Non-traditional machining selection: Which process is best for producing parts with large curved surfaces and thin sections?

Introduction / Context:
Complex aerospace skins, contoured panels, and thin webs require material removal over broad areas with minimal residual stresses or distortion. Traditional chip-removal can warp thin sections. The question tests recognition of the process that excels in thinning large, curved surfaces.

Given Data / Assumptions:

• Large-area, shallow, controlled material removal.
• Curved or contoured geometry.
• Thin sections sensitive to mechanical loads and heat.

Concept / Approach:
Chemical milling (chem-mill) removes material by controlled chemical dissolution using masks to protect regions. It applies uniform etching over large areas, ideal for weight reduction pockets and contoured skins, while imparting negligible machining forces and minimal heat.

Step-by-Step Solution:

Verification / Alternative check:
Industry practice in aerospace (aluminum, titanium) uses chem-mill to create lightening pockets and maintain contour fidelity.

Why Other Options Are Wrong:

• Hot machining: assists hard-to-cut alloys but still uses cutting forces; not ideal for very thin skins.
• Ultra-sonic machining: best for small features in hard, brittle materials; not efficient for large areas.
• ECM: precise but equipment/fixturing best suited to localized cavities, blades, or intricate shapes rather than large broad-area thinning.

Common Pitfalls:
Overlooking masking cost and undercut in chem-mill; process planning must include allowance for etch factor and dimensional control.

Final Answer:
Chemical milling