This page contains the manufacturing processes.For every manufacturing process the first step is to select the suitable material. The proper selection of the material include Thermal, Mechanical, Chemical & Environmental properties. The fist and foremost consideration is Cost. There are different types of materials that are existing in the universe and they are divided depending upon their properties. The following gives the classification of materials.
TYPES OF MATERIALS
Materials can be classified into 3 basic types.
- Metals 2.Ceramics 3.Polymers
The Properties of the Metals are hard, malleable, (meaning capable of being shaped), and somewhat
flexible materials. Metals are also very strong. Their combination of strength and flexibility makes them useful in structural
applications. When the surface of a metal is polished it has a lustrous appearance; although this surface luster is usually
obscured by the presence of dirt, grease, and salt. Metals are not transparent to visible light. Also metals are extremely good
conductors of electricity and heat.
A metal is most likely a pure metallic element, (like iron), or an
alloy, which
is a combination of two or more metallic elements, (like copper-nickel),
the atoms of a metal, similar to the atoms of a ceramic
or polymer, are held together by electrical forces. The electrical
bonding in metals is termed metallic bonding. The simplest
explanation for these types of bonding forces would be positively
charged ion cores of the element, (nucleus's of the atoms and
all electrons not in the valence level), held together by a surrounding
"sea" of electrons, (valence electrons from the atoms).
The electrons in the "sea" moving about not bound to any particular
atom. This is what gives metals their properties such malleability
and high conductivity.
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| BASIC MICRO STRUCTURE OF METALS |
The Properties of the Ceramics are very hard and strong, but lack flexibility making them brittle.
Ceramics are extremely resistant to high temperatures and chemicals. Ceramics can typically withstand more brutal environments
than metals or polymers. Ceramics are usually not good conductors of electricity or heat.
Ceramics are compounds between metallic and non-metallic elements. The
atomic bonds are usually ionic, where one atom, (non-metal), holds the
electrons from another, (metal). The non-metal is then
negatively charged and the metal positively charged. The opposite charge
causes them to be bond together electrically. Sometimes
the forces are partially covalent. Covalent bonding means the electrons
are shared by both atoms, in this case electrical forces
between the two atoms still result from the difference in charge,
holding them together. To simplify think of a building framework
structure. This is what gives ceramics their properties such as
strength and low flexibility.
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| THE BASIC MICRO STRUCTURE OF CERAMICS |
The Properties of the Polymers are soft and not as strong as metals or ceramics. Polymers
can be extremely flexible. Low density, and viscous behavior under elevated temperatures are typical polymer traits. Polymers
can be insulative to electricity.
Polymers are often composed of organic compounds and consist of long
hydro-carbon chains. Chains of carbon, hydrogen, and often other elements or compounds covalently bonded together.
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| THE BASIC MICRO STRUCTURE OF POLYMERS |
In the above figure (a) represents a simple hydrocarbon chain, each group of hydrogen and carbon is called a mer, there are 13 mers shown in the diagram the dotted lines indicate that the pattern is continuing indefinitely. Polymers chains often contain thousands upon thousands of mers each. The [R] in (b) indicates a variable element or group of elements that could occupy a certain position in the chain. The [X] in (c) also represents another variable element or group that could occupy another position, this one being at the end or beginning of a polymer chain. The chains themselves bond to each other through secondary bonding forces. To simplify polymer structure, think of a bowl of spaghetti.
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| AMORPHOUS MICRO STRUCTURE |
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| CRYSTALLINE MICRO STRUCTURE |
When heat is applied the
weaker secondary bonds , (between the strands), begin to break and the chains
start to slide easier over one another. However, the stronger covalent bonds,
(the strands themselves), stay intact until a much higher temperature. This is
what causes polymers to become increasingly viscous as temperature goes up.
The fundamental idea of manufacturing or production is to create, (or produce), something that has a useful form. This form is most likely predetermined, calculated, with a certain physical geometry. Usually this geometry has certain tolerances that it must meet in order to be considered acceptable. A tolerance outlines the geometric accuracy that must be achieved in the manufacturing process. The "tightness" of the tolerances or in other words the allowed variance between the manufactured product and the ideal product is a function of the particular application of the product.
GOALS AND CORE PRINCIPLES IN MANUFACTURING
MANUFACTURING
Manufacturing is applicable in all areas of our lives, so much so that we often don't realize or think about it. From the cars we drive, the containers our food comes in, the TV's, computers and other devices we use, power tools, heaters, air conditioners, the pipes that deliver our water, and the list goes on and on to include just about everything defining our modern society. These things are all manufactured or build from manufactured components.The fundamental idea of manufacturing or production is to create, (or produce), something that has a useful form. This form is most likely predetermined, calculated, with a certain physical geometry. Usually this geometry has certain tolerances that it must meet in order to be considered acceptable. A tolerance outlines the geometric accuracy that must be achieved in the manufacturing process. The "tightness" of the tolerances or in other words the allowed variance between the manufactured product and the ideal product is a function of the particular application of the product.
