Development of a mathematical model for the prediction of surface roughness in end milling of stainless steel SS 304

The use of advanced computer-based systems for the selection of optimum conditions of mechanical components during process planning becomes essential for today’s complex products. Computer aided manufacturing (CAM) has widely been implemented to obtain more accurate machining data and to ensure that optimum production is achieved. Machinability of a material provides an indication of its adaptability to be manufactured by a machining process. In general, machinability can be defined as an optimal combination of factors such as low cutting force, high material removal rate, good surface integrity, accurate and consistent workpiece geometrical characteristics, low tool wear rate and good curl or breakdown of chips. In machinability studies investigations, statistical design of experiments is used quite extensively. Statistical design of experiments refers to the process of planning the experiment so that the appropriate data can be analyzed by statistical methods, resulting in valid and objective conclusions [1]. Design and methods such as factorial design, response surface methodology (RSM) and Taguchi methods are now widely use in place of one-factor-at-a-time experimental approach which is time consuming and exorbitant in cost. A machinability model may be defined as a functional relationship between the input of independent cutting variables (speed, feed, depth of cut) and the output known as responses (tool life, surface roughness, cutting force, etc) of a machining process [2]. Response surface methodology (RSM) is a combination of experimental and regression analysis and statistical inference. RSM is a dynamic and foremost important tool of design of experiment (DOE), wherein the relationship between response(s) of a process with its input decision variables is mapped to achieve the objective of maximization or minimization of the response properties [3]. Many machining researchers have used response surface methodology to design their experiments and assess results. Kaye et al [4] used response surface methodology in predicting tool flank wear using spindle speed change. A unique model has been developed which predicts tool flank wear, based on the spindle speed change, provided the initial flank wear at the beginning of the normal cutting stage is known. An empirical equation has also been derived for calculating the initial flank wear, given the speed, feed rate, depth of cut and workpiece hardness. Alauddin et al [5] applied response surface methodology to optimize the surface finish in end milling of Inconel 718 under dry condition A dimensional-accuracy model for the peripheral milling of aluminum alloys under dry and down-milling conditions was presented by Fuh and Chang [6]. Gu et al. [7] presented a new model for the prediction of surface flatness errors in face milling. Their method called equivalent flexibility influence coefficient method. In this chapter, the technique is used to develop a mathematical model that utilizes the response surface roughness methodology and method of experiments to predict the surface roughness when milling stainless steel SS 304 using TiN coated Tungsten carbide inserts

Elimination of burr formation during end milling of Polymethyl Methacrylate (PMMA) through high speed machining

A burr is a raised edge or small pieces of material remaining attached to a workpiece after it has undergone machining. The Burr, Edge and Surface Technology (BEST) Division, the Society of Manufacturing Engineers defines a burr as “an undesirable projection of material that results from cutting, forming, blanking or shearing operation [1]. The first stage, chip formed in front of the cutting tool with a positive shear angle, φ. The plastic zone around the primary shear zone is extended towards the work edge when cutting tool advance toward the work edge.There are four basic types of burr that have been defined by researchers which are: poisson, roll-over, tear burr and cut-off burr [2-3]. The four specific types of burr are: Roughness refer to the small, finely spaced deviations from the nominal surface, which is determined by the material characteristics and the process that formed the surface [4]. The theoretical surface roughness, �� can be estimated using the following equation [5] �� = �� � / 32(R ± ���� / π) (1) Where �� is the surface roughness, �� is the number of teeth on the cutter, R is the radius of the cutter, �� is the feed per revolution and the (+) sign refers to up-milling and the (-) sign refers to down milling.The above equation does not consider many factors that in reality can affect the surface roughness. For this reason the surface roughness will generally be higher than that predicted by Eq. (1). Statistical models that include such factors as depth of cut and spindle speed in addition to feed rate have been developed [6]

Relative performances of preheating, cryogenic cooling and hybrid turning of stainless steel AISI 304

Chatter is an unwanted phenomenon in machining due to its adverse effects on the product quality, operation cost, machining accuracy, tool life, machine-tool bearings, and machine-tool life. The term defines the self-excited violent dynamic motion between the cutting tool and work piece [1]. During high speed machining of steel, large amount of energy is used in shearing process and substantial energy is converted to heat. Heat generation becomes more intensified in machining of high strength materials because the machining process requires more energy than that in cutting a low strength material. The rapid escalation of temperature at the cutting zone is the primary cause accountable for high diffusion wear rate leading to shorter tool life. High tool wear rate leads to high degree of chatter and poor surface finish. It is therefore essential to design effective cooling systems to bring down the temperature at the cutting zones. Cryogenic cooling is being looked at as a potential replacement of conventional mineral oil based coolants because the latter is being rejected on grounds on serious environmental and health problems that it causes [2].Cryogenic cooling is the cooling approach to replace conventional coolant by liquefied gas in machining process [3].The impact of cryogenic cooling on chip breaking and tool wear intensity during end milling and turning has been investigated by various researchers [3-7], but there has not been any study on the impact of cryogenic cooling on chip formation and chatter.Tungsten-inert-gas (TIG) plasma heating could be used to replace Laser Beam heating and high frequency heating since TIG plasma heating also offers high heating capacity and at the same time the use of inert gas would be able to protect the work surface against oxidation during machining. In this research the TIG or tungsten-arc welding machine would therefore be used as an well controlled and precise heat source to preheat the uncut layer of the work material before it enters into the shearing zone. The major advantages of the plasma preheating are increased metal removal rates, results in no metallurgical damage to the work piece and increase in tool life [8].Similarly there has been some works [9] on the influence of workpiece preheating using induction heating on machinability of work materials and chatter during end milling operation, the application of preheating technique in turning should be explored further to confirm its effectiveness of different heating process. It was found that preheating resulted in substantia

