G. Hussain

Forming Parameters and Forming Defects in Incremental Forming of an Aluminum Sheet: Correlation, Empirical Modeling, and Optimization: Part A

Single point incremental forming (SPIF) has potential to be employed commercially and can replace conventional sheet stamping process if its defects, such as poor geometrical accuracy, can be overcome. In the present article, three forming defects, namely, squeezed out wall formation, corner fold corner, and bulge height, are introduced. It is demonstrated that the formation of these defects has adverse effect on the formability in SPIF. In order to eliminate, if possible, the formation of these defects, the potential effect of operating (i.e., tool radius and step size), geometrical (i.e., wall angle), and material (i.e., sheet thickness and material property) parameters and their interaction on the defect formation and growth has been quantitatively investigated by employing response surface design method. With the help of proposed empirical models, the investigated defects can be overcome through parametric optimization.

Guidelines for Tool-Size Selection for Single-Point Incremental Forming of an Aerospace Alloy

Single-point incremental forming (SPIF) is relatively a novel sheet forming process to produce small lots with low cost. In this article, guidelines for tool size selection for SPIF of an aerospace grade alloy (AA-2024) are presented. The role of tool size, with respect to sheet thickness employed, on the formability in SPIF (i.e., spifability) is clarified. The response surface method is employed in order to study the significance of sheet thickness (t o) and tool radius (r) on the spifability. The results of analysis of variance (ANOVA) show that the sheet thickness and tool radius are not significant individually, however, a strong interaction between these parameters exists. Moreover, for a particular sheet thickness, there exists only one r/t o value at which the spifability can be maximized under a given set of conditions. Furthermore, for a given sheet thickness, if a tool with radius lesser than a particular value is used (i.e., r/t o < 2) the material squeezes out from the tool/sheet interface. And, such a condition adversely affects the material spifability. FEA using LS-DYNA has also been carried out.

A rule-based system for trade-off among energy consumption, tool life, and productivity in machining process

With ever-increasing understanding of environmental and societal concerns, the focus of manufacturing industries, worldwide, is fast changing from mere profit-making to ensuring sustainability. The companies are striving hard to make their manufacturing processes more environment-friendly, in addition to being cost effective and time- and resource-efficient. The paper presents an experimental investigation and an application of fuzzy modeling for trade-off among energy consumption, tool life, and productivity of a metal cutting (machining) process. A total of 54 grooving experiments are performed under various pre-determined combinations of the workpiece material hardness, cutting speed, cutting feed, and width of cut. The respective measurements are taken for tool damage, energy consumed, and cutting and feed forces. A fuzzy rule-based system is developed that consists of two modules: optimization and prediction. The former suggests the most suitable settings for the cutting parameters that would lead to accomplishment of various combinations of the objectives related to energy consumption, tool life, and machining productivity. The prediction module works out the predicted values of all the responses based on the finalized values of the four input parameters.

The pillowing tendency of materials in single-point incremental forming: Experimental and finite element analyses

The pillow is a defect that adversely affects the geometrical accuracy as well as the formability in single-point incremental forming. With a main objective to control this defect, the effects of mechanical properties of material on pillowing are examined in this work. To identify the mechanical property that significantly affects pillowing, single-point incremental forming tests are conducted using a variety of materials (i.e. 11). It is found that a property (i.e. area reduction at tensile fracture) that controls the formability of a material in single-point incremental forming does not have any significant effect on its pillowing tendency. Interestingly, hardening exponent (i.e. a property that has controlling influence on the stretch-ability of material) appears to be the most influential property that determines the pillowing tendency of sheet metals in single-point incremental forming. Furthermore, the pillowing tendency of a material decreases with the decrease in this particular property. This, according to finite element analysis, occurs because strain localization around the tool/sheet contact correspondingly increases. To select and rank materials with respect to the pillowing behavior, a formula describing the property–pillowing relationship is proposed. As a secondary objective, the correlation between pillowing and forming depth is also investigated in this work. It is shown that initially the pillow progresses as the forming depth increases. However, after forming has been carried out to a certain depth, the pillow begins to regress, most likely due to strain hardening of sheet metal. In conclusion, it is suggested to lower the hardening exponent of sheet metals in order to control pillowing in single-point incremental forming.

High-Speed Incremental Forming Process: A Trade-Off Between Formability and Time Efficiency

Making use of “optimal experimental design,” the paper attempts to investigate individual and interactive effects of predictor parameters, namely tool size, pitch size, feed rate, spindle rotational speed, and blank thickness, on sheet formability in single point incremental forming (SPIF) process. For the sake of precision, a novel sensor system was developed and employed to detect crack as it initiates on SPIF test specimens. A novel benchmark for formability in SPIF was established by addressing normal strain along sheet thickness, maximum attainable forming angle, and the rate of variation in forming angle. The process was finally optimized in terms of maximum achievable formability and minimum processing time. Accordingly, high-speed forming (with forming speed of at least 5000 mm/min) was realized to be perfectly viable, whereas the sheet formability remains quite satisfactory (over 90% of the maximum value). The key role of high spindle speed (up to 3000 rpm) was also highlighted in this regard.

