Properties Of Workpiece Research Articles

FEM-Based Simulation of Temperature in Speed Stroke Grinding with 3D Transient Moving Heat Sources

The grinding process is one of the most important finishing processes to obtain high surface quality. Nowadays, grinding is also considered as a high performance process with high material removal rates. Nevertheless, to avoid thermally-induced structural changes poses a major challenge for this manufacturing technology. Until now, the Finite Element Method (FEM) has been widely applied as a proper numerical technique to predict workpiece properties in machining processes. However, actual models in grinding are limited to conventional grinding processes with simple workpiece profiles and low table speeds. In this paper, finite element simulations are expanded to 3-dimensional (3D) models with temperature-dependent material properties and heat source profiles derived from experimental results, i.e. tangential forces. Both temperature simulation and measurement were conducted for deep grinding, pendulum grinding and speed stroke grinding in the table speed range of vw = 12 m/min to 180 m/min and specific material removal rates of Q’w = 40 mm³/mms. Overall, the simulation results show a good agreement with the measured temperature and surface integrity after grinding. This research indicates that a 3D FE model with temperature dependent material properties can predict realistic temperature fields in speed stroke grinding. Therefore, the experiment and measurement costs and time can be reduced by FEM simulation.

Machining capacity measurement of an industrial product service system for turning process

Machining capacity measurement is of great importance in an industrial product service system for turning processes (TP-iPSS) owing to its roles in TP-iPSS evaluation, accounting, and optimization. In this paper, the concepts of potential machining capacity (MCp), real machining capacity (MCr), and total machining capacity (MCt) are presented. As for a configured TP-iPSS whose lathe is given and determined, MCp is majorly influenced by the lathe's attachments, especially the cutting tool, MCr is majorly correlative with cutting parameters (cutting depth, cutting velocity and feed) and workpiece properties besides parameters of cutting tool. Combining different cutting tool with the TP-iPSS, different MCp and potential machining area ( Ap) can be obtained, then the measurement models of MCp and Ap are established through using multivariate regression analysis, and MCr is calculated with the product of MCp and the ratio of Ap to Ar (real machining area). In addition, MCt in a time interval can be calculated with the sum of MCr in the time interval. Finally, a case is studied to demonstrate the MCp, MCr, and MCt models and their basic applications to TP-iPSS evaluation, accounting, and optimization.

Prediction of simultaneous dynamic stability limit of time–variable parameters system in thin-walled workpiece high-speed milling processes

A method for predicting simultaneous dynamic stability limit of thin-walled workpiece high-speed milling process is described. The proposed approach takes into account the variations of dynamic characteristics of workpiece with the tool position. A dedicated thin-walled workpiece representative of a typical industrial application is designed and modeled by finite element method. The curvilinear equation of modal characteristics changing with tool position is regressed. A specific dynamic stability lobe diagram is then elaborated by scanning the dynamic properties of workpiece along the machined direction throughout the machining process. The results show that, during thin-walled workpiece milling process, material removing plays an important part on the change of dynamic characteristics of system, and the stability limit curves are dynamic curves with time–variable. In practical machining, some suggestion is interpreted in order to avoid the vibrations and increase the chatter free material removal rate and surface finish. Then investigations are compared and verified by high-speed milling experiments with thin-walled workpiece.

Automated design of fixtures based on FEM simulations

With the aim of improving the availability and performance of machine tools, gentelligent® components for machine tools are developed at the Institute of Production Engineering and Machine Tools (IFW), Germany, starting with a fixturing system. Being the interface between the machine tool and the workpiece, these systems allow a first evaluation of the potentials of a gentelligent production system. This paper presents an approach for the design of the fixturing as a component of a sensing machine tool on the basis of finite elements simulations. The fixture design is adapted to the workpiece geometry and properties as well as to the loads resulting from the machining process. This is achieved by minimising the deformation of the workpiece and thus increasing the accuracy. The method developed comprises five stages: the analysis of fixture elements, the preprocessing of input (G-code), reduction of input data for the sake of computation time, computation of subconfigurations and assessment and comparison of all subconfigurations.

