"Optimizing Lathe Process Capability Using Non-Metallic Gears: A Comparative Analysis of Machining Performance"

doi:10.21203/rs.3.rs-5288850/v1

This paper presents the effects of non-metallic gears (cast nylon, nylon, and Hylam) in the process capability performance of a lathe machine in turning operations in comparison with metallic gears. Machining of 216 shafts has been carried out under different setups of spindle speed, feed rate, and depth of cut. Process capability indices in terms of (Cp, Cpk) have been calculated and control charts - X-bar and R-charts were used to analyze the performance. The results also reveal that the Hylam gear outperforms the other gears, with higher process capability due to its superior density and flexural strength. This analysis reveals there is considerable scope for the application of non-metallic gears to develop surfaces that can achieve better surface finish by taking up process control and machining precision at lesser cost than metallic gears in modern lathe machining.

Lathe machine

Nonmetallic gears

Control charts

Process capability

Surface roughness

In scenarios where the modern manufacturing industries are highly under pressure to produce high-quality products in minimum lead time, the use of lathe machines in precision machining would be developed positively through process capability studies, an evaluation of how well the machine operations meet the customer and industrial standards. The indices of the process capability, namely Cp and Cpk, report on the performance of machine tools, thus enabling manufacturers to make optimal changes to production processes. This research aims at comparing the capability of a lathe machine for a process between using non-metallic gears compared to traditional metallic ones, considering especially the surface quality produced and the accuracy of the machined parts. [1]

In today's competitive manufacturing environment, industries face pressure to provide products of very high quality with shorter lead times and with environmental sensitivities. There is a great need for consistent quality in products produced because manufacturers must respond to changing customer needs and ever-shorter lifetimes of products produced. Process capability has become a critical element for the production systems to ensure production can consistently meet requirements by optimizing machining processes. [2]

This is the measure of a process's capability to be manufactured within controlled conditions to produce products within specified limits of tolerance. In short, the process capability is the measure for manufacturers to evaluate how far their processes are efficient and accurate to achieve the most productivity, cost effectiveness, and customer satisfaction. In this regard, nonmetallic gears, in the forms of cast nylon, nylon, and hylam, have been proven to be potential elements that can be used during lathe machine operations in improving performance and extending the service life of machine parts while upholding quality control standards. [3]

The process capability of turning operations produced on a lathe machine utilizing nonmetallic gears will be analyzed through this study. The effect of gear material on machining process is investigated by substituting the traditional metallic tumbler gear mechanism with plastic gears. The studies in this paper examine spindle speed, feed rate, and depth of cut with various gear combinations in pursuit of higher-precision lathe machining operations and better surface finish. Findings from this research will also be useful in an application of nonmetallic gears to processes of machining using optimized performance and capability of the lathe machine. [4]

Analysis into the process capability is necessary when relating to performance analysis in machining operations. In this respect, with the industry changing towards more efficiency levels and precision, studying the process capability might really uncover the efficiency of particular manufacturing tools such as lathe machines that use nonmetallic gears.[5]

Lathe machines are really crucial in machining processes, and some factors considered upon it particularly on spindle speed, feed rate, and depth of cut. Traditionally, metallic gears have been used in lathe mechanisms. However, recent studies have made an interest in the use of non-metallic gears that have many operational benefits for instance cost effectiveness, quiet, and sometimes ample materials. [6]

It can thus explain the capability of a process for producing its output within specified tolerances. Process capability indices are useful in quality control as they would connect voice of customer with the production capabilities. Existing studies argue that PCIs play an important role in turning operations, especially in feed rate and spindle speed's role in affecting surface finish and dimensional accuracy (process capability). [7]

Several studies have discussed the implementation of PCIs in cutting operations. For example, Prabakaran et al. (2018) talked about grinding machine process capability, and results indicate that further continuous improvement of the machining parameters highly improves the overall performance or capabilities of the processes. [8]

Other researchers, like Arajpure and Padole (2016), focused on plastic gears used in lathe machines, and results indicated improvement in machining accuracy due to the introduction of plastic feed boxes or their capabilities. [9]

