Cold spraying of automotive engine blocks requires a gun adaptation for inner diameter spraying with a very short nozzle. In this work, 316L coatings are sprayed with such a gun and the behavior of particles impacting aluminum and stainless steel surfaces is studied in order to understand the factors that affect coating adhesion and cohesion. Correlations between spraying parameters and coating properties were investigated via design of experiments and the effect of process parameters on deposition efficiency and coating thickness was optimized for mass production. Post-process honing was also employed as part of the study and smooth coatings with small pores were obtained.

In times of duality of combustion engine and electric motor propulsion the automotive industry is developing both powertrain systems. Weight reduction and enhancement of efficiency plays a vital role in the conception of combustion engine for passenger cars. The thermal spray technology therefore is trend-setting as it achieves both aims. GROB-WERKE have, as reported previously, developed and integrated their GTS (GROB Thermal Spray) process for steel deposits in aluminum cylinder bores into their production lines. Further effort was now made to improve performance and versatility. The application of measurement and simulation technics hand in hand with extensive experimental investigation in spray deposit diagnostics as well as plasma and particle jet analysis led to highly developed and advanced deposit microstructure and cylinder bore topographies. Complex and extensive CFD (Computational Fluid Dynamics) simulation of the gas and particle flow gave the thermal spray process the highest performance, efficiency and product cleanliness.

Several surface preparation techniques are being used like grit blasting, HP water jet roughening as well as mechanical roughening for the preparation of Aluminum cylinder bore surfaces before a thermal spraying can be applied. However, in case of spray-repaired CI cast iron engine blocks the conventional mechanical roughening processes - using cutting inserts with small dovetail-undercut geometry - are not applicable due to the high hardness and high material toughness. Therefore such CI engine blocks are bored oversize in order to remove the bore wear damage and subsequently this rough-machined surface is coated by a NiAl-bond coating material in order to provide sufficient bond strength for the functional top coating material. In this paper it will be demonstrated that the 2-step spray-repair process can be replaced by a single-step process by using a new diamond-roll-roughening method. This process leads to significant higher bond strength values than the conventional process, including the bond coating material. PAT Adhesion test results as well as microstructural cross sections of coated cylinder bores will be presented. The principle of the roll-roughening process is outlined. In addition it will be shown that different mechanical roughening methods can be combined to obtain high bond strength values for spray-repaired aluminum blocks which require a higher coating thickness to compensate for the depth of the original mechanical bore activation.

This paper discusses some of the challenges encountered and overcome in the development of a thermal spray production cell and its integration into a production line for aluminum engine blocks. Examples of thermal spray coatings applied to cylinder bore surfaces are presented and discussed.

A390 alloy is a hypereutectic aluminum alloy with attractive mechanical properties at high temperature, good wear resistance and appropriate thermal properties making it challenging candidate material for automotive and aerospace applications. Currently, this alloy is widely used in automotive industry engine components production. In case of engine blocks, fatigue strength and wear resistance are the main cause of failure. Generally, the surface properties of aluminum alloys, in particular as hardness and wear resistance concerns, are insufficient to fulfill some requirements. Nowadays, there is an increasing interest toward the study and the development of innovative protective coatings suitable to enhance the wear resistance of such alloys. The goal of this paper is to develop appropriate protective coatings for A390 aluminum alloy enhancing its wear resistance. The study has been carried out to characterize the morphological, mechanical and wear resistance properties.

This paper presents an overview of the engineering and innovation behind BMW’s use of thermal spraying in the production of automotive engines at its light metal foundry in Landshut, Germany. It discusses the factors that drive engine development at BMW, the different approaches in play for improving the performance of cast aluminum crankcases, and the opportunities made possible by thermal spray technology. It describes the aluminum crankcase production process, from die casting to honing, with emphasis on BMW’s state-of-the-art implementation of twin wire arc spraying. It explains how the spraying process is controlled and how key process steps and parameters are monitored and optimized in real time along with coating properties and microstructures. If a coating defect is detected, it is documented on the fly and, in many cases, corrected in a subsequent process step. A few examples of defect detection at work are presented.

In this investigation, high carbon steel wire is deposited on aluminum cylinder bores with different surface profiles by plasma transferred wire arc (PTWA) spraying. The first part of the study deals with feedstock materials, process parameters, droplet formation, and splat morphology. The second part deals with bead profiles, build rates, and the influence of substrate composition, temperature, and surface profile on coating characteristics including microstructure, morphology, composition, and bond strength.

