Slideway oil affects both the machining precision and service life of metalworking fluid. By Imtiaz Ahmed, Asia Pacific Mobil SHC brand manager, ExxonMobil Lubricants
The metalworking industry in the Asia Pacific is booming due to a rise in urbanisation, cheaper manufacturing costs and increasing automation in the region. This has in part been driven by strong growth and an optimistic outlook in the Asia Pacific region as it remains an attractive manufacturing hub for regional and global exports.
According to the IDC Manufacturing Insights Spending Guide, manufacturing spending in the Asia Pacific, excluding Japan, will grow at a compound annual growth rate (CAGR) of 4.8 percent for the 2015-2019 period. Manufacturers are moving towards automation and digitalisation to ensure that their factories are operationally efficient. The rise in intelligent manufacturing calls for more complex machine tools and machining processes, creating a demand in the metalworking industry.
Consequently, the expansion in metalworking has resulted in a demand for metalworking lubricants. The global metalworking fluids market was estimated to be worth US$8.3 billion in 2014 and is expected to reach US$9.74 billion by 2020 based on a CAGR of 3.2 percent from 2015-2020. This growth is in part driven by the use of removal fluid as coolants across the manufacturing industry to maintain optimum temperature and to remove unwanted metal chips during the grinding, drilling, and other processes.
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A lot of friction and heat is produced, whether from the simple production of nuts and bolts to more complex, tougher metalworking processes. In addition, these heavy-duty processes require machines to be both precise and efficient in their working, which is why lubricants and coolants play a vital role in the machine’s performance and maintenance.
In addition, companies are looking for ways to reduce costs while increasing profitability and many players in the metalworking industry are adopting green practices, including using vegetable-based coolants, and finding ways to reduce wastage such as implementing recycling programs or reusing coolants instead of disposing of them.
However, not all cutting fluids can be reused as they do not meet the lubrication, cooling and protection requirements of each application for every machine. This is why choosing the right combination of high-quality lubricants – slideway oils, water-soluble cutting fluids and neat cutting oils – ensures machine tools run smoothly for a longer time, and helps to cut costs and reduce wastage, ultimately enabling the machines to be more operationally efficient.
Slideway operations, in particular, require special attention to friction to ensure it runs smoothly and with precision. When moment frictional control is lost, this can cause inaccuracies, ultimately resulting in lost productivity.
Slideways move in a linear motion, therefore the slides would have to stop when they reach the end and move again in the opposite direction. Their stepwise manner of operations would mean that they need to use mixed lubrication to operate efficiently. Consequently, a mixed lubrication setting would make slideways more susceptible to the stick-slip phenomenon.
Stick-slip occurs when there is more static friction than dynamic friction. This causes jerky movements to the slide and the attached work tool. Uncontrolled motion such as this can result in inaccuracies in operations, poor quality and loss in production. To have better friction control, friction modifiers such as special additives are being added to the lubricant.
Choosing the right slideway oils enhances the productivity of modern machine shops as they affect both the machining precision and service life of the metalworking fluid. Slideway oils must provide outstanding friction control and excellent separability from aqueous coolants that are commonly used in metalworking operations.
Such lubrication usually happens in an open machine system, which increases the chances of contamination in the coolant circulation system. The contamination between slideway oils and aqueous coolants will eventually form tramp oil.
Tramp oil is a primary contaminant in these systems and causes a lot of problems that affect the working life of the equipment:
- High volumes of tramp oil in aqueous coolants can also change coolant concentrations and cause coolant foaming, which makes monitoring more difficult.
- Lubricity in the machine may be reduced, which leads to tool wear and poor precision finish.
- Coolant pH levels can also be reduced, which causes corrosion.
- There is also a risk of increased bacterial growth and the formation of undesirable odours in the machine shop. These complications reduce the life of coolants and cause health problems for employees.
Tramp oil can also enter the metalworking fluid in more than one way, including leaks from way, gear, spindle, and hydraulic oils, or oil on parts from previous operations. The more oil is used, the more tramp oil will need to be removed, resulting in an increase in operational and maintenance costs, as well as reduced productivity in the long-run.
What To Look For : Coolant Separability
Knowing what properties to look out for when choosing slideway lubricants is vital to prevent the formation and contamination of tramp oil.
A key factor is the ability of slideway oils to separate from water-soluble coolants quickly and completely. If the separation between the oil and the coolant is not complete, the performance of the aqueous coolant can be severely affected, which results in high operational costs and unscheduled machine downtime. A slideway oil with good coolant separability properties will also allow machine tools to operate with optimal precision. This will help enhance the life and performance of the aqueous coolant and improve metalworking processes.
Proper Maintenance of Machining Processes
While slideway oils are the most common source of oil contamination in aqueous coolants, other lubricants such as hydraulic oil, gear oil and grease can interfere with the life of the coolant. Metalworking operators need to adopt maintenance practices to prevent contamination from interfering with a machine shop’s operational efficiency.
Operators need to monitor coolant concentration on a regular basis to maximise coolant life. This is to ensure that there is no build-up of tramp oil as a result of slideway oil emulsification.
Tramp oil can be detected in the system by using lubricant analysis. Operators can test for coolant concentration by measuring by titration and then compare the results with new, unused coolant to determine the levels of emulsified tramp oil.
Removal of tramp oil is done by automatic skimmers that can be found in many modern machine tools available today. Filter and centrifuges can also be used is larger systems to remove contaminants. Alternatively, contaminants can also be removed manually by using specialised equipment such as an industrial vacuum cleaner.
On top of choosing the right slideway oil and coolant for your metalworking needs, using a single supplier for both metalworking fluids can help limit compatibility and contamination issues. This, combined with proper maintenance and regular testing, play a part in ensuring precise and efficient operations.
Driving Efficiency And Advancing Productivity
Metalworking fluids such as slideway oil and coolants were once considered as a basic necessity to keep machine tools operating. Today, they have become important factors to enable machine shop operators to improve operational efficiency so as to reduce costs and increase profit margins. Metalworking fluids are now considered as liquid tools and they should be treated with the same degree of importance as machines tools since they have a direct impact on productivity and profitability.
While the selection process of slideway oils and coolants is dependent on the variety of applications in machine shop, choosing good quality metalworking fluids will work for most applications such as turning, drilling, milling, forming and stamping. The metalworking industry needs to ensure operational excellence with the right lubrication solutions and proper maintenance allowing them to focus on innovation to capitalise on future growth opportunities.
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