Furthermore, Funda Kahraman et al. in 2012 demonstrated that process capability analysis would improve the quality of turning operations by optimal values of the key parameters including cutting speed, feed rate, and depth of cut. [10]

The article by Erameh et al. (2016) "Lathe process capability" illustrates the relevance of SPC methods in machining. Since these statistical process control techniques aid in judging the performance in controlled conditions for a long time, the machines work according to the tolerance range specified.[11]

The paper by Shinde and Katikah, "Importance of Process Capability and Process Performance Indices in Machine Tool," discussed the crucial role of process capability and process performance indices (Cp, Cpk, Pp, Ppk) in determining the machine tool productivity and reliability. Such statistical measures determine the proficiency of a process on its operation within tolerance limits. The paper looks into how indices for performance in machine tools are useful in quality measures and testifies to the research conducted on ensuring quality, controlling variability, and improving productivity by manufacturers. The authors, in discussing practical applications of process capability studies, also establish that optimization of machine tool operations enhances both better product quality and cost-effectiveness. [12]

Shreehah's paper "Extending the Technological Capability of Turning Operation" describes improvements in turning to enhance technological capability in turning operation. The present research is based on the method of optimized turning operation parametrically for some key parameters like cutting speed, feed rate, and depth of cut. It explores their influence on surface finish, material removal rate, and tool wear. It engages theoretical models and experimental data while assessing performance improvements. The results indicate that through the improvement of tooling materials and machining techniques, significant productivity and quality enhancements can be made in turning operations, thus turning out to be a far more versatile and efficient process for a number of applications. [13]

Titled "Improving the Process Capability of a Boring Operation by the Application of Statistical Techniques," the paper by Rajvanchi and Belokar reports a study aimed at improving boring operation performance through statistical methods. Process variability identification and precision improvement by applying Statistical Process Control (SPC) techniques and process capability indices such as Cp and Cpk are highlighted in this paper. The authors have presented how these techniques assist in detecting deviations, minimizing defects, and optimization of machining parameters. It is observed that these statistical methods improve the process capability, hence efficiency, quality of products, and reduced operation cost.[14]

In the paper "Extending the Technological Capability of Turning Operation" by Shreehah in 2010, there was an exploration of methods to better the technological capabilities of turning operations within manufacturing. For this research, it optimizes key machining parameters, including cutting speed, feed rate, and depth of cut to elevate process efficiency. This study evaluates experimental data together with theoretical models in terms of the influence of such parameters on machining outcomes, such as surface finish, tool wear, and material removal rates. The obtained results showed that improvements in cutting tools and manufacturing technologies significantly contribute to improving turning operation performance and, therefore to making this process even more efficient and versatile in manufacturing almost the entire spectrum of industrial materials.[15]

Therefore, it can be concluded that non-metallic gears can be used in lathe machines, and it could be a good alternative to metallic gears in process capability enhancement. Future research studies should continue to investigate the relationships between material property and machining efficiency and long-term practicality of utilizing non-metallic gears in various industrial applications.

Literature Summary

Literature Review In the literature review, it deals with the heart of process capability that adds on to improving machining operations. It started from the point of shifting of focus of industries towards precision and efficiency as the research work on process capability unfolds the assurance of machine tools like lathes. Traditionally, the one followed is the use of metallic gears. But due to cost-effectiveness, quiet running, and the availability of materials, gears produced were of non-metallic material.

It is of great importance to use such indices as Cp and Cpk in the field of quality control, as these are the indicators that link customer requirements with production capabilities. The review explains how feed rate and spindle speed can be used in turning operations to affect both surface finish and dimensional accuracy.

3.1 Experimental Setup

Above all figure shows four different gear combinations mounted on a lathe machine. The gear combinations are made of various non-metallic materials, including cast nylon, nylon, and hylam. These combinations replace the traditional metallic gears in the feed gear train.

