The role of chemical wear in machining iron based materials by PCD and PCBN super-hard tool materials

The chemical compatibility of PCBN and PCD tool materials with iron has been evaluated by means of the static interaction diffusion-couples technique. Experiments were undertaken at different temperatures (700 °C, 900 °C, 1100 °C and 1300 °C) in order to establish the maximum temperature at which the tool and workpiece materials are chemically compatible. Computational equilibrium thermodynamics was used to calculate the chemical solubility of the different tool materials in iron and to identify the interaction phases formed. The agreement between the experimental results and the thermodynamic calculations was excellent. Machining tests were performed in order to assess the relative importance of the chemical wear on the overall rate of tool wear. The results of these machining tests agreed perfectly with the chemical compatibility study, thereby indicating that under certain machining conditions, chemical wear is the main wear mechanism for these materials in machining iron based materials.     

Suppression of diamond tool wear in machining of tungsten carbide by combining ultrasonic vibration and electrochemical processing

As an important ceramic material, tungsten carbide (WC) is utilized as the typical mold in precision glass molding, which has replaced conventional grinding and polishing to provide a highly replicative process for mass manufacturing of optical glass components. Ultra-precision grinding, which is time consuming and has low reproducibility, is the only method to machine such WC molds to high profile accuracy. Although diamond turning is the most widely used machining method for fabrication of optical molds made of metals, diamond turning of WC is still considered challenging due to fast abrasive wear of the diamond tool caused by high brittleness and hardness of WC. Ultrasonic vibration cutting has been proven to be helpful in realizing ductile-mode machining of brittle materials, but its tool life is still not long enough to be utilized in practical diamond turning of optical WC molds. In the current study, a hybrid method is proposed to combine electrochemical processing of WC workpiece surface into the diamond turning process. Cutting tests on WC using poly-crystalline diamond tools were conducted to evaluate its effect on improvement of tool wear and surface quality. Validation cutting tests using single crystal diamond tools has proven that the proposed hybrid method is able to significantly reduce the diamond tool wear and improve the surface quality of machined ultra-fine grain WC workpiece compared to ultrasonic vibration cutting without electrochemical processing.     

Analysis of CNC machining technology in production of plaster moulds

Abstract

The present paper continues the further application of machining techniques in the ceramics industry with the aim of optimising company resources in new competitive markets. The work is focused on plaster model and mould generation by computer based geometric design, machine tool path creation, and subsequent production through CNC machining using a robotic machining centre. Many constraints were identified related specifically to the machining of plaster used in the manufacture of ceramic ware. Because of the limited information, since most machining investigations have only considered metal machining or fired ceramics, a large number of machining experiments were conducted. It is concluded that substantial advantages are gained through the use of this new approach for ceramic production processes, and the subjects for follow on research are defined.     

Micromechanics of machining and wear in hard and brittle materials

Hard and brittle solids with covalent/ionic bonding are used in a wide range of modern-day manufacturing technologies. Optimization of a shaping process can shorten manufacturing time and cost of component production, and at the same time extend component longevity. The same process can contribute to wear and fatigue degradation in service. Educated development of advanced finishing protocols for this class of solids requires a comprehensive understanding of damage mechanisms at small-scale contacts from a materials perspective. The basic science of attendant deformation and removal modes in contact events is here analyzed and discussed in the context of brittle and ductile machining and severe and mild wear. Essentials of brittle–ductile transitions in micro- and nano-indentation fields are outlined, with distinctions between blunt and sharp contacts and axial and sliding loading. The central role of microstructure in material removal modes is highlighted. Pathways to future research—experimental, analytical, and computational—are indicated.     

Cutting performance and tool wear of SiAlON and TiC-whisker-reinforced Si3N4 ceramic tools in side milling Inconel 718

Cutting performance and tool wear of two ceramic tools, SiAlON and TiC-whisker-reinforced Si₃N₄, in the side milling processes of Inconel 718 are evaluated in comparison, including cutting force, temperature, surface morphology, tool wear and corresponding mechanism. Results show that these two ceramic tools has advantages and disadvantages respectively, due to the properties of ceramic matrixes and the evolutions of build-up edges. SiAlON ceramic tool has better resistance to wear, but causes poor surface quality. TiC-whisker-reinforced Si₃N₄ ceramic tool generates better surface quality, but bears severe wear. Brittle damage, as the main mode of wear, occurs to both ceramic tools in different formations. SiAlON ceramic tool is featured by crater-like damage on blades while TiC-whisker-reinforced Si₃N₄ ceramic tool is featured by whole-layer damage on flank faces.     

Surface integrity in electro-discharge machining, ultrasonic machining, and diamond saw cutting of ceramic composites

Good surface integrity is frequently required for structural ceramic components, since the lifetime of a ceramic component is in most cases determined by its surface features. In this study, the surface integrity of electro-discharge machined, ultrasonic machined, and diamond saw cut ceramic composites has been investigated and compared. The surface roughness, hardness, and topography of the machined surface were examined. Flexural strength and its distributions were used to evaluate the effect of machining process on the surface integrity of the machined specimens. Results show that the machining process had an important effect on the surface quality of the machined ceramics. Electro-discharge machining of ceramics created a heat-affected surface layer with poor surface integrity, such as cracks and craters, and the variable surface damages on the electro-discharge machined specimens resulted in low Weibull modulus. Within most machining conditions, the ultrasonic machined and diamond saw cut specimens behaved fairly consistently, and the flexural strength and Weibull modulus were higher than that of the electro-discharge machined specimens.     

