The geared turbofan technology is one essential way to reduce the fuel consumption, the environmental footprint and the noise pollution of civil aircrafts. An added gearbox between the fan and the low-pressure compressor that reduces the fan speed, which allows higher bypass ratios, achieves the mentioned benefits of geared turbofans. To withstand the high mechanical loads, large double helical gears are used. Gear hobbing and gear grinding require large tool maneuvering spaces. This leads to a larger required space between the single gears of the double helical gear. As a result, the gears are larger and heavier, which leads to a reduced economy of the aircraft. The tool maneuvering space of five-axis milling with solid carbide end mills is much smaller. This enables the design of smaller, lighter and more efficient aircraft engines. However, manufacturing these gears in tolerances better than IT5 is very challenging on five-axis milling machine tools. This paper presents investigations about finish machining of hardened gears on five-axis machine tools. In the investigations performed, varying tool substrates and tool coatings have been investigated together with tool travel paths in order to reduce the tool wear, which is key to achieve the demanded tolerances. Finally, the five-axis milled gears were compared to conventionally manufactured gears on test benches to enable statements regarding the expectable service lives of the manufactured gears.

The aviation industry has been growing continuously over the past decades. Despite the current Covid-19 crisis, this trend is likely to resume in the near future. On an international level, initiatives like the Green Recovery Plan promoted by the European Union set the basis towards a more environmentally friendly future approach for the aero-industry. The increasing air traffic and the focus on a more sustainable industry as a whole lead to an extensive need for a more balanced assessment of a products life cycle especially on an ecological level. Blisks (or IBRs) remain a central component of every current and very possible every future aero engine configuration. Their advantages during operation compared to conventional compressor rotors are met with a considerably complex manufacturing and production process. In the high-pressure compressor segment of an engine, the material selection is limited to Titanium alloys such as Ti6Al4V and heat-resistant Nickel-alloys such as Inconel718. The corresponding process chains consist of numerous different process steps starting with the initial raw material extraction and ending with the quality assurance (cradle to gate). Especially the central milling process requires a highly qualified process design to ensure a part of sufficient quality. Life-Cycle-Assessments enable an investigation of a products overall environmental impact and ecological footprint throughout its distinct life-cycle. Formal LCAs are generally divided by international standards into four separate steps of analysis: the goal and scope definition, the acquisition of Life Cycle-Inventory, the Life-Cycle-Impact-Assessment and the interpretation. This content of this paper focuses on a general approach for Life-Cycle-Assessment for Blisk manufacturing. • Firstly, the goal and scope is set by presenting three separate process chain scenarios for Blisk manufacturing, which mainly differ in terms of raw material selection and individual process selections for blade manufacturing. • Secondly, the LCI data (Life-Cycle Inventory) acquisition is illustrated by defining all significant in- and outputs of each individual process step. • Thirdly, the approach of a Life-Cycle-Impact-Assessment is presented by introducing the modelling approach in an LCA-software environment. • Fourthly, an outlook and discussion on relevant impact-indicators for a subsequent interpretation of future results are conducted.

The widespread adoption of blade integrated disks (blisks) made of titanium demands tailored re-generation processes to increase sustainability and economic efficiency. High standards regarding geometrical accuracy and functional properties as well as the unique characteristics of each type of damage complicate the repair. Thus, flexible and well-designed processes are necessary. Typically, material deposit is followed by a milling or grinding process to restore the original shape. Here, not only the individual repair processes have to be controlled, but also their interaction. For example, depending on the resulting microstructure of the welded seam, the re-contouring process needs to be adapted to minimize tool wear as well as shape deviations of the complex blade geometries. In this paper, the process chain for a patch repair is examined, consisting of a TIG welding process followed by 5-axis ball nose end milling. Conventional TIG as well as a modified TIG process producing a finer grain structure and enhanced mechanical properties of deposited material were investigated. Grain refinement was achieved by SiC particles added to the weld pool. Based on the characteristics of the fusion material and static stiffness of the component, a methodology is introduced to minimize shape deviation induced by the subsequent milling process. Special attention is given to tool orientation, which has a significant impact on the kinematics and resulting process forces during milling. An electromagnetic guided machine tool is used for compensation of workpiece deflection.

