Properties Of Workpiece Research Articles

Modeling and experimental validation of the force–surface roughness relation for smoothing burnishing with a spherical tool

The effect of a smoothing-burnishing process strongly depends on the initial roughness of a workpiece. This factor has not been considered by existing classical models of the processes. In this paper, assuming a model of burnishing with a spherical tool, in the form of wedges of surface roughness deformed with a force normal to the base line, expressions describing the relation between burnishing force and displacement of the tops of surface asperities is derived. The expression includes the effect of mechanical properties of the workpiece material, geometry of contact of the tool with the workpiece and the roughness of the burnished surface. Using the derived expressions it is possible to determine an optimum burnishing force. This has been verified experimentally. The experiment made it possible to demonstrate that the optimum burnishing force of the ground 42CrMo4 steel samples was 11–15 daN and that the burnishing effect depends a lot not only on the mechanical properties of the machined workpiece and the geometry of the contact area between the tool and the workpiece but also on the initial surface roughness. The applied optimum burnishing force, calculated on the basis of the theoretical, assumed model-derived dependences, is 12–13 daN. The above proves the validity of the adopted assumptions and the formulas worked out.

Numerical Simulation of Pressure Influence on Workpiece Properties during Thixoforging

Numerical simulation of pressure influence on the relative densities of both solid and hollow cylindrical workpieces during Thixoforging was carried out by using ANSYS software. The results showed that there was a big difference in relative density between different points within the workpiece during Thixoforging with the use of a single punch. Therefore, partial feeding with the help of assembly punches was proposed to improve workpiece density uniformity and properties, and the effectiveness of this approach was well-demonstrated by numerical simulation.

A Study on the Surface Characteristics with the Vibration Factor in the Micro-Machine

In conventional machining, cutting conditions such as cutting speed, feed rate, and depth of the cut have great influence on the surface roughness. In micro machining, however, the surface shape is affected by not only the machining parameters mentioned earlier but also tool stiffness, system stability, and workpiece properties caused by the miniatured structure and cutting tool. Especially, in a micro-machine system, the difference between the cutting forces in the recursive cuts introduces the vibration easily. A high spindle causes instability of the system, increases the temperature in the cutting process, and also changes the tool’s shape. This study introduces a method to predict the surface shape of the workpiece based on the machining conditions in micro milling. The micro-milled surfaces in different machining conditions are predicted by a computer simulation including the vibration model and the simulated results show good agreement with the experimental results.

Material Flow Curve Influence on Macroscopic Residual Stresses in the Workpiece Bottom in High-Pressure Sheet Metal Forming

The further development of innovative forming processes like sheet metal hydroforming is only possible with the help of detailed knowledge about the workpiece properties and their formation depending on the process strategy. Up to now, the knowledge about the formation of macroscopic residual stresses in high-pressure sheet metal forming (HBU), regarding the influence of the sheet material properties, is still insufficient. The characteristics of the specific forming procedure HBU lead to specific stress and strain gradients in the sheet cross-section, and therefore lead to a characteristic distribution of the induced macroscopic residual stresses, particularly in the workpiece bottom zone. This paper decribes the investigations on the influence of the sheet material flow curve on the macroscopic residual stress distribution in the workpiece bottom.

INFLUENCE OF MATERIAL REMOVAL ON THE DYNAMIC BEHAVIOR OF THIN-WALLED STRUCTURES IN PERIPHERAL MILLING

Machining is a material removal process that alters the dynamic properties during machining operations. The peripheral milling of a thin-walled structure generates vibration of the workpiece and this influences the quality of the machined surface. A reduction of tool life and spindle life can also be experienced when machining is subjected to vibration. In this paper, the linearized stability lobes theory allows us to determine critical and optimal cutting conditions for which vibration is not apparent in the milling of thin-walled workpieces. The evolution of the mechanical parameters of the cutting tool, machine tool and workpiece during the milling operation are not taken into account. The critical and optimal cutting conditions depend on dynamic properties of the workpiece. It is illustrated how the stability lobes theory is used to evaluate the variation of the dynamic properties of the thin-walled workpiece. We use both modal measurement and finite element method to establish a 3D representation of stability lobes. The 3D representation allows us to identify spindle speed values at which the variation of spindle speed is initiated to improve the surface finish of the workpiece.

