Manufacturing Technology

By Tomislav Maric, global product manager zinc flake coatings, Atotech

Fully automated assembly lines in the automotive manufacturing process present constant new challenges for fastener suppliers – with automotive OEMs prioritising a range of factors for fixing elements, such as weight reduction (downsizing fasteners), faster screwing (productivity increase), cost optimisation, and process reliability in fastening.

Financial pressures to reduce the fastener portfolio necessitate coatings that can both be applied universally and work reliably. Furthermore, they must also be effective when used with the various materials that are often involved in the automotive engineering process. 

The coatings must demonstrate identical mounting properties, regardless of whether the fastener is screwed against steel, e-coat or aluminium – materials that are increasingly used in varying combinations on internal vehicle components. In addition to the coefficient of friction (CoF) properties that must be fulfilled by fastener surface finishes, additional factors such as heat loosening requirements and corrosion protection functionalities must also be taken into consideration.

Challenging coefficient of friction windows 

OEMs have instituted economisation measures to simultaneously increase uniformity across parts, as well as to increase profitability. For instance, the introduction of MBN 10544, the latest Mercedes-Benz standard, coincided with the transformation of various OEM platform strategies, and features, that ultimately greatly affect the productivity of fastener mountings, such as defining new requirements for the coefficient of friction. Besides prescribing higher speed tightening, adapted to the latest assembly technologies, the following single values are calculated in the test setting: Multiple mountings for each bolt and the use of new washer materials including steel, e-coat and aluminium. Also in MBN 10544, the standard window for the CoF must remain within a narrow range of µtot 0.08 and 0.14. For multiple mountings against different washer materials, Mercedes-Benz has specified corresponding CoF ranges that must be met. The demanding MBN 10544 specification requires a coating system that can be used for a vast range of Mercedes-Benz fasteners.

Fulfilling tough requirements

Atotech’s zinc flake coating system Zintek^® 200 + Zintek^® Top LV meets the complex automotive requirements for the coefficient of friction windows as defined in MBN 10544, as well as VW 01131 and BMW GS 90100

Zintek^® 200 is a versatile silver base coat and provides excellent cathodic corrosion protection. Meeting the highly demanding CoF specifications requires a sophisticated top coat – the clear finish Zintek^® Top LV. Thanks to its reactive properties, the thin layered, water-based top coat lends effective added corrosion protection. Its integrated lubrication ensures that the complex CoF requirements set by MBN 10544 (Figures 1 to 3) can be met with ease. Zintek^® Top LV top coat is especially advantageous for use in the automotive market when combined with the Zintek^® 200 base coat. 

The system has also been approved for Volkswagen’s TL 245 specification, where it fulfils similarly demanding multiple mounting and heat loosening property requirements (VW 01131). In addition, the zinc flake coating system fulfils BMW’s requirements in terms of corrosion protection and CoF behaviour (BMW GS 90100). It performs excellently in corrosion testing, including in trials that involve prior thermal pre-conditioning for 96 hours at a temperature of 180°C, which is a process typically required by members of the German Association of the Automotive Industry (VDA).

One coating system that fits all

The Zintek^® 200 + Zintek^® Top LV coating system is a top of the line zinc flake coating system that fulfils the stringent requirements of major German automotive OEMs, such as Volkswagen, Mercedes-Benz and BMW. This approach creates synergy across the production chain and has advantages for both applicators and tier companies. It represents a revolutionary system that is applicable to all three major German OEMs.