The life cycle of an automobile begins with concept and design and concludes
with retirement (end-of-life scrapping). Today, a vehicle consists of approximately 15
000 parts. Steel, iron, glass, textiles, plastic, and non-ferrous metal dominate automobile
construction. A common trend in the material composition of a car is toward increasing the use of lightweight
materials, especially numerous types of plastics and light metal alloys (such as
aluminum and magnesium). Сopious
amounts of energy are consumed in heating, cooling, and producing millions of
tons of steel, aluminum, plastic, and glass. Processing these materials involves a variety
of heavy metals, toxic chemicals, chlorinated solvents, and ozone depleting chemicals.
More than half of all releases and transfers of pollutants originate from the painting and
coating operations.
Opportunities for environmental improvement exist during each life-cycle stage of
an automobile. Significant changes in the material and process selection and management
are necessary to reduce the overall environmental impact throughout the entire life
cycle of an automobile.
Мaterials used in agricultural machinery
Material groups.In this chapter the following systematics will be followed:
1. Structural steels
2. Alloyed steels
3. Cast materials
4. Light alloys
5. Wearing materials
6. Synthetic material
-Structural steels.Structural steel is still the classic material for the load-bearing structures of our agricultural
machinery.
-Alloyed steels.Alloyed steels are used in the production of gears, thus for shafts and gear wheels.
-Cast materials. As they are the classic materials, flake-graphite cast iron (GG), nodular-graphite cast iron (GGG), malleable cast iron (GT) as well as cast steel (GS) are used.
-light alloys. Light alloys are used mainly for parts made of aluminium alloys. They are used wherever weight reduction is crucial.
Synthetic materials. In modern agricultural machinery, synthetic materials are employed in versatile forms.
The most obvious use, however, is certainly the field of machine design.
Cutting tools and equipment
Cutting tools must be made of a material harder than the material which is to be cut, and the tool must be able to withstand
the heat generated in the metal-cutting process. Also, the tool must have a specific geometry, with clearance angles designed so that the cutting edge can contact the workpiece without the rest of the tool dragging on the workpiece surface. The angle of the cutting face is also important, as is the flute width, number of flutes or teeth, and margin size. In order to have a long working life,all of the above must be optimized, plus the speeds and feeds at which the tool is run.
Linear cutting tools include tool bits (single-point cutting tools) and broaches. Rotary cutting tools include drill bits, countersinks and counterbores, taps and dies, milling cutters, reamers, and cold saw blades. To produce quality product, a cutting tool must have three characteristics:
Hardness: hardness and strength at high temperatures.
Toughness: so that tools do not chip or fracture.
Wear resistance: having acceptable tool life before needing to be replaced.
Mechanical engineering processes
The production process is the set of all human actions and the means of production required for the manufacture or repair of products.
The production process includes not only the main, are directly related to the manufacture of parts and assembly of products, but also all the support processes that provide the ability to manufacture products (eg, transportation of materials and parts, control parts, production tools and tool repair tool sharpening, etc.. d.).
Technological processes of machining is the part of the production process, directly related to the change in shape, size or properties of the workpiece performed in a certain sequence.
For example:
Boring,
turning,
milling
etc.;
ALLOYS
Alloy is a substance with metallic properties that consists of a metal fused with
one or more metals or nonmetals. Alloys may be a homogeneous solid solution, a heterogeneous
mixture of tiny crystals, a true chemical compound, or a mixture of these. Alloys
are used more extensively than pure metals because they can be engineered to have specific
properties.
Steel is a metal alloy whose major component is iron and carbon. Carbon acts as a
hardening agent. Steel with increased carbon content can be made harder and stronger
than iron, but is also more brittle.
There are different types of steels. Chromium steel finds wide use in automobile
and airplane parts on account of its hardness, strength, and elasticity, as does the chromium-
vanadium variety. In a modern sense, alloy steels have been made since the advent
of furnaces capable of melting iron, into which other metals may be thrown and mixed.