Correct use of coolant can achieve 20% increase in cutting speed with ISO S classified materials
The demand for faster, cheaper, and greener aerospace solutions is increasing, but building zero-emissions aircraft comes with significant challenges. CO2 emissions during aircraft operation have been the main focus, but the impact of material processing during manufacturing operations is equally crucial as it effects production rates, efficiency and quality control. Fortunately, a solution to these challenges is correctly applying coolant to maximize output, enhance process security and improve tool performance — and why the aerospace lubricants market is growing at a projected compound annual growth rate (CAGR) of 19% from 2022 to 2027. Here, Henri Sevonen, Senior Industry Segment Manager – Aerospace for the metal cutting specialist Sandvik Coromant, explains the benefits of high precision coolant and innovative tooling concepts.
The role of coolants in machining aerospace parts has undergone somewhat of an evolution. Machine shops have for many years used coolants by directing tubes that flood the machining zone, particularly on the materials that need coolant to be machined. But now, by applying coolant with high precision accurately into the machining zone, new advantages are available. Broad access to this technology has been made possible by higher coolant-supply capacity of many CNC machines as well as by new tooling concepts.
Making a difference
If coolant is to be applied effectively and make a difference, it needs to be applied as jets at high precision, in sufficient volume and directed correctly. Just having a stream of coolant or even flooding the machining zone with coolant is not enough. Qualified application of high precision coolant can, on the other hand, make a distinct difference with regards to chip formation, distribution of heat, smearing of workpiece material on the cutting edge, surface integrity and tool wear.
These basic machining factors affect manufacturing through the objects of improvement to achieve higher competitiveness in terms of productivity, tool life, chip control and chip evacuation and component quality.
When applied correctly, precision coolant maximizes output, increases process security and improves tool performance and component quality. The positive effects start at low coolant pressure, but the higher the pressure is, the more demanding material can successfully be machined.
The application of precision coolant can make a difference to machining in general, especially for stainless steel and low-carbon steel. But it is when machining more demanding materials, such as heat resistant super alloys (HRSAs) and titanium alloys, that the practice makes a dramatic difference. It is of consequence then that a number of recent developments have made high precision coolant even more interesting and more readily available.
High precision coolant as standard
Many modern CNC machines have coolant supplies at pressures of 70 to 100 bar as standard or as an option with capable tanks and pumps. This is sufficient to incorporate high precision coolant, which makes a noticeable difference to performance and results on more commonly used machining centres, turning centres, vertical lathes and multi-task machines. Standard equipment is sufficient with easy channelling of coolant to where the jet is applied.
An essential basis for high precision coolant machining are modular tools, partly to ensure quick tool changes for minimizing machine stoppages, but also to efficiently secure coolant connections and channels from the machine to cutting edge. The modular quick-change tooling system Coromant Capto® is today the basis for new standard high-precision coolant tooling. This system is ideal as a modular platform, designed with internal coolant supply and also suited as the means with which to supply coolant at high precision. It is an established ISO standard and option on many CNC machines with stationary and rotating tools.
Precision over coolant precisely directed towards the cutting zone improves chip control and process security. Under coolant increases tool life and productivity, especially in applications generating a lot of heat in the insert.
Precision coolant for turning.
Turning tools with precision coolant are equipped to give accurate coolant jets with laminar parallel flow. The jets give rise to a hydraulic wedge between insert and chip, affecting the chip form and flow and reducing temperature in the machining zone. Employing nozzles, mounted close to the cutting edge, accurately projecting the high-velocity jets, forces the chip off the insert face and cools and breaks the chips into smaller lengths, helping to evacuate them.
Benefits in finishing operations have been established even at lower pressures, down to ten bars in material including steel, stainless steel, aluminum, as well as titanium and heat resistant super alloys. Apart from higher security brought about by better chip control, precision coolant can bring about a considerable improvement of tool life and a potential for higher cutting speed. By applying precision coolant, 50% tool life increases can often be the result.
Cutting speed affects the temperature, and thus tool wear, more than any other factor. Increasing the cutting speed in titanium outside the more limited machinability window reduces tool life dramatically. But when the feed is increased on a similar scale, a smaller reduction in tool life is typical. This often makes the feed an attractive route to improved metal removal rate with low effect on tool life. However, high feed is not always an option in these machines because of higher cutting forces as well as the effect on chip control.
Turning of a HRSA turbine disc
Precision coolant can play a vital role in ISO S machining. The effect of precision coolant can therefore provide the potential to raise performance by way of higher cutting speeds without the usual rise in temperature and loss in tool life. There is a clear cooling effect and not the higher cutting forces through higher feeds. For ISO S classified materials, a 20% increase in cutting speed can be achieved while maintaining the same cutting length.
Internal turning is also an area where precision coolant can provide an important role to help ensure good chip formation, as well as improving shearing properties in demanding materials such as titanium. In this way the concept adds higher security and longer tool life to boring operations. When machining relatively large, deep holes with boring bars, such as in landing gear components, modular tooling at the back as well as the front end of the tool can be advantageous.
Being able to change the small cutting head on the clamped bar provides quick, easy and accurate changing, adding considerable flexibility for various cuts in one set-up. CoroTurn® SL combines damped boring bars with serrated locking of heads for boring larger holes with depths of ten times the diameter and is also equipped with precision coolant facilities.
Variation in component surface integrity is affected by the temperature and forces generated during machining. Coolant certainly plays its part in controlling the temperature and consequently precision coolant has been shown to provide a more reliable surface result. Tool nozzles are aimed directly at the part of the insert in contact with the finished surface. Since the nozzles are non-adjustable a lot of the variables are eliminated, resulting in a more secure and consistent machining process.
Optimization of correctly established operations
With the ability to force a fluid wedge into the machining zone, especially in operations classified as medium to finish turning, the chip thickness is more controllable and the fluid wedge easier to apply than in roughing operations.
The application of high precision coolant machining should not be seen as a means with which to compensate shortcomings due to other application factors — such as unsuitable inserts, instability or incorrect cutting data. Precision coolant is an optimizer when operations are correctly established. The concept will provide the means for shorter cycle times, improved component quality consistency and higher process security in turning and milling.
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