We decided our senior year of high school to do something
fun for our first semester engineering project. The two of us decided to design and build Kevlar armor plates scaled to our bodies. Over the course of 18 weeks we designed, built and refined our armor plates using several processes including vacuum-forming composites and CNC routing from CAD design on a large scale.
Over the course of this Instructables, we will show you two slightly different approaches to producing Body armor plates with end results differing upon the number layers used.
WARNING: This process requires a large amount of Kevlar weave and access to several large and expensive tools and machines.
THIS WILL NOT MAKE YOU SUPERMAN: This process will not make you bullet-proof armor. A more appropriate term is bullet resistant. More than one direct hit to a plate will pierce through and there are far too many armor chinks for the overall product to be practical. Please do not get shot by anything: Arrows, Guns, Tasers, etc.
Step 1: Gathering of Materials
What you will need:
Several Dozen feet of Kevlar Prepreg (Resin already in Fabric)
Measuring tape or implement
Rivet Gun and Rivets
High Quality Composite Scissors
Silver Sharpie or other High Contrast Marker
Drill and ¼ Drill bit(s)
¼ Carbide End Mill (Router Compatible)
CNC Routing Machine
CAD Software compatible computer
Carbon-fiber cutting Band Saw
3.5 square feet of Carbon Fiber Prepreg (Resin already in fabric)
1/8-1/4 Machine Rivets of various lengths
Motor-Driven Fan Shop Vacuum.
Water-resistant Spray Paint
Finishing Sealant Spray Paint
Heavy Duty Long Sleeve Shirt
Step 2: Measuring
Use your measuring implement and take measurements according
the diagram above. This is crucial for creating a complete armor plate set-up that not only fits your torso proportionally, but also produces a design aesthetically pleasing to the eye.
For the front measure the collar bone length, the width of
the torso at the middle and bottom of pectoral muscle. Measure the width of your desired abdominal plating directly below the ribs and at belt level.
Next Measure the height of your torso and the height of the pectoral muscle. Lastly measure from the bottom of the ribs to belt level.
For the back measure the Shoulder width, Width from middle and bottom of scapula. Additionally measure the width of back on the belt line.
With these measurement you should be able to affectively design a CAD drawing for your plating.
Step 3: CAD Creation Part 1
Create a new file in your software in the units of whatever unit you used during measurement. For our project we used the CAD software Rhino and inches. By using the given measurements (and then dividing them in half for one side) you should end up with an image similar to this.
Step 4: CAD Creation Part 2
This series of line represent the various curves of your body that the plates have to protect. In order to build armor plating that is effective it is important to remember the basic shapes of your body, i.e. more of an oval shape for your pectoral plates and more of a curved rectangle for your abdomen plates. One of us took a more angular shape to the plates while the other had armor plates that flowed with more curves and less angles. Here are the two separate results. After you are happy with your finished product, remove the width lines and you will be left will a sketch like the ones above. Then proceed to mirror the design across the midline which gives you a complete set of identical plates for the left and right sides of the body.
Next add lines for stablization on your design. Here they are depicated in red. This connects the plates together and allows them to not be ruined or removed during the process of routing it out of the kevlar. In additon you will leave your thinner interior piece in almost this fashion post-routing in contrast to your thicker plates which you will cut out and seperate from each otehr entirely.
The next step is saving your file as a STL and then post-process it to the G-Code software associated with your CNC Router: ours uses V-Carve. After transitioning the software and selecting the cutting appropriate toolpaths, you are ready to cut out your part.
Step 5: Compostites Layup Setup
The first step of the composite layup is to cut the sheets of Kevlar into usable rectangles. You’ll want the rectangles similar in size to your measurements that you took of the front of your torso, however make sure to add some space for error when cutting.
For the chest plates we first cut 20 layers of Kevlar, however this proved to be significantly thicker than we would’ve hoped. On the second version of the chest plated we cut 5 sheets for both the inner and outer plates.
After cutting out the sheets it is time to start the layup process: get an aluminum plate that will fit all the components you have cut out but will also fit in your oven. Make sure the entire surface of the plate is clean and then, leaving a 1 inch border clear of solution, coat the entire plate in a release agent (Free Coat or Wax). A good way to make sure your border stays clear is using making tape over the area you would like to remain uncoated. Use 3 coats of the non-bonding solution in order to assure no gaps in coverage.
Step 6: Composites Layup Prep.
Now you’re ready to put your sheets of Kevlar onto the aluminum plate. Make sure to remove the protective film from every layer of Kevlar, it will be on both sides. An efficient method we found was to use a box cutter at a slight angle but relatively parallel to the sheet, making a slight incision on the protective layering but not damaging the Kevlar sheet.
Make sure the plates are spaced in a way that the suction plugs have adequate distance from the center of each plate. For a small plate only about 2 or 3 plugs will be necessary however with plates bigger than 6.5 sq ft use 5 or more. Secure each plug to the plate with Teflon tape but be careful to not interfere with the seal of the plug.
