How lubricants can help in improving CNC machine performance

By OEM Update Editorial April 12, 2017 12:15 am IST

A round up on how lubricants can improve the performance of CNC machine.

There are several different variables that need to be taken into consideration by manufacturers who are in search of improving the performance and health of their CNC machines. Most important is to consider specifically the material that is being machined and also the correct lubrication processes.

In case of lubricants, specifically, two types of lubricants are used in CNC machine operations.First is the metalworking or cutting fluid that is used on the cutting surfaces. Second is the lubricants that assists the internal machinery. This lubricant is also called as behind-the-scenes lubricant.

Making the right choices for both is essential to maximizing machine performance and health. Using the wrong metalworking fluid has the potential to be disastrous, as it not only affects tool life, but also directly impacts product quality. Likewise, drilling speeds, feed rate and the type of material being machined all impact the life of the metalworking tool, as well as the productivity of your CNC machinery.

Chipping and Built Up Edge, commonly known as BUE is one big problem when a big piece of metal is worked upon. At times, materials like aluminium, steel, and titanium are prone to chip welding. This causes extra metal chips to break off during the cutting process which get welded back on the cutting tool. This happens due to extreme heat and friction. This can quickly lead to a broken cutting tool, or a tool that won’t delivered desired results—such as lower quality product, and more maintenance—but can all be avoided by using the proper metalworking fluid for your operation and material.

Lubrication helps the tool to cut more easily. This generates less heat and friction and clears the chips away from the cut. Even if coatings are believed to be used on the tool and provide lubrication, they tend to be fragile and don’t deal with the problem as well as a mist or flood metalworking fluid.

Along with preventing BUE and reducing the heat and friction of the tools, there are several benefits of lubricants. Overheating the tool can increase the wear and tear exponentially resulting into dullness of the machines. This can lead to bending of the tool totally out of shape. As the name implies, coolant is essential for cooling off the tool during the cutting process. The right coolant for the material and process will help extend the life of the tooling.

While metalworking fluids are typically the most effective lubricant for CNC machines, aftermarket tool coatings can also provide some of the same benefits. Sending out tools to get these protective coatings is a service that can provide beneficial return. For example, aluminium oxide can help reduce cycle times, while also improving tool life, feed rates, and cutting speeds.

Lubricants are not only used for reducing the down time of the machines and reduce the friction. in addition to this, lubricants also play a major role in improving the performance of CNC machines. We speak to some of the experts in the lubricants sector who openly discuss about the role of lubricants in improving the performance of CNC machines.

Computer Numerical Control (CNC) machines automate the machine tools by means of computers executing pre-programmed sequences of machine control commands. This is in contrast to machines that are manually controlled by hand wheels or levers, or mechanically automated by cams alone. Any particular component might require the use of a number of different tools – drills, saws, etc. – modern machines often combine multiple tools into a single ‘cell’. In other installations, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine.

Companies specialising in producing nuts and bolts, complex gear sets or high precision valves, pay high emphases on efficient functioning of the components of their computer-controlled cutting machines for long term profitability. Speaking about role of lubricants in improving the overall performance of the CNC machines, Shankar Karnik, General Manager, Industrial, ExxonMobil Lubricants Pvt Ltd says, “Lubrication plays an integral role in reducing friction between critical rotating and moving machine components, which then translates into equipment durability, longevity and continued uptime.”

Karnik further says that in order to make sure that the machine runs smoothly, it is important to choose a combination of high-quality metal working lubricants such as slideway oils, water soluble cutting fluids and neat cutting oils.

Slideway Oils
Throwing light on the role of slideway oils, Karnik says, “Poorly formulated slideway oils may not separate readily from aqueous coolants.” As a result of this, tramp oil if formed. The tramp oil compromises the effectiveness of the coolant by shortening its effective life and adversely altering cutting performance. Adding further, he says, “The Tramp oil can also lead to bacterial growth resulting in foul odour, short service life and potential health as well as safety concerns.”

Speaking about how one can identify high performance slideway oils, Karnik suggests that the maintenance professionals should seek out products such as Mobil Vactra Oil Numbered Series of slideway oils with the following performance characteristic:

Exceptional coolant separability which enhances the performance and life of water based metal working fluids, outstanding frictional properties which enable increased machine accuracy and reduced chatter, and stick-slip.

Sharing the details of one of the company’s offerings, Karnik adds that Mobil Vactra OilNo.2 is a premium-quality ExxonMobil slideway lubricants specifically designed to meet the requirements for accuracy, aqueous coolant separability, and equipment protection of precision machine tools.

