Design For Accessibility: Getting it right from the start
114722893 cnc-milling-report
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1.0 TITLE : CNC Milling (Non Traditional Machining)
2.0 OBJECTIVE
1. To develop more understanding about development and principle of CNC machine
2. To understand the fundamentals of NC programming which need to be taken for
completing a successful CNC program
3. To learn how to produce a product through the process
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3.0 INTRODUCTION
Non-traditional manufacturing processes is defined as a group of processes that remove
excess material by various techniques involving mechanical, thermal, electrical or chemical
energy or combination of these energies but do not use a sharp cutting tools as it needs to be used
for traditional manufacturing processes.
Extremely hard and brittle materials are difficult to machine by traditional machining
processes such as turning, drilling, shaping and milling. Non -traditional machining processes,
also called advances manufacturing processes, are employed where traditional machining
processes are not feasible, satisfactory or economical due to special reasons
Numerical control (NC) refers to the automation of tools that are operated by abstractly
programmed commands encoded on a storage medium, as opposed to manually controlled or
mechanically automated via cams alone. The first NC machines were built in the1940s and '50s,
based on existing tools that were modified with motors that moved the controls to follow points
fed into the system on paper tape. These early servomechanisms were rapidly augmented with
analog and digital computers, creating the modern computer numerical controlled (CNC)
machine tools that have revolutionized the design process.
In modern CNC systems, end-to-end component design is highly automated using
CAD/CAM programs. The programs produce a computer file that is interpreted to extract the
commands needed to operate a particular machine, and then loaded into the CNC machines for
production. Since any particular component might require the use of a number of different tools,
modern machines often combine multiple tools into a single “cell”.
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Figure 1: CNC Milling Machine
Modern CNC milling differs little in concept from original model built at MIT in 1952.
Mills typically consist of a table that moves in the Y-axis, and a tool chuck that moves in X and
Z (depth). The position of the tool is driven by motors through a series of step-down gears in
order to provide highly accurate movements, or in modern design, direct-drive stepper motors.
As the controller hardware evolved, the mills themselves also evolved. One change has been to
enclose the entire mechanism in a large box as a safety measure, often with additional safety
interlock to ensure the operator is far enough from the working piece for safe operation.
Mechanical manual controls disappeared long ago. CNC like system are now used for any
process that can be described as a series of movement and operations. This include laser cutting,
welding, friction stir welding ultrasonic welding, flame and plasma cutting, bending, spinning,
pinning, gluing, fabric cutting, sewing, tape and fiber placement, routing, picking and placing
(PnP), and sawing.
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4.1 INDUSTRIAL APPARATUS
Figure 8: CNC Milling Machine
Limitations:
- Relatively high initial cost of the equipment.
- The need and cost for programming and computer time.
- Special maintenance with trained personnel.
- High preventive maintenance since breakdowns are costly.
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5.0 EXPERIMENTAL PROCEDURE
We were only shown simplified procedure by the lecturer, machine setting and
specification is done by lecturer on side. The below procedure is the simplified
procedure:
1. At first, we have to check the programs to ensure that the machinery will
function properly and that the output will meet specifications. We downloaded the NC
program to the controller by key in the data, cabling RS232 or APT after the
programming work is completed.
2. Tool layout. Before the machining was started, the tool layout must be check so that
we got the desired shape of work piece.
3. Work piece setting. In this step, operator loaded the proper cutting tools into the tool
holder and positions the work piece that is piece of metal or plastic that is being shaped
on the CNC machine tool.
4. In machining process, after operator load work pieces and cutting tools into a machine,
after that the start button was pressed. Operator monitored the machine for problems, and
measure the parts produced to check that they match specifications.