Step 7: Composites Layup Final Check
After laying all the Kevlar sheets on top of one another cut a sheet of perforated heat resistant paper that fits on the sheet while clearing the border you made earlier with the masking tape. Cut holes out in the plastic where the plugs are in order to assure a good seal. Make sure the entire circular surface of the plugs is clear of any plastic covering. After you are satisfied with the coverage of your plastic film it is time to add some sort of wick on top of the film. Using a thick absorbent sheet made of cotton works well as well as a fiberglass pad that fit the size of the plate. Since the Kevlar we used had a very high epoxy content, using cotton is highly suggested. Make sure to cut the same holes in this pad as you did in the perforated plastic covering. The final layer of covering will be an airtight heat resistant plastic covering. Remove the masking tape from the border of your plate and lay down mastic in order to secure the covering to the plate.
After making sure every inch of the border is covered by mastic you are ready to secure your covering to it. Cut out a piece of the heat resistant film that covers the entirety of your plate and place it onto your plate make sure the seal between the mastic and the covering and the seal between the mastic and the plate is completely airtight. Using some sort of smoothing tool will help lay the covering over the mastic to ensure a good seal. Cut very slight slits in the covering over the entry points of the suction plugs in order to secure the male end of the suction plugs to the female end. Secure the plugs. When it is finished it should look something like this. Test your layup to make sure it is air tight, using a vacuum attached to your suction plugs remove all air from the inside of your layup.
Review the second photo as layering guide
Step 8: Pressure and Cooking Your Plates
Add a pressure gage to one of the plugs in order to observe how well your layup stays airtight. After turning off the vacuum if the pressure gage drops quickly there is a leak in your layup and this must be fixed before putting your layup in the oven. If the pressure gage does not move or drops very slowly you have a good seal and you’re ready to put your layup in the oven.
Set the composite oven to its preset for composites or adjust for a 450 degrees cooking cycle. This requires you to do additional research into how to set the temperature for your specific composite oven brand. Make sure to have your vaccum sealing taking place addtionally inside the oven. Remove your gauge and replace it with another heat resistant vaccum tube.
Attach the end of each tube securely to the corropoding vaccum spout on the interior of the oven. Make sure to double check each tube's connection to the plugs on the plate inself.
Step 9: Cutting Out Your Plates
After your plate has been cooked and allowed adequate time
to cool, typically the remainder of the day you cooked it in, remove it from the oven and set in on a stable surface. Chisel or pry the slight bond your plate has made with the aluminum. If you applied enough non-bonding solution then it should come off with minimal effort. Take your two square plates of material to your router and affix one to the bed. We routed out the thinner internal plates first because they would be the easier plates to redo if an error occurred. What order you choose to cut the two plates is entirely up to you however. Load your file into the router and set your XYZ zeros for the program and load the ¼ Carbide Burr. For cutting we suggest continual vacuuming and setting the spindle speed to one in order to avoid smoking up your shop and/or melting the material. After you are finished your plates should look something like the picture below but following your design.
Next remove the supporting chucks between your plates carefully with a Band Saw. If you have a Carbon Fiber top plate then insure that your Band Saw has a Carbide blade and insure that your vacuum is fan cooled to insure you do not fry the engine with carbon flakes. After the plates have all been separated then sand the edges of your plates with a machine sander and then additionally refine the edge with sandpaper.
FOR THE THINNER INTERNAL PLATE
Cut down the plates so that it mimics a rib cage with all the plates still attached together in the middle like this.
This insures a consistent placement system for mounting your plates
You could stop here and have finished plates. The remainder of this Instructable details the mounting of the plate onto a shirt and the refinement of the plates’ appearance.
Step 10: Prepping Plates
After you have successfully removed your plates from each
other on the larger plate and have dealt with the thinner one as specified, prepare to drill and paint your plates. Space your holes evenly and cosmetically appealing. Either measure the exact spacing on the hole placement on both plates or clamp the plates securely together and drill them simultaneously. This insures uniform placement between both plates. Be sure to observe proper safety procedures for drilling through Kevlar.
After all holes are completed then next use your preferred color of spray paint on your plates (We used black to match our carbon fiber) and apply several coats on all exposed sides until you are satisfied. Next apply a weather sealant to preserve the color and plate integrity.
Step 11: Mounting and Riveting
Before you make any cutting into
your chosen shirt, overlay your inner plate on the outside of your shirt and use a marking implement such as a pen to mark all the hole placements on your plates onto your shirt with correct spacing. If you want a quality end product then this part is very important. Next poke a small hole at each marked spot with some sharp pointed object and place the inner plate on the inside of the shirt. Place a rivet in each hole with the brad facing upwards and lining each one up with its corresponding hole in the shirt. The line up the outer plates with the brads protruding from the shirt and use the rivet gun from inside the shirt to rivet the outer plates to the inner plates. After all of your plates are riveted together your armor is finished. Make sure no sharp edges or protruding pieces are present.
During this process we also produced back, oblique and forearm plates. We cut the shapes straight out of Kevlar weave and bi-passed the CNC router steps. If having back plates such as these appeal to you as well, make sure to follow the same steps but instead of cutting out rectangles in Kevlar
Step 12: Conclusion
We created this project, fun aside, for the purpose of lightweight protection while mountain biking. We frequently find when I bike on single-track trails that low lying branches often hit us on our shoulderblades and chest so we created armor with the intention of stopping the annoyance of such brusies while biking. One of us addtionally added strips of kevlar on the forearm aswell with the same purpose.
We enjoyed this process emensely and learned a lot about the various processes involved in the production of composite products and were able to implement our learning onto our successful product.