Joseph P. Domblesky

A parametric study of process parameters in external thread rolling

Abstract This paper summarizes the results of a numerical study conducted to analyze the effect of selected process parameters on material flow and thread profile in external thread rolling of large diameter blanks. Based on the previous work where a plane strain model was found to provide a reasonable approximation of the thread rolling process, the effect of varying thread form, friction factor, flow stress, and blank diameter on effective strain and thread height was analyzed using the finite element code DEFORM. The results of the study show that for the range of conditions considered, that blank diameter had little effect on the as-rolled thread while flow stress (K and n), friction factor, and thread form all had significant impact on effective strain at the thread root and crest and the achievable thread height. While the rate of work hardening was found to have an effect on the crest profile, the results indicate that it is not the primary factor responsible for seam formation in rolled threads.

Development and validation of a finite-element model for multiple-pass radial forging

Abstract This paper includes a discussion of the techniques which were used to model multiple-pass radial forging using the finite-element method. The model was used to predict the thermomechanical history of an Alloy 718 workpiece during billet conversion. The techniques which were developed and used to measure the strain and temperature profiles in the forged billet in order to validate the finite-element model are also presented. Results of the model validation show that an axisymmetric approximation of the radial forging process provides reasonable predictions of the billets thermomechanical history whilst yielding acceptable simulation times.

Grain Size Modeling and Optimization of Rotary Forged Alloy 718

The study presented describes the simulation procedure and methodology used to develop two models for predicting recrystallized grain size in Alloy 718 billet. To simulate multiple pass forging of billet, controlled, high temperature compression testing was used to apply alternate deformation and dwell cycles to Alloy 718 specimens. Grain size obtained by simulation was found to be in excellent agreement with grain size from forged billet when cooling rate was included. The study also revealed that strain per pass and forging temperature were the predominant factors in controlling the recrystallized grain size. Both models were found to accurately predict the recrystallized grain size obtained by compression tests performed at super-solvus temperatures.

Investigation of the Scanning Microarc Oxidation Process

Scanning microarc oxidation (SMAO) is a coating process which is based on conventional microarc oxidation (MAO). The key difference is that deposition in SMAO is achieved by using a stainless steel nozzle to spray an electrolyte stream on the substrate surface as opposed to immersing the workpiece in an electrolyzer. In the present study, SMAO discharge characteristics, coating morphology, and properties are analyzed and compared to results obtained from MAO under similar conditions. Results show that MAO and SMAO have comparable spark and microarc lifetimes and sizes, though significant differences in incubation time and discharge distribution were evident. Results also showed that the voltage and current density for MAO and SMAO demonstrate similar behavior but have markedly different transient and steady-state values. Results obtained from coating A356 aluminum sheet show that oxide thickness and growth rate in SMAO are strongly dependent on interelectrode spacing and travel speed. Analysis of the SMAO coating morphology and structure showed that a denser and slightly harder layer was deposited in comparison to MAO and is attributed to reduced porosity and increased formation of α-Al2O3. Preliminary results indicate that SMAO represents a viable process for coating of aluminum surfaces.

Predicting Distortion in Butt Welded Plates Using an Equivalent Plane Stress Representation Based on Inherent Shrinkage Volume

Due to the adverse effect that distortion has on assembly fit-up and fabrication costs in welded structures, the ability to predict dimensional changes resulting from joining represents an important engineering concern. While distortion can be analyzed using a full 3D finite element (FE) model, this often proves to be computationally expensive for medium and large structures. In comparison, a 2D FE model can significantly reduce the time and effort needed to analyze distortion though such analyses often have reduced accuracy. To address these issues, a plane stress modeling approach based on inherent shrinkage volume is proposed. By inversing the plastic shrinkage zone geometry, an equivalent plane stress representation and eccentric loading condition can be developed and used to predict distortion in butt welded plates. The model was validated using deflection data obtained from welded plates and found to provide good accuracy over the range of thicknesses considered. Results obtained from welding of a large municipal containment tank are also presented and further confirm the utility of the method.