Function-oriented characterisation for surface metrology

With the availability of new and sophisticated surface measurement techniques extremely high resolved topography and structure measurements are possible. But now, one detects that conventional surface parameters are insufficient to provide information about the technical functional ability of the workpiece. In order to find out the appropriate parameters for characterising the functional behaviour, a parameterised mathematical model based on physics of the function of the surface is to be derived. In a second step measurement procedures and evaluation algorithm must be defined in order to characterise the functional ability based on the geometrically measured surface. A concept to characterise the surface with function-oriented parameters has been developed. With this method, it is possible to investigate cause-effect relations and to link geometrical and functional properties of workpieces. Based on this approach two examples, wettability and friction of technical surfaces, are given.

Process Signatures – an Alternative Approach to Predicting Functional Workpiece Properties

The prediction of functional workpiece properties has attracted much interest in academia, as well as in industry over the last 50 years. Although considerable progress has been made for single, well-understood processes it is basically still not possible to predict surface and subsurface properties from known workpiece and machining parameters. This keynote paper aims at suggesting a solution to this problem by describing machining processes by their converted and dissipated energy in the workpiece material, significant process state variables and their generation dynamics. For this new approach the introduction of the term process signature is suggested.

Surface Roughness Generation and Material Removal Rate in Ball End Milling Operations

Surface roughness plays an important role in the performance of a finished part. Surface roughness generated in machining operations is influenced by an enormous set of factors such as cutting parameters, cutting tool characteristics, workpiece properties, or cutting phenomena. Cutting geometric characteristics, when ball end mill is used, clearly affect surface crests generated. In this paper, we study the influence of the geometric characteristics of ball end mill cut on the theoretical surface roughness obtained. The crests height on the surface (h) and roughness average parameter (Ra) are calculated as function of cutting tool radius (R) and radial depth of cut (Ae). Surface angularity is also considered. This work also analyzes cutting parameters implication on material removal rate (MRR) of ball end milling operations. The equations and especially the figures presented in this paper can be easily applied in workshops to improve quality and productivity of ball end milling operations. Finally, experimentation carried out permits to observe and quantify the deviations of the theoretical approach.

Manufacturing of complex functional graded workpieceswith the friction -spinning process

In recent years, the demands on lightweight constructions with respect to their functional qualities and their potential to save resources by reducing weight have increased significantly. Tailor-made components with functionally graded properties manufactured by a novel so-called friction-spinning process meet these demands very well. This new process combines elements from metal spinning and friction welding to a new thermo-mechanical process for the manufacturing of complex hollow parts made of tubes, profiles, or sheet metals. In the process a workpiece, for example a tube, is set into rotation in a conventional spinning machine while a pressure or friction plate works in axial direction on the tube end. In the contact zone the temperature increases strongly by friction. A further movement of the friction plate and optional supplemental forming tools allow the deformation of the warm material and the generation of the desired geometry. With this new process it is possible to extend existing forming limits and to produce complex geometries like flanges or hollow structures, which are not producible by conventional processes. Furthermore, it is possible to influence the workpiece properties or grain structure locally in a defined way. It is possible to realize intense grain refinement in the deformation zone during this thermo-mechanical forming operation.

A framework for machining optimisation based on STEP-NC

Inappropriate machining conditions such as cutting forces cause tool failures, poor surface quality and worst of all machine breakdowns. This may be avoided by using optimal machining parameters, e.g. feed-rate, and continuing to monitor it throughout the machining process. To optimize feed-rate, we propose a system that consists of an optimisation module, a process control module and a knowledge based evaluation module. STEP-NC is the underlying data model for optimisation. Given the nominal powers, the cutting force can be estimated based on the higher-level production information such as workpiece properties, tool materials and geometries, and machine capabilities. The main function of the Process Control module is process monitoring and control. The output is the desired actual feed-rate. Finally, the actual feed-rate is recorded and evaluated in the Knowledge Based Evaluation module.

The effects of circular sawblade diamond segment characteristics on marble processing performance

Utilizing a fully instrumented block-cutter, an experimental study was carried out to investigate the effects of diamond/metal matrix properties on the sawing performance of segmented circular sawblades. Six commercially available sawblades differing in segment compositions were used in the sawing experiments of Afyon Tiger Skin Marble. Bond compositions of the tested sawblades were determined by carrying out energy dispersive X-ray spectrometer analysis. The sawing tests were performed in the down-cutting mode. The sawing performances of the sawblades were evaluated in terms of cutting specific energy (SE), cutting force, axial force, and force ratio (ratio of tangential to normal force). The worn surfaces of the diamond segments were examined by scanning electron microscope micrographs. Upon evaluation of the experimental data, it was concluded that the determined performance criteria from laboratory sawing tests can aid manufacturers in the design of appropriate sawblades for specific rock types. Valid for the employed machining parameters, tested sawblade types, and workpiece properties, the results of a multiple linear regression analysis have indicated that the Sn percentage of the segment matrix, the diamond concentration, and the matrix hardness are the common dominant variables that affect cutting SE, axial force, and cutting force.