Evaluation of surface roughness in laser-assisted machining of aluminum oxide ceramics with Taguchi method

This paper evaluates laser-assisted machining (LAM) as an economically viable process for manufacturing precision aluminum oxide ceramic parts. Because it is locally heated by an intense laser source prior to material removal, LAM leads to higher material removal rates, as well as improved control of workpiece properties and geometry. To assess the feasibility of the LAM process and better understand its governing physical phenomena, experiments were conducted to obtain different measures of surface roughness for Al 2O 3 workpieces machined by laser-assisted turning using a Nd:YAG laser. The experimental results were analyzed using the Taguchi method, which facilitated identification of optimum machining conditions. The findings indicate that rotational speed, with a contribution percentage as high as 42.68%, had the most dominant effect on LAM system performance, followed by feed, depth of cut, and pulsed frequency. LAM's most important advantage is its ability to produce much better workpiece surface quality than does conventional machining, together with larger material removal rates (MRR) and moderate tool wear.

Modeling and simulation of load heating in heat treatment furnaces

The simulation of heat transfer in heat treatment furnace is of great importance for the prediction and control of the ultimate microstructure and properties of workpieces. In this paper a hybrid method based on numerical simulation and analytical equations are proposed to calculate the radiation, convection and conduction heat transfers in heat treatment processes. In the radiation model view factor between the furnace and workpieces, among workpieces are calculated by the exposed surface area over the total surface area. In the conduction model workpieces are classified into lumped capacitance and massive objects. And workpieces are further classified into three basic shapes: sphere, cylinder and sheet for the application of Fourier differential equation. Natural and forced convections are solved by analytical algorithms for aligned and staggered load patterns. Other thermal terms such as gross heat input, heat storage in the furnace, heat storage in load, heat loss from the walls and openings, shell cooling and so on, are included in the furnace model. The optimization of workpiece loading and the thermal schedule are achieved. Two case studies are given for the validation of the models.

Computer Aided Nonlinear Analysis of Machine Tool Vibrations and a Developed Computer Software

A computer program package is developed by using Visual Basic programming language in order to analyze one and two degree of freedom of machine tool chatter vibrations. The developed software accepts the machine tool properties, work piece properties and cutting parameters as inputs, calculates the time responses of selected cutting parameters and displays the results in graphical form. Hence the appropriate values of cutting parameters can be predicted for chatter-free operation of the machine tool.

Properties of Large-Scale Structure Workpieces in High-Pressure Sheet Metal Forming of Tailor Rolled Blanks

In order to manufacture components optimised in regard to lightweight construction, the use of innovative forming processes like high-pressure sheet metal forming (HBU) in combination with the use of tailor rolled blanks (TRB) as innovative semi-finished material is a promising solution. Fundamental investigations on the HBU of TRB have been carried out in a joint research project at the Institute of Forming Technology and Lightweight Construction (IUL), University of Dortmund, and the Institute of Metal Forming (IBF), RWTH Aachen. The experiments performed with cylindrical parts have provided basic knowledge on the sheet material flow and resulting part properties. To achieve sufficient process reliability, a non-adjustable as well as an adjustable seal system have been tested and proved to be suitable solutions, depending on thickness ratio and thickness gradient within the TRB. In order to demonstrate the lightweight potential of this process chain, a forming tool for an automotive body structure has been designed and tested. The experiments have shown that this large-scale structure can well be manufactured in the HBU process from a TRB.

