Vacuum forming is a thermoforming process that offers benefits such as low manufacturing cost, reduced molding costs, and high efficiency in manufacturing high-quality. From smaller parts like pharmaceutical blister packs to larger auto parts, vacuum forming is used across many industries.
However, several intricacies surround the process, necessitating understanding the process before its selection. This article explains the process, compatible materials and machines, and its applications.
What is Vacuum Forming?
Vacuum forming is a plastic manufacturing process that involves using a machine to heat a plastic polymer till it is pliable before pulling it over a mold. It is an important process in the low-volume production of plastic parts.
The process is compatible with thermoplastics and thermoset materials despite their differences. Therefore, using any should only occur after a proper understanding of their properties. Nevertheless, most manufacturers, however, prefer thermoplastics due to their recyclability.
How Does Vacuum Forming Work?
Vacuum forming is a straightforward manufacturing process that involves five major steps explained below:
Step 1: Creating the Vacuum Forming Mold
Manufacturers use cast aluminum, wood, structural foam, or 3D-Printed plastics to make a vacuum mold. Each material has its peculiar benefits and limitations. For instance, 3D-printed plastics are easier to make, and one can create more complex designs in the mold. On the other hand, aluminum may be the appropriate choice when strength is a determining factor.
Most times, the molds have thousands of vent holes in them. These holes are a passage for trapped air during forming to prevent air entrapment. Furthermore, the mold must be able to conduct heat to decrease the cooling time of the final product. Just as in urethane vacuum casting, it is important to preheat the mold before the plastic vacuum molding process begins.
Step 2: Clamping Process
After placing the mold in the machine, place the plastic sheet on the machine properly. The clamp must be strong enough to hold the plastic throughout the forming process; its strength depends on the machine. Most clamps can hold materials with thicknesses ranging from 6-10mm.
Step 3: Heating Process
This involves using a heater to melt the plastic sheet below the glass transition temperature. The heater comes with a radiation source to perform its function, and the heating time depends on the type of plastic one is working with.
Note: it is important to apply the heat evenly throughout the plastic sheet.
Step 4: Vacuuming Process
After stretching the heated plastic sheet using pressured air, apply a vacuum to pull and distribute it over the mold’s surface. The vacuum removes trapped air as the plastic sheet takes the shape of the mold.
It is necessary for the part to cool down sufficiently as insufficient cooling can lead to the deformation of the final part.
Step 5: Trimming and Finishing
Trimming involves cutting off excess plastic materials. You can trim with a hand knife or band saw depending on the size and texture. Furthermore, the vacuum forming products may need extra holes or other designs to make them complete.
For this reason, manufacturers employ drilling, roller cutting, CNC machining, and many more to create precise and accurate holes and features. Also, you can improve the part’s quality and appearance using post-finishing processes like vacuum metalizing.
Types of Vacuum Forming Machines
Every machine used in the manufacturing process has its unique qualities and features. As a result, you should understand the different machines available. Below are the main types.
Industrial Vacuum Forming Machine
This machine type takes up a large space and is most suited for commercial manufacturing. Also, it can produce parts with complex shapes and designs. An important feature of machines under this class is that designers can modify the current parameters without interrupting the production cycle.
Mid-size Vacuum Forming Machine
Manufacturers use machines under this class to manufacture small to medium-sized plastic parts for prototyping and small-scale production. With mid-size vacuum forming machines, one has more autonomy over the process because of the semi-automatic feature
Tabletop Vacuum Forming Machine
This machine class is portable, easy to use, and designed for personal forming applications. Tabletop vacuum forming machines are best for materials with thicknesses not exceeding 6mm.
DIY Vacuum Forming Machine
This is a perfect educational tool for children and teenagers. It is manually operated, and one can only use them for parts with simple features.
Materials for Vacuum Forming
There are several materials compatible with the manufacturing process. Each has unique properties for example, polycarbonate has high tensile strength making it applicable in structural parts. Common materials for the process include:
- Acrylonitrile Butadiene Styrene (ABS)
- Polycarbonate (PC)
- Polypropylene (PP)
- Polyvinylidene fluoride (PVDF)
- Polyethylene terephthalate glycol (PETG)
- Polyvinyl Chloride (PVC)
- High Impact Polystyrene (HIPS)
- Acrylic (PMMA)
- High-Density Polyethylene (HDPE)
Advantages of Vacuum Forming
Manufacturers use vacuum molding because of the following benefits.
Vacuum forming is the most affordable plastic processing method for low-volume production. This is associated with the lost cost of prototyping and creating the vacuum forming mold. The mold cost is low because manufacturers make them from affordable and easily accessible materials. Also, when making similar parts, you can reuse the mold.
2. Turnaround Time
When compared to conventional processing methods, the time to produce the tooling mold is short, and it is even shorter if the molds are 3D printed. With vacuum forming, the time between creating the design for manufacturing and actual production is short. This increases production efficiency and reduces the time your product gets to market.
3. Design Flexibility and Versatility
Though one mold produces parts with the same design, designers can modify these molds to suit their needs better. This increases creativity as one can experiment with new ideas and create prototypes without significant costs or delays. Furthermore, vacuum molding offers more color options and customization. With this, manufacturers can create unique designs and personalized parts at a fair price.
