1. of automation highlights the key difference1. of automation highlights the key difference

1.
Objective

To
discuss the development of CNC technology and structure of programs by
identifying machining tools, machining sequence and machining parameters. Apply
the CAD/CAM concept for CNC codes generation and machining.

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2.
Literature Research

Present-day
computer numerical control (CNC) machines follow a set of protocols based on
the older numerical control (NC) system first developed in the mid-twentieth
century. With the advent of NC machines, the metalworking industry began
relying on the use of paper punch-tape applications (or “G-Codes”) to program
instructions used for manufacturing components. This continued for several
decades, until the late 1960’s, when more advanced CNC programs became the
industry standard.

Figure
1: Punched tape used for transfer part program to NC machine

Sophisticated
CNC Machinery can automatically monitor the quality of the work being
performed, and relay its findings to other segments of the machining process,
such as the loading and unloading phase. If the controller notices a defect or deviation
from intended product design, it can sometimes make a correction in real-time
by replacing dull tools or notifying the manufacturer about any problems. This
level of automation highlights the key difference between the two conceptually
similar programming methods: while NC controllers must function within the
parameters of direct, simple tasks, CNC programming enables machinery to analyse
data and adapt to changing circumstances.Advantages of
CNC Machining               

Since computer-controlled machining has evolved over the course of several
decades, its current iteration is more advanced in terms of precision,
automation, and production speed than any of its earlier forms, including NC
programming. Some of the benefits provided by the most recent type of CNC
machining include: 