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7.0 DISCUSSION OF RESULT
For our experiment, our aims are to learn and understand the use and capabilities of
computer numerical control (CNC) milling machine. For the set up of the CNC operation, the
computer numerical control is attached to the milling machine. Firstly, Computer Aided Design
(CAD) is used to make a design of a product. In CAD, it involves a special symbolic
programming languages or codes that determine the coordinate points of corner, edges and
surfaces of the work piece. Once the design is completed, we transfer the coding that we made
using ISO NC programmed to the CNC milling machine. All the data about the process from the
beginning to the end is included in those codes. Wrong coding will damage the work piece. In
order to prevent damage, we need to view the simulation on the CNC screen and do some final
editing so that the milling machine is operating in a good condition as we will obtain perfect
work piece. Any errors or mistakes will affect the work piece as well as the machine. The
machine‟s cutting tool might break. We have to set up the h of cutting tool, cutting fed, cutting
speed , spindle speed that is suitable with the specimen to avoid error occur during the process.
From the experiment, we can say that our product is perfect and thus our experiment is 100%
success. The product follows the original design and the surfaces are completely smooth. From
the product obtained, the coordinate system plays an important role to make sure the product is
not defected.
While CNC machines are expensive and complicated, they have a lot of advantages.
These are some advantages of CNC machine:
1. It improves automation, removing the need of an operator for all but a few parts of the
work. CNC machines can be left unattended for hours or even days if necessary, allowing
operators to focus on other tasks.
2. CNC machines can be used continuously 24 hours a day, 365 days a year and only need
to be switched off for occasional maintenance.
3. CNC machines can be updated by improving the software used to drive the machines.
4. Training in the use of CNCs is available through the use of „virtual software‟. This is
software that allows the operator to practice using the CNC machine on the screen of a
computer. The software is similar to a computer game
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8.0 CONCLUSION
From the experiment, we learned the principle of CNC machine. We gained better
understanding in the modes of operation of CNC machine. There is various type of modern CNC
machines use in industrial. Different preparatory (G codes) and miscellaneous function (M
codes) is used in CNC part programming for completing a successful CNC program.
Specifically, CNC milling machine works with a computer numerical control that writes and read
G-code instructions to drive machine tool to fabricate components with a proper material
removal rate. G-codes are commands for CNC machines to follow so that they can operate on
their own without human control. Zero set up is very important step to obtain an accurate
geometry of the work piece. We also gain information about the advantages and disadvantages of
CNC machines and its application.
CNC machine can be used to cut complex shapes of metal and other solid materials. The
advantages of CNC machine over Traditional Machine (TM) besides the availability of low cost
programmable controllers played a major role in the successful implementation of CNC on
manufacturing plants.
From the experiment, we can conclude that the objective students with Numerical
Control (NC) Programming and Computer Numerical Control (CNC) milling machine has been
successfully achieved.
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9.0 RECOMMENDATION
Getting the appropriate feeds and speeds for the work piece material, tooling, and cutting
conditions is the most important first step. Consistent speeds and feeds will make a huge
difference on the surface finish. Getting the right speeds and feeds is just as important to obtain a
good surface finish.
Good chip clearing is essential to both surface finish and tool life. It's impossible to get
good surface finish if chips are being re-cut over and over again. If chip clearance is minimal,
clumped up chips can jam the cutter to the point where it breaks.
Flood coolant or an air blast should be used to clear the chips at all times. Aside from
cooling the tool, the coolant cools the work piece. Sometimes this is helpful to accuracy, as a
work piece that heats up is a work piece that is moving due to thermal expansion. Another
advantage of coolant is that it lubricates the tool/work piece interface.
The primary impact of work holding on surface finish is vibration. In the worst case
vibration will turn into chatter, which is a harmonic effect that will be very visible in your
surface finish. Clearly, the more solid we can make our work holding, the less likelihood of
vibration there will be. Make sure the work piece is supported and clamped over as much area as
possible surrounding the cut while still leaving room for the cutter to get in there and do its job.
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10.0 REFERENCES
1) Kalpakjian, S., and R.S. Schmid, “Automation of Manufacturing Process”,
Manufacturing Engineering and Technology, 4th. Edition, Prentice Hall, 2000.
2) Youssefi, K, “Computer Numerical Control (CNC)”, Product Design and Manufacturing
Minicurriculum, 6 Oct. 2004.
3) Mikell P. Groover , Principles of Modern Manufacturing, 4th
Edition, Wiley 2011.
4) http://www.technologystudent.com/despro2/cncsys1.htm
5) http://en.wikipedia.org/wiki/Milling_machine
