In precision machining processes such as grinding,for example,analysis of machined surface is important one of most parameters to evaluate process performance.Equally important is to perform tribological analysis to u...In precision machining processes such as grinding,for example,analysis of machined surface is important one of most parameters to evaluate process performance.Equally important is to perform tribological analysis to understand chip formation and abrasive wheel wear,thus enabling manufacturing of components free of thermal damages.In grinding,due to high hardness of abrasive grains that remove material from workpiece in chip form and very low values of radial depth of cut,combination of low roughness values and tight dimensional tolerances is attained.Accordingly,the parameters involved in this process are determinant in surface quality that is primarily evaluated in terms of surface roughness and workpiece functionality.In this work,surface roughness(Rt parameter)and scanning electron microscope(SEM)images of ground surfaces of the AISI 420 martensitic stainless steel samples were evaluated.Tests were carried out in surface grinding with a white aluminum oxide wheel and an environmentally-friendly semisynthetic water-soluble coolant.Two values of radial depth of cut(10μm and 25μm)were tested.The results showed that the highest roughness values,deeper grooves on the machined surfaces as well as poorer surface quality were obtained after grinding under the severest cutting conditions.展开更多
The Nickel base Superalloys are the most famous complicated and useable of Superalloys to make hot zone components of the gas turbines. The complicated dimensional tolerances, specially at the root of the blade show i...The Nickel base Superalloys are the most famous complicated and useable of Superalloys to make hot zone components of the gas turbines. The complicated dimensional tolerances, specially at the root of the blade show importance of grinding processes at the production of blades root. The prediction of the effect of machining parameters on the soundness of component surface strengthening for reaching to a suitable surface finishing and avoiding from crack formation at the work part during machining operation often is not easy and feasible so needs to more industrial investigation. This research is about frame 5 blade designed by GE and made from Superalloy IN738LC has been investigated. The formation of a plastically deformed and heat affected zone during grinding of Superalloy IN738LC with a high depth of cut but slow work speed (creep feed grinding) was investigated. Parameters such as work speed, depth of cut and radial dressing speed have been considered as variables and their effects have been studied. During experimental performed, the voltage and current of motor measured and power and special energy calculated. Some samples heat-treated (of the 1176°C for 1 hr under neutral argon gas and cooling rate of 15°C /min up to 537°C and then air cooling) to study grains recrystallization. Other samples have been created from the roots of blades and then coated by Nickel to measure boundary layer micro-hardness. The results show that increasing work speed leads to increasing the use power. Increasing the depth of cut, by increasing material removal rate, and the radial dressing speed, by decreasing power, lead to decreasing special energy. The temperature created by grinding lead to decreasing plastic deformation and boundary layer formation. When the radial dressing speed changes from 1 to 0.6 u,m/rev and other parameters are kept unchanged the roughness of surface increases and the special energy decreases. Sufficient dressing is very essential in limiting the width of the molten zone to few micrometers. As a result, it was found that local melting at contact spots to be a rather common mechanism during grinding of superalloys, lead to so-called white layers which can easily be observed on metallographic cross sections.展开更多
文摘In precision machining processes such as grinding,for example,analysis of machined surface is important one of most parameters to evaluate process performance.Equally important is to perform tribological analysis to understand chip formation and abrasive wheel wear,thus enabling manufacturing of components free of thermal damages.In grinding,due to high hardness of abrasive grains that remove material from workpiece in chip form and very low values of radial depth of cut,combination of low roughness values and tight dimensional tolerances is attained.Accordingly,the parameters involved in this process are determinant in surface quality that is primarily evaluated in terms of surface roughness and workpiece functionality.In this work,surface roughness(Rt parameter)and scanning electron microscope(SEM)images of ground surfaces of the AISI 420 martensitic stainless steel samples were evaluated.Tests were carried out in surface grinding with a white aluminum oxide wheel and an environmentally-friendly semisynthetic water-soluble coolant.Two values of radial depth of cut(10μm and 25μm)were tested.The results showed that the highest roughness values,deeper grooves on the machined surfaces as well as poorer surface quality were obtained after grinding under the severest cutting conditions.
文摘The Nickel base Superalloys are the most famous complicated and useable of Superalloys to make hot zone components of the gas turbines. The complicated dimensional tolerances, specially at the root of the blade show importance of grinding processes at the production of blades root. The prediction of the effect of machining parameters on the soundness of component surface strengthening for reaching to a suitable surface finishing and avoiding from crack formation at the work part during machining operation often is not easy and feasible so needs to more industrial investigation. This research is about frame 5 blade designed by GE and made from Superalloy IN738LC has been investigated. The formation of a plastically deformed and heat affected zone during grinding of Superalloy IN738LC with a high depth of cut but slow work speed (creep feed grinding) was investigated. Parameters such as work speed, depth of cut and radial dressing speed have been considered as variables and their effects have been studied. During experimental performed, the voltage and current of motor measured and power and special energy calculated. Some samples heat-treated (of the 1176°C for 1 hr under neutral argon gas and cooling rate of 15°C /min up to 537°C and then air cooling) to study grains recrystallization. Other samples have been created from the roots of blades and then coated by Nickel to measure boundary layer micro-hardness. The results show that increasing work speed leads to increasing the use power. Increasing the depth of cut, by increasing material removal rate, and the radial dressing speed, by decreasing power, lead to decreasing special energy. The temperature created by grinding lead to decreasing plastic deformation and boundary layer formation. When the radial dressing speed changes from 1 to 0.6 u,m/rev and other parameters are kept unchanged the roughness of surface increases and the special energy decreases. Sufficient dressing is very essential in limiting the width of the molten zone to few micrometers. As a result, it was found that local melting at contact spots to be a rather common mechanism during grinding of superalloys, lead to so-called white layers which can easily be observed on metallographic cross sections.
