Injection molding machines (also known as injection presses) are generally categorized based on their drive system, or based on what powers their major components. The three basic types of drive systems are electrical, hydraulic, and hybrid drives, each of which is suited to unique injection molding applications. Below is a brief explanation of each of these drive types, their main advantages/disadvantages, cost, and general applications.
Hydraulic injection molding machines are considered the first "modern" injection molding machine and were developed in the early 1900s. They utilize hydraulic drives to clamp the injection mold halves together and push molten plastic into the mold cavity. They consume hydraulic fluid and need constant energy input to both pump and cool their hydraulic systems.
Because hydraulic injection molding machines are an established technology stretching back decades, they are the least expensive, and most rugged, and easiest to source and repair. Hydraulics also offer unparalleled clamping forces in their clamping unit (3-4 tons per square inch!), making them ideal for larger molds.
However, hydraulic injection molding machines are energy inefficient and require higher temperatures for molding which can ruin some heat-sensitive plastics. Both hydraulic pumps and coolant need continuous power input and require additional infrastructure to support them. Also, these types of machines can be problematic as they carry the risk of hydraulic fluid leaks, and they produce more noise than other injection molding machines.
Hydraulic injection molding machines tend to be cheaper than all-electric machines, costing anywhere from $3,000-$100,000+ depending on size. They will also require additional maintenance and infrastructure costs, estimated roughly to be around $17,000/year, plus the cost of worker wages for upkeep and operation. They can last up to 7-10 years with proper maintenance, but their hydraulic systems make them prone to frequent issues that can shorten their lifespan with improper care. These types of drive systems are mainly for larger, thick-walled applications such as those found in the automotive industry.
Electric injection molding machines (also known as all-electric machines) are an update to the traditional hydraulic machines, having been first developed in the 1980s in Japan. They implement several digitally controlled servo motors that allow for precise independent control of the four axes of injection molding: injection, extruding, clamping, and ejecting.
Servo motors used can idle when not in use, saving users up to 75% on power demands when compared to hydraulic models that need continuous pumping power. Electric injection molding machines also highly simplify the injection molding process with no necessary consumables, making them easier to run, repair, and scale down for small-to-medium-sized applications. All-electric machines are ideal for cleanroom applications needing high accuracy and a clean, quiet, and energy-efficient machine.
Electric injection molding machines do have some disadvantages. The first disadvantage is lower clamping power compared to hydraulic injection molding machines. The second disadvantage is that electric injection molding machines tend to be more expensive and difficult to repair compared with hydraulic versions.
Electric injection molding machines' prices depend on size and features but generally hover around $5000 to $200,000+ depending on the needed size. All-electric machines will last on average 20+ years with proper maintenance and are mainly specified in cleanroom applications for the production of small to medium-sized parts for medical, biochemical, and pharmaceutical products.
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