Vacuum Forming: Process, Materials & Benefit
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Vacuum Forming: Process, Materials & Benefit
The manufacturing industry today requires production methods that are efficient and cost-effective to meet the growing demands of consumers.
In this context, various manufacturing techniques are widely applied, and one such technique, namely Vacuum Forming, has broad applications in the manufacturing industry. Whether it is the production of plastic parts, automotive components, medical devices, or electronic products, vacuum forming is a fast, flexible, and economical method.
In this article, we will explore the basic principles, scope of application, and advantages of vacuum forming technology to better understand this widely used manufacturing technique.
What is Vacuum Forming?
Vacuum forming is a method of thermoforming used to shape plastic using heated plastic sheets, a mold, and a vacuum. Other types of thermoforming include injection molding and pressure forming.
Vacuum forming is a very popular approach to plastic production. It produces various plastic items, from food packaging supplies to automotive and highly sought-after medical parts. Vacuum forming is popular due to its low cost, efficiency, and ease of use.
How Does Vacuum Forming Work?
To summarize quickly, vacuum forming is a process in which a layer of plastic is heated, placed onto a mold, and then formed into shape.
Manufacturers that use this process need plastic sheets, clamps, frames, a heat source, a vacuum, and a mold. Many manufacturers use infrared elements as a heat source, while others may also use used.
The Steps of Vacuum Forming:
1. Clamp: The plastic sheet is clamped onto an open frame. These clamps must be strong enough to firmly hold the plastic sheet during forming.
2. Heat: Heat is applied to the plastic sheet until it reaches the desired temperature and is softened/pliable. This heat must be applied uniformly to the plastic sheet.
3. Vacuum: The pliable plastic sheet framework is lowered onto or over the mold. A vacuum applies suction to pull the sheet into place. Plastic sheets fitted to male molds need no further work during this step, but plastic sheets fitted to female molds typically need tiny holes drilled into the crevices. This will allow the vacuum to pull the sheet into the desired shape.
4. Cool: The sheets are allowed to cool. Manufacturers sometimes use fans and/or misters to speed this step along, particularly when larger products are being made.
5. Demold: The cooled plastic is removed from the mold and released from the framework. The plastic must be completely cooled before undergoing this step. If released too soon, the product may be deformed and rejected.
6. Trim: Any excess material is removed, sanded, or smoothed away. This step also includes drilling holes, slots, or cutouts into the product if required. Once this step is completed, the product can move onto the final stages of production (design, etc.) or be released for final sale.
6 Types of Vacuum Forming
1. Female Mold Vacuum Forming
The most common method of vacuum forming, concave vacuum forming, uses atmospheric pressure to form softened plastic sheets against the mold.
Air under the sheet is removed once the softened sheet is successfully placed over the mold, and that removal of air causes the plastic to form the mold. Once the plastic has cooled, compressed air is used to blow out the completed product.
This type of vacuum forming is only suitable for products with a small depth. Products with too large of a depth will cause the plastic sheet to stretch too much, creating an uneven finished result. The bottom of the product would be too thin.
2. Male Mold Vacuum Forming
Convex vacuum forming is a good option for molding plastics that require a high degree of dimensional accuracy – such as thin-walled plastic parts with convex shapes. Softened plastic is drawn over the mold, and the mold forms the inside of the item.
3. Female & Male Mold Vacuum Forming
Concave and convex successive vacuum forming are where manufacturers use male and female molds simultaneously to form a product.
To do this, they heat the plastic sheet until softened and then blow compressed air through the mold to bulge the plastic sheet. The mold is then inserted downward into the bulging sheet, and the sheet is vacuumed into the mold; at the same time, compressed air is passed into the female mold so that the plastic sheet is pushed against the outer surface of both molds and formed.
This vacuum forming method is used for forming plastic parts with deep cavities. Because the softened sheet is blown and stretched before forming, the sheet has a relatively uniform thickness.
4. Blown Vacuum Forming
Parts that require a more uniform wall thickness are vacuum formed with plastics that have been heated, put into an airtight box, and then stretched into a balloon-like shape using compressed air.
Once blown up, the mold is raised under the sheet, and the air is removed from the airtight box. Atmospheric pressure causes the sheet to collapse around the mold. Because the plastic sheet is stretched before forming around the mold, the thickness of the final part will be uniform.
5. Auxiliary Male Mold Vacuum Forming
Auxiliary convex vacuum forming is another type of convex vacuum forming, also known as upward vacuum forming.
For the upward vacuum forming process, the plastic sheet is heated over the mold in an airtight container, and then the mold is pushed up so that the air inside the container pushes out and stretches the plastic sheet. Once that is completed, the air is removed from the container, and the sheet collapses around the mold using regular vacuum forming.
Upward vacuum forming results in a more uniform and sturdy final result – mostly because the plastic sheet does not contact the mold until it has expanded.
6. Vacuum Forming with an Air Buffer Device
This method involves using a plunger and compressed air to force a softened plastic sheet until placed. Both are pushed against the sheet once it’s softened, and then compressed air is blown into the cavity around the mold, fitting the plastic around it.
The sheet is formed between two air buffer layers until the air is removed, and the plastic sheet is directly formed against the mold.
Vacuum forming with an air buffer device allows for a final product with a uniform wall thickness and deeper cavities.
An explanation of Male mold and Female mold
Male (or Positive) Molds: These molds are convex-shaped. In other words, their mold juts outward. The plastic must be sucked around the mold to shape it using the vacuum correctly.
Female (or Negative) Molds: These molds are concave-shaped. In other words, their mold juts inwards. The vacuum will need to suck the plastic inwards around this mold, and the plastic may need to be drilled for the vacuum to be effective.
