Tests of drills with a new geometry
Company Nastroje CZ, s.r.o., has put its longtime experience into the development of the new types of the spiral ground drills with straight shank according to its own developing line CZ. The aim of the company is to develop and produce comprehensive range of drills for various groups of machined materials, whose geometry will guarantee not only high geometric exactness of drilled holes, but also achieving long lifetime and durability of drills and thereby also productivity of work.
Is it still possible to change something on the geometry of the standard metal drills? Of course, it is. At the beginning of May 2007, after almost 12 months of intensive development and tests not only in the onwn test room, but also in the plants of the end users, the company Nastroje CZ, s.r.o., brought out two new types of metal drills from its own development line CZ under designation CZ002 and CZ004.
Drills CZ002
Drills CZ002 replace most worldwide spread and thereby most used drills designated according to the international norm DIN 338 RN HSS or domestic norm PN 2913. The uniqueness of drills CZ002 isn´t in the different material used for their production (it is standard steel CSN19830 or DIN W.Nr.1.3343), but in the new, absolutely revolutionary geometry of the complete tool. The nose of drill CZ002 thanks to is optimum chosen geometry significantly brings higher stability to the drill even when drilling at high cutting speeds and at the same time guarantees high dimensional and geometric exactness of the drilled holes. Very thin core, which is constant in the certain lenght of the front part of the drill CZ002, significantly reduces magnitude of necessary axial force for drilling and following heat build-up with the maintaining of big drill rigidity thanks to the multiple increase of the core thickness in the direction to the nose of the drill CZ002. At the same the revolutionary geometry of the core of the drill CZ002 gives a possibility of its resharpening with keeping repeatedly same geometry of its nose. Drills CZ002 are intended not only for steel drilling up to the rigidity 900 Mpa, but also for non-ferous metals, like aluminium and its alloys, brass and copper.
Drills CZ004
Drills CZ004 were developed especialy for drilling holes into the tough steels resistant to corrosion and they differ from drills CZ002 not only by modification of the geometry of their nose, but also by using multialloyed materials for their production, which contain especially 5% cobalt (steel DIN W.Nr.1,3243, M35) or 3% vanadium (steel DIN W.Nr.1,3355, HS 6-5-3). Drill CZ004 replace drills produced according to the interantional norm DIN338 Rti HSSCo5 and DIN 338 RN HSSCo5 or according to the domestic norm PN2907. These drills were in the past and still are referred to as universal for drilling into stainless and high-strenght steels. Its wide core is at the nose lightened by special cross relief type C according to the DIN norm 1412. When the nose adjusted in this way enters the material, it badly centralize the drill, the material is discomposed and „dances“, thereby especially the geometry exactness of drilled hole suffers. Secondary lips created by cross cutting relief tend to a quick dulling, which leads to the necessity to expound extensive axial force for next continuation of drilling .The result is a big heat build-up, which leads to the fast wear-out of drill cutting edges and thereby of its resharpening with keeping repeatedly same geometry of its nose. Drills CZ002 are intended not only for steel drilling up to the rigidity 900 Mpa, but also for non-ferous metals, like aluminium and its alloys, brass and copper. course to its very short lifetime. Moreover because of the special geometry of nose relief, it is very difficult practically, considering the standard equipment of companies, to repeatedly resharpen the drill with required exactness.
Advantages of the new geometry
The new geometry of the metal drills CZ002 and CZ004 minimalize the above described lacks.The result of drilling is the exact, fine machined hole without a necessity of preboring, at the substantialy higher cutting conditions and the substantialy higher lifetime compared to the above mentioned current drills. Not less important is the fact, that the drills CZ002 and CZ004 are possible to regrind with achieving repeatedly the same geometric exactness. Drills CZ004 are intended for drilling especially stainless, high-speed and tough high-alloy steels with the tensil strenght up to 1200 Mpa. Advantages, which are brought by the new geometry of drills CZ002 and CZ004 are proved by the award from the 14th International Machinery Fair in Nitra (Slovakia), where the drills were awarded by the Award for the new generation of metal drills. The revolution of the new geometry of the drills CZ002 and CZ004 is proved also by the fact, that in the Czech Republic for this geometry of drills there was a Certificate about the registration of the utility design given, which is filed under document number 17537 and under mark file PUV 2007-18528. The aplication for the European patent is filed under number EP07005754. Drills CZ002 and CZ004 currently create the bearing production programme of the company Nastroje CZ, s.r.o., and are on stock in the diameters from 0,30 up to 16,00 mm.
Company NÁSTROJE CZ, s.r.o., established professional cooperation with the University of technology in the year 2007, concretely with the Institution of engineering technology at the Faculty of mechanical Engineering, where its new drills CZ002 were put through the longtime testing.
Information about the new type of the metal drills CZ002 were published in the 9th copy of MM Industry Spectrum in 2007, where until that time, the almost unknown company NÁSTROJE CZ, s.r.o., from Kyjov, introduced them. These drills are already on the market and are kept on stock in the sizes from 0,30mm up to 16,00 mm.
Pict.no.: 1 Diagram of measuring through the use of piezoelectric system Kistler
Tests of the drill force load
Currently there was one stage of the tests completed. There were short-term tests of force load of drills CZ002 carried out. At the same time there was carried out a comparison of drills CZ002 with the drills produced according to the domestic norm PN 2913 and the International norm DIN 338 RN HSS made by two top czech manufactures, which replace these drills. The aim of these tests was the comparison of cutting features of drills by the help of short-term tests of their force load, expresssed by the help of feed force and cutting moment. List of the tested samples and the conditions of the cutting test are stated in the tabels. For measuring of the feed force and the cutting moment there was used a Piezoelectric silicon dynamometer Kistler 9257B, equiped by Charge amplifiers Kistler 9011A, fully controlled by PC. (Pict.no.: 1).
Tested types of drills went in the short-time cut test and achieved results are possible to compare with the referential cut tool with the labelling A. Cut test lied in the record of feed force and cutting moment when drilling first na afterwards every next 10th hole from the total 122 holes by each tested tool. The choise of cutting coditions resulted from the recommendation of the producer for referential cutting tool and these conditions were for the whole time of the test constant. According to the agreetment requirements the drilling of each hole was proceeded without interrupting up until the depth 3xD = 18mm.
Pict.no. 2: Test results
Results
By anylysis of the force load there was found out, that the lowest average rate of feed force when drilling all holes showed the drill with the labelling A,drill CZ002 (pict.no.:2). The lowest average rate of the cutting moment when drilling all holes, showed also the drill with the labelling A, that means again CZ002 (pict.no.: 3). Morover the holes cut by the drill with the labelling A, showed essentially higher geometrical exactness and significantly lower roughness of the machined surface as compared with the holes cut by drills with the labelling B and C, which showes the evidence of it great stability and a very good chip disposal...
Pict.no.: 4 The tests were lead by doc. Ing. Miroslav Piska, Csc.
On the bases of the stated results, it is possible to say, that the drills CZ002 significantly exceeded till now used drills PN 2913 and DIN 338 RN HSS, not only in the both monitored values, but also in the geometric exactness and in the surface quality of the drilled holes.
Ing. Emil Nečesánek
