Why is injection blow molding machine Better?
Blow Molding vs Injection Molding - RCO Engineering
Blow Molding vs. Injection Molding: Differences and Comparison
Blow molding is a process used to create hollow plastic products such as bottles or containers. The most commonly used plastic for blow molding is HDPE (High-Density Polyethylene), although most thermoplastics can be blow molded. Inspired by the techniques used in the ancient art of glass blowing, Enoch Ferngren and William Kopitke invented plastic blow molding in . The next big step in the development of blow molding was the introduction of HDPE in the s. In the s, PET was added to the list of materials that could successfully be blow molded. Both of these materials were significantly easier to process than the earliest materials tried, and the performance characteristics of the end products were also improved.
Blow molding machines work by extruding a tube of softened plastic called a parison. The parison is enclosed and sealed inside by the two halves of the mold. Pressurized air is pumped into the parison, and the softened plastic expands to match the shape of the mold. The flash at the split line of the mold is trimmed after the formed part is released. This excess material is then recycled back into the process.
Blow molding is preferred to injection molding for parts with thin walls, such as bottles, fuel tanks, and consumer product casings. Thin-walled parts are not easily injection molded. The blow molding process can be seen below:
Injection molding machines work by injecting molten thermoplastic into a two-part mold. The first injection molding machine was developed in by John Wesley Hyatt. This machine was used to mass produce items like buttons. The first screw injection molding machine, which is what modern machines are based on, was built in by James Watson Hendry.
The process works by melting plastic resin pellets inside a barrel. The barrel contains a screw with a shaft whose diameter increases along its length. As the screw rotates, the plastic is forced into an incrementally smaller area. This compression is the primary mechanism responsible for melting the plastic. The barrel is also heated to further aid the melting process. Once enough plastic to fill the mold has melted, the screw retracts. The screw is then pushed forward to force the plastic into the mold at very high pressures.
Injection molds are made from at least two parts. They are held together with hydraulic rams so that the high-pressure plastic injected into the mold cannot escape from the parting line. The mold has cooling channels that cool the part enough so that it can be ejected from the mold without damaging it.
Injection molding can achieve high production volumes unmatched by any other plastic processing technique. It can easily produce millions of parts per machine annually. Injection molding can create complex parts. It is used for everything from gears to garden chairs. Injection molding is better than blow molding for the high-volume production of complex plastic parts. To learn more, see our guide on the Molding Manufacturing Process.
Cost comparison: Injection molding and blow molding are used for different types of applications. However, blow molding tends to be cheaper than injection molding due to the cheaper tooling, equipment costs, and lower energy requirements, i.e. injection molding operates at high injection pressures.
Speed comparison: Blow molding and injection molding can both produce high volumes of parts, especially in parts that are made in parallel. Both technologies are limited, however, by how quickly the plastic can be cooled to the temperature required to be able to eject parts from the mold without damaging them. Depending on the material, the size of the part, and the effectiveness of the cooling system, parts can be produced in seconds or minutes.
Volume comparison: Blow molding and injection molding are both high production-volume manufacturing technologies. Blow molds are inexpensive. Because of that, many molds can be built and used to carry out "parallel production," compensating for slow cycle times and allowing large-volume production. Injection molds are significantly more expensive. Producing multiple molds for parallel production is cost prohibitive. However, multi-cavity molds are possible and can reduce costs while increasing production capacity. Both technologies are capable of producing millions of parts per machine annually.
Materials comparison: Both blow molding and injection molding can make use of most thermoplastics. Polyethylene is widely used for blow molding applications due to its useful mechanical and chemical properties as well as its ease of manufacture. Injection molding can make use of a wide range of polymers, including thermoplastics, thermoplastic elastomers, and thermoplastic polyurethane. Even metal powder bound in a polymer matrix can be injection molded.
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