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Hydraulic, Electric, and Hybrid Plastic Injection Molding: Which Process is Right for You?

Posted by Jill Worth

11/18/16 1:30 PM

Design engineers have various options when choosing a plastic injection molding process to best suit their specific application. Each of the three primary methods — hydraulic, electric, and hybrid — feature unique benefits and drawbacks. To make the right selection for your project, it’s important to have a full understanding of how these methods differ and what they can offer you.

Hydraulic Plastic Injection Molding

First coming into existence in the late 1930s, hydraulic plastic injection molding machines (IMMs) once dominated the market, but their dominance has been impacted since the introduction of all-electric machinery. Hydraulic machines may still be the best option depending on your specific needs, electricity costs, and personal preferences.

These machines employ hydraulic cylinders to clamp together two halves of a mold at high pressure. Plastic substrate pellets are then melted, and the liquid is injected into the mold cavity. Once the plastic has cooled and hardened, the mold halves are separated, the part is extracted, and the process is repeated. 

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To prevent the mold from being pushed open by injection pressure causing excessive material to “flash” around the parts, the clamping unit must be able to supply enough locking force to keep the mold shut during injection. Roughly 3-4 tons of clamp force per square inch of cavity is needed for parts with thin wall sections and deep draw depths. For thick wall sections and shallow draw depths, about 2 tons per square inch is needed.

Today’s hydraulic IMMs are able to control clamp forces up to and exceeding 8,000 tons and can create parts weighing in at more than 50 pounds. Hydraulic molding is a popular choice for the automotive industry, which requires the production of large, heavy parts such as bumpers.

Advantages

Hydraulic injection molding is the preferred option for actuating core pulls, ejectors, and valve gates, as well as thick-walled parts that require long hold times. Some of its benefits over all-electric machines include:

  • Greater clamp force for large parts
  • Better injection rates
  • High durability
  • Larger shot size
  • Better ejection capability
  • Available with gas accumulators to make up for slower clamp movements
  • Lower initial purchase price

Disadvantages

Because they’re so powerful, hydraulic machines consume large amounts of energy even when idle. While a typical electric machine may consume about 2.55 kWh during an injection molding process, hydraulic machines may consume 5.12 kWh. Hydraulic IMMs are also noisier and less precise than all-electric presses.

However, as clamp forces increase and control systems improve, hydraulic machines’ precision performance also improves.


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Electric Plastic Injection Molding

Introduced in 1984, all-electric injection molding machines are fairly new to the market but account for over half of all IMM machines sold in the United States.

These machines are powered by digitally controlled high-speed servo motors rather than hydraulics, allowing for a faster, repeatable, more precise, and energy-efficient operation.

Advantages

Since it poses no risk of oil contamination, electric injection molding is well-suited to cleanroom applications. Because of its high precision, this process is also ideal for small- to medium-sized parts and medical products such as Petri dishes and syringes. Other advantages include:

  • Precision and repeatability with reduced scrap rates
  • Energy savings from 30% to 70%
  • Quieter operation; reduced motor noise below 70 dB
  • Higher rapid injection speeds and faster clamp motion
  • Shorter startup time and up to 20% faster cycles

Disadvantages

Although electric machines are faster and more energy efficient, they are unable to achieve the clamp forces produced by hydraulic machines and also come with a higher initial cost. They are toggle-clamp machines that are driven by ball-screws, both of which are wear items, and can be expensive to replace.

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Hybrid Plastic Injection Molding

Combining the best of both worlds, hybrid injection molding machines combine the superior clamping force of hydraulic machines with the precision, repeatability, energy savings, and reduced noise of electric machines. This allows for better performance for both thin- and thick-walled parts. These machines have become increasingly popular over the last few years due to their efficiency and ease of use. Here at The Rodon Group, we recently added six hybrid presses to our lineup, and now have 22 total.

Nearly 66% of energy in a hydraulic press goes toward screw recovery. So while hybrid presses are more costly upfront, their electrified screw rotation can result in significant savings, which can then be passed on to customers. Our hybrid machines have all the force delivered by full-hydraulic machines, with virtually the same energy-efficiency of an all-electric.

How The Rodon Group Can Help

No matter what your specific application, an injection molding machine — whether hydraulic, electric, or hybrid — should provide you with reliable, high-quality parts while keeping costs down. To meet your unique needs, The Rodon Group has 111 Nissei presses at our facility, 75% of which are hydraulic, 20% hybrid, and 5% all-electric. We also plan on adding six more machines by the end of the year. To learn more about our capabilities or to discuss how we can help you with your high-volume production needs, reach out to us today.   

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Topics: Plastic Injection Molding, Plastic Manufacturing, Plastic Injection Molds and Presses

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