Types of Plastic Blow and Injection Moulding
Every plastic part requires a different manufacturing process and it is different from every product. The injection molding is used to manufacture solid components and on the other side, the blow molding is used to make plastic products with hollow areas like bottles and containers.
The injection stretch blow moulding has the process of injection moulding and blow moulding processes. First, the plastic is moulded into a solid preform to create a threaded bottleneck. After the preform is cooled down it fed into a stretch blow mould machine. After that, the preform is reheated with an infrared heater and blown into a plastic bottle with compressed air.
The Injection and Blow moulding are two core processes for plastic manufacturing. The products made with these processes are widely used in industries like automotive, foodservice packaging, electronics, medical devices, irrigation, dental, firearms, energy, and environmental industries.
For a better understanding of different manufacturing methods, we have provided information about the main types of injection and blow moulding methods used by plastics manufacturers.
Injection Moulding Process
The injection moulding is used for the manufacturing of higher volume quantities of plastic products ranging in size from large components to small components where micro-precision is required.
There are many other types of manufacturing methods like thermoplastic injection molding, over-molding, insert molding, cold runner molding, and hot runner molding.
Thermoplastic Injection Moulding
For the thermoplastic injection molding, the thermoplastic polymer is used and it changes to a liquid state when it is heated. The thermoset plastics are cool down into permanent solid. The thermoplastics can be remitted to the liquid after cooling into a solid.
Over molding
Overmolding or two-shot molding is a process that covers an injection mould over another substance like metal to improve the performance or durability of the product. The rubber-like compound name thermoplastic elastomer (TPE) is widely used for over mould material. The example f TPE in overmold application is the handle grips on a toothbrush. Overmolds can also be used to seal the products with parts made from several injection molds.
Insert Molding
Like overmolding the insert molding is an injection moulding process that has two or more components into a single finished product. In the insert injection, a component is inserting into the injection mold cavity and plastic material is filled around the insert. The inserts can add strength to the product and eliminate the need for additional parts to reduce the product weight.
Cold Runner Injection Molding
The cold runner molds use a sprue o fill the runners that inject plastic resin into the mould cavity. In the two plate molds, the runner system and parts are attached, and the ejection system may be used to separate the pair from the mould. This cold runner can reduce the waste by recycling and regrinding the material but it is also increasing the total cycle time. The cold runner systems can be used for a wide variety of polymers and also allow for easy color changes.
Hot Runner Molds
In the hot runner mould the material is heated and the plastic resin is sent to the material through a gate to fill the mold cavity. The hot runner molds are heated externally and internally. The externally heated molds can be used with a polymer that is less sensitive to thermal variations and internally heated hot runner molds are for better control of material flow.
The hot runner moulding does not require the runners the potential waste materials are reduced and the recycling and regrind the process of virgin plastic does not impact the total run cycle time.
Blow Molding Process
In the blow moulding process, the raw plastic material is shaped into a hollow tube with one open end called a parison. The parison is pressed into a cooled metal mold and compressed air is forced into the parison. When the formed plastic cools down and hardens the metal mold opens and expels the product.
There are mainly three types of blow molding processes.
1. Injection Blow Molding
In the injection blow molding, a blow or core rod is used in the process. First the parison is injected into a split mold cavity around the rod. The parison is formed looks similar to a test tube. The core rod transfers the parison to the blow mold machine where the forced air creates the final shape. After that, the rod then transfers and extrudes the finished product from the machine.
2. Extrusion Blow Molding
The extrusion blow molding can be continuous or intermittent. In the continuous extrusion blow molding, a parison will constantly be fed into the mold and each form will be cut off with a blade as it forms. In this intermittent extrusion blow molding expels each new plastic from the metal mold when it is cooled and the parison is fed into the mold only after the preceding parison is expelled.
The extrusion blow molds are less expensive than injection blow molds and also manufacture in a shorter time. It is suitable for smaller manufacturing. The advantage of this machine is it is cost saving on tools and shorter production. The disadvantages of this process have lesser control of wall thickness and have a greater amount of scrap material.
3. Injection Stretch Blow Moulding
The Injection stretch blow molding process is a combination of injection molding and blow molding. First, the plastic is molded into a solid perform to create a threaded bottleneck.
After the preform is cool down it is fed into a stretch blow mold machine. After that, the preform is reheated using an infrared heater and blown into a plastic bottle with forced compressed air.