SHEET METAL PRESSINGS

Evening Star, Issue 25941, 5 November 1946, Page 10

SHEET METAL PRESSINGS

HIGH COST OF DIES

NEW METHOD USES HUBBER BLOCK

One of the. most expensive items, associated with the building of bodies for motor cars is- the extremely high cost of dies for sheet metal pressings. Such dies need to be very accurately made by highly-skilled craftsmen, and further skill is required to set up the dies in the actual press. Any slight error not only causes the resulting pressings to be inaccurately formed or actually torn, but may ruin the dies themselves, As much as 24 hours may be spent in setting up' the macliine. Most motorists are familiar with the normal principles of sheet metal pressings. If, for example, the intention is to make a pr essing / .the shape .of a saucer, two dies are used—one is a convex affair, which will exactly mate with the inside of the saucer, and the other is concave and corresponds to the under side. Obviously, one has only to insert a flat, blank of sheet metal between the two and apply sufficient’ pressure, and out comes a saucer-shaped pressing when the dies are separated. The expense of cutting dies and setting up a press is not an economic proposition where only a small number of articles is required. That is why some car manufacturers with relatively small outputs.still resort to hand-beating for body pamels, etc; The cost per car is high, but it is much less than would be the case were special i dies cut 1 and presses set up where only a small “■run 'is involved. ■ ' During the war, the need for • something between these, two methods became very Apparent: 1 in aircraft work. The result was to bring to the fore in Great Britain a type of: press of which comparatively little had been heard previously.. It has only one die, and instead of its counterpart, a mass of rubber is substituted. The result is exactly the same as pressing a : piece of silver paper on a penny with one’s thumb—the silver .paper .is left with an exact impression of the coin. For the penny- substitute the single! die employedthe silver paper corresponds with the blank of sheet metal and the thumb is the counterpart of the rubber. The real difference is one of degree. Just how great the degree may be gathered from the fact that a, press being used for rubber die pressing by a leading British ' car manufacturer is capable of exerting a pressure of 5,340 tons. One advantage, claimed for this system is that a number of single dies can be employed simultaneously—a 10inch thick rubber block, housed in the top of the hydraulic press, forcing blanks into their respective dies' under a pressure of 3J tons per square inch. Although originally developed, for soft metals such as aluminium, copper, and brass alloys, this siinnle system is now being used successfully in England for sheet steel up to 18 and 20 gauged It is of interest to mention that, during the war years, this {system of press work was used successfully in Australia for the rapid and accurate production of sheet metal parts needed, in relatively small quantities, for aircraft construction.