The four images in the figure are labeled as follows:

Metallic gear combination: Fig. 1 show the original gear combination, which is made entirely of metal.
Cast nylon gear combination: Fig. 2 shows a gear combination where the feed gear is made of cast nylon.
Nylon gear combination: Fig. 3 shows a gear combination where the feed gear and the idler gear are both made of nylon.
Hylam gear combination: Fig. 4 shows a gear combination where the feed gear and the idler gear are both made of hylam.

3.2 Machine and Tool Specifications

Lathe machine: General-purpose 1675 (5'6") lathe with an all-geared headstock and a 2 HP motor.
Cutting tool: Carbide single-point cutting tool with a rake angle of 5°, relief angle of 8°, and nose radius of 0.5 mm.

Table 1

Lathe machine specification
Sr. No.	Size	5’-6”
1	Size length of bed	1675 (5’-6”)
2	Width of bed	324
3	Height of Cener	254
4	Swing over Bed	455
5	Swing over Cross Slide	255
6	Swing in Gap	725
7	Spindle Bore	54
8	Aprox Weight	1200 Kg
9	Tail Stock Taper	MT-4
10	Tail Stock Ram Travel	175
11	Lead Screw Dia	38
12	Lead Screw Thread	4 TPI
13	No. of Spindle Speed	8/30 To 495 RPM
14	Range of Thread	1 to 6 mm/ 2 to TPI
15	Electric Motor/Speed	2 HP/1440 RPM

3.3 Materials Used

The workpieces used in this study are bright mild steel bars with the following properties:

Elastic modulus: 210 GPa
Tensile strength: 585 N/mm²
Yield strength: 530 N/mm²
Hardness: 197 HB
Length: 100 mm
Diameter: 16 mm

The material was turned to a diameter of 15 mm over a length of 50 mm, with each workpiece cut to 100 mm.

3.4 Experimental Procedure

1. Gear Mounting:

Mount the metallic gear combination in the feed drive mechanism.

2. Speed and Feed Rate Settings:

Set the spindle speed to 415 rpm.
Adjust the feed rate to 0.47 mm/sec, 66 mm/sec, or 1.05 mm/sec.

3. Depth of Cut and Turning:

Set the depth of cut to 0.1 mm.
Turn three different workpieces at the current speed and feed rate.
Repeat the above step with a depth of cut of 0.2 mm.

4. Speed Variation and Repetition:

Increase the spindle speed to 630 rpm and repeat steps 2–4.
Increase the spindle speed to 1000 rpm and repeat steps 2–4.
Repeat the entire procedure (steps 1–4) for the cast nylon, nylon, and hylam gear combinations.

5. Data Collection:

Perform straight-turning operations on a total of 216 workpieces.
After completing all turning operations, measure the workpiece dimensions, surface roughness, spindle speed, and other relevant parameters using digital micrometer, digital tachometer, dial indicator, Mitutoyo surface roughness tester, and Fluke digital multimeter.
Record the measured values on a statistical data sheet.

4.1 Observations

4.1.1 Metallic Gear combination

Table 2

Observations for Metallic Gear combination
Depth of cut 0.1m
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.832	14.954	14.883
2		0.66	14.813	14.902	14.881
3		1.05	14.879	14.892	14.927
4	630	0.47	14.813	14.902	14.881
5		0.66	14.892	14.982	14.912
6		1.05	14.891	14.956	14.967
7	1000	0.47	14.992	14.982	14.912
8		0.66	14.913	14.902	14.881
9		1.05	14.978	14.907	14.972

Table 3

Observations for Metallic Gear combination
Depth of cut 0.2mm
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.879	14.807	14.829
2		0.66	14.971	14.842	14.89
3		1.05	14.882	14.913	14.925
4	630	0.47	14.901	14.841	14.947
5		0.66	14.889	14.931	14.873
6		1.05	14.981	14.942	14.89
7	1000	0.47	14.979	14.907	14.961
8		0.66	14.801	14.841	14.917
9		1.05	14.989	14.939	14.973