Multiple technology chains are able to manufacture fir tree slots for the mounting of turbine blades including broaching, milling, non-conventional machining strategies and combinations of the named technologies. The advantageousness of the possible technology chains depends on many boundary conditions such as the capacity, the floor space, scheduled delivery, material, shape of the fir tree slots and many more. Within this paper different technology chains are assessed considering productivity and costs under the assumptions of different scenarios. The manufacturing technologies as well as their interdependencies have been investigated within a project providing technological boundary conditions for the assessment like tool lifes and required manufacturing times. The data was combined with organizational and financial data from a manufacturing OEM to enable a proper and holistic assessment. The technologies include broaching with HSS and cemented carbide as well as milling with ceramic and cemented carbide. The scenarios include different assumptions regarding the slot shape and size, the capacity and the demand for discs as well as a comparison of a brown field and green field approach. Based on the results, key parameters are deducted affecting the advantage of the considered technologies. For reasons of confidentiality, the results are obtained in a relative manner.

A transonic centrifugal compressor was aerodynamically optimized by means of a numerical optimization process. The objectives were to increase the isentropic efficiency and to reduce the acoustic signature by decreasing the amplitude of pre shock pressure waves at the inlet of the compressor. The optimization was performed at three operating points on the 100% speed line in order to maintain choke mass flow and surge margin. At the design point, the specific work input was kept equal. The baseline impeller was designed by using ruled surfaces due to requirements for flank milling. To investigate the benefits of arbitrary blade surfaces, the restrictions of ruled surfaces were abolished and fully 3D blade profiles allowed. In total therefore, 45 parameters were varied during the optimization. The combined geometric and aerodynamic analysis reveals that a forward swept leading edge and a concave suction side at the tip of the leading edge are effective design features for reducing the shock strength. Beyond that the blade shape of the optimized compressor creates a favorable impeller outlet flow, which is the main reason why the performance of the vaneless diffuser improves. In total a gain of 1.4%-points in isentropic total-to-static efficiency, evaluated by CFD at the exit plane of the vaneless diffuser, is achieved.

Today, there are 3 primary methods Solar Turbines, Inc. uses for manufacturing shrouded centrifugal impellers for the Oil and Gas industry. Impellers can be made by an investment casting process, single piece integrally-machined using point milling, or fabricated using a flank milled, open faced impeller and brazing a shroud in place. Investment cast impellers give the aero designer the greatest flexibility in the design, since the designer doesn’t need to be concerned about tool access or other manufacturing constraints. It is common to use this process for any impeller. Single piece integrally-machined impellers are relatively straightforward for high flow coefficient impellers, as the wide flow-path provides plenty of room for tool access. For lower flow coefficients, brazed shrouded impellers can be made very precisely, but at a substantially higher cost than the other methods. Each of these manufacturing methods also has a cost and aerodynamic performance associated with them. With the advent of high-speed machining and better cutting tools, integrally-machined impellers can offer an alternative manufacturing process over cast or fabricated impellers. However, determining the ability to integrally-machine an impeller historically is done late or even after the detailed design process. This can lead to costly redesigns to make sure the impeller can be machined, with flow-path and blade adjustments done after the aerodynamic design. Sometimes these adjustments are unsuccessful and the manufacturing process is abandoned. In this paper, 2 medium flow coefficient impellers are redesigned. These impellers are used in pipeline applications for the transmission of natural gas. The original designs were cast. By incorporating highly customized commercial software written exclusively for defining tool paths of integrally-machined shrouded impellers into the aerodynamic design process, new impeller geometry was defined that was able to be integrally-machined, while meeting or exceeding existing impeller performance and improved design cycle time. This paper will discuss how the machining software was used concurrently with CFD and FEA analysis during the design process. Test results from rig tests will be presented, showing measured results from both the original and redesigned stages.

