Machining Of Compacted Graphite Iron Research Articles

Tool wear when tapping operation of compacted graphite iron

The automotive industry has made increasing use of compacted graphite iron in the manufacture of several components traditionally made of gray iron. However, in some cases, the poor machinability of compacted graphite iron compared to that of gray iron renders production costs uncompetitive. Several researches have focused on the machinability of compacted graphite iron, particularly in turning, milling and drilling operations. However, tapping, which is a more complex operation, has received little attention. The main objective of this work is to investigate the performance of cemented carbide taps when tapping ASTM A450 compacted graphite iron using TiAlN-coated M13 × 1.5 taps with four straight flutes. Cutting tools with different wear levels were analyzed after their use in machining engine cylinder blocks. Tool wear was measured and analyzed using scanning electron microscopy and optical microscopy. The main wear mechanisms observed were adhesion and abrasion.

Modulation-assisted high speed machining of compacted graphite iron (CGI)

The application of controlled, low-frequency modulation (∼100Hz) superimposed onto the cutting process in the feed-direction – modulation-assisted machining (MAM) – is shown to be quite effective in reducing the wear of cubic boron nitride (CBN) tools when machining compacted graphite iron (CGI) at high machining speeds (>500m/min). The tool life is at least 20 times greater than in conventional machining. This significant reduction in wear is a consequence of the multiple effects realized by MAM, including periodic disruption of the tool–workpiece contact, formation of discrete chips, enhanced fluid action and lower cutting temperatures. The propensity for thermochemical wear of CBN, the principal wear mode at high speeds in CGI machining, is thus reduced. The tool wear in MAM is also found to be smaller at the higher cutting speeds (730m/min) tested. The feed-direction MAM appears feasible for implementation in industrial machining applications involving high speeds.

Wear Model in Milling Compacted Graphite Iron with Different Lead Angle Using Ceramic Cutting Tools

The objective of this study is to reveal the influence of the lead angle variation on tool wear in the process of face milling of compacted graphite iron with ceramic cutting tools. To achieve this goal, 36 milling experiments were carried out with different lead angles, cutting speeds and feed rates at the 2.5 mm constant depth of cut. The tool flank wear was strongly affected by the lead angle variations. SEM analyses of the cutting inserts were performed and experimental results have been modelled with artificial neural networks (ANN) and regression analysis. A comparison of ANN model with regression model is also carried out. The R2 values for testing data were calculated as 0.992 for ANN and 0.998 for regression respectively. This study is considered to be helpful in predicting the wear mechanism of the ceramic cutting tool in the machining of compacted graphite iron. A quicker method for the estimation of tool life is proposed, which requires less consumption of workpiece material and tools.

Machinability of compacted graphite iron (CGI) and flake graphite iron (FGI) with coated carbide

Compacted graphite iron (CGI) has an important role in manufacturing of new generation engines. Better strength of CGI, as compared to flake graphite iron (FGI), allows CGI engine to perform at higher peak pressure, higher fuel efficiency and lower emission rate. However, the machinability of CGI is as poor as compared to FGI. The machinability of CGI is an area that needs to be studied in a better way to cut the production cost of the engine. It is a well known fact that the as-cast engine block has varying microstructure and mechanical properties due to different cooling rates at different locations of such a geometrically complex component. This has highlighted the need for studying machinability as a function of microstructural and mechanical properties so that the machining process could be optimised. For this reason, machinability of 18 different types of CGI materials along with two FGI materials has been studied, in terms of cutting force and tool life, in a turning operation in this work.

An Experimental Investigation of the Influence of Cutting-Edge Geometry on the Machinability of Compacted Graphite Iron

Compacted graphite iron (CGI) is considered as the potential replacement of flake graphite iron (FGI) for the manufacturing of new generation high power diesel engines. Use of CGI, that have higher strength and stiffness as compared to FGI, allows engine to perform at higher peak pressure with higher fuel efficiency and lower emission rate. However, not only for its potential, CGI is of an area of interest in metal cutting research because of its poor machinability as compared to that of FGI. The higher strength of CGI causes a faster tool wear rate in continuous machining operation even in low cutting speed as compared to that for FGI. This study investigated the influence of cutting edge geometry at different cutting parameters on the machinability of CGI in terms of tool life, cutting force and surface roughness and integrity in internal turning operation under wet condition. It has been seen that the cutting edge radius has significant effect on tool life and cutting forces. The results can be used to select optimum cutting tool geometry for continuous machining of CGI.

