Vacuum Forming
Vacuum forming is one of the most common methods of manufacturing packaging for various goods. From store-bought mixed salads to the lid of your take-out coffee, and even high-end electronic devices, vacuum forming is used to make lightweight, cost-effective packaging. Vacuum forming process is relatively simple. It requires four main components: a mold or tool, which will shape the finished part, a plastic sheet, a heat source and a vacuum pump. The plastic sheet is heated as evenly as possible until it becomes soft and pliable, it is then placed on the mold or tool. the vacuum is then applied and the part is allowed to cool before it is removed from the mold. Making molds for vacuum forming through traditional manufacturing processes, such as machining or casting, is time-consuming and costly, especially when the shapes are complex, the surfaces are textured or have fine features. Designers and engineers are increasingly turning to 3D printed molds and tools for vacuum forming because they are faster and less expensive to make. In addition, it is easy to incorporate fine details such as text and intricate textures into these 3D printed molds and tools without increasing the cost of the part. Design Instructions As with any other manufacturing process, specific design instructions need to be followed for successful vacuum forming. Let’s start by defining some terms before looking at some of the best practices for vacuum forming tool design. Mold Styles There are two main types of molds for vacuum forming: male and female. To make a domed part, the male mold will have a convex shape while the female mold will have a concave shape. Some parts can be formed without a draft angle, but this generally facilitates their demolding and gives a homogeneous finish on all vacuum formed parts. A draft angle of 4 to 5 degrees is recommended for male molds. For female molds, the draft angle can be lower, between 1.5 and 3 degrees. For deeper parts, increasing the draft by a few degrees can help produce quality parts that are easy to demold. Textured surfaces will require higher draft angles in most cases, so consider this if your part is highly textured. When the part has interior cavities, it is often necessary to add vents to the mold or master model. This allows for vacuum throughout the mold, and allows the softened plastic to be well plated. Without evacuating the air from the negative areas, the plastic will tend to drape around the contours rather than press firmly against the shape. The addition of vents allows the interior cavities to be evacuated, making vacuum forming easier. Sharp corners on the edges of the mold should be rounded or chamfered if possible, to reduce stress concentration on the finished part and to reduce the risk of tearing or wrinkling the plastic during vacuum forming. Part Depth and Stretch Ratio It is important to keep the depth of the vacuum formed part as shallow as possible. The deeper the part, the more stretching of the plastic sheet will be required. This will mean a thicker starting sheet, more frequent wall thickness variations, and overall more difficulty in getting the operation right. The stretch ratio is calculated by a simple formula and is a good indicator of whether a part will form properly. It gives the minimum thickness of the plastic sheet needed for the formed part to have the desired thickness. The stretch ratio is the total area of the part divided by the area of the base. A 3:1 ratio is generally the maximum allowed for most vacuum forming operations. To determine the starting sheet thickness, multiply the desired value of the part thickness by the draw ratio. This gives the minimum thickness of the starting sheet. An example of a part with printing supports on the bottom only. Differences in print configuration for male and female molds The peel forces that detach the part from the resin tray during printing depend on the size and shape of the part. A closed cavity, formed by a female mold oriented parallel to the manufacturing platform, will experience more stress during printing due to the possible suction effect of the cavity formed. Solid male molds do not present the same risk and are better suited for direct printing on the manufacturing platform. In some cases, male molds can be printed directly on the manufacturing platform to reduce printing time. Post-processing of printed molds After printing, the next steps are to clean the surface of the parts from residual resin and post cure them to their optimal physical properties. Cleaning vacuum formed parts Most of the time, vacuum forming will produce parts with virtually clean shapes. This means that some aspects of the part will need to be addressed before the manufacturing process can be considered complete. Most vacuum forming plastics are easily cut by hand with a sharp knife or with a machine tool, such as a router or milling machine.