Dynamic simulation of boring process

This article presents a model to simulate the dynamics of boring process. In boring operations the boring bar should be long and slender; therefore it is easily subjected to vibrations. Tool vibrations result in reduced tool life, poor surface finish and may also introduce chatter. Hence, predicting the vibrational behavior of boring process for certain cutting conditions and tool work-piece properties is of great importance. The proposed method models the cutting tool geometry by B-spline parametric curves. By using B-spline curves it is possible to simulate different tool geometries with a single approach. B-spline curves also enable the modeling of the kinematics of chip formation for different tool work-piece engagement conditions with a single formulation. The boring bar has been modeled by the Euler–Bernoulli beam theory. The simulation process has been implemented with MATLAB. The algorithm consists of different computational modules that are interconnected by a main program. Experimental machining tests have been conducted to verify the validity of the proposed model. Proposed dynamic models have been able to predict the dynamic cutting force components and vibration frequencies with less than 15% deviation. The proposed model has been also able to predict the chatter onset correctly.

Microstructure and mechanical properties of TA15 titanium alloy under multi-step local loading forming

In this paper six different local loading processes were proposed to study the effects of local loading conditions (temperature, deformation degree, loading pass, heats, cooling modes and heat treatment) on the microstructure and mechanical properties of TA15 titanium alloy workpieces including room and high temperature tensile properties, impact property, fracture toughness and high temperature duration property. It is found that it is better to finish the local loading forming in one heating time, if multi-fire forging needed the optimal forging technique as follows: adopting conventional forging (950 °C) at first and then following near-beta forging to control the proportion of the equiaxed primary α phase and the transformed β phase, allocating deformation degree of each loading pass rationally and using WQ cooling mode. Thus the workpiece with good compositive mechanical properties can be obtained.

Stability Prediction during Thin-Walled Workpiece High-Speed Milling

A method for predicting the stability of thin-walled workpiece milling process is described. The proposed approach takes into account the dynamic characteristics of workpiece changing with tool positions. A dedicated thin-walled workpiece representative of a typical industrial application is designed and modeled by finite element method (FEM). The workpiece frequency response function (FRF) depending on tool positions is obtained. A specific 3D stability chart (SC) for different spindle speeds and different tool positions is then elaborated by scanning the dynamic properties of workpiece along the machined direction throughout the machining process. The dynamic optimization of cutting parameters for increasing the chatter free material removal rate and surface finish is presented through considering the chatter vibration and forced vibration. The investigations are compared and verified by high speed milling experiments with flexible workpiece.

An approach to reduce the influence of tool wear on workpiece properties during hard turning

Tool wear during hard turning of steel materials leads to unfavourable changes of the workpiece subsurface layers. Due to progressive flank wear at the cutting edge, thermal and mechanical loads affect adversely the residual stresses at the workpiece subsurface and white layers occur within the microstructure. These effects lead to a reduction of the functional behaviour of such machined components at operational conditions, especially under dynamic mechanical loads. This paper presents a method to avoid negative influences at machined subsurface layers in terms of residual stress. A modified cutting edge micro geometry is applied to assure a reliable process even with worn cutting tools by limiting the contact conditions between the tool and the workpiece interface at the tool flank face.

205 同期型スピニング加工による非軸対称成形に及ぼす被加工材性質の影響(材料力学V)

205 同期型スピニング加工による非軸対称成形に及ぼす被加工材性質の影響(材料力学V)

In-process force measurement for diameter control in precision cylindrical grinding

This article shows the theory and implementation of a force measurement-based approach to controlling workpiece diameter in cylindrical grinding. A simple model proposed is used to relate infeed velocity to grinding force. The model is extended to accurately control the amount of material removed in outer diameter plunge grinding given the normal force, which may be monitored in real-time. The model incorporates the key parameters, including the structural loop stiffness, the plunge infeed velocity, and the wheel and workpiece properties. However, only the infeed velocity must be explicitly known. The contribution of this work is experimental validation that the lag between infeed and stock removal can be predicted using force feedback without a priori knowledge of the grinding system. This allows very accurate diameter control (0.25 μm of nominal), even in the presence of thermal drift, wheel wear, and machine error.