This paper describes the development and implementation of a twin wire arc spraying process used to apply iron-carbon alloy coatings to cylinder bores in aluminum engines made for high-performance luxury vehicles. It presents and analyzes measurement data that quantify the uniformity of the coatings and the speed at which they are applied. It also discusses key technological achievements and their impact on the coating process.

This study evaluates the effect of laser texturing on the bonding strength of cylinder bore coatings deposited by plasma transferred wire arc (PTWA) spraying. Experiments were carried out on an AlSi 9 Cu 3 engine block sectioned along a plane through the length of the bores. Cylinder surfaces were laser textured on one side and degreased and grit blasted on the other. Laser power, beam angle, and pulse count were varied to determine their effect on hole morphology and coating adhesion. After surface treatment, the engine block sections were rejoined and the cylinder bores were PTWA sprayed with high carbon steel. Coating samples were examined by SEM and cross-sectional analysis and adhesion tests were conducted. The bonding strength of the coatings on the laser textured portion of the cylinder bore was significantly higher than that of the coatings on grit-blasted surfaces and is shown to vary with laser power, beam angle, and total pulses or impacts per hole.

To meet new regulations and specifications for internal combustion engines, new approaches to significantly decrease fuel consumption and emissions are needed. The deployment of tribologically functional coatings applied by supersonic flame spraying represent a promising technology for achieving these targets. Thermally sprayed coatings can help in improving efficiency of internal combustion engines by reducing the internal friction and improving the durability and wear resistance of the engine’s cylinder wall thereby facilitating extreme engine downsizing concepts. Thermal spraying is also capable of processing highly corrosion resistant materials like alloys and ceramics to enable the safe utilization of biofuels in modern combustion engines. In addition, specific surface structure of thermal spray coatings, including their intrinsic porosity, shows the benefit of reducing the friction by sustaining hydrodynamic friction even in spots with low relative movement, e.g. top and bottom dead center. On top, the open surface porosity can reduce the oil consumption and thereby decrease the polluting emissions of internal combustion engines. The thermally sprayed coatings were applied using HVOF and HVSFS processes deploying various materials, including novel nanostructured powders. The coated cylinders and engines have been compared to state-of-the-art components with respect to friction coefficient, wear and oil consumption.

In an effort to inhibit a climate change, the European Union has decided to reduce the CO 2 emissions by approx. 30% by year 2020, as compared to the level of emissions in year 1990’s. In general, traffic is responsible for 20% of all CO 2 emissions and 84% of those emissions result specifically from road traffic. In accordance with the present targets of the CO 2 emission reduction the automotive industry has to meet strict regulations. The strict emission goals can only be reached by weight reduction of the vehicle and by an improved efficiency of engine and drive train. Close to 50% of the friction losses in a combustion engine result from the interaction between the piston ring and the cylinder bore surface. Therefore the cylinder bores as well as the piston rings were coated with new, low-friction materials. The friction behaviour was characterized in linear reciprocating tribometer-test in order to identify the best combination of bore and ring coatings.

The application of thermal coatings in cylinder bores is depending on above all functionality, process reliability and economy of pre treatment of the substrate surfaces. Different removing processes like water jetting or sand blasting are increasingly substituted by mechanical machining. Thereby great importance is attached to functionality and degree of automation. For an assured engine function, high bond strength is required. The roughening process as a modified cutting machining meets the requirements of modern production lines. Removing overspray after thermal coating by a water jetting process, is a further contribution for a higher automation degree. The final machining of sprayed surfaces is effected by a multi stage honing process. The composite structures of thermal coated layers call for high performance diamond abrasives. The finished functional cylinder surface comprehends cavities of thermal coated layer and smooth honing pattern. The technological description of roughening and honing, the process components as well as the machining results will be presented. Pre and post treatment are essential processes, which enable the application of high performance thermal coating materials in friction optimized combustion engines.

This study compares the tribological performance of HVOF and HVSFS coatings applied to gray cast iron and aluminum cylinder liners. Five different materials, including Fe alloy, FeCrMo, CrC-NiCr, NiCrBSi, and WC-Co, were sprayed using a conventional HVOF torch operated by a six-axis robot while the liners were manipulated by means of a rotary table. A similar setup was used to spray TiO 2 -TiC coatings, but the gun was modified for nano-sized particles in a suspension fed axially into the combustion chamber. Coating microstructures were examined using optical and SEM imaging and friction and wear properties were determined through oscillating friction wear tests. The results obtained are compared to state-of-the-art cylinder liners.

