Abrasive Flow Machining Essay

1. Introduction Abrasive flow machining (AFM) was firstly developed fifty years ago by Extrude Hone Corporation, USA. By using the liquid viscoelastic material with easy flowability made of polymer and abrasive grains, AFM can be used to polish, deburr and radius for the workpiece. There are three kinds of AFM: one-way AFM, two-way AFM and orbital AFM [1]. In this case to manufacture the cylinder heads, consider of two-way AFM is much more widely used and its technology is more mature, we also choose the two-way AFM to do the surface finishing. Schematic of two-way flow shows in figure below. Figure 1 principle of material removal mechanism in two-way AFM process [1] Prior to machining, liquid abrasive will be put into the lower medium cylinder, the designed fixture which clamping the workpiece will be fixed between two cylinders. The upper medium, lower medium cylinder and fixture will form a confined space. After heat the whole system to working temperature, by forcing the lower piston (usually by hydraulic), the liquid abrasive will be pressed into the channel formed by clamp and workpiece, then flow into the upper medium cylinder. After the stroke of lower piston finished, the upper piston will force the liquid abrasive back into lower cylinder [2], an operating cycle will be finished. See more: Beowulf essay essay 2. Three key elements of AFM 1) Machine tool Use to fasten the workpiece and fixture, and control the pressure applied on the workpiece, to adjust the degree of abrasive accuracy. 2) Liquid Abrasive Liquid abrasive is abrasive tool in the AFM, it should has following properties, a) Non-corroding and don’t adhere to the workpiece and human skin. b) Good adhesive properties between different abrasive grains. c) Be able to maintain the viscoelasticity for a long time d) Non-volatile and non-deteriorate after a long time preservation. e) Strong cohesion. For these properties, the conventional liquid abrasive is made from Semi-solid carrier which has viscoelasticity, flexibility and cutting property mixed with abrasive grains. Different intrinsic viscosities of different carriers, different types and size of abrasive grains can affect the final tolerance and roughness [2]. The most frequently used abrasives are silicon carbide, carborundum, Cubic Boron Nitride(CBN), aluminum oxide, the size of grain vary from 0.005mm to 1.5mm. Abrasive with high viscosity is mainly used to polish the walls of workpiece and large through-hole while low viscosity abrasive is primarily for radiusing the edge and polishing the small through-hole. 3) Fixture The function of fixture, a) Positioning and fixing the workpiece. b) Bearing clamping force for some workpiece. c) Constitute a channel for liquid abrasive with some machined surface of workpiece in suitable size and section. d) Realizing simultaneous machine multiple workpiece in one device. 3. Advantage of AFM, Abrasive flow machining has accuracy, stability and flexibility. It uses liquid abrasive to remove the metal material infinitesimally, deburr and radius the internal intersections of workpiece. At present, AFM is widely used in automotive industry and other manufacturing. The fundamental advantage of AFM is the liquid abrasive can reach the positions which are not easily be machined by tradition surface finish methods since the complexity of workpiece, polished surface evenly and in integrity, batch processing has the same result. These characteristics improve the performance of part, extend the working life, avoid the multifarious manual labour, and lower the intensity of labor. For example, when polish the intake-tube of vehicle by traditional process, the tube need to be cut into half, then welding after polishing, but using the AFM, cut and welding can be avoided [3]. 4. Geometrical and thermal effects. Viscosity of liquid abrasive will decrease when the working temperature enhances [3], and working ability of abrasive depends on its viscosity as the figure 2 shown. Figure 2 the machining effects of different viscosity of abrasive materials [5] Since cutting force is proportional to viscosity, so higher viscosity means stronger grinding ability, as a result abrasive with higher viscosity will get a better surface. In conclusion, temperature is a very important factor during the process. While the abrasive grains polish the surface, it will generate heat, enhancing the temperature as the figure 3 shown. Figure 3 Variation of rise in temperature of workpiece with number of cycles [4] The rise of temperature will make the working ability reduce. So cooling system is need during the process to ensure the best machined surface. Geometry of cylinder head also affects the result of surface finishing. Many small through-holes exist in the cylinder head, flow rate of abrasive is much bigger in these through-holes according to fluid mechanics, even these accelerations enhance grinding ability, but due to shearing force generated by abrasive being extrusion at narrow pass, it is evident that temperature will rise rapidly, lower the grinding ability. So geometrical effect need to consider when design a cylinder head. 1. Rhoades L.J., Kohut T.A., Reversible Unidirectional AFM, US patent number 5,070,652, Dec 10th, 1991. 2 Szulczynski, Hubert, Uhlmann, Eckart, MATERIAL REMOVAL MECHANISMS IN ABRASIVE FLOW MACHINING 3 Guizhen Song, THEORETICAL ANALYSIS AND EXPERIMENTAL RESEARCH ON ABRASIVE FLOW MACHINING 4 Rajendra K. Jain, V. K. Jain. Specific energy and temperature determination in abrasive flow machining process[J]. International Journal of Machine Tools & Manufacture, 2001(41):1689-1704 5 Tang Yong, Zhou De-ming, Yang Gang, Machinability of Abrasive Flowing Machining. Journal of south china university of technology, 2001-9