What are composite ?
Composites is a material made from two or more constituent elements with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. The individual parts remain separate and distinct within the finished structure. Details from Wikipedia
Plywood is bes example of composite, we all are this matrial during shopbot week. Plywood is manufactured from sheets of cross-laminated veneer and bonded under heat and pressure with durable, moisture-resistant adhesives. By alternating the grain direction of the veneers from layer to layer, or “cross-orienting”, panel strength and stiffness in both directions are maximized. Details from Wikipedia
For knowing ore about composite and varies ways of manufacturing refer the compositelab
Composites are made using two types of mateials, Matrix and Reinforcements.Reinforcement provides strength and stiffness. Reinforcement usually adds rigidity and greatly impedes crack propagation. Thin fibers can have very high strength, and provided they are mechanically well attached to the matrix they can greatly improve the composite's overall properties.Mainly used materials for reinforcement are carbon fiber, glass, aramid, burlap, cotton cloth etc. Matrix protects the reinforcement material from environmental and external damage and transfers the load between them.
For making the composite, we have two type of material, in our lab epoxy and Matrix as cotton and Burlap. The epoxy material in our lab is transparency on with two parts partA and Part B.Mix part with Part B as the ratio of 100:50. First, we test run some various combination of composites. We took three layers of Burlap and two pieces of linen cloth for making each test pieces.
The strength of the composite depends on the alignment between the arrangement of various layers of matrix. Alignment means the way we oriented the layers one over other. We are going to make 3 test pieces using linen and burlap
First test piece in which two layers of linen is arranged at 90 degrees and three layers of burlap is arranged 45 degrees. Second pieces Two layers of Linen having an angle 90 degree and the middle layer of burlap having 45 degree and other two layers with 90 degrees. The third consists of Two layers of Linen having an angle of 90 degrees and three layers of Jute having 90 degrees. Here in all test processes which linen is placed top and bottom and burlap is on the middle
We took a cup and poured Easy Cast Epoxy parT A and PartB of ratio 100:50 and mixed well. Next, we use protective gloves and goggles. , soak the matrix material in the reinforcement we made and arrange them as shown above
Kept these for 24 hours and then we took the parts and checked the strength and finally found that Two layers of Linen having an angle 90 degree and three layer of burlap having 45 degrees has more strength among the three. Placing Matrix in 45 degrees gives the excellent power which transfers the load to all parts effectively.
Completing the test composite making next I need to make my composite structure; I plan to make a small lunch plate for children. Now I am familiarised in fusion 360, so I decided to go with fusion for 3D modelling the Lunch plate
After opening fusion 360 I just draw a rectangle of 110mm, and then perform the revolve function.It creates a solid cylinder.This is the base of my plate.
Next give some slots in lunch plate to hold the food, so I used Line tool and arc to draw the same. After drawing excrude the shape forms two slots on the plate /p>
Next we need to create the side wall so i draw the sketch and again perform the revolve function.So my plate creates a small side which have a small angle not in 90 degree
After completing the 3D design next, I need to make the mould using shopbot. The first step is to find the material for forming this, in our lab, we have only 18mm plywood. My design has a depth of 25mm, so I found two waste pieces of 18mm plywood, take them and join together with the help of the wood adhesive. Vishnu also helps me to make that thing, I also use some nails on the corner of the plywood and kept it for 3 hours to join the two pieces. After three hours matrial for making mould is ready.I was the first on starting the shopbot for this week, so I need to go it fastly because others are waiting for me to complete
Here I am using two pieces of plywood stuck together by wood addition, so we need to be careful while placing this on the shopbot bed. Put the material on the bed and use screws to fix it with bed and check that if any loose fittings or vibrations occur it ended with break the end mill. I downloaded.STL file from fusion 360. Like V curve software shopbot also have another software named part3D for making the mould. In part 3D software, we need to do six stages to complete the G-Code generation
Mould making using shopbot goes with two stages Rough cutting and Finish cutting. The rough cutting machine only removes the parts and make the first shape of our mould, and in finish cutting, it makes the original smooth model of our mould.Open the .stl and choose the top part, Model size, and units as mm. Then we give the starting position (origin for me, I set it as the centre part so that I can check if the bit goes beyond the material or not, trail run). After that, I choose the roughing toolpath her select the endmill from 6mm, Spindle speed of 14000rpm ( rotational frequency of the spindle of the machine, measured in revolutions per minute (RPM)), the feed rate of 40 mm per minute( distance travelled by the tool in one complete spindle revolution), pass depth of 2.5mm (is the depth of cut in each pass). And stepover of 3mm( it means the overlapping the cutting area in the previous move).Details from Wikipedia
Initially, the rough cutting toolpath is to be path calculated and goes next option for finishing toolpath. For finishing gave a step over as 0.3mm, spindle speed of 12000rpm, the feed rate of 30.After providing data and then calculate the toolpath. Then save the g-code for rough and finish separately. We are plan to use the same bit for rough cutting and finish cutting for save the time.