GOALS AND CORE PRINCIPLES IN MANUFACTURING
- Meeting performance requirements (ie. tolerances, strength, weight, ect.)
- Meeting cost of production requirements.
- Ability to reproduce constant quality during mass production.
- Large manufactured components should have uniform material properties throughout the component.
it is fundamental to develop an understanding of the relationship between the process used and the properties of the finished product.For this it is important to know what conditions a particular process will subject a material to, and how different manufacturing materials respond to different conditions, (ie. stress, heat).
All manufactured products are made from some sort of material. Similar
to the geometric tolerance, the properties of the
material of the final manufactured product are of utmost importance.
Hence, those who are interested in manufacturing should
be very concerned with material selection. An extremely wide variety of
materials are available to the manufacturer today. The
manufacturer must consider the properties of these materials with
respect to the desired properties of your manufactured goods.
Simultaneously one must also consider manufacturing process. Although
the properties of a material may be great, it may not be
able to effectively or economically be processed into a useful form.
Also since the microscopic structure of materials are
often changed through different manufacturing processes -dependent upon
the process- variations in manufacturing technique may yield
different results in the end product. Therefore a constant feedback must
exist between manufacturing process and materials
optimization.
MANUFACTURING PROCESSES
This is a summary of the basic and most commonly used manufacturing processes in industry today. Any of these processes can be used to produce a manufactured component. Also remember when deciding how to produce manufactured items, a part may require a combination of these processes to facilitate its completion. For example, a cast part may require some machining before it becomes the final product. Or, a part may be made through a powder metallurgy process, then undergo some kind of forming operation. The following describes the methods and techniques involved in each of these manufacturing processes. Always keep in mind how material properties relate to manufacturing process.
Casting: Definitely one of the
oldest manufacturing processes. Castings have been
found dating back 6000 years. Fundamentally, casting involves filling a
mold with molten material, which upon solidification takes
the shape of the mold. Castings can be made into the same shape as the
final product, being the only process required. Or
sometimes a casting is the first process in the production of a
multi-process manufactured part. Casting can be used to make
parts with complicated geometry both internal and external. With casting
intricate parts can be made in a single piece. Casting
can produce very small parts like jewelry, or enormous parts weighing
several hundred tons, like components for very large
machinery. Although careful influence of casting parameters and
technique can help control material properties; a general
disadvantage to casting is that the final product tends to contain more
flaws and has a lower strength and ductility compared to
that of other processes such as forming.
Forming: The category of manufacturing by forming includes a large group of processes, that use force to induce a shape change in a material by mechanical working and plastic deformation. The most desirable quality of a manufacturing material as a candidate for a forming process is high ductility and malleability, and a lower yield strength of the material. When working with metals an increase in temperature will result in a higher ductility and a lower yield strength. In manufacturing industry materials are often formed at elevated temperatures. In addition to shape change the forming process will usually change the mechanical properties of the parts material. Forming can close up vacancies within the material, break up and distribute impurities, and establish new, stronger grain boundaries. For these reasons the forming process is known to produce parts with superior mechanical properties. With relation to temperature there are 3 types of forming. Cold working, (room temperature), warm working, and hot working. Also with relation to the surface area-to-volume of a material there are 2 main categories, bulk deformation, and sheet forming.
Powder Processing: Powder processing is a manufacturing technique that produces parts from the powder of a certain material. The powders are pressed into the desired shape, (called pressing), and heated sufficiently to cause the particles to bond together into a solid component, (called sintering). There are many advantages to powder processing. With powder processing you can obtain excellent dimensional control of the product, keeping very tight tolerances, (+/- .005"). It also can produce parts with good surface finish. Parts can therefore be made into their final shape, requiring no further processing. With powder processing there is very little waste of material. Since powder processing can be automated it minimizes the need for skilled labor, and large numbers of complex parts can be produced at high speed. Metals that are difficult to work with other processes can be shaped easily, (ie. tungsten). Also certain alloy combinations and cerments that can't be formed any other way can be produced with this technique. Lastly, parts can be made with a controlled level of porosity, due to the nature of the process. Powder processes also have a number of disadvantages. The first is high cost. Powders are expensive compared to solid material, they are also difficult to store. Sintering furnaces and special presses are more complicated to construct than conventional machinery. Tooling is also very expensive. Since powders do not easily flow laterally in a die when pressed, there are geometric limitations to the parts that can be made. Powder parts may have inferior mechanical properties, (unless they undergo a forging process). Finally variations in material density throughout the part may be a problem especially with more intricate geometries.
