A UK agricultural equipment maker used a die-cast aluminium bracket needing machining, powder coating and two bushes. A glass-filled nylon redesign cut weight by 59%, cost by 38% and three components to one.
Key numbers
A UK agricultural equipment company used a die-cast aluminium mounting bracket on several of its machines. It worked, but it was expensive: after casting, each bracket was machined, powder coated and fitted with two press-fit bushes. Purchasing had squeezed the casting supplier for years. The cost barely moved, because most of it was not in the casting.
The situation
The bracket carried moderate loads in an outdoor environment, with vibration from the machine and occasional impacts. Annual volumes were steady and high enough to justify a moulding tool if the business case worked.
What the data showed
A cost breakdown of the aluminium part showed where the money went.
Machining, finishing and assembly made up almost half the $14.20 cost. The casting itself was not the main problem; everything done to it afterwards was. That pattern makes a part a strong candidate for conversion to plastic, where features can be moulded in rather than added.
What changed
The bracket was redesigned for plastic, not copied from the metal original:
- Material: PA66 with 30% glass fibre, chosen for stiffness, strength, temperature range and outdoor durability.
- Geometry: a rib structure sized by FEA, following the rib design rules for stiffness without sink, with uniform walls and generous radii at load paths.
- Integration: the two press-fit bushes replaced by moulded-in features, removing an assembly step and two components.
- Creep: long-term behaviour at 60 °C checked against a ten-year load case, because sustained load at temperature is where plastics differ most from metals.
- Validation: prototypes passed vibration and impact testing, using parts in the production material rather than machined approximations, as recommended in prototype or simulate.
Results
Part weight fell from 412 g to 168 g, a 59% reduction. Part cost fell from $14.20 to $8.80, a 38% saving. Three components became one. The moulding tool paid back in under eight months.
Why it worked
The conversion succeeded because the bracket was redesigned around plastic's strengths: integration, ribs for stiffness and no secondary operations. A straight copy of the metal geometry in plastic would have been heavier, weaker and probably not cheaper.
Lessons for your operation
- Look at cost breakdowns. Parts with heavy machining, finishing and assembly costs are the best conversion candidates.
- Design for plastic: ribs, uniform walls and integrated features, not thick sections.
- Check creep at operating temperature for any sustained load.
- Validate with moulded parts in the real material, under realistic loads.
