Investigation of cutting characteristics for worm machining on automatic lathe — Comparison of planetary milling and side milling

A worm and worm wheel gearing is widely used in a geared motor unit for the convenience and safety of an automobile. For mass production of a high quality worm, the current rolling process is substituted with the milling process. The milling process offers comparatively accurate machining quality and high production capacity for worm manufacturing. Moreover, since the milling process enables the integration of all operations of worm manufacturing on a CNC lathe, production efficiency can be remarkably improved. However, there are several important factors to be considered for producing high quality worms such as cutting force, tool-workpiece interference, and others. Planetary milling and side milling are generally applied to machine worms. In this study, the cutting characteristics of worm machining on an automatic lathe are investigated for two types of milling processes and those processes are compared with each other. A tool-tip trajectory model based on tool-workpiece interaction is proposed, and then tool-workpiece interference and cutting force are simulated with the model. The simulation results are verified through numerous experiments. The experimental results show the cutting characteristics of each milling process and the efficiency for mass production of a high quality worm. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim     

Exploring Operation Mechanisms of the Flexible Metal-to-Metal Face Seal: Part I—Numerical Modeling and Validations

A numerical model was developed for a special type of metal-to-metal face seal to evaluate its performance under various operating conditions. The model considers interactions among surface deformations due to thermomechanical twists, oil transport in the sealing band, and heat transfer in the seal pair simultaneously. In the meantime, experimental efforts have been made to measure the friction coefficients and seal temperatures during different operations. The model predictions were then compared with the experiment results through the two above-mentioned quantities. The comparisons show that the numerical simulations consistently overestimate the friction by 15–20%. However, the overall trend of friction variation with speed and some details of the friction have been captured, indicating that the current models are able to properly predict tribology of seal operations.     

Rheological Behavior of Greases: Part I—Effects of Composition and Structure

The aim of this work is to show the correlation between grease rheological behavior and its composition and structure (base oil viscosity, soap nature, and concentration).

A rheological investigation was carried out under the controlled stress mode. The results, obtained over different time intervals, show that grease behaves like a non-Newtonian viscoelastic material, with a narrow linear domain.

The soap nature and concentration are the dominant parameters when grease is submitted to low shearing. This was confirmed by TEM observations: the closer networks gave the highest rheological properties. Base oil viscosity influenced grease behavior only under high strain rates.

Some properties are discussed with respect to their influence on the contact replenishment, which is a critical point for mechanism lifetime prediction.

Finally, the authors suggest using rheometry as an alternative technique to standardized methods. Yield stress varies in the same way as penetration does, but is further influenced by the sample macrostructure.     

Investigation of the effect of machining parameters on the surface quality of machined brass (60/40) in CNC end milling—ANFIS modeling

Brass and brass alloys are widely employed industrial materials because of their excellent characteristics such as high corrosion resistance, non-magnetism, and good machinability. Surface quality plays a very important role in the performance of milled products, as good surface quality can significantly improve fatigue strength, corrosion resistance, or creep life. Surface roughness (Ra) is one of the most important factors for evaluating surface quality during the finishing process. The quality of surface affects the functional characteristics of the workpiece, including fatigue, corrosion, fracture resistance, and surface friction. Furthermore, surface roughness is among the most critical constraints in cutting parameter selection in manufacturing process planning. In this paper, the adaptive neuro-fuzzy inference system (ANFIS) was used to predict the surface roughness in computer numerical control (CNC) end milling. Spindle speed, feed rate, and depth of cut were the predictor variables. Experimental validation runs were conducted to validate the ANFIS model. The predicted surface roughness was compared with measured data, and the maximum prediction error for surface roughness was 6.25 %, while the average prediction error was 2.75 %.     

Mechanical testing machine stiffness: Part I—Theory and calculations

The importance of elastic interaction between specimen and testing machine in many mechanical property tests is discussed, and drawbacks to the usual methods of calculating machine stiffness are considered. Two expressions are proposed for calculating the effective testing machine stiffness, which is actually a composite stiffness including machine, grips or platens, load cell, insulation and lubricant. This stiffness is calculated from data acquired during compression tests in the LASL Cam Plastometer. The derived expressions can be adapted to calculate stiffness of many types of programmed testing machines; and they are so adapted to apply to both tensile and compressive testing in constant crosshead speed machines.Stiffnesses were calculated for over 200 tests in the LASL Cam Plastometer, and for a few tests in compression and a few in tension in constant crosshead speed machines. From the results of these calculations it was concluded that machine stiffness is a variable quantity which generally tends to increase as the applied load increases.Finally, because under sensibly identical experimental conditions there are large differences in calculated stiffnesses, it was concluded that it is necessary to perform such calculations for each mechanical test. Only by so doing can the specimen-machine interaction be properly taken into account when calculating stress-strain curves from load-time or load-displacement data.     

Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part II—simulation results and experimental validation

As the mathematical model has been developed in part I, the simulation results of the transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 aluminum alloy and the experimental validation are presented in this paper. Modeling results showed that the solute concentration in the solidified region continuously increases during the solidification process. As the temperature is lower than the coherent temperature (i.e., the temperature at which the coherent mushy zone is just formed), the strains accumulated in the coherent mushy zone increase with the increasing solid fraction. The amount of strain in the mushy zone is primarily determined by the life (i.e., time span) of the coherent mushy zone, which is determined by the solidification range and solidification time. The increased solidification range and consequently solidification time extend the life of the coherent mushy zone, which increases the amount of strain and thus increases the likelihood of solidification cracking. The modeling results are in agreement with the experimental results. Both the experimental and modeling results exhibited that solidification cracking is prone to occurring near the top surface and middle part of the weld bead and an increase of laser power leads to the higher cracking susceptibility.     

Evaluating automated manufacturing technologies: Part I — Concepts and literature review

Automated manufacturing technologies offer improved productivity and flexibility. Adoption of such technologies requires an evaluation and justification process. A survey of existing literature on the evaluation of automated systems indicates that several techniques have been used in the justification process. In this paper we review some of these techniques, and develop a classification scheme for the justification techniques based on the knowledge of the decision environment.     

Formulation,rheology and thermal ageing of polymer greases—Part I: Influence of the thickener content

The aim of this work is to show the correlation between polymer greases’ rheology and its formulation. The tested polypropylene (PP) thickened greases were evaluated regarding their thickener content and its effect on the rheological properties. An artificial ageing procedure was performed by heating fresh grease samples in an oven to study the thermal degradation. The ageing evaluation was performed through rheological measurements, FT-IR spectra, oil loss, bleed-oil viscosity changes and bleed rate. The rheology measurements were performed on a rotational rheometer, emphasizing on the storage and loss moduli values at the Linear Visco-Elastic (LVE) region. The flow curve of each grease was also measured. A modified Herschel–Buckley model was applied and the data was correlated to the thickener content.     

Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part I—the mathematical model

In this work, the oscillating arc narrow gap all-position gas metal arc (GMA) welding process was developed to improve efficiency and quality in the welding of thick-walled pipes. The statistical models of narrow gap all-position GMA weld bead geometry were developed using response surface methodology (RSM) based on central composite design (CCD). The developed models were checked for their adequacy and significance by ANOVA, and the effects of wire feed rate, travel speed, dwell time, oscillating amplitude and welding position on weld bead dimension were studied. Finally, the optimal welding parameters at welding positions of 0° to 180° were obtained by numerical optimization using RSM.     

Technology and system of constraint programming for industry production scheduling — Part I: A brief survey and potential directions

The use of techniques and system of constraint programming enables the implementation of precise, flexible, efficient, and extensible scheduling systems. It has been identified as a strategic direction and dominant form for the application into planning and scheduling of industrial production. This paper systematically introduces the constraint modeling and solving technology for production scheduling problems, including various real-world industrial applications based on the Chip system of Cosytec Company. We trend of some concrete technology, such as modeling, search, constraint propagation, consistency, and optimization of constraint programming for scheduling problems. As a result of the application analysis, a generic application framework for real-life scheduling based on commercial constraint propagation (CP) systems is proposed.     

Solid Lubrication of Silicon Nitride with Cesium-Based Compounds: Part I — Rolling Contact Endurance,Friction and Wear

The high temperature rolling contact endurance, friction, and wear of 16 cesium-based compounds with solid lubricating properties were investigated on silicon nitride (Si₃N₄). Some were also investigated on bearing tool steels and several state-of-the-art high temperature solid lubricants were investigated for comparison. Experiments were conducted in air at temperatures up to 650°C, contact stresses up to 4.34 GPa, and a pure rolling surface speed of 1.8 m/s. Although all of the cesium-based compounds exhibited self-lubricating properties, the best overall performance was achieved with a cesium silicate reaction film formed in-situ (Cs₂O·xSiO₂) and a hydrated cesium silicate bonded coating (Cs₂O·3SiO₂·nH₂O). Bonded coatings of cesium oxythiotungstate + tungsten disulfide mixture (Cs₂WOS₃ + WS₂) and cesium hydroxide (CsOH) also performed well. It is hypothesized that high temperature chemical reactions between the cesium-containing compounds and the silicon nitride surface form a lubricious cesium silicate film.     

