Influence of Design on Quality and Cost

The cost of electroplating is often greatly influenced by the complexity of the workpiece. Simple shapes can be processed through all cleaning and plating sequences, with a minimum of approximately 33 ^m (1300 ^in.) of copper and nickel and 0.25 ^m (10 ^in.) of chromium, in approximately 50 min. Providing these minimum thicknesses on complex shapes requires longer plating periods, special fixturing, special anodes, and current shields. Plating costs are increased by each of these factors, although buffing and cleaning costs may be unchanged. Equipment and overhead costs per workpiece also increase in direct proportion to the plating time. In addition, the cost of materials is increased, because more metal is plated unnecessarily on projections and other areas of high current density. Figure 2 indicates the approximate increase of plating costs with plating time at a fixed current density.

Plating time at a fixed current density, min

Fig. 2 Plating cost-time relationship

Extreme workpiece complexity can preclude the application of a truly corrosion-protective deposit by conventional plating procedures. The influence of some design features on platability and plating cost are described in Table 1.

Table 1 Influence of design on platability of zinc-base die castings

Design feature

Influence on platability

Better design

Convex surface. Ideal shape. Easy to plate to uniform thickness, especially where edges are rounded.

Flat surface. Not as desirable as crowned surface. Use 0.015 mm/mm (0.015 in./in.) crown to hide undulations caused by uneven buffing.

Sharply angled edge. Undesirable. Reduced thickness of plate at center areas. Requires increased plating time for depositing minimum thickness of durable plate. All edges should be rounded. Edges that contact painted surfaces should have a 0.8 mm ( — in.) min radius. 32

Flange. Large flange with sharp inside angles should be avoided to minimize plating costs. Use generous radius on inside angles and taper abutment.

Slots. Narrow, closely spaced slots and holes cannot be plated properly with some metals (e.g., nickel and chromium) unless corners are rounded.

Blind hole. Must usually be exempted from minimum thickness requirements.

Sharply angled indentation. Increases plating time and cost for attaining a specified minimum thickness and reduces the durability of the plated part.

Flat-bottom groove. Inside and outside angles should be rounded generously to minimize plating costs.

V-shaped groove. Deep grooves cannot be plated satisfactorily; should be avoided. Shallow, rounded grooves are better.

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Fins. Increase plating time and costs for attaining a specified minimum thickness and reduce the durability of the plated part.

Ribs. Narrow ribs with sharp angles usually reduce platability; wide ribs with rounded edges impose no problem. Taper each rib from its center to both sides and round off edges. Increase spacing, if possible.

Deep scoop. Increases time and cost for plating specified minimum thickness.

Spearlike jut. Buildup on jut robs corners of electroplate. Crown base and round all corners.

Ring. Platability depends on dimensions. Round corners; crown from center line, sloping toward both sides.

Note: Distribution of electroplate on design shapes is intentionally exaggerated by solid black outline. Cross-hatched areas indicate part before plating.

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