Product Details Supplier Info More products

Arburg’s new micro-injection moulding module, which combines an 8mm injection screw with a second screw for melting the material, is suitable for the manufacture of miniature and micro parts.

Manufacturing products exactly in series with shot weights that are often just a few milligrams, corresponding to the weight of a single grain of granulate, is only possible if the dwell time of the melts in the injection unit and the level of material shearing can be kept correspondingly low.

According to the company, the prepared melts must be perfectly homogeneous, both thermally and mechanically.

In addition, it must be possible to regulate the cylinder temperature precisely and the plasticising process must be reproducible.

It is also important that the entire range of ‘normal’ plastics can be used and not just the specially prepared materials such as micro-granulates.

The new micro-injection module from Arburg operates using two screws, which ‘share’ the preparation, dosing and injection of the material.

First, a servo-electrically driven screw pre-plasticising section, which is installed at 45deg to the horizontal injection unit, ensures that standard granulates are prepared under suitable conditions.

In terms of screw channel depths, the plasticising screw used is similar in design to a conventional three-zone screw.

The molten material is then transported from the pre-plasticising stage to the injection unit.

The injection screw is used purely for transport purposes.

It has a diameter of 8mm, is fitted with a non-return valve and operates according to the screw/piston principle.

This permits small shot weights to be achieved with precision and at the required travel distance.

At the same time, the interplay of screw pre-plasticising and injection ensures excellent processing that is gentle on the plastic, according to the company.

The melt is continuously fed from the material inlet to the tip of the injection screw.

This ensures that the first-in, first-out principle is fully observed.

Constant injection conditions through dosage control – a prerequisite for continuously high part quality – is a homogenous melt feed.

In order to achieve this, the pressure at the transfer point between the pre-plasticising screw and the injection screw is monitored and regulated.

For this purpose, appropriate nominal pressure and maximum permissible screw circumferential speed (limitation) values for the pre-plasticising screw are entered via the Selogica control system.

If the actual pressure deviates from the nominal pressure, this deviation is compensated by adjusting the rotational speed within specified limits.

A homogeneously prepared, newly dosed melt is available for every shot.

This keeps the material dwell times correspondingly short, preventing thermal damage to the material.

The result is said to be high processing quality; an additional advantage of the design with two screws is the leak tightness of the system.

Arburg has also maintained the modularity of its components with this new development.

The micro-injection module is designed specifically for use on electric Allrounder A machines with a size-70 injection unit.

Its enclosed construction means that it can be changed rapidly and then used on various machines, as with any other Arburg cylinder module.

This also means that the range of the machine’s applications is not limited to micro-injection moulding.

Consequently, other larger cylinder modules can also be used on this machine when a product change is required.

View full profile