MTE594 Coatings and Surface Treatments
1. Read the posted information.
2. Watch the presentations and YouTube videos.
3. How is surface roughness specified at your UTC area?
I am stationed in overseas supplier which makes major assembly components for Sikorsky Aircraft. I usually deal with sheet metal parts and some precision manufactured flight safety parts which are supplied by Sikorsky.
Surface roughness and allowable surface imperfections are explained in Sikorsky product design criteria specifications.
Irregularities, such as nicks, dents, scratches, machining tool marks and scuff marks, on Flight Safety parts with critical characteristics, are allowable when they are .0005 inch deep or less. For all other parts, irregularities, such as nicks, dents, scratches, machining tool marks and scuff marks, are allowable when they fall within drawing specified finish requirements.
We use stylus to measure surface roughness. The rider supports the stylus and guards against damage.
4. Why is surface roughness specified?
Surface roughness is specified in engineering design. It limits irregularities on the surface. If the surface is in the acceptable limits for surface roughness we can say that it may comply with quality and engineering requirements.
Roughness plays an important role in determining how a real object will interact with its environment. Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces
Roughness is often a good predictor of the performance of a mechanical component, since irregularities in the surface may form nucleation sites for cracks or corrosion.
5. Identify the coatings and surface treatments that are used in your product line.
Surface treatments include various hardening techniques, from chemical to laser, and range all the way to thin films, an example also of artificial structuring. In general, the treatments offer a way to tailor the surface properties of a material without changing the bulk properties. This allows very hard cutting tools to have great strength and toughness, for example, or allowing materials to survive very corrosive conditions.
For my production line, I have anodic coatings which are chromic, sulfuric, boric and phosphoric acid anodize per drawing requirement. In addition I have plating process applications which are cadmium and silver plating.
I also have shoot peening and case hardening process to improve mechanical properties on the working surface.
6. What is residual stress? How does it develop? Where is it important to you?
Residual stresses are stresses that remain after the original cause of the stresses (external forces, heat gradient) has been removed. They remain along a cross section of the component, even without the external cause. Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment. Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses
When the work pieces are subjected to plastic deformation that is not uniform throughout the part, they develop residual stresses. These are stresses that remain within a part after it has been formed and all the external forces are removed.
It is important criteria for my flight safety parts. Residual stresses can play a significant role in explaining or…