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Dörrenberg is one of the few companies in central Europe to provide CVD coating for heavy-duty forming tools as a subcontracting service. ausSICHT (our customer magazine) interviewed Harald Schmidt, head of the Surface Treatment Division, and Stefan Winkler, master craftsman in CVD coating, to discuss the advantages, special characteristics and fields of application for CVD coatings.

Mr. Schmidt, Mr. Winkler, there are many opinions and prejudices circulating about this technology. What are the actual strengths of CVD coatings? Why is CVD an "unrecognised genius"?

Harald Schmidt: Many customers are uncertain about the possibilities that CVD coatings can offer. Many suppliers recommend operators to use PVD coatings for situations where CVD would actually be the only choice. For example, there are a vast number of heavy-duty forming tools coated with PVD although CVD would be the significantly better and more cost-effective solution. In many cases, CVD ensures a substantially longer service life compared to PVD-coated tools.

Could you give us an example from your experience for this?

Stefan Winkler: Let's have a look at this drawing ring coated with CVD sandwich (right image), which is used for forming corrosion-free metal sheets with a thickness of 1.2 mm. The number of strokes of the press is 42 per minute. Attempts to try to shape this type of metal sheet using PVD-coated tools failed prematurely.

HS: In such cases, economically satisfying results can only be achieved with a CVD coating. Moreover, many forming processes wouldn't even be possible without CVD coatings.

For which tools is CVD coating the most reasonable and suitable method?

HS: The main fields of application are in metal sheet forming. Predominantly for conditions with abrasive and adhesive wear. Long production runs and large batch numbers make the process particularly profitable. The economic advantages of CVD are so obvious that it ought to be considered for many applications. PVD coating has its strengths in other areas. Which coating method to be used for which tool is individually defined for each specific case and always by taking into account the requirements, regardless of the process.

So what is the reason for customers uncertainty if this process has so many convincing advantages?

SW: Precise agreement and coordination between coaters and customers is mandatory for CVD. Ideally, the two parties should agree on a suitable material already during the planning stage for tool construction. The dimensional accuracy of the tools during subsequent hardening and coating is ensured by specific production steps in which we discuss and determine the material and tolerances together with the customer.

HS: After pre-processing the tool, we recommend a "special heat treatment geared to later CVD coating". This treatment ensures optimum structure formation while simultaneously ensuring dimensional and structural stability. Specific dimensional tracking during initial hardening allows us to specify grinding dimensions for the customer, in order to obtain the nominal dimensions during later CVD coating (coating temperature approx. 1,000 degrees Celsius) and re-hardening and to achieve the required material properties. The previously mentioned drawing ring is coated with the CVD sandwich coat.

What are the other coatings systems available with CVD?

SW: The different versions of CVD coats are specifically tailored to the requirements of different tools and processes. For example, the CVD sandwich coat is suitable for processing galvanised and austenitic metal sheets, i.e. for adhesive wear; while CVD TiC is ideal for highly abrasive materials due to its hardness. Another field of application of CVD coats is thick-sheet processing. For such purposes we have developed a special coating system, the so called CVD USB coat: this is a multi-layer coat providing particular adhesion strength combining a low-tension structure in the individual layers and maximum hardness in the top coat.

What are the future prospects for CVD coats in your opinion?

HS: I think the prospects are clearly positive, even now with current economic developments: while PVD coating is slowing down at our company, the sales volume for CVD technology has remained almost unchanged.

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CVD – unrecognized genius

Dörrenberg is one of the few companies in central Europe to provide CVD coating for heavy-duty forming tools as a subcontracting service. more


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