Differences between vacuum forming, thermoforming and pressure forming
Thermoforming is a manufacturing process in which a plastic sheet is heated to make it flexible, then formed or shaped with a mold and finally trimmed to create a finished part or product. Vacuum forming and pressure forming are two different types of thermoforming. The main difference between pressure forming and vacuum forming is the number of molds used in the process. Vacuum forming is the simplest method of thermoforming plastic. It requires a mold and negative pressure to achieve the desired part geometry. It is ideal for parts that only need to be accurately formed on one side, such as shaped food packaging or electronic devices. There are two main types of molds: the male or positive mold, which is convex, and the female or negative mold, which is concave. For male molds, the plastic sheet is laid over the mold to match the inside dimensions of the plastic part. For female molds, the thermoplastic sheet is placed inside the mold to precisely form the outer dimensions of the part. In pressure forming, a heated plastic sheet is pressed (hence the name) between two molds instead of being pressed onto a single mold by suction. Pressure forming is ideal for making plastic parts that need to have a very precise shape on both sides and/or require higher pressure (they need to penetrate further or deeper into the mold), such as appliance housings that need to have a nice aesthetic appearance on the outside and high precision on the inside. How does vacuum forming work? The successive steps of the vacuum forming process are as follows: Clamping: A plastic sheet is positioned on an open frame and clamped in place. Heating: The plastic sheet is softened with a heat source until it reaches the proper forming temperature and becomes pliable. Vacuuming: The frame holding the heated and pliable plastic sheet is lowered onto a mold and the sheet is pressed against it by a vacuum created on the other side of the mold. Female (or convex) molds must be drilled with tiny holes in the cavities so that the vacuum can effectively shape the thermoplastic sheet into the desired shape. Cooling: Once the plastic is formed around or inside the mold, it must be cooled. For large parts, fans and/or misting are sometimes used to speed up this stage of the production cycle. Demolding: When the plastic has cooled, it can be separated from the mold and removed from the frame. Finishing: The molded part still needs to be cleaned of excess material and its edges may need to be chamfered, sanded or polished. Vacuum forming is a relatively quick process, with the heating and vacuuming steps usually taking only a few minutes. However, depending on the size and complexity of the parts to be produced, cooling, finishing and mold creation can take considerably longer. Advantages and disadvantages of vacuum forming Many manufacturers, designers, and other professionals prefer vacuum forming because it offers flexibility in model shape at a relatively low cost compared to other manufacturing methods. The following is a non-exhaustive list of the advantages of vacuum forming: Low cost Vacuum forming is generally more affordable than other manufacturing methods such as plastic injection molding, especially for small production runs (250 to 300 units per year). The low cost of vacuum forming is due in large part to the lower tooling and prototyping costs it requires. Depending on the surface area of the part to be produced and the dimensions of the clamping frame, tooling for injection molding can cost two to three times more than for the same part made by thermoforming or vacuum forming of plastic. Production Time Vacuum forming allows for a shorter production cycle than other traditional manufacturing methods because the tooling it requires can be made more quickly. The tooling production cycle for vacuum forming is typically twice as short as for injection molding tooling. When 3D printers are used to create the molds, the production time can be even shorter. By improving the efficiency of the production process, vacuum forming allows companies to bring new designs to market faster. Flexibility Vacuum forming gives designers and manufacturers the flexibility to test new designs and make prototypes without incurring exorbitant costs or delays. Molds can be made of wood, aluminum, structural foam or 3D printed plastic so they can be replaced and/or modified more easily than with other manufacturing processes. Vacuum forming also allows designers to offer a wider range of colors and customizations to consumers. This gives many companies the freedom to offer their customers unique designs and make custom products such as dental appliances for an affordable price. Use of sterile and food-grade materials Manufacturers often use vacuum forming to produce food-grade containers and parts for the medical industry because the process is compatible with sterilizable or contaminant-resistant plastics. For example, high-density polyethylene (HDPE) is often used in vacuum forming