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Selection of coolant for titanium alloy processing

The use of independent laboratories to test different coolants can provide the necessary data for the correct selection of coolants for titanium alloy processing.

In today's difficult economic environment, increased cutting tool life can provide an important competitive advantage.In the process of processing, the selection of suitable coolant can increase the tool life by 15%-30%.But how will the end user know which coolant is the right choice?

Proper selection of coolant is especially important in aerospace parts manufacturing, where competition is fierce.The uncertain economic environment has increased pressure on component manufacturers to control costs.They optimize processing procedures, test new tool technologies, and upgrade machine tools.

Because of its high strength, light weight and corrosion resistance, many aircraft parts are made of titanium alloy.However, the thermal conductivity of titanium alloy is poor, the temperature generated in the cutting process can be as high as 1100℃, will lead to the rapid passivation of the tool, and with the passivation of the cutting edge processing may produce more heat, further shortening the tool life.Adequate lubrication is essential to the efficient machining of titanium alloys because insufficient lubrication is a common cause of cutting tool failure.

Effectiveness evaluation

How can the effectiveness of coolant in prolonging tool life and optimizing the machining cycle be assessed?Milton Hoff, vice President of strategic technology development at Master Chemical Corp.Spindle motor load can be monitored very effectively.Most machine tool controllers can monitor the maximum current load in a standard cutting cycle.If the machine does not have this monitoring function, a separate ammeter can also be set up to measure the current changes in a machining step.Either way, the starting current and the maximum current need to be measured.

When processing titanium alloys, careful consideration is required to determine which metal cutting fluid to use.Synthetic cutting fluid has less foam, good filtering, cleanliness and heat dissipation, while soluble cutting oil has better lubrication.Semi-synthetic cutting fluids provide effective lubrication and cleanliness while also helping to extend the life of the tank, which is the best of both worlds.Finally, a number of factors must be considered, including the needs of machine tools and operators, water quality, the management of cutting fluids, and the delivery and pressure of cutting fluids.

In order to perform the most effective analysis, cutting tests need to be performed using the same tool and workpiece materials as the process being evaluated."When a workpiece is machined, all parameters except the coolant are kept constant," Hoff said.

The results of these tests within the enterprise are questionable, as conditions such as the suitability of the machine, different operators, and the maintenance of the coolant can vary, potentially distorting the results.Evaluation of cutting fluids by external laboratories can provide unbiased scientific data needed for effective decision-making.Masdar chemical, for example, has been working with the machining laboratory at owens community college, also in perrisburg, to test cutting fluids and processes.

Problem solution

A tier 1 aerospace parts manufacturer processes a large number of Ti6Al4V parts in its affiliated plants and notes the rapid growth in the use of this titanium alloy.Since each plant USES a different metal cutting fluid for processing titanium alloys, the manufacturer is interested in choosing a cutting fluid to extend tool life and thus reduce tool costs.In order to further reduce processing costs, manufacturers want to choose the most efficient titanium alloy processing process.

When processing titanium alloy, the tool cost is very high, therefore, in the premise of ensuring the quality of the workpiece, to maximize the tool life is crucial.Because the manufacturers don't have the relevant data (these figures can show what kind of cutting fluid used is the best choice of the standardized processing), and the factory site test is not a good choice, so the aviation manufacturers decided to cooperate with masdar chemical company, using the owens community college test apparatus to evaluate the coolant used in the factory.The use of the college's cutting laboratory can provide the manufacturer with fair results and without the need to use its own resources.The laboratory will determine which coolant will provide adequate lubrication by measuring the cutting parameters during the test.

The requirement of cooling fluid for cutting titanium alloy machine tools is: low atomization degree, reduce the possibility of slipping when workers are walking on the worktable of large machine tools to clean up the chip, and avoid residual sticky cooling fluid that causes the chip of titanium alloy to stick to the machine.After the cutting tests have been completed, the laboratory will also conduct tests to compare some of the important non-cutting functions of the cutting fluid, including biological stability, tank life, and some of the performance related to health and safety.

The test object was identified as Weldon tools co. 's M42 cobalt high speed steel end mill (4 slots, diameter 19.05mm, uncoated, corner radius 3.175mm).The cutting parameters on the full diameter are: axial cutting depth 8.90mm, cutting speed 60sfm, chip load 0.1143mm per tooth, feed rate 100mm/min.Adopt the way of milling.

The test stipulates that each cutting fluid shall be used to cut twice the Ti6Al4V blank (size 180mm×200mm×1500mm) provided by the aerospace parts manufacturer, and the Ti6Al4V plate shall be cut once, that is, each cutting fluid shall conduct a total of three cutting tests.The test was performed at the Haas VF4 vertical machining center in the owens college cutting laboratory with a CAT40 taper shank and computer-controlled coolant flow.