Next, I set the zero axis manually in shopbot and then is start with rough cut it takes around 1 hour and after that, I go with finish cutting. After 3hours all my Moldmaking for this week is complete.
After performing the finishing cut now got a perfect 3d mould of the plate, the First step of composite making is applying to release agents to mould. The release agent is a chemical used to prevent other materials from bonding to surfaces. Release agents provide the critical barrier between a moulding surface and the substrate, facilitating separation of the cured part from the mould. Without such a restriction in place, the substrate would become fused to the mould surface, resulting in difficult clean-up and dramatic loss in production efficiency. There is a wide variety of releasing agents mainly wax, silicone solvents, plastic sheets etc. Here we are using cello tape as the releasing agents who stuck over the surface and create a separation layer between composite and mould. While using cello tape as the separation layer ensure a clean finish any bulgy or overlap will affect finishing of the composite.
Details from Wikipedia
Next step is getting materials ready for putting into the mould I made this week. I plan to use linen cloth as the fabric material and an epoxy resin. I cut three pieces of cotton cloth. Nearly equal to the size of my mould. I along with Akhil is making composite at the same time so what we have done is making the resin jointly. In our lab, we have Easy Cast epoxy 33 an epoxy resin. It has two parts part A and Part B, mixed in a ratio of 100:50. We took 150 gram of part A and 76 gram of part B, mixed it well, and made the resin.
I put safety glove and mixed the resign well. The resin is exothermic and will start to get hot after mixing. After mixing I first painted the mold with resin and then put cotton over there then again painted with resin and again place the cotton over that.I used three layers of cotton to make this.
I layered the epoxy resin using painting method, first I place the cotton cloth and painted over it by epoxy.then using my hands pressed everything together to make sure I removed all the air bubbles.
After completing the composite making, I made a vacuum bag and place the mold in that, use a vacuum pump to create the vacuum inside that. It helped to make the cotton and resign tight to mold. After that, I seal the material put below some weight.
I then left the mold to cure overnight under the weight.The next day I came and take out the mold and pried open my mold, it's hard to take from that.The part came out beautifully. The surface finish is good. but some trimming is required. so I used a handsaw to cut the unwanted parts and make it good.
Its hard to take out my part from mould because if forget to consider draftangle while design the mould, To release the part from the mould, we need to consider some design parameter" Draft Angle". This is the angle of the sides of the mould compared to its base mould with zero drafts has flat sides perpendicular to the bottom. On a mould with the positive draft, the sides are wider at the top than they are at the base. Parts will easily pop out of moulds with positive draft. The sides of a mould with negative draft are tighter at the top than at the bottom. For obvious reasons, parts are impossible to remove from a mould with the negative draft. Shapes which have to be moulded with negative draft must be made in multiple-piece moulds. Draft angles greatly reduce friction between the finished, cooled part and the side of the mould.Draft angle Reduces the chance of damage to the part due to friction during release and Reduces wear and tear and chances of damage to the mold.general guidelines:Are below
what I would do differently next time.
Lots of information got from this week. Before this week I don't know how to make the composite, even I don't think about that. After making my plate using composite, Weight of the plate is decidedly less but its super hard. I am interested in making quadcopter, for making it we need a frame, its weight is high. What I think is design a model in fusion 360 and build a structure using carbon fibre as the matrix. So we can get a reasonable frame with less weight.