Water Soluble Cutting Fluids
“To optimise productivity it is very important to choose technology-leading aqueous coolants. The highest performing coolants can reduce maintenance requirements by resisting biological attack thereby extend batch life,” explains Karnik. According to him, the ease of maintenance needs to be balanced with performance as well as protecting the CNC machine components from corrosion and sticky deposits.
In addition, the fluids should meet the latest health and safety regulations, be easy to monitor and maintain in service. Collectively, these properties will help deliver long service life, excellent cutting performance and reduced maintenance downtime.

Exxon Mobil has come up with a new Mobilcut series that comprises of milky emulsions, high performance micro-emulsions and a fully synthetic grinding fluid. “The high performance, long life semi-synthetic cutting fluids in particular have been designed to meet the wide variety of applications and operations found in medium to small sized CNC machines,” claims Karnik.

As per the claims of the company, Mobilcut 250 is a high performance semi-synthetic fluid formulated to enhance performance when machining aluminium and aluminium alloys and where low staining potential is important on sensitive components. Containing high levels of lubricity agents, it provides high machining performance of carbon and alloy steels and yellow metals.

Neat Cutting Oils
Neat or straight cutting oils are used in applications which are beyond the typical performance profile of aqueous coolants, such as tapping and threading of high alloy steels. “They improve machining in high speed automated machining centres through outstanding cutting performance, reduced tool wear and enhanced surface finish,” explains Karnik.

Throwing light on the offerings in the neat cutting oil section, Karnik adds, “Specially designed to meet the increasing demands of today’s sophisticated machining centres, tooling trends and health and safety regulations, Mobilmet series of cutting oils and the new series of Mobilgrind grinding oils from ExxonMobil have been developed for applications where excellent surface finish, high precision machining and improved productivity are the primary objectives.”

Spindle oils
Spindle oils are used for high speed spindle bearings and equipment where high speeds and fine clearances are involved. It provides exceptional lubrication of close-tolerance bearings which helps keep the bearings running cool and helps maintain the precision required by many of today’s critical machine equipment. “These are designed for spindle bearings and they exhibit the required properties to function as low pressure hydraulic and circulating oils as long as the proper viscosity is selected,” adds Karnik.

As per the claims by the company, the Mobil Velocite oils are premium performance products primarily designed for the lubrication of high-speed spindles in machine tools. They are also used in some critical hydraulic, circulation systems and air line oilers where the appropriate viscosity grade is selected.

Right choices maximise machine life
Explaining how lubricants help in improving CNC machine performance, Akhil Jha, Chief Technology Officer, Shell Lubricants India says, “ There are two types of lubricants that are used in CNC machine operations – the metalworking or cutting fluid, that are used on the cutting surfaces and the behind-the-scenes lubricant that lubricates the internal machinery, mainly hydraulic oils, slide-way oils and greases.”
Jha believes that making the right choices for both is essential to maximise machine health and performance. He further adds, “Other than the basic performance – lubrication, protection, cooling, cleaning and sealing, lubricants help in improving CNC machine performance in the following ways:

• Reduce rejections by precision movement of tool to achieve desired dimension of the job.
• Increase tool life by protecting the tool against rapid wear, which in turn reduces per component cost.
• Protects equipment from corrosion as the machine handles large amount of water in the form of coolant (in case of water soluble lubricant)
• Maintains a cleaner system due to filterability which in turn supplies adequate fluid for protection.
• CNC machines also have the challenge of water washout of slide-way oils, which increases consumption of both slide-way oil and the water soluble coolant.

It is believed that even though each lubrication point is important, more emphasis is given to the slideway operation in any CNC machine for precise movement of the tool and job. Adding further, Jha says, “A slideway lubricant must provide a stable, adhesive lubricant film to protect machine slideways even in the presence of metalworking fluids in varying feed and pressure conditions.”

Jha lists down the following criteria that must be followed when it comes to slideway lubricants. They are as follows:

• Lower friction on slide-way
• Avoid jerking motion of tool/work (Stick-Slip)
• Should Separate from coolant (Demulsibility) for tramp oil collection ease.
• Resist wash-out by soluble cutting fluid (Adhesiveness)
• Protect from Corrosion (Corrosion Inhibition)
• Should not affect life of Soluble Cutting Fluid (Compatibility)
• Be compatible with guide materials

The above mentioned properties are not present in hydraulic oils. Speaking about this, Jha says, “A good quality hydraulic oil in a CNC machine is used for creating clamping force for work or tool.”

Jha feels that it is imperative to choose the right hydraulic oil in order to avoid change in properties of oil like viscosity. Also, the absence of pressure drops causes lower clamping force and tool vibration. It should also be compatible with seals and hose material to avoid leakage and hose burst. It also has a lower down-time due to pump or hose burst failure.

Conclusion
For most CNC operations, metalworking fluids are necessary for ensuring the highest quality cuts and end product, while also helping to maximise the efficiency of the process. The effective usage of the correct lubricants will help the manufacturers make the most of the CNC machines.