4.1.2 Cast Nylon gear combination

Table 4

Observations for Cast Nylon gear combination
Depth of cut 0.1m
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.925	14.956	14.897
2		0.66	14.915	14.898	14.967
3		1.05	14.933	14.861	14.907
4	630	0.47	14.902	14.813	14.951
5		1.05	14.941	14.865	14.907
6		0.66	14.914	14.926	14.908
7	1000	0.47	14.908	14.899	14.917
8		0.66	14.92	14.905	14.807
9		1.05	14.905	14.812	14.926

Table 5

Observations for Cast Nylon gear combination
Depth of cut 0.2mm
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.799	14.945	14.815
2		0.66	14.856	14.937	14.841
3		1.05	14.947	14.822	14.802
4	630	0.47	14.803	14.813	14.806
5		0.66	14.951	14.872	14.936
6		1.05	14.79	14.816	14.824
7	1000	0.47	14.784	14.904	14.818
8		0.66	14.824	14.882	14.75
9		1.05	14.891	14.825	14.791

4.1.3 Nylon gear combination

Table 6

Observations for Nylon gear combination
Depth of cut 0.1m
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.802	14.824	14.857
2		0.66	14.952	14.935	14.911
3		1.05	14.807	14.952	14.871
4	630	0.47	14.965	14.928	14.877
5		0.66	14.859	14.922	14.833
6		1.05	14.841	14.932	14.909
7	1000	0.47	14.955	14.908	14.897
8		0.66	14.869	14.912	14.831
9		1.05	14.921	14.965	14.957

Table 7

Observations for Nylon gear combination
Depth of cut 0.2mm
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.811	14.902	14.844
2		0.66	14.874	14.931	14.918
3		1.05	14.917	14.815	14.897
4	630	0.47	14.913	14.921	14.907
5		0.66	14.865	14.947	14.979
6		1.05	14.893	14.943	14.989
7	1000	0.47	14.905	14.955	14.964
8		0.66	14.965	14.847	14.959
9		1.05	14.981	14.94	14.909

4.1.4 Hylam gear combination

Table 8

Observations for Hylam gear combination
Depth of cut 0.1mm
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.982	14.892	14.915
2		0.66	14.932	14.839	14.901
3		1.05	14.967	14.975	14.969
4	630	0.47	14.883	14.866	14.973
5		0.66	14.961	14.965	14.849
6		1.05	14.929	14.874	14.917
7	1000	0.47	14.923	14.829	14.831
8		0.66	14.933	14.953	14.953
9		1.05	14.986	14.958	14.977

Table 8 Observations for Hylam gear combination

Depth of cut 0.2mm
Sr. No.	Spindle speed (RPM)	Feed Rate (mm/s)	Job 1	Job 2	Job 3
1	415	0.47	14.937	14.981	14.956
2		0.66	14.971	14.877	14.949
3		1.05	14.823	14.927	14.965
4	630	0.47	14.941	14.811	14.928
5		0.66	14.951	14.973	14.912
6		1.05	14.937	14.981	14.956
7	1000	0.47	14.971	14.983	14.922
8		0.66	14.951	14.937	14.939
9		1.05	14.941	14.911	14.928

4.2 Control Charts

Table 9

Constants for control charts
	Control Limits Factor	Divisors to Estimate σx	Factors for Control Limits
Subgroup size (n)	A2	d2	D3	D4
2	1.880	1.128	-	3.267
3	1.023	1.693	-	2.574
4	0.729	2.059	-	2.282
5	0.577	2.326	-	2.114
6	0.483	2.534	-	2.004
7	0.419	2.704	0.076	1.924

