Material Swap for a Solar Lantern Housing
SunTrail is preparing a 20,000-unit production run of a portable solar lantern for outdoor use. The housing is currently molded from PC/ABS at a material cost of €2.10 per unit; the total unit cost is €5.60 against a target of €4.80. A supplier proposes UV-stabilized polypropylene at €1.20 per unit. PP would reduce injection cycle time from 45 s to 35 s on the same 2-cavity tool, but it has lower stiffness and is more prone to warping and UV degradation. The lantern must survive a 1.5 m drop at −10 °C and 1,000 hours of outdoor UV exposure without cracking or excessive color shift. The current PC/ABS housing passes drop but shows a ΔE of 2.1 after 1,000 hours. A glass-filled PP option costs €1.55 and improves stiffness but may reduce impact strength. The tooling can be modified for €12,000 and three weeks. Launch is in 14 weeks. Write a feasibility recommendation.
1. Quantify the cost impact of each material option, including the tooling modification and any assumptions. Which options are financially viable against the €4.80 target?
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Current unit cost is €5.60, so the gap to target is €0.80. Straight PP saves €0.90 in material, which appears to close the gap, but the €12,000 tooling modification adds €0.60 per unit over a single 20,000-unit run, giving €5.30-still €0.50 above target. The cycle-time saving is smaller than it looks: 10 seconds saved per 2-cavity cycle is 5 seconds per part, about 0.0014 hours; at a €30/hour machine rate that is roughly €0.04 per unit. Glass-filled PP saves only €0.55 in material and also needs tooling, so it is worse on cost unless it avoids a separate stiffness fix. The financial conclusion depends on amortization: if the tooling is spread over three or more runs, PP becomes more attractive, but the launch run alone does not meet €4.80. A €0.50 gap must be closed elsewhere (electronics, packaging, assembly) or by negotiating PC/ABS price. Do not treat the material saving as the full business case.
2. Assess the technical risks of switching to PP and propose a validation plan with measurable pass/fail criteria. What would make you reject the switch?
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Technically, PP is not a drop-in substitute. Lower stiffness can cause the housing to deflect and transfer impact to the internal PCB; warping can affect the seal and lens fit; UV stabilization must be proven in the actual color and wall thickness. The validation plan should use production-intent parts: 20 drop tests at 1.5 m and −10 °C, 20 at 23 °C, and 10 at 40 °C; 1,000-hour QUV or xenon-arc exposure with color and gloss measurement; a 500-hour heat/humidity test; and a warpage check on a coordinate measuring machine. Pass/fail: no cracking, no battery or PCB exposure, ΔE ≤ 3.0, and dimensional variation within the seal's tolerance. Reject the switch if any drop test exposes internal parts, if UV color shift exceeds ΔE 3.0, or if warpage prevents a consistent seal. A glass-filled grade must also pass impact; higher stiffness does not guarantee better drop performance.
3. Recommend a decision for the 14-week launch, including contingency.
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For the 14-week launch, keep PC/ABS for the first 20,000 units and launch on time, while running PP validation in parallel as a cost-reduction project for the next run. Reason: the PP business case does not meet the €4.80 target on one run, and the technical risks could cause a launch delay or field failure. The contingency is to qualify UV-stabilized PP with a production tool insert and, if it passes by week 10, use it for a second production batch; if it fails, retain PC/ABS and value-engineer €0.50 from other cost buckets. Do not modify the tool for PP until the drop and UV results are in, because a tool change is hard to reverse close to launch. Set a decision gate at week 8 with the test data, and keep a dual-source material strategy. This protects the launch while preserving the cost opportunity.