This Weeks Assignment

Design a mold and use composite materials to build a part.

Part 1: Flower Pots

The idea here was to use flower pots as a 2 part mold and make a part using my son Shane's old cotton T-Shirt. This is an example of compaction using a closed mold.

Steps:

Prepare work area with bench covered in multiple layers of clingfilm to protect against spillages.
Apply clingfilm to outside of inner pot.
Cut cotton material, 4 pieces, slitted to provide overlap.
Gloves, mask, safety glasses.
Mix epoxy resin and hardener, equal number of pumps from each can, mix for 1 minute.
Cover cotton pieces with epoxy mix using squeegee. Target complete coverage but avoid excess.

Epoxy resin and hardener

Apply each layer of cotton over inner pot.
Apply one layer of clingfilm then perforate layer to allow bleeding.
Apply bleeder or batting.
Apply mold release to inside of outer pot.
Mount outer pot and clamp in position - leave overnight.

Clamped Pots

Clamped assembly

The outcome was reasonable but requires some finishing. The structural properties were excellent. For final finishing, the intent is to load the part on a lathe. The molds had to be broken to release the part.

Flower Pot Outcome

Part 2: Bowl

The idea here was to use a bowl as a mold and make a part using cotton. This is an example of using an open mold. The same process had been used previously to make a nice bowl using a nylon material.
The steps followed were similar to those above. A faster acting epoxy was used in the wet layup. A heating fan was used to speed up the drying process. The outcome was reasonable but not great. The structural strength was excellent but the finish had a significant number of gaps on the outside. The cotton did not adhere to the bowl as nicely as the nylon had done. In hindsight, vacuum bagging would have been a good idea on this attempt.

Bowl mold and part

Learnings

Working with composites appears to be some science with a little art. It was a great learning process and future attempts will be better. The flower pot finish was good where the mold was fully closed but obviously the finish was less good where the mold was open.

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