Comparative Study of Ultrasonic and Laser Assisted Machining for Sustainable Leather Cutting in Greener Industry Practices

Abstract

The leather industry is increasingly adopting sustainable production strategies to minimize environmental impact and improve process efficiency, aligning with the United Nations Sustainable Development Goals (SDGs) such as Responsible Consumption and Production (SDG 12) and Climate Action (SDG 13). This study presents a comparative analysis of ultrasonic assisted machining (USC) and CO₂ laser assisted machining (LBM) for leather cutting, emphasizing sustainable leather processing.

Ultrasonic cutting utilizes high-frequency vibrations to cut leather with minimal resistance, enhancing edge quality and reducing material waste, thereby supporting SDG 12. Experiments on 1.4 mm thick buffalo leather evaluated surface roughness and kerf width as key parameters. USC demonstrated reduced thermal damage, maintaining an average surface roughness of 0.008 μm and kerf width of 0.2899 mm, while CO₂ laser cutting caused significant thermal damage and carbonization, with surface roughness of 0.012 μm and kerf width of 0.1391 mm.

Energy consumption analysis revealed that ultrasonic cutting consumes less energy than laser machining, resulting in lower emissions and a significantly reduced carbon footprint, contributing to SDG 7 (Affordable and Clean Energy) and SDG 13. The study highlights the advantages and limitations of each technique, advocating for ultrasonic machining as a greener industrial practice that promotes sustainable manufacturing with reduced environmental impact.

Introduction

Leather, a biomaterial with extensive applications, faces challenges in machining efficiency and environmental sustainability. Traditional leather machining methods generate hazardous waste contributing to soil and air pollution, conflicting with SDG 15 (Life on Land) and SDG 3 (Good Health and Well-being). Laser Beam Machining (LBM) offers precision but induces carbonization and thermal damage, leading to toxic emissions and environmental concerns.

Ultrasonic cutting (USC) emerges as a promising alternative by eliminating heat-induced decomposition, reducing emissions, and enhancing machining quality. USC aligns with SDG 9 (Industry, Innovation, and Infrastructure) by promoting innovative technologies for sustainable industrialization. The study addresses the Leather Nesting Problem (LNP) to optimize material utilization, supporting SDG 12.

Materials and Methods

Ultrasonic Assisted Leather Cutting

The ultrasonic assisted leather cutting system integrates mechanical and ultrasonic energy to enhance precision and efficiency. High-frequency vibrations (19,850 Hz to 20,250 Hz) reduce friction and heat generation, minimizing leather deformation and thermal damage. The system includes a pneumatic piston applying constant force, a piezoelectric transducer converting mechanical vibrations to ultrasonic frequencies, and a horn transmitting vibrations to the cutting tool.

Key process variables include:

1. Delay Time (DT): Time from switch-on to ultrasonic wave generation (0.1–0.4 s).
2. Cutting Time (CT): Duration of ultrasonic wave generation (0.02–0.12 s).
3. Shaking Time (ST): Duration of ultrasonic vibration application during cutting (0.02–0.08 s).

These parameters were optimized using a Taguchi L₉ orthogonal array design to achieve minimal surface roughness and kerf width.

CO₂ Laser Assisted Leather Cutting

Buffalo leather specimens were cut using a GL-1680 CO₂ laser cutter with a spot diameter of approximately 2 mm and power density of 3822 W/cm². Process parameters included:

• Laser Power: 20–30 W
• Cutting Speed: 10–30 m/min
• Standoff Distance (SOD): 1.5–1.9 mm

Experiments followed a Taguchi L₉ design to optimize surface quality, focusing on surface roughness and kerf width.

Results and Discussion

Surface Quality and Morphology

Microscopic analysis revealed that ultrasonic cutting produces clean, carbonization-free cuts with superior surface morphology, supporting SDG 12 by reducing waste and emissions. In contrast, CO₂ laser cutting caused carbonization and thermal damage, degrading leather quality and potentially releasing toxic emissions, which conflicts with SDG 3 and SDG 13.

Surface Roughness and Kerf Width Analysis

Ultrasonic cutting achieved an average surface roughness as low as 0.004 μm and kerf width of 0.0672 mm under optimized parameters (DT = 0.4 s, CT = 0.12 s, ST = 0.05 s). CO₂ laser cutting showed surface roughness down to 0.008 μm and kerf width of 0.0202 mm at 30 W power, 30 m/min speed, and 1.7 mm SOD.

ANOVA results indicated:

• In USC, cutting time was the most influential factor on surface roughness and kerf width.
• In LBM, laser power dominated the variation in surface roughness and kerf width.

Energy Consumption and Environmental Impact

Ultrasonic cutting consumes less energy than laser cutting, resulting in a lower carbon footprint and reduced emissions of volatile organic compounds (VOCs) and particulates. This contributes to SDG 7 and SDG 13 by promoting energy efficiency and climate action. The precise cutting reduces material waste, supporting SDG 12 by encouraging responsible consumption and production.

