Study and Analysis of Metallized electrode fabricated with FDM Rapid Prototyping technique for Electro discharge machining (EDM).

Transcription

1 Study and Analysis of Metallized electrode fabricated with FDM Rapid Prototyping technique for Electro discharge machining (EDM). Fefar Savan D. 1, Mr.J.S.Karajagikar 1 PG Student, Department of Production Engineering and Industrial Management, College of Engineering, Pune-11 00, fefar.7@gmail.com. Assistant Professor, Department of Production Engineering and Industrial Management, College of Engineering, Pune-11 00, jsk.prod@coep.ac.in Abstract Electro Discharge Machining (EDM) is a non-traditional machining process for the manufacturing of complex or hard material parts that are difficult to machine by traditional machining processes. In Die-Sinking EDM, the electrode shape is mirrored on the workpiece. Hence, instead of the machining problems, the process of electrode manufacturing becomes critical. The conventional methods of electrode manufacturing are not competent with the emerging demands of complex structures and shorter lead time. Rapid tooling (RT) technique by rapid prototyping (RP) process has potential to overcome the problem of conventional methods of tool manufacturing. In the present work, Fused Deposition Modeling (FDM) process of rapid prototyping is employed to develop the electrode for electro discharge machining. The ABS electrode produced by FDM process was metallized by electroless copper coating to make the RP-electrode conductive. Experimental work and analysis are carried out to investigate the feasibility of RP-electrode for EDM. The various input parameters such as discharge current, discharge Time, and discharge Voltage are observed and further analysis of Material Removal Rate (), Tool Wear Rate () and surface roughness (R a ) are carried out. Keywords: Electro discharge machining (EDM), Rapid Tooling (RT), Fused Deposition Modeling (FDM), 1 Introduction To reduce manufacturing time and cost is the ultimate goal and tremendous requirement of any firm. Tool manufacturing is one of the major area where the cost associated with the production is very high. Tool Cost and lead time will increase with increasing complexity of the tool shape and Accuracy required. Rapid Prototyping (RP) or Additive Manufacturing (AM) is one of such technique by which the parts can be produced directly from the D CAD model, thus nullifying the requirements of any special tooling and/or machineries for producing any kind of shapes. When these RP techniques are applied directly or indirectly for the production of tool it is termed as a Rapid Tooling (RT). Electro discharge machining is one of the nontraditional machining technique which have being used extensively for producing Dies or generating complex shapes on the surfaces which are hard or difficult to machine. In this study an attempts have been made to produce a rapid tool by using fused deposition modeling (FDM), a RP technique. Methodologies In this Experimental work, comparative study was carried out in between RP-electrode and Solid copper electrode for the machining of En-19 alloy steel. Both electrodes having the same dimensions and geometry (i.e. 0 mm diameter and Cylindrical Shape)..1 Electrode Preparation Electrode 1: First of all a RP-component of desired shape and Dimension was produced on FDM RP machine Stratasys Dimension 78. Then electroless copper coating of 0 microns was done on the RPcomponents of ABS material. Electrode : Machining of The solid copper rod is done on CNC machine to get the desired dimensions. Copper (Cu) used in preparation of both the electrodes are commercially pure copper (i.e % Cu).

2 .1 Experimental set-up. Experiments are carried out on a die sinking EDM machine model, ELEKTRA- EMS 00 PULS S 0ZNC (Figure 1), with servo head (constant gap).commercial grade EDM oil (specific gravity= 0.78, freezing point= 10 C) was used as dielectric fluid. Positive polarity for electrode and side flushing was used to conduct the experiments. Where, Peak (I p ) is in ampere, Gap Voltage (V g ) is in voltage and Pulse on Time () is in microseconds. Table 1 Input parameters with their levels Parameter Low Medium High Peak (I p ) Gap Voltage (V g ) Pulse on Time () 0 7. Data Collection The initial weight of the work piece and electrode tool was measured. The work material was mounted on the fixture table and clamped. The electrode was mounted on toolholder as shown in figure and its alignment was checked. The machining time was set as minutes for each experimental run. After each machining operation, the work piece material and electrode are taken out and their weights are checked to find out the weight loss. Afcoset electronic weight balance (least count gm) is used to check the weight difference. (a) Figure RP-electrode and Workpiece during machining. Calculation of Responses (b) Figure 1 (a) Electro Discharge Machine, (b) Control panel. Design of Experiments Experimental design was carried out by Box-Behnken Design (BBD) of Response Surface methodogy (RSM) for input parameters with levels, as given in Table 1. Material Removal Rate () can be calculated by using the equation (1). Where, Wi=Weight of the workpiece before machining, (1)

