Exercise 14 Composites


Requirement

  1. design and make a 3D mold (~ft2)
  2. produce a fiber composite part in it

Introduction

Composites are combinations of two materials in which one of the material is called the reinforcing phase, is in the form of fibers, sheets, or particles, and is embedded in the other material called the matrix phase. The advantages of composites are: weight ratio, tensile strength, toughness, better performance, fatigue resistance and design flexibility.

The requirement is to build something that is at least one square foot big. I decided to make a frisbee after checking out some of the following past projects for inspirations.

Making a composite mold of a frisbee

Materials & Methods

The material I have chosen to use as my positive mold is a blue modelling foam as it is lightweight and strong to withstand the compaction of air pressure subsequently in the vacuum bagging process. As for the composite materials, I will be using natural fibre, namely cotton and felt. The method used is vacuum bagging. Vacuum bagging (or vacuum bag laminating) is a clamping method that uses atmospheric pressure to hold the adhesive or resin-coated components of a lamination in place until the adhesive cures. This process requires a vacuum pump and epoxy resin. The following is a list of some of the technical terms associated with this process.

Steps involved


Milling process

I designed the frisbee using Inventor, then import to Mastercam to create the toolpath. Subsequently, the file needs to be converted to g-code that the CNC router can understand.


Milling the positive mold


Vacuum Bagging process

Preparing the base plate and applying wax to the mold
Preparing the layers of materials and measure the resins
Mix the right proportion of resin to hardener and pour on each layer. After the last layer, apply vacuum suction to hold the epoxy in place.
Let vacuum suction continue for 24 hours while the epoxy cure. Then peel layer by layer.
Peeling off of release fabric, and bleeder layers
What was left is the composite of felt and cotton


Hero shot after trimming the edges




Reflections

It would not have been possible to complete this week's assignment without my course mate, Tham for lending his pair of helping hands in much of the processes. I am also grateful for the Composite Technology Laboratory located in Workshop 14 in Singapore Polytechnic for allowing us to use the lab and the resources for this week's project.



Download Week 14 work files


References