Facing a high demand for aircraft engines over the next decades in combination with new challenging materials, aircraft engine manufacturers are striving for new manufacturing processes. The manufacturing of profiled grooves for the mounting of the turbine blades on the disc is a bottle neck process today due to the exclusive use of High Speed Steel (HSS) tools in broaching. Because of the limited hot hardness of HSS, the applied cutting speeds are low compared to other conventional machining processes, i.e. 2–5 m/min. Furthermore, the broaching process has some more drawbacks regarding flexibility, capital commitment for machinery and tools as well as costs. Nevertheless, broaching offers outstanding properties regarding surface finish, manufacturing accuracy and is still a productive process due to the many cutting edges applied. There are some alternative process chains which are not yet in industrial use, which are able to substitute and/or complement the HSS-broaching process. In this paper, results are presented on two different roughing strategies for the manufacturing of profiled grooves in Nickel Based Alloys Allvac718plus and Inconel718. On the one hand, rough broaching with cemented carbide tools using indexable inserts was investigated at different cutting speeds, which are up to five times higher than the applied cutting speeds in industrial applications with HSS-tools. Two different carbide grades were investigated varying the cobalt content and the grain size. Cemented carbide is not state of the art in broaching Nickel Based Alloys due to its low fracture toughness. Different cutting edge inclination angles were applied and their effect on cutting forces, wear and tool chipping tendency were analyzed. On the other hand, rough side milling with ceramic cutting tools was investigated. Ceramic cutting tools excel in high hot hardness and thus can be used at very high cutting speeds i.e. up to 1000 m/min in Nickel Based Alloys. However, being very brittle and sensitive to alternating loads and thermal shock, machining processes with ceramic tools require extensive process design. In side milling experiments, Whisker reinforced as well as SiAlON and Oxide ceramic were investigated. In a first step, a window for machining parameters was identified. Then, tool life tests were conducted varying the feed at a fixed cutting speed of 1000 m/min. Subsequent to the experiments, the rim zone of the roughed grooves was investigated depending on the wear state of the used tools. The condition of the rim zone is a major criterion for the assessment of the adequacy of the roughing processes, because it can affect the subsequent finishing process. In further work, the interdependencies between the investigated roughing processes and finishing will be addressed.

Residual surface roughness is often introduced in the manufacture process with ball-end or fillet-end milling. Instead of paying extra cost to remove these small-scale residual surface structures, there is a potential usage of them as flow control device. This numerical study therefore explores the ability of engineered surface structure in controlling the endwall secondary flow in turbomachinery. The CFD method is validated against the existing experimental data obtained for a 90 degree turning duct flow with a single rib fence placed on the end-wall. The working principle of the engineered surface structure is revealed through detailed analysis on the flow produced by multiple small fences and grooves mimicking the residual surface. The results consistently show that addition of engineered residual structure on flow surface can effectively reduce the magnitude of stream-wise vorticity associated with secondary flow and alleviate its lift-off motion. In the end, a general working mechanism and design guideline for optimizing the residual structure are summarized.

Due to lightweight construction numerous parts in turbomachinery industry with aerodynamic properties exhibit thin-walled features. Typical examples are compressor blades or turbine blades. Finish-milling depicts a stage of the manufacturing process of these parts with significant value creation. A major limitation of productivity is process stability in terms of self-excited or forced vibration. Different simulation approaches attempt determining a priori the process stability to avoid a bad surface quality, accelerated tool wear, tool breakage or scrapped parts. One distinctive part of these simulations is a cutting force model which incorporates material and tool dependent coefficients. The simulation accuracy directly depends on the exactness of these coefficients. Usually, these coefficients are identified experimentally from cutting force measurements with piezoelectric sensors, whose transmissibility is nonlinear. In this paper a multidimensional stationary inverse filter for compensating the influence of the nonlinear transmissibility of force sensors is presented. In a subsequent step, a Levenberg–Marquardt algorithm is used to identify cutting force coefficients from filtered force measurements. The functionality of the filter is validated by comparing highly nonlinear and almost linear piezoelectric force measurement sensors connected in series during finish-milling experiments. The accuracy of the identified cutting force coefficients is assessed by comparing cutting force simulations to measurements.

