Case Study: Replacing an Aluminium Engine Cover with Reinforced PA6

Background and constraints

The incumbent part was a die-cast aluminium cover weighing 1.35 kg, with expensive machining and finishing. Three constraints governed the redesign: continuous service at 120 °C, engine vibration, and no cracking under oil splash.

Candidates were PA6 GF30 and PA66 GF35. Since 120 °C does not approach the limit of PA6 and PA66 costs more to process, a heat-stabilised PA6 GF30 was selected.

Results

Weight: 0.78 kg, a 42% reduction. After geometry optimisation the wall was standardised at 3.0 mm with four ribs controlling deflection.

Cost: machining and anodising disappeared, so despite higher material cost total piece cost fell about 28%. Cycle time dropped from days of casting plus machining to 55 seconds of injection.

Tooling investment must be weighed: injection tooling costs more up front, and the switch becomes clearly economic only above roughly 30,000 parts.

Three critical tests passed

Heat ageing: 82% tensile strength retention after 1000 hours at 150 °C, against a customer minimum of 75%.

Oil resistance: 168 hours constant-strain immersion in 120 °C engine oil with no cracking and less than 5% strength loss.

Vibration fatigue: 10⁷ cycles to the customer rig specification without cracking or loosening.