Enhancing Tool Life in High-Speed Machining of Compacted Graphite Iron (CGI) Using Controlled Modulation

The application of controlled, low-frequency modulation superimposed onto the cutting process—modulation-assisted machining (MAM)—is shown to be quite effective in reducing the wear of cubic boron nitride (CBN) tools when machining compacted graphite iron (CGI) at high machining speeds (>500 m/min). The tool life is at least one order of magnitude greater than that in conventional machining. The improvement in wear performance is a consequence of a reduction in the severity of the tool–work contact conditions in MAM: reduction in intimacy of the contact, formation of discrete chips, enhanced fluid action, and lower cutting temperatures. The propensity for thermochemical wear of CBN, the principal wear mode at high speeds in CGI machining, is thus reduced. The MAM configuration employing feed-direction modulation appears feasible for implementation at high speeds and offers a potential solution to this challenging class of industrial machining applications.

Modeling the effect of compacted graphite iron microstructure on cutting forces and tool wear

The characteristic mechanical (and physical) properties of compacted graphite iron (CGI) are contingent upon its unique microstructure. To model and simulate compacted graphite iron (CGI) in machining meaningfully, the metal's microstructure should not be overlooked throughout the process.In this work, modeling the microstructure of CGI in machining is implemented using a commercial general-purpose finite element package; ABAQUS/EXPLICIT (v 6.8). Segmental chip is modeled by the introduction of a new chip formation modeling technique. The cohesive zone elements are used to model the graphite–matrix interface. The methodology pursued to implement the finite element model is based upon an iterative interaction between comprehensive metallurgical investigations and finite element formulation of the problem in hand. Metallurgical examination of fractured and machined chips is not solely performed as a tool of validation, but rather as a tool of modeling.Vital model inputs are based upon metallurgical investigations of fractured CGI samples and machined chips. Subsequent comparisons between (1) simulated chips and (2) cutting forces trends, to experimental findings are used to validate the finite element model. The effects of cutting forces and temperature are comprehensively investigated to elaborate on their effects on tool wear. The effect of cutting speed (and feed rate) on cutting forces and cutting temperature determine the type of tool wear in CGI machining. Variation of the cutting speed triggers the deviation from mechanical to thermal tool wear mechanisms. This behavior is captured through the investigation of the cutting forces and simulated temperature trends in the finite element model. Other important findings are documented to serve as an optimization technique for tool material selection and machining conditions of compacted graphite iron (CGI) for which automotive and locomotive industries are of significant need to date.

Effect of tool geometry on the wear of cemented carbide coated with TiAlN during drilling of compacted graphite iron

Abstract The improvement of machinability of compacted graphite iron (CGI) is a constant goal of automotive industry. The application of compacted graphite iron (CGI) in parts such as cylinder block to replace the traditional cast irons presents as advantages the higher mechanical strength and the resistance to thermal shock at the CGI. However, these characteristics represent much more problems in the manufacturing process due to the CGI poorer machinability. Metallurgical variables controlled from casting parameters have been studied, but the manufacturing aspects such as tool geometry are few explored yet. Among the machining operations drilling is the most common one in the automotive industry. This study investigated the effect of three tool geometries on the wear of cemented carbide coated with TiAlN during drilling of CGI, with eutectic composition (4.3% of equivalent carbon). The influence of the chisel edge of drills was studied. The wear of drills was monitored at five steps: set-up, 25%, 50%, 75% and at the end of the tool life monitored through the VB bmax flank tool wear on the tools cutting edge. Images from scanning electron microscope showed abrasion as a predominant wear mechanism. The results showed the importance of the drill geometry selection in order to achieve better productivity. The geometry with tip radius obtained the best results, double the life of the tool to grind into spiral point drill which is used as reference due to its application in the production of engine blocks. It was also observed that the tool geometry influences the surface roughness of holes, and these results can be related to shape of chips.

Modeling the effect of the microstructure of compacted graphite iron on chip formation

The unique mechanical and physical properties of compacted graphite iron (CGI) have awarded the material such desirable and increasing demands in both automotive and locomotive industries. The graphite round edges combined with irregular graphite boundaries highly enhance crack arrest resistance within the matrix and participate into the good adhesion of graphite–matrix interface, compared to gray cast iron. However, the praised mechanical performance of compacted graphite iron (CGI) compared to gray iron, and its superior thermal properties compared to nodular iron (ductile iron) have come with CGI's relative poor machinability. Finite element simulation of the microstructure of CGI will provide better understanding of the behavior of the metal during machining and will establish a good foundation of CGI machining optimization. Modeling of the microstructure of CGI chip considering the three main constituents of the metal; graphite, pearlite, and ferrite, was possible using the accumulated plastic strain fracture criterion. Although there is no distinctive boundary line between adiabatic shearing and surface crack initiation chip formation principles in real metal cutting, chip formation simulation showed that it was predominantly due to crack initiation and propagation. Cracks initiated at either the graphite particles or the graphite–matrix interface promoted by the fracture of surface graphite particles then progressed through the matrix. The characteristic segmental chip produced in CGI machining was mainly driven by the presence of graphite embedded in the matrix. Chip segments formation initiated at the graphite particles (or graphite–matrix interface) then progressed towards the chip-tool tip. Modeling of the graphite/matrix interface was based on the utilization of cohesive zone elements. Comparison between the modeled CGI microstructure and graphite-free modified microstructure highlights the significant role of graphite on chip characteristics. Comparison between the simulated segmental chip and real CGI chip validated the proposed simulation and proposes it as a valid foundation for further CGI machining optimization.