Interleukin-18 as an in vivo mediator of monocyte recruitment in rodent models of rheumatoid arthritis

Abstract Introduction The function of interleukin-18 (IL-18) was investigated in pertinent animal models of rodent rheumatoid arthritis (RA) to determine its proinflammatory and monocyte recruitment properties. Methods We used a modified Boyden chemotaxis system to examine monocyte recruitment to recombinant human (rhu) IL-18 in vitro. Monocyte recruitment to rhuIL-18 was then tested in vivo by using an RA synovial tissue (ST) severe combined immunodeficient (SCID) mouse chimera. We defined monocyte-specific signal-transduction pathways induced by rhuIL-18 with Western blotting analysis and linked this to in vitro monocyte chemotactic activity. Finally, the ability of IL-18 to induce a cytokine cascade during acute joint inflammatory responses was examined by inducing wild-type (Wt) and IL-18 gene-knockout mice with zymosan-induced arthritis (ZIA). Results We found that intragraft injected rhuIL-18 was a robust monocyte recruitment factor to both human ST and regional (inguinal) murine lymph node (LN) tissue. IL-18 gene-knockout mice also showed pronounced reductions in joint inflammation during ZIA compared with Wt mice. Many proinflammatory cytokines were reduced in IL-18 gene-knockout mouse joint homogenates during ZIA, including macrophage inflammatory protein-3α (MIP-3α/CCL20), vascular endothelial cell growth factor (VEGF), and IL-17. Signal-transduction experiments revealed that IL-18 signals through p38 and ERK½ in monocytes, and that IL-18-mediated in vitro monocyte chemotaxis can be significantly inhibited by disruption of this pathway. Conclusions Our data suggest that IL-18 may be produced in acute inflammatory responses and support the notion that IL-18 may serve a hierarchic position for initiating joint inflammatory responses.http://deepblue.lib.umich.edu/bitstream/2027.42/112330/1/13075_2010_Article_2890.pd

High speed end milling of single crystal silicon using diamond coated tools

Brittle materials are hard to machine while maintaining the surface roughness desired. A brittle material will have little tendency to deform before it fractures when it is subjected to stress. Brittle material is also consider as a material which fails in tension rather than shear and has little or no evidence of plastic deformation before it fails. Thimmaiah et al. [1] specified that brittle materials, silicon by their inherent properties, are difficult to machine while maintaining the desired surface roughness but J. Yan et al. [2] reviewed that silicon is a nominally brittle material that can be deformed plastically in machining, yielding ductile chips under the influence of high hydrostatic pressure. Mariayyah [3] , stated that under certain controlled conditions, it is possible to machine brittle materials in ductile regime so that material removal is by plastic deformation, leaving a damage free surface. Rusnaldy et al. [4] research on the cutting parameters effect. They study about the effect of the depth of cut, feed rate and spindle speed. Rusnaldy et al. [5] showed that the dominant ductile cutting mode was achieved for Ft/Fc>1.0, which indicates that the thrust force is dominant over the cutting force. Cutting to a very small uncut chip thickness can cause ploughing, resulting in a poor surface due to high friction. Siva [6] proposes a predictive model to determine the undeformed chip thickness in micro-machining of single crystal brittle materials, where the mode of chip formation transitions from the ductile to the brittle regime. The proposed model would support the determination of the cutting conditions for the micromachining of a brittle material in ductile manner without resorting to trial and error. Furthermore, Sreejith [7] was able to obtain ductile mode of machining on silicon nitride by using Poly Crystalline Cubic Diamond (PCD) tools. His findings show that there is a maximum value of rake angle which will obtain ductile mode machining. Thimmaiah et al. [1] also did machining on silicon nitride but performed it using single point diamond turning. Their result indicates that small values of feed, small tooltip radius and at high speeds; conditions of pressure and temperature exist that facilitate ductile behaviour during machining. Negative rake angles are more likely to cause brittle to ductile transition when compared with the positive or zero degree rakes. These findings also correspond with Thimmaiah et al. [1] findings which also show that cutting force and thrust force increases as the rake angle becomes negative. The experimentation results differ with a crossover at between thrust force and cutting force at -45º.Furthermore, J. Yan et al (2000) stated that there is no inherent advantage in using rake angle more negative than -40º

