City Guilds Model Questions Vol1 2024 Engineering Question 8

A component made of mild steel requires a cylindrical hole of diameter 20 mm and depth 50 mm with a surface roughness of \(Ra\le 0.8\ \mu\text{m}\) and a dimensional tolerance of \(\pm0.02\) mm. Two machining routes are considered for a batch of 200 parts: (a) drilling the hole followed by reaming, (b) CNC boring. The following data are supplied: - Drilling cycle time per hole: 15 s; tool‑change time: 5 s; drill tool cost per use: $0.20; drill tool life: 100 parts, replacement cost $5. - Reaming cycle time: 10 s; tool‑change time: 5 s; reamer cost per use: $0.30; reamer life: 100 parts, replacement cost $5. - CNC boring cycle time: 30 s; tool‑change time: 5 s; boring tool cost per use: $0.45; boring tool life: 200 parts (no replacement cost). - Labour cost: $0.05 per second. Determine which route gives the lower total cost (labour + tool + replacement) and state the total cost for each route and the saving achieved by the preferred route.