Image Processing for Surface Roughness Quantification

Advanced image processing techniques using MATLAB enabled non-contact, real-time measurement of surface roughness, enhancing quality control and process optimization. This approach supports SDG 9 by fostering innovation and sustainable industrial practices.

Conclusion

• The study compared ultrasonic and CO₂ laser assisted leather cutting, focusing on surface roughness and kerf width as performance metrics.
• Ultrasonic cutting with minimal delay time (0.1 s), optimized cutting time (0.12 s), and shaking time (0.05 s) achieved superior surface quality and precision.
• CO₂ laser cutting optimized at 30 W power, 30 m/min speed, and 1.7 mm SOD improved surface finish but caused thermal damage and carbonization.
• Ultrasonic cutting supports greener industry practices by minimizing environmental impact, reducing waste, and improving energy efficiency, aligning with SDGs 7, 12, and 13.
• Ultrasonic cutting preserves leather integrity, enhancing product durability and supporting sustainable manufacturing.
• Future research should explore integration of ultrasonic and laser technologies within smart manufacturing systems to further enhance sustainability and efficiency.

Implications for Sustainable Development Goals (SDGs)

• SDG 7 (Affordable and Clean Energy): Ultrasonic cutting reduces energy consumption compared to laser cutting.
• SDG 9 (Industry, Innovation, and Infrastructure): Adoption of advanced machining technologies promotes sustainable industrial innovation.
• SDG 12 (Responsible Consumption and Production): Minimizing material waste and emissions through optimized cutting processes supports sustainable production.
• SDG 13 (Climate Action): Lower carbon footprint and reduced emissions contribute to climate change mitigation.
• SDG 15 (Life on Land): Reducing hazardous waste and pollution from leather processing protects terrestrial ecosystems.
• SDG 3 (Good Health and Well-being): Minimizing toxic emissions improves air quality and public health.

Recommendations

1. Implement ultrasonic assisted cutting in leather manufacturing to achieve sustainable production goals.
2. Optimize process parameters to balance precision, surface quality, and environmental impact.
3. Integrate real-time monitoring and image processing for continuous quality control.
4. Explore hybrid machining systems combining ultrasonic and laser technologies for enhanced sustainability.
5. Invest in research to scale ultrasonic cutting for large-volume industrial applications.

1. Sustainable Development Goals (SDGs) Addressed in the Article

1. SDG 9: Industry, Innovation and Infrastructure
   • The article focuses on innovative machining technologies (ultrasonic assisted machining and CO₂ laser assisted machining) to improve leather cutting processes, enhancing industrial efficiency and sustainability.
2. SDG 12: Responsible Consumption and Production
   • Emphasis on sustainable leather processing, minimizing material waste, reducing carbon footprint, and promoting greener manufacturing practices aligns with responsible production and consumption.
3. SDG 13: Climate Action
   • Reduction in energy consumption and emissions through ultrasonic cutting supports climate action by lowering environmental impact and carbon footprint.
4. SDG 3: Good Health and Well-being
   • Reduction of toxic emissions and hazardous waste from leather cutting processes contributes to improved air quality and health safety.
5. SDG 11: Sustainable Cities and Communities
   • Cleaner industrial practices reduce pollution, contributing to sustainable urban environments.

2. Specific Targets Under Identified SDGs

1. SDG 9: Industry, Innovation and Infrastructure
   • Target 9.4: Upgrade infrastructure and retrofit industries to make them sustainable, with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies.
2. SDG 12: Responsible Consumption and Production
   • Target 12.2: Achieve the sustainable management and efficient use of natural resources.
   • Target 12.4: Achieve environmentally sound management of chemicals and all wastes throughout their life cycle.
   • Target 12.5: Substantially reduce waste generation through prevention, reduction, recycling and reuse.
3. SDG 13: Climate Action
   • Target 13.2: Integrate climate change measures into national policies, strategies and planning.
4. SDG 3: Good Health and Well-being
   • Target 3.9: Reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination.
5. SDG 11: Sustainable Cities and Communities
   • Target 11.6: Reduce the adverse per capita environmental impact of cities, including by paying special attention to air quality and municipal and other waste management.

3. Indicators Mentioned or Implied in the Article to Measure Progress

1. Energy Consumption
   • Measurement of energy used in ultrasonic cutting vs. CO₂ laser cutting to assess efficiency and carbon footprint reduction.
2. Surface Roughness (Ra and Rq)
   • Quantitative measurement of surface roughness using image processing techniques to evaluate quality and precision of leather cuts.
3. Kerf Width
   • Measurement of kerf width to assess precision and material waste during cutting processes.
4. Carbon Footprint and Emissions
   • Implied measurement of carbonization and toxic emissions (e.g., volatile organic compounds, chromium oxides) during laser cutting to evaluate environmental impact.
5. Material Waste Reduction
   • Assessment of material utilization efficiency and waste minimization through optimized cutting parameters and techniques.
6. Process Optimization Parameters
   • Use of Taguchi L₉ orthogonal array and ANOVA for optimizing process parameters (delay time, cutting time, shaking time, laser power, cutting speed, standoff distance) to improve sustainability and quality.

4. Table of SDGs, Targets, and Indicators

Source: nature.com