Understanding manufacturing processes
How does manufacturing happen? What are different processes of manufacturing?
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Mechanical engineers are well know for their ability to build stuff. In the earlier days, when technology was still developing, world relied on mechanical engineers to build any product. There were different manufacturing processes which were used to build simple product like a pipe and even bigger and complex machines.
To build means to manufacture, so let us take a look at how different manufacturing processes work.
One of the oldest and widely popular method of manufacturing is sand casting. It is a reliable and efficient way to replicate and produce components of metals. What happens in sand casting?
Sand casting is a process involving steps such as assembling the sand mold, pouring liquid metal into the sand mold, allowing the metal to cool, then breaking the sand mold and removing the cast product. These steps might look straight forward but things are more complex in actual process.
In hot days of summer, we all enjoy a cold and chilled candy. It is simple to make. Prepare the syrup, pour it in the tray, allow it to freeze in the freezer and just like that it is ready.
This process is similar to sand casting. Ever noticed that the shape of the candy is like the tray in which we pour the syrup? Same happens with sand casting. The shape of the final product depends on how we prepare the mold.
The first step of mold assembly is to partially fill the drag with sand. The mold cavity is shaped by the pattern, a full size model of the part that makes an impression in the sand mold. The pattern, core print, cores, and gating system are placed near the parting line. The cope is then assembled to the drag. Additional sand is poured on the cope half until the pattern, core, and gating system are covered, and then the sand is compacted by vibration or mechanical means. Excess sand is removed with a strike off bar.
The pattern is removed from the mold to leave cavity for casting. Some preliminary checks are done over the casts such as lubricating the mold, position and guide are aligned for drag and cope placement, the mold is checked for any cracks. Once the checks are completed, the complete mold is assembled and the cavity is filled with molten metal at steady rate. Metal is poured through gating system which is again a important element is casting.
Poured metal is allowed to cool. The rate at which the metal is cooling also affects the strength of the final product. To facilitate gas eruption and avoid pores forming in the cast, vents are provided on the mold for gasses to escape. Once the metal is cooled, the sand is shaken off and product is taken out. Not as simple as making candy right? The process does not end here. There are certain post casting operations done to provide proper finish. Excess profiles are removed and polishing is done by either brazing or galvanizing.
This process is 1000s of years old but it is still followed. Why is that?
The process is cost efficient. The sand used to create mold can be reused to create another mold. The excess metal can be melted and reused for another product.
This also makes the process is environment friendly. The raw material is reused.
In sand casting, the mold can be made of any geometry and shape. This gives advantage of prototyping any product before going for mass production.
Just like sand casting, there are some other manufacturing processes where the a single cast mold is used multiple times.
As the name suggests, rolling involves rollers. In this process, metals and alloys are plastically deformed into finished products by being pressed between two rolls which are rotating. The metal is initially pushed into the space between two rolls, thereafter once the roll takes a bite into the edge of the material, the material gets pulled in by the friction between the surfaces of the rolls and the material. The material is experiences a high compressive force as it is squeezed by the rolls. This is a process which deals with materials in bulk in which the cross-section of material is reduced and its length increased. The final cross-section of the product is determined by the impression cut in the roll surface through which the material passes and into which it is compressed.
Rolling is done both hot and cold. In a rolling mill attached to a steel plant, the starting point is a cast ingot of steel which is broken down progressively into blooms, billets and slabs. The slabs are further hot rolled into plate, sheet, rod, bar, rails and other structural shapes like angles, channels etc.
Rolling process does not necessarily produce products with circular cross section.
Rolling is a very practical and cost-effective method of generating commercially significant pieces. In the case of steel, almost three-quarters of all steel produced in the country is marketed as a rolled product, with the remainder being used as forgings, extruded goods, and cast items. This demonstrates the significance of the rolling process.
We all enjoy eating pasta. But do you know how it is made?
The batter of pasta is passed through a machine with rollers which produces the type of pasta we like.
Although the material is compressed between two rolls during the rolling process, the width of the material does not grow or increases just little. Because the volume of material entering and leaving the rolls is equal, and the thickness of the material decreases, the velocity of material leaving the rolls must be greater than the velocity of material entering the rolls.
There are primarily two types of metals, brittle and ductile. Brittle metals break when excessive force is applied on them whereas the ductile metal deforms. This property of material is put in advantage in the manufacturing process known as Forging.
If we hit something hard enough it's going to leave a mark!
The same philosophy goes for forging operation. By repeatedly striking metal and alloys with a hammer, they are deformed into the desired forms. It is normally done in a heated environment, although it can also be done in a cold environment. The raw material is commonly a round or square cross-section piece that is slightly larger in volume than the volume of the finished product.
Forging is done by hand or with the help of power hammers. Sometimes hydraulic presses are also used for forging.
Under the action of the compressive forces due to hammer blows, the material spreads laterally i.e., in a direction at right angles to the direction of hammer blows. Obviously brittle material like cast iron cannot be forged as it will develop cracks under the blows from hammer. An ordinary blacksmith uses an open-hearth using coke (or sometimes steam coal) as fuel for heating the metal and when it has become red-hot, blacksmith’s assistant uses a hand held hammer to deliver blows on the metal piece while the blacksmith holds it on an anvil and manipulates the metal piece with a pair of tongs. This type of forging is called “hand forging” and is suitable only for small forgings and small quantity production.
Hand forging should only be used for minor forgings. When a massive forging is required, comparatively light strikes from a hand hammer or a sledge hammer held by the striker will not be enough to induce significant material plastic flow. As a result, more powerful hammers are required. Various types of electric, steam, and compressed air-powered power hammers have been used for forging.
Extrusion is a method of exposing metal to plastic flow by confining it in a closed chamber with only one opening: a die. The material is frequently prepared so that it can go through plastic deformation quickly enough to squeeze out of the hole in the die. During the process, the metal takes on the shape of the die opening and emerges as a long strip with the same cross-section as the die opening. The metal strip created will, by the way, have a longitudinal grain flow.
When we use toothpaste, we squeeze the tube and the paste comes out of the circular opening. This is a simple demonstration of extrusion.
Extrusion is most typically used to make solid and hollow sections of nonferrous metals and alloys, such as aluminum, aluminum-magnesium alloys, magnesium and its alloys, copper, brass, and bronze, among others. Extrusion is used to make various steel goods as well.
Cast ingots or billets form the stock or material to be extruded.
Extrusion can either be done hot or cold. The cross-section of extrusion products vary widely.
Some advantages of extrusion process are described below:
The complexity and range of parts which can be produced by extrusion process is very large. Dies are relative simple and easy to make.
The extrusion process is complete in one pass only. This is not so in case of rolling, amount of reduction in extrusion is very large indeed. Extrusion process can be easily automated.
Large diameter, hollow products, thin walled tubes etc. are easily produced by extrusion process.
Good surface finish and excellent dimensional and geometrical accuracy is the hall mark of extruded products. This cannot be matched by rolling.
The conventional manufacturing processes involve sand casting, forging, rolling and extrusion. These are the basic types and there are different steps and methods within these processes.
In sand casting the shape of the pattern determines the shape of final product. A pattern is designed with consideration of different factors such as shrinkage allowance, taper angle for easy removal, etc.
Wire drawing is one of the extrusion process. Long string wires can be produced with wire drawing.
Forging is most suited for ductile material as they have high endurance for impact and can undergo deformation.
There are many other manufacturing processes just like these. Today we see 3D printing as the future, even though these conventional manufacturing processes are more suited for mass production. Subscribe to our page to know more about Mechanical Engineering!!
Source: Manufacturing Processes. H. N. Gupta