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New Process and Machinery for Microparts Moulding based on Ultrasound excitation

Final Report Summary - SONOPLAST (New Process and Machinery for Microparts Moulding based on Ultrasound excitation)

Introduction

Optics, biotechnology and microelectronic are currently critical fields in which technologies for large scale microfabrication present a strategic interest to gain technology and economic benefits for Europe. In this context, injection moulding processes have been shown as one of the most precise, flexible and cost efficient technologies for part replication at large scale. However, the current technologies applied to the microscale by most of manufacturers of injection machines are mainly based on the same concepts (process and tooling) used for the injection of bigger parts. By one side, this explains the limitations of the current approach in terms of dosage precision, process accuracy and repetitiveness. But now, a completely revolutionary concept of plastification and moulding process has been developed. The project SONOPLAST introduces the first ultrasound injection moulding machine exclusively designed for the replication of microparts.

The state-of-the-art shows the use of ultrasounds in the field of plastics is not new. Examples of applications include welding of plastic components (installed on the machine nozzle to enhance melting flow), ultrasounds based ejection systems implemented in the mould, and others. Likewise, ultrasounds can also be used for melting reduced volumes of thermoplastics. In spite of this, no commercial applications have been brought to market so far, what confirms the innovation of SONOPLAST project's initiative.

Background

Ascamm's previous trials confirmed that it was possible to fill tiny cavities of a mould with plastic melted through an ultrasound piezoelectric transducer. This equipment acts providing heat for melting the polymer while producing the required filling pressure. Taking only few tenths of a second, the energy provided by the ultrasounds also allows filling the mould applying significantly less pressure compared to solutions currently in use.

Mentioned advantages were critical when deciding to set up SONOPLAST consortium aiming at developing the first ultrasound microinjection machine. Based on such results, it was feasible to think of a compact moulding machine, as the clamping force can be provided by small electric motors.

Another important advantage to consider involves eliminating the plastification unit. Along with the reduction of the sprue volume, those characteristics represent an important cost advantage in terms of raw material and power consumption. The ultrasound transducer gives more energetic efficiency to the process than the electrical heater bands used in conventional injection moulding. Finally, the shorter cycle time exposures the raw material to a significant less risk of plastic degradation, reducing the waste.

Goals

The original objective of SONOPLAST, now successfully achieved, was the development of the first ultrasounds moulding machine for the production of micro and mini plastic parts. Such development followed a new concept of mould and plastic feeding system adapted to the physical principles of ultrasounds and mechanical features (kinematics) of the new moulding machine.

The steps initially proposed for overcoming those challenges were established as follows:
1. Study of the influence on the plastic melt rheology of the ultrasounds parameters. Determination of the most important process variables and their impact on the plastic melt behaviour.
2. Development of the ultrasound moulding machine mechanical concept.
3. Development of the new mould concept.
4. Development of the feeding system.
5. Development of the process control strategies and systems adapted to ultrasound moulding machine and implementation of the sensor system needed.

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