in Vol. 18 - May Issue - Year 2017
Surface Finishing – Power For Your Parts
Fittings - Optical and haptic characteristics
Drive components - safety aspects
Eyewear components - aesthetics required
What is decisive for the success of a product? It has to reliably serve its purpose, for example it must work (bicycle lock, vacuum cleaner, Notebook power supply, ironing board) or be beautiful (earrings, vase) or both (mobile phone, coffee machine, ceiling light, stereo, bicycle, car, wristwatch, bathroom fittings, door handle, ballpoint pen…) What do all these products have in common? The surface of the components must be "good". Nevertheless, what does "being good" mean? What benefit does a "good surface" deliver?
Perfect surfaces are more than just "decorative" or "functional". For a long time, the benefit of a surface finish was reduced to these two aspects. However, the quality of surfaces is much more than that. In my column, I would like to explain to people who do not think about this every day, what the positive effects and the benefits of a surface finish are. Since we are constantly surrounded by products with a more or less elaborate surface finish, it makes sense to sharpen your senses.
I will look at the elements of security, touch and feel, hygiene, durability and aesthetics and establish a link with modern surface finishing processes.
Safety! A surface finish may be mass finishing or shot blasting for example; following the production of components made of metal or plastic; these processes improve surface quality or edges and remove burrs and other irregularities from the surface. In the manufacture of gearwheels, for example, there are two main criteria when it comes to surface and contours: A clean deburring or edge rounding, and the roughness of the tooth flanks. Good deburring with shot blasting operations, mass finishing operations and abrasive brushing operations is particularly crucial for safety. Material residues or burr residues can cause malfunction later and thus compromise safety. Another example from practice is the manufacture of (unfortunately) sharp-edged punched parts. Components are often assembled manually. Sharp edges can cause personal injuries during assembly. Mass finishing operations are a safe and efficient way of avoiding such a risk and increasing safety.
Touch and feel! Consumers are becoming increasingly aware of this: assessing a product requires more than just visual perception. How does it feel? Especially for products that are touched a lot it makes sense to test whether the surface has a pleasant feel to it. What "pleasant" means can vary a lot from person to person: some consider a satin-finished surface with slight roughness pleasant, and others prefer touching a smooth, polished surface. To accommodate all preferences, Apple for example offers its latest generation iPhone in a polished and in a satin-finished design. After the mechanical surface finish, an additional coat can have a positive effect on touch and feel. Polyurethane powder coating, for example, makes the surface feel warmer and softer.
Hygiene! In the food industry, the quality of the surface plays an important role. All technical equipment and machines used in the manufacturing and processing of food must be easy to clean and it must not be possible for food components to become deposited or left behind. All surfaces must be easy to clean and disinfect. This is only possible if the surface meets certain required quality criteria. A certain level of roughness (µm) is often required, which is generally achieved through grinding and polishing processes. Mass finishing operations, for example, are also successfully used as a basis for a clean coating process and thus a smooth and finely structured surface.
In medical technology, such as in the manufacture of surgical instruments or joint implants, surfaces are processed with hygiene aspects in mind. Smoothed or polished surfaces are easier to clean and sterilise.
Durability! As a rule, smooth surfaces have better sliding properties when rubbing against other surfaces (for example in drive technology). The reduction of frictional resistance improves the wear properties of components. A high level of durability with regard to functionality thus means longer availability. A practical example is the gearwheels of large gears. The tooth flanks are smoothed to a roughness of Rz < 2.4μm / Ra < 0.3μm to ensure low-wear and low-vibration. In some applications, the exact opposite is the case. If a system works without lubricants (e.g. baffle plates for the safety belt in cars), it is of advantage if the surface has more of a rough structure. If, once the surface has been roughened, a shot blasting operation is used to apply a coating with Teflon components, this increases durability because it reduces frictional resistance.
Aesthetics! In science, the term aesthetics refers to the entire range of properties that determine how people assess the objects they perceive. Decorative surfaces are appealing. Whatever is looked at or touched is assessed. Beautiful or ugly, smooth or rough, pleasant or unpleasant. A well thought-out and well-functioning product is easier to market if the surfaces satisfy the consumers‘ aesthetic preferences. This can be a high-quality coating, a polished or a satin-finished surface. Whether a product is made of metal, plastic or wood, the aesthetics of the surface must be contemporary, both with regard to texture and structure, and colour.
In conclusion, we can say that there are various aspects that can be used to describe the benefit of a perfect surface. During the initial planning steps of the manufacturing process of a product, surface processing must be paid close attention to. The preferences of the target group as well as technical requirements and aspects of quality must be precisely analysed in order to take into account and plan the necessary process steps in a timely manner.
by Dirk Gather, Contributing Editor MFN and Managing Director of surfaced GmbH, Germany