Haydar Livatyali

Prediction and elimination of springback in straight flanging using computer-aided design methods: Part 2: FEM predictions and tool design

Abstract Part 1 of this two-part paper presents the laboratory experiments on straight flanging, in which the influence of process variables, such as die shoulder radius, punch-die clearance, punch nose radius, pad force and material properties were discussed. This second part summarizes the FEM predictions for flanging and compares these results with some experimental data. Furthermore, flanging with coining to reduce springback has been investigated and evaluated by FEM for better dimensional control in flanging and hemming processes.

Prediction and elimination of springback in straight flanging using computer aided design methods: Part 1. Experimental investigations

A computer aided design method for straight flanging using finite element method is presented. The predictions have been validated with some laboratory experiments, and this method was applied on a specific type of flanging in which the edge is coined at the end of the operation. The experiments included die corner radius, punch–die clearance, punch nose radius, pad force and material type as the main variables. Some selected cases from the experiments were simulated using two commercial finite element programs: DEFORM™ and ABAQUSTM, and the results were compared with the experiments and the sources of error were discussed. Next, flanging with coining was investigated as a method to eliminate springback and to improve part quality. This first paper in a two-part series presents the experimental investigations on the effect of process variables on springback in straight flanging process. The second paper covers the finite element analysis of flanging, and evaluates the influence of flanging with coining on pre-hemming and hemming processes.

Improvement of hem quality by optimizing flanging and pre-hemming operations using computer aided die design

Abstract Flanging and hemming of straight edge-flat surface (plane strain) aluminum killed-draw quality steel was investigated restricting the study to the radius flat hem with an inner sheet. The major process parameters in straight edge hemming were determined and relations between them and some forming defects were established. Among these parameters were flanging die corner radius, pre-hem path, pre-hem stroke and final hemming force. Possible process and tool design modifications, which may lead to quality improvements in hemming were tested experimentally and using FEM. The commercial finite element program DEFORM was used to simulate the flanging and hemming operations including springback, and the predictions were compared with limited experimental results. Results of the experiments and simulations were summarized in the form of trend-lines for the use of process and die designers.

Experimental investigation of forming defects in flat surface–convex edge hemming

Abstract In this paper, flanging and convex edge hemming of aluminum killed draw quality steel was investigated. The investigation was focused on the study of the radius flat hem with an inner sheet. The objective of the study was to determine the influences of the contour radius and flange length on wrinkling, hem-out, roll-in (creep or creepage) and roll-out (growing). A set of complete factorial experiments was designed and conducted in order to determine the effects of the selected experimental parameters. Experimentation provided a design map of failure zones for wrinkling and hem-out as well as fundamental knowledge of important factors in convex edge hemming and factor interactions during different process stages. Results of the experiments were summarized for the use of process and die designers. A future experimental study will focus on pure roll and warp without any wrinkling and hem-out.

Computer aided die design of straight flanging using approximate numerical analysis

Abstract Prediction of springback and minimum bending radius without failure are the main issues in die design for straight flanging process. The previously developed analytical and numerical models for sheet bending were observed to be inaccurate for straight flanging with relatively small bending radii. Finite element analysis with 2D models can be used to predict springback, bendability and tool loads accurately, but the analysis can take several hours, and pre- and post-processing are even more time consuming. Alternatively, in this paper, this problem is solved using advanced bending theory, implementing the geometric details of the straight flanging process to a mathematical model and computerized numerical analysis. The proposed method predicts springback and tool loads, particularly the minimum pad force necessary to prevent pad lift by dividing the deformation zone into three segments as pure elastic deflection without contact, elastic–plastic bending without contact and elastic–plastic bending in full contact with the die shoulder. The shift in neutral radius is modeled using an iterative procedure and taking the tool pressure and local thinning into account. The results are compared with limited experimental data as well as finite element simulations.

Investigation of crack formation on the Galvalume coating of roll formed roof panels

Abstract Roll forming of pre-coated and pre-painted sheet metal is a common industrial practice. Cracking of metal coating and/or paint at the sharp edges need to be considered and eliminated during the roll design phase of a new product. The sheet deformation in the lateral (transverse) direction during roll forming is a combination of pure bending and stretching in a step-by-step gradual deformation. Closed form equations of simple bending cannot model this type of deformation. Moreover, due to the free edges, approximations for draw bending cannot be used either, and thus the use of finite element analysis is necessary. In this paper, an investigation on roll forming of pre-coated and pre-painted roof panels have been conducted to eliminate the reported crack formation on the coating and paint. Finite element method was used to test various roll designs, and optimal roll geometry was proposed.

Design of Threaded Fatigue Test Specimen for Machining

Design and machining of the fatigue test specimens have significant effects on the duration and reliability of fatigue test. Fatigue test specimens essentially consist of three parts: the center or critical test section, which is the region where required conditions are simulated as closely as possible, and the two ends, which serve to transfer the load from the grips to the center section. When high strength materials are used for a complex geometry, such as a thread need to be tested, design and manufacturing of the specimens become more influential on the reliability and duration of the tests. Threaded fatigue test specimens were designed, machined, and tested in a four-point rotary bending fatigue testing machine. An innovative threaded fatigue test specimen that consistently fails at the critical test section was designed, machined, and tested successfully to give the required fatigue notch factor. Because of full scale fatigue testing with threaded parts is very expensive and sometimes dangerous, evaluated threaded fatigue specimen can be used in fatigue testing and it reduces duration of the experiment more than 60% for machined threaded specimens.

PREDICTION AND EXPERIMENTAL ANALYSIS OF CUTTING FORCES DURING MACHINING OF PRECISION EXTERNAL THREADS

External thread cutting is a complex 3-D process in which the cutting conditions vary over the thread cutter profile. It is accepted as a mature; however, heavily experience based technology and there are few academic work published. Determining the cutting forces during machining is crucial to explain formation of the surface layer, residual stresses, selection of the most appropriate machine tool and optimizing the process. This investigation is an attempt to predict thread cutting forces by dividing the thread chip into three parts, one thread root and two side faces. Variation of the cutting parameters including the shear angle, mean cutting temperature and friction force on the flank face of the tool along the thread tool root and sides are determined. In the thread root and sides, chip compression ratios for the V-shaped single piece and separately cut chip zones are measured and cutting forces are calculated and compared for precision metric thread cutting on a SAE 4340 steel bar.