Coke Formation from Aircraft Turbine Engine Oils: Part I — Deposit Analysis and Development of Laboratory Oil Coking Test

The authors report here the results of a study undertaken to determine how aircraft engine oil degrades to form coke in static films on engine components and the impacts of additives and surface materials upon the coke production processes. The research is presented in two parts. This first paper deals with the initial research to develop a simple laboratory oil-coking test capable of monitoring antioxidant depletion, oil degradation, and coke formation of stressed aircraft turbine engine oils. Details of the analytical chemistry experiments performed on the stressed samples to quantitate the percentage of oil, polymer dissolved in the oil, and insoluble coke are also presented. The second paper (Part 2) (I) deals with more quantitative measurements of the degradation of thin layers of oil on heated surfaces. Effects of different oils and surfaces are explored.

The results presented in Part I show that simple open-vial laboratory tests involving thin films of oil produce polymer and coke similar to the deposits seen on failed face seals taken from operating aircraft engines and isolated from used engine oils. Coking reactions require oxygen to deplete the antioxidant package and to polymerize/decompose the ester basestock of the oil. After the antioxidant package is depleted, the ester basestock polymerizes to form small oil-soluble polymers. As the oil spends additional time at elevated temperature, these polymers increase in molecular weight and change in chemical composition becoming insoluble in the oil, producing deposits. Although the antioxidants inhibit the polymer/coke reactions, the antioxidants are incorporated in the formed deposits increasing the deposit amount. Consequently, these results indicate the proper concentration and choice of antioxidants will allow elimination, not just reduction, of deposits on engine components coated with thin layers of static oil films.     

Measured Performance of Tilting-Pad Journal Bearings over a Range of Preloads—Part I: Static Operating Conditions

This article presents the measured static characteristics for five tilting-pad journal bearings with a range of preload factors. The bearings had five shoes with static forces applied both on the pad and between pads. The journal diameter was 70 mm, with a length-to-diameter ratio of 0.75, a pivot offset ratio of 0.50, and a nominal assembled radial clearance of 81.3 μm. The rocker-backed pads have nominal radial machined clearances of 176.8, 114.3, 91.4, 73.7, and 61.0 μm. These clearances constitute a range of preloads from ?0.333 to 0.540. Most tilting pad bearings are intentionally designed with positive preloads, although with pivot wear and/or pad and pivot distortion or machining tolerances, bearings can operate with zero or negative preloads. Measured results for bearings with negative preload factors have not previously been available. Measurements reported here were made for a variety of speed-load conditions encompassing a Sommerfeld number of 0.1 to 4.5. The measured parameters are eccentricity magnitude, attitude angle, film thickness, and temperatures sufficient to define thermal boundary conditions. Also measured are oil supply pressure, flow rate, and on-shaft pressure profiles. The focus of the work presented herein is to quantify the influence of preload on film thickness, maximum pad temperature, and eccentricity magnitude and attitude angle. Measurements showed preload had a moderate influence on operating eccentricity but not on attitude angle. Negative preloads resulted in the greatest temperature rise, although all temperature rises were relatively small.     

Characterization of Model Perfluoropolyalkylethers by Miniaturized Thermal Oxidative Techniques—Part I: Modified Oxidation-Corrosion Test

The metal catalyzed thermal oxidative stability of commercially available, and model perfluoropolyalkylelher (PFPAE) fluids was investigated by oxidation corrosion tests. Using model PFPAE fluids, prepared via direct fluorination of hydrocarbon analogues, a wider variety of specific molecular structures were available for study than previously available from more conventional PFPAE chemistry synthesis procedures. Because of a limited supply of the model fluids, a miniaturized oxidation corrosion test, using only 6 ml of fluid, was devised. This test, conducted at constant temperatures, was compared to a similar test using 20 ml of fluid on the more abundant commercial fluids and then extended to the model fluids. Details of the miniaturized test procedure and apparatus are presented. Also presented are the chemical structure-thermal oxidative stability relationships of the fluids as derived from this study. The destabilizing effect of an -OCF₂- group is confirmed and other more subtle effects are noted.     

