How It Works: Science and Technology - Vol. 15

By Wendy Horobin | Go to book overview

Sheet Metal

Die makers finishing a
25-ton (22.5-tonne) die
set for drawing automobile
floor pans. Drawing
involves stretching and
bending the sheet metal—
mild steel—into the
correct shape in the dies.

Refrigerators, office furniture, cars, and many other consumer products use sheet metal in their manufacture. Most of this sheet metal is steel, but copper, brass, aluminum, and other metals are also formed into various shapes by pressing them between dies in a power press.


Presses

The power press is used in forging and drawing metals, minting coins, forming automobile body parts, and many other industrial processes. The press has tools called dies installed in it; the material to be shaped is placed in the machine between the dies, and the machine closes, forming the material.

In many cases, the press is powered by hydraulic mechanisms or by steam pressure. For example, some types of forging require a slow, steady squeeze on a piece of metal heated to a state of plasticity; hydraulic actuators provide the pressure. Other types of forging require repeated heavy hammer blows—the hammer may be lifted by means of steam pressure and dropped, the pressure being provided by the weight of the tool itself or, in a double-acting hammer, forced down by the steam pressure as well. For ordinary sheet-metal forming, the machine is often a simple mechanical press.

The lower part of the press is a table called the bolster plate on which the lower die, or female, is installed. The upper part of the machine, which goes up and down between guides installed in the frame, is called the ram. The punch, or male die, is installed on the ram. In a mechanical press, the ram is connected by means of one or more connecting rods to a crankshaft, which turns in bearings installed, like the guides, in the frame of the machine, one on each side. On the side of the machine, a clutch, a brake, and a flywheel are connected to the end of the crankshaft. An electric motor drives the flywheel, either by means of several rubber V-belts running in grooves around its perimeter or by means of gear teeth, in which case the flywheel is in effect a large gear with teeth around its perimeter. When the operators push all the buttons, the clutch is activated, the crankshaft makes one revolution, and the ram makes one trip down toward the bolster plate and back up again. The upper die strikes the piece of metal placed on the lower die, forming it by means of the pressure or impact. The pressure provided by the various types of presses varies from less than 1 ton to more than 5,000 tons (0.9–4,500 tonnes). Some hydraulic forging presses have a capacity of up to 50,000 tons (45,000 tonnes).

Some presses have a geared flywheel on each side and intermediate geared shafts, pulleys, or gearwheels between the motor and the flywheel. There are also presses with eccentric shafts instead of crankshafts; an offset section of the shaft functions like a cam. Some presses have large gearwheels enclosed in the top of the

-2064-

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How It Works: Science and Technology - Vol. 15
Table of contents

Table of contents

  • How It Works® Science and Technology 2017
  • Title Page 2019
  • Contents 2020
  • Salvage, Marine 2021
  • Satellite, Artificial 2024
  • Schlieren Techniques 2030
  • Screw Manufacture 2032
  • Seaplane and Amphibian 2035
  • Sea Rescue 2038
  • Security System 2042
  • Seismology 2046
  • Self-Righting Boat 2050
  • Semiconductor 2052
  • Servomechanism 2055
  • Sewing Machine 2058
  • Sextant 2062
  • Sheet Metal 2064
  • Ship 2067
  • Shutter 2074
  • Silicon 2076
  • Silicone 2078
  • Silver 2079
  • Sine Wave 2081
  • Siphon 2083
  • Ski and Snowboard 2084
  • Skin 2087
  • Skyscraper 2090
  • Slaughterhouse 2096
  • Sleep 2099
  • Smell and Taste 2103
  • Soap Manufacture 2107
  • Soft-Drink Dispenser 2109
  • Soil Research 2110
  • Solar Energy 2114
  • Solar System 2118
  • Solenoid 2124
  • Sonar 2126
  • Sorption 2129
  • Sound 2131
  • Sound Effects and Sampling 2136
  • Sound Mixing 2138
  • Soundproofing 2140
  • Sound Reproduction 2142
  • Soundtrack 2146
  • Space Debris 2150
  • Space Photography 2152
  • Space Probe 2156
  • Index i
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