Emerald Group Publishing Limited
Copyright © 2008, Emerald Group Publishing Limited
Titanium: light but so hard to machine!
Titanium: light but so hard to machine!
Its name derives from the oldest dynasty of deities in Greek mythology, its characteristics are remarkable: for example its tremendous strength in relation to its relatively low density and its high resistance to corrosion. Titanium is becoming increasingly important in aircraft construction. Although it is a light metal, it requires 10-12 times more machining time compared with aluminium. According to DST conventional machining centres, such as those used to machine steel, produce unsatisfactory results. This is why they, DST GmbH have designed and implemented a machining centre to cope with titanium. When roughing and finishing it is said to achieve a great deal more than the machining performance of conventional solutions.
As a material for use in aircraft construction titanium meets the requirements of weight reduction. And the trend within the aerospace industry to use carbon fibre-enhanced compounds requires the use of titanium because, chemically and mechanically, it is the ideal partner to such materials. The main workpieces concerned here are structural components and fittings. Added to the high strength of the metal, is the advantage that titanium indicates low- heat expansion properties as well as a high level of dimensional stability. However, under the pressure of international competition aircraft manufactures demand efficient, i.e. extremely accurate and extremely productive machine technologies. High rigidity, damping and feed force are the fundamental requirements of today. In DST's opinion, conventional tool-based machines, for example for separate roughing and finishing processes, are no longer suitable. Solutions with vertical working spindles can no longer achieve the rate of chip removal at the machining performances required. Multi-spindles lack the required flexibility.
This is why DST has adopted another route. The synergy between proven modules ensures the success of the new machining centre in coping with difficult-to-machine titanium. Its name is: ECOFORCE (Figure 5). The machining heads which are automatically changeable via pick-up magazine achieve machining rates of up to 450cm3/min for three-axis roughing and 140cm3/min for five-axis finishing with the proven fork type milling head. The internal high-pressure cooling system of up to 150bar also contributes to this excellent machining performance. The pallets on the ECOFORCE types 2035 and 2060 accept workpieces weighing up to 8,000 and 12,000kg, respectively. The dimensions of the vertical clamping pallets are 3,500 and 6,000mm wide and 2,000mm high. Permanently high- machining capacity and high damping are obtained by means of hydrostatic guides for the linear axes and on the B- axis (turntable) for a horizontal table group. The A-axis rotates by ±95º and the C-axis is continuous×360º. When roughing the three-axis milling head has a capacity of 60kW, 4,000Nm at 2,000rpm, while for finishing, the five- axis Fork Type Head can achieve a capacity of 40kW, 1,100Nm and 5,000rpm. The WERO tool magazine provides space for up to 210 tools. The pallets travel out of the workstation for loading and unloading. Part loading is easy since the system swivels to horizontal. As an option, and depending on the geometry of the workpiece, the machine can also be designed to contain a horizontal table group and pallet changer.
Figure 5 The ECOFORCE design is based on a group of standard proven and field-tested modules
Figure 6 Five-axis Finishing Fork Type Head – providing full five-axis capabilities
The result is that ECOFORCE benefits from the machining solutions jointly developed with the aerospace industry for aluminium, composites and high-strength steels. In this way DST is combining its expertise in the field of difficult machining and machining five- axis aircraft components to meet the challenges of machining titanium for the aerospace industry (Figure 6).