4. Accuracy and Precision
Plastic vacuum forming is an accurate manufacturing process. The final part takes the mold’s exact shape, leading to a consistency in shape and size from batch to batch when using the same mold. Accuracy and precision are crucial for components that must fit into another part. As a result, it is applicable in parts assembly.
Vacuum molding is compatible with most plastic materials. For example, manufacturers can produce both transparent and translucent parts which are appliable in food packaging. Common materials compatible with the process include polycarbonate, propylene, and high-density polyethylene.
The vacuum forming process does not harm the environment as it produces little to no waste. Also, one can easily recycle the excess plastic material and use it for future production.
Disadvantages of Vacuum Forming
Vacuum molding has some limitations though it offers many benefits. These include:
Though you can create customized parts, a mold only produces so much detail, and vacuum forming may not be effective for parts with a high level of detail. Hence, the shape must be simple, and the designs must be straightforward.
Not Suitable For Large Scale Production
The process of vacuum forming involves the productuon of one part a time making it suitable for small volume production. However, it may be time consuming for large scale production.
Risk of Warping
Vacuum forming is suitable for plastics with thin walls. Thicker walls increase the risk of plastic warping. To avoid this, one must stretch the plastic sheet to reduce the wall thickness.
The advantage of reusing a vacuum forming mold to save costs can be a limitation, as any damage to the mold results in significant damage to the final product, and this can lead to product recall and losses.
Applications of Vacuum Forming
The vacuum forming process is used to manufacture many products across industries. Some of the common applications are:
Automotive and Transportation
Plastic vacuum forming is an affordable way to produce car parts as it can make detailed designs on parts and is compatible with small and large car parts. Aside from that, plastic material is stretched to a very thin sheet, reducing the part’s weight and increasing fuel efficiency.
Car part manufacturers use vacuum forming to produce window blanks, bumpers, trays, interior panels, spare wheel covers, and many more.
Vacuum molding is applicable in the food packaging industry because it can mold food-grade plastics easily. Because this plastic grade, like polycarbonate, is easily sterilizable, prevents contamination, reduces food damage, and preserves freshness.
There is an endless list of vacuum forming products used in making consumer goods. This is because vacuum forming is ideal for parts that are required to be lightweight, durable, and aesthetically pleasing. Examples include children’s toys, bath and shower trays, storage boxes, and many more.
Custom Parts and Special Effects
Manufacturers across many industries use vacuum molding to customize unique parts, and this is important for adding designs and properties for special effects. With vacuum forming, one adds complex logos and symbols on a part.
What are the Differences Between Vacuum Forming, Thermoforming, and Pressure Forming?
Thermoforming is the umbrella term that describes manufacturing a 3D part from a plastic sheet. Vacuum forming and pressure forming are the two main types of thermoforming. The difference lies in the forming principle, types and number of molds used.
Pressure forming involves using air under pressure to push the heated sheet of plastic into one mold before placing the other on the formed plastic. On the other hand, vacuum forming uses vacuum pressure to pull the warm plastic over or into the mold.
Types and Number of Molds
There are two types of molds used a male (which has a convex shape) and female (which has a concave shape) in thermoforming. When using a male mold, the plastic sheet is placed over it to fit inside the part. And when using a female mold, it fits around the thermoplastic sheet and forms its outer dimensions precisely.
Generally, one can use the male or female mold in vacuum forming that uses a single mold and vacuum pressure to give parts their desired shape.
Pressure forming works differently. Instead of suctioning around one mold, a heated sheet of plastic is pressed between two molds. This is useful for making plastic parts that need to be accurately shaped on both sides, or when a deep draw is required.
Vacuum forming is the simplest method to make repeatable plastic parts economically. It uses vacuum pressure and heat to perform its operation. Manufacturers often combine this vacuum forming with other manufacturing processes to enhance functionality and aesthetics.
There are several aspects of vacuum forming that determines the success of the operation. For example, choosing the best mold and material. As a result, this article discussed part of vacuum forming. At WayKen, our engineers and designers can cater to your low-volume part production needs from prototyping to full production runs.
Furthermore, we are an ISO-certified rapid prototyping manufacturer, and increase your profit by shortening the lead time and offering our services at a competitive price. Do you have any projects for help? Feel free to contact us today.
When is vacuum forming not the right choice?
Though vacuum forming offers many benefits, this process may not be best if the parts you want to produce have very complex designs and features, the intended product is on a large scale, time to get products to market is short. In any of these situations, consider other suitable alternatives.
What can go wrong with vacuum forming?
Like other manufacturing processes, it is important to take some precautions when forming parts. Defects like warping and uneven wall thickness of the final part can occur. These flaws can affect the part’s functionality. Hence, one should avoid them by adjusting the air pressure and other parameters.
Are vacuum casting and vacuum forming the same thing?
Though the principle for both may be the same, there is a difference. In vacuum casting, the starting material is a liquid resin while it is a solid plastic sheet in vacuum forming.