Turbine engine manufacturers permanently aim to improve the efficiency of their products. This is often accompanied by the development of new materials which have to be introduced to manufacturing. As a consequence, engineers responsible for machining process development are regularly confronted with the question, how to identify the optimal machining conditions in order to deal with the new constraints. Nowadays, the effort and success of such identification processes are to a significant degree depending on technology expert skills and experiences. From the process planning perspective, however, this circumstance is characterized by a significant degree of uncertainty. This article presents an innovative concept for a technology assistance system (TAS) for milling. The TAS supports the operator to determine optimal machining conditions by autonomously evaluating machinability criteria such as cutting force, tool wear or surface roughness for certain work piece material/ tool combinations. This includes the planning and organization of milling experiments, its standardized and automated execution as well as the generation of surrogate models to describe the machinability criteria for a given parameter range, serving as input for a future optimization. All functionalities of the TAS are conceptually described and first results achieved using a prototype solution are introduced and discussed.

During an exercise to determine the optimum conditions for metal removal and tool wear, three ultra high strength steels investigated were 18% Ni maraging steel, a Ni-Cr-Mo steel (designated REX 685), and a 5% Cr-Mo-V steel (designated H50). These were machined in the fully heat treated condition (120 tsi U.T.S.). Metallurgical etch inspection techniques were used to assess the metallurgical surface conditions created by the machining operations, which were turning, milling, drilling, reaming and grinding. Stress corrosion and fatigue tests were carried out on specimens machined under optimum and sub-optimum conditions, “sub-optimum” being used to describe machining under conditions outside those recommended but which can develop during normal workday practice.

Metal removal processes disturb or alter the surface layer creating characteristics which may be quite different from those of the base metal. A wide variety of surface alterations can be produced by conventional machining as well as by a variety of electrically and chemically assisted metal removal methods. The effect of variables in milling and grinding will be reviewed. Photomicrographs illustrating surface alterations produced in martensitic steels, titanium and nickel alloys will be presented, as well as microhardness data illustrating the types of hardness changes found in these surfaces. Data on residual stresses produced in some of these materials as a function of machining variables will also be presented. The fatigue characteristics of these alloys, as affected by conventional metal removal process variables, are summarized and explained. It can be concluded that the method of machining and the variables chosen for a particular machining method are significant in relation to the mechanical performance of finished parts. Machining methods must, therefore, be carefully evaluated in their relation to the performance of highly stressed components which are subjected to a variety of hostile environments.

Part programming by interactive graphics is a technique of communicating with a computer by means of simple words and diagrams on a cathode ray tube. A basic mini-computer system is described and an example of geometry input and tool path generation is given. The toolpath of a production lathe tape and examples of future 3 and 5 axis milling applications are shown. The current benefits of the system are also outlined.

Turbomachinery rotors may be engineered to be machined on 5-axis, numerically controlled machines using flank milling techniques. Engineering data can be converted to a graphic or computer data set which lends itself to unsophisticated numerically controlled programming for five-axis machines with short lead time production and a high degree of change flexibility.