Study of Scanning Micro-arc Oxidation and Coating Development

Micro-arc oxidation (MAO) continues to be the focus of numerous investigations, whereas relatively few studies have considered scanning micro-arc oxidation (SMAO). In the present work, an experimental study was performed using stationary and moving electrodes to investigate coating development in SMAO and discern the effect of key process parameters. Examination of oxide deposits made on A356 aluminum show that coating thickness and growth rate are inversely related to inter-electrode spacing and travel speed. An evaluation of SMAO deposits made by stationary and moving nozzles revealed that coating thickness profiles follow a Gaussian distribution due to the electrolyte flow field in the impingement zone. Hardness surveys and scanning electron microscope analysis of SMAO coatings revealed that micro-hardness distributions and cross-sectional morphology are similar to MAO for a stationary nozzle but that a denser outer layer develops when a moving nozzle is used. This is attributed to a high density of discharge occurring in micropores of the oxide film and remelting which results from the moving electrolyte column. Analysis of voltage–current characteristic curves shows that the resistance of the electrolyte column is essentially linear over the range considered and results indicate that it can be modeled as a variable length resistor. While further testing is needed, results confirm that SMAO is suitable for coating large, planar parts and for repairing worn surfaces.

A Cutting Rate Model for Reciprocating Sawing

In the present paper, the reciprocating sawing process is analyzed, and a model for linear cutting rate is developed. The resulting model is based on an orthogonal approximation of cutting at individual teeth and accounts for elastic and plastic indentation. Cutting rates obtained from an instrumented sawing fixture show good agreement with predicted results for the range of conditions considered. Cutting rate was found to be proportional to thrust force and reciprocating rate though this behavior is influenced by edge radius and flow stress at higher levels. While it was not possible to decouple the effect of pitch and blade set, it was confirmed that coarser pitch blades do provide higher cutting rates.

Investigation of Welded Preforms for Use in Forging

While laser-welded preforms provide significant advantages in sheet metal stamping, similar technology has not been developed for forging. In the present paper, the case for solid-state welded preforms in forging is considered and the workability and mechanical properties of selected base metal combinations are analyzed. Results demonstrate that welded preforms have adequate workability based on upsetting and side pressing tests though flow tends to be non-uniform in bimetal preforms. Tensile tests indicate that the mechanical properties of side pressed preforms are equivalent to those of annealed base metal pieces. While work is ongoing to develop their use, results indicate that friction-welded preforms have potential for use in forging.

Residual Stress Reduction in Single Pass Welds Using Parallel Line Reheating

Current postweld heat treatment (PWHT) methods rely mainly on static thermal sources or line heating using dispersed beams which require significant capital investment and often pose limits on weldment size. In the current study, an alternative PWHT method based on line heating is presented and analyzed. The method, which is intended to perform low temperature stress relief, employs parallel oxyacetylene torches to induce a tensile stress in the vicinity of the weld toe. X-ray diffraction (XRD) measurements taken from bead-on-plate (BOP) welds made using ASTM A572-50 showed a 37% decrease in the peak longitudinal stress after parallel line reheating was performed. A corresponding reduction in the stress gradient on the plate surface was also observed. Welding and reheating were also modeled in sysweld to assess how torch placement affected the longitudinal stress distribution and an optimum offset was identified for the 8-mm plate thickness used. Analysis of the thermomechanical history in the vicinity of the weld toe indicates that a tensile stress is superposed during reheating and is concurrent with the reduction in the peak longitudinal stress.

A Prediction of Total Cutting Time When Crosscutting Rounds, Pipe, and Rectangular Bar With a Portable Bandsaw

Portable bandsaws are gaining in popularity for their use on jobsites to efficiently crosscut structural materials such as bar, pipe, angle, and channel. Some of the increased popularity is also due to the recent introduction of lithium ion batteries, which has further improved the portability of bandsaws by making them cordless. However, with cordless portable bandsaws, knowledge of cutting rates becomes more important as battery runtime limits productivity. Unlike industrial bandsaws that typically have feed rate control, portable bandsaws use operator applied pressure and gravity to control feed rate. While some research has highlighted the cutting mechanics of bandsaws and related wear processes, there is a lack of progress in the area of predicting total cutting time as a function of sawing parameters, such as applied thrust force, blade speed, workpiece material properties, and geometry of the cross section. This paper presents research that was conducted to develop and experimentally verify a mechanistic model to predict cutting rates of various cross sections with a gravity fed portable bandsaw. The model was used to predict the time required to cut steel tube for several conditions of thrust force and blade speed. Model predictions were verified by experiment to a reasonable degree of accuracy. The model serves as the algorithm for a software application to assist contractors in developing jobsite estimates of time and material.© 2012 ASME