High speed machining (HSM) offers manufacturers many productivity benefits but to get the real edge over the competition machinists need to use the right cutting tool. Katherine Crichton reports.
WHILE much of the discussion surrounding high speed machining tends to revolve around the role played by the machine tool, this intense focus on one aspect of the HSM equation can often shift attention away from the other key components in the process.
A common misconception is that the machine tool is the most costly investment in the HSM process but often over the entire life of the machine tool, the amount of money spent on cutting tools can exceed that of the machine.
With this in mind, it is important to recognise the benefits of using premium cutting tool technologies. Tool manufacturers and suppliers are staying on the cutting edge of HSM developments by providing more advanced, sophisticated tools in order to deliver the reduction of lead times possible with HSM without sacrificing quality.
Jason Theobald, productivity engineer with Sandvik Coromant, said improvements in materials (substrates) geometry and coatings as well as innovations in insert location, are helping to meet the higher temperatures and increased data that HSM demands.
“Technology such as Stressless coating, which is a treatment to the top coating, is enabling machining at high metal removal rates which improves the resistance to crater wear and plastic deformation.
“These coatings are made of a thick MT-CVD coating which not only provides better surface finish generation but by removing the top coating of tin leaving black AlO2, leaving the gold Tin coating around the periphery, allows for a better detection of wear and tear on the tool,” Theobald explained.
“HSM in hardened steel has also come a long way, especially in regards to solid carbide cutters. Dedicated carbide grades and cutting flute designs are available that can comfortably machine hardened steel to 63 HRc.”
However even the best designs and coatings in the world are of little value if they are not applied to the appropriate substrates. One of the most notable indicators of a quality substrate said to be the size of the grain and typically, the smaller the grain size, the better suited the tool is for HSM applications.
“New substrate technology, which has an ultra fine grain structure coupled with the above mentioned coating technology, is enabling tool manufacturers to produce indexable inserts that are capable of machining hardened steel,” Theobald said.
“Another development which is paramount in delivering a high quality tool suited to HSM is innovative, secure and accurate insert location.”
Coromant has developed a number of insert location methods, so for example inserts with serrations that match serrations in the tool.
“With an increase in cutting speed, comes an increase in centrifugal force trying to pull the insert out and the serrations help keep the insert in place as it takes the load bearing requirement away from the insert screw,” Theobald said.
The cutting tool manufacturer also laser etches a max RPM value on its cutter bodies to help ensure there is no guess work involved in the safe and efficient use of the cutting tools.
Making the cut
Having the most up-to-date tooling is only one ingredient in the recipe for successful HSM with other elements such as the machine tool, software, workholding, machine design (rigidity) and workpiece the other obvious components in this process.
However a key factor that often gets overlooked, at least until there is a problem, is the cutting tool supplier.
Tony Thornhill, managing director of Thornhill Machine Tools Australia, explained that while manufacturer/supplier support is important in any manufacturing operation, it is essential when it comes to HSM.
“Even though the practice has been around for years, it is vital to have helpful and informative supplier support.
“When there’s a problem with a surface finish or metal removal rate, quick response is essential so the operation gets back on the road,” he said.
“The tool manufacturer can assist with issues such as incorrect chip clearance and coatings which can render parts useless in applications which have strict quality control, such as the defence and aerospace industries,” he said.
“Work with the cutting tool manufacture to get the best result for HSM. Look for companies which have a focus on service and support as well as the manufacture of good quality cutting tools. Global manufacturers tend to be good as they have world-wide contacts and are better resourced to fix machining problems as they occur.”
Another point Thornhill stresses is for customers to look at the whole HSM picture and not just focus on capital cost of machinery.
“When buying equipment, particularly for HSM applications, many make the mistake of focussing just on price than the technology.
“Just looking at the cheaper option may end up costing more in the long run,” he said.
“Premium cutting tools use stronger substrates, specifically-tailored geometry and more efficient coatings that improve tool life and surface finish.
“Higher quality standards dictate a higher initial investment on the part of the end user, but the trade off to the is dramatically reduced benching time, faster cycle times and repeatable quality that allows operators to leave machines running unattended with total confidence.
“People pay for good quality cars but won’t invest in the machinery and tooling. In the future it is foreseeable that HSM will do away with electrical discharge machining (EDM) and if done properly, will be the future of machining.”
Thornhill Machine Tools Australia
03 9532 1452