of food containers. HDPE’s resistance to acidic compounds also makes it a suitable material for vacuum forming of cleaning product containers. Medical grade plastics are used in vacuum forming to create parts that can withstand sterilization processes and meet stringent medical and/or pharmaceutical standards. Limitations of Vacuum Forming While vacuum forming has a number of advantages, it also has its limitations. It is only suitable for parts with relatively thin walls and simple geometries. Finished parts may not have a consistent wall thickness, and concave parts with deep recesses are difficult to produce when vacuum forming. In addition, while vacuum forming is often the most cost-effective choice for small to medium production runs, other plastic manufacturing processes may be cheaper for very large production runs. The different applications of vacuum forming Nowadays, it would be hard to go a day without coming into contact with at least one part made by vacuum forming. This manufacturing process is used to produce a wide variety of parts in many different industries. Here are a few examples: Automotive and transportation Manufacturers use vacuum forming to create a wide range of parts
Types of Vacuum Thermoformers
Vacuum thermoformers vary widely in size, cost, complexity and functionality, which means that independent designers, DIYers and professional makers of all levels can find the right machine for them. The different sizes of vacuum thermoformers range from desktop models that cost a few hundred dollars to industrial machines that are worth thousands. Industrial vacuum thermoformers, such as those produced by Ridat or Belovac, are ideal for commercial applications and large-scale part manufacturing. Medium size vacuum thermoformers, such as the Formech line of floor machines, offer the most versatility. Mid-size vacuum formers are capable of manufacturing small to medium parts without requiring as much floor space as industrial machines. Desktop vacuum thermoformers, such as the Mayku FormBox that uses a standard household vacuum cleaner to create the air vacuum, are perfect for small businesses and professionals working from home. Do-it-yourself vacuum forming machines can also be effective, and the actual process of making the machine is a perfect educational project for children and teenagers. When using a vacuum forming machine, always remember to follow the manufacturer’s operating instructions, wear the proper safety equipment, and only use the machine in a well-ventilated environment. Materials suitable for vacuum forming A wide range of thermoplastics are compatible with vacuum forming. Some of the most widely used plastics include Acrylic (PMMA) Acrylonitrile butadiene styrene (ABS) Polycarbonate (PC) Polyethylene (PE) Polyethylene glycol terephthalate (PETG) Polypropylene (PP) Polystyrene (PS) Polyvinyl chloride (PVC) 3D printed molds Many companies use 3D printing to create vacuum forming molds because it allows for shorter production times and lower costs, especially for limited runs, custom parts and prototype models. printing also offers unparalleled design freedom to create complex and highly engineered molds.
Vacuum forming, pressing and rolling
Where is vacuum used in forming, pressing and rolling applications? Vacuum forming, pressing and rolling are widespread processes in many industries and manufacturing technology. These processes are used to combine a wide variety of materials or to give them a shape by means of a specific mold. For forming, it is important that a clearly defined vacuum is used to insert the material into the mold. Thermoforming, a classic process used for many products, is used to shape plastic films. In this process, the plastic films are heated to soften them. A vacuum is applied through the mold. This has the effect of pulling the film, which has been softened by the heating process, into the mold. Once the film cools, it retains the shape of the mold. This method can be used to create food packaging and other products, and even preformed plastic shapes to make garden ponds. Vacuum pressing is used in the wood industry, for example, when several layers of wood are glued together and mechanical pressing cannot be used due to the geometric shape of the product. Vacuum is also used to attach veneers or synthetic materials to wooden profiles, e.g. on the front of kitchen furniture. Vacuum lamination is a process used to bond different layers of materials together, and is typically used in the semiconductor and electronics industries. Solar modules, flat panel displays and smartphone screens are created in this way. Examples of vacuum use in forming applications: Mold evacuation – To produce wind turbine blades Thermoforming – for the production of various packaging materials Examples of the use of vacuum in pressing applications: Veneer presses – For attaching synthetic veneers to furniture surfaces Vacuum Resin Transfer Molding (VRTM) Examples of the use of vacuum in lamination applications: Laminating flat panel displays Solar panel lamination