Composites 101

Report
Composites 101
An introduction to composites design and
manufacturing
Potential Instructors
Bo Pollett
Fred Briggs
Class list
 11/23/13 – 13:00
 Corry Lazarowitz
 David Stewart
Overview
 Introduction to Composites
 Manufacturing Techniques
 Part Selection

Simple parts

Complex parts
 Vacuum Mold Making

Vacuum Thermoplastic Forming

EEOP
 Tool Prep
 Wet Layup
 Trimming
Introduction
 A composite part is defined as something that is made with more than one
material
 The most commonly engineered composites are filament reinforced plastics
like carbon fiber and epoxy
Materials Overview - Fibers
 Different fibers provide different
physical properties as well as a different
look. Here are some general material
categories:
 Fiberglass is a great all around material with
medium strength, a low cost and lower
weight than wood, plastic, or metal
 Carbon fiber ranges from still to really stiff
and is well suited for aircraft and
performance applications where weight
reduction is worth the high cost
 Kevlar is in between fiberglass and carbon in
terms of stiffness, cost, and weight, but has a
very high impact energy resistance and is
well suited for impact resistant applications
like boat sails and sports equipment
Materials Overview - Matrix
 The glue that holds the fibers together
is called a matrix. It is usually a long
chain hydrocarbon based plastic, but
there are lots of specialty matrix
materials as well. Here are a few
examples of common matrix materials:

Polyester or Vinylester resin is a 1 part liquid
that required a few drops of MEKP catalyst
to begin hardening. It is low cost and low
strength material. Good for everyday
applications like civil engineering or
commercial products like surfboards.

Epoxy is a 2 part resin that has very specific
mixing ratios based on the manufacturer.
This resin is stronger than the esters but
also more expensive.

Ceramic matrix is a powder that is kiln fired
like clay to create a brittle but very high
temp composite. This is often found in
rocket motor parts or brake pads.
Manufacturing With a Mold Tool
 Painting resin on fabric is called “wetting
out”
 Placing carbon fabric on a tool and painting it
with resin will cause the carbon to harden in
the shape of the tool
Mold Tool
Wet Layup
Cured Part
Mold Tool Basics

Mold tools for a new part are often made with a cnc
machine

If a part already exists, a mold tool can be made for
less cost by using the original part as a “master” or
“plug”

The mold tool will be an inverse of the part, called a
“splash”

It is important to factor in material thickness when
deciding which side of a part to use for the splash

A splash can be made using various methods and
materials


Vacuum thermoplastic forming

Composite wet layup

Resin casting

Latex painting
Different tool making methods have unique strengths
and weaknesses
Simple Parts
 Select a part to use as a “master” or
“plug”
 The part should have a smooth
surface
 The part cannot be “trapped”
 The part must have holes sealed up
with tape or clay
 The part should have a continuous
edge that can be extended
 The part should be 1-sided or multisections
Complex Parts
 Closed structures require
special layup methods
 Closed or trapped structures
require special tooling
 Complex and accurate cutouts
must be made with a cnc router
or a waterjet cutter
 Core or other inter-laminate
inserts
Vacuum Thermoplastic Forming

Vacuum forming can be used to create composite
molds

Place the plug (original part) on the vacuum table

Hold the plug in place with tape, clay, or pins

Create an extended edge of part (EEOP) if the plug
has hard edges (see next slide)

Heat plastic sheet

Place hot plastic sheet over part and apply vacuum

When plastic is cool, remove it from the vacuum
table

Locating pins and edge of part scribes can be added
to the plug in order to improve the accuracy of the
final product
Extended Edge of Part (EEOP)
 An EEOP will allow the tool
layup to go beyond the edge
of the part creating a
continuous edge
 The composite part will be
trimmed afterward and
maintain the exact same
shape as the original part
Tool Prep
 The resin will soak into the fabric and cure in
any shape, which is why an accurate mold
tool is important
 Resin will stick to almost anything when it
cures, so a release agent like wax must be
applied to the mold tool before putting resin
on it
 The plastic sheet tool may be flimsy and
require reinforcement of some kind
Wet Layup