Investigation of tool wear mechanisms in CGI machining

In this study, the tool wear, including wear mechanisms on coated cemented carbide inserts were investigated in the turning of Compacted Graphite Iron (CGI) materials with varying nodularity. The results showed that increasing nodularity, in the range of 5-62%, affects wear at moderate and high cutting speeds without having the same impact at lower cutting speeds. A small difference in nodularity, in the lower range, such as an increase from 5% to 20%, has a more significant impact on wear than an increase from 20% to 62%.

The Effect of Interlamellar Distance in Pearlite on CGI Machining

Swedish truck industry is investigating the possibilityfor implementing the use of Compacted Graphite Iron (CGI) in theirheavy duty diesel engines. Compared to the alloyed gray iron usedtoday, CGI ...

Effects of tool material, tool topography and minimal quantity lubrication (MQL) on machining performance of compacted graphite iron (CGI)

This paper addresses the tribological challenges involved in the machining of compacted graphite iron (CGI) through an investigation of the effects of tool material, local tool surface topography and minimal quantity lubrication (MQL) on machining performance. Turning experiments were undertaken using four different tools (flat coated carbide, grooved coated carbide, grooved coated cermet and chamfered ceramic) under dry and MQL conditions. The tests were conducted at two different cutting speed conditions with a constant feed and depth of cut. Results reveal that at low speed, the cermet tool provides a significant reduction in cutting forces in comparison to coated carbide. Cutting forces show an increase with the usage of MQL at high speed, suggesting a negative influence of the cutting fluid on CGI machining performance. Scanning electron microscopy/energy dispersive X-ray analysis of the tested tools reveal the absence of MnS layer on tools used for CGI machining, thereby reconfirming the findings by other researchers.

Analytical investigations concerning the wear behaviour of cutting tools used for the machining of compacted graphite iron and grey cast iron

Compacted graphite iron (CGI) is the material for the upcoming new generation of high-power diesel engines. Due to its increased strength compared to grey cast iron (CI) it allows an increase in the cylinder-pressures and therefore a better fuel economy and a higher power output are possible. First examples of such engines are the 3.3 L Audi V8 TDI and the 4.0 L BMW V8. The reason why CGI is not used to a larger extent in large scale production up to now is its much more difficult machinability as compared to conventional CI, especially at high cutting speeds. In modern transfer lines high cutting speeds are used in the cylinder-boring operation. And especially in these continuous cutting operations the tool life decreased due to the change from CI to CGI by about a factor of 20. As was found out previously by us, the difference in tool lifetime can be explained by the formation of a MnS-layer on the tool surface in the case of CI. This layer cannot form when machining CGI because the formation of MnS-inclusions is not possible in this material due to the higher magnesium content which in turn is responsible for the formation of the graphite vermicles. The MnS-layer acts as a lubricant and prevents the adhesion of workpiece particles. This is the reason for the greatly reduced wear of CI in high speed machining operations. This MnS-layer is inspected closer by X-ray diffraction, X-ray induced photoelectron spectrometry, atomic force microscopy and secondary ion mass spectrometry in this work. Furthermore, available information on the performance of MnS as lubricant in PM-steels is comparatively discussed. This knowledge led to an economic solution of high productivity machining of CGI. The key was to reduce the cutting speed, replacing single insert tools with multiple insert tools. This allowed to increase the feed rate. By increasing the feed rate in the same amount as decreasing the cutting speed, the same productivity can be realized. This concept is leading to a number of multiple insert tools thus realizing a high productivity machining of CGI cylinder-bores with multi-layer-coated carbide tools.

Laser-assisted machining of compacted graphite iron

Compacted graphite iron (CGI) is a material currently under study for the new generation of engines, including blocks, cylinder liners, and cylinder heads. Its unique graphite structure yields desirable high strength, but makes it difficult to machine, thus resulting in a machining cost. Laser-assisted machining (LAM) is adopted to improve its machinability and hence machining economics. The machinability of CGI is studied by varying depth of cut, feed, and material removal temperature and then evaluating resultant cutting forces, specific cutting energy, surface roughness, and tool wear. At a material removal temperature of 400 °C and a feed of 0.150 mm/rev at a cutting speed of 1.7 m/s, it is shown that tool life is 60% greater than conventional conditions at a feed of 0.100 mm/rev. Surface roughness is improved 5% as compared to conventional machining at a feed of 0.150 mm/rev. CGI microstructure evaluated post machining by sectioning and polishing shows no change. An economic analysis shows that LAM can offer an approximately 20% cost savings for the machining of an engine cylinder liner.