Machining: In machining, a manufactured part is created to its desired geometric dimensions by the removal of excess material from a workpiece via a shearing force exerted through a certain cutting tool. Qualities of a desirable manufacturing material for this purpose would be:
1) Lower Shear Strength (to make cutting easier)
2) Shock Resistant (to withstand impact loading)
3) Material must not have a tendency to stick to the cutting tool
A materials relative ability to be machined is called machinability. Ceramics have high shear strengths making them difficult to cut. Also they are not shock resistant, which causes them to fracture from the impact loading between the tool and workpiece. Polymers although having low yield strengths, melt from the heat generated in the process, causing them to stick to the tool. For these reasons ceramics and metals have poor machinability. Machining is generally applicable to metals. Machinability varies among metals, hardened metals present a particular problem due to a very high shear strength. Often metals are machined as close to their final shape as possible before hardened. That way the hardened material only has to undergo minimal finishing operations. Machining has many advantages. Machining can produce extreme dimensional accuracy, often more so than any other process alone, (tolerances of less than .001"). Machining can produce sharp corners and flatness on a part that may not be able to be created through other processes. Machining accuracy allows it to produce surface finish and smoothness that can't be achieved any other way. By combining different machining operations, very complex parts can be made. Machining does have disadvantages Machining is a removal process and wastes material. Although economical if the number of parts to be made is small; labor, energy equipment, and scrap cost are relatively high for large runs.
Forming: The category of manufacturing by forming includes a large group of processes, that use force to induce a shape change in a material by mechanical working and plastic deformation. The most desirable quality of a manufacturing material as a candidate for a forming process is high ductility and malleability, and a lower yield strength of the material. When working with metals an increase in temperature will result in a higher ductility and a lower yield strength. In manufacturing industry materials are often formed at elevated temperatures. In addition to shape change the forming process will usually change the mechanical properties of the parts material. Forming can close up vacancies within the material, break up and distribute impurities, and establish new, stronger grain boundaries. For these reasons the forming process is known to produce parts with superior mechanical properties. With relation to temperature there are 3 types of forming. Cold working, (room temperature), warm working, and hot working. Also with relation to the surface area-to-volume of a material there are 2 main categories, bulk deformation, and sheet forming.
Powder Processing: Powder processing is a manufacturing technique that produces parts from the powder of a certain material. The powders are pressed into the desired shape, (called pressing), and heated sufficiently to cause the particles to bond together into a solid component, (called sintering). There are many advantages to powder processing. With powder processing you can obtain excellent dimensional control of the product, keeping very tight tolerances, (+/- .005"). It also can produce parts with good surface finish. Parts can therefore be made into their final shape, requiring no further processing. With powder processing there is very little waste of material. Since powder processing can be automated it minimizes the need for skilled labor, and large numbers of complex parts can be produced at high speed. Metals that are difficult to work with other processes can be shaped easily, (ie. tungsten). Also certain alloy combinations and cerments that can't be formed any other way can be produced with this technique. Lastly, parts can be made with a controlled level of porosity, due to the nature of the process. Powder processes also have a number of disadvantages. The first is high cost. Powders are expensive compared to solid material, they are also difficult to store. Sintering furnaces and special presses are more complicated to construct than conventional machinery. Tooling is also very expensive. Since powders do not easily flow laterally in a die when pressed, there are geometric limitations to the parts that can be made. Powder parts may have inferior mechanical properties, (unless they undergo a forging process). Finally variations in material density throughout the part may be a problem especially with more intricate geometries.
Machining: In machining, a manufactured part is created to its desired geometric dimensions by the removal of excess material from a workpiece via a shearing force exerted through a certain cutting tool. Qualities of a desirable manufacturing material for this purpose would be:
1) Lower Shear Strength (to make cutting easier)
2) Shock Resistant (to withstand impact loading)
3) Material must not have a tendency to stick to the cutting tool
A materials relative ability to be machined is called machinability. Ceramics have high shear strengths making them difficult to cut. Also they are not shock resistant, which causes them to fracture from the impact loading between the tool and workpiece. Polymers although having low yield strengths, melt from the heat generated in the process, causing them to stick to the tool. For these reasons ceramics and metals have poor machinability. Machining is generally applicable to metals. Machinability varies among metals, hardened metals present a particular problem due to a very high shear strength. Often metals are machined as close to their final shape as possible before hardened. That way the hardened material only has to undergo minimal finishing operations. Machining has many advantages. Machining can produce extreme dimensional accuracy, often more so than any other process alone, (tolerances of less than .001"). Machining can produce sharp corners and flatness on a part that may not be able to be created through other processes. Machining accuracy allows it to produce surface finish and smoothness that can't be achieved any other way. By combining different machining operations, very complex parts can be made. Machining does have disadvantages Machining is a removal process and wastes material. Although economical if the number of parts to be made is small; labor, energy equipment, and scrap cost are relatively high for large runs.
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