Begin by preparing all the material you will
need for the whole layup process, a checklist
can help

Covered work table, gloves, mixing stick, resin,
mold tool, paintbrush, cut fabric, cleaning supplies

Mix the resin as specified by the directions,
the ratio has to be very accurate and mixing
has to be very thorough

Paint a layer of resin on the tool

Lay the first ply of fabric on the tool being
sure to press it into all the corners

Gently brush a layer of resin on top of the
fabric, be sure not to pull the fabric or it will
come off the surface of the tool

Add the next layer of fabric and repeat until
every ply has been used

The amount of fabric and thickness of resin
coats will determine the strength and weight
of the part

Set the part aside so it can cure undisturbed
at 70-85 F
Trimming
 The part will come out of the mold
with long, rough edges
 The part will have to be trimmed
back to the original edge of part line
 This can be done with scissors or may
require a rotary tool depending on
the thickness and material
 The final edges should be sanded to
remove any splinters
 Be careful when cutting or sanding
composites, the material has very
sharp edges and makes toxic dust,
always wear proper breathing and
eye protection when trimming
Safety Precautions
1.
Wear a mask when working with resin and work in a well ventilated area. Working
outdoors on a warm day is the best option. Be sure not to work in an area where others
may be effected by the fumes of the resin.
2.
Resin can “cook off” if it is left in the cup too long. This is due to the fact that a higher
volume causes more reactions and a more exponential runaway of the chemical
reaction. This reaction can reach 300F and cause burns or damage. If this occurs, put the
cup into a well ventilated area immediately away from other people or objects.
3.
Fibers can cause rash or skin discomfort. Wear gloves when handling large amounts of
material. Do not get material in contact with face, eyes or soft tissue.
4.
Wear a mask when sanding or trimming composites. Composite dust is especially
dangerous since it is so fine. Sanding or trimming can cause dust to get into the air,
lungs, and eyes. Be sure to sand in a well ventilated area away from other people.
Carbon dust is also conductive and will cause electronics to short out. Kevlar materials
are especially tough and can overheat and destroy power drilling and cutting tools. Be
sure to have proper cutting bits and blades for composites. When drilling composites, be
sure to clamp down parts so that they cannot get caught in a drill and begin spinning.
Process Overview
1.
Gather prep materials: scissors, painters tape, release agent
2.
Prepare mold surface: mold tool sealed or a permanent plug sanded
1.
Optional vacuum bagging materials: plastic film, peel ply (breather), bleeder cloth, sealant tape,
suction ports (frogs), vacuum line, vacuum gauge, vacuum pump
3.
Cut fiber to size: woven sheet, filament tow, braided sock, etc.
4.
Gather mixing materials: Mixing materials: cups, stir sticks, gloves, mask, cleaning
agents, brushes
5.
Mix matrix: polyester resin, vinylester resin, epoxy, etc.
6.
Apply fibers and resin to mold surface, ensure complete wet out
7.
Allow matrix to cure per manufacturers instructions
1.
Apply vacuum bag for lower weight final product
8.
Remove part from mold using rubber or plastic shims
9.
Trim part with proper rotary tools, be sure to use a mask and proper ventilation
Resources
Questions
Project 1 – Light Switch Plates
 Thermoform a light switch plate
 Be sure to cover the holes with tape or clay
 Leave witness marks to make trimming easier
 Use the thermoform as a tool for layup
 Use one ply of carbon and one ply of glass
 Vacuum bag all the plate covers in one envelope bag
 Use the Blacktoe CNC router to trim the holes
 A jig may be used to locate the hole centers and make the process go faster
Project 2 – Wine Bottle Holder
 Lay carbon up carbon ply on the convexed surface
 Add class plys for strength if needed
 Place the core on the center of the convexed surface
 Add glass plys for strength if needed
 Cover with carbon ply
 Peel ply the bag side
 Vacuum bag
 Demold and trim
 Clear coat the bag side for gloss finish

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