This document provides information about various mechanical engineering topics submitted as a lab assignment. It discusses welding processes like arc, gas, and resistance welding. It also describes injection molding, CNC wire cut machines, milling machines, and CNC lathe machines. For each topic, it explains the basic principles and applications. The assignment was submitted by Suhail Ahmed to his instructor Mr. Dawood Bukahri for a BS in Aircraft Maintenance Technology course.

1. MECHANICS OF MATERIAL LAB
ASSIGNMENT
SUBMITTED BY: SUHAIL AHMED
BSAMT02161001
SEMESTER#03
BS AIRCRAFT MAINTENANCE
TECHNOLOGY
LAB ASSIGNMENT no#02
SUBMITTED TO: MR DAWOOD
BUKHARI
DATE: 14 April 2017

2. Welding:
Welding is the process of joining metals by melting the parts and then using a
filler to forma joint. Itcan be done using different energy sources, froma gas
flame or electric arc to a laser or ultrasound.
Until the beginnings of the 20th century, welding was done via a process known
as forge welding, which consists of heating up the pieces to be fixed together and
then hammering them until they amalgamate. With the advent of electricity, the
process became easier and faster, and it played an important part of the industry
scene during World War I and II.
There are different welding processes in use in modern times:
Arc welding:
Arc welding is donethrough the use of an electrical current, and can be performed
by using inexpensive equipment.

3. Gas Welding:
Gas Welding is widely used for repair work, especially in anything involving pipes
and tubes. It is common in the jewelry industry, as well as for connecting plastics
and other materials that cannot stand higher temperatures.
Resistance welding:
Resistance welding involves the use of additional sheets of metal to encase the
pieces to be welded together. It is the most environmentally-friendly of all
methods, but it requires costly equipment that cannot be used in all situations

4. Energy beam welding:
Energy beam welding also known as laser beam welding, is one of the most
modern techniques used. This method is fast and accurate, but the high equipment
cost makes it prohibitive for many industries.
Welding cannot be done with all types of metals, as some materials, such
as stainless steel, areproneto cracking and distortion when overheated. Alloys are
particularly problematic, since it's hard to know the exact chemical composition of
the metal. Welding has become highly automatized over the last decade, and the
use of robots is now commonplace in certain industries, such as the automotive
manufacturing plants.
Itis possibleto weld items in unusualconditions,including underwaterand in outer
space. Underwaterwelding is widely used in the repair of pipelines and ships,while
that performed in space is currently being researched as a possible way to put
together space stations and other structures.
What is injection molding?
Injection molding along with extrusion ranks as one of the prime processes for
producing plastic articles. Itis a fastprocess and is used to produce large numbers
of identical items from high precision engineering components to disposable
consumer goods.
Most thermoplastics can be processed by injection molding; the most common
materials used include:

5. Acrylonitrile-Butadiene-Styrene ABS
Nylon PA, Polycarbonate PC,Polypropylene PP
Injection moldings count for a significant proportion of all plastics products from
micro parts to large components such as car bumpers and wheelie bins. Virtually
all sectors of manufacturing use injection molded parts. The flexibility in size and
shape possible through use of this process has consistently extended the
boundaries of design in plastics and enabled significant replacement of traditional
materials thanks to light weight and design freedom.
How Does Injection Molding Work?
Material granules for the partis fed via a hopper into a heated barrel, melted using
heater bands and the frictional action of a reciprocating screw barrel. The plastic is
then injection through a nozzleinto a mold cavitywhereit cools and hardensto the
configurationof the cavity.The mold tool is mounted on a moveableplaten – when
the part has solidified, the platen opens and the part is ejected out using ejector
pins.
After a productis designed, usually by an industrialdesigner or an engineer, molds
are made by a mold maker (or toolmaker) from metal, usually either steel or
aluminum, and precision-machined to form the features of the desired part.

6. CNC Wire Cut Machine:
Electrical discharge machining (EDM), also known as spark machining, spark
eroding, burning, die sinking, wire burning or wire erosion, is a manufacturing
process whereby a desired shape is obtained by using electrical discharges
(sparks). Material is removed from the workpiece by a series of rapidly recurring
current discharges between two electrodes, separated by a dielectric liquid and
subjectto an electric voltage. One of the electrodes is called the tool-electrode, or
simply the "tool" or "electrode," while the other is called the workpiece-electrode,
or "workpiece." The process depends upon the tool and workpiece not making
actual contact.
Principle of wire cut machine:
CNC wire cut EDM machine puts impulse voltage between electrode wire and
workpiecethroughimpulsesource,controlled byservosystem,to get a certain gap,
and realize impulse discharging in the working liquid between electrode wire and
workpiece. Numerous tiny holes appears due to erosion of impulse discharging,
and therefore get the needed shape of workpiece.
Electrode wire is connecting to cathodeof impulse power source, and workpieceis
connecting to anode of impulse power source. When workpiece is approaching
electrode wire in the insulating liquid and gap between them getting small to a
certain value, insulating liquid was broken through; very shortly, discharging
channel forms, and electrical discharging happens. And release huge high

7. temperature instantaneously, up to more than 10000 degree centigrade, the
eroded workpiece is cooling down swiftly in working liquid and flushed away.
CNC Milling Machine:
CNC milling is a specific form of computer numerical controlled (CNC) machining.
Milling itself is a machining process similar to both drilling and cutting, and able to
achieve many of the operations performed by cutting and drilling machines. Like
drilling, milling uses a rotating cylindrical cutting tool. However, the cutter in a
milling machine is able to move along multiple axes, and can create a variety of
shapes, slots and holes. In addition, the work-piece is often moved across the
milling tool in different directions, unlike the single axis motion of a drill.
Virtually every type of material that can be drilled or cut can be machined by a CNC
mill, although most of the work performed is done in metal. As with drilling and
cutting, the proper machine tools must be selected for each material in order to
avert potential problems. The hardness of the work-piecematerial, as well as the
rotation of the cutting tool must all be factored before beginning the machining
process.
CNC lathe Machine:
 A CNC lathe is typically designed to utilize modern versionsofcarbidetooling
and processes. A partcan be designed for customization, and the machine’s
tool pathsareoften programmedusingthe CADor CAMprocesses.However,
a programmer can manually design a part or tool path as well. The resulting
coded computer file is then uploaded to the CNC machine, and the machine
will then automatically produce the desired parts for which it was
programmed to design.
 A CNC lathe is controlled by a menu-type interface on a computer. The
operator who manages the process can actually see a visual simulation of
how the machine will function during the production phase. Thanks to this
technology, the machine operator generally does not need to know as much

8. about the specifics of the machine he or she oversees compared to what
machine operators must know about more traditional lathes that require
some manual labor.
 CNC lathes are designed in a variety of ways, based on the manufacturer
producing the machine. However, mosthave some significant similarities in
their composition. A turret is a part of the machine that holds the tool
holders and indexes them accordingly. The spindle is designed to hold the
work piece. In addition, there are slides that allow the turret to move in
multiple axes at the same time. CNC machines are typically completely
enclosed for health and safety reasons of any operators present.
 There has been considerable growth in the CNC machining industry,
particularly when it comes to the design and use of CNC lathes. Different
lathe manufacturers utilize a variety of user interfaces, which can be a
challenge to the operators. Butthese systems aremostly based on the same
principles across the board since a CNC lathe is programmed to perform
similar functions in terms of what it is intended to manufacture.
 Like other CNC machines, CNC lathes have become a major part of the
manufacturingindustryin recent years.So,it is expected that the operations
of such machineswill continue to improveand carrysignificantweightin this
field.