The machinability of a cast aluminium alloy-graphite particle composite

The microstructure of a cast Al---Si alloy-graphite particle composite is examined using optical and analytical scanning electron microscopy. Specimens containing different percentages of graphite were machined by orthogonal planning with 25° and 45° rake angle tools at both 6.5 and 13.2 m min−1. The machining forces are reported and the chip-rake-face friction coefficients and shear flow stresses are calculated. It is shown that the reduction in machining forces with increasing graphite content is due mostly to a decrease in the shear flow stress rather than to lower chip-rake-face friction. Both the polished and the machined surfaces of the composite are rougher than those of the simple alloy, apparently owing to the greater porosity, the tearing out of graphite particles, or the opening of cracks at the graphite particles in the wake of the tool.

Improved damping capacity and machinability of graphite particle-aluminum alloy composites

The damping capacity of cast graphitic aluminum alloy composites has been measured using a torsion pendulum at a constant strain amplitude. It was found that flake-graphite particles dispersed in the matrix of aluminum alloys increased the damping capacity; the improvement was greater, the higher the amount of graphite dispersed in the matrix. At sufficiently high graphite contents the damping capacity of graphitic aluminum composites approaches that of cast iron. The ratio between the damping capacity and the density of graphitic aluminum alloys is higher than cast iron, making them very attractive as light-weight, high-damping materials for possible aircraft applications. Machinability tests on graphite particle-aluminum composites, conducted at speeds of 315 sfm and 525 sfm, showed that the chip length decreased with the amount of graphite of a given size. When the size of graphite was decreased, at a given machining speed, the chip length decreased. Metallographic examination shows that graphite particles act as chip breakers, and are frequently sheared parallel to the plane of the

γ-Y2Si2O7, a machinable silicate ceramic: Mechanical properties and machinability

In this paper, the mechanical properties of bulk single-phase γ-Y2Si2O7 ceramic are reported. γ-Y2Si2O7 exhibits low shear modulus, excellent damage tolerance, and thus has a good machinability ready for metal working tools. To understand the underlying mechanism of machinability, drilling test, Hertzian contact test, and density functional theory (DFT) calculation are employed. Hertzian contact test demonstrates that γ-Y2Si2O7 is a "quasi-plastic" ceramic and the intrinsically weak interfaces contribute to its machinability. Crystal structure characteristics and DFT calculations of γ-Y2Si2O7 suggest that some weakly bonded planes, which involve Y-O bonds that can be easily broken, are the sources of the low shear deformation resistance and good machinability.

Processing and fiber content effects on the machinability of compression moulded random direction short GFRP composites

The random direction short Glass Fiber Reinforced Plastics (GFRP) have been prepared by two compression moulding processes, namely the Preform and Sheet Moulding Compound (SMC) processes. Cutting force analysis and surface characterization are conducted on the random direction short GFRPs with varying fiber contents (25 similar to 40%). Edge trimming experiments are preformed using carbide inserts with varing the depth of cut and cutting speed. Machining characteristics of the Preform and SMC processed random direction short GFRPs are evaluated in terms of cutting forces, surface quality, and tool wear. It is found that composite primary processing and fiber contents are major contributing factors influencing the cutting force magnitudes and surface textures. The SMC composites show better surface finish over the Preform composites due to less delamination and fiber pullouts. Moreover, matrix damage and fiber protrusions at the machined edge are reduced by increasing fiber content in the random direction short GFRP composites.

Machinability assessment and surface integrity characteristics of Austempered Ductile Iron (ADI) using ultra-hard cutting tools

The application of austempered ductile iron (ADI) is gaining an ever greater share of the worldwide ferrous product market, specifically centering on the aerospace, automotive and shipping industries. ADI is a heat treated cast iron, which exhibits remarkable mechanical properties and provides an attractive material for designers and engineers to displace conventional materials. Previous attempts, however, to machine ADI using carbide or ceramic cutting tools produced poor tool life characteristics due to the relatively poor machinability of the workpiece. This paper presents a research study that has applied the advanced technology of modern ultrahard cutting tools, in an attempt to achieve enhanced machinability performance. This performance was evaluated through the analysis of cutting forces, tool wear, surface finish and roundness.

Evaluating cutting fluid machinability performance

Changes in the metal-working industry, as a result of new environmental legislation or health and safety initiatives, creates the need for constant re-formulation of soluble cutting fluids. In order for there to be confidence in the product's ability to perform its required function successfully, there must be some clearly defined test methods for assessing machinability. Such a test methodology must provide comprehensive data on the fluid's lubrication and cooling properties, which are likely to occur in application. This paper describes the functions of soluble cutting fluids and discusses ways in which performance has been previously determined. Furthermore, it presents a new method for assessing machinability which is proposed as the basis for the development of a new and universal test protocol.