Determination of moisture content in sunflowers with electronic moisture meters

Accurate estimates of moisture content in sunflower seeds (achenes) with electronic moisture meters require that the sample be adequately equilibrated before testing. Seed which has undergone a rapid drying of the hull (pericarp) surface and is tested without sufficient equilibration time will indicate a moisture content that is 0.2–2.0 percentage points lower than the true moisture content. Seed can be properly equilibrated by placing them in a sealed container for 12 hr. Calibration curves based on quadratic equations provide a better estimate of sunflower seed moisture content over a greater range than do linear equations.     

Determination of moisture content and moisture content profiles in wood during drying by low-field nuclear magnetic resonance

In this article, the low-field nuclear magnetic resonance was used to measure the moisture content (MC) and MC profiles in poplar wood during real-time drying. The T₂ distribution curve at each drying stage measured using the Carr–Purcell–Meiboom–Gill pulse sequence provided detailed information in the dynamic change of free water as well as bound water of the whole wood sample. In addition, a new developed SE-SPI pulse sequence was first used to evaluate the spatially resolved T₂ distribution of the successive nondestructive sliced layer of wood. Combined with the area integration method, the moisture content in each layer was calculated, and the change of MC profiles within wood at the MC above and below fiber saturation point was well reflected.     

帘布含水率的控制

帘布含水率受空气相对湿度影响较大，夏天、雨季时含水率较高。实际监测数据表明，通过适时调整压延干燥系统的干燥时间和温度、在雨季适当增大含水率测试频率、改善帘布存放环境，可以使帘布含水率保持在较低水平，从而保证轮胎质量。     

Computer model of drying behaviour of ceramic green bodies with particular reference to moisture content dependent properties

A numerical model was developed to predict the drying behavior of ceramic green bodies. Resolution of the simultaneous heat and mass transfer equations involved finite elements and the Backward Euler method. Based on experimental data, the model uses equivalent moisture diffusivity, water activity, thermal conductivity and heat capacity as input parameters which depend on moisture content. In particular, the equivalent moisture diffusivity is a key parameter controlling water transport from the body interior to the surface. A simple method was used to estimate the effect of shrinkage on drying rate during the initial drying stage. Predictions of the internal moisture distribution, drying rate and surface temperature as a function of time gave good agreement to experiment for green bodies of alumina paste. External conditions of convection coefficient and relative humidity are shown to sensitively control drying rate and surface temperature evolution during the constant rate period.     

Cutting performance and wear mechanisms of the graphene-reinforced Al2O3-WC-TiC composite ceramic tool in turning hardened 40Cr steel

The Al₂O₃-WC-TiC-graphene composite ceramic tool (AWTG0.5) fabricated by two-step hot pressing was used to continuously turn the hardened 40Cr steel at different cutting speeds, and its cutting performance and wear mechanisms were compared with the homemade graphene-free AWTG0 ceramic tool and the commercial ceramic tools SG4 and LT55. The cutting performance of the AWTG0.5 tool was significantly better than that of the AWTG0, SG4 and LT55 tools. The contributions of graphene to the mechanical properties, lubricating properties and thermal conductivity of the AWTG0.5 tool were responsible for its higher cutting performance. The main wear mechanisms of the AWTG0.5 tool were adhesive wear and abrasive wear. In addition, it was also found that the anti-friction and wear resistance performances of the AWTG0.5 tool were superior to those of the other three tools. Its good anti-friction and wear resistance performances could be attributed to the formation of a self-lubricating layer induced by graphene pull-out.     

Monolithic and composite ceramic machining flaw-microstructure-strength effects: model evaluation

A model giving the size, c, of flaws from machining of ceramics as c ∝ (E/H)^1/3(F/K)^2/3, where F= the vertical force on abrasive particles, and H, K, and E= respectively local values of hardness, fracture toughness (i.e. small crack values) and Young's modulus is shown to be consistent with material, microstructural and machining parameter effects on flaws and strengths. Specifically this model is consistent with effects of machining flaw sizes on strengths due to effects of: (1) porosity and grain size in monolithic ceramics, (2) matrix grain size, and dispersed particle size and volume fraction in ceramic particulate composites, and (3) machining parameters such as grit size in monolithic and composite ceramics. Such a model emphasizes the role of microstructural and compositional dependence of properties impacting strengths via both flaw introduction as well as via flaw propagation to failure, which provides a broader perspective on strengths of typically machined ceramics.     

Effect of chemical composition of semifinished ceramic products on the accuracy of determining their moisture content using an IR-hygrometer

Translated from Steklo i Keramika, No. 4, pp. 18–19, April, 1991.     

Two-dimensional two-phase numerical model for tool design in electrochemical machining

Tool design in electrochemical machining is investigated including the effects of thermal-fluid properties of the electrolyte. A two-dimensional two-phase numerical model is used to predict the thermal-fluid field. Simulation indicates that, as the curvature of the electrode shape varies widely, the two-dimensional phenomenon of the flow is apparent and the two-dimensional model should be used during the numerical simulation. In addition, a higher electrolyte flow rate slightly reduces the two-dimensional effects. As the curvature of the electrode shape varies only slightly, one-dimensional analysis is accurate and capable of reducing the calculation time.