A total of 5 cutting fluids were evaluated, including TRIM MicroSol 585 from masdar chemical and 4 from other competitors.Each cutting fluid was diluted with deionized water to a concentration of 6%.Tool life is the decisive factor in the test.After the test, all chips and materials were returned to the aerospace parts manufacturer.

Measurement and results

According to the above parameters of the cutting test, the expected life of the tool is 3 hours.The tool was examined by OGP optical comparator, and the detritus tumor was measured and micrograph was taken.To avoid the effect of work hardening, a measurement is made after each tool has completed a tool walk on the specimen (the cutting time is approximately 30 minutes).At the same time, the reading value of spindle current load meter was recorded.

According to the original plan, we need to measure the wear on the back of the tool.However, since the tool is helical and fan-shaped, no straight edge can be used in the laboratory as a reference point for measuring the actual wear of the rear tool surface, so the chiffolidoma was chosen as an alternative indicator.After observing the preliminary tests in the cutting laboratory, the material and process engineers of the aerospace parts manufacturer found the test scheme satisfactory.

The maximum current load recorded by the machine tool controller was used to compare the five cutting fluids.For each coolant, the motor's current load increases gradually during processing.The lower the current change slope, the longer the tool life (cutting fluid A and B have the lowest slopes).Record the average value of the maximum current of the motor in all cuts, and record the upper and lower limits of the maximum current in the actual processing.The smaller the mean value of the maximum current and the distribution interval of the upper and lower limits are, the longer the tool life is (or indicates that cutting fluids A and B perform better).

Tool life can also be predicted by measuring the maximum lumps found on any of the four cutting edges after the set number of walking times.This is because the tool with the larger lumps is more passivated and therefore has a shorter life.The average chip height of the cutting fluid A and B was the lowest, and the distribution interval of the upper and lower limits of the chip height was the smallest, indicating the longest tool life.

In the experiment, the tumor was measured after each processing, and 139 photos were taken with the OGP optical comparator.For each cutting fluid, the cutting edge with the largest chip tumor in the 4 cutting edges appeared after the 26th and last cutting tool.

Some important non - cutting functions (including residual property, biological stability and corrosion resistance) of 5 cutting fluids were tested.In each category, the best performer is given a score of 5, the second best is given a score of 4, and so on.The scoring system is unweighted (that is, all test items are considered of equal importance).In the residual test, cutting fluid A and E obtained high scores, while cutting fluid B and D had large residues on the machine tool, test equipment and surrounding areas.It can also be determined that the two cutting fluids on the machine tool workbench residual wet liquid is more likely.Cutting fluid residue will also lead to increased cutting fluid consumption.

In the foam dissipation time test, cutting fluids B and C showed excellent foam characteristics.In the corrosion test of black metal in cutting fluid mixed with tap water, cutting fluid A, D and E obtained high scores, while cutting fluid C produced severe corrosion of black metal.In the biological stability test, cutting fluid C and D were highly rated, while cutting fluid B scored very low due to the possibility of rancidity.In the fungal stability test, cutting fluid C and E were the best, while cutting fluid B showed poor fungal stability.According to laboratory test results, cutting fluid A and C total score ranked the highest.According to the overall evaluation of all non-cutting and cutting performance, cutting fluid A (MicroSol 585) is the best choice.

Upon completion of the test, the test data will be provided to the aerospace parts manufacturer for review."By evaluating the test data, we can help select the coolant that maximizes tool life during processing," Hoff said.This is, of course, a controlled test that does not take into account some of the variables that may or will arise in actual processing.But it points you in the right direction to choose the lubricants that are acceptable to the process."

Chuck Gee, manager of aerospace processing at masdar chemical, used the case study to illustrate the advantages of external testing."I showed the case to a manufacturing engineer who was evaluating our products for his company."The idea of making decisions based entirely on scientific data has great appeal, and he is working on a review schedule for his company."

Although external testing of metal cutting fluids is not yet widespread in the industry, demand is growing.Masdar chemical provides the service approximately once a month."You can make decisions based on the data.When you put data, graphs and tables in front of an engineer, when he knows this is an independent study under controlled environmental conditions, he trusts the results."

The benefit for users is that they can make decisions based on science.Knowing which coolant can extend tool life by 20 percent means significant savings in processing time and cost.Knowing which coolant is most effective at preventing foam problems, extending tank life, and providing biological stability will improve the overall quality of the workpiece.


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