4.2.1 Metallic Gear Combination

Table 10

Control limit values for metallic gear combination (0.1 mm)
Depth of cut 0.1 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.88967	14.91104	14.99026	14.83181	0.122	0.077444	0.199342	0
2	14.86533	14.91104	14.99026	14.83181	0.089	0.077444	0.199342	0
3	14.89933	14.91104	14.99026	14.83181	0.048	0.077444	0.199342	0
4	14.86533	14.91104	14.99026	14.83181	0.089	0.077444	0.199342	0
5	14.92867	14.91104	14.99026	14.83181	0.09	0.077444	0.199342	0
6	14.938	14.91104	14.99026	14.83181	0.076	0.077444	0.199342	0
7	14.962	14.91104	14.99026	14.83181	0.08	0.077444	0.199342	0
8	14.89867	14.91104	14.99026	14.83181	0.032	0.077444	0.199342	0
9	14.95233	14.91104	14.99026	14.83181	0.071	0.077444	0.199342	0

Table 11

Control limit values for metallic gear combination (0.2 mm)
Depth of cut 0.2 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.83833	14.90519	14.98896	14.82141	0.072	0.081889	0.210782	0
2	14.901	14.90519	14.98896	14.82141	0.129	0.081889	0.210782	0
3	14.90667	14.90519	14.98896	14.82141	0.043	0.081889	0.210782	0
4	14.89633	14.90519	14.98896	14.82141	0.106	0.081889	0.210782	0
5	14.89767	14.90519	14.98896	14.82141	0.058	0.081889	0.210782	0
6	14.93767	14.90519	14.98896	14.82141	0.091	0.081889	0.210782	0
7	14.949	14.90519	14.98896	14.82141	0.072	0.081889	0.210782	0
8	14.853	14.90519	14.98896	14.82141	0.116	0.081889	0.210782	0
9	14.967	14.90519	14.98896	14.82141	0.05	0.081889	0.210782	0

4.2.2 Cast Nylon Gear Combination

Table 12

Control limit values for Cast Nylon gear combination (0.1 mm)
Depth of cut 0.1 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.926	14.90305	14.9767	14.82939	0.059	0.072	0.185328	0
2	14.92667	14.90305	14.9767	14.82939	0.069	0.072	0.185328	0
3	14.90033	14.90305	14.9767	14.82939	0.072	0.072	0.185328	0
4	14.88867	14.90305	14.9767	14.82939	0.138	0.072	0.185328	0
5	14.90433	14.90305	14.9767	14.82939	0.076	0.072	0.185328	0
6	14.916	14.90305	14.9767	14.82939	0.018	0.072	0.185328	0
7	14.908	14.90305	14.9767	14.82939	0.018	0.072	0.185328	0
8	14.87733	14.90305	14.9767	14.82939	0.113	0.072	0.185328	0
9	14.881	14.90305	14.9767	14.82939	0.114	0.072	0.185328	0

Table 13

Control limit values for Cast Nylon gear combination (0.2 mm)
Depth of cut 0.2 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.853	14.84738	14.94482	14.74993	0.146	0.09525	0.245174	0
2	14.878	14.84738	14.94482	14.74993	0.096	0.09525	0.245174	0
3	14.857	14.84738	14.94482	14.74993	0.145	0.09525	0.245174	0
4	14.80733	14.84738	14.94482	14.74993	0.01	0.09525	0.245174	0
5	14.91967	14.84738	14.94482	14.74993	0.079	0.09525	0.245174	0
6	14.81	14.84738	14.94482	14.74993	0.034	0.09525	0.245174	0
7	14.83533	14.84738	14.94482	14.74993	0.12	0.09525	0.245174	0
8	14.81867	14.84738	14.94482	14.74993	0.132	0.09525	0.245174	0
9	14.83567	14.84738	14.94482	14.74993	0.1	0.09525	0.245174	0

4.2.3 Nylon Gear Combination

Table 14

Control limit values for Nylon gear combination (0.1 mm)
Depth of cut 0.1 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.82767	14.896	14.97466	14.81734	0.055	0.076889	0.154011	0
2	14.93267	14.896	14.97466	14.81734	0.041	0.076889	0.154011	0
3	14.87667	14.896	14.97466	14.81734	0.145	0.076889	0.154011	0
4	14.92333	14.896	14.97466	14.81734	0.088	0.076889	0.154011	0
5	14.87133	14.896	14.97466	14.81734	0.089	0.076889	0.154011	0
6	14.894	14.896	14.97466	14.81734	0.091	0.076889	0.154011	0
7	14.92	14.896	14.97466	14.81734	0.058	0.076889	0.154011	0
8	14.87067	14.896	14.97466	14.81734	0.081	0.076889	0.154011	0
9	14.94767	14.896	14.97466	14.81734	0.044	0.076889	0.154011	0

