A fundamental study on Ti–6Al–4V’s thermal and electrical properties and their relation to EDM productivity

(BQ) In the study, temperature measurements have been made for Ti–6Al–4V workpieces with various duty factors to clarify the essential causes of difficulty in machining titanium alloys and observe the optimal duty factor in terms of productivity and quality.
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A fundamental study on Ti–6Al–4V’s thermal and electrical properties and their relation to EDM productivityj o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 2 ( 2 0 0 8 ) 583–589journal homepage: www.elsevier.com/locate/jmatprotecA fundamental study on Ti–6Al–4V’s thermal and electricalproperties and their relation to EDM productivityPeter Fonda a , Zhigang Wang a,∗ , Kazuo Yamazaki a , Yuji Akutsu babDepartment of Mechanical & Aeronautical Engineering, University of California, Davis, One Shields Avenue, Davis, CA 95616, USASodick Corporate Headquarters, 1605 N. Penny Lane, Schaumburg, IL 60173, USAa r t i c l ei n f oa b s t r a c tArticle history:There are strong needs for productive/quality machining strategies of notoriously “difficult-Received 21 June 2007to-machine” aerospace materials. The current means of machining these materials isReceived in revised formdominated by mechanical cutting methods, which are costly due to high tooling costs,15 August 2007poor surface quality and limitations in the workpiece features and operations that can beAccepted 24 September 2007machined. The newest EDM technology may be able to circumvent problems encounteredin mechanical machining methods. In this paper, the EDM technology has been used tomachine titanium alloy Ti–6Al–4V to investigate the effect of Ti–6Al–4V’s thermal and elec-Keywords:trical properties on the EDM productivity. In the study, temperature measurements haveEDMbeen made for Ti–6Al–4V workpieces with various duty factors to clarify the essential causesTemperature stabilityof difficulty in machining titanium alloys and observe the optimal duty factor in terms ofDuty factorproductivity and quality.Titanium alloys1.IntroductionIn aerospace industry, titanium alloys have been widely usedbecause of their low weight, high strength or high temperatures stability. For example, a typical Boeing 747 aircraftcontains approximately 40,000 pounds of titanium, a little over10% of its total weight (Guitrau, 2006). Titanium alloys havealso seen an increase in demand due to the increased efficiency and higher operating temperatures of aero-gas turbineengines. Dating back to the 1960s, the use of both titaniumalloys has increased while the use of steel and aluminum hasdecreased as shown in Fig. 1. With the increased application oftitanium alloys, the ability to produce parts products with highproductivity and good quality becomes challenging. Owing totheir poor machinability, it is very difficult to machine titanium alloys (Rahman et al., 2006) with traditional mechanicalcutting. The energy-based technique, such as electrical discharge machine (EDM), has continued to advance and gain∗Corresponding author. Tel.: +1 530 554904; fax: +1 530 7524158.E-mail address: zgwang@ucdavis.edu (Z. Wang).0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2007.09.060© 2007 Elsevier B.V. All rights reserved.favor as an alternative to traditional machining methods.Different from traditional machining methods, the materialremoval in the EDM process is achieved through melting andvaporization.EDM technology has developed rapidly and become indispensable in manufacturing applications such as die and moldmachining, micro-machining, prototyping, etc (Kunieda et al.,2005). Among all EDM processes, die-sinker EDM is widelyused. Fig. 2 shows that die-sinker applications are typicallydominated by plastic injection and various other mold fabrications, the key to continued use and expansion of theEDM process’s capabilities are new applications for growingindustries such as the aerospace industry. As shown in Fig. 2,there is no large percentage of EDM applications focusedon either the production or modification of aerospace components. Up to now, EDMs have been successfully used tomachine hard materials that pose problems for traditionalmechanical cutting, yet aerospace materials, namely titanium584j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 2 ( 2 0 0 8 ) 583–589then the workpiece temperature is measured at different dutyfactors, and the effect of materials thermal and electric properties on the EDM productivity is investigated.2.Effects of material properties on EDMprocessesFig. 1 – Material usage in aero-gas turbines (Ezugwu et al.,2003).Fig. 2 – Die-sinker EDM usage by application (Anon., 2006b).and nickel-based alloys, are rarely machined using the EDMprocess. Their low thermal conductivity and high strengthat elevated temperatures complicate mechanical cutting processes, which makes achieving a high quality product difficult.By applying modern EDM technology, however, these materials may be able to be EDMed effectively and efficiently andeventually increase the application of EDMs in the aerospaceindustry.Chen et al. (1999) i ...