All posts by : Emanda Gibson

In the manufacturing process of plastic, two common techniques are often used to form the plastic into a desired shape: molding and forming, or thermoforming. Each process requires the manipulation of molten plastic, followed by a setting period. Each technique offers unique features and benefits, making them ideal for specific applications.

What’s the Difference?

Several key differences separate plastic molding and thermoforming. Each process can accommodate different production volumes. Plastic injection molding is generally used for large, high-volume production runs, while thermoforming is used for smaller quantities. Another variable is the molding process produces finished pieces, while thermoforming often requires secondary finishing processes.

Injection molding can accommodate difficult geometries and tight tolerances, making it great for creating smaller, intricate, and complex parts. Conversely, thermoforming accommodates simpler geometries and larger tolerances, which works well for larger parts with more basic designs.

Molding can be used for a wide variety of plastics, whereas thermoforming is more limited in terms of what types of materials can be worked.

Thermoforming

Simply defined, thermoforming is the process of applying a heated plastic sheet to the surface of a mold. Common types of thermoforming are vacuum forming and pressure forming. Depending on the scope of a project, thermoforming offers several distinct advantages:

• Lower tooling costs
• Speedy product development
• Ample color and texture options
• Adaptable and easy to adjust
• Good choice for small production quantities

Molding

Injection molding and related processes require significant upfront engineering to create detailed molds. Molds made from stainless steel or aluminum are injected with molten liquid polymers at very high pressure, and later cooled to create a final plastic product. Advantages of molding include detailed tooling and mold options, precise processing for large product volumes, and efficient material use.

Types of Molding

Casting: A basic molding process. Plastic is heated to a fluid state and then transferred into a mold to cool.

Injection Molding: Used to create three-dimensional products. Plastic is melted in a hopper and the injected into a chilled mold.

Blow Molding: Plastic is heated until molten and then injected into a cold mold. Air is blown into the plastic to form it around the mold.

Compression Molding: Molten plastic is poured into a mold and a second mold squeezes the plastic into the desired shape.

Which Process is Best?

For some industries and applications, both processes may be used to manufacture plastic parts. Many industries select a specific method based on project need. To determine which process is best for you, carefully assess your project’s characteristics and requirements.

While most of us are unfamiliar with vacuum forming, the process is responsible for the packaging surrounding millions of everyday products. Vacuum forming is actually a simplified version of thermoforming, in which a thin sheet of plastic is heated to a high temperature so the plastic can be stretched onto a mold by use of a vacuum.

The process offers a wide range of benefits to manufacturers with its high-volume capability and simplicity of storing large quantities of plastic sheets. High quality, high volume, and low cost are all attractive to customers as well.

Vacuum Forming At Work

Left to its own devices, vacuum forming is only capable of producing shallow products such as plastic signs, covers, and product packaging for small items. Ubiquitous blister packs and clamshell packaging use this process.

To obtain three dimensions, manufacturers combine vacuum forming with line bending equipment, making it possible to create everyday products like TVs, speakers, point of sale displays and plastic containers. In fact, vacuum forming has proven to be highly adaptable and is used today for a variety of display marketing and promotional items. It’s fast, low cost and easy, making for reliable turnaround.

Vacuum Forming Mold Material

The first step of the vacuum-forming process is to create your mold, also known as “tooling.” This is usually the most in-depth step of the process. The most commonly used plastic in vacuum forming is acrylonitrile butadiene styrene (ABS). Other plastic will work, but keep in mind that the thicker the plastic is, the more heat and vacuum pull you need.

There are several ways to create vacuum forming mold; the one you use ultimately depends on your end goal, available resources, and how long you need the tool to last. Molds used in vacuum forming are made of an array of materials including: cast, plaster, clay, resin, wood, aluminum, and polyurethane.

Here is a look at the most common mold material options:

• Wood or MDF. Best for smaller production runs or teaching the basics of the technology as opposed to producing usable parts.
• Cast Resins. Ideal for larger production runs because resin tools can be sanded to a very smooth finish.
• Cast Aluminum. Cast aluminum tools may require extra finishing but the end product is very strong and this option is ideal for large production runs.

Other mold materials can also work well, depending on your project needs. To determine which mold is best suited to an application, you’ll want to analyze the inherent details and select a mold material that results in the highest quality with most efficient resource use.

Odds are good that you will purchase some kind of consumer product today. It might be anything from a package of new AA batteries to a toy for your child. Whatever the item is, it will likely be ensconced in vacuum sealed plastic. Indeed, a large majority of today’s products all over the world are sealed and made sale-ready in some form of plastic packaging.

Have you ever wondered how companies wrap products in such form-fitting dress? The process is called thermoforming, which is a plastic molding manufacturing technique that heats thin plastic sheets to a pliable temperature, at which the plastic is easy to manipulate and form over a mold. Vacuum forming is a simplified sub-process of thermoforming, where heated plastic is stretched onto a mold and forced against the mold via a vacuum force.

Vacuum Forming’s Inspiration

Innovative people have used natural rubbers and cellulose to accommodate many different life needs for thousands of years. The development of synthetic plastics, however, didn’t really get its start until the 19th century. Celluloid was the world’s first highly-usable plastic, developed by inventor John Wesley Hyatt. His cellulose creation was an improved version of parkesine, a plastic created by Alexander Parkes, one of Hyatt’s English inventor colleagues. In addition to improving celluloid, Hyatt also patented the first injection molding machine.

When it comes to vacuum forming, we salute a trio of innovative minds. The first thermoforming machine patents were filed by H.L. Helwig of the Rohm & Hass Company, and R.E. Leary, an engineer at DuPont. These crafty inventors employed a variety of methods to heat plastic, such as convection and radiant heat, or using hot oil or steam. In 1947, along came G.W. Borkland from Indiana, who filed a patent for a “vacuum forming” machine. Borkland would go on to make many other improvements in the world of vacuum thermoforming, and his influence introduced the world to a new form of product sealing.

Vacuum Forming In Action

The vacuum forming concept is relatively simple: A vacuum is used to produce an even distribution of pressure on a material’s surface to allow the material to conform to the shape of a mold. Thin sheets of plastic are fed into a vacuum thermoforming machine and heated until they are malleable, and then forced onto the mold in a very precise process.

In addition to sealing everyday items, vacuum sealing is also used to create intricate and incredibly strong products such as road signs, boat hulls, and an array of protective covers.