The mechanics of multi-point sandwich forming

Multi-point sandwich forming (MPSF) is a sheet metal forming process of recent innovation, in which a reconfigurable bottom die and a rubber top die are used. Also, a reusable die sheet is placed on the pins of the reconfigurable die to form a continuous surface. Because a simple press may be used and the cost of altering the tooling to make a new part shape is small, MPSF is a suitable method for forming small-batch quantities of a particular part. However, the basic deformation mechanics of MPSF have not yet been investigated and thus the best configuration of tool components to make a given part shape has to be determined by trial and error, which detracts from the low-cost aspect of the process. Therefore, in this paper, the results of investigation of the effect of workpiece and tool component dimensions and workpiece properties on the characteristics of the formed part shapes are presented. To enable the effect of tool and process parameters to be revealed more readily, plane strain deformation is used and a cylindrically shaped die surface was chosen for the bottom die. Three kinds of metal sheet and two kinds of rubber were used in the experiments. Experimental results show that for the die sheet, forming force increases and dimple size reduces with increase in the thickness of the sheet. Dimples occur on the surface of 1 mm LF21 aluminum sheet workpieces, however no dimples are formed on 2-mm-thick Q235B and ST12 steel sheet workpieces. The stiffness of the interpolator has an effect on the final shape accuracy. Also, the forming force of the workpiece reduces and shape accuracy increases, when lubrication is used in the surfaces of a workpiece.

Development of New Combined Manufacturing Technologies ‐ Influence of the Cutting Process on Workpiece Properties

Properties of materials for high‐strength structure components are influenced by production processes. These influences can be augmented by a combination of two presently consecutively executed process steps. The presented work shows first results in the development of novel combined manufacturing technologies, which along with prospective tools use this effect to adjust the material properties locally, adapted to the requirements. The combination consists of a merging of the process steps ‘material separation’ (metal cutting) and ‘changing properties’ (rubbing, rolling) to one single process step. For this purpose novel combined tools have to be developed. For the estimation of the possibilities of properties changes by combined processes at first the influences of single processes have to be determined. This contribution presents results of a “material separation” process. The investigated material is the industrially important aluminium wrought alloy AI7075‐T6, the applied process is orthogonal turning, the process parameters varied are cutting speed and feed as well as the tool geometry. Cutting force and feed force are measured, and the process influences on surface and subsurface properties are determined.

Springback control of sheet metal air bending process

Press brake bending is a commonly used process for sheet metal part fabrication. It has been observed that the final bend angle, which is the angle achieved upon removal of the punch, is smaller than the initial bend angle. This springback is due to the elastic recovery of the sheet metal. Various theoretical models have been proposed to predict the springback using the tooling geometry and the known properties of the sheet metal. However, in a production environment, the actual properties of any given workpiece may vary from the nominal properties of the lot. This variation causes the actual springback to deviate from the theoretical predictions. This paper presents a practical incremental bending methodology to control punch displacement to achieve more accurate final bend angles. In the proposed approach, workpiece properties are estimated from measured loaded and unloaded bend angles. The estimated properties are used to determine the final punch position required to obtain the desired bend angle after springback. A series of bending experiments was performed. It was found that the proposed method can better predict springback and effectively control the bend angle variation in a production environment.

Methodology to describe the influence of manufacturing processes on the part functionality

The performance of a value-adding process chain is significantly characterised by a stable and function orientated interaction of its manufacturing processes. To achieve this, it is necessary to define manufacturing tolerances for the significant work piece properties and to produce these tolerances safely. The allowed tolerance ranges are primarily defined by the functionality of the entire part. Thereby, not only macro- and micro-geometrical work piece properties are being tolerated in dependence of the part functionality, but also properties of the rim zone, magnetical properties, optical properties (e.g., reflection) and physical material variables. Within the process chain, these properties and manufacturing processes are interacting, but not all work pieces and process properties have direct influence on the final part functionality. Rather, they are only affecting parts of the process chain. Respectively, in the following a methodology to analyse, evaluate and describe the influence of manufacturing process properties on the final part functionality is described.