Long flow paths with low tolerances and multiple cavities

Arburg relied on the expertise of REGLOPLAS for its powder injection molding "key fob" development project. Learn how this solution made long flow paths at constant temperatures possible and thus ensured the highest possible quality of the final product.

Arburg, a leading German machine builder of electrical, hybrid and hydraulic plastic injection moulding machines, and REGLOPLAS are fostering a long-term and successful collaboration. It is for this reason that Arburg approached REGLOPLAS for the “Key fobs” development project in the field of powder injection moulding. The focus for the powder injection moulding of ceramics and metal was on the challenge of shortening the sprue runner. Particularly in the use of PIM (powder injection moulding) process for metal powder, in the REGLOPLAS VARIO version, the hot runner is required in combination with the REGLOPLAS 200Smart temperature control unit.

There is currently a noticeable trend towards multiple cavities in the powder injection moulding market. When it comes to multiple cavities, it is essential that the route of the runner to each part (cavity) is of equal length. For this purpose, the sprue runner must be branched accordingly. To guarantee this parameter, Arburg opts for using a temperature-controlled liquid hot runner. The solution developed by REGLOPLAS for this purpose produces quality products of the highest standard with stable process reliability.

 

Problem

For multiple cavities, the hot runner must be set up for several slides with sprue runner lengths of more than 13 cm (see figure 1). The challenge here is to direct the hot runner as close as possible to the multiple cavities despite the very limited space available. This enables the cold runners to be significantly shortened.

The particular challenge for the temperature controlling of multiple cavities is that the feedstock (main raw materials used for manufacturing a product) needs to be evenly temperature-controlled. In addition to this, it must not be allowed to overheat at any time, or this would result in a degradation of the feedstock. Stable temperature controlling cannot be sufficiently guaranteed using electric hot runners. Therefore, this temperature controlling, free of fluctuations, is to be achieved using a REGLOPLAS temperature control unit run with oil.

An increased injection rate often leads to density differences in the green parts being produced. This lack of homogeneity in the density generates strong warpage in the sintering. Depending on the feedstock, separations occur around the injection point and along the flow path. To avoid these shortcomings to the part, the tool temperature must be brought to melting temperature at the point of injection. At the same time, the feedstock requires stable and very precise temperature controlling of the hot runner, which heats the runner area separately from the tool. This keeps the feedstock in the runner area permanently free-flowing, preventing premature freezing. In addition to this, it allows longer flow paths to be created since the compound first begins to cool in the cavity.

 

Objective setting

Powder injection moulding should enable long flow paths with minimal tolerances and thin wall thicknesses in multiple cavities. This requires an optimal hot runner, which is operated using temperature control free of fluctuations.

 

Procedure

In order to achieve the targets, one of the core competences of Arburg, in this case powder injection moulding, is complemented by the core competence of REGLOPLAS in the field of temperature control. The “key fob” development project was carried out in cooperation. This included the sharing of mould data, end product data, technical specifications of materials and further information. This generated an initial, customer-specific temperature control calculation from which it was possible to calculate and design the desired hot runner. REGLOPLAS also supported Arburg on site with the test run, the fine tuning of the parameters and the measurement of the final production values.

The feedstock used has a viscosity that is extremely temperature dependent. In order to guarantee the highest possible quality of the final product, a constant feedstock viscosity is required. It is therefore essential that the hot runner with the temperature-controlled medium exhibits the best possible temperature constancy.

For Arburg's requirements, a temperature control unit, which was to fulfil Arburg's specifications (e.g. maximum temperature deviation in the control unit of +/- 1 K), was calculated and developed by REGLOPLAS.

Using the 200Smart, which was developed specifically for Arburg by REGLOPLAS (see figure 2), the first test runs of the hot runner could be carried out.

For the first trials, a test mould for manufacturing a key fob was developed. Green parts with various different shapes are shown in figure 3. The mould lengths are 1.3 and 2.3 cm. The mould is set up for a temperature-controlled liquid hot runner (REGLOPLAS 200Smart).

Using a temperature-controlled liquid hot runner and the oil temperature control unit specially developed by REGLOPLAS, the REGLOPLAS 200Smart (figure 2) enables a constant input temperature with deviations of less than +/- 1 K. This guarantees effective control of the flowability of the feedstock. Figure 4 shows the hot runner system for the production of a key fob.

 

Summary

With its customer-specific solutions, REGLOPLAS offers individual products for special customer requirements.
The advantages of a project with Arburg are:

  • By using the REGLOPLAS 200Smart, it guarantees the highest possible quality of the final product (key fob).
  • Extremely constant temperature-control in the hot runner with deviations of less than +/- 1 K
  • Long flow paths are possible at a constant temperature.
  • Very high reproducibility of parts.
Further info
Product groups:
Periphery, products for plastics processing
    Temperature control

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Siegfried Hohlbaum

Regloplas AG

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