Die casting began as a way to make printing type
The machines that now stamp out car parts and appliance housings trace back to 1838, when die casting was invented to produce movable type for printers. By forcing molten metal into steel moulds under high pressure, it turned intricate metal parts from costly handwork into something factories could churn out cheaply.
The process uses two hardened steel dies, machined to shape, that close together like the halves of an injection mould. Molten metal is driven into the cavity, cools, and the casting is pushed out by pins in one half, called the ejector die. Equipment and dies are expensive, so the method pays off mainly for large production runs, but with only four basic steps the cost of each extra part stays low.
Printing drove the early history. The first related patent, in 1849, covered a small hand-cranked machine for making type. In 1885 Ottmar Mergenthaler's Linotype machine cast an entire line of text as one piece, and it almost entirely replaced setting type by hand. The Soss machine, made in Brooklyn, became the first die-casting machine sold on the open market in North America, and cheap intricate parts soon fed the spread of consumer goods and household appliances.
Most castings use metals other than iron. Zinc is the easiest to cast and keeps dies lasting long; aluminium is light and handles thin walls and complicated shapes; magnesium is the lightest common choice and the easiest to machine; copper alloys are the hardest and strongest, approaching steel. Lead and tin give very precise dimensions but are kept out of anything that touches food.
Designers add a slight taper, called draft, so parts slide free of the die, round off sharp corners, and use ribs to add strength without thicker walls. Hot-chamber machines draw metal from a pool through a gooseneck, while alloys such as aluminium are melted separately and ladled into cold-chamber machines. As of 2008, aluminium castings were thought to top out around 32 kilograms, but by late 2019 giant presses were making single aluminium chassis pieces weighing over 100 kilograms.
Source: Die casting
