What is the Extrusion Thermoforming Process?
The extrusion thermoforming process is a well established manufacturing process that is used to produce items with a predefined shape from a heated material. First the material is extruded to create a single sheet. Then it heats to a pliable temperature. After that it is formed to a specific shape in a mold. Finally the molded shape is trimmed to create the product. Extrusion thermoforming process is hardly understood if the words ‘extrusion’ and ‘thermoforming’ are Greek to you. Therefore the best way to understand the thermoforming process is to know the extrusion and thermoforming processes first.
Extrusion is well known manufacturing process that is used to create objects with a fixed cross-sectional profile such as tubes and pipes. This process involves drawing or pushing a material through a die with a desired cross section. Continuous or semi continuous products such as tubes, pipes, rods, rails, sheets, films, seals, bars, etc. can be produced using the extrusion process. Plastic extrusion and extruded metals are among the widely used applications of the extrusion process. The extrusion process may be warm extrusion or cold extrusion depending on the application. Cold extrusion is usually applied for metals like aluminum, copper, steel, etc. Cold extrusion process has the advantages like faster extrusion rates, higher strength, closer tolerances, and decreased oxidation.
What is the Thermoforming Process?
In the thermoforming process a plastic sheet is formed to a desired shape in a mold after heating to the forming temperature. In the industry, large production machines are used to form and heat the plastic sheet. Usually they are capable of producing very large volumes of finished products in a very short period of time. Once thermoformed, it is trimmed to get the finished shape.
Depending on the application, the thermoforming process uses thing or thick films. Thin films are used to manufacturing trays, containers, disposable cups, blisters, etc. They have wide applications in the food, fast moving consumer goods, and medical industries. Thermoforming industry is already a billion dollar industry in North America with annual sales in excess of USD 1, 000 million.
Understanding the Extrusion Thermoforming Process
There is no much difference between thermoforming and extrusion thermoforming processes. Since you have an idea about extrusion and thermoforming processes, it is easy to understand the extrusion thermoforming process. Usually this process is also called in line thermoforming. In this case an extrusion unit is attached to the thermoforming unit and the both processes are done in one step.
As in the case of thermoforming, the extrusion thermoforming process begins with forming a sheet of material that is formed by the extrusion process. If the material is thin (thickness is less than 1/16 inch), then it is fed in rolls in to the mold. If the material is thick (thickness is up to ½ inch), then it is fed in sheets.
Next step is to heat the sheet to a pliable temperature for ease of formation using electric heaters. Controlling this temperature is very important to get the desired results. Once heated, the sheet is flexible but not liquid or gooey. Without any winding, the thermoforming unit is fed by the sheets which are coming directly from the die. This is one of the main differences in thermoforming and extrusion thermoforming.
Now the soften sheet is placed on the mold and the desired shape is obtained by applying an external pressure.
Finally finishing processes such as trimming, drilling, etc. are carried out when the shape is cooled and hardened. Then the final product is obtained.
These are the main steps of the extrusion thermoforming process. The following illustration may give you a clear understanding about how the process is really going on. Here the sheet is fed in to the molding unit passing through the heating section that is displayed in yellow and red colors. Then the pressure is applied on the sheet to create the product. The extrusion unit hasn’t showed here.
Advantages and Disadvantages of the Extrusion Thermoforming Process
Energy and storage savings are among the main advantages of the process. But it is difficult to operate which is a huge disadvantage. Here are some of the main advantages and disadvantages of the process.
- Energy Savings – When the sheet comes from the extruder it possess a certain amount of heat that was provided for the extrusion. Therefore the heat needed for thermoforming is less or not required. So heating unit for thermoforming unit can be reduced or removed saving a lot of energy.
- Less storage requirements – Less storage is needed since extrusion and thermoforming units are combined.
- Utilization of the machines is optimized.
- Easy to control defects – It’s quick to detect quality issues and take necessary actions to solve them.
- The process is more difficult to operate.
- Due to involvement of heat and other factors, it takes long time to transfer from one production operation to another.
Applications of the Extrusion Thermoforming Process
Knowing the applications might be quite useful to understand the extrusion thermoforming process. Most thermoplastic materials can be used for producing various items utilizing this method. They include Acrylic (polymethylmethacrylate), PVC, ABS, Polystyrene, Polyethylene, etc. Many of the applications are can be seen in the packaging industry. Disposable cups, toys, containers, clamshells, trays, etc. are among the extrusion thermoformed products.
Thermoforming and extrusion are major industrial processes. The extrusion thermoforming process is just a simple sub category of it. But it is becoming an important industrial segment today. So understanding the extrusion thermoforming process would be beneficial for many technical people.