Plating and other finishes are usually last in the manufacturing process; frequently the effect of part design on finishing is totally overlooked. A part is frequently designed and specified in a way that adds considerable cost to the finishing step.
Whenever plating is specified the design engineer should identify the "significant surfaces" of a part. A significant surface receives a deposit of specified quality, that is, thickness, brightness, coverage, durability, and so on. A significant surface on a decorative part such as an automotive bumper or grille, is the area normally seen by the consumer. A significant surface for engineering applications is the area that gives a part the particular properties the engineer needs for specified function. An example of a significant surface on engineering applications is the journal of a crankshaft plated with hard chromium. The journal is the bearing wear surface and, therefore, is a significant surface. The adjacent web area is of no concern for electroplating. Hence, the journal area is the only significant surface and should be specified to be 100% covered with a high quality deposit.
When designing a part to be electroplated the engineer should consider the following.
Racking is the method used to suspend a part through the various steps of the plating process. A place should be provided where electrical contact can be made on an insignificant surface. This racking point will not usually receive as good a deposit as the other areas due to the effect of having a conductor near the surface to be plated.
Drainage of the part for proper rinsing should also be considered. Frequently a part will have inside corners or curved surfaces that may trap the solution. This is undesirable and should be avoided whenever possible. When these corners and curved areas are necessary from a design standpoint, they present a significant problem to the electroplater. This problem can, however, be alleviated by placing a hole in the lowest position of that area so that good drainage can be accomplished.
Air entrapment is a problem of concern when racking of the part is considered. If a cupped area is positioned in the solution in such a manner that it will trap air, it is obvious that solution cannot contact that particular area. Solution contact is necessary the part is to be processed properly. Proper racking or placement of a hole will alleviate this problem and ensure a quality deposit.
Plating distribution is also of consideration to the design engineer. As mentioned previously, a part protrusion will tend to receive a greater deposit thickness than a recessed area. Complex shapes are always more costly to electroplate than are simple shapes.
The following guidelines should be followed, whenever possible, in designing a part to assure platability.