Table 15

Control limit values for Nylon gear combination (0.2 mm)
Depth of cut 0.2 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.85233	14.91448	14.99666	14.8323	0.091	0.080333	0.206778	0
2	14.90767	14.91448	14.99666	14.8323	0.057	0.080333	0.206778	0
3	14.87633	14.91448	14.99666	14.8323	0.102	0.080333	0.206778	0
4	14.91367	14.91448	14.99666	14.8323	0.014	0.080333	0.206778	0
5	14.93033	14.91448	14.99666	14.8323	0.114	0.080333	0.206778	0
6	14.94167	14.91448	14.99666	14.8323	0.096	0.080333	0.206778	0
7	14.94133	14.91448	14.99666	14.8323	0.059	0.080333	0.206778	0
8	14.92367	14.91448	14.99666	14.8323	0.118	0.080333	0.206778	0
9	14.94333	14.91448	14.99666	14.8323	0.072	0.080333	0.206778	0

4.2.4 Hylam Gear Combination

Table 16

Control limit values for Hylam gear combination (0.1 mm)
Depth of cut 0.1 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.92967	14.92341	14.99286	14.85396	0.09	0.067889	0.174746	0
2	14.89067	14.92341	14.99286	14.85396	0.093	0.067889	0.174746	0
3	14.97033	14.92341	14.99286	14.85396	0.008	0.067889	0.174746	0
4	14.90733	14.92341	14.99286	14.85396	0.107	0.067889	0.174746	0
5	14.925	14.92341	14.99286	14.85396	0.116	0.067889	0.174746	0
6	14.90667	14.92341	14.99286	14.85396	0.055	0.067889	0.174746	0
7	14.861	14.92341	14.99286	14.85396	0.094	0.067889	0.174746	0
8	14.94633	14.92341	14.99286	14.85396	0.02	0.067889	0.174746	0
9	14.97367	14.92341	14.99286	14.85396	0.028	0.067889	0.174746	0

Table 17

Control limit values for Hylam gear combination (0.2 mm)
Depth of cut 0.2 mm
Sr. No.	Avg. x- bar	x-Dbar	UCL	LCL	Range	R bar	UCL	LCL
1	14.958	14.93552	15.00599	14.86505	0.044	0.068889	0.17732	0
2	14.93233	14.93552	15.00599	14.86505	0.094	0.068889	0.17732	0
3	14.905	14.93552	15.00599	14.86505	0.142	0.068889	0.17732	0
4	14.89333	14.93552	15.00599	14.86505	0.13	0.068889	0.17732	0
5	14.94533	14.93552	15.00599	14.86505	0.061	0.068889	0.17732	0
6	14.958	14.93552	15.00599	14.86505	0.044	0.068889	0.17732	0
7	14.95867	14.93552	15.00599	14.86505	0.061	0.068889	0.17732	0
8	14.94233	14.93552	15.00599	14.86505	0.014	0.068889	0.17732	0
9	14.92667	14.93552	15.00599	14.86505	0.03	0.068889	0.17732	0

4.3 Results

4.3.1 Metallic Gear combination

Table 18

Evaluation of process capacity index for metallic gear combination (Depth of cut 0.1 mm)
σ	Rbar/d2	0.045744
3σ	3 × σ	0.137232
6σ	6 × σ	0.274463
Cp	(USL-LSL)/6σ	1.457389
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.105657
Cpk lower	(Xdbar-LSL)/3σ	0.809121

