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The Advantages and Disadvantages of Vacuum casting
2021.02.26
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Vacuum casting is born under the fast development of technology and has become popular between manufacturers, entrepreneurs, and corporations. As one of the most economical low volume production ways, vacuum casting ensures the same quality and consistence. However, nothing is perfect. Vacuum casting is limited in tolerance, risk of continuous flaw, material options, etc. If you are wondering whether vacuum casting is a good choice, the following article will tell you the detailed advantages and disadvantages of vacuum casting.  
 
The advantages and disadvantages of vacuum casting
Advantages Disadvantages
Fast Production Production Restriction
Low producing cost Loose Tolerance
Superior material simulation Continuous Flaw
Excellent surface treatment;  Plastic Material Only
Part consistence Potential bubble or hollowness issue
Thin-wall casting Additional Mold Maintenance

 

What is Vacuum Casting?

Vacuum casting is a copy manufacturing way that uses silicone mold. It is an ideal method for low volume production and rapid prototyping. The working principle is the same with injection molding. Both ways produce parts by a mold. However, vacuum casting differs significantly from injection molding in the specific process.
 

Master Model

Upon confirmation of the CAD files, the technician starts to make the master model through 3D printing or CNC machining. Each chamfer, shape should be printed perfectly.
 

Silicone Mold

The master model will be placed into a casting frame and filled with liquid silicone. The silicone mold will be cut into 2 parts after well cured.
 

Casting Part

As per the design request, the technician will measure the proper proportions of polyurethanes. Then the polyurethanes will be poured into the silicone mold and be cured in the vacuum casting machine. The vacuum condition is capable to remove any trapped bubbles for smooth finishing.
 
Depending on design intent and part performance, vacuum casting has wide material options. ABS is one of the most used materials due to its superior material property and low cost. PP is good at forming. Besides, rubber, PE, glass-filled material, and others can offer better strength and rigidity. You need to talk with your technician about suitable material.


Vacuum casting process-2fprototypes
Vacuum casting process - 2fprototypes
 

Advantages

 

Advantanges img
What are the advantages of vacuum casting?

Fast Production

The silicone mold can be made within a day. One mold produces around 30-50 parts less than 20 days. Vacuum casting is capable to achieve continuous production. Compared to CNC machining and 3D printing, vacuum casting is time-saving for machine preparation. Similar injection molding can make the parts faster, it will be weeks for the necessary aluminum mold to be manufactured. Vacuum casting has a time advantage over other manufacturing ways.  
 

Low producing cost

Aluminum material is more expensive than silicone. Under the same condition of volume, the price of liquid silicone is around 45% higher than aluminum. As a subtractive producing way, CNC machining cuts the aluminum block until it has an ideal mold cavity. The cut material is another material cost. Before the CNC processing, there is mass calculation and setting-up. All these preparations results in higher labor cost. Vacuum casting copies parts without waste of materials. It is more friendly to the environment.    
 

Superior material simulation

Material is one of the key factors to make vacuum casting popular. The polyurethanes can simulate the most material properties. Such as:
PMMA - High Transmittance
ABS - High impact strength, low heat resistance
Rubber - High flexibility
More materials
The polyurethanes are required to perform various properties of rigidity, smoothness, flexibility, etc. as per the product functional request. For low volume production, vacuum casting achieves the same effect as other manufacturing ways.


Plastic material img
Photo Credit: Pixabay
 

Excellent surface treatment

After the 3D printing or CNC machining, the master model will be performed surface finishing as per customer request. After that, the cured silicone mold can have a detailed surface reduction to the master model. This one-shot surface treatment save dozens of cost and time to the following copies.
 

Part consistence

Consistent appearance and function are conducive to market research and testing. The silicone mold produced by the master model ensures every copied part that has the same features of shape, size, finishing, etc. Thats why we need volume production. Consistence and fast turn-around are more flexible to the user preference. Vacuum casting is ideal for low volume production.  
 

Thin-wall casting

Thin-wall casting will be lightweight with less material and higher technical requirements. It is necessary under some special conditions. Products with functional shell requires thin-wall to target the maximum effect. Products with complicated internal structure relies on conduction between thin-wall parts. In traditional manufacturing, the thin-wall casting is hard to be poured thoroughly, which is the key reason for the high failure rate. Under the constant vacuum pressure, the structure of the manufactured part can be compact and thin-wall.   
 

Disadvantages

 
Disadvantage img

What are the disadvantages of vacuum casting?

Production Restriction

Vacuum casting is born for low volume production. The crash silicone mold has a short lifespan. It can produce as many as 50 parts. The mold will lose the shape gradually once the part quantity is exceeded. The high cost of time is the other reason to restrict the production. The silicone mold produces only one part at a time. The cured time of each copied part is long. Accordingly injection molding is more suitable for the mass production of plastic parts.
 

Loose Tolerance

The silicone molding is formed by tightly clinging to the master model. Liquid silicone shrinks after curing which is normal for its nature. The shrinkage helps the molding to copy part authentically, but result in inaccuracy. The shrinkage rate of liquid silicone is from 1% to 4%. Though better silicone has a lower shrinkage rate, the average shrinkage rate is around 2%. Engineers will try the best to predict and improve the shrinkage. The shrinkage might still be around 0.15%. Vacuum casting is not a good choice for precise parts.
 

Continuous Flaw

Molding manufacturing can cause continuous flaws easily. Part from CNC machining and 3D printing can be checked and improved separately. The master model and the silicone mold are the two factors that link to the flaws. The double risks make higher cost than other manufacturing ways.

plastic img
Photo Credit: Pixabay
 

Plastic Material Only

Polyurethanes can simulate kinds of material properties but metal materials. The melting point of aluminum, steel, and brass is over 660°C, which is extremely higher than the silicone mole (200°C-450°C). Excessive temperature will destroy the mold of vacuum casting.
 

Potential bubble or hollowness issue

The curing speed of the outer side is faster than the central side when the wall thickness is too thick. Accordingly, insufficient filling from the central side occurs the bubble or hollowness. These issues are unrelated to the actual measurement but related to the experiences of engineers. Now we have vacuum casting machines to minimize the hollowness issue. It still depends on the actual manufacturing and proficiency of the machine operating. Thats why we need a professional and experienced manufacturer.
 

Additional Mold Maintenance

Each manual open and taking out from the mold will leave debris and wear. The debris affects the surface finishing and smoothness if they cant be removed timely. Mold maintenance and cleanliness should be performed after each copied part. These additional maintenance will increase the cost of vacuum casting.  

Vacuum casting products-2fprototypes
Vacuum casting products - 2fprototypes
 
Based on above the advantages and disadvantages, the merits of vacuum casting include speed, low volume, and low cost. Depending on product quantity, target, technique requirement, and other factors, you will find whether vacuum casting is suitable for your project. Vacuum casting is widely used in the application of product pilot run, prototyping, and testing.  
 
Before the new product to the market, a rapid and authentic prototype can get feedback easier. It is more convenient and economical to improve the design. Low volume production helps the startups to recycle the money faster and iterate the products.
 
Please feel free to contact us if you are not sure about the manufacturing way for your project.

 
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