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/lp/emerald-publishing/the-manufacture-of-alloy-stampings-Q901wRClc0
- Publisher
- Emerald Publishing
- Copyright
- Copyright © Emerald Group Publishing Limited
- ISSN
- 0002-2667
- DOI
- 10.1108/eb030061
- Publisher site
- See Article on Publisher Site
Abstract
June, 1936 AIRCRAFT ENGINEERIN G 175 Th e Production of Stampings for Crankcases, Pistons, Connecting Rods and Airscrew Blades H E increasing demand for the mass screws and crankcases, weigh five tons or more After inspection, the impressions are, if production of light but strong articles each and are valued at £1,000 a pair, the cost possible, filled with molten lead, which is well t o very close limits has caused a big of the steel alone running into many hundreds hammered down to fill up every corner. This advance in the technique of drop stamping, of pounds. These dies take five to six weeks is sent to the customer for approval before which is rapidly replacing casting in the manu to complete. The making of the dies calls puttin g the dies into use, but for larger work facture of aero-engine parts. Crankcases, for great skill on the part of machine men, i t is necessary actually to make a sample pistons, connecting rods and airscrews, to usually die millers, who cut out the shape in stamping before production is started. mention bu t a few items, are now made in the th e steel blocks. The design is carefully marked When finally passed for use, the dies are stam p shop, as the metal is more uniform on to the die, which is then placed on a milling take n to the stamp shop where they are fixed in structure and free from blow holes, hard machine, where the operator carves the shape in the drop stamps. These massive hammers spots or cavities. Machining is reduced to ou t of the solid metal, all vertical faces being consist of a very heavy anvil, or base, to which th e minimum, the direction of the grain can given a slight taper of 3 to 7 deg. to facilitate th e bottom die is fixed, and a movable "tup, " be controlled, and waste material, an important th e withdrawal of the hot stamping. Without t o which is fastened the top die, capable of being item with the expensive aluminium alloys, is this taper or "draw " the finished stamping raised by merely pulling a cord, the force of reduced to a negligible amount. It is common cannot be withdrawn from the impression. th e blow naturally increasing with the height practice in acro-engine work for only ten- Also, because metal expands when heated, from which it drops. For the 15-ton hammer, thousandth s of an inch to be allowed for th e dies must also be made slightly larger which is the largest size yet made, an anvil machining after stamping, which is a practically tha n the finished article, to allow for con weighing 205 tons is used to resist a weight of impossible limit for castings or forgings. A tracting after heating, so that the stamping 21 tons falling from a maximum height of very high rate of production can be obtained, will cool to the correct size, the allowance 8 ft. with a force of 168 ft.-tons. This blow a s a few blows with the hammer produces for aluminium alloys being 0·008 in. can be delivered 17 times a minute. The 8-ton a n article, perfect in contour, in a fraction of Th e dies are passed from the machines to size illustrated (Fig. 2) is used for crankcases th e time required by any other method. th e die sinkers who remove all rough places and airscrews, delivering a blow of 104 ft.-tons Drop stamping consists of hammering pieces and chip out with a hammer and chisel any 22 times a minute. In spite of a 40-ft. bed of of hot metal between two hardened steel blocks part s tha t are inaccessible to the millers. The concrete, the thud of the blow can be felt into which suitable impressions have been cut. finished impression is given a glass-like surface nearly half a mile away. The complete 15-ton Actually, half the impression of the required to prevent the hot metal from sticking to the hammer weighs 316 tons without foundations. article is cut into the bottom block or die sides. Inspectors now check over all the Great care is necessary for the heating of which is fixed to the base of the hammer, and dimensions, because if the die is faulty then aluminium alloys which must not come into half is cut into the top die which is raised every article produced will also be faulty. contact with naked flames, or disfiguring t o a height and repeatedly dropped. Th e limits are very close, often being ±0·001 in. blisters will appear all over th e surface. Liquid on small work, although for the large dies Th e success or failure of drop stamping bath s of special salts or electric furnaces are i t is impossible to keep much closer than depends upon the dies, which are cut out of used to raise the metal to a maximum tem ±0·00 5 in. To work on a 4-ft. cube of steel toughened nickel-chrome-molybdenum or car perature of 500 deg. C , above which the metal weighing 5 tons and cut out an intricate design bon steel with a Brinell reading of 340 to 440. is spoiled for future heat treatment. The fact to such a fine margin requires considerable skill. Large dies, as used for the production of air tha t the alloy cannot be raised above this temperatur e is a decided drawback to stamping, as the metal is not hot enough to flow easily, so requiring heavier blows than if iron or steel were used. The heated alloy, roughly forged to shape, is placed on the bottom, impression, and a few blows of the top die produces the correct shape, the ragged fin of waste metal being removed with a punch and die in a punch ing machine.
Journal
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jun 1, 1936