1. High-pressure coolant on flank and rake surfaces of tool: investigations on surface roughness and tool wear
Advanced Machining
Sajjad Ahmadpoor
Amirkabir University of Technology

2. High-pressure coolant on flank and rake surfaces
of tool in turning of Ti-6Al-4V: investigations on surface
roughness and tool wear
Main Content
the pressurized coolant was directed towards the rake and flank surfaces of the tool
The quality of the machined surfaces was examined in respect of different cutting speed and feed rate
The improvement of surface finish, achieved as result, by HPC is attributed to the effective cooling and lubrication, low-material adhesion, reduced chip rubbing, and elimination of built-up edge. Furthermore, the applied coolant prolonged tool life by approximately 40 %

3. Experimental methodology
The experimental setup is comprised of:
machine,
work material,
cutting tool,
high-pressure coolant system, and
performance-measuring instruments

4. Experimental methodology
the present study is focused to the surface quality and the tool wear
To represent the surface quality, herein, the average surface roughness parameter (Ra) has been measured and investigated while the tool wear has been defined and scrutinized in two ways:
Firstly, the amount of average principal (VB) and auxiliary (VS) flank wear was measured and studied
secondly, to investigate and better understand the wear mechanisms of the coated carbide tools, the inserts were analyzed by the SEM images

5. Results and discussion
Effects of cooling and lubrication
Results:
In comparison to single jet, double jet action enhances the heat transfer significantly.
the high-speed jets, acting on both faces, remove heat from the heated zone and enhance the cooling ability.
high-pressure coolant reduces the fluid consumption by four times.
The high-pressure coolant jet reaches the point of highest temperature by overcoming the obstruction created by the chips and then lifts the chip by acting as a wedge which eventually eases up the better penetration of the coolant.
the penetrated coolant creates a thin lubricating layer at the tool-work piece which reduces the friction, and thus, reduces the cutting temperature.

6. Results and discussion
Surface roughness
Results:
surface roughness decreases when the high-pressure coolant is applied.
high cutting speed with high coolant pressure decreases the surface roughness, the low cutting speed with high pressure induces higher surface roughness by the sliding of chips over the tool surfaces.
The increased feed rate results in higher surface roughness for both dry and coolant cutting.
The surface roughness is significantly affected by the increment in feed rate as higher feed rate means more material sliding thus creating a wider peak-to-valley distance.

7. Results and discussion
Surface roughness
Results:
the low cutting speed tends to generate high-surface roughness; in addition, the high-feed rate creates the highest mean surface roughness.
It is discernable that the speed, feed and cutting conditions have significant interactions in determining the mean value of surface roughness. The increased feed rate results in higher surface roughness for both dry and coolant cutting.
the very low cutting speed (≤ 70 m/min) is associated with an increase in specific cutting pressure and built-up-edge formation.

8. Results and discussion
Tool wear and tool life
Results:
The crater wear affects the effective rake angle, and when it reaches an excessive level, it hampers the tool performance and it can even cause a sudden tool failure.
faster cooling can produce micro-chipping and thermal cracking.
In connection with this fact, the notch wear is expected to be higher under high-pressure coolant jet, but in reality, there is no sign of notch wear under HPC.
The effective cooling by high-pressure coolant reduces the possibility of tool wear ignited by thermal effect rather establishes the chance of the mechanical wears.

9. Results and discussion
Tool wear and tool life
Results:
The high-pressure coolant reduces the tool wear although the progression pattern of the tool remains same.
The average principal flank wear in dry cutting approaches the tool rejection criteria of 300 µm in 5 min, whereas the same limit is reached under high-pressure coolant in 7 min; consequently, 40% tool life improvement is attained.
on the ground of average auxiliary flank wear, the tool life is extended by 70 % (5.3 to 9 min by extrapolation) by the pressurized cooling.

10. Results and discussion
Tool wear and tool life
Results:
during dry cutting, the tool reaches the tool rejection threshold value of surface roughness, i.e. 1.6 μm in 3.3 min, whereas that limit in high-pressure coolant is touched in 6 min.
by using the surface roughness based tool rejection limit, the tool life is prolonged by 80 % when machined under high-pressure coolant.

11. Results and discussion
Cause-effect diagram for machining performance:

12. Conclusions
The improved cooling and lubrication are achieved by high-pressure coolant owing to the better penetration ability of the jets. In addition, the double jets simultaneously accelerate the heat transfer rate and hence the high- pressure coolant is suggested to apply with double jets.
The average surface roughness reduction under HPC is due to the better lubrication at the tool-work piece interface. The wedge action of jets maintain the clearances and prevents the chips from rubbing over the machined surfaces.
The dominant wear mechanism in dry turning is crater and notch wear, while in coolant condition excessive rubbing on the rake and nose area is discernable along with adhesion. The material softening due to low-thermal conductivity of Ti alloy in dry cutting and the thermo-mechanical effect by HPC are responsible for these wears.
Tool life is found to be increased by at least 40% if high- pressure coolant is implemented owing to its superior cooling and lubrication at the tool-work piece interface.
The cause-effect diagram illustrates the possible connection of parameters to define a better machining performance with detail causes. Hence, it is proved to be a useful tool to point out how to improve the machining performance.