Emo Rubik, a professor at the University of Budapest in Hungary, designed the now famous Rubik’s Cube in the mid-1970’s. It is made up of 26 smaller cubes and has six faces, each made up of nine different colors: red, yellow, blue, white, green and orange. His intention in designing it was to demonstrate to his students three-dimensional relationships. When he showed the prototype to his students, it was an instant hit not so much as a teaching tool but as a game.
The parts of the cube are manufactured through injection molding of thermoplastics. Each component will either be an edge, a corner or a center piece. The cubes are then assembled, labeled, and packaged. The design of the mold for each piece is crucial for the smooth operation of the cube. In the injection molding process, liquid plastic is shot into the mold and, when it cools, it takes on the shape of the mold. The mold is designed to precise tolerances. In fact, the cavities are highly polished to eliminate any flaws on the surface. The parts are then hand inspected to remove any defects. A two piece mold is typically employed. The molds are produced with a slight draft called a release angle so the parts can be readily removed. Finally the molds are designed to take into consideration the shrinkage of the plastic they are made from. Most plastics will shrink a little as they cool. One well known exception is nylon which is hydrophobic and tends to swell as it absorbs a little water after molding. However, most molds are slightly bigger than the pieces that they ultimately produce. The cube is then assembled and colored stickers are affixed to it. Each side of the cube is one of six colors. The Rubik’s cube has red, yellow, blue, green, white, and orange colors. In its solved state, each color is on only one face. When the cube is rotated, the edges and corners move and the cube becomes scrambled.
The plastics used in the Rubik’s cube are acrylonitrile butadiene styrene (ABS) and nylon. Other plastics that might be used include polypropylene (PP), high impact polystyrene (HIPS), and high density polyethylene (HDPE). The pieces of the Rubik’s Cube are molded in black. Colored stickers made of polypropylene are affixed to each side to denote the color of the side. It is a good choice as human hands tend to be somewhat acidic and the polypropylene prevents degradation of the colored stickers. Additionally, polypropylene takes color well and can be easily extruded into a film. The excess plastic from the process could be reused by regrinding but reground plastics often degrade, resulting in poor quality parts. Rubik’s Cubes are always made from virgin materials.
Ok, here’s what you have been waiting for…what are the tricks to solving it? It is not just a cube with approximately 43 quintillion possible arrangements but only one solution. There are some rules. The commercial cube is composed of six fixed cubes, eight movable cubes on the corners and 12 movable cubes on the edges. The center cubes are each fixed and only rotate in place. While it appears that all of the small faces can be moved, only the corners and edges can actually move. When the cube is taken apart (see left) it can be seen that the center cubes are each connected by axles to an inner core and each of the six axis of the core have springs in them to facilitate the smooth movement of the cube. The corners and edges are not fixed to anything. In other words, there are limitations to how the cube can move. As we know each of the nine faces on the current Rubik’s Cubes are covered by stickers. When solved the white side is opposite yellow, blue is opposite green, orange is opposite red and the red, white and blue faces are arranged in that order in a clockwise rotation. To see someone actually demonstrate the solution, check out Youtube.
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