Plastic injection moulding

Manufacturing range: Thermoplastics injection moulding

At etm, manufacturing of thermoplastic injection moulding components is realised on state-of-the-art injection moulding machinery with fully automatic loading systems for insert moulding of inserts like standard threaded inserts and article-specific design components. Most of the injection moulding machinery is equipped with discharge systems for separation including measurement and assessment systems to ensure compliance with the highest quality requirements.

• 1K single-component injection moulding:
• Processing of technical plastics with the highest requirements for the automotive industry.
• Technology competences in injection moulding of article-specific, larger design components by assembly injection moulding.
• 2K multi-component injection moulding:
• Manufacturing of plastic components of two different materials with different application-specific properties and, if required, two colours by means of one injection moulding system with process-oriented dies in one manufacturing cycle.
• Insert moulding (detachment, acoustic / mechanic) or sealing by
• direct moulding of respective “sealing lips”

Injection moulding:

Process sequence for thermoplastics Plastication (melting on) and metering of the thermoplastics is realised in one processing step in a screw-type shear extruder that is also the material buffer to provide the defined gross injection volume (measuring the screw position = metering process).

1. Cycle start: Injection: During the injection phase, the injection unit is positioned at the nozzle side of the injection moulding die and applied with the nozzle to pressurise the screw from behind. In this process, the molten material is metered and injected under high pressure (mostly between 500 and 2000 bars) through the open runner and the sprue or the sprue system (hot and cold channel system) of the injection moulding die into the shaping cavity. A back flow valve in the extrusion unit prevents back flow of the molten material into the material feed / filling hopper.
2. After-pressure and cooling: As the die has a lower temperature (material-typically between 20 and 150 °C) than the plastic material (typically for material: between 200 and 360 °C), the molten material in the mould cools down and solidifies on reaching the solidification point. Cooling is accompanied by a volume contraction negatively affecting the dimensional accuracy and surface quality of the work piece. In order to partly compensate for this contraction, a reduced pressure is maintained after filling of the mould to enable a material flow to compensate for the contraction. This after-pressure can be maintained until the sealing point (solidification of the sprue) or the defined process parameters (times / volume etc.) are reached.
3. Following the after-pressure, the nozzle (the nozzles for multiple injection / multi-cavities with hot channel systems) are closed. In the injection unit, the plastication and metering process for the next moulded component is already being initiated. The material in the mould is cooled down further during the residual cooling time until the “soul”, the still liquid core of the work piece, is also solidified and the work piece is sufficiently solid for demoulding.
4. For demoulding, the die halves are opened on the ejector side of the closing unit and the articles are ejected by ejector pins entering the cavity. The work pieces either fall down (bulk goods = out-of-die articles) or are removed by means of corresponding handling equipment and stored in an orderly manner or directly supplied for further processing.
5. End of cycle (after demoulding, the die is closed and the cycle restarted).

To increase efficiency, the sprues are automatically removed and separately resupplied to the process online. If injection moulding without sprues is applied with hot channel systems with sprue systems permanently exceeding the solidification temperature, the material in the system can be used for the next “injection”.

Special injection moulding processes (FIT) GID + WIT:

etm uses internal pressure injection moulding, also referred to as fluid injection technology (FIT), as a special injection moulding process to manufacture hollow work pieces. After the first working step of conventional injection moulding or after defined partial filling of the injection mould, a temporary filling substance (water or inert gas, usually nitrogen) is injected into the partly filled mould in such a way that it acts as an internal moulding piece (die / core). By displacement of the melt in the centre, a cavity is formed inside the component and the melt is pressed against the outer mould. After solidification of the melt, the fluid is discharged through a defined (controlled) outlet.

Applications:

Removal of non-required material from the component core and the internal after-pressure applied by the fluid almost without any pressure loss enable new designs and otherwise unreachable component quality particularly in terms of the surface. Targeted forming of a cavity that already needs to be considered during design of the moulded component enables considerable savings in material at comparable durability and thus more economical and lighter design variations in contrast to conventional injection moulding. Additionally, the cycle times are reduced by quicker cooling thanks to the injection of water or gas.