An Overview of High-speed Machining of Titanium Alloys (original) (raw)

Abstract

Titanium alloys have been widely used in the aerospace, biomedical and automotive industries because of their good strength-to-weight ratio and superior corrosion resistance. However, it is very diencult to machine them due to their poor machinability, which has led many large cempanies to invest much in developing techniques to minimize machining cost. During machining oftitanium alloys, their poor therrnal conductivity results in the higher temperature closer to the cutting edge, and there exists strong affTmity between the tool and worlrpiece material. When machining titanium alloys with the conventional tools, the wear rate progresses rapidly, and the cutting speed is generally diencult to be over 60mlmin. Other types of tool materials, including cerarnic, diamond, and cubic boron ninide (CBN), are highly reactive with titanium alloys at higher temperature, and consequently they are not effective to be used in HSM of titanium alloys. The binder-less CBN (BCBN) tools, which neither have any binder nor a sintering agent or a catalyst, have a remarlcal)ly longer tool life than conventional CBN inserts under all cutting conditions (up to 400mfmin). The BCBN appears to become a new cutring tool material for HSM oftitanium alloys both economically and functionally. In order to get deeper understanding ofHSM oftitanium alloys, the generation of mathematical models is essential, Therefore, analytical models are needed to be established to predict the machining pararneters for HSM of titanium alloys. This paper aims to give an overview of recent developments in machining and HSM oftitanium alloys, geometrical modeling ofHSM and cutting force models for HSM of titanium alloys.

Figures (5)

be BELUE WU The inventor of HSM, C. Salomon, found out that from a certain cutting speed upward machining temperatures start dropping again. His fundamental research showed that there is a certain range of cutting speeds where machining cannot be made due to excessively high temperatures. For this reason, HSM can also be termed as cutting speeds beyond that limit. In compliance with modern knowledge, some researchers defines high-speed machining as being such that conventional cutting speeds are exceeded by a factor of 5 to 10, as shown in Fig.1 ™, With the wide use of CNC machines together with high-performance CAD/CAM systems, high-speed machining (HSM) has demonstrated its superior advantages to other rapid manufacturing techniques. In addition to the increased productivity, HSM is capable of generating high-quality surfaces, burr-free edges and a virtually stress-free component after machining, and it can be used to machine thin-wall workpieces, because the cutting forces in HSM are lower. Another significant advantage of high-speed machining is minimization of effects of heat on machined parts. Most of the cutting heat is removed, reducing thermal

be BELUE WU The inventor of HSM, C. Salomon, found out that from a certain cutting speed upward machining temperatures start dropping again. His fundamental research showed that there is a certain range of cutting speeds where machining cannot be made due to excessively high temperatures. For this reason, HSM can also be termed as cutting speeds beyond that limit. In compliance with modern knowledge, some researchers defines high-speed machining as being such that conventional cutting speeds are exceeded by a factor of 5 to 10, as shown in Fig.1 ™, With the wide use of CNC machines together with high-performance CAD/CAM systems, high-speed machining (HSM) has demonstrated its superior advantages to other rapid manufacturing techniques. In addition to the increased productivity, HSM is capable of generating high-quality surfaces, burr-free edges and a virtually stress-free component after machining, and it can be used to machine thin-wall workpieces, because the cutting forces in HSM are lower. Another significant advantage of high-speed machining is minimization of effects of heat on machined parts. Most of the cutting heat is removed, reducing thermal

Lei and Liu “” developed a new generation of driven rotary lathe tool for high-speed machining of a titanium alloy Ti6AI4V. In their study, high-speed cylindrical turning experiments were conducted using the driven rotary tool (DRT) and a stationary cutting tool with the round tungsten carbide inserts. From the experimental results, they found that the DRT can significantly increase tool life, and the increase in tool life with DRT is more than 60 times compared to that with a stationary cutting tool under certain conditions. The effects of the rotational speed of the insert were also investigated experimentally in their study. Cutting forces were found to decline slightly with increase of the rotational speed, and tool wear was observed to increase with the rotational speed in a certain speed range. tga

Lei and Liu “” developed a new generation of driven rotary lathe tool for high-speed machining of a titanium alloy Ti6AI4V. In their study, high-speed cylindrical turning experiments were conducted using the driven rotary tool (DRT) and a stationary cutting tool with the round tungsten carbide inserts. From the experimental results, they found that the DRT can significantly increase tool life, and the increase in tool life with DRT is more than 60 times compared to that with a stationary cutting tool under certain conditions. The effects of the rotational speed of the insert were also investigated experimentally in their study. Cutting forces were found to decline slightly with increase of the rotational speed, and tool wear was observed to increase with the rotational speed in a certain speed range. tga

(c) 2=0.125mm,f—0.075mm/r,v=400m/min (d) a=0.075mm,=0.075mm/r,v=400m/min Figure 2 SEM of the flank of BCBN tools at four different conditions where the non-uniform flank wear is the dominant wear for these four cases

(c) 2=0.125mm,f—0.075mm/r,v=400m/min (d) a=0.075mm,=0.075mm/r,v=400m/min Figure 2 SEM of the flank of BCBN tools at four different conditions where the non-uniform flank wear is the dominant wear for these four cases

conditions, there are only some adhered materials mainly found on the flank face, rather than on the rake face after failure of the tool. Based on the EDX output of chips, dissolution of material from the tool by diffusior into the adjacent zones of the chip happens. This may cause diffusion-dissolution wear for BCBN tools, but i is not the main wear mechanism. Figure 3. SEM and EDX of the flank face (a) An enlarged rectangular region of flank face under cutting conditions of a = 0.100mm, f= 0.10mm/r, v = 350m/min; (b) EDX of (a) shows the fragment in the rectangular region of Fig. 3 (a) coming from the tool material

conditions, there are only some adhered materials mainly found on the flank face, rather than on the rake face after failure of the tool. Based on the EDX output of chips, dissolution of material from the tool by diffusior into the adjacent zones of the chip happens. This may cause diffusion-dissolution wear for BCBN tools, but i is not the main wear mechanism. Figure 3. SEM and EDX of the flank face (a) An enlarged rectangular region of flank face under cutting conditions of a = 0.100mm, f= 0.10mm/r, v = 350m/min; (b) EDX of (a) shows the fragment in the rectangular region of Fig. 3 (a) coming from the tool material

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