Lars Pejryd

Machining aerospace materials with room-temperature and cooled minimal-quantity cutting fluids

The impact on the cutting forces and tool wear in the turning of the four most common aero-engine alloys (Inconel 718, Waspaloy, martensitic stainless steel, and titanium alloys) with minimal-quantity cooling lubrication fluids both at room temperature and when cooled have been investigated for different cutting conditions. Parameters such as the fluid-type and cutting insert materials used were varied, as were the cutting parameters. Methods of statistical experimental design were used in order to extract, in the smallest number of experimental runs, the maximum amount of information from the collected data in the presence of noise. In this work, no evidence is found that lubrication plays a significant role during the turning of high-temperature alloys. When using room-temperature liquids, the cutting forces show in most cases either no significant changes or an increase. For the cooled cases, both significantly increasing forces and significantly decreasing forces can be observed. The most favourable industrial result is the reduction in the tool wear that can be seen for the machining of titanium alloys.

Energy and Cost Efficiency in CNC Machining from a Process Planning Perspective

The role of process planning as an enabler for cost efficient and environmentally benign CNC machining is investigated in the paper. Specific energy is used as the principal indicator of energy eff ...

Investigation of Minimal Quantity Lubrication in Turning of Waspalloy

In order to achieve a more productive and environmentally friendly manufacturing of aerospace propulsion components, minimal quantity lubrication (MQL) can potentially replace the traditionally used flood cooling in different machining operations. These components are manufactured of difficult to machine alloys, which show great hardness even at elevated temperatures. Waspaloy is one of the more demanding super alloys to machine and serve as reference material in this investigation. In this paper, a turning operation is used to investigate the influence of MQL parameters such as oil type together with cutting data on cutting forces and tool wear. As a reference flood and air cooling was used. Two different type of oils were investigated, ester vs. fatty alcohol. The aerosol was directed towards the tool by two different nozzles. Responses that were measured include particle size, aerosol generation capability, cutting forces and tool wear. The experiments were conducted as a D-optimal design of experiments and evaluated by a regression analysis. No evidence of any lubrication effect can be seen. The most plausible explanation of the effects seen is the effects of cooling and heat transfer.

The modeling of coating thickness, heat transfer, and fluid flow and its correlation with the thermal barrier coating microstructure for a plasma sprayed gas turbine application

The plasma sprya deposition of a zirconia thermal barrier coating (TBC) on a gas turbine component was examined using analytical and experimental techniques. The coating thickness was simulated by the use of commercial off-line software. The impinging jet was modeled by means of a finite difference elliptic code using a simplified turbulence model. Powder particle velocity, temperature history, and trajectory were calculated using a stochastic discrete particle model. The heat transfer and fluid flow model were then used to calculate transient coating and substrate temperatures using the finite element method. The predicted thickness, temperature, and velocity of the particles and the coating temperatures were compared with these measurements, and good correlations were obtained. The coating microstructure was evaluated by optical and scanning microscopy techniques. Special attention was paid to the crack structures within the top coating. Finally, the correlation between the modeled parameters and the deposit microstructure was studied.

Cutter Exit Effects during Milling of Thin-Walled Inconel 718

During milling of thin-walled components, chatter vibrations give rise to process issues. These include dimensional inaccuracy, damaged and scrap parts, and damaged cutting tools. This, in turn, leads to loss of production time with increasing cost as a consequence. This paper identifies the force profile during a single cut milling process. It focuses on the exit and post-exit behavior of the cut and discusses the process dynamics. The force profiles of various tool-to-workpiece positions are analyzed as regards the exit and post exit phases. A standard on-the-market cutter and a specially designed zero rake cutter are used in the investigation. Finally, a time-domain simulation of the force is performed and compared to the experimental results. The study concludes that a small change in exit angle may result in a considerable improvement in cutting behavior. In addition, the tool position should be chosen so that the cutter exits in the least flexible direction possible for the workpiece.

A dual-energy approach for improvement of the measurement consistency in computed tomography

Computed tomography is increasingly adopted by industries for metrological and material evaluation. The technology enables new measurement possibilities, while also challenging old measurement meth ...

A survey of metal working companies' readiness for process planning performance measurements

The paper presents an investigation regarding the potential and the readiness for implementing performance indicators and performance measurement systems of the process planning work for metal working companies. The paper is based on a questionnaire survey distributed to process planners in the Swedish metal working industry. The main outcome of the investigation is a foundation for understanding the implementation of performance measures of the process planning work for CNC machining. The survey revealed a few strengths and short comings in the studied companies.

Isothermal Oxidation Behavior of EBM-Additive Manufactured Alloy 718

Oxidation of Alloy 718 manufactured by electron beam melting (EBM) process has been undertaken in ambient air at 650, 700, and 800 °C for up to 168 h. At 800 °C, a continuous external chromia oxide enriched in (Cr, Ti, Mn, Ni) and an internal oxide that was branched structure of alumina formed, whereas at 650 and 700 °C, a continuous, thin and protective chromia layer was detected. The oxidation kinetics of the exposed EBM Alloy 718 followed the parabolic rate law with an effective activation energy of ~248 ± 22 kJ/mol in good agreement with values in the literature for conventionally processed chromia-forming Ni-based superalloys. The oxide scale formed on the surface perpendicular to the build direction was slightly thicker, and more adherent compared to the scale formed on the surface along the build direction, attributed to the varied grain texture in the two directions of the EBM-manufactured specimens. The increased oxygen diffusion and high Cr depletion found on the surface along the build direction were attributed to the fine grains and formation of vacancies/voids along this grain orientation.

The Use of Machine Tool Internal Encoders as Sensors in a Process Monitoring System

Tool wear in machining changes the geometry of the cutting edges, which affects the direction and amplitudes of the cutting force components and the dynamics in the machining process. These changes ...

Process stability strategies in milling of thin-walled Inconel 718

Trends in Aerospace development have led to thin-walled, reduced-weight engine designs. The demands in manufacturing have forced production speeds and material removal rates (MRR) to increase. As component wall thickness gets thinner, the consequence oftentimes is an increase in chatter vibrations. This paper suggests that a correctly chosen tool-to-workpiece offset geometry may lead to a robust and chatter free process. The results show the differences in force response for three geometries while varying the height overhang of the workpiece. This is part of a concerted effort to develop a robust methodology for the prediction of chatter vibrations during milling operations of thin-walled Aerospace components. This paper gives guidelines on how to accomplish robust machining practices. It also answers the following questions: How critical is the choice of offset between tool and workpiece during milling setup? And what effects do the entry and exit of cut have on system vibrations?