To get the best return on the production of any part, every element in the manufacturing process must be optimised. Cutting tool life is one of them and it can be a significant factor. An increase of between 15% and 30% can be achieved by simply adopting the best coolant for the job.
In the aerospace industry, where titanium alloys are commonly employed, this is especially important. The machining processes can often result in temperatures at the point of cut of around 1,000 °C, which can quickly dull cutting tools. And the situation gets worse, if not addressed, as worn cutting tools generate even more heat.
So how do you go about choosing the right coolant for the job? The approach that Master Chemical (01449 726800) advocates is to measure spindle motor load. This can be effectively established by the measurement of current change during the cutting process.
Different types of metalworking fluids must also be considered. Synthetic fluids are low-foaming, have good filterability and cleanliness, and dissipate heat. Soluble oils offer enhanced lubricity. Semi-synthetics can provide the best of both worlds: clean running and lubricity. In the end, multiple factors must be reviewed, including machine and operator requirements, water quality, fluid management, fluid delivery and pressure.
The most effective analysis requires cutting the same materials of manufacture with the tools used in the process under evaluation. Everything, with the exception of the coolants under test, must remain constant. This allows an accurate assessment of which coolant provides greater lubricity, based on the measurement of spindle load.
In the production environment, normal day-to-day variables, such as different machine operators and inconsistent coolant maintenance, can distort results. It is therefore better to use an outside machining laboratory to achieve the consistency needed. Such a facility is ideally suited to providing the impartial scientific data needed for effective decision-making.
In one example, a Tier 1 aerospace manufacturer was machining large quantities of Ti-6 Al-4V at its various plants, with each site applying a different metalworking fluid. Clearly, savings could be made by choosing the best and applying it universally, but also the manufacturer wanted to select the coolant that maximised tool life and optimised the machining process.
Working in partnership with Master Chemical, the company opted for independent testing to determine which fluids provided sufficient lubricity by measuring the cutting parameters. Multiple performance factors needed to be taken into account when selecting the best coolant for cutting titanium. In all, five machining fluids were evaluated, including Master Chemical's TRIM MicroSol 585XT and four competitive cutting fluids. Each fluid was tested on a Haas VF4 vertical machining centre and run at 6% concentration, diluted in de-ionised water.
Based on both cutting and non-cutting function, the results show that Master Chemical's MicroSol 585XT would be the best overall choice, based on laboratory test results.
While independent laboratory testing of metalworking fluids is still not common within the industry, demand is increasing. Master Chemical reports significant interest amongst its customers, as it allows a decision to be made based on science.
COOLANT FOULING NO MORE
At the Airbus plant at Broughton, Flintshire, coolant fouling has been eliminated, thanks to Alfa Laval's AlfaPure Z3 coolant treatment system (01276 413632).
The AlfaPure Z3 is employed on a line producing aluminium stringers, machined from solid aluminium billets 200 mm wide and up to 1 tonne in weight. It takes approximately 4.5 hours to machine a 15 m billet of 20/26 aluminium and 27,000 litres of water-based coolant to enhance tool life and maintain the correct operating temperature.
Although a coolant and swarf management system decontaminates the swarf and solid scrap produced by machining, ready for disposal, it does not treat the coolant itself. Tramp oils entrained in the coolant can cause bacterial growth and represent a potential health hazard. They can also coat the surfaces inside the CNC machine, allowing foreign objects to adhere to them.
Initially, Airbus engineers addressed these problems by frequent cleaning of the production line and regular coolant replacement, an expensive option, thanks to high coolant costs and the need to employ specialist waste disposal contractors. After considering a number of options, Airbus chose Alfa Laval's centrifugal separator-based system, the AlfaPure Z3 system, to recover and recycle the coolant.
The system cleans and recycles 3,000 litres of coolant per hour and since its installation, the company has eliminated problems caused by contaminated coolant. Bacterial growth is a thing of the past, as are unscheduled breaks for clean-up operations. Over a two-year operating period, any additional coolant needed was purely for topping-up fluid lost on workpieces or scrap.
At subcontractor Roscomac, as part of its lean initiative, the company identified non-core elements of its business, in order to drive up the efficient use of its own people and resources. One area has been cutting fluid management, with Jemtech (01825 767640) offering its assistance in the matter. "In the past few months, we have invested over £3 million in new machine tools, including six horizontal machining centres – four with 630 mm3 pallets and two with 500 mm3 pallets," says Joe Martello, Roscomac's managing director. "I would much rather my people are focused on ensuring these machines are making components, rather than worrying about whether the coolant is at the correct concentration."
To address this, Roscomac has signed a fluid management agreement with Jemtech (UK) to provide a supplier-driven, cost-effective fluid monitoring service for all of the company's machine tools. As part of that service, Jemtech is on site three mornings per week to monitor fluid use, pH values, coolant concentrations, and carry out general checks to ascertain whether tramp oil and odours are an issue.
Image: Roscomac has signed a fluid management agreement with Jemtech (UK)
If any issues are notified to, or identified, by Jemtech, then it has the autonomy to carry out a root and branch investigation to resolve them. "We have direct contact with the senior people at Jemtech and, if we raise any issues, they are dealt with immediately. As a result of the support they are providing, and since they have replaced our cutting fluids with Blaser products, we have had no health and safety issues, or skin-related problems, while tool life has increased dramatically,10-fold in some applications."
Before Roscomac invited Jemtech to undertake this fluid management project and switch all of its machines over to Blaser Swisslube products, it may have had up to 10 people with some level of responsibility for monitoring cutting fluids. As this was only a part of their job function, the temptation was for them to keep it at a stage where it was okay, rather than investigating why a situation may have arisen and remedying it.
"In Jemtech, we have a supplier that has a highly pro-active, can-do attitude, and one of the reassuring things about working with Jemtech is that we can give them our instructions and be confident that they will be carried out completely, if not improved on," Mr Martello says. "This means that we are able to totally rely on them to maintain our cutting fluids and, by default, the performance of our machines. Having taken this decision to outsource fluid management, we do not want to be spoon-feeding our supplier. With Jemtech, they turn up, do what needs to be done and leave; we hardly notice them, which is a sign that the process is working extremely well."
First published in Machinery, June 2011
An Armenian language version of this article is available here