• Complex and intricately shaped part fabrication can be performed with greater
accuracy and faster turnover rates.
• Quality control and equipment inspection systems can be semi- or fully
automated.
• Shorter CNC machine set-up and integration times result in greater
productivity.
• In some cases, computer-controlled networks can reduce the number of machines
required for a particular project.
• CNC programs can be modified, making them adaptable to a wide range of
machining tasks.• There is less need for prolonged machining trial
runs under CNC programs. Figure below shows the CNC milling
machine used to machine the workpiece.Figure 2: CNC milling machine used with
labels       3.
Dimension and Work holder device3.1
DimensionFigure
3.1: Dimension of workpieceThe dimension of workpiece used was 100mm x 100mm x
10mm.3.2
Work holder deviceFigure
3.2: Plain vice that holding workpiece during milling processThe work holder device that used during milling
process was vice as vices are most common appliance for holding work on milling
machine table. According to its quick loading and unloading arrangement. Vices
consist of three types that are plain vice, swivel vice and universal vice.Plain vice was the one that used throughout the
entire process. For your information, plain vice that is directly bolted on the
milling machine table is the most common type of vice used on plain milling
operations, which involves heavy cuts, such as in slab milling. It is
especially low construction enables the work to remain quite close to the
table. This reduces the chance of vibration to minimum. The base carries slots
to accommodate ‘T’ bolts to fix the vice on the table. Work is clamped between
the fixed and movable jaw and for holding work pieces of irregular shape
special jaws are sometimes used.                         4.
Tool and Datum4.1
ToolThe
tool that used for the milling process was End Mill SC (18) with 5mm diameter. End
mills are tools which have cutting teeth at one end, as well as on the sides,
they are used for a variety of things including facing an edge, and cutting
slots or channels. Besides that, an end mill is a type of milling cutter, a
cutting tool used in industrial milling applications such as profile milling,
tracer milling, face milling, and plunging.Figure
4.1: End Mill SC (18) 4.2
DatumFigure
4.2: Datum for X, Y and Z in Fanuc SimulatorThe datum set in this milling assignment was:X = 0.00Y = 0.00Z = 0.005.
Machine Codes5.1
Machine code block number with parts it cut                                    5.2
Machine codes in Fanuc SimulatorO5000N5 G17 G21 G40
G80 G90N10 G91 G28 Z0.N15 G91 G28 X0. Y0.N20 T1 M6                                              
Initialisation code N25 G90 G54 G0 X-15. Y-15.N30 G43 H1 Z30.N35 S1200 M3N40 G0 Z-4.N45 G41 G1 D1
X2.5 Y0. F100.   N50 G1 Y97.5                                  N55 G1 X97.5N60 G1 Y2.5                                         Left side compensation
use to contour the            N65 G1 X2.5                                         external
shoulder for the first layer of depth of 
N70 G0 Z2.                                           4mm.
N75 G0 X0. Y0.N80 G42           N85 G1 Z-2.     
N90 G1 Y0.N95 G1 X-2.5                Right side compensation used to
contour the external   N100 G1 X100.             shoulder for the second layer of
depth 2mm.N105 G1 Y100.N110 G1 X0.N115 G1 Y0.N120 G40 G1 Z3.N125 G0 X50. Y-10.N130 G1 Z-3.N135 G1 X50. Y7.5N140 G1 Z-5.N145 G2 X50.
Y7.5 I0. J12.5 F80 N150 G1 Z2. F100.                           N155 G0 X40. Y30.N160 G1 Z-5.N165 G1 X15. Y70.N170 G1 Z2.N175 G0 X60. Y30.                     N180 G1 Z-5.                                                     
N185 G1 X85. Y70.N190 G1 Z2.N195 G0 X57.5 Y50.N200 G1 Z-5. N205 G2 X42.5 Y50. I-7.5 J2.784 N210 G1 X35. Y65.                         N215 G3 X15. Y70. I-12.643 J-8.072 N220 G0 Z3.N225 G0 X57.5 Y50.N230 G1 Z-5.N235 G1 X65. Y65.N240 G02 X85. Y70. I12.643 J-8.072N245 G0 Z3N250 G0 X50. Y7.5N255 G1 Z-3.N260 G1 Y10.N265 G2 X50. Y10. I0. J10. F50. N270 G1 Z-1. F750                         N275 G1 Y12.5N280 G2 X50. Y12.5 I0. J7.5N285 G0 Z0.N290 G0. X10. Y85.N295 G1 Z0.                                N300 G2 X20. Y85. I5. J0. Z-5.N305 G3 X30. Y85. I5. J0. Z0.N310 G2 X40. Y85. I5. J0. Z-5.N315 G3 X50. Y85. I5. J0. Z0.N320 G2 X60. Y85. I5. J0. Z-5.N325 G3 X70. Y85. I5. J0. Z0.N330 G2 X80. Y85. I5. J0. Z-5.N335 G3 X90. Y85. I5. J0. Z0.N340 G0 Z3.N345 G0 X0. Y0.N350 G99 G91 G81
X12.5 Y12.5 Z-8. R3 K1 F10N355 Y12.5N360 Y12.5N365 Y12.5N370 X75.                                                                           
N375 Y-12.5N380 Y-12.5N385 Y-12.5N390 G80 G00 Z5.N395 G0 Z30.N400
M5N405 G91 G28 Z0.N410 G91 G28 X0. Y0.N415 M30     6.
Complexity of WorkpieceFigure 6: Different view of machined workpiece at Fanuc
Simulator         7. Machined WorkpieceFigure 7: Different view of
machined workpiece through CNC Milling machine      
   8.
Investigation and Discussion8.1
Limitation of the machineFor
the CNC milling machine used for machining, the machine limits the only 3 axis
of cut that are X, Y and Z axis. Thus, this machine cannot produce much more
complex workpiece as some designation of workpiece require 5 or more axis to
produce the final shape. Figure
8.1: Example of CNC milling machine with 5 axisBesides
that, the cost of the milling machine is high as well as the milling cutters.
Thus, the initial investment is high. Furthermore, the maintenance cost is high
as any parts of the machine break will require skilled worker to repair or
replace with a new parts.Lastly,
one of the limitations of the milling machines is training is required for the
operator. This is because the operation of the milling machine is complicated.
When training is less for operator, when the operation undergoes problems, he
may not know how to solve it and will cause the machine damage. Therefore, more
training is needed for the operator to make sure the milling machine can be
function properly.       8.2
Products compliance to the drawing and comments on the processOverall,
the machined workpiece is exactly the same as our design drawing as well as the
final shape on the Fanuc Simulator. However, there some difficulties we faced
during the process of coding as well as the machining process. Besides that, there
are some precautions need to take in order to get the machined workpiece
compliance to the design drawing. If want to consider the only different
between the machined workpiece and the design drawing was the right external
shoulder width is bigger than the left external shoulder width.This
is due to the workpiece dimension that set in the Fanuc Simulator was 100 x 100
x 10mm but the actual workpiece dimension we measured, was 98 x 100 x 12mm.
Therefore, when workpiece was machined based on our Fanuc Simulator code, the
width of the shoulder was different. 8.2.1
Coding ProcessWhen
coding at the simulator, the problem faced was how to convert the R to I and J
at the Victor logo edge because coding I and J require the center point.                              Figure
8.2.1(a): Victor Logo edge                                         
Dimensioning          Figure
8.2.1(b): Dimensioning feature in Fanuc SimulatorThus,
how the problem was solved is we make use of the Fanuc Simulator feature that
is dimensioning. From dimensioning function on Fanuc Simulator, the centre
point of any curvature can be found very easily by just click on the curve.Besides
that, the precaution taken during the coding process was the change of
feedrate. The feedrate was lower when some curvature feature is carrying out,
for example, when making the circle with different layer, the feedrate was only
50 to avoid damaged and crack on the workpiece.Futhermore,
one of the essential precaution was the retract amount of tool during drilling
cycle. Initially, the retract amount was 0.1mm but with the consideration of
the thickness of workpiece will not be exactly 10mm, thus the retract amount
was changed to 3mm. This was successfully prevent the tool from collide with
the workpiece when the workpiece thickness was not exactly 10mm.8.2.2 Machining ProcessWhen
there is error of the coding during machining process, the error light will
turns on red and the type of error will show on the screen of control panel.Figure
8.2.2: Control panel of CNC Milling machineThe
first type of error shown during the machining process was error 007. Error 007
is the decimal point error when referring to lab manual. Some of the X and Y
value had overlap decimal point that caused error, after checked and edited the
decimal points, the process continue to run.The
second error faced was the G42 at machine code block N80 to N115 used to
contour external layer was not carried out. Instead of cutting the workpiece,
the tool went around the workpiece in the air and cut nothing. To solve this
problem rapidly, G40 was used to machine the layer instead of G42.9.
Design DrawingFigure
9.1: Top view of Autocad drawing of the design of workpiece Figure
9.2: Side view of Autocad drawing of the design of workpiece      10.
Conclusion and ImprovementIn
a nutshell, simulator is different from the real machining process. In real
machining process, many aspects need to be consider in order to achieve the
final shape of design drawing. For example, the feedrate need to be smaller
when come to relatively curve or precise part as higher feedrate will results
in cracking on workpiece. Besides that, true machining process had lead us to
real life working whereas how to handle CNC milling machine when there is an
error during the machining process. The error shown on control panel can be
refer to lab manual and find out the types of error. Furthermore, as a
professional engineer, all the possible conditions that will happen during
machining process should be consider. For example, the thickness of workpiece
may not be exactly 10mm and it might be 10.2mm sometimes, therefore the retract
amount be should be 0.1mm to avoid such conditions.

The
improvement that can be made for this milling assignment is roughing cycle and
finishing cycle should be include in the machine code to ensure a better
surface finish. Besides that, tool change should be allowed in this machining
process so that much more features can be produce by using different tools.