- Fire Retardance
- The quality of the product is based on its physical appearance.
- Temperature resistance
- Colors and Tints.
- Range of surface finishes.
- UV stability
The materials to be used in vacuum casting must accurately mimic a wide range of industrial products including Polycarbonate, ABS, glass-filled nylon, polypropylene, and elastomer rubber.
Vacuum casting materials can mimic the following materials and properties. And, the following production materials and properties are listed below.
- ABS – The high rigidity and strength.
- Polyamide and glass-filled nylon – high rigidity
- Rubber – high flexibility.
- Filled ABS – fire resistance and retardance.
- Polycarbonate and PMMA – It is shock resistance, translucence, high-temperature resistance.
- Polypropylene and HDPR – high elasticity.
- STAR – PU Classic ABS – One of the classic and most popular ABS Compound.
- STAR – PU PC – It is transparent, and also mainly simulates filled ABS or PC.
- STAR – PU ABS – It is a UL94-V0 specification and a flame retardant resin.
- STAR – PU Classic PU – Typically it can be bent about 30 to 50 times before breaking, and it is a PP resin compound. Living hinges are possible here.
- STAR – PU Silicone – It is a translucent silicone. Also, it can act as a VC mold tool and fabricate the parts in a vacuum.
Vacuum casting parts have a wide range of applications in various sectors that includes, telecommunications and engineering, automatic and aerospace, pharmaceutical and medical, food production, and consumer goods.
When the vacuum casting should be used?
Vacuum casting is used in various aspects including pre-production prototypes, limited production volumes, assembly line trails, and functional marketing. It is used for marketing purposes too, e.g. presentations and trade shows. It also adds value to the projects.
Some of the characteristics of vacuum casting are,
- Vacuum casting is the most economical and effective way to produce high-quality, and low-volume plastic parts which are similar to injection molding parts.
- These high qualities parts are more likely applicable for fit, form, and function tests during the whole embodiment design stages. It is used for marketing, field user testing, and product design verification purposes.
- The vacuum casting materials are also available to create parts that are completely opaque, and completely transparent.
- In some occurrences, the high-quality wax masters can be produced from vacuum casting for investment casting. It helps in increasing the finer details of all the features.
- Currently, more vacuum casting resins are commercially available that are used for making parts to meet all the design requirements includes temperature requirements, hardness, and different surface textures, etc.
Benefits of the Vacuum casting process
- Complex shapes, different sizes, and features can be easily accomplished by using multi-segment molds and cores.
- It is well-known for its high precision feature and providing fine details to the finished products of the vacuum casting metal
- There are many vacuum casting resins that are suitable for various applications such as rubbery, flame retardant, clear, and food-grade.
- Master patterns make use of multiple components for reducing the time of the product design prototyping stage and also the cost of new product development.
- Brass in molds and aluminum inserts can also be used for better results.
- The vacuum casting process always makes sure to maintain the quality of the product to be designed.
- Helps in lowering the production costs.
- Polyurethane casting is used to produce tiny batches of high-quality molding-type parts for prototypes models. It is also used to create low-volume end-use parts for low stress.
- Here, the resin type can be modified easily without the help of retooling to test various types of materials for a specific part.
Disadvantages of the Vacuum casting process
- The mold manufacture using soft silicon generally lasts for about 30 to 50 parts. Sometimes, the bigger parts, rough surface textures, and few features reduce the life span of mold. It totally depends on the surface textures, and size.
- Sometimes, it is irregular, overly thin, and thick features are deviated from normal tolerance due to shrinkage.
- Sharp corners of the vacuum casting molds with rounded edges do not give more durability to the product.
- Generally, the surface finish depends on the post-processing of the parts. It is limited to only the outside features, not to some internal features of the mold patterns.
- The shrinkage rate of the molds range from 15 percentage to 0.25 percentage due to the thermal expansion of the liquid. In some aspects, the manufacturer does allow to add shrinkage tolerance according to the product design before the order.
- It always needs plugs and cores to be applicable for few more features.
Applications of the Vacuum Casting process
Vacuum casting plays a vital role in various industries including the commercial industry, household products, and the food and beverage industry. Most industries opt for this process because of its fast production and cost-effective nature.
Food and Beverages Industry
The food and beverages industry makes use of vacuum casting for packaging purposes, which more likely helps in the manufacturing of plastic bottles and tins. This process enables the production of products faster and on a larger scale.
Commercial Products Sector
The commercial industry uses vacuum casting for packaging commercial products. Some of the products manufactured using this process are mobile cases, sunglasses, pens, food, and drinks packaging. It paves a way for creating more employment offers for people who want to venture into selling off some of the products.
Manufacturing Sector of Household Products
Household products are also made using a vacuum casting process. Some products such as washing detergents, cosmetics, and food processing are made using this method. Most of the high-quality and branded companies do use vacuum casting processes for making such products.
Aerospace and Automotive Parts Industry, medical devices, consumer goods, and prosthetics are some of the production plastic-based parts and prototypes made using the vacuum casting process. Decorative objects including custom ornaments, showpieces, and wall plaques are also made using this technique.
As we learned, the vacuum casting process is the most innovative and effective method in this modern era for creating more prototypes on a larger scale with high-end and cost-effective products.
And, vacuum casting has been always the go-to method opted by experts especially when in the need of meeting the requirements of the industry standards.
With all honesty, the vacuum casting manufacturing technique has a great scope now and also in the future because of its capability of solving all entrapment issues that will arise in the molding process.