3 Wf = Weight of the workpiece after machining, ρ= Density of the workpiece = gm/mm T= Machining time minutes. Tool Wear Rate () can be calculated by using the equation (). Where,Ei= Weight of electrode before machining, Ef= Weight of electrode after machining, ρ= Density of the electrode = gm/mm T= Machining time minutes. Surface Roughness (R a ) R a is measured with very fine Increments of 0.01mm by using SURFTEST SJ-10 (Mfg. by Mututoyo). Results and Discussion: The Change in output parameters Material removal rate (), Tool wear rate () and Surface Roughness (Ra) with respect to change of experimental input parameters (I p ), Voltage (V g ), and Pulse on time () are observed. Experimental details for the solid copper electrode and RP-electrode is shown in Table and Table respectively. Run Order Table Experimental details for Solid Copper electrode I p (A) V g (V) (µs) (mm /min) () (mm /min) Ra (µm) Table Experimental details for Metallized RP- electrode Run Order I p (A) V g (V) (µs) (mm /min) (mm /min) R a (µm) Figure Workpiece after machined by RP-electrode with marking of Run Order

4 Analysis Analysis of variance (ANOVA) has been derived for each response to find the significant of each input factors. As per this technique, if the calculated P value of the developed model does not exceed the standard tabulated value of P for a desired level of confidence (say 9%), then the model is considered to be satisfactory within the confidence limit. Analysis of the resulted output was carried out by using Minitab v.1 Software and important results are illustrated by contour plots in section.1 and.. The contour plot is a two-dimensional representation of the response across the selected factors. The full range of two factors at a time can be displayed. results have been obtained for the solid copper electrode for the all responses..1 Solid Copper Electrode Contour Plot of vs, < > Table ANOVA Table of for RP-electrode 0 Source DF Seq SS Adj SS Adj P F MS Voltage Error Total The P value less than 0.0 indicates model terms are significant. In this case current is most significant model term. Table ANOVA Table of for RP-electrode 0 (a) Contour Plot of vs, < > 0.8 Source DF Seq SS Adj SS Adj P F MS Voltage Error Total The P value in Table and Table, clearly indicates that the response and are highly influenced by current and least affected by voltage. Table ANOVA Table of Ra for RP-electrode Source DF Seq SS Adj SS Adj P F MS Voltage Error Total From table it is found that followed by current, voltage is second most significant factor for response Ra. The similar Voltage (b) Contour Plot of Ra vs Voltage, (C) Ra < >.

5 . Metallized RP-electrode Contour Plot of vs, 0 0 (d) Contour Plot of vs, 0 < > 10 < > 0.0 From contour plots (b) and (e), It can be observed that increases steeply with increasing Ip from A to A for any value of. This occurs due to melting and erosion of tool at high temperature as a result of intense spark. However the is found very low at lower current in case of RP-electrode [contour plot (e)]. This may be occurred due to the thin coating of copper on RP-electrode, which permits the current flow with least resistant when the electricity passed (Joule s effect). From contour plots (c) and (f), Ra is found increasing with increase in current and spark on time (), it can be considered as a result of excessive heat energy produced in the tool work interface. Since the is also increased with increasing I p, tool s surface is subject to distort and results in a production of rough surface. Conclusion From the above experiments and study it can be concluded that, RP-electrode worked very similar to that conventional electrode in all aspects and can work even better for finishing operations. Hence it is feasible solution to replace the conventional electrode manufacturing process to evolutionary RP-electrode process. Voltage (e) Contour Plot of Ra vs Voltage, (f) Ra < >. Observations and Conclusion From the Contour plots the following important things are observed. The contour plots (a) and (d) for, shows relation to the process parameters such as discharge current (Ip) and pulse-on-time (). It can be observed that for any value of, the tends to increasing with discharge current from A to A due to more heat generation as a result of intense spark. Future Scope For the ease of experiments and comparative study in stipulated time, here very basic shapes of electrodes had been employed for the experiments. However it would be have better comparison and analysis if complex shapes of electrode can be employed with wide range of input parameters (i.e. rough machining, semi rough machining and finishing) in the experimental test. References 1) Fred L. Amorim & Armin Lohrengel (01), Performance of sinking EDM electrodes made by selective laser sintering technique, Int J Adv Mfg Technology (:1 18). ) Yucheng Ding, Hongbo Lan, Jun Hong (00), An integrated manufacturing system for rapid tooling based on rapid prototyping, Robotics and Computer-Integrated Manufacturing ( 0: ) ) M. Monz ona, A.N. Benı teza, (008), Validation of electrical discharge machining electrodes made with rapid tooling technologies, journal of materials processing technology (19:109 11).

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