Effects of Trace Elements on the Microstructural and Machinability Characteristics of Al–Si–Cu–Mg Castings

This study was undertaken to emphasize the influence of Sn and Bi addition on the machinability of Sr-modified, grain-refined, and heat-treated Al–Si B319 and 396 alloys. Drilling and tapping tests were conducted to examine the cutting forces, tool life, tool wear, built-up edge evolution, and chip shape. Microstructures were examined using optical and electron microscopy. Drilling test results show that the B319.2 alloy with 0.15%Sn yields the longest drill life, i.e., twice that of the B319.2 alloy containing 0.5%Bi, and one-and-a-half times that of the B319.2 alloy containing 0.15%Sn + 0.5%Bi. The presence of 0.5%Bi in the B319.2 alloy causes a deterioration of drill life (cf., 1101 holes with 2100 holes drilled in the B319.2 alloy containing 0.15%Sn). The α-Fe phase in the 396 alloy produces the highest number of holes drilled compared with alloys containing sludge or β-Fe. The presence of sludge decreases the drill life by 50%. Built-up edge (BUE) measurements and optical photographs show little change in the BUE width for different numbers of holes except for the B319.2 alloy containing 0.5%Bi, which shows a slightly lower width (0.166 mm) compared with that containing 0.15% Sn (0.184 mm) or 0.15%Sn + 0.5%Bi (0.170 mm).

The Effect of Biomass Shapes on Combustion Characteristic in Updraft Chamber

Combustion of agricultural residues and wastes for energy applications is still popular. However, combustion of biomass with different shapes leads to many side effects such as agglomeration, emission and incomplete combustion. The aim of this study was therefore to investigate the effects of biomass shapes on combustion characteristics in an updraft combustion chamber. The rubber wood chip, coconut shell, oil palm empty fruit bunch, corn straw, rubber wood sawdust, and mixed palm cake were used as fuel and they were categorized as 3 shapes namely, chip shape, fiber shape, and powder shape. The biomass sample was combusted in simple cylindrical shape combustion chamber. The diameter of combustion chamber was 20 cm and its height was 160 cm. The biomass sample (moisture content below 20%) with amount of 1 kg was used to perform the experiment. The ambient air that had velocity of 0.50, 0.75 and 1.00 m/s (corresponding to an equivalence ratio of 1-3.5) was supplied to combustion chamber. The temperature at different positions along combustion chamber height and the properties of flue gases (carbon monoxide) were then measured. The results showed that the biomass shape had effect on combustion characteristics. Combustion of fiber shape biomass led to low combustion temperature, while the carbon monoxide in flue gases was high. This indicates the improper combustion process. The chip shape biomass was well combusted at a higher air velocity and the flue gases had lowest carbon monoxide. The highest combustion temperature was obtained from combustion of powder shape biomass. However, it led to the problem of unburned biomass such in case of sawdust. This is because the sawdust powder was carried from combustion chamber before burning completely.

Modelling and controlling the process of cutting with complex-geometry tools to improve efficiency of mining machines and plants

Constant quality improvement through automation of production processes is an important prerequisite for increased viability of mining machines and plants. Factors that limit the automation of the cutting machining operations include the problem of controlling the chip formation and chip crushing. Solution of this problem necessitates theoretical description of the material cutting conditions for tools with curvilinear surfaces. The paper describes basic principles of modeling the cutting process using complex-geometry tools with curvilinear rake. The theory is based on the concept of chip formation as a process of inhomogeneous strain in the plastic zone where the chip originates. Based on the analysis of the stress-strain state in the cutting zone, criterial relationships were derived that correlate the geometric parameters of the chip shape and machining conditions of the curvilinear-rake tool. Prerequisites for chip breaking are stability of the chip shape during cutting, stable chip-to-obstacle contact, high chip stiffness and low flexibility. The machining conditions leading to chip fragmentation could be found by solving the strength problem. Through establishing the cause-and-effect relationships of the processes of chip formation, curling and breaking, new approaches to achieving favorable chip shape may be found by exerting deliberate impact on the plastic zone of the chip formation through optimizing the conditions for the chip flow off the tool. The established relationships between the output parameters of the cutting process and process conditions of cutting with a complex-geometry tool offer the way to control the chip flow parameters in various machining operations. The research is aimed at creating scientifically informed design codes and optimization of cutting parameters for tools with curvilinear chip-curling and chip-breaking rake surfaces.

Investigations on chip formation of turned novel AM alloy

Manufacturers across varied segments look for materials having appreciable machinability and surface integrities. Machinability of Mg alloys is a vital aspect during their acceptance for different applications. The chip shape generated in the cutting operation is a crucial attribute dominating the surface roughness, besides the dimension’s precision and the tool lifespan. The study discusses the chip-formation through the dry turning of a novel AM alloy (Mg alloy with 7 wt%Al-0.9 wt%Mn) using carbide insert with a 0.4 mm nose radius. During the experiments, three chip dimensions, namely chip-thickness, chip-length, and chip-width were measured. The turning variables, namely cutting speed( v), depth of cut (DOC), and feed ( f) is altered and applied to the workpiece. The chip shape was mostly dependent on the grouping of turning parameters. It was seen that favorable continuous chip formed at high feed and low DOC. The % contribution of each turning parameter on the chip shape was calculated. The experimental results are validated with the help of analysis of variance (ANOVA). The results show that the % contribution of feed, speed, and DOC on chip-thickness is 58.49%, 28.91%, and 12.49%; the contribution on chip-length is 76.89%, 20.81%, and 2.23%; and on chip-width, it is 25.28%, 0.48%, and 74.33%, respectively. Further, the chip shapes were compared with the shapes that were predicted by FEM software. The study offers vital insights for parameter selection to improve chip shape, which, in turn, contributes to higher surface quality.

Cutting Forces and Chip Shaping When Finish Turning of 17-4 PH Stainless Steel under Dry, Wet, and MQL Machining Conditions

This paper analyses three components of total cutting force and chip shape changes when finish turning 17-4 PH (precipitation hardening) stainless steel. A Finite Element Method (FEM) simulation of cutting forces was also performed using the Johnson–Cook constitutive model. The results were compared with those obtained from experimental studies. Variable feeds of 0.05–0.4 mm/rev and depth of cut of 0.2–1.2 mm with a cutting speed of 220 m/min were used. The studies were carried out under dry and wet cooling conditions and with the use of minimum quantity lubrication (MQL). This research was realized based on the Parameter Space Investigation (PSI) method. Statistical analysis of the obtained results was carried out using Statistica-13 software. It was found that the cutting force Fc and feed force Ff depend on the depth of cut and feed, and the passive force Fp depends mainly on the feed. Compared to dry cutting conditions, a reduction of 43% and 39% of the cutting force Fc was achieved for wet machining and MQL machining, respectively. Regardless of the cooling conditions, a favorable chip shape was registered for ap = 1–1.1 mm and f = 0.25–0.3 mm/rev. Compared to the experimental studies, the FEM simulation showed differences of ~13% for the cutting force Fc and of ~36% for the feed force Ff.

Light-directed on-chip shape transformation of a single gold nanoparticle

Surface plasmons enable controllable shape transformation based on the dissolution and re-deposition of gold nanoparticles (Au NPs).