Study of the machinability of compacted graphite iron for drilling process

CGI - Compacted Graphite Iron - has reached an important status for automotive industry, mainly in the last ten years. The material has been used for manufacturing parts as brake discs, exhaust manifolds, engine heads and diesel engine blocks. The superior strength characteristics of CGI, as compared to gray iron, allows the manufacturing of engines for higher pressure operating combustion chambers, therefore more efficient and with lower emissions levels. Also thinner walls are possible, generating lighter engines. However there are some technical challenges to overcome, mainly related to the machining process of the parts. This research intends to study the machinability of CGI, in order to develop a new alloy with improved characteristics of machinability, so the production costs for CGI automotive parts can be reduced. The study uses a reference material, gray iron FC-250, widely used for engine blocks manufacturing. The machinability of the referred material is compared to five different CGI alloys by means of drilling experiments. The considered machinability criteria are the tool wear and the cutting forces. The experiments led to the development of a CGI-450 with machinability 83% (relative to FC-250), therefore with excellent potential qualities for engine block and other auto parts manufacturing.

Machining of Compacted Graphite Iron (CGI)

The industrial application of compacted graphite iron in the automotive industry is taking a rather long time due to its uneconomic machinability, because of a significant decrease in tool life. After six years of holistic research of the PTW in cooperation with foundries, manufactures and material scientists, the wear mechanism was understood and clarified: Sulphur in the microstructure of cast iron has direct influence on the formation of a manganese-sulphur layer on the cutting edge. For machining gray cast iron this layer protects the cutting edge against abrasive wear. In case of CGI no layer formation occurs. Against the abrasive wear new cutting materials and tools for the machining of CGI must be developed. Spanende Bearbeitung von Gusseisen mit Vermiculargraphit (GJV) Der industrielle Einsatz von Gusseisen mit Vermikulargraphit (GJV) in der Automobilindustrie verzögerte sich aufgrund seiner unwirtschaftlichen spanenden Bearbeitung, welche auf den Abfall des Standwegs zurückzuführen ist. Nach 6 Jahren ganzheitlicher Forschung am PTW in Zusammenarbeit mit Gießereien, Endanwendern und Materialwissenschaftlern, wurde der Verschleißmechanismus identifiziert. Der Schwefelgehalt im Gusseisen hat einen direkten Einfluss auf die Bildung einer Mangansulfid Schicht auf der Schneidkante. Bei der Bearbeitung von lamellarem Gusseisen (GJL) schütz diese Schutzschicht die Schneidkante vor abrasivem Verschleiß. Im Falle der GJV Bearbeitung bildet sich keine Schutzschicht auf der Schneidkante, was die Entwicklung neuer Schneidstoffe und Werkzeuge erfordert.

Investigation of the wear mechanism of cubic boron nitride tools used for the machining of compacted graphite iron and grey cast iron

Various experiments were performed to investigate the wear mechanism of cubic boron nitride (cBN) tools used for the machining of compacted graphite iron (CGI). Comparative studies for tools used to machine grey cast iron (CI) were also performed in order to find out why in this case the tool lifetime is significantly higher. Two main effects were found that are responsible for tool wear, namely: (1) oxidation of the tool, and (2) interdiffusion of constituting elements between tool and CGI. These wear mechanisms are more or less the same for the machining of CGI and grey CI. The difference in tool lifetime can be explained by the formation of a MnS layer on the tool surface in the case of grey CI. This layer is missing in the case of CGI. The MnS layer acts as a lubricant and as a diffusion barrier and is the reason for the reduced wear in the case of grey CI.

SIMS Analysis of the wear of boron nitride tools for the machining of compacted graphite iron and grey cast iron

Cubic boron nitride (cBN) is a common material for tools for the machining of cast irons at high cutting speed. During the machining of compacted graphite iron (CGI) in continuous cutting the wear of the cBN tools was found to be significantly higher compared to the machining of grey cast iron. This is possibly a result of a heating of the tool surface during the cutting of CGI. One possible reason for the wear is diffusion of some elements from the cutting tool into the CGI or from the CGI into the cutting tool. SIMS measurements were carried out which prove the existence of such diffusion processes. A static model experiment has been performed by heating cBN tools to 700 °C while in contact with CGI or cast iron (CI). SIMS depth profiles of the cBN tools and of CGI/CI show that there is a diffusion of several elements in both directions (B, W and Ti from the cBN tools into the CGI or CI, Fe and Si from the CGI or CI samples into the cBN) up to a depth of 20 μm.