ThinKing August 2020: The “magic” of magnesium: warped becomes even, heavy becomes light



Die-casting: less material and weight saves money

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Table saws need to be stable and heavy, so they may not necessarily be considered a typical area for lightweighting. However, with its base frames and tables made of die-cast magnesium, German manufacturer Torun Bark Magnesium GmbH has demonstrated that lightweighting does indeed make sense here – and even offers benefits for the user and the environment.

The Development Agency for Lightweighting Baden-Württemberg presents this innovation in its August 2020 edition of ThinKing. Under this label, Leichtbau BW GmbH provides a platform every month for new innovative lightweighting products or services from Baden-Württemberg.

At a glance:

- Lightweight: Weight savings of approximately ten percent due to a weight reduction of more than three kilograms compared to die-cast aluminium
- Efficient use of materials through optimised design
- Cost-effective: One less step in the production process
- Easier handling of the saw

“Its low specific density alone makes magnesium a lightweighting material. But the real innovation lies not in the substitution of materials, but in the weight-optimised design and production of the table,” says Dr. Cyrus Bark, Managing Director of Torun Bark Magnesium GmbH.

The mere size of the table already poses a challenge, as the magnesium sheets previously produced by the company are significantly smaller. The table measures approximately 45 x 75 x 1 cm, and features a slot for the blade, making it more difficult to manufacture. The base frames and the table of the table saw are made of die-cast magnesium.

Regarding the specific requirements for the table, Bark explains: “The component geometry of the table was a particular challenge, as it needs to be absolutely even to ensure clean guidance of the workpieces during sawing. In addition, the surface quality of the table is also crucial, as for Festool GmbH, a premium manufacturer of power tools, the impression of quality of this power tool is an important factor for professional users such as carpenters, joiners and woodworkers.”

Evenness achieved through cooling alone

Very often, the tables for table saws are made of aluminium, with the surface being CNC-machined and coated after die-casting. At Torun Bark Magnesium GmbH, the evenness of the magnesium table is not achieved by additional machining, but rather by “pre-stressing” in the die-casting tool. This eliminates a costly machining step in the production of the component.

“The component we cast in the die-casting tool is deliberately warped, so that, when it cools down after the casting process, it straightens outs – and becomes perfectly even,” says Bark with a smile. “Thus, the surface does not need to be reworked, and all we need to do is apply a powder coating to protect it against corrosion.”

Optimised design to save resources

All this is made possible due to an innovative sprue design and – following numerous simulations – an optimised, sophisticated and thin-walled component design. In some places, the component wall is less than 1.5 mm thick.

To obtain the required stiffness, the underside of the table features ribbing and honeycomb structures. These structures not only increase the stability of the table with significantly less mass; in combination with flow aids such as the so-called “crow's feet”, they also ensure optimum distribution of the molten metal in the mould during the die-casting process.

Light, yet stable

This production method yields a table which is particularly thin-walled, and therefore not only light in weight but also efficient in its use of materials. Compared to the aluminium tables, which weigh almost four kilograms, the 2.5-kilogram magnesium table is more than 30 percent lighter. With the base frames also being made of die-cast magnesium, the total weight reduction lies at more than three kilograms. Considering that the entire table saw weighs around 45 kilograms, this amounts to almost ten percent of the total weight of the tool.

This particular field of application requires a fine balance between stability and mobility. While the reduction in weight is a noticeable advantage for mobility on a construction site, the table saw is still heavy enough to provide the steadfast stability needed for sawing.

Magnesium – the specialist among lightweighting materials

To use magnesium as a lightweighting material in a meaningful way, certain key factors must be observed. The material is ideal for creating a particularly light component, due to the low specific density of magnesium and the possibility of thin-walled designs. In addition, this non-ferrous metal is 100-percent recyclable and very temperature-resistant. However, unlike aluminium or GRP, it is susceptible to corrosion. Moreover, producing die-cast components is generally only worthwhile for medium to large series.

Providing an outlook on the future of this lightweighting material, Dr. Cyrus Bark explains: “The experience we have gained from these components can also be transferred to other industries. For example: previously, the material had not been approved for use in aviation. But now, there are flame-retardant magnesium alloys which can also be die-cast, opening up further fields of application in areas such as civil aviation and electromobility.”

About Torun Bark Magnesium GmbH

Historically operating under the name CC Bark Metalldruckguss und Formenbau GmbH, Bark has specialised in magnesium die-casting for three generations. Last year, Torun, a group of companies operating internationally, became a shareholder in the Swabian magnesium specialist, leading to the foundation of Torun Bark Magnesium GmbH. This new company is now part of a group of companies that can offer its customers not only magnesium die-cast parts, but also die-cast parts made of aluminium, brass and stainless-steel components.