Keywords

1 Introduction

While cutting fluids are a small part of the machining process, they are of particular interest when studying the sustainability of those processes. Cutting fluids may contain components that are harmful to both the environment and workers exposed to them. Mist coolant and lubrication systems can be especially harmful due to their aerosolizing effects. Special care must be taken to select the proper fluid and reduce worker exposure. In terms of sustainable machining processes, another area of interest that is often neglected is waste management. Cutting fluid requires a hazardous waste fluid stream in order for it to be properly disposed. In plants that include other sources of waste fluid, this is not a significant issue. However, many bandsaw users do not have other fluid waste sources beyond small volumes of hydraulic oil. Specialized handling can add significant cost to use and financial incentives for improper disposal.

In traditional machining, cutting fluid has been an active area of study for many years [1, 2]. Researchers have studied sustainable solutions for traditional machining processes such as minimum quantity lubrication [3], targeted cutting fluid application [4,5,6,7,8], and cryogenic application [9]. However, studies investigating cutting fluid in band sawing have been very limited. Further, band saw cutting fluid sustainability, and economics are almost entirely unexplored. Band sawing differs significantly from traditional processes, making lesson carry over between sawing and traditional machining difficult. Band sawing has a lower depth of cut than traditional machining [10,11,12]. The combination of small depth of cut, multi-tooth interrupted cutting, and high-speed steel (as tool material) in bandsawing has produced accelerated edge wear. In order to reduce the edge wear, flood coolant is predominately used in the band sawing process irrespective of the workpiece material. MQL (minimum quantity lubricant) mist system are popular in the industry for cutting structural workpieces (I-beam, tubes etc.) as the flood system causes clutter and has potential safety hazards [9]. The mechanics of sawing make sustainability-focused innovations like targeted fluid and through tool coolant difficult or impossible.

2 Literature Review

For traditional machining processes such as turning, facing, milling, drilling, grinding, researchers have investigated the effectiveness of the cutting fluid on machining performance metrics such as tool life, surface finish, machining induced surface residual stresses, and economics, etc. [1,2,3, 13]. In contrast, the overall number of peer-reviewed papers for bandsawing applications is far fewer than traditional manufacturing processes. A review of the published literature is shown in Table 1, shows that the effects of the cutting fluids were not studied until recently. Sawing has a long and storied history stretching back to at least the ancient Egyptians who made hardened bronze saws. Somewhat unexpectedly, sawing of ferrous metals has existed for more than 140 years. Grimshaw, in his 1880 essay on saws, discusses the recommended saw type and conditions for wrought iron and steel beams [14]. Grimshaw discusses the lubrication of saw blades with grease to prevent gumming or buildup of resin when sawing wood. The 1880’s literature also discusses the possibility of misted water to cool and lubricate circular saw blades [14]. However, after that, experimental-based studies to find the effectiveness of the cutting fluid while bandsawing have been minimal, as shown in Table 1. In his 1976 report, Taylor showed that using a flow rate of 2 l/min and soluble oil coolant allowed an increase in the production rate of 30% by increasing the feed rate [15]. The same study found that cutting fluid had minimal effect on useable band speeds [15]. Soderberg et.al’s 1983 experimental work to cut medium carbon steel, alloy steel, and stainless steel with molybdenum-based steel tool tipped band saw blades, did not study the effect of the cutting fluids [16]. Their study found that sawing speed for bimetal should be tuned to the highest speed where a BUE is still formed to protect the tooth from the heat generated at the primary shear zone [16]. Soderberg et.al’s 1986 experimental study to determine tool tip wear mechanism with similar work material and different tool tip material did not consider cutting fluids [17]. Similarly, Doraisingam [18], Khan et. al [19], Sarwar et. al [20], Thaler e. al [21], and Orlowski et. al. [22] experimentally studied the effects of coatings, tool tip material while bandsawing different work piece material without considering the usage of cutting fluid. Other studies that reported usage of the cutting fluid while cutting materials such as Ti-7, Inconel 718, and medium carbon steels, did not evaluate the effect of the cutting fluids [23,24,25,26].

Table 1. A literature review: experimental-based research in metal band sawing process
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However, the recent studies by Rakurty et al. have shown that the cutting fluid amount, type, and workpiece geometry effects the performance of the band saw blade [10, 11]. Their study focused on researching the effects of using sustainable solutions in bandsawing solid and structural I-beam sections on tribological parameters such as cutting forces, and cut surface characteristics. Cutting forces, surface roughness, tool wear variations showed little correlation with different types of sustainable conditions. The sustainable conditions studied in their work are dry, Minimum Quantity Coolant (MQC), Minimum Quantity Lubricant (MQL), and industry-standard flood coolant [7, 8]. Based on the literature review, one can easily conclude that a comprehensive study on the effects of cutting fluids on band sawing is very much needed, and also, more importantly, the effects of the sustainable solution need more attention and research to be effectively used in the industry. One of the first steps in developing sustainable solutions in bandsawing process, an essential manufacturing process, is to review the cutting fluids used in the industry globally and use a metric-based approach to provide state of the art report. A metric-based approach for evaluating the sustainability of manufacturing processes, such as ProcSI, was developed and used in traditional manufacturing processes [2, 29, 30]. The Process Sustainability Index (ProcSI) provides a quantitative assessment for any manufacturing process [31].

Thus, in the study, along with a comprehensive literature review, a global survey is conducted to report state of the art in the industry for evaluating the sustainability impact of the cutting fluids systems used in the band sawing.

