1. Introduction
Turning is one of the machining process which involves cutting and trimming a workpiece to their
desirable final dimension. A cutting tool typically a non-rotating tool bit, defines a helix tool path by
travelling almost a linear line of motion while the workpiece is rotating around it’s axes. The motion of
the workpiece may be defined as a straight line or in some set of curvature of angle specified according
to the needs of the final product. Although however, it is essentially linear in all the turning process.
The objective of this experiment is to understand and practice the turning process in product fabrication.
This experiment also aims to determine the advantages and difficulties of turning process.
2. Theoretical Background
Turning is a machining process aims to trim and cut a workpiece to the desirable final dimensions. [1]
The process involves the removal of unwanted material from the workpiece by means of rotating
workpiece and a tool bit. The tool is moved linearly in a direction parallel towards the workpiece which
is rotating under high speed. As can be seen in Figure 1, the tool bit is fed linearly towards the rotating
workpiece and the trimming and cutting process commence. To get an accurate final dimension, the
workpiece must be locked inside the spindle (with chuck) firmly so that it would not move while rotating
under high speed.
Figure 1: Turning Operations
Turning is traditionally carried out by a turning machine having a few components such as bed, speed
control, tailstock, cross slide, and spindle. While the spindle provides the rotational motion of the
workpiece, the tailstock assembly controls the depth and shape of the cutting process. The turning
process is usually conducted by a machine commonly referred as lathe machine having a versatile tool,
manually operated, and widely used in low and medium production. The headstock contains the drive
unit used to rotate the spindle attached to it where it spins the workpiece about one the axis. The tailstock
assembly is where the tool bit can be inserted and change according to the operation. It is in the opposite
direction of the headstock. This assembly is manually operated, and it pushes the tool bit towards the
workpiece which is currently rotating as the operation commence. [2] This helps the workpiece to be
trimmed and cut to their final dimensions. [3]
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3. Apparatus and Experimental Setup
The material used in this experiment is mild steel, a low carbon steel (approximately 0.05% to 0.25%
carbon content). Figure 2 shows the assembly of a turning machine and their main components.
Figure 2: The Assembly of a Turning Machine and Their Main Components.
4. Experiment Procedure
1. The initial dimension of the specimen is measured to be 205.1 mm in length and 24.52 mm in
diameter.
2. The workpiece is mounted onto the workpiece holder at the spindle by using handle lathe chuck
wrench key.
3. The tailstock assembly is unlocked and pushed towards the workpiece until the dead centre is
almost touching the end of the workpiece.
4. The lathe machine is turned on and the coolant is poured onto the contacting point between the
dead centre and the end of the workpiece.
5. The handwheel is rotated to push the dead centre into the workpiece and drill a centre hole.
6. The tailstock assembly is locked so that the workpiece will not move during the turning process.
7. A cutting tool is mounted at the tool post. Compound and cross slide is adjusted to provide the
appropriate cutting angle at the workpiece.
8. The plane turning process is done by adjusting the cutting tool to a depth of 1 mm by using the
cross-slide hand wheel at the end of the workpiece.
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9. A chalk is used to mark the cutting region along the workpiece to identify the rough, medium
and smooth region.
10. By adjusting the cross-slide hand wheel and carriage hand wheel, the cutting tool is positioned
at the marked point and a slight turning process is done on the workpiece to give it a permanent
mark.
11. The cutting tool is set until it touches the workpiece surface. Then, the cross-slide hand wheel
is set at 0 mm. The carriage is brought to the end of the workpiece and the cross-slide hand
wheel knob is turned to 4.06 mm.
12. The lathe machine and the coolant are set on at a speed of 340 rpm.
13. Step 11 to 12 is repeated by changing the cross-slide hand wheel knob and rotational speed to
0.82 mm at 185 rpm and 3.62 mm at 92 rpm.
5. Results and Discussion
Figures below shows the final dimensions and surface roughness of each part of the workpiece.
Figure 1: Final product
Figure 2: Part A
Parts
Spindle speed (rpm)
Roughness
Length (mm)
Diameter (mm)
Figure 3: Part B
A
B
340
185
Rough
Medium
51.22
45.38
22
18.3
Table 1: Results obtained from the experiment
Figure 4: Part C
C
92
Smooth
54.24
15.1
The material used in the turning process is mild steel that has a low carbon percentage steel. From the
experiment, it is observed that the surface roughness is directly influenced by the spindle speed, feed
rate and depth of cut. The quality of the surface significantly improves fatigue strength, corrosion
resistance, and creep life. Therefore, accurate feed rate, spindle speed, and depth of cut are selected to
reach the required quality of surface finish. [3]
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Feed rate is the rate at which the tool advances along its cutting path. The surface roughness increased
with increased feed rate. [3] At the lower feed rates, the BUE (Built up edge) forms readily and is
accompanied by feed marks resulting in increased roughness. With the increase in feed rate, the rate of
increase in surface roughness is less due to the reduced effect of BUE. [4]
Spindle speed refers to the rotating speed of the work piece. From the experiment, the surface roughness
decreased with increased spindle speed. [3] At 92 rpm, (low cutting speed) the temperature between the
machining interfaces is more enough to create the unstable larger BUE and the chips fracture readily
producing the rough surface this may cause adhesive wear on tool. As the cutting speed increases, the
machining time will reduce and the BUE vanishes, chip fracture decreases, and hence the roughness.
[4]
It shows that when higher depth of cut given its results in poor surface finish. The shear angle and HAZ
(Heat affected zone) is depend on the depth of cut. The depth of cut increases the HAZ and shear angle,
thus increase in cutting force, friction and rise in temperature and causes deposition of removed material
on rake face of a tool. Hence, the surface roughness increases along with increase in depth of cut. [4]
Turning process gives many advantages for product fabrication. The product will be more precise and
accurate compared to products fabricated manually. It will be easier and faster to manufacture parts,
thus consume less time. It will also cost lesser than CNC Machining. Besides, the finished products will
have an excellent quality of surface finishing.
There are few difficulties that can be found during the turning process. Students must ensure the tool
bit used is suitable with the material or it will cause significant tool wear. Besides, the turning machine
should be set up properly with the accurate spindle speed for a desired surface finish. Turning process
is only limited to rotational parts. Turning machine cannot machine square or irregular parts.
6. Conclusion
From this experiment, students can understand and practice the turning process in product fabrication.
The surface roughness of turning products are affected by spindle speed, feed rate and depth of cut
effect. The surface roughness increased with increased feed rate and depth of cut. However, the surface
roughness decreased with increased spindle speed. Besides, students are also able to determine the
advantages and difficulties of turning process.
7. References
[Journal]:
[1] Yang,WP, Tarng , YS. Design optimization of cutting parameters for turning operations based on
the Taguchi method. J Mater Proc Technol 1997,84: 122-129.
[2] Darwish, SM . The impact of the tool material and the cutting parameters on surface roughness of
supermet 718 nickel superalloy. J Mater Proc Technol 2000; 97: 10–18.
[3] Kumar, N., Shetty, A., Ananth, K. (2012). Effect of Spindle Speed and Feed Rate on Surface
Roughness of Carbon Steels in CNC Turning, Procedia Engineering, Vol. 38, pp. 691-697
[4] Anil, K.C., Vikas, M.G., Sreenivas, K.V. (2017). Effect of Cutting Parameters on Surface Finish
and Machinability of Graphite Reinforced Al-8011 Matrix Composite, Materials Science and
Engineering
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