Characteristics of forming presses and recent developments for precision and net shape forming

The trend in metal forming is to produce parts with increased precision and geometric complexity. Thus, research and development is being conducted worldwide to develop presses and tooling for near-net and net shape forming of difficult-to-form components. As a result, presses with increased precision and multi-action tooling are being used routinely by advanced companies around the world. This paper will discuss the interactions between press characteristics and part production in precision forming and review some of the new press and tooling designs recently developed by various domestic and foreign manufacturers.     

Estimating the quality of process yield by fuzzy sets and systems

Fuzzy grading is a multi-class problem, and is used for grading the product according to the degree of fitness for use, customer acceptance or commercial value. In this respect, the production system requires intelligent adjustments. Fuzzy set theory has a variety of applications in different fields. The most fruitful applications are in the field of modeling and control of production systems. Fuzzy logic may be used to control the key quality parameters, grade product quality to reduce the variations and adjust to the specification limits.Fuzzy grading expresses the quality level of product by membership degrees in which belonging or not-belonging to a quality set is gradual. Similarly, the quality control charts are also focused on the reduction of variability and grading the key quality characteristics. The control limits are used to establish the natural spread or range of process so the controller will not signal changes in the process until the natural limits are exceeded. However, there is a logical inconsistency in control chart approaches, due to their crisp grading nature which are expressed as either conforming (good) or nonconforming (poor) to specifications. In this study, a new fuzzy grading approach was developed based on a fuzzy expert system. The outcomes of the fuzzy grading system were clearly proven to be more vigorous and flexible than the crisp control methods.     

Process Modeling for Precision Forming of Discrete Parts – State of the Technology and Critical Issues

This paper presents an overview on the application of FE simulation as a virtual manufacturing tool in designing manufacturing processes for precision parts. The processes discussed include forging, sheet metal forming and hydroforming. Determination of reliable input parameters to simulate a process is a key element in successful application of process simulation for process design in all the mentioned areas. These issues are discussed in detail. Practical examples of application of FE simulation are presented for improvement of the existing metal forming process and/or designing new metal forming process for manufacturing discrete precision parts in forging, sheet metal forming and hydroforming.     

FLOW STRESS DATA FOR FINITE ELEMENT SIMULATION IN METAL CUTTING: A PROGRESS REPORT ON MADAMS

To obtain reliable results from Finite Element (FE) simulation of machining processes, it is necessary to have as input the properties of the workpiece and tool materials as well as the characteristics of the tool/chip interface. These input parameters include physical and thermal data, friction and heat transfer, and most importantly the flow stress of the workpiece material under high strain, strain rate and temperature conditions that exist during the process. This paper presents a brief review of FE simulation of machining processes, a review of the approaches used to determine the flow stress at high deformation rate, and the examples of different constitutive equations used to represent such flow stress data. A material property database (MADAMS) has been developed and provides useful information to conduct simulations of machining processes. The main objectives of the material database are to assist researchers in areas of machining analysis and material modeling and to promote collaboration between various international research groups.     

Investigation of Spin State Transition of [FeC<Subscript>17</Subscript>H<Subscript>31</Subscript>N<Subscript>7</Subscript>]<Superscript>2+</Superscript> Compound by Using the Density Functional Method

The symmetry of the [FeC₁₇H₃₁N₇]²⁺ novel compound is close to octahedral which has spin crossover properties (SCO). In this study, geometrical optimization, IR vibration frequencies, and HOMO-LUMO energy differences at various temperatures of the compound were calculated by DFT. It is realised that the computed splitting energies and splitting free enthalpies together with the mole fraction of HS state are compatible with the experiment.     

FORECASTING OF MULTIVARIATE PERIODIC AUTOREGRESSIVE MOVING-AVERAGE PROCESSES

Abstract. Minimum mean square error forecasting of multivariate autoregressive moving-average processes with periodically varying parameters and orders is considered. General expressions are obtained for the forecasts, their errors and the covariance matrices of the forecast errors. Recursive evaluations of these quantities are shown to follow from the conditional expectation approach. Prediction ellipsoids and intervals for future values of the process are given. Update equations for the forecasts are obtained. The general results are illustrated and verified for a particular case of the process. A simulated example is given.     

Process modeling in machining. Part II: validation and applications of the determined flow stress data

The flow stress data, determined in Part I of the present study, is validated by using it as an input to the finite element method and analytical based computer programs to predict process variables in metal cutting. The predicted process variables in two-dimensional orthogonal turning and three-dimensional face milling operations, are compared with the published experimental data and the results of experiments conducted in the present work. The majority of the predictions have been found to be in reasonable agreement with the measured results. The comparisons have been discussed and, in the case of unsatisfactory agreement, the reasons for inaccurate predictions are reviewed. The flow stress data of AISI H13 tool steel (46 HRC), determined in Part I is used in this study to investigate the influence of edge preparation on forces in the cutting and feed directions, tool stresses and cutting temperatures. It has been concluded that the hone-radius edge with a hone radius of 0.1 mm provides the maximum resistance to chipping and the chamfered edge (20°×0.1 mm) has the minimum flank and crater wears for the conditions used in the present study.     

Determination of forces in high speed blanking using FEM and experiments

The increasing demand for micro-formed and stamped parts such as connectors in the electronic industry is forcing manufacturers to push the speed limit of conventional press technologies to improve throughput. Designing dies/tooling for higher speeds and obtaining extended tool life requires a thorough understanding of the process. This paper discusses an experimental study of the interaction between punch, stripper plate and sheet material at various blanking velocities up to 1600 mm/s. The effect of velocity on punching force is also studied. A methodology to obtain high strain and strain rate dependent material flow stress data using blanking test and finite element modelling is presented.     

Evaluation of stamping lubricants at various temperature levels using the ironing test

Lubricants are employed in stamping operations in order to (a) improve the material flow into the die cavity, (b) reduce wear and galling in the die and (c) obtain good surface finish of the part. Process conditions such as high temperatures and pressures could cause the lubricant to fail, thus resulting in galling or tearing of the part, damage to the tooling, and lost production. Therefore, selection of an appropriate lubricant based on the process conditions is important in the stamping industry. Several benchmark tests emulating stamping operations have been developed and are used to evaluate the performance of candidate lubricants. The major drawback of most of these tests is their inability to emulate high contact pressures and sliding velocities, which are crucial parameters for lubricity, especially in the case of high-speed progressive or transfer die operations involving ironing. Moreover, most of these tests are conducted at room temperature, while in reality; the process temperature can reach as high as 200 °C. The ironing tribotest developed at the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) induces high contact pressures and temperatures, thus emulating the conditions in a production environment. Application of the test to screen candidate lubricants for stamping operations involving the ironing process is discussed in this paper.