Q&A Immaculate surfaces at the highest possible performance capacity

Editor: Rosemarie Stahl

In the last decade, the manufacturing requirements for plastic injection moulding have become significantly more strict. Thus, the demand for pre-hardened plastic mould steels with uniform hardness combined with excellent burnishing qualities and high wear resistance has increased.

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Daniel Frie, Technical Customer Service at Deutsche Edelstahlwerke, is aware that the requirements for plastic mould steel are comparatively high.
Daniel Frie, Technical Customer Service at Deutsche Edelstahlwerke, is aware that the requirements for plastic mould steel are comparatively high.
(Source: Deutsche Edelstahlwerke)

In order to comply with increasing market expectations, Deutsche Edelstahlwerke continually works on the development of these steel solutions. Daniel Frie is Technical Customer Service representative at Deutsche Edelstahlwerke, a producer and processor of special long steel products. For the three materials groups of engineering steel, tool steel and stainless, acid and heat-resistant steel, Deutsche Edelstahlwerke offers a wide range of product dimensions, from drawn wire with a diameter of 0.8 mm to open-die forgings with a diameter of 1,100 mm. As a technical partner, Deutsche Edelstahlwerke also develops innovative, individual special steels for complex applications. Over the past few years, the company constantly improved the quality of its steel products. Last year, Deutsche Edelstahlwerke has presented its latest pre-hardened plastic mould steel, Formadur 400.

In this interview, Daniel Frie explains how the requirements on the material have changed and which technological challenges the company has to face when it develops steel solutions.

In which way have the customers' requirements for plastic injection moulding changed in the past few years?

When producing for high-tech sectors such as the automotive industry, plastic injection processes are required that produce faultless products with the highest possible manufacturing efficiency. In the last few years, there has been a trend towards ever-higher injection pressures that are required to optimise the cycle times. At the same time, the surface finish of the plastic product must be high-grade and consistently repeatable. A prerequisite for the manufacturing of the required plastic moulds is tool steels that can be forged with the greatest accuracy grade while being robust in use. In application areas where large-sized, complex plastic moulds are used, the demands made on the material are disproportionately higher. Few steel manufacturers have the technological resources and material grade know-how to produce mould steel that meets these requirements.

Which steel grade solutions does Deutsche Edelstahlwerke offer and what is innovative about them?

We had already initiated the development of the pre-hardened plastic mould steel Formadur 320 approximately ten years ago in order to fulfill increasing demands on improved burnishing qualities and resistance to wear and tear. The basis for this is standard steel grades 1.2311 and 1.2738, which are standard solutions for frames and moulds for plastic injection moulding.

We have significantly increased the hardness of the steel and optimised its machinability. In order to guarantee a consistently perfect surface finish, the hardness of the steel must be uniform from surface to the core of the block. Even at that point we had reached a milestone in the area of plastic mould steel by achieving delivery hardness of up to 355 HB with Formadur 320.

However, continuously setting new standards is the key point for being an innovation leader – and that is a guiding principle for the entire Schmolz + Bickenbach Group, to which Deutsche Edelstahlwerke belongs. In co-operation with our customers, we now have the new product Formadur 400 ready for serial production. With a hardness of up to 410 HB, this high-grade steel provides an excellent hardness level for mould steels, which results in great burnishing qualities.

The properties of Formadur steels in comparison. Especially for injection moulding, the steel needs to have an optimal hardness uniformity from its surface to its core.
The properties of Formadur steels in comparison. Especially for injection moulding, the steel needs to have an optimal hardness uniformity from its surface to its core.
(Source: Deutsche Edelstahlwerke)

What are the biggest technical challenges in developing specifically requested steel, and how do you accomplish this?

One of the biggest challenges is to ensure the homogeneous hardness of large steel blocks. This must be guaranteed even at the core of the block in order to ensure uniform and repeatable surface qualities of the plastic product. The minimal differences in the hardness profiles of Formadur 320 and Formadur 400 show the advancement we have made in this area.

Our technological competitive advantage includes heat treatment furnaces and quenching tanks suitable for heat treatment of largest steel blocks. For end-users who require even higher steel standards, we also offer our Formadur steels in Superclean condition. By using the electro-slag-remelting process, we achieve the highest possible degree of purity and an extraordinarily homogeneous structure. This becomes noticeable with the excellent results in terms of polishing, texturing and durability. As a result, the quality, resistance and lifetime of the plastic mould are increased. The bottom line is that the production of high-standard plastic mould steels is in the end dependent on experience and technological resources.

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