All-electric injection molding: Cleanroom compatible but lacking in power

What?

All-electric injection molding machines are increasingly replacing hydraulic machines, particularly in cleanroom environments. They are driven by digitally controlled servo motors that operate efficiently and at high speeds.[1] Each axis is controlled by an independent motor for injection, extruder, clamping and ejection.[2] Unlike hydraulics, all-electrics do not rely on multiple parts driven by pumps that require hydraulic fluid (i.e., oil), the need for which is a major source of variability in operation. Furthermore, all-electrics do not require an intricate filtering system to keep [oil] clean and ensure proper valve operation,[1] like hydraulic machines. All-electric processes do not vary over time since they have no hoses to expand, no valves to potentially stick and no hydraulic fluid to heat up or compress.[3]

Why?

Use of all-electric molders not only improves reliability, but can dramatically decrease operation costs. They typically use less power since they consume no energy when idle, generate less waste materials, are easier to cool, can carry out multiple tasks simultaneously, and produce plastics more consistently. Their standardization is easier to perform, as is validation, diagnostics, and trouble-shooting. The machines themselves are quieter, which improves the workroom environment.

Importantly, all-electric molders are cleanroom compatible because they do not use oil. Oil moving in and out of the reservoir in hydraulic machines can be released into the air as a mist, often contaminating the output product. This is particularly relevant in the field of medical device—such as syringes, bandages, and surgical implants—manufacture, which must meet sanitation standards (see: FDA,[4] WHO,[5] and the European Commission[6]).

Other high-volume/mass-produced plastics such as automotive parts and containers can also benefit from all-electric injection molding.[2]

Who Where When?

All-electric injection molder manufacturers are continually improving their machines, for increasingly specialized (or increasingly general) use.[7] Major manufacturers include: Nissei, Milacron, Niigata, Sumitomo, and Toshiba.

How?

Run by computers, all-electrics have precision control over their moving parts. This is essential for operation free from error, and for operation by less-experienced workers.

Recent developments in valve gates have improved hot runner systems. Hot runners have long made processing more efficient and cost effective while improving part quality. However, in cleanroom applications, those benefits have been offset by the need to use pneumatic hot runners with slower response times and weaker closing forces. Enter a new solution in hot runner technology: the electric valve gate (EVG) hot runner system…The EVG delivers the powerful, fast, positive shut-off needed for faster cycle times, reduced material waste, and better part quality. It integrates well with the all-electric injection molding machines commonly used in medical environments.[3]

These gates operate with controllable speeds and can improve the co-injection process needed for the fabrication of larger plastics, which require sequencing.

But?

All-electrics tend to have less power than hydraulic machines and may not provide enough force to fill a mold.  To remedy this, molders are increasingly using hybrid machines. However, while a typical hybrid machine has an electric screw drive, three of the four axes are hydraulic—the hoses, valves and pumps associated with a hydraulic system are still part of the machine. So, much of the unreliability of hydraulic machine is incorporated into the hybrid.

New-generation hybrid molders can get  “…all the benefits of an electric machine, but with injection rates up to 300+ cubic inches per second (compared to all-electric machines, which top out around 100). These rates are necessary especially for applications with thin-walled parts with high length over thickness (L/T) ratios, in which the material must fill the entire part before setting in the thinnest areas”.[2]

Literature

All recent work on medical device design and manufacture are reported as patents. For example:

J. L. Parker, Methods of forming feedthroughs for hermetically sealed housings for active implantable medical devices using two-material powder injection molding, WO2011066478 A1.

M. Reiterer, Method of manufacturing a cofired feedthrough including injection molding a ferrule for a medical device, WO2011025667 A1.

K. Hayakawa, Method of producing medical device and medical device assembly, WO2009119670 A1.

Background

Injection Molding Machines, F. Johannaber, Hanser Gardner Publications, 2007.

Injection Molding Handbook, Dominick.V. Rosato, Donald V. Rosato, M.G. Rosato, Springer, 2000.

References

  1. It's electric: Injection molding machines get a jolt, 23 June 2011.
  2. Electric injection molding basics, Accessed 1 September 2011.
  3. Advantages of all-electric technology for molding, Accessed 1 December 2010.
  4. Overview of device regulation, Accessed 1 September 2011.
  5. Medical devices, Accessed 1 September 2011.
  6. Medical devices, Accessed 1 September 2011.
  7. Injection molding machinery product watch, Accessed 1 September 2011.

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