The Carborundum Company has been involved in the manufacture of alpha SiC for close to 100 years. The historical usage of this material has been as a coarse grain for the abrasive industry. Several Carborundum manufacturing plants are in existence worldwide and each has a capacity of approximately 40,000 tons/year of SiC powder produced by the Acheson process in which a graphite electrode is encased in a mixture of sand (SiO 2 ) and coke. After the mass is heated to 4000°C and allowed to cool, the crystalline SiC grain is obtained directly (Figure 1). A milling and classification procedure is then employed to produce the desired grain sizes. In 1975, researchers at Carborundum discovered a process for making high density, high strength monolithic shapes of alpha SiC (1) . This involved using a submicron sized powder blended with sintering aids (boron and carbon). The mixture is green compacted and heated to above 2000°C under inert gas at atmospheric pressure. A solid state grain boundary diffusion process results in a densification process with an accompanying linear shrinkage of approximately 18%, to produce a body with 95–99% of theoretical density (3.21 gm/cc), and properties which are of interest for engineering applications. The pressureless sintering allows the formation of complex geometries by a net shape process without grinding, thus, creating the potential for the economical production of precision components in high volume.

This paper describes two gas turbine related research projects in the department of Mechanical Engineering at the University of British Columbia. Of the two projects described, one involves fundamental turbomachinery research while the second is a more applied project concerned with gas turbine based cogeneration systems in process industries. In the fundamental research area, both an experimental and computational study of unsteady boundary layer development on turbomachinery blading is described. The applied research program involves an engineering and economic assessment of a gas turbine based cogeneration system for sawmills. The system is designed to use wood-waste generated during the saw-milling process as a source of heat for an indirectly fired gas turbine. Studies to date indicate that such a system could result in many sawmills becoming completely energy self-sufficient.

The efficiency of steam- and gasturbines is mainly influenced by the geometry and the surface roughness of the turbine blades. Therefore the profile contour of the blades must be machined as accurate as possible. High speed cutting (hsc) offers a lot of advantages for surface finishing of turbine blades. The paper describes the influence of different cutting parameters as well as the importance of tool geometry for the surface quality achievable by high speed milling. Specific requirements for machine tools for high speed milling will be discussed.

It is generally conceived that a blade surface is flank millable if it can be closely approximated by a ruled surface; otherwise the slow machining process of point milling has to be employed. However, we have now demonstrated that the ruled surface criterion for flank milling is neither necessary nor sufficient Furthermore, many complex arbitrary surfaces typical of our blades in fans, axial compressors, and centrifugal impellers in aviation gas turbines are actually closely flank millable and can be rendered exactly flank millable with one or more passes per surface often without sacrificing, indeed sometimes with gain, in performance.

Biomass fuelled combined cycle with gas turbine for co-generation, has the promise of being able to produce electricity at competitive cost. The sugar cane industries in the developing countries are targets for near term-applications of this technology. Different options for increasing the electricity generation in the sugar mills by using more advanced steam process and combined cycle technology, using cane trash and bagasse as a fuel for has been analyzed. The TPC sugar mill in Tanzania was selected as a case study for investigation. Introduction of a combined gas turbine/steam turbine process will make it possible to increase the electricity output from 2.5 MW to 30 MW at this plant during milling season. By using cane trash as fuel during the off-season period, the electricity generation can be increased by a factor of 20 compared to what is generated at TPC sugar factory today. The financial evaluation indicated that the annual profit would range from US$ 3.5 million for the advanced steam process with 6.5 years pay-back time, to be US$ 4.7 million for the combined gas turbine/steam turbine process with 6.8 years pay-back time.

A large proportion of modern centrifugal impellers are machined from solid forgings rather than made from cast metal. The CNC milling process offers options to manufacturers to minimise manufacturing costs whilst also enhancing performance of the impeller. Efficient manufacturing can result in cutter tool marks and paths and associated roughness remaining on the hub and blade surfaces of impellers as a result of minimising passes and maximising the cut. The goal of manufacturers is to allow these marks to be as deep as possible to minimise machining costs but without any negative effects in performance and possibly even enhancing it. There are existing modelling methods that predict the influence of roughness on compressor performance using the definition of an equivalent sand grain roughness. The purpose of this study is to relate the performance directly to the tool mark characteristics that are by-products of machining, namely cusp height, cutter path roughness and orientation of the cutter path relative to the local flow velocity, to review the current modelling techniques for predicting the influence of surface condition on compressor performance and to show the scope for optimisation of manufacturing and performance considerations.