Physical product

Design for manufacturing

A plastic pannier rack, designed to be ready for manufacture.

A black-and-white photo of a cyclist riding through a city, with the black pannier rack added to the back of the bike.

At a glance

Role
Product design student
Team
Individual project
Tools
Fusion
Timeline
Third year of my BSc Product Design (2020–2021)
Status
College project, BSc Product Design at TU Dublin

What it shows

  • Designing for injection moulding
  • Stress testing to a 3.00 factor of safety
  • Ribbing and snap fits
  • Draft angles, ejection pins and split lines

Highlights

  • 3.00 factor of safety, kept through numerous stress tests
  • 1 mould needed, because the rack is symmetrical

Discover

A project that I worked on recently was to design a pannier rack that was made from plastic. This was one of the more difficult projects, as it had to be ready for manufacture. Therefore it meant exploring many new routes that I had not done before.

How it came together

5 steps · 1 rework · 1 milestone

  • Step
  • Rework: went back and changed something
  • Milestone
  1. 1Define1 step
  2. 2Design3 steps · 1 rework
  3. 3Deliver1 step
  4. 4Outcome1 milestone

  1. 1Define

    1. Step 01

      The brief

      A pannier rack made from plastic, ready for manufacture.

  2. 2Design

    1. Step 02

      Minimising material

      Ribbing, and numerous stress tests in Fusion, keeping within a 3.00 factor of safety.

      Reworked later in05

    2. Step 03

      A symmetrical rack

      So only one mould would need to be used.

    3. Step 04

      Snap fits for injection moulding

      Snap fits that work with both the design of the product and the injection moulding expectations.

    4. Rework 05

      The CAD restarted, multiple times

      Back to 02: Minimising material

      Why: Designing for manufacture changed the way I look at projects: I ended up having to restart my CAD multiple times.

  3. 3Deliver

    1. Step 06

      Drafts, ejection pins and split lines

      The drafts of each face made compatible with a mould.

  4. 4Outcome

    1. Milestone 07

      Final renders

Define

Being ready for manufacture meant the rack had to:

  • use as little material as possible without losing strength
  • need only one mould
  • snap together in a way that suits injection moulding
  • have faces that release from a mould, with room for ejection pins and split lines

Design

I had to find ways to minimise the material use in the design while ensuring that its strength was not affected. This meant the use of ribbing, and numerous stress tests through Fusion to ensure that the product remained within a 3.00 factor of safety.

Exploded render of the pannier rack with callouts: an area to wrap the bag strap through, ribbing to cut down on material use, an M5 bolt to mount it to the seat, a snap fit, off-the-shelf parts to mount it onto the bike, ribbing for added strength, and negative space to cut down on cost and materials. Along the bottom: £50, HDPE (recycling code 2) and 900 g.
The rack’s features.
Stress analysis of the rack’s triangular side in Fusion: a blue mesh, with arrows showing loads pressing down on the top edge.
A stress test of the rack’s side.

In order to ensure a more realistic design, I had to find a way to make the rack symmetrical, so that only one mould would need to be used.

I had to design snap fits that worked in conjunction with the design of the product and the injection moulding expectations. This entire process changed the way that I look at projects, as I ended up having to restart my CAD multiple times.

Deliver

Finally, I had to ensure that the drafts of each face were compatible with a mould, along with the inclusion of potential ejection pins and split lines.

Draft analysis of the rack’s side, with the faces coloured by their draft angle.
Checking the draft of each face for the mould.
  • 3.00Factor of safety the rack stayed within through numerous stress tests
  • 1Mould needed, because the rack was made symmetrical

Outcome

Renders of the final design.

What’s next?

  • A physical prototype. Testing the snap fits, how the rack mounts to a real seat post and how it carries a packed bag would check the CAD and the stress tests in the real world.
  • A manufacturer’s review. A toolmaker could check the mould design (the drafts, ejection pins and split lines) and confirm the cost before anything is made.