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Micromolding of medical products  #7 (89), 2010

Recent progress in medicine and biotechnology requires wide application of miniature plastic products for medical use. Thereby Sumitomo (SHI) Demag Plastics Machinery GmbH offers to its medical customers complex micromolding solutions

To produce very small components in the injection moulding process requires maximum possible accuracy and repeatability. From the material and machine to the mould, everything must be streamlined to this objective. To produce such minimal items, Sumitomo (SHI) Demag Plastics Machinery  offers optimized systems allowing to purposefully handle shot weights of merely a few grams and component weights of as little as a few tenths or even a few centigrams.
In order to process plastics of minimal size Sumitomo (SHI) Demag Plastics Machinery engineers developed the micro injection unit for shot weights of 5 to 0.1  g.
The special worm with a special geometry and integral back-flow lock can be used for injection pressures of up to 2,700 bar. Thus, the most delicate injection or dosing profiles can be easily produced while maintaining the required residence time. Naturally, this whole system can be integrated in the lower machine series for clamping forces up to 500 tons resulting in utmost precision and cost-efficient production.
Benefits of the Sumitomo (SHI) Demag microinjection unit include
cost-efficient production of components through the use of standard granulates,
highest precision through ultrasonic displacement measuring systems and active tool protection, and
special programmes for micro injection moulding applications.
Optic products such as lenses and magnifying glasses are widely used in medicine and other industries. Their production requires a high degree of precision in combination with a high degree of reproducibility and cleanliness of the production environment.
Determining process-relevant parameters or their tolerance limits and to establish permanent quality control for the products to be produced require complex and expensive measuring equipment.
Even smallest component defects or deficiencies such as fisheyes, silver streaks or flow marks will mean outright reject.
In addition to the capacity of massively influencing the filling and holding pressure cycles, injection molding offers the benefit of influencing a whole range of qualitative benefits for optical injection molded parts. Which benefits this process offers in terms of quality and reproducibility, has been explored by Sumitomo (SHI) Demag Plastics Machinery experts in comparative studies for various optical materials performed on the IntElect model all-electric injection moulding machine.
The adequate selection of the plasticizing cylinder is a matter of particular importance in order to achieve optimal product quality. Here, specifically parameters such as the shot weight, stroke utilization, residence time or the required injection moulding pressure are of special importance. The shot weight is determined by the design or material specifications. These should be used to select the right screw size such that the stroke utilization will ideally be between twenty percent and sixty percent, or, in an extreme case, no more than seventy-five percent (75%). The required injection moulding pressure must be absolutely considered very closely in the design and configuration of the system as transparent materials are mostly strongly viscous. In this context, also the holding pressure should be assessed accordingly.
The decision in favor of an all-hydraulic, an all-electric or rather a hybrid drive concept for molding of miniature articles will depend on several factors:
shot weight
component geometry
holding pressure times
precision
cleanliness
Owing to the mostly mechanical power transmission, the approached positions are maintained in a very precise and stable manner. Also, there will be more energy saving in the passive stages of the process such as residual cooling time. The major benefit of oil-driven injection moulding machines undoubtedly is their long holding pressure capacity at a high level. This is supplemented by a higher injection capacity such as it can only be provided by hydraulic accumulators.
Thanks to their special properties including no danger to health, no taste or flavor and thermal stability, liquid silicone rubbers find wide application in molding of medical articles, such as mouthpieces, aspirators, respiratory masks. Basically, all Sumitomo (SHI) Demag injection moulding machines with corresponding ancillary equipment are suitable for processing LSR. The deciding factor for achieving the required quality is the stability of the process parameters. Therefore, Sumitomo (SHI) Demag Plastics Machinery recommend machines with precise stroke measuring systems and absolutely precise control of pressures and speeds.
It is well-known that the most of medical products such as single-use syringes, catheters and inhalers should be produced under ideally clean conditions with injection molding machines equipped with dust protection system. However, for a long time, clean-room technology has no longer been a synonym exclusively for the production of medical products, semiconductors or microchips. Increasingly, other technical applications pose increased cleaning requirements on the production environment – be they molded parts with particularly demanding surfaces or parts with sensitive microstructures. Regardless of that, many molders have now realized that particularly “clean”, i.e. largely dust-free, ambient conditions have a positive influence on the quality of the formed parts produced and, thus, on the cost-effectiveness of the production. That is why solutions from Sumitomo (SHI) Demag for this field find extensive application.

Micromolding at first hand
With their Application and Process Engineering Departments, Sumitomo (SHI) Demag provides expert consultations, machine acceptance and performance tests and also capacity for technology elaboration for customers at its factories in Schwaig and Wiehe. The machine shops are constantly equipped with the latest range of injection moulding machines. The selected range vary from standard injection moulding machines and all-electric machines of the IntElect type to fast-cycling injection moulding machines of the El-Exis type.
Recently, Sumitomo (SHI) Demag Plastics Machinery headquarters housed a seminar devoted to micromolding technologies. The event was visited by more than 140 company's customers. All the visitors utilized an opportunity to extensively review micromolding technologies thanks to well-known experts who took part in the seminar as well as special print materials provided by organizers.
The speakers from Kunststoff-Zentrum in Leipzig gGmbH, Jenoptik Polymer Systems GmbH, Stamm AG, M.A.I. GmbH, Sumitomo (SHI) Demag Plastics Machinery GmbH highlighted the questions of production process flexibility for micromolding and unmolding which is very important both for production as a whole and end user.
Furthermore the visitors were provided with information about specific micromolding features for example in optic products manufacturing.


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