Surface Topography

In many applications, the functionality of products is determined by the characteristics of their surfaces and often surfaces with very low roughness are required. Depending on the material and number of items to be produced, different processes can be applied to generate the parts in a cost effective way while achieving low surface roughness. The presentation will describe the characteristics of surfaces produced by different processes suitable for fine surface generation and discuss the factors affecting surface quality and topography features. Suitable process chains for reduction of surface roughness while maintaining high geometrical accuracy in components as well as moulds and dies for polymer replication will be presented. An indication of the cost efficiency of processes for reducing surface roughness will be given.

DFM offer the most accurate measurement in Denmark regarding quantification of surface topography. The measurement capability covers e.g. surface roughness, period and step heights from the nanometre scale to millimetres using atomic force microscopy, contact profilometry, optical microscopy and fast non-imaging optical methods. The presentation will discuss how to best select parameters describing the surfaces functionality and how to efficiently achieve accurate numbers and prove the correctness and traceability to international approved measurement standards. Industrial cases involving the surface of e.g. injection moulds and 3D printing will be discussed as well as more scientific cases involving e.g. super smooth surfaces. The limitations and pitfalls for each method will be assessed.

Food contact surfaces and their hygienic performance is exemplified and their surface characteristics are related to EU legal requirements, EHEDG demands and industrial practice. This will be related to results, which show the practical cleanability of different surfaces finishes of stainless steel. EHEDG is introduced with a short introduction to key hygienic design criteria, the EHEDG certification scheme, EHEDG guidelines and specifically the EHEDG view on hygienic surface characteristics.

Stainless steel is by far our most important food contact material, and it is difficult to imagine any dairy or pharmaceutical plant without a few square kilometres of stainless steel. As cleanability and corrosion resistance are of utmost importance, so are the surface condition of the steel. Stainless steel belongs to a large group of passivating alloys, which display a different corrosion pattern from the ones where a general “activation” takes place. The steel becomes much more sensitive to local weaknesses, which reflects the importance of the steel surface treatment. The ideal surface is therefore very much a matter of both functionality and design. So which types of surface is actually the best? How is the ideal surface defined? How is the surface controlled? And is Ra really a good measure of corrosion resistance and cleanability of the surface?

DFM is Denmark’s national measurement institute, and has the highest measurement competence in Denmark within a number of key measurement areas. The lab tour includes a showing of the Danish national “platinum metre”, which was in service until 1988, lasers realizing the meter at the highest accuracy level, advanced optical microscopes, atomic force microscopes, contact profilometers, fast non-imaging optical methods and mass calibration.

3D volume models from CT scanning provide comprehensive data about inner and outer characteristics of a part. This presentation will give examples of full field geometry inspection on injection and vacuum molded parts and different software tools to understand the manufacturing process.

The very high demands of surface roughness quality combined with the need for documented validation often requires control of the surface quality on external equipment. If this validation fails, it can require a new operation to redo the surface or even the need to do a new part from scratch, which can be potentially costly. We will show examples of measuring with Scattered Light technology and the benefits it provides, using an instrument from the German company Optosurf. Using this type of instrument makes it possible to measure surfaces inline in a production without making physical contact with the parts.

This presentation will teach the fundamentals of X-ray microscopy and show applications relative to 3D printed parts.