Table 19

Evaluation of process capacity index for metallic gear combination (Depth of cut 0.2 mm)
σ	Rbar/d2	0.048369
3σ	3 × σ	0.145107
6σ	6 × σ	0.290215
Cp	(USL-LSL)/6σ	1.37829
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.031702
Cpk lower	(Xdbar-LSL)/3σ	0.724879

4.3.2 Cast Nylon Gear combination

Table 20

Evaluation of process capacity index for Cast Nylon gear combination (Depth of cut 0.1 mm)
σ	R bar/d2	0.042528
3σ	3 × σ	0.127584
6σ	6 × σ	0.255168
Cp	(USL-LSL)/6σ	1.567593
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.327502
Cpk lower	(Xdbar-LSL)/3σ	0.807683

Table 21

Evaluation of process capacity index for Cast Nylon gear combination (Depth of cut 0.2 mm)
σ	Rbar/d2	0.056261
3σ	3 × σ	0.168783
6σ	6 × σ	0.337566
cp	(USL-LSL)/6σ	1.184952
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.089218
Cpk lower	(Xdbar-LSL)/3σ	0.280685

4.3.3 Nylon Gear combination

Table 22

Evaluation of process capacity index for Nylon gear combination (Depth of cut 0.1 mm)
σ	Rbar/d2	0.045416
3σ	3 × σ	0.136247
6σ	6 × σ	0.272495
cp	(USL-LSL)/6σ	1.467919
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.231237
Cpk lower	(Xdbar-LSL)/3σ	0.704601

Table 23

Evaluation of process capacity index for Nylon gear combination (Depth of cut 0.2 mm)
σ	Rbar/d2	0.04745
3σ	3 × σ	0.142351
6σ	6 × σ	0.284702
cp	(USL-LSL)/6σ	1.404979
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.005738
Cpk lower	(Xdbar-LSL)/3σ	0.804221

4.3.4 Hylam Gear combination

Table 24

Evaluation of process capacity index for Hylam gear combination (Depth of cut 0.1 mm)
σ	Rbar/d2	0.0401
3σ	3 × σ	0.120299
6σ	6 × σ	0.240599
cp	(USL-LSL)/6σ	1.66252
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.299204
Cpk lower	(Xdbar-LSL)/3σ	1.025837

Table 25

Evaluation of process capacity index for Hylam gear combination (Depth of cut 0.2 mm)
σ	Rbar/d2	0.04069
3σ	3 × σ	0.122071
6σ	6 × σ	0.244143
cp	(USL-LSL)/6σ	1.638387
Cpk
Cpk upper	(USL-Xdbar)/3σ	2.166615
Cpk lower	(Xdbar-LSL)/3σ	1.110159

4.4 Process Capability Analysis

The process capability indices (Cp) were calculated for each gear combination and depth of cut:

Table 26

Process capability values
Gear Combination	Cp Value (0.1 mm Depth of Cut)	Cp Value (0.2 mm Depth of Cut)
Metallic Gears	1.45	1.37
Cast Nylon Gears	1.56	1.18
Nylon Gears	1.46	1.40
Hylam Gears	1.66	1.63

Hylam gears demonstrated the highest process capability due to their higher density and flexural strength, which helped to minimize vibrations and improve surface finish.

4.5 Discussion:-

The discussion on the results focuses on the process capability analysis of different gear combinations used in lathe machines, considering two depths of cut (0.1 mm and 0.2 mm). The process capability index (Cp) and Cpk were calculated for each gear type (Metallic, Cast Nylon, Nylon, and Hylam gears), providing insights into the efficiency of each combination.

