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hpt 2022 #4

  • Text
  • Diamond tools
  • Cbn
  • Cvd
  • Pvd
  • Pcd
  • Cryogenic process cooling
  • Filtration
  • Precision tools
  • Sustainability
  • Harnischcom
  • Processes
  • Automation
  • Materials
  • Solutions
  • November
  • Titanium
  • Milling
  • Grinding
  • Cooling
  • Machining
■ Productivity and sustainability are not mutually exclusive ■ Precision tool cutting edge cooling ■ Filtration in machining processes ■ Retrofit unit for cryogenic process cooling ■ Automation of tomorrow

cover story

cover story High-performance titanium drilling, in one shot Titanium is a high-performance material and poses a chip removing machining challenge. Also not all titanium is alike. Depending on whether it is pure titanium or alloyed titanium, the chip removing process behaviour differs. Mikron Tool has come up with different drill series that are perfectly tailored to the various titanium grades allowing to machine them safely with higher cutting performance results and longer tool life. Alberto Gotti PhD, head of research & development at Mikron Tool Titanium is highly popular in the medical technology field; due to its elasticity in conjunction with a high level of fatigue strength, titanium materials have unrivalled high bio-functionality Drilling into stubborn titanium is exceptionally challenging, partly because of the combination of high elasticity and tensile strength properties. The great toughness of this metal means that chip breaking is difficult to achieve. Due to the lower thermal conductivity, heat is not moved from the cutting area through the chip; but still needs to get rid of somehow. Also titanium has a propensity to create edge built-up which in turn can lead to higher levels of wear and reduce process reliability when drilling. Mikron Tool specializes in developing drilling technologies that are perfectly tailored to the material properties of pure titanium and titanium alloys. This is a complex task but then offers enormous production benefits for users. TITANIUM Titanium is by no means rare; in fact, it is the 9 th most common element in the continental crust. However, pure titanium is rarely found on earth, it is produced from titanium ore or rutile. Today we still use a procedure that was developed by William Justin Kroll, a metallurgist from Luxemburg, in 1930 for the complex production of titanium: it became possible to produce the metal for commercial applications thanks to the introduction of the industrial reduction of titanium (IV)-chloride with magnesium. The production process used here is extremely complex, as reflected by the very high price for titanium. Some call titanium a temperamental diva that screams when treated incorrectly. Titanium developed into an ultra-material for the industry due to its excellent properties. The application horizon is broad: aerospace, motor racing, medical and dental equipment, surgical orthopaedics and the jewellery and watch sectors all use it. Titanium is also ideal for eyeglass frames. In short, this metal is very popular in industry thanks to the broad market base. 330.000 sh tn are processed every year. Titanium’s supernatural image is the reason for this figure. Rightly so because it is indestructible. It hardly weathers when it encounters oxygen because it is coated in a thin, transparent oxide layer. Even the most aggressive media, like acids, have very little impact on titanium. It is almost as light as aluminium, but much stronger, almost on a par with tempered steel. It is also biocompatible and anti-magnetic. 6 no. 4, November 2022

cover story figure 1 Titanium: “Like drilling into rubber” “It’s like drilling into rubber”, says Alberto Gotti, head of R&D at Mikron Tool. “Drilling titanium is much more challenging than milling; and it is even more difficult when the diameter-drilling depth ratio increases”. It becomes problematic above 3 x d. Titanium’s viscoelastic properties cause the drill to jam, which increases the pressure on the cutting edges. Material build-up on the cutting edges and margins increases the cutting forces which, in turn, can cause cutting edge breakout. Once the surface is compromised, even more material will build up and lead to higher friction. Also, the chip shape becomes problematic because the titanium chips tend to accumulate in the tip area and prevent smooth flowing of chips. In turn, this often leads to uncontrolled drill breakage. A further compounding factor are the high temperatures to which edges are exposed. From a temperature of 600 ° Celsius the cobalt binding matrix in the carbide substrate becomes ‘soft’ and is no longer able to bind the hard tungsten carbide optimally. That leads to plastic deformation and micro-wear, and ultimately cutting-edge breakouts. Material-specific tools are the solution One remedy are cutting edges which need to be very sharp and very stable at the same time – a contradiction in itself. Mikron Tool has developed an ingenious specific cutting geometry that manages this balancing act and, as a result, cutting pressures can be reduced significantly. As described above, the heat needs to be moved from the machining area. The solution: two cooling channels with very large crosssections deliver large quantities of coolant through to the drill tip to guarantee constant cooling, including lubrication of the cutting edges. At the same time, the solid coolant jet flushes the chips through the polished flutes and prevents jamming chip backup. (figure 1) There is nothing new here, but: the patented special design of the cooling channels by Mikron Tool allows four times the amount of coolant quantity to be shot into the tool with constant pressure. This is a further key to success and stands for innovation in the thermal dissipation and chip removal technology. Three years of meticulous development work has gone into the sensational ‘divine’ drills for titanium by Mikron Tool no. 4, November 2022 7

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