Thermoforming is a major manufacturing process in today’s world, especially when it comes to shaping plastic to desired shapes and products. So, how does a thermoforming machine work? In order to help you grasp the thermoforming machine process, this section will detail what happens in each part of a typical thermoformer. These sections include loading, heating and cooling, forming, trimming, and stacking stations.
How a Thermoforming Machine Works
The thermoforming machine process involves several stages: First, plastic sheets or film are fed through a heating unit which dries them out and makes them more pliable. Then, the sheets go through a shaping and cooling mechanism – this can be anything from a simple vacuum, positive pressure, or mechanical system to a complex mechanism that uses a combination of these three.
After forming, the products are trimmed to remove waste material, either separately by hand or automatically in a trimming station within the machine. Below is how a thermoforming machine works in more detail.
Loading the Thermoforming Machine
Before a thermoformer can begin to create products, it must be loaded with the necessary raw material which, in this case, is the thermoplastic. The plastic can be rigid or highly flexible and translucent or opaque, depending on the required end product.
Some of the types of thermoforming materials that can be used include ABS, acrylic, polypropylene, polystyrene, and polyesters. Some of these thermoplastics, such as polypropylene, suit food applications more than others while others like polyesters fit permanent application items.
The thermoforming process begins by indexing a continuous sheet of thermoplastic from a stock roll (or extruder) or by shuttling single thermoplastic sheets into the heating station. In a small, manual thermoformer, this is done manually. Large industrial thermoformers often use automatic or semi-automatic system.
One the machine has been loaded with the raw material, the thermoforming process will begin. The thermoform sheet advances into the heating station (or is manually placed). Here, it meets a bank of heaters which heat it to the optimal level for the thermoforming process.
Thick gauge thermoforming plastic is heated on both sides (top and bottom). This helps to ensure uniform heating. It also speeds up the process for shorter cycle times. The heating in a thermoformer can happen in one of these ways depending on the type of machine:
- Conduction– heating panel and rods coming into contact with the thermoplastic
- Convection– using hot air circulating the forming area
- Radiation– Using infrared heating to bring the plastic to a soft or pliable state
The heating process must be accurately monitored and controlled. Most plastic thermoforming machines use thermocouple or thermistor operated systems for this purpose and evenly spaced heaters in the heating station. Once the sheet is heated, it goes into the forming station where one or more molds are in place.
Shaping the Thermoplastic
The forming station contains parts and mechanisms to shape and cool the heated plastic. Depending on the type of machine, plastic thermoforming will take place with the help of negative pressure (vacuum), positive pressure (air pressure), mechanically, or through a combination of two or more methods.
In a thermoforming vacuum machine, a pump system draws the air (around 14 Psi) from the area between plastic sheet and mold. The air evacuates air through openings that have been drilled in the mold itself. A pressure forming machine uses positive air pressure (50-100 Psi) to push the plastic toward the mold. Mechanical forming, on the other hand, relies on two molds to shape the plastic.
During the forming steps, clamp frames hold the plastic against the mold as it cool offs, usually via water circulating the mold. This ensures the formed product will maintain its shape and reproduce the mold’s detail. Once the plastic has cooled off, its removed from the mold.
Trimming the Thermoformed Product
In a majority of processes, the thermoformed products must be trimmed. Trimming removes unwanted material and helps shape items to the required dimensions. Several different methods are used: manually using hand saws, or by an automated mechanism involving CNC routers.
Hand sawing is most suited for processes that only create a few items and that do not require critical tolerances. The method is simple but laborious to the thermoformer operator and other workers. There’s also the problem unavoidable inconsistency. Machine sawing is faster but only suitable for rough trims. Just like hand trimming, its main disadvantage is lack of consistency.
Steel rule cutting is a more sophisticated trimming method and suited to thin products (0.30-0.100 inches). For higher production thermoforming processes, match shearing is one of the most used techniques. However, it requires a more costly and high-maintenance setup.
CNC routers provide state-of-the-art trimming mechanisms and are regarded as the most efficient trimming equipment of a thermoformer. . These consist of computer guided trimming bits and blades and are necessary for high-quality product trimming and automation purposes. The most common routers for thermoforming machines are the 3-axis and 5-axis routers.
Stacking thermoformed Products
Today’s thermoforming technology involves many automated process. After the parts have been formed and the excess material removed, some thermoforming machines include a stacking station. The machine may also count the formed products in addition to stacking them.
Further processing of thermoforming products may also be performed. These include coating (UV resistant and ESD coats), painting, and labeling. It can also be customized requirements such as punching vents or drilling mounting holes.
These secondary thermoformed product processes are either performed manually or automatically and largely determine the product quality and application. Industrial production lines will usually have most operations automated.
The thermoforming machine process is a straightforward yet important manufacturing technique. You can use it to create varied products and for a broad range of industries including automotive, food and drink, advertising, and so on. The state of finished product or even its manufacturing possibility depends on the type of machine used, though. In the coming part, we take a look at these types of thermoformers and their most suitable applications. .