A case study on effect of feed rate on machinability of austempered ductile iron

Austempered Ductile Iron (ADI) is a type of nodular, ductile cast iron subjected to heat treatments - austenitising and austempering. Whilst machining is conducted prior to heat treatment and offers no significant difficulty, machining post heat treatment is demanding and often avoided. Phase transformation of retained austenite to martensite leading to poor machinability characteristics is a common problem experienced during machining. This case study explains the effect of feed rate on machinability of ADI using cutting force analysis and tool failure analysis. The experimental design consists of conducting drilling trials on grade 1200 and 1400 at constant depth of cut, 25mm; constant speed, 45m/min; no coolant and variable feed rates from 0.2 to 0.35 mm/rev (increment of 0.025mm/rev). Metallography and X-ray diffraction technique was carried out in order to identify and quantify the microstructural phases before and after drilling. The results from the trial infer that the best way to machine ADI efficiently without tool failure is using low feeds and high speeds and without coolant.

Machinability and phase transformation study of nanobainite steels

There is an increasing demand for high strength materials with the development of technology and critical applications. Nano materials are newly developed materials with extremely high strength for this purpose. Nanobainite is a dual phase material containing alternate layers of bainitic ferrite in nano dimensions and retained austenite. Nanobainite is produced by isothermally holding austenitized steel at a temperature of 200°C or less, depending on the chemical composition, for 6 10 days until bainite forms and then cooling to room temperature using austempering. The experimental design consisted of face milling under 12 combinations of Depth of Cut (DOC)-1, 2 and 3mm; cutting speed-100 and 150m/min; constant feed-0.15mm/rev and coolant on/off. The machinability of the material is assessed by means of analysis, such as surface texture and microhardness. The assessment also involves microstructural comparisons before and after milling. Future work involves quantifying the microstructural phase before and after milling using XRD. The results obtained are used to assess the most favorable condition to cut this new variety of steel.

Machinability assessment of Ti-6Al-4V for aerospace applications

Titanium alloy Ti-6Al-4V is the most commonly used titanium alloy in the aerospace and biomedical industries due to its superior material properties. An experimental investigation has been carried out to evaluate the machinability of high performance aerospace alloys (Ti-6Al-4V) to determine their in service performance characteristics based on different machining strategies. Nearly 80-90% of the titanium used in airframes is Ti-6Al-4V. The experimental design consist of face milling Ti-6Al-4V at 12 different combinations of cutting parameters consisting of Depth Of Cut (DoC)- 1, 2 and 3 mm; speeds- 60 and 100 m/min; coolant on/off and at constant feed rate of 0.04mm/tooth. Post machining analysis consists of cutting force measurement, surface texture analysis and metallographic analysis. The future work consists of in-depth investigation into the phase transformational reactions during machining.

A preliminary study on machinability assessment of nanobainite steel

The demand for high strength materials and improvements in heat treatment techniques has given rise to this new form of high strength steel known as nanobainite steel. The production of nanobainite steel involves slow isothermal holding of austenitic steel around 200oC for 10 days, in order to obtain a carbon enriched austenite and cooling to room temperature using austempering. The microstructure of nanobainite steel is dual phase consisting of alternate layers of bainitic ferrite and austenite. The experimental design consists of face milling under 12 combination of Depth of Cut (DoC)-1, 2 and 3mm; cutting speed-100 and 150m/min; constant feed- 0.15mm/rev and coolant on/off. The machinability of the material is assessed by means of analysis such as metallography and cutting force analysis. The results obtained are used to assess the most favorable condition to machine this new variety of steel. Future work involves study on phase transformation by quantifying the microstructural phase before and after milling using XRD.

A preliminary assessment of machinability of titanium alloy Ti 6Al 4V during thin wall machining using trochoidal milling

Titanium alloys are of great demand in the aerospace and biomedical industries. Most the titanium products are either cast or sintered to required shape and finish machined to get the appropriate surface texture to meet the design requirements. Ti-6Al-4V is often referred as work horse among the titanium alloys due to its heavy use in the aerospace industry. This paper is an attempt to investigate and improve the machining performance of Ti-6Al-4V. Thin wall machining is an advance machining technique especially used in machining turbine blades which can be done both in a conventional way and using a special technique known as trochoidal milling. The experimental design consists of conducting trials using combination of cutting parameters such as cutting speed (vc), 90 and 120 m/min; feed/tooth (fz) of 0.25 and 0.35 mm/min; step over (ae) 0.3 and 0.2; at constant depth of cut (ap) 20mm and using coolant. A preliminary assessment of machinability of Ti-6Al-4V during thin wall machining using trochoidal milling is done. A correlation established using cutting force, surface texture and dimensional accuracy.