Forming Parameters and Forming Defects in Incremental Forming Process: Part B

Single point incremental forming (SPIF), at present, is suffering from defects. With an aim to enhance understanding on their development to control them methodically, FE analyses by varying four parameters are performed in the present study. It is found that, while deforming sheet, stresses develop in the bottom of part. The SPIF defects are in fact outgrowth of these stresses. More precisely, the ratio of vertical- to horizontal-stress is a principal factor that controls (or causes) defects. The development of wall defect depends on the stress ratio in the tool/blank contact (zone A), while that of pillow defect depends on the stress ratio both in the tool/blank contact (zone A) as well as in the center of parts bottom (zone B). Moreover, the magnitude and nature (tension or compression) of the stress ratio, subject to the type of parameter, varies as a parameter is varied. These variations in the stress state in turn affect the defects growth (or size). It is concluded that the stress ratio both in zone A and in zone B needs to be simultaneously controlled so as to overcome the SPIF defects.

SPIF of Cu/Steel Clad Sheet: Annealing Effect on Bond Force and Formability

Clad sheet metals offer a better combination of different properties than a monolithic sheet does. In the present study, the formability of a cold bonded Cu/Steel clad sheet was investigated in single point incremental forming (SPIF). In order to relieve deformation stresses, the sheet was annealed over a range of temperature and time. It was found that the sheet ductility increases as the annealing temperature increases, and as a result the formability increases. On the other hand, the bond force at the interface of constituent sheets was observed to decrease with the increasing of temperature. Moreover, the annealing time was found to have no significant effect both on the formability and bond force. Therefore, performing annealing for low times can satisfactorily serve the purpose. The most appropriate annealing temperature for maximizing the formability was 700°C, because higher temperature was noticed to cause severe delamination of Cu layer, thus deteriorating the clad sheet. As a promising aspect of the study, there was no delamination of laminates during forming till the maximum achievable angle. The correlations presented herein study can act as guideline for the users. This study is the first report of its nature.

Machinability comparison of AISI 4340 and Ti-6Al-4V under cryogenic and hybrid cooling environments: A knowledge engineering approach

Efficient removal of heat from the deformation zones in machining of difficult-to-cut materials is vital for attaining viability with respect to cost and productivity. The recently embraced heat removal and lubrication methods include applications of cryogenic fluids and minimum quantity of lubrication. This article presents an experimental investigation, complemented with a fuzzy modeling approach, for comparing the efficacies of using various combinations of CO2 snow and minimum quantity of lubrication in machining two tempers each of AISI 4340 and Ti-6Al-4V. In addition, cutting speed and feed rate are also included as predictor parameters, and their effects on tool damage, machining forces, and specific cutting energy consumption are evaluated. A total of 144 experimental runs are performed for developing the fuzzy knowledge–based model, and additional 20 experiments are conducted for testing its prediction accuracy. The model is also made capable of suggesting optimal settings of the cutting parameters and the most appropriate choice of cooling against various combinations of the objectives. In a nutshell, the cooling option of applying CO2 snow at the rake and flank faces of the tool proved beneficial for machining the titanium alloy while the option of using CO2 snow at the flank face and minimum quantity of lubrication at the rake face outshone the others in the case of the alloy steel. This article claims novelty with regard to machinability comparison of AISI 4340 and Ti-6Al-4V, application of cryogenic cooling to machining of hardened steels, investigation of hybrid cooling (CO2 snow plus minimum quantity of lubrication), and intelligent modeling of cryogenic machining of AISI 4340 and Ti-6Al-4V combined.

Experimental investigations on the role of tool size in causing and controlling defects in single point incremental forming process

Single point incremental forming is a cost-effective alternative of conventional stamping process. However, due to inadequate knowledge, the process has not yet been employed on industrial scale. In this study, the role of tool radius in causing and controlling development of defects in single point incremental forming is investigated. Throughout the course of investigations, AA1060 aluminum is used as the experimental material. Initially, a range of tests with tool radius (r) ranging from 1to to 2.35to (where to is sheet thickness) are conducted. It is found that defects, namely, pillow, wall and material-fold, develop in a part if forming is performed with an unduly small tool (i.e. r<2to). Furthermore, as a result of these defects, the part accuracy and sheet formability reduce. In the second stage, the effect of selected process parameters (i.e. feed rate, yield strength, wall angle, sheet thickness and step size) on the growth (or size) of aforesaid defects is examined. The test results reveal that the investigated parameters, excluding feed rate, are significant. In order to prevent inappropriate selection of tool and thus to simultaneously control all the defects, a least-radius limit is defined (i.e. rl), and as a last stage of investigations, its correlation with the short listed significant parameters is determined. To do so, a comprehensive design of experiments is performed. According to the design of experiment findings, the radius limit rl varies as a process parameter is varied. Moreover, this variation effect of parameters is highly interactive. Finally, an empirical formula to predict the said radius limit is proposed and its correctness is verified.

Force Variations with Defects and a Force-based Strategy to Control Defects in SPIF

The control of defects and forces is, respectively, necessary to produce robust components and to preserve machine tool and energy. In the present work, the variations in forces with the evolution of various SPIF (single point incremental forming) defects are studied by employing the pyramid geometry. It is found that the forming force increases as the size of pillow and wall defects increases, and contrarily decreases as the size of corner-fold increases. Further, to carry out defect-free forming, the corner requires more force than the straight-wall of pyramid (i.e., F cr > F sw). This fact appears in the form of spikes corresponding to corner location in the force curve. Therefore, online monitoring of the force curve is proposed as a strategy to control defects in SPIF. Finally, following the condition F cr > F sw, force models describing the defect–force–parameter relationship are developed. These models will help the users to simultaneously predict and optimize the force as well as defects.