Grinding of High-Strength Materials

The joint research of scientists of two countries deals with cylindrical and surface grinding with abrasive wheels of heat-resistant steel Inconel 625 (KhN77TYu GOST 5632 – 72 Russian Federation standard), (analogues include Hastalloy, N07080, Alloy 80A, Nimonic 80A, 2.4952 ASTM B637/ASME SB637, UNS N07080). The article shows the results of studies of the features of high-temperature steel during grinding with a fastened abrasive. The results of experiments are given to determine the optimal characteristics of grinding wheels, grinding modes, cooling-lubricant fluids. Experimental data about geometric accuracy, surface roughness, resistance of wheels are demonstrated as well. The ways to prevent from defects during cylindrical and surface grinding of high-strength steel are proposed. The recommendations to increase the tool resistance and output of the process are given.

EFFECTS OF GRINDING WHEEL WEAR ON THE THERMO-MECHANICAL LOADS IN THE GRINDING PROCESS

A large amount of the energy produced during grinding is converted into heat. Since not all of the heat can be dissipated by the cooling lubricant, thermally induced displacements in machine components occur, which has a negative influence on the component quality. The generation and distribution of heat is influenced by the change of the grinding wheel topography due to wear.Therefore, the wear mechanisms of grains were identified and quantified and their effect on heat generation was investigated. For this purpose, creep feed grinding investigations on bearing steel were conducted with electroplated CBN grinding wheels with different grain specifications.

Influence of a Discontinuous Process Strategy on Microstructure and Microhardness in Drilling Inconel 718

Nickel-base alloys are proven materials in the fields of the aerospace and oil industry, which is due to their characteristic material properties of high temperature strength, high toughness and good oxidation resistance. These properties are beneficial to applications in technical components in general. However, they also represent challenges for machining. Especially while drilling Inconel 718, high temperatures occur in the chip-formation zone that implicate high thermal load in the material and thus, influence the surface integrity, for example, by causing white layers. Hence, the development of strategies to improve the ability to supply cutting edges with cooling lubricant is becoming increasingly important. In this context, an alternative process design, the discontinuous drilling, takes place, characterized by a periodic interruption of feed motion and thus, chip formation. A minor retraction movement from the contact zone enables the cooling lubricant to reach the cutting edges and to reduce their thermal load. In comparison to the conventional process of drilling Inconel 718, the effects of discontinuous drilling with varying numbers of interruptions on the resulting surface integrity and further parameters of drilling qualities are analyzed. Thereby, the prevention of process-related phase transformations due to thermal impact was discovered when a discontinuous drilling strategy was implemented.

Dornhonen ohne Kühlschmierstoff/Single-pass honing without cooling lubricant – Feasibility of a dry honing process and determination of the effects during machining

Bei der Intensivzerspanung mit einem bohrungsfüllenden Werkzeug ist nach heutigem Wissensstand der Einsatz von Kühlschmierstoffen obligatorisch. Jüngste Untersuchungen haben gezeigt, dass eine Überlagerung niederfrequenter Schwingungen beim Dornhonen die Spanabfuhr, die Prozesskräfte- und momente sowie die Arbeitsergebnisse positiv beeinflusst. Darauf aufbauend wurde in dieser Arbeit das schwingungsüberlagerte Dornhonen ohne Kühlschmierstoff untersucht.   According to the current state-of-the-art, the application of cooling lubricants is mandatory while using a bore-filling tool for intensive machining. Recent investigations have shown that a superposition of low-frequency oscillations in single-pass honing improves the local chip removal and work results while reducing process forces and torques. Following this, the oscillation-superimposed single-pass honing without cooling lubricant has been conducted in this work.

The Development of a Feeding Device for a Cooling Lubricant Technological Tool with Automatic Temperature Control System

The article presents a feeding device designed for a cooling lubricant technological tool and an automatic control system for controlling the temperature mode of parts when milling. The device implements a new method of separate cooling and lubrication of the cutting area with sprayed liquid and ionized gas. To develop the device, an engineering-physical search design method is used, which makes it possible to obtain a set of possible options of technical solutions for the desired device and determine the most promising options for the design implementation. The method is based on constructing a model of the physical principle of operation using application software. The design of the new device is developed, mathematical modeling is performed, and the parameters of the transfer function of the automatic temperature control system are calculated. The proposed device can increase the efficiency of machining when milling workpieces and make a significant improvement to working conditions by reducing the content of harmful impurities in the air.

Influence of hard rolling and the cooling lubricant on the material properties and the rolling strength of PM gears

Purpose The lower density of powder metallurgical (PM) gears compared to solid steel gears leads to not only a lower weight but also a lower load-carrying capacity. Therefore, PM gears are cold rolled before hardening to increase the density in the highly stressed surface zone and, thus, the flank load-carrying capacity. A further approach to increase the flank load-carrying capacity is the reduction of friction and wear in the tooth contact. The purpose of this paper is to analyze the hard rolling process as a new manufacturing step in the PM process chain to influence the boundary layer. Design/methodology/approach The investigation includes the new process of hard rolling, the variation of the cooling lubricant in the hard rolling process and the evaluation of its influence on the material properties and the flank load-carrying capacity. Therefore, the additives of the cooling lubricant are varied regarding the sulfur and phosphorous content. The load-carrying capacity is evaluated on disk-on-disk test rig and the material properties are evaluated by metallographic tests and boundary layer. Findings The results of the specimen characteristics in the micro and nano range show a significant influence of hard rolling on the residual stresses and the chemical surface composition. Because of hard rolling, residual compressive stresses as well as roughness are reduced and the flank load-carrying capacity is increased by high phosphorous content of the cooling lubricant. Originality/value This paper investigates a new manufacturing step to increase resource efficiency by increasing the flank load-carrying capacity of spur gears.