The electro-discharge machining characteristics of TiNi shape memory alloys

The electro-discharge machining (EDM) characteristics of TiNi shape memory alloys (SMAs) have been investigated in this study. Experimental results show that the material removal rate of TiNi SMAs in the EDM process significantly relates to the electro-discharge energy mode, involving the pulse current I _P and pulse duration _P. It also has a reverse relationship to the product of the melting temperature and thermal conductivity of TiNi SMAs. In addition, a longer pulse duration _P and a lower pulse current I _P should be selected to have a precise EDM machining of TiNi SMAs. Many electro-discharge craters and re-cast materials are observed on the EDM surface of TiNi SMAs. The re-cast layer consists of the oxides TiO₂, TiNiO₃ and the deposition particles of the consumed Cu electrode and dissolved dielectric medium. The thickness of the re-cast layer initially increases, reaches a critical value, and then decreases with increasing pulse duration _P. The specimen's hardness near the outer surface can reach 750 Hv for EDM TiNi SMAs. This feature originates from the hardening effect of the re-cast layer. The EDM TiNi SMAs still exhibit a nearly perfect shape recovery at a normal bending strain, but a slightly reduced shape recovery at a higher bending strain due to the depression of the re-cast layer. All the Ti₄₉Ni₅₁, Ti₅₀Ni₅₀ and Ti₅₀Ni₄₀Cu₁₀ SMAs exhibit similar EDM characteristics although they have different crystal structures and mechanical properties at room temperature.     

Surface damage in ZrB2-based composite ceramics induced by electro-discharge machining

Electro-conductive ZrB₂-based composite ceramics, containing SiC and B₄C, were machined with an electro-discharge machining (EDM) process. The EDMed surfaces were covered with resolidified ZrB₂ layers. Many open pores and surface cracks were observed on the surfaces. The strength degradation of the ceramics caused by machining was evaluated by three point bending tests of the partially EDMed bending specimens. The effects of pulsed current, pulse duration and duty factor on the strength and the roughness of EDMed surfaces are discussed. The strength of EDMed specimens was increased with decreases in pulse current, pulse duration and duty factor. The roughness of EDMed surfaces was decreased with decreases in pulse current, pulse duration and duty factor. The reliability of the ceramics EDMed with the appropriate conditions was as high as that of the ceramics ground with a 400 grit diamond wheel. It would be possible to use the carefully EDMed ZrB₂-based composite ceramics as structural components without any additional finishing processes.     

Optimization analysis on the economy of the electro-discharge machining process using electronic pulse generator

Research is yet to be clone on the direct economy of the electro-discharge machining process which is a vital criterion for the users of the machine. In this paper an expression for contribution rate, as a function of process variables, which is a direct indicator to measure the economic objectives of the process for a production system is derived and a methodology forestimating the process and hence the objective function with respect to the process variables is cited.

Further, in this paper a Complementary Geometric Programming algorithm is used to optimize the contribution rate under technical and technological constraints.

This paper also compares the contribution rates obtained from the results of the optimization problem with the following objective functions under compatible sets of restrictions: (i) Contribution rate. (ii) Material removal rate.

(iii) Electrode wear rate.

(iv) Ratio of material removal rate to electrode wear rate.

The data, for this paper is generated from JUSPA III, the electro-discharge machine based on the electronic pulse generator installed in the Machine Tool Research Laboratory at Jadavpur University, India.     

Role of electro-discharge machining on the fatigue performance of 15–5PH stainless steel component

Precipitation hardened stainless steel of 15–5PH grade is used for fabrication of actuator components. During one of the qualification tests, a piston made of this steel was fractured under cyclic loading. Analysis revealed that fracture initiated at the electro-discharge machined surface and propagated under cyclic loading.Efforts were made to establish role of various parameters of electro-discharge machining to the fatigue performance of the material.This paper brings out the details of investigation and suggests remedial measures to improve performance of material under fatigue.     

Use of measurement heads in machining centers

Translated from Izmeritel'naya Tekhnika, No. 9, pp. 24–26, September, 1990.     

Multi-objective parametric optimization of powder mixed electro-discharge machining using response surface methodology and non-dominated sorting genetic algorithm

Powder mixed electro-discharge machining (EDM) is being widely used in modern metal working industry for producing complex cavities in dies and moulds which are otherwise difficult to create by conventional machining route. It has been experimentally demonstrated that the presence of suspended particle in dielectric fluid significantly increases the surface finish and machining efficiency of EDM process. Concentration of powder (silicon) in the dielectric fluid, pulse on time, duty cycle, and peak current are taken as independent variables on which the machining performance was analysed in terms of material removal rate (MRR) and surface roughness (SR). Experiments have been conducted on an EZNC fuzzy logic Die Sinking EDM machine manufactured by Electronica Machine Tools Ltd. India. A copper electrode having diameter of 25?mm is used to cut EN 31 steel for one hour in each trial. Response surface methodology (RSM) is adopted to study the effect of independent variables on responses and develop predictive models. It is desired to obtain optimal parameter setting that aims at decreasing surface roughness along with larger material removal rate. Since the responses are conflicting in nature, it is difficult to obtain a single combination of cutting parameters satisfying both the objectives in any one solution. Therefore, it is essential to explore the optimization landscape to generate the set of dominant solutions. Non-sorted genetic algorithm (NSGA) has been adopted to optimize the responses such that a set of mutually dominant solutions are found over a wide range of machining parameters.     

