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In addition, since titanium is able to osseointegrate, they are used in orthopaedic implant applications. Skeletal loads are more evenly shared between bone and implant, leading to a lower incidence of bone degradation due to periprosthetic bone fractures. However, titanium’s stiffness is still more than that of the bone so adjacent bone bears a greatly reduced load and may deteriorate. Cutting In The Scale Of Microns Micro cutting, particularly micro milling, and laser micromachining are some of the micromachining processes. In order for micro cutting to take place, the cutting speeds and feeds to remove material at an acceptable rate must be increased, requiring specialised high-speed spindles. In addition, cold air guns and misters are preferred to flood coolant in cooling during cutting. Another aspect to consider is the end mill selection as it is important to maintain tool life and fixturing. The tool bit for milling should follow a diameter as small as 0.1 mm with a high-speed spindle rotating at 20,000 to 150,000 rpm. It is capable of milling steel, brass and aluminium with depth of cut at about 30 microns and feed rates of 120 to 240 mm per min to provide
surface quality finishes as good as 0.2 microns. In spite of micro milling being applied in manufacturing biomedical components, one common problem that many users have identified is the breakage of the tool bit, which is usually caused by the amount of force associated with removing material at the particulate level. During the process of removing metal, specific energy required increases as the chip thickness decreases. As such, the micro tool bit is subjected to greater resistance as the depth of cut decreases, as if the workpiece material becomes harder during micro machining. The resistance force is strong enough to exceed the bending strength limit of the tool bit before the tool experiences any wear and tear. As such, the edge radius of the tool bit has to be larger than the chip thickness. Moreover, the micro cutting machine should have high tolerance as small vibrations are amplified relative to the tool diameter as it is reduced. Such vibrations not only cause reduced precision, but can also fracture end mills. Makino tackles this problem by producing the direct tool-change type spindle. It reduces the total run-out caused by tool holder variation by eliminating the use of a tool holder.
APMen_ASIEN_3406147_EMO Hannover 2011 18.03.11 13:36 Seite 1
INFO: VDW – Generalkommissariat EMO Hannover 2011 Verein Deutscher Werkzeugmaschinenfabriken e.V. Corneliusstrasse 4, 60325 Frankfurt am Main, GERMANY Tel. +49 69 756081- 0, Fax +49 69 756081-74 emo@vdw.de ¡ www.emo-hannover.de
ENQUIRY NO 062
The world of metalworking
April 2011 metalworking equipment news
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