Thermohydrodynamic Analysis of a Journal Bearing in a Turbulent Flow Regime—Part I: Theory

An attempt is made to formulate a thermohydrodynamic model of fluid-film lubrication that is valid in turbulent flow regimes. The model considers the flow to be a small perturbation of turbulent Couette flow. The modified Reynolds equation is obtained for the turbulent flow and the integro-differential energy equation makes the turbulence analysis easier by replacing the conductive terms in terms of the convective boundary conditions at two solid surfaces. Sample results applying the perturbation method agree well with available experimental data and theoretical methods.     

The Friction Reducing Properties of Molybdenum Dialkyldithiocarbamate Additives: Part I — Factors Influencing Friction Reduction

Abstract

Calcium sulfonate complex greases have excellent extreme pressure, antiwear, and anticorrosion properties and are widely applied in rolling bearings, particularly in humid environments. In this article, the shear stability of dry and water-contaminated lubricating calcium sulfonate complex greases is described using a novel aging method. Unlike lithium and polyurea greases, no shear softening is observed for the dry greases due to the good mechanical stability of the particle-like thickener structure. For water-contaminated greases, no water separation was found during the prolonged aging. Instead, a homogeneous water–calcium sulfonate thickener micellar structure is generated. These micelles function as apparent thickeners and effectively increase the thickener concentration, which thickens the grease. This may explain why calcium sulfonate complex grease has excellent water absorption properties.     

Clearance Regulation of Mechanical Gas Face Seals: Part II—Analysis and Control

This article presents the analysis and control of noncontacting mechanical gas face seals based on the state space model developed in Part I. Methods to analyze the controllability and observability of axial and tilt modes are described. The controllability analysis determines to what extent the dynamic response of the seal system modes can be shaped in a closed-loop feedback system, and the observability analysis determines if the seal system modes can be reconstructed from specific state measurements of the axial clearance and stator tilts. The error state-space method is employed to design a tracking controller to regulate the seal at a prescribed axial clearance. The control law is a function of all axial states; therefore, reduced order linear observers are designed to observe the unmeasured axial and tilt seal states. The axial clearance and tilt state estimates are used to reconstruct the gas film axial force and moments, which cannot be directly measured, for design and analysis. The analysis and control techniques are applied to the illustrative example presented in Part I. The results demonstrate that the gas film forces and moments can be estimated well and the seal system can be satisfactorily regulated with a sufficiently damped response that is within the bandwidth of today's electropneumatic actuators.     

The Durability of Gear and Disc Specimens—Part II: Post Failure Examination and Gear-Disc Correlation

In this paper the authors present a post failure examination of the gear and disc tests reported in Ref (I) on a standard carburized steel (BS SI56), a temper resistant carburized steel (AISI M50NiL), and a carburized and nitrided temper-resistant steel (AISI M50NiL Duplex).

An analysis of the relationship between the gear and disc tests is also presented. The fatigue lives of the gear tests correlated well with the chamfered disc tests. However, this was thought to be fortuitous, due to the different stressing of the specimens. The fatigue lives of the crowned disc tests gave longer lives than the gears for equivalent stresses. As the slide-roll ratio was increased towards that of the highest point of single tooth contact (?0.26) the correlation improved. At a slide-roll ratio of ?0.28 on the disc specimens, where the correlation of pitting life might have been expected to be the best, scuffing of the disc occurred, possibly due to the higher temperatures. Several factors thought to be responsible for the difference in lives between gear and disc specimens have been discussed. The roughness and slide-roll ratio have been deemed the most important.     

Morphology,structure and chemistry of extracted diesel soot—Part I: Transmission electron microscopy,Raman spectroscopy,X-ray photoelectron spectroscopy and synchrotron X-ray diffraction study

Inclusion of soot in lubricating oil can result in increased wear and decreased lubricity. In this study we have attempted to gain fundamental insight into the morphology, structure and chemistry of diesel soot. Energy dispersive spectroscopy using TEM suggests interaction between lubrication additives and crankcase soot resulting in the presence of C, Ca, S, P, O and Zn. Synchrotron X-ray diffraction indicates the presence of different sulfates of calcium as well as the presence of amorphous zinc based compounds. Raman spectroscopy and selected area diffraction using TEM indicates that the turbostratic structures of the carbon in both are very similar.