Not Rivals After All

Text: Thomas Masuch; Photos: Zikomm / Th. Masuch, Listemann - 02/09/2018

Mold-makers have a whole range of technologies to fall back on when it comes to conformal cooling: Listemann and Renishaw combine the strengths of additive manufacturing and vacuum brazing under one brand.

The tool- and mold-making industry is quite conservative. »But for form-makers, there is no getting away from additive manufacturing,« states Günther Rehm, head of marketing and sales at Listemann Technology AG. »In fact, some injection molding companies are already explicitly demanding it.« And Rehm should know what he is talking about: few people know as much as he does about the world of mold-making in German-speaking countries and beyond.

The Liechtenstein-based company Listemann does not offer additive manufacturing. »In fact, we used to think of additive manufacturing technologies such as 3D printing as rival technologies,« recalls Rehm. After all, Listemann is one of the few companies to specialize in vacuum brazing and has amassed a wealth of technical expertise over the years in the production of molds featuring conformal cooling channels. Increasingly, however, additive manufacturing technologies are also being used to produce these tools.

»The investment generally pays off very quickly.«

BRAZING VERSUS ADDITIVE MANUFACTURING

Rehm and his colleagues later realized that there is very little overlap between the two technologies and that vacuum brazing and additive manufacturing complement one another very well. The strengths of one technology compensate for the weaknesses of the other. Listemann decided years ago to take advantage of the strengths of both technologies by teaming up with LBC Engineering (which was later acquired by Renishaw GmbH).

In 2017, Listemann and Renishaw established the »iQ temp« brand to offer powerful conformal cooling solutions to its customers using vacuum brazing and additive manufacturing technologies. Depending on which technology is used, the form inserts are either brazed in Liechtenstein or produced using additive manufacturing on one of 12 machines at Renishaw’s Pliezhausen site.

Vacuum brazing involves separating the form insert or core into several components, which are usually machined. At Listemann, these components are then fused together in a vacuum furnace, at the curing temperature of steel and under a negative pressure of less than 10-5 mbar, in a process known as vacuum brazing. The braze material is a foil that can be as thin as 50 ?m, which melts and softens at the brazing temperature, flowing out to wet and bond the surfaces of the individual components. The metallurgical bonds formed in this multi-stage process are exceptionally strong – possessing 70 to 90% of the tensile strength of tool steel, according to Günther Rehm.

SOPHISTICATED HIGH-TECH PARTS

Vacuum brazing is the core business of Listemann Technology AG, which employs around 50 staff at its three sites in Liechtenstein, Switzerland, and Poland. And form-making companies are not its only customers. Listemann also supplies extremely sophisticated, high-tech vacuum-brazed parts to customers in the mechanica

Compared to additive manufacturing, the vacuum-brazing process is significantly less expensive – »sometimes by factors, depending on the application,« according to Rehm. Vacuum brazing is therefore ideal for large form inserts while additive manufacturing is more suitable for intricate, complex cooling circuits. Another advantage of vacuum brazing identified by Rehm is the variety of materials that can be used. »Currently, only two types of steel can be used to produce form inserts using additive manufacturing: 1.2709 and Corrax.« Vacuum brazing, on the other hand, can be used to join an almost unlimited range of materials, from steel and copper to ceramics and diamond.

Günther Rehm is convinced of the advantages of conformal cooling, since it not only decreases cycle times but also results in higher- quality components. For this reason, it can sometimes pay to use it even for small quantities of components. Although the tempered tools may be more expensive, Rehm estimates that the additional costs are in the region of a few percent. »The investment generally pays off very quickly – in some cases, within a matter of days.«

»EVER-INCREASING DEMAND«

Listemann supplies several hundred mold-makers in German-speaking countries as well as further afield. In Rehm’s experience, most customers are receptive to new technologies such as additive manufacturing or vacuum brazing. »Every now and then, however, you still come across traditionalists who have been drilling cooling channels in their tools for 30 years and don’t want to do things any other way.«

Overall, Rehm expects the demand for tempered tools to continue to rise. Because, in addition to injection molders, die casters have now also discovered the benefits of having cooling circuits integrated into their tools. The use of these technologies in die casting is still in its infancy and, according to Rehm, is lagging around 20 years behind its use in mold-making. »But demand is also increasing in this area.«

Vacuum brazing

Vacuum brazing is a thermal joining process with which high-strength joining compounds are produced. Connections are possible from the same material as well as from different materials. The decisive factor is the solder, which is used as foil, paste, or wire, depending on the component geometry. Common solders being used in vacuum brazing are, for example, Ni, Cu and Ag alloys. The effect of the solders is based on the ability to dissolve in the molten state constituents of the base materials and to create a metallurgical compound. The joining in vacuum prevents an interaction with the environment.

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