Small Mill Cuts Tough Materials
Those “crazy” Swiss at Mikron Tool (U.S. office in Monroe, Conn.) are at it again with the introduction of CrazyMill Cool at EMO 2013. It complements the company’s line of Crazy Drills, which have been in the market for some time.
Designed to mill stainless steel, titanium, chrome-cobalt alloys as well as the so-called super alloys, the newly conceived small milling cutter improves cutting data results in these and other materials. Hence, new benchmarks apply immediately for cutting speeds, feeds, performance, tool life and surface finish quality in hard-to-machine materials.
Machining stainless steels can be a challenge because tools become extremely hot due to poor heat conductivity of these materials accelerating tool wear, creating premature damage to the cutting edge.
With the new line of CrazyMill Cool cutters, Mikron Tool created a solid carbide end mill with through coolant capability in the diameters from 0.3 mm to 4 mm (0.02 inch to 0.15 inch), doing justice to the product’s somewhat wild name. Slot or pocket milling into solid material and contour milling are among its capabilities. According
to the company, the tool combines roughing and finishing, promising higher time in the cut efficiency, long tool life and a much better surface quality.
Clean Sheet of Paper
With success of the Crazy Drill line, the engineers at Mikron sharpened their pencils to develop another product in the Crazy Tool line of high performance, small diameter cutting tools for precision machining applications.
One of the first considerations the engineers tackled is the raw material from which to make the cutting tool. To that end, they developed a new micro-granulate carbide grade, which fulfills the requirements of hardness as well as toughness. The demands of milling difficult materials requires that the cutting tool be hard enough to lift a chip and tough enough not to break prematurely.
Next, the researchers looked at the design of the tool
and how to optimize its cutting geometry, which is specific, but not limited for the machining of stainless steels and helps the tool to achieve its improved performance characteristics. A combination of different geometric characteristics leads to the desired results. A robust cutting body, a radial relief and a very specific cutting edge preparation afford a very high cutting edge quality and stability.
An important contribution for the tool life is also the coating, which is innovative and also very specific for hard-to-cut metals. With an extremely low friction coefficient and a reduced affinity with steel, build up at the cutting edges is avoided.
Furthermore, the coating has a high oxidation resistance and heat hardness. This helps to maintain the temperature in the green range and a “burning” of the cutting edges is avoided, which in turn, contributes to longer tool life and improved surface quality.
Putting ‘Cool’ in the Tool
However, the key development of the milling cutter line is connected to the “cool” part of the tool’s name. It is generally
accepted in machining practice that dry machining is not recommended when working with stainless steels. This recommendation is due primarily to the poor heat conductivity of the material, which causes tools to become extremely hot, resulting in burn out of the cutting edges and tool failure.
Therefore, the use of coolant is a must. Mikron’s CrazyMill microcutter has three to four internal coolant channels (depending on diameter), which go through the shaft and bring coolant along the diameter to the cutting edges. In effect, the cutting tip and cutting shank are enveloped by coolant.
The result is a targeted and massive cooling effect where it’s needed—at the cutting edges. Moreover, unlike external coolant lines, this coolant flood is applied in every machining position the cutter is programmed to make.
In addition to stabilizing the temperatures in the cutting zone, the coolant flow continuously flushes chips away from the milling area, which is a key to improved cutter life and workpiece quality. In relation to the small diameters of the milling cutters, the cooling channels are rather large.
The large volume of coolant created is highly efficient; the friction heat is substantially absorbed and removed by the coolant. Part of the cutter design included that these cutters have no special requirements necessary for filtering and coolant pressure, which allows their use on conventional machines.
General practice milling suggests an infeed of 0.1 – 0.2 ×D is recommended to mill a channel in solid material. The CrazyMill Cool is able to achieve depths of 1 – 1.3 × D directly.
Mikron’s Markus Schnyder points out that one does
not have to be a calculus genius to realize that with
up to 5 times faster cutting speed and a comparable increase in feed rates, the efficiency of the milling cutter is improved by a factor of 10 to 20. Interestingly, it is in the “difficult” materials where the performance difference is seen the most.
Also, according to the company, the surface quality in these materials is equally impressive. Even though the
cut goes into solid material, the CrazyMill Cool boasts Rz values, which are 2 to 3 times better than what can be expected from conventional cutters.
In the near future, a complete inventory of standardized, small milling cutters will be available for applications in industry segments such as watchmaking, medicinal
and surgical technologies. The first series of cylindrical, small cutters in diameter of 0.3 mm to 4 mm (0.02 inch to 0.16 inch) has been launched. Also available are short versions for maximum depths of 1.5 × D, a medium version for 3 × D and a long version for 5 × D. All of these tools have a cutting head of 1.5 × D.