On-machine measurement of tool nose radius and wear during precision/ultra-precision machining

The tool state exerts a strong influence on surface quality and profile accuracy during precision/ultraprecision machining. However, current on-machine measurement methods cannot precisely obtain the tool nose radius and wear. This study therefore investigated the onmachine measurement of tool nose radius on the order of hundreds of microns and wear on the order of a few microns to tens of microns during precision/ultra-precision machining using the edge reversal method. To provide the necessary replication, pure aluminum and pure copper soft metal substrates were evaluated, with pure copper exhibiting superior performance. The feasibility of the measurement method was then demonstrated by evaluating the replication accuracy using a 3D surface topography instrument; the measurement error was only 0.1%. The wear of the cutting tool was measured using the proposed method to obtain the maximum values for tool arc wear, flank wear, and wear depth of 3.4 lm, 73.5 lm and 3.7 lm, respectively.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00397-y     

Slotted electrodes for the improvement of machining performances in EDM drilling

In electrical discharge machining (EDM), poor debris removal may occur under certain conditions. This leads to debris accumulation and degrades machining efficiency. In this study, the rotation and retracting movements of slotted electrodes were coordinated during EDM to realize a pumping effect for expelling debris in the gap between the electrodes and workpieces. The study compared the performance of different slotted electrodes with that of a regular cylindrical (RC) electrode. Moreover, a computational fluid dynamics module was adopted to simulate the effects of the RC and slotted electrodes on debris removal capability in EDM under different conditions. The experimental results demonstrated that among all slotted electrodes, the deep slotted electrode engendered the most-favorable debris removal capability. The deep slotted electrode saved machining time by shortening the electrode jump time or even obviating electrode jumping. This increased the material removal rates by 120%–153% during EDM drilling.     

The state of heat measurement in the USSR

By heat measurement is meant a set of methods and facilities for obtaining information on heat flux densities. The formal basis for this survey is that the scientific division headed by the author for over 30 years has coordinated work on that line in this country. Also, during the last 15 years, All-Union conferences have been held every 2 years at which heat measurement has been discussed. The last conference was held in September 1989, and its papers form the basis of the present survey.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 3, pp. 516–522, September, 1990.     

Investigations into the effect of cathode material on temperature distribution during electrochemical machining

Electrochemical machining (ECM) is one of the most widely used unconventional manufacturing processes. Its capabilities have not been fully exploited mainly because of some inherent problems associated with tool design. Most of the models available for tool design in ECM ignore the effect of the heat transferred through the cathode and anode and its effects on the variation of different process parameters during ECM.

In the present paper, a simple thermal-resistance model of the ECM process is proposed. Using this model, the effects of the heat transferred through electrodes on temperature distribution, electrolyte conductivity, anode profile, metal removal rate (MRR), etc. have been studied. The experimental data have then been used to test the accuracy of the model.

The tests show that, for accurate determination of the anode profile, any model which takes no account of the heat transferred through the electrodes will yield erroneous results.     

Probability distribution of machining center failures

Through field tracing research for 24 Chinese cutter-changeable CNC machine tools (machining centers) over a period of one year, a database of operation and maintenance for machining centers was built, the failure data was fitted to the Weibull distribution and the exponential distribution, the effectiveness was tested, and the failure distribution pattern of machining centers was found. Finally, the reliability characterizations for machining centers are proposed.     

Effects of coolant on temperature distribution in metal machining

Abstract

The effects of coolant on tool temperature in metal turning operations were studied both experimentally and theoretically. Values for the coefficient of heat transfer from the tool to the coolant were obtained. Experimentally, a medium carbon steel was turned at a feed rate of 0·254 mm rev ^?1, at cutting speeds of 33–61 m min^?1, with high speed steel tools and water based coolant. Tool temperatures estimated from structural changes in the tool were compared with values calculated by finite element analysis. Heat transfer coefficients from tool to coolant between 10³ and 5 × 10³ W m²K^?1, depending on coolant flow rate, best match theory and experiment. Further, it is shown by the calculations that tool temperatures are particularly sensitive to changes in heat transfer coefficient between 10³ and 10⁴ W m^?2K^?1. This is the range in which coefficients are to be found in practice, explaining the critical nature of cutting fluid formulation, supply rate, and direction of application in those operations where cooling is important.

MST/809     

Cutting mechanism during machining of hardened steel

Abstract

Chip segmentation and the tool forces involved during cutting of hardened steel are discussed. AISI 4340 steel was machined on an engine lathe to study chip morphology, tool forces, and the surface generated. It was found that chip segmentation occurs when the hardness of the steel exceeds a certain value, and that the tool forces associated with chip segmentation are very high. A transformed layer of untempered martensite and retained austenite was produced when the cutting conditions were severe.

MST/469     

An inverse heat transfer problem for optimization of the thermal process in machining

It is evident that machining process causes development of large quantities of thermal energy within a relatively narrow area of the cutting zone. The generated thermal energy and the problems of its evacuation from the cutting zone account for high temperatures in machining. These increased temperatures exert a pronounced negative effect on the tool and workpiece. This paper takes a different approach towards identification of the thermal process in machining, using inverse heat transfer problem. Inverse heat transfer method allows the closest possible experimental and analytical approximation of thermal state for a machining process. Based on a temperature measured at any point within a workpiece, inverse method allows determination of a complete temperature field in the cutting zone as well as the heat flux distribution on the tool/workpiece interface. By knowing the heat flux function, one defines criterium and method of optimization, the inverse heat transfer problem transforms into extreme case. Now, the task of optimization is to determine most favourable ratio between heat flux parameters in order to preserve exploitation properties of the tool and workpiece.     

Deterioration of electrodes subjected to concentrated heat fluxes in a pulse discharge

The problem of the nonstationary thermal deterioration of a metal with the motion of the phase boundaries (melting and evaporation) taken into account is solved. The results of a computation are compared with experimental data.