Paweł Sułkowicz

Traverse grinding of low-stiffness shafts with the use of a grinding wheel’s path correction

This paper presents a method of increasing the shape and dimensional accuracy of low-stiffness shafts manufactured in traverse grinding process. In order to achieve that, grinding force measurement was used. It allowed to calculate such a correction of a grinding wheel’s path, that allowed to decrease dimensional and shape errors of grinded workpieces.

Cylindricity error measurement and compensation in traverse grinding of low-stiffness shafts

Axio-symmetric parts account for nearly half of the parts manufactured for the needs of the engineering industry. Among them, about 12% are shafts with low stiffness, i.e. those in which the length-to-diameter ratio l/d is greater than 10. They are used in many industries, including in the aviation industry (turbine shafts, spring shafts, elastic and torsional shafts), tool (drills, reamers, special tools), machine tools (rotor, pumps and generators shafts, guides) or automotive (driveshafts, axle-shafts) [1, 2]. Shafts with low stiffness are usually made of highstrength alloy steels. Typical methods of their machining include external turning and grinding. Turning machining should provide 8÷11. tolerance class and roughness Ra = 0.63÷2.5 μm, while grinding operation 5th or 6th tolerance class for roughness Ra < 0.63 μm [3]. The low stiffness of parts causes problems with achieving the required shape and dimensional accuracy. During grinding of such parts, elastic deformation occurs, resulting in errors in the cylindricity and dimension of the parts being made [4]. Many studies show that the pliability of the tailstock and headstock centers and the workpiece whose length / diameter ratio is greater than 10 is about 90% of the total machine tool – tool workpiece systems pliability [5]. Fig. 1 shows the elastic displacements of these elements. The elastic displacement of the workpiece x1, resulting from the displacements of the headstock center xw and the tailstock center xk can be calculated from the following equation:

Zastosowanie systemu Omative w obróbce łopatki turbiny ze stopu Inconel 718

The modern aviation industry is increasingly demanding its components, while striving for maximum efficiency and maximum profit. New construction solutions make it necessary to use special materials such as heatresistant super alloys. These are alloys based on nickel, cobalt or iron. Of these, one of the best properties is Inconel 718 [1, 2]. The advantages of this alloy are particularly important in those engine points that are subjected to the largest loads. The turbine blades work in the most difficult temperature and load conditions. The blade end speed reaches 390 m/s, the gas temperature is even 1200 °C and their speed is 600 m/s. The turbine blade material, in addition to high strength, must be characterized by high heat resistance, high temperature creep resistance, corrosion and oxidation resistance and high hardness. Density of the alloy, which affects the weight of the engine, is also important in generating centrifugal forces [3, 4]. Inconel 718 is one of the hardest materials to work on. Blade locks are currently being successfully developed in the Creep-Feed Grinding (CFG) process. This method allows for efficient machining of elements made of super alloys and other hard-working materials. It allows the parts to be polished after heat treatment and ensures high surface quality [5]. On the other hand, in the case of free surfaces of the blades, the method of their execution is simultaneous process of five-axes milling. Due to the complexity of this machining, the presence of high milling strength components and the high cost of the workpiece and tooling, it is legitimate to use a system that monitors the correctness of the cutting process. They are based on the measurement of selected physical quantities, such as: cutting force, vibration, power and engine torque, sound emission or coolant flow. Measured signals (after processing) serve to obtain process measures

The influence of the cutting edge shape on high performance cutting

Purpose The purpose of this paper is to determine the influence of the shape of a cutting edge on high-performance milling high-performance cutting. The main purpose of the test was to determine the possibility of increasing the efficiency of machining AlZn5.5CuMg alloy, which is used mainly for the thin-walled structural aerospace components. Design/methodology/approach In all, eight cutters for machining aluminum alloys with different shape of the cutting edge (1 – continuous, 4 – interrupted, 3 – wavy) were tested. The influence of different shapes of a cutting edge on cutting force components and vibration amplitude was analyzed. Furthermore, the impact of a chip breaker on the form of a chip was determined. Findings The conducted test shows that using discontinuous shapes of a cutting edge has impact on the reduction of the cutting force components and, in most cases, on the increase of vibration amplitude. Moreover, using a chip breaker caused significant chip dispersion. The optimal shape of a cutting edge for cutting AlZn5.5CuMg alloy is fine wavy shape. Practical implications Potential practical application of the research is high-performance milling of AlZn5.5CuMg alloy, for example, production of thin-walled aerospace structural components. Originality/value Different shapes of a cutting edge during high-performance milling of aluminum alloy were tested. The influence of tested geometries on HPC process was determined. The most favourable shape of a cutting edge for high-performance cutting of AlZn5.5CuMg alloy was determined.