Conformal cooling irons out production problems

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Moulding techniques to suit the parts

Rowenta uses a variety of multi-component techniques, including turning plate systems, rotary table tools and indexing plate technology. In general, rotating tools are the preferred choice, Maier noted, as this approach keeps the injection-moulded part on the core during the subsequent over-moulding stages. However, the final decision is made on the engineering strategy that best suits the particular iron model – a turning plate design allows for a three-component solution that would very likely be too large for the clamping dimensions on a rotary table, he said.

The tooling decision will also take into account factors such as capacity planning and batch size. Irons are produced in a number of different colour combinations and, perhaps surprisingly, it is a cyclical business in demand terms. “Six model series translate to about 60 different individual models. And the model cycles are shorter than you’d expect – a new range is added every four years,” Maier said. “Fewer irons are bought at the beginning of the year. At that point we manufacture about 6,000 irons a day. But later in the year, that number jumps to between 9,000 and 10,000.”

Do-it-yourself moulding provides flexibility

Since Rowenta carries out its moulding in-house, it is able to use multi-component technology that is highly customised. The aim, according to Maier, is to automate everything that is feasible in each production cell. Conformal cooling is used in the most critical parts of the tools – sections with complex ribs or where space is restricted – to ensure the tight dimensional control required for trouble-free automated module assembly, he explained.

Selecting the right additive process for inserts

The company uses conformal cooling tool inserts produced with Hofmann Innovation’s Laser Cusing technology, and the parts are integrated into conventionally built and tempered moulds. Hofmann’s system (which is marketed by its Concept Laser subsidiary) uses an additive building process that creates a mould insert layer-by-layer from metal powder melted together by a laser. It is claimed to create a 100% fully dense metal component and is said to be able to process a range of stainless and tool steels.

Putting the cooling where it is needed most

The additive building technique allows for cooling channels to be placed close to the mould surface and to follow the surface contour – thus the term “conformal”. Typically, cooling channels of around 5mm in diameter are used and placed between 2-3mm from the surface. According to Hofmann, when applied selectively in a mould tool, the use of inserts made with Laser Cusing is cost- neutral.

For engineering and functional reasons, irons are well suited to the application of conformal cooling due to the pronounced ribbing in the front area. Maier said, “The key benefit is the lack of distortion. It accounts for the positive assembly characteristics, that is, the excellent dimensional accuracy of all the different mandrels and metal tubes that have to fit perfectly.”

In a three-component part, there are clearly identifiable cycle time improvements, too, Hofmann said. It cited typical cycle time reductions of between 10 and 30%. Maier added that start-up is also much faster, with the required dimensional accuracy being achieved very quickly.

With close to a decade of conformal cooling experience, Rowenta has developed a good understanding of how to get the best out of the conformal technology. Maintaining a high volume of coolant flow is essential and corrosion inhibitors are used to prevent build-up of sediment and particulate contamination. Coolant channels also have to be appropriately sized and positioned — parallel cooling is used at particularly challenging points to ensure maximum cooling of the cavity surface. This is all determined during the product development process and carried out in conjunction with the project managers and engineers at Hofmann Tool Manufacturing.

Additional Information

Shop talk with the lead developer at Concept Laser

ETMM: Concept Laser recently opened a new development centre. Was the reason for this rapid expansion occurring in additive manufacturing at the moment?

Florian Bechmann: That's true. The industrial applications are currently exploding, literally. Laser-melting with metals exerts a strong fascination when it comes to the components of the future. As the technology leader, we must support this market process by introducing innovations. When it comes to complex systems, we must ensure a wide-ranging interplay between optics, design, control technology, software and the powder material. At our new development centre, my colleagues and I are hard at work on "discrete innovations" not intended for disclosure to the general public. Certain industries are quite sensitive.

ETMM: What is currently going on in terms of quality requirements, and how important have they become for your customers?

Bechmann: From the customer's perspective, this is currently the most important area. Customers are interested in geometry, density, productivity and, above all, quality. Two approaches are expedient here: active process monitoring using machine technology and developments in materials. This includes the certification of materials, such as in medical technology, or manufacturer-specific instructions, which must be complied with in the automotive and aerospace sectors.

Working together to meet the safety standards

Irons are subject to safety checks by national or international testing organisations, such as the VDE, GS or UL inspections. The majority of checks are carried out at Rowenta to shorten the release time. This requires a certain degree of flexibility from all involved. Toolmakers, such as Hofmann, are brought on board in the very early stages of a project and remain involved throughout the development process. As Maier noted, “In a standard range, this means about 12 months of project time, from design studies through model-making to the finished series-production tools. For an innovative product with new electronic functions, a project of this kind could last up to 16 months.”

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