The Materials of Vacuum Forming
A variety of thermoplastics are used in vacuum forming manufacturing. Some commonly included plastics are:
Polycarbonate (PC)
Polycarbonate vacuum forming parts are virtually unbreakable, highly resistant to damage, UV protected on one or both sides and lightweight. They are easy to install and handle in a vacuum forming machine. PCs are commonly used to make machine parts, skylights, etc.
Polyvinyl chloride (PVC)
Polycarbonate vacuum forming parts are virtually unbreakable, highly resistant to damage, UV protected on one or both sides and lightweight. They are easy to install and handle in a vacuum forming machine. PCs are commonly used to make machine parts, skylights, etc.
Polystyrene (PS)
Polystyrene’s affordability, lightweight nature, thermal insulation properties, and impact resistance make it an excellent choice for vacuum forming.
PMMA (Acrylic)
PMMA’s combination of optical clarity, ease of processing, durability, lightweight, and aesthetic appeal make it a highly versatile material for vacuum forming.
Acrylonitrile butadiene styrene (ABS)
ABS’s combination of impact resistance, chemical resistance, good surface finish, dimensional stability, and ease of processing make it a highly versatile material for vacuum forming. It is commonly used in a variety of industries, including automotive, consumer goods, and electronics.
Polypropylene (PP)
PP has good impact resistance, which makes it ideal for applications where the formed parts may be subjected to high levels of stress or impact, such as in automotive parts. And it easy to process, making it a good choice for vacuum forming.
Polyethylene (PE)
Polyethylene is a plastic sheet made from petroleum. Manufacturers often use polyethylene because of its low cost and high resistance to water and chemicals. It is also very stable in cryogenic environments and very malleable.
Polyethylene terephthalate glycol (PETG)
PETG is a transparent thermosetting plastic used in vacuum forming because it is easy to mold and form. It has high durability, high strength, and is generally resistant to harsh environments. Polyethylene terephthalate glycol is also FDA food safe.
Mould Materials of Vacuum Forming
Vacuum forming also requires other materials, such as the materials used to create the molds. Mold design is a very important part of the vacuum forming process. Choosing the right material can determine the effectiveness of the process. Molds can be made out of a variety of materials such as:
Aluminum
Aluminum is a popular choice for vacuum forming molds due to its excellent thermal conductivity and durability. It is also relatively easy to machine and can be used for both small and large production runs.
Steel:
Steel is another popular choice for vacuum forming molds due to its high strength and durability. It is ideal for applications where high volumes of parts are required, as it can withstand the wear and tear of repeated use.
Advantages and Disadvantages of Vacuum Forming
Manufacturers often choose vacuum forming because the process offers a good mix of design flexibility and cost. Vacuum forming is a great option for manufacturers that are testing new products, are interested in custom colors, and/or are interested in smaller production runs.
The benefits of vacuum forming are:
Low tooling cost
Vacuum forming molds are relatively inexpensive to produce compared to other manufacturing methods, such as injection molding. This makes vacuum forming a cost-effective option for small to medium-sized production runs.
Ability to create complex shapes
Vacuum forming allows for the production of complex, three-dimensional shapes with undercuts and intricate details. This makes it a popular choice for applications where aesthetics are important, such as in product packaging and display units.
Wide range of material options
Vacuum forming can be used with a variety of thermoplastic materials, including ABS, polycarbonate, and PVC, among others. This makes it a flexible process that can be adapted to a range of applications and industries.
Rapid prototyping
Vacuum forming allows for the quick and easy production of prototypes and small production runs, which can be useful in the product development process.
Reduced waste
Vacuum forming produces less waste compared to other manufacturing processes, such as injection molding, as excess material can be trimmed and reused in future productions.
Fast cycle times
Vacuum forming has a relatively fast cycle time, which means that parts can be produced quickly and efficiently. This makes it a popular choice for applications where time is a critical factor, such as in the automotive and aerospace industries.
The drawbacks of vacuum forming are:
Limited material selection
While vacuum forming can be used with a variety of thermoplastic materials, the selection is not as wide as with other manufacturing processes, such as injection molding. This may limit the range of properties and characteristics that can be achieved with the final product.
Limited precision
Vacuum forming may not be as precise as other manufacturing processes, such as CNC machining or injection molding. This may lead to slight variations in part dimensions or surface finishes.
Limited part thickness
Vacuum forming is typically limited to thinner parts, as thicker parts may not form correctly due to material distribution and cooling issues.
Limited part size
The size of the parts that can be produced with vacuum forming is limited by the size of the vacuum forming machine. Large parts may require multiple forming cycles or may not be possible to produce at all.
Surface finish limitations
The surface finish of vacuum formed parts may not be as smooth or consistent as with other manufacturing processes. This may require additional post-processing steps, such as sanding or painting, to achieve the desired finish.
Limited production volume
While vacuum forming can be used for small to medium production runs, it may not be as efficient or cost-effective as other processes for larger production volumes.
FAQs
Q: What is the difference between vacuum forming and thermoforming?
A: Thermoforming is a broader term that refers to the process of heating a thermoplastic material until it is pliable, then forming it into a specific shape. Vacuum forming is a specific type of thermoforming that involves using a vacuum to force the material into a mold shape.
Q: What types of products can be produced with vacuum forming?
A: Vacuum forming is used to produce a wide range of products, including product packaging, display units, automotive interior components, and more.
Q: Is vacuum forming an environmentally friendly manufacturing process?
A: Vacuum forming produces less waste compared to other manufacturing processes, such as injection molding, as excess material can be trimmed and reused in future productions. However, the use of thermoplastic materials can have environmental impacts if not managed properly.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.