Alcoa Case Study: Rear Tray Mould Tool Design for a Car

Material Selection in Design | 3rd Year | Duration: 1 Months

Overview

​Our chosen case study was set by Alcoa, it required us to design an injection mould tool to manufacture the rear tray of a car.

Objectives:
  1. Choose a suitable material for the manufacture of the tool
  2. Give reasons for the choice over other materials
  3. Outline the design considerations taken into account when designing the mould and how they are accounted for in the design (including the manufacturing process of the tool).
Initial Design Constraints:
  • Inside material to be moulded set as Polypropylene
  • Part dimensions are 1557 x 650 x 330mm (not the tool dimention)
  • Tool used to make parts in the tens of thousands (life of the tool)
  • The produced part is visible to the consumer (surface finish of the tool)
Required outcomes:
  • ​Produce a 4 page report detailing the material selection and our reasoning, manufacturing process and other considerations taken into account
  • Produce and present an 8 minute presentation

Contribution

During the project, I designed the tool using solidworks and ran preliminary simulations looking at the heat transfer through the tool and the stresses due tot he clamping force used to hold both sides of the tool together.

​I then wrote about the my design desicions to contribute to the report, this included reasons for the placement of the sprue (waste) which leaves behind a mark, the ejector pins and the cooling channels.

I along with another team member produced and presented the an 8 minute long presentation (audience size roughly 150)

Material Selection

The main requirements for the material were:
  • High thermal conductivity - to allow quick cooling reducing the cycle time enabling more part to be made per minute
  • High hardness - as the tool should not deform under compression
  • Low themal expansion - which will cause the inside part to be larger than intended
  • Low cost - this is partly dependant on market proce of the material, a low density material allows for easier operation and cheaper transport
Taking this into consideration the Granta material selection software* was utilised.

Note: we later learnt about how materials can have different properties at different depths which we had not considered.
*produced by team members

Tool Design

Design consideration:
  • ​Drafting Angle (3ᵒ) - to allow clean ejection of the Polypropylene part from the tool as it shrinks (reduces tool wear)
  • Shrinkage (1%) - the Polypropylene shrinks as it cools so the tool dimentions had to be scaled up by 1% to offset this effect
  • Sprue Placement - the extra material left as the Polypropylene is injected is removed later but leaves marks on the surface, this required concealing from view
  • Cooling Channels - the placement of the cooling channels is important to the cycle time and to ensure uniform cooling (my placement was not the best)
  • Split Line - as the 2 halves of the tool release it leaves a line on the part where they met, this was not an issue as the core-cavity design allowed the line to be on the edges so it looked natural
  • Markings - The ejector pins would leave marks ​requiring them to be small in diameter
Simulation assumptions and cost-per-part
File Size: 301 kb
File Type: pdf
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