Composites
Design
I have used onshape for designing the workpiece for composites.
Mill Mold
Modella player is used to make the toolpath,the steps taken to make the toolpath are shown below.
Step 1
Open the model in modella player and choose the face to be milled as shown in the figure below.
Step 2
Select the origin
Step 3
Choose the type of process either roughing or finishing
Step 4
Select the tool diameter
Step 5
Set the cutting parameters as shown in figure below.
The completed toolpath is shown below.
Finished product
Preapring Composites
I used plastic tape as release agent.
Then i applied one layer of polyester resin. Polyester resin is being prepared using MEKP catalyst and cobalt. From the specification sheet 250ml resing requires 15ml mekp and two drops of cobalt.
Then next layer is of glass fibre mat infused in resin in regtangular patches.
Then i applied two more layers of the same to fill the crease area of first layer.
Compaction
To compress the layers sand bag is used.
(1)Take a empty plastic bag.
(2)Place a thin sheet of plastic on your test coupon.
(3)Spread the plastic bag uniformly on the work piece and start pouring the sand in the bag.
(4)While pouring the sand keep noticing that it should be uniformly spread over the entire work area.
Final Product
The final composite which is used as lamp shade is shown below.
Observations
The strength of the composite is good.
The finishing of the composite was not good.
It tool more than 5 days to become dry.
Safety Instruction
Click here to find the safety instruction for polyester resin
Click here to find the technical data sheet for polyester resin
Learning from TDS
Shelf life of polyester resin is 6 months when properly stored.
Geltime is 20-27 mins at rrom temperature (@ 25 degree C), whereas it decreses to 3.5-4.5 mins at elevated temperature (tested @ 60 degree C)
Compression Process.
Below below you can find the steps followed for preparing test panel to demonstrate compression composites technique.For a good composite it is necessary to maintain good resin to fibre ratio and thats the reason we use compression tecquinues.
STEP 1: First i have taken two plywood boards, jute cloth and cotton cloth.
STEP 2: Now apply the realeasing agent on the plywood, in my case i used thin plastic sheet.
STEP 3: Prepare the mixuture by taking part A (159.6226 grams) and 80 grams of Part B (50% of Part A).
STEP 4: We used epoxy resin and jute cloth for fibre. Then we soaked each layer of cotton,jute in the epoxy resin for fibre and place them layer by layer as shown below.Put other plyboard on top of it and press it tightly to squeeze the extra resin put.
STEP 5: Now, for compacting the mixture. I layed out a big plastic bag with little sand in it over the composite. This way the weight of the sand compresses the composite allowing extra resin to seep out, as shown below.
Final Output
The composite plate came out very strong after drying for 2 days.
Observations-As it was a simple enough mold the composite conformed to mold closely. There was a very gentle curve in mold hence it might be easy to spot how well the composite conformed to the mold. Compaction allowed exess resin to flow out and gave optimal height for the composite of 3mm. There was no air bubbles in the composite and it came out uniform. The material came out rigid and thin. It was bendable but retained it's shape.
Comparison with natural fiber, epoxy composite.
The jute soaked much more resin and epoxy was much less viscous as compared to polyester resin. Jute was widely spaced and was thick as compared to glass fibre mat and it might not have allowed better fiber to resin ratio even with compression molding.