3 Cutting Fluid Usage Band Sawing: Global Case Studies

3.1 Economic Analysis

To evaluate the global sustainability impact of cutting fluid used in the bandsawing industry, bandsaw users from four different countries (Indonesia, India, Northern Ireland, and the USA) were chosen. The case studies from Indonesia, India, and the USA (California) use flood coolant to cut both solids and structural cross-sections, whereas, in Northern Ireland, they use MQL system to cut structural material. In the band sawing industry, typically, the flood coolant system uses a water-soluble cutting fluid mixed at a specific ratio with water, whereas the MQL system uses unmixed oil (no water). For the sake of brevity, in this survey, machine cost, workpiece geometry variation, cutting tool type, and the conditions are not considered. All the data from this section of the study is from the end users of The M. K. Morse Company. The saw blade [32] end users provided the information such as coolant type, quantity, frequency of recycling, method of recycling, etc., per year. Also, provided the time required to maintain the cutting fluid system and saw blade life, usage per year. Using the information provided by the saw blade users, the following case studies are evaluated.

Typically, in the bandsaw industry, cutting fluid costs are not considered when a job’s manufacturing cost is evaluated/estimated. In this paper, the economic impact of cutting fluid in bandsaw industries is evaluated by comparing it to the cutting tool cost. This study evaluates both direct and indirect costs associated with using cutting fluids and also cutting tools. The average annual cutting fluid (direct and indirect cost) and average annual cutting tool cost for the financial year 2020–2021 were collected as part of the survey for all four case studies. Figure 1 shows the manufacturing cost as a percentage of cutting tool cost and cutting fluid cost for all four case studies. As expected, the cutting tool cost was over 90% of the total cost (cutting tool and cutting fluid) for all four cases. It is interesting to note that cutting fluid costs were 8% of the total cost for the flood coolant users in India and California, whereas MQL user in Northern Ireland was just 2%. This difference is attributed to the economic benefits of using the MQL system. MQL system typically uses 30–300ml/hr. of cutting fluid, whereas flood uses 4–6l/hr. of cutting fluid. Further, MQL system users do not have any disposal/recycling costs associated with it.

Despite using flood coolant, the cutting fluid cost is only 4% of the total cost for the case study in Indonesia. On further investigation, it was found that the user in Indonesia does not recycle/dispose of their cutting fluid and hence does not have any cost associated with it. Figure 2 shows the cutting fluid cost as a percentage of maintenance cost and disposal cost. Cutting fluid maintenance costs includes cutting fluid costs, labor cost associated with coolant maintenance, and water cost (applies to flood only).

Fig. 1.
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Manufacturing cost as a percentage of cutting tool cost and cutting fluid cost

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Fig. 2.
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Total cutting fluid cost as a percentage of maintenance cost and disposal cost

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3.2 Sustainability Index (SI) Evaluation

An initial attempt was made to adapt the ProcSI technique to the bandsawing process to evaluate the sustainability index of the flood coolant and MQL systems used predominantly in the industry. The ProcSI consists of five major categories: manufacturing cost, energy consumption, waste management, environmental impact, and personal health. The only quantitative analysis that could be effectively performed with these case studies is the cost associated with cutting fluid. The manufacturing cost category was evaluated using the direct and indirect costs associated with the cutting fluid. The other factors/categories in the ProcSI were evaluated using a sustainability scale developed by Tao Lu [29]. A score close to zero is theoretically a worst-case scenario, while a ten is a best-case scenario. Also, a score of four meets the minimum requirement, while six is above average status [29]. These factors are scored relatively by comparing the differences between the flood coolant and the MQL systems. Table 2 shows the ProcSI evaluation of cutting fluid application/usage for both systems. In general, bandsaw blade users are not using changing or monitoring the cutting fluid for productivity or cutting performance; thus, an attempt is made to approach a metric-based study to alter the approach of bandsaw blade users.

Table 2. ProcSI evaluation for flood coolant and MQL systems [29]
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Production, transportation, and maintenance are the sub-categories considered under energy consumption. The flood coolant system uses a filtration system and a motor to circulate the coolant, while the MQL system uses compressed air and a motor to deliver the mist at the cutting edge. The maintenance of the MQL system is relatively more straightforward than the flood system due to the lower volume and no water consumption. Further, frequent recharge/ replenishment of the coolant is necessary for flood coolant systems due to water evaporation and coolant losses with the workpiece. The coolant disposal in the flood coolant system is another burden for manufacturers, causing further financial impact and contributing to waste generation.

In contrast, the MQL system generally uses biodegradable vegetable oils. The aerosol effects of the MQL system may cause concern for personal health, whereas the flood coolant system generates hazardous waste fluid. For simplicity, the overall ProcSI is calculated by equally weighing all the sub-categories considered in this study. There is a clear difference between the flood and MQL systems, further validating the importance of understanding the effects of different cutting fluid systems.

4 Conclusions

The literature review highlighted that cutting fluid effects in bandsawing are seldom studied and need more attention from both academic and industry research. Further study could potentially reduce the usage of the cutting fluid and improve the band saw blade life, thereby increasing the sustainability of the band sawing process. A global survey of the cutting fluid usage in the band sawing application has shown that the majority of the industry is employing flood coolant application with flow rate of more than 4–6 l/min. The flood coolant application cost can be as high as 8% of the total consumables (cutting fluid and cutting tool) cost of the band sawing process. An initial attempt at evaluating the flood coolant application and MQL using ProcSI, a metric-based sustainable index, has shown that a sustainable solution such as MQL can be economic, environmental, and energy-friendly. Future research is recommended to assess ProcSI metrics for other sustainable solutions such as MQC and dry along with their industrial applicability.