PROBLEM I want to manufacture cheaper and lighter replicas. SOLUTION By using rotational molding we can replicate plastic pieces a lot of times using less material than other molding techniques. I found rotational molding a cheaper way to replicate things.
work-plan
you can review the machine design week assignment clicking here you can review the 2d design week assignment clicking here
ABOUT ME
OPTIONS RESEARCH
After a fast research i found a lot of rotomolding machines prototypes. I found that the easiest way to do the mechanism is using two square frames mechanically conected by a pinion and an axle. who's done what beforehand?: there is a rotational molding machine from the 2015 fabacademy made by saverio silli i like the circular design but the frame was small for the things that we want to cast in the fablab so i decided to make my own version. you can review the saverio silli web page clicking here 1.- design the frames according to the size of the mold chosen. 2.- look for the motor that will move the machine and the axle 3.- design the pinion according to the size of the motor axle and the transmission axle 4.- look for the bearings 4.- build the machine 5.- design the control (electronics) 6.- build the electronics 7.- test the machine 8.- design a mold 9.- look for the best material to use (for now i choose resin) 10.- test the molding process sketch
before i build anything i made a 3D dsign of the machine in solid works I START BY SOLDERING THE FRAMES WITH ELECTRIC WELDING
i make the design of the gears ans supports for the axles in auto cad to laser cut the metal sheet you can download the design in .dxf format by clicking here i send the file to my fabacademy classmate eduardo ramirez from fablabdf to laser cut the file in his metal laser cuter machine you can follow the fabacademy project of eduardo and see what he do in fablab df clicking here I CONTINUE WELDING THE LASERCUT METAL PARTS WITH THEIR RESPECTIVE AXLES
the next step is making the bearing holders. i tried different methods to test the size and the design fit i laser cut in mdf the bearing holder using layers and gluing it it work but obviously the mdf isn't hard enough. I 3d printed the model but the 3d print isn't accurate enough so the bearing didn't fit even if the design had the right measures as it was a simple design i decided to make an mdf mold gluing layers and test if it work. even if it was a hard/hard mold it work but the simple resin was very fragile and it broke. i test with resin plus calcite charge in two different concentrations to find the right resistance of the material and i laser cut the mold 6 times to prepare the mix once and all the bearing holder had the same resistance and mechanical properties.
you can download the dxf design of the pieces of the mold clicking here you an review the molding and casting week assignment clicking here the next step was to 3D print the pinions. i use the 3D design i did the week 2 assignment i just had to change the drill hole to fit the axle diameter
the next step was to extract the shapes of the structure from the 3D model, cut it in the cnc router and assemble it
you can download the dxf file with the design of the structure clicking here after i assemble the structure i design and laser cut in mdf the case for the electronics and motor you can download the dxf file with the case design clicking here now that i have most of the makable parts done,i decided to work with the parts that i buy. i drill holes rough the internal frame to put the elastic bands and make the fixing net i did maintenance to the motor and the bicycle chain that were used parts to ensure its smooth operation in my machine and avoid damages in the new parts. after i get all the mechanical parts i decided to assemble the mechanism and test it with a variable power supply holding the motor with a C clamp. in this step i noticed that the gears and pinion were adding to much weight to one side of the external frame so i tape pieces of metal to balace the frame.
when i see the mechanism work i fixed the motor with omega screw-in clamps , i welded good measured rectangular hollow sections i paint the frames and i started with the design of the electronics. i will separate the electronic boars in 4 parts communication (the bluethoot module) inputs (effect hall sensor) outputs (mosfet transistor circuit to drive the motor with pwm ) control (mother board that will connect every module )
once i solder all the boards i test the control board with the program that will control the machine and i install the hall sensor board with the magnets in the motor axle. you can download a zip file with all the boards that i did clicking here this is the code for the mother board so we will just send numbers to select the speed and turn off the machine. #include <SoftwareSerial.h> SoftwareSerial mySerial(1,2); char c; void setup() { mySerial.begin(9600); mySerial.println("conected"); pinMode(7, OUTPUT); } void loop() { if (mySerial.available()) { c=mySerial.read(); switch(c) { /////////////speed1 case'1': mySerial.println("Speed1"); analogWrite(7, 70 ); break; /////////////speed2 case'2': mySerial.println("Speed2"); analogWrite(7, 90 ); break; case'3': mySerial.println("Speed3"); analogWrite(7, 110); break; case'4': mySerial.println("OFF"); analogWrite(7, 0); break; } } } i test the program with a blue-tooth terminal app that conects to the bluetooth module and sends anything we write in the terminal to the micro controller once it works with the app that sends trough the blue-tooth connection i program an app inventor app that will send the same numbers using buttons in a friendly interface once it works with the ayou can download the apk file clicking here
this was a test with all working together now i will show you tests that i did using the rotational molding machine with different materials and speeds.
the next step that i want to take is to improve the quality of the resin copies. i will make the silicon ruber mold in a vacuum chamber to extract all the bubbles also i want to work more in the app and the arduino code to make the process automatic using a timer and adjusting the speed by a slider i want to continue trying with chocolate so i will buy the apropiate silicon ruber for food. and for the celebration of dia de muertos in mexico in november 2 i want to make a complex shape chocolate skull like the ones that the artisans sell in this celebrartion. this is the Bill Of Materials
i hope all the people that follow my fab academy assignments and final project enjoy as much as i do all the process. also i want to thank all the people that help me and gave me tips like: oliver ochoa eduardo ramirez oscar velazquez rolando maroño octavio muñoz luis camacho huber girón mariano jesús
ASSIGNMENTS
FINAL PROJECT video presentation 3d machine design
you can review the week 2 asignemet clicking here
i clean and lubricate the used parts with wd40
FINAL PROJECT
CONTACT
Carlos Pérez Ramírez