Hypoeutectic AlSi engine blocks of modern passenger cars are generally equipped with cast iron liners in order to provide cylinder running surfaces that meet the tribological requirements. A very promising alternative to the use of cylinder liners lies within the application of thermally sprayed coatings onto the walls of cylinder bores as friction partners for the piston rings. This work describes the development of a novel iron based wire feedstock as well as its application by the Plasma Transferred Wire Arc internal diameter coating system. The material developed within the frame of this work leads to partially amorphous coatings with embedded nanoscale precipitations if processed by thermal spraying. The coatings were applied onto the inner diameters of test liners made of Aluminium EN AW 6060 and onto cylinder bore walls of in-line 4 cylinder engines. All substrates were mechanically roughened in order to obtain high bond strengths of the sprayed coatings. The coatings microstructure was analysed by light optical microscopy, hardness measuring by transmission electron microscopy. Furthermore the oil storage capacities of the honed surfaces were determined.

Crank cases of modern car-engines are made in general of light metal alloys, mostly aluminium alloys. Due to the low hardness of these materials, the use of cylinder liners, in general made of grey cast iron is required. The use of cylinder liners also leads to several disadvantages, such as the increase of the engines weight. The aim of this work in the long term is to replace these cylinder liners with a thermally sprayed nano-structured composite coating, characterised by high hardness. Therefore in this study a coating process employing a plasma transferred wire arc unit and a cored wire are used.

Since about the year 2000, cast aluminum automobile engine blocks have been coated in production lines using internal plasma spraying technology. Using this approach, the coefficient of friction between the cylinder wall and the piston assembly can be reduced to 30% and oil consumption is reduced of a factor two in comparison with cast iron. The extremely low wear rate of the friction elements increases engine life and reduces maintenance costs. The fuel consumption of the cars can be reduced from 2 to 4% in the case of gasoline and diesel engines. The coating costs are strongly dependent on production volume. For high volume production, the costs can be similar to those for cast iron liners. This paper reviews results from laboratory and field tests evaluating the performance and cost efficiency of plasma sprayed engine block liners.

Different thermal spray processes are being used to provide coatings for cylinder bores in automotive engines. The internal plasma spraying technology described in this paper applies protective layers to cylinder surfaces in engine blocks made of AlSi cast alloys. This method enables a significant reduction in the coefficient of friction, a reduction in oil consumption, and an increase in wear resistance compared to cast iron, the standard material for cylinder liners. Paper includes a German-language abstract.

This paper describes a coating process, called internal centrifugal projection coating, in which rotating additive materials and substrate surfaces are melted by an electron beam to facilitate adhesion. It explains that the process was developed mainly to apply coatings inside engine bores and examines the microstructure of a molybdenum coating centrifugally projected onto an aluminum substrate. Paper includes a German-language abstract.

This paper evaluates a wide range of thermal spray coatings for potential use lining cylinder bores in aluminum engines. Coatings were applied by atmospheric plasma spraying (APS) and high-velocity oxyfuel (HVOF) techniques. More than a dozen coating materials were screened, including ceramics, cermets, and metals. The paper describes the equipment and procedures used in the investigation and assesses the resulting coatings based on their microstructure, hardness, friction coefficient, wear resistance, bonding strength, and residual stress.

In the Automotive Industry the need for lower manufacturing costs, the use of less strategic material, and easier, faster, and more flexible routes for manufacturing are being looked for continuously. The environmental concerns relating to the use of galvanic coatings is growing. This has led to the examination of the plasma-powder spray process for the application of coatings for surface modification. In the area of engine cylinder bore coatings a major advance is taking place in the use of a rotating plasma spray device. This paper covers the use of a plasma-powder spray process for the coating of aluminum-silicon cylinder block bores using a rotating plasma gun capable of producing coatings of reliable microstructure and integrity. Properties and microstructures of the applied coatings will be presented. Test results will be shown that the necessary bond strength of the coating can be achieved without the use of a bond coat. Surface preparation prior to coating and surface finishing methods after coating will also be discussed. Experience in Europe, Japan and the Unites States will be discussed which show that the plasma-powder spray process offers a performance proven and cost effective solution for the coating of cylinder bores, thus demonstrating the future application potential for this technology.