Finishing is the last thing to happen to a fabricated part and the first thing a customer sees, and it reaches backwards into the design more than any other stage. Coating thickness affects fits, masking affects cost, and the choice between plating and powder coating decides whether a part can be earthed or threaded without further work.
The options and what each is for
Deburring and tumbling remove sharp edges and are essentially mandatory. Graining gives a directional brushed appearance on stainless and aluminium. Plating gives corrosion protection with a thin conductive layer. Anodising hardens and colours aluminium. Powder coating gives a thick, tough, coloured layer at low cost. Wet paint covers the colours and effects powder cannot.
Powder coating and what it demands
The part is cleaned, pretreated, electrostatically coated with powder and cured in an oven. The coating is thick enough to matter: threads fill, close fitting holes shrink, and earthing paths are broken. So the drawing must say what is masked, and every thread either gets a mask, a plug, or is chased afterwards. Also check that the part can hang without the hook mark landing somewhere visible.
Masking is a real cost
Every masked feature is manual work applied and removed on every part. A design with a dozen masked holes is expensive to finish forever. Where possible, group features that need masking, use hardware installed after coating, or accept a coated thread and chase it, which is often cheaper than masking it.
Sequencing and lead time
Finishing is usually subcontracted, so it adds days rather than hours and it adds a transport leg. Welding must happen before coating, hardware insertion usually before, and any machined fit either after coating or with the feature masked. Getting this order wrong is the most common reason a fabricated part misses its date.
Questions people ask about sheet metal finishing
Does powder coating affect dimensions?
Yes. The coating is thick enough to fill threads and shrink close fitting holes, so masking or post coating chasing has to be planned.
Which finish is cheapest?
Powder coating, generally, for a durable coloured finish. Deburring alone is cheaper still where appearance and corrosion do not matter.
How do I specify masking?
On the drawing, feature by feature, with a note saying what must remain uncoated and why. Masking is manual work on every part, so keep the list short.
Should hardware go in before or after coating?
Usually before, so the pressing operation does not damage the coating, with the hardware itself masked. Some hardware is designed to be installed after coating instead.