MEASUREMENT OF HYDROGEN CONTENT IN ELECTRICAL DISCHARGE MACHINED COMPONENTS

ABSTRACT During electric discharge machining (EDM) process, localized high temperature electric discharges occur in the presence of hydrocarbon dielectric such as kerosene. Hydrogen that can get incorporated into the workpiece during the process can dramatically affect the mechanical properties of the machined workpiece. In the present work the hydrogen content in workpieces machined by EDM and electric discharge abrasive drilling (EDAD) have been measured by a relatively new diagnostic technique called Elastic Recoil Detection (ERD), which utilizes He+ ions of mega electron volt energy obtained from a particle accelerator. Workpieces made up of high-speed steel and cemented carbide were machined at different pulse-on-times, and their hydrogen content was measured. From the experiments reported in this paper, it is concluded that hydrogen diffusion takes place in the workpiece surface.

Machinability of 90MnCrV8 steel during high-speed machining

The paper presents some investigation regarding term “machinability” of materials at different cutting conditions. The very same material may shows different behavior when it is cut at for example conventional conditions then at high-speed cutting conditions. The author's intention was to find how would reaction of some steel with, for conventional cutting conditions, good machinability, look like in slightly changed cutting conditions. Investigation was performed on following material – steel 90MnCrV8 – DIN, known as material that has a “good machinability”. Cutting conditions as well as workpiece properties (primarily hardness) were set to enclose transition region from conventional to high-speed machining [Ekinović, Dolinšek]. Machined surface quality has been choose as measure of machinability.

Analysis of Process Parameters and Forming Mechanisms within the Electromagnetic Forming Process

Electromagnetic forming (EMF) is a typical high speed forming process using the energy density of a pulsed magnetic field to form workpieces made of metals with high electrical conductivity like e.g. aluminium. In view of new lightweight constructions, special forming processes like EMF gain importance for the associated materials. For a better understanding of the working mechanisms and the process prediction a coupling of electromagnetical and structure-mechanical models, advanced simulation tools as well as detailed experimental investigations with on-line measurements of the ultra-fast deformation of significant workpiece areas is required. New results of research concerning correlations among workpiece properties, strain rate, and acting magnetic pressure are presented.

Residual Stress Computation in Bent Profiles Using Analytical Approaches

Approaches to the theoretical treatment and calculation of residual stresses without the utilization of experimentally determined values are made for different reasons. First, the experimental determination of residual stresses requires the use of very expensive devices and is very time-consuming. Second, the experimental determination cannot be carried out before the manufacturing or further processing of the parts to be measured has been finished. Therefore, residual stresses are not recognized before the workpieces are actually manufactured and a pre-estimation, still in the design phase, of the effect of these stresses on the workpiece properties is not possible. In this paper, an improved computation method for the determination of residual stresses within bent profiles is presented. The computation algorithm is based on analytical approaches taken from the literature. The residual stress computation is integrated into a semi-analytical process simulation that allows the fast determination of process and product data for the manufacturing of profile structures.

Effects of Material Properties on Elastic Characteristics of Cold Forged Part

The dimension of cold forged part is larger than that of the die cavity. The difference could be originated from the various features, such as the elastic characteristics of die and workpiece, thermal influences, and machine-elasticity. Among these features, elastic behavior of die and workpiece has been considered as the most important element for the precision cold forging. In the present study, the effect of material properties of both workpiece and die on the dimensional precision of forged part was investigated using FE and experimental analyses. Three materials, such as SCM420H, Cu-OFHC and Al6061 alloy, were used to divide the effect of the elastic modulus and flow stress on the dimension specifically. From the results of FEA, the elastic deformation of die was found to be more dominant than that of workpiece. The die expansion depends on the flow stress of workpiece during a loading stage. On the other hand, the die contraction during unloading was affected by both the flow stress and elastic modulus of workpiece. The elastic modulus of workpiece affects the elastic recovery of forged part after ejecting stage.

