Mad about Science: Lego

By Brenden Bobby
Reader Columnist

LEGO bricks are an intergenerational phenomenon. They have been used by kids and adults alike for decades, and are such a powerful indicator of creativity and intelligence that they’re used as part of applications for certain engineering jobs.

It may surprise you to know that I was never a LEGO kid. I personally found them to be tedious and frustrating to assemble; but, regardless of my personal feelings toward LEGO, they’re a fascinating collision of science and culture and certainly worth exploring.

LEGO began as a company in 1932, founded by Ole Kirk Christiansen, a Danish carpenter and woodworker. Applying his trade, Christiansen built wooden toys in the wake of the Great Depression. By the mid 1940s, their focus had shifted to interlocking plastic bricks that would define the brand to this day.

These bricks are made of acrylonitrile butadiene styrene, or ABS. LEGO bricks are one of the prime examples of ABS, though it can also be used in 3-D printing, so long as the user is taking proper precautions and ventilating the area well, as the polymer produces toxic fumes when heated.

ABS is used by LEGO because of its permanence. It is a thermoplastic that isn’t prone to warping, even after years of use and exposure to a wide range of temperatures and environmental conditions. LEGO bricks made during the 1980s are still circulating in near-pristine condition among collectors today, and ABS is to thank for that.

LEGO bricks begin their journey as ABS pellets trucked into the LEGO factory in shipping containers that can transport up to 28 tons of plastic in a single load. The plastic pellets are deposited into massive silos that feed into the rest of the factory.

One of the first steps is to mix color pigments with the raw plastic. LEGO has very strict parameters and guidelines for what the color of each brick should be. These pigments are very thoroughly mixed with the plastic to create uniformity in color once they enter the injection molding machine.

Plastic is heated to 230 degrees Celsius inside of the machine and then injected into steel molds. Twenty-nine thousand pounds per square inch of pressure presses the molten plastic into its desired shape, and then the bricks are cooled over about 10 seconds before being released.

This forming creates a high level of precision and uniformity, allowing for each brick to fit exactly as it should to within 0.005 millimeters. Malformed or defective LEGO bricks are extremely rare.

Plastic injection molding like this is used at an industrial scale for almost any molded plastic. It works exceptionally well for detailed and exact parts, like Warhammer miniatures. An inexpensive quantity of plastic can be injected into a mold upward of 200,000 times before the mold needs to be replaced and recycled — at least for aluminum molds used in polystyrene injection molding.

LEGO uses steel molds, which can be used up to 15 million times before they are replaced. They carry a cost of between $20,000 and $150,000, depending on the complexity of the part. This certainly explains why LEGO sets are so darn expensive.

LEGO bricks undergo an intense quality assurance process. Optical sensors analyze each brick from every angle, scanning for everything from minute scratches to misalignments in the brick that would throw off the ability for the bricks to connect even slightly. Bricks that fail these tests are collected and ground back down into plastic pellets to begin the process all over again.

Bricks that pass are collected in bins. Once these bins are full, sensors are triggered to summon an AGV, or automated guided vehicle. This is a robot that collects full bins and replaces them with empty bins before transporting the finished LEGO bricks to a conveyor where the bin is scanned and added to a tracking database, allowing the staff to record exact quantities and locations of individual batches through the entire process.

LEGO Minifigs go through an extra stage of production than bricks. The faces and clothing details aren’t painted on, nor are they decals. Instead, they are fed through a machine that automatically picks up ink from an inkpad and stamps each piece. It’s a lot like your local librarian stamping due dates on your books, except these machines are capable of stamping thousands of Minifigs per minute.

The pieces are binned again and sent to a sorting facility within the factory — a massive warehouse with storage bins that reach up to 121 vertical feet. The batches are cross-referenced within the database for a specific production run, such as a Star Destroyer from Star Wars, and then those bins are automatically sorted by precise counting machines to batch the pieces together and fit them into bags. Up until this point, the entire process has been completely automated.

During final sorting, humans package the bagged parts and instructions and prepare them for distribution. This is the final stage of quality control, ensuring that everything that needs to end up in the consumer’s hands shows up in the box. During peak production, the factory can complete up to 50,000 boxes in a 24-hour window.

Distribution from that point onward is a massive endeavor and worthy of its own article, provided that article’s writer could sum up global logistical chains in fewer than 900 words.  

Stay curious, 7B.