Dupilumab Improves Nasal Polyp Burden and Asthma Control in Patients With CRSwNP and AERD

In the difficult-to-treat subgroup of patients with chronic rhinosinusitis with nasal polyps (CRSwNP) and comorbid aspirin-exacerbated respiratory disease, dupilumab significantly improved CRSwNP disease outcomes, along with asthma control and lung function. This is preliminary evidence of the effect of dupilumab in patients with CRSwNP and comorbid aspirin- exacerbated respiratory disease

A new method for chatter suppression and improvement of surface roughness in end milling of mild steel

Chatter is an abnormal tool behaviour which it is one of the most critical problems in machining process and must be avoided to improve the dimensional accuracy and surface quality of the product [1]. The most critical limitation in machining productivity and part quality is the occurrence of the instability phenomenon called regenerative chatter [2]. According to Ravikumar and Bhaskar [2] chatter is a self-excitation phenomenon occurring in machine tools, in which the cutting process tends to decrease the machine structural damping ending with an unstable behaviour. It results in heavy vibrations of the tool, causing an inferior work piece. According to Patwari and Amin [3] chatter is a very important phenomenon that needs to be taken into consideration whenever machining process is being performed. It is very important to avoid chatter in machining as it will effect others parameters which then will increase the cost of production. In a micromilling process, where the spindle rotates an end mill to remove a portion of the workpiece, the unstable phenomenon, regenerative chatter also occurs due to changes in the chip thickness similar with the macro machining [4-5]. Altintas and Chan [6] stated that one of the major limitations on productivity in metal cutting is chatter vibration, which causes poor surface finish and tool damage. Kim et al. [7] explained that most of the drawbacks that come from chatter are excessive tool wear, noise, tool breakage, and deterioration of the surface quality. Moreover chatter also results in reduced material removal rate (MRR), increased costs in terms of time, materials and energy, as well as the environmental impact of dumping non-valid final parts and having to repeat the manufacturing process as quoted from Quintana [8]

Inhibitory effect of Labisia pumila leaf extract on angiogenesis via down-regulation of vascular endothelial growth factor

Purpose: To investigate the anti-angiogenic activity of a methanol leaf extract of Labisia pumila (ME), and its bioactive water fraction (WF), using in vitro models.Methods: The antioxidant activity and total phenolic contents of ME and WF were assessed using DPPH and Folin–Ciocalteu reagents. Antiproliferative effects of extracts towards human umbilical vein endothelial cells (HUVECs) were evaluated using MTT assay. Isolated rat aortic ring and matrigel tube formation assays were performed to assess the antiangiogenic potential of Me and its WF. Levels of VEGF protein in the cell lysates were measured using ELISA kit.Results: Among all the extracts prepared, ME and its WF showed higher total phenolic contents and exhibited moderate antioxidant effects. Significant (p < 0.001) suppression of microvessels outgrowth with half-maximal concentration (IC50) values of 20 and 26 μg/mL for ME and WF, was observed in rat aortic ring assay. ME and its WF halted proliferation and tube formation capacity of HUVECs in in vitro assays. Marked reduction in VEGF levels was observed in lysates of HUVECs treated with ME and its WF.Conclusion: Labisia pumila leaf extract and its water fraction halted angiogenesis by blocking VEGF secretion leading to inhibition of endothelial cells proliferation and differentiation which is suggested to be due to its phenolic antioxidant contents.Keywords: Labisia pumila, Anti-angiogenesis, Antioxidant, Tube formation, Rat aort

Accelerated development of arthritis in mice lacking endothelial selectins

The selectins, along with very late antigen-4 and CD44, have been implicated in mediating leukocyte rolling interactions that lead to joint recruitment and inflammation during the pathogenesis of rheumatoid arthritis. Previously, we showed that P-selectin deficiency in mice resulted in accelerated onset of joint inflammation in the murine collagen-immunized arthritis model. Here, we report that mice deficient either in E-selectin or in E-selectin and P-selectin (E/P-selectin mutant) also exhibit accelerated development of arthritis compared with wild type mice in the CIA model, suggesting that these adhesion molecules perform overlapping functions in regulating joint disease. Analyses of cytokine and chemokine expression in joint tissue from E/P-selectin mutant mice before the onset of joint swelling revealed significantly higher joint levels of macrophage inflammatory protein-1α and IL-1β compared to wild-type mice. IL-1β remained significantly increased in E/P-selectin mutant joint tissue during the early and chronic phases of arthritis. Overall, these data illustrate the novel finding that E-selectin and P-selectin expression can significantly influence cytokine and chemokine production in joint tissue, and suggest that these adhesion molecules play important regulatory roles in the development of arthritis in E/P-selectin mutant mice