A new experimental approach to determination of critical depth in high speed machining of soda-lime glass

Abstract. Soda-Lime glass is a very hard and brittle material which is commonly used as window panels and many other common applications. Due to its low fracture toughness it is very difficult to machine and obtain good surface finish under nornal cutting conditions. Hence, machining has to be done in ways to avoid brittle fracture on the finished machined surface. Such machining is only possible under ductile mode machining conditions when the removal of material is performed in the plastic state. However, ductile mode machining requires that during machining the temperature generated in the cutting zone in the working temperature range of glass to avoid crack formation during machining. This makes all types of machining of glass an extremely challenging affair, given the current state and mode of mechanical machining. This research paper elucidates the results of an experimental study for determination of critical depth of cut as a function of cutting parameters in high speed end milling of soda-lime glass. The critical depth is defined as the depth of cut at which crack formation the material is initiated for a given high speed attachment. In determining the critical depth as well as the ductile brittle transition depth, machining was performed on a tapered surface. Vibration signals from an accelerometer in time domain (amplitude vs. time display) and the surface characteristics were used in identifying the critical depth of cut. The new method has been found to be useful in online determination of the critical depth, as well as the brittle-ductile transition depth, for generating crack-free surfaces with good surface finish in high speed end milling of soda lime glass

The implementation of Taguchi method on EDM process of tungsten carbide

In this paper, the cutting of Tungsten Carbide ceramic using electro-discharge machining (EDM) with a graphite electrode by using Taguchi methodology has been reported. The Taguchi method is used to formulate the experimental layout, to analyse the effect of each parameter on the machining characteristics, and to predict the optimal choice for each EDM parameter such as peak current, voltage, pulse duration and interval time. It is found that these parameters have a significant influence on machining characteristic such as metal removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR). The analysis of the Taguchi method reveals that, in general the peak current significantly affects the EWR and SR, while, the pulse duration mainly affects the MRR. Experimental results are provided to verify this approach

Statistical Approach for the Development of Tangential Cutting Force Model in End Milling Of Ti6Al4V

Dynamic change in cutting force is one of the major causes of chatter formation in metal cutting which affect machining accuracy. Thus, accurate modeling of cutting force is necessary for the prediction of machining performance and determination of the mechanisms and machining parameters that affect the stability of machining operations. The present paper discusses the development of a mathematical model for predicting the tangential cutting force produced in endmilling operation of Ti6Al4V. The mathematical model for cutting force prediction has been developed in terms of the input cutting parameters cutting speed, feed rate, and axial depth of cut using response surface methodology (RSM). Effects of all the individual cutting parameters on cutting force as well as their interactions are investigated in this study. Central composite design was employed in developing the cutting force model in relation to the primary cutting parameters. The experimental results indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors that are being investigated

Influence of preheating on performance of circular carbide inserts in end milling of carbon steel

Circular inserts have much higher tool life as compared to conventional rectangular inserts because of their capability to be indexed through small angles for repeated use. Their only limitation is high chattering tendencies due to high contact length in conjunction with small uncut chip thickness. Experimental investigations were conducted to investigate the influence of preheating on performance of circular cemented carbides inserts in end milling operation of mild steel performed on vertical machining center (VMC) with rigid structure. Three TiN-coated circular cemented carbide inserts fitted on a 32 mm diameter tool were used in the experiments. Variable cutting parameters were cutting speed and feed. Depth of cut was kept constant at 1 mm. Performance of the inserts under room temperature and preheated machining was compared in terms of vibration stability, surface roughness, tool life and chip integrity. Vibration signals were recorded using an accelerometer type transducer and a Dual Channel Portable Signal Analyzer. The recorded signals were analyzed using the PULSE Labshop software. Surface roughness values were measured using a surface roughness measuring instrument-Mitutoyo Surfacetest model SJ-400. Worn tools and pitches of serrated chip teeth were studied under a scanning electron microscope (SEM). It was observed that during machining with and without preheating the main chatter frequencies remained practically constant and close to the natural frequencies of the system components while the amplitudes varied with cutting conditions. The amplitudes of chatter during preheating were found to be much lower than those during room temperature machining, as a result of which the surface roughness and tool wear were found to be much lower during preheated machining. The effect of chatter was also reflected on chip serration and segmentation. It was also observed that feed rate and cutting speed have considerable effect on surface roughness and tool wear in the cases of both hot and room temperature machining

Male with rhinosporidiosis of urethra: A case report

A 45-year old male presented with a six months history of a polypoidal lesion at external urethral meatus. There was a history of dysuria with bloody discharge from the lesion. The past and personal history was insignificant except for occasional bathing in a water pond. General physical examination and examination of nose, oral cavity and eyes was unremarkable. On local examination, a small red, fleshy, sessile lesion was seen at the external urethral orifice measuring 0.7 x 0.6 x 0.2 cm, clinically resembling a urethral caruncle. Urine routine examination showed presence of red cells. The lesion was completely resected under spinal anaesthesia. Histopathology showed stratified squamous lined tissue which reveals many sporangia containing endospore. Subepithelial region shows granulation tissue and is infiltrated with chronic inflammatory cells suggestive ofrhinosporidiosis. No other treatment was given. Patient was well after 3 months with no evidence of recurrence during follow up