Analysis of Residual Stresses in High-Pressure Sheet Metal Forming

The further development of innovative forming processes like sheet metal hydroforming is only possible with the help of detailed knowledge about the workpiece properties and their formation depending on the particular process strategy. Up to now, the detailed understanding regarding the formation of residual stresses in hydroforming processes like the high-pressure sheet metal forming (HBU) is insufficient. Therefore, numerical (FEM) and experimental investigations on the residual stresses induced in HBU-formed workpieces have been carried out. The results show that a higher fluid pressure leads to significantly lower residual stresses in addition to an improved accuracy of form and dimensions.

被加工材性質がスピニング成形性に及ぼす影響に関する解析的検討(G04-2 先進加工技術とその評価,G04 機械材料・材料加工)

被加工材性質がスピニング成形性に及ぼす影響に関する解析的検討(G04-2 先進加工技術とその評価,G04 機械材料・材料加工)

Evaluation of interfacial friction in material removal processes: the role of workpiece properties and contact geometry

In this work, the interfacial friction is investigated during a material removal test. Based on specially programmed experiments conducted on 6061 Al at 24 different conditions, it was found that the friction coefficient significantly varies in different temperature ranges. Using optical and transition electron microscopy, these variations were found to be dependent on phase changes within the workpiece crystalline structure and the amount of oxidation on the surface of the workpiece. The interfacial friction was also found to change with the geometry of the cutting tool, where larger tool wedge angles increased the shear stress in the shear plane.

A computational approach to evaluate temperature and heat partition in machining with multilayer coated tools

In this paper, analytical models for estimating the interface temperature and heat partition to the chip in continuous dry machining of steels with flat-faced tools treated with multilayer coatings are presented. The database for modeling includes changes in the thermal properties of both workpiece and substrate/coating materials and the Peclet and Fourier numbers occurring at actual interface temperatures. Process outputs involve the average tool–chip interface temperature, the tool–chip contact length, the friction energy and the heat balance between the moving chip and stationary tool. It was found that the heat partition coefficient varies significantly from 0.65 to 0.8 when using multilayer coated tools, and changes from 0.5 to 0.6 for uncoated carbide tools. This implies that the use of multilayer coated tools causes about 30% more heat generated due to friction to be transferred into the moving chip. In general, both power and linear models can be used to estimate the interface temperature.

Wear properties of punch with sheared edge

Metal forming through punching finds wide interest in industry. The punch life and the end product quality depend on the punch and workpiece properties as well as punching conditions. Recently, TiN coating of the punch surface has reported to improve considerably the tool life and the end product quality. This is because of the high hardness and low friction coefficient of TiN coating. In the present study, the wear properties of sheared edges punch is investigated through SEM micrograph and EDS analysis. Mild steel is selected as workpiece material while the punch material is cold‐work tool steel (A2). The punch surface is coated with TiN (PVD) and an uniform coat thickness is assured. It is found that the wear mechanism is governed by adhesive and abrasive wear through shearing. The TiN coating protects the punch surface in the initial cycles of the punching process. As the punching cycle progresses, local defects in TiN coating are observed, i.e. coating is locally worn away.

Modeling and simulation of the tool wear in nanometric cutting

Tool wear is a significant factor affecting the machined surface quality. In this paper, a molecular dynamics (MD) simulation approach is proposed to model the wear of the diamond tool in nanometric cutting. It includes the effects of the cutting heat on the workpiece property. MD simulation is carried out to simulate the nanometric cutting of a single crystal silicon plate with the diamond tip of an atomic force microscope (AFM). The wear mechanism is investigated by the calculation of the temperature, the stress in the diamond tip, and the analysis of the relationship between the temperature and sublimation energy of the diamond atoms and silicon atoms. Microstrength is used to characterize the wear resistance of the diamond tool. The machining trials on an AFM are performed to validate the results of the MD simulation. The results of MD simulation and AFM experiments all show that the thermo-chemical wear is the basic wear mechanism of the diamond cutting tool.