COMPOSITES


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ASSIGNMENT


Design and fabricate a 3D mold and produce a fiber composite part in it.

COMPOSITES


A composite is made from combining two materials with differing chemical properties to produce a material with different characteristics.

In this assignment I will be using fiberglass, a fibre-reinforced polymer which offers particular material properties in terms of weight, surface quality, thermal and tensile/compressive strength.

MOLD DESIGN AND CAM


I decided to design a skull mask.

First, create a cube and a sculp form.

Create a symmetry line using the symmetry option in the tool menu.

Sculp tool-pane allows to easily manipulate the object by modifying faces and edges.

To create the eyes, select the face divisions and create sub-divisions.

Fusion 360 will automatically create subdivisions on the other side of the symmetry line as well.

Use similar procedure to create the nose and the mouth.

The sculp tool allows to modify edges and corners. Use this feature to create the outlines.

Last step is to resize the design, I extrude the cube and resize the skull to fit a foam cube of (200x200x80)mm

Next, go to Fusion360's CAM mode.

As I plan to use a cloth to cover the design and then glassfiber, I would only need a roughcut.

Set up a new job by choosing the right coordinate orientation. This step is very important as doing it wrong is not only dangerous but will definitely waste time and material.

After setting the coordinate system, carefully measure the stock material and insert the values in the corresponding fields..

Next, after the set-up is ready - create a new 3D adaptive milling job.

Create the tools in Fusion 360 by carefully measuring the parameters needed for the tool holder and milling tip.

Below, I created a new tool for the milling tip and for the tool holder.

Next, select the parameters for the cut.

Choose the pass tolerance and stepdown.

Simulate the cut and make sure there are no collisions.

Finally, use the post-processor to export the milling design's g-code. In my case, I use a plugin for the elsign CNC machine.

Design is ready to mill.

MILLING


Easy Worker MasterPro 2513 is used to mill the design.

The device's maximum speed is 19,000 mm/min and the working area is of (2600x1400x300)mm

Elsign CNC is the proprietary software of the machine, it supports Gcode and HPGL.

First, I cut the cube according to the dimensions set in the CAM parameters (i.e. 200x200x80mm).

First, the foam cube is fixed on a piece of scrap material with double-sided tape and carefully positioned on the vacuum bed.

Home is set for the milling machine, as well as the z-position.

Paremeters are triple-checked and the job is launched.

Final piece look as follows - not the best of rough cuts. It could be greatly improved with a finishing cut with a ball-end mill. However, it was not necessary for my final design.

Next, I put 3 layers of silicone spray before laying out the cloth and glassfiber on the mold.

Note: As natural fiber is to be used as the base material for the layering process, the milled piece does not need a finishing mill as the cloth layer itself is thick enough to provide the slopes at different places.

FINISHING THE COMPOSITE


Epoxy resin used and epoxy hardener information can be found here and here.

The epoxy resin used cures at room temperature and has a processing time of about 2 hours.

Mixing ratio was 100:30, further details are found in the datasheet, I used the hardener B1:

Next after mixing the two components, layers of glass fiber were cut carefully with protective gloves and layed alternatively with natural fiber.

The mold and fiber layers is later put inside a vacuum machine, for the curing time.

After curing this is the result:

The result was not satisfactory, the foam mold is completely attached to the fiber and some fiber layers did not cure as expected; however the material strength increased as expected and it partly took the shape of the skull design.

OTHER CONSIDERATIONS


Fabric layering process: Four layers are alternately layered on top of the milled piece - one natural layer and one fiber glass layer

Amount of resin: Three of us worked together on their pieces. We prepared approximately two batches of 500ml of Epoxy resin 3321 with its respectivehardener B1 of 150ml.

Measurements: Measurements for the fabric layers were done by laying a bigger piece and cutting with scissors and protective gloves. Similarly, resin amounts were weighted carefully on a protective cup.

Vacuum: The machine, Columbus Combitherm, is easily operable. First the workpiece is placed in the machine table, the membrane frame is closed and the vacuum pump is turned on so the pressing process starts. The piece was left overnight inside the vacuum machine. A protective cloth is put on top during the process.

Picture below, shows the vacuum machine. The green square denotes the locking mechanism and the red square the control panel.

To activate the pump, the handle is simply moved to on.

How can the process be improved for the future? More care should be placed while laying the fabrics. I perhaps should have worked on the piece more slowly to obtain better results. Additionally, using only one type of fabric is more recommended than using two types.

LESSONS LEARNED


This assignment was a great first time experience in experimenting the creation of composite materials. I learned that when using natural fibers, even though the roughness of the milling cut does not have to be necessarily super smooth, it helps if the depth of detail is higher.

Additionally, when laying the layers of glass fiber and natural fiber and mixing them with the epoxy and hardener mixture; it is important to do it slowly and patiently. The time to prepare the materials should follow the amount of detail and quality of the finished product is aimed for.

I will try in the future again to create a composite, this time I will not make the same mistakes as this week. Overall, a great experience.

FILES


SKULL DESIGN

RESOURCES


Bolton guide to composites


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