1. Metallic Gear Combination:

For 0.1 mm depth of cut, the Cp value was 1.45, and the Cpk was calculated with upper and lower bounds, indicating good process control but a lower tolerance. (Refer Table 18)
At 0.2 mm depth, Cp dropped slightly to 1.37, showing reduced process capability compared to the 0.1 mm depth. The upper Cpk value was 2.031702, and the lower value was 0.724879. The overall capability was decent, but lower compared to other materials. (Refer Table 19)

2. Cast Nylon Gear Combination:

With 0.1 mm depth of cut, the Cp value was 1.56, indicating a high process capability. The upper Cpk was 2.327502, and the lower Cpk was 0.807683. This suggests that Cast Nylon gears perform very well under this setting. (Refer Table 20)
At 0.2 mm depth, the Cp value decreased to 1.18, showing that the process becomes less capable as the depth increases. However, the upper Cpk value remained fairly high at 2.089218, but the lower Cpk dropped significantly to 0.280685. (Refer Table 21)

3. Nylon Gear Combination:

For 0.1 mm depth of cut, the Cp value was 1.46, demonstrating good process capability. The upper Cpk was 2.231237, and the lower Cpk was 0.704601. (Refer Table 22)
At 0.2 mm depth, the Cp value remained relatively high at 1.40, showing consistent performance even at greater depths. The upper and lower Cpk values were 2.005738 and 0.804221, respectively, indicating a balanced capability across different cutting depths. (Refer Table 23)

4. Hylam Gear Combination:

Hylam gears displayed the highest process capability, with a Cp value of 1.66 at 0.1 mm depth of cut and 1.63 at 0.2 mm depth. This suggests that Hylam gears can maintain high process control and quality even at higher depths. The upper and lower Cpk values for 0.1 mm were 2.299204 and 1.025837, and for 0.2 mm, they were 2.166615 and 1.110159, respectively. (Refer Table 24, 25)

Summary of Findings

(Refer Table 26)

Hylam gears showed the highest overall process capability, attributed to their higher density and flexural strength, which helps to minimize vibrations and improve surface finish.
Cast Nylon gears also performed well at shallower depths, but their process capability dropped significantly as the depth of cut increased.
Metallic gears demonstrated decent process control but lagged behind the other materials in terms of maintaining consistent process capability across different depths.
Nylon gears offered a balanced performance, with relatively stable process capabilities across different depths of cut.

These findings help in understanding how different gear materials influence the process capability of lathe machines, with Hylam gears standing out as the most capable for ensuring consistent and high-quality machining results

The experimental analysis of process capability for turning operations using non-metallic gears in a lathe machine demonstrated that the material properties of the gears significantly affect the machine's performance. Among the four gear combinations tested—metallic, cast nylon, nylon, and hylam—hylam gears showed the highest process capability indices (Cp values of 1.66 at a 0.1 mm depth of cut and 1.63 at a 0.2 mm depth of cut). This suggests that hylam's superior density and flexural strength contribute to better rigidity, reduced vibration, and improved machining quality. The use of non-metallic gears, particularly hylam, enhances the lathe's process capability, making it a cost-effective and viable alternative for precision machining in light-duty applications. This study underscores the importance of considering material properties when optimizing machine tools for better surface finish and efficiency, providing valuable insights for industries aiming to improve production performance.

Ethics approval and consent to participate

This study did not require ethical approval as no human or animal subjects were involved.

Consent for publication

Not required as manuscript does not contain any individual person’s data in any form.

Competing interests

The authors declare that they have no competing interests.

Funding

No funding was received for this study.

Author Contribution

TAK conceptulized the study and planned the experimentation and written the manucript. VGA supervised the experimentation and recommnded the corrections for betterment. VHP reviewed the manuscript and finalised it.

Acknowledgments

We thank our colleagues from GF's Godavari College of Engineering, Jalgaon, for their insights and expertise, which greatly assisted our research. We are also grateful to Prof. Kishor Mahajan for his valuable assistance and suggestions, which significantly improved the manuscript. Furthermore, we would like to express our gratitude to Kavayitri Bahinabai Chaudhari, North Maharashtra University, Jalgaon, for sharing their wisdom with us during this research. Additionally, we are immensely thankful to the members of the RAC from KBCNMU, Jalgaon, for their comments on an earlier version of the manuscript. Any errors, however, are our own and should not tarnish the reputations of these esteemed individuals.

Availability of data and materials

All data generated or analyzed during this study are included in this published article.

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