Workpiece Size Research Articles

A discrete system model for form error control in surface grinding

Precision and quality have been the critical issues for many industries. For better machining quality, effective models will be needed in order to realize precision control. Surface form error is a difficult issue among the three main geometric features, which are size, form error, and roughness. There are little studies on modeling for form error control. In this study, a discrete system model for form error control in surface grinding is proposed based on three key relationships. Mathematical models describing the workpiece size reduction profile together with workpiece form error profile in relation to grinding pass number are presented. The grinding force constant k w and the unit force deflection y pg( x, z)/ P g can be estimated through experimental testing. Many operational process parameters are actually reflected in the proposed model and further separate studies are necessary for specific and accurate relationship between the operational process parameters and the model parameters. The results of the experimental testing are in good agreement with the theoretical results. For the average size reduction c n , the average relative error is as low as 1.34%. This shows that the proposed model is quite accurate. The proposed model is seen effective in obtaining the theoretical tangential force F t ntheo . The stringent point to point spatial comparison shows that the error between theoretical and experimental results is less than 2.3 μm and the average relative error is less than 6.93%. The proposed model is seen effective in size reduction prediction, which can be used to determine surface form profile y n ( x, z). The average relative error in the temporal comparison is 5.31%. It shows that the proposed model can be used to predict size reduction along the time axis, which is represented by the grinding pass. The results give confidence for use of the proposed control system model for form error control. To avoid the assumption of zero error in the initial workpiece surface, in-process form profile sensor is necessary. Further studies are needed for more accurate verification of the proposed model.

Compact design for high precision machine tools

Due to raising functional integration in micro fluidic, micro mechanic, micro electronic and micro optical systems the trend to scaling down the work piece sizes while increasing its complexity requires high precise machine accuracy. With respect to the process and geometrical parameters, most of the finishing manufacturing processes can be covered by milling and grinding operations with three or five machine axes. But whereas the available machine tools hardly achieve the required process dynamic and accuracy in all degrees of freedom, the requirements still increase. For this reason the Fraunhofer IPT has developed high precise machine tools following a compact design strategy by reducing the overall machine dimensions as far as conventional machine components such as measuring or drive systems were available. The developments of two compact machine tools exemplify the dynamic and accuracy enhancement by compact design and are described in the following.

Industrial computed tomography image size measurement

As one of the most useful modern detection technologies, Industrial Computed Tomography (ICT) image size measurement can correctly non-destructively measure the size of workpieces’ inner construction, and it is considered as the standard for quality assurance and reverse engineering. In view of the advantages and disadvantages compared to conventional methods, this paper improves the precision of image size measurement with a new algorithm that uses an approximate function to describe edge degradation. First, this algorithm constructs the approximate function and determines the optimal point of edge detection, based on image intensity and inflexions. Then, in order to accurately extract the image edge, this algorithm is used to revise the primary image, completing construction of the CT image. Excellent results are obtained from simulations and experiments. The experimental results indicate that the relative error is 2% for the CT image when the step evolution of the image edge is pooled. The relative error of this method is decreased by as much as 1.5% compared to wavelet transformation and ridgelet transformation. Therefore, this new algorithm demonstrates increased effectiveness in extracting an accurate measurement of the CT image edge.

Study on Edge Contact Area and Surface Integrity of Workpiece in Point Grinding Process

During cylindrical grinding process, the geometric configuration and size of the edge contact area between the grinding wheel and workpiece have the heavy effects on the workpiece surface integrity. In consideration of the differences between the point grinding and the conventional high speed cylindrical grinding, the geometric and mathematic models of the edge contact area in point grinding were established. Based on the models, the numerical simulation for the edge contact area was performed. By means of the point grinding experiment, the effect mechanism of the edge contact area on the ground surface integrity was investigated. These will offer the applied theoretic foundations for optimizing the point grinding angles, depth of cut, wheel and workpiece speed, geometrical configuration and size of CBN wheel and some other grinding parameters in point grinding process.

Kinematical analysis on the several linkage drives for mechanical presses

In this paper, a kinematical analysis is preformed to see mechanical characteristics of various linkage drives for a mechanical press. Mechanical characteristics of conventional and newly designed drives are investigated and compared in terms of slide velocity, productivity, load capacity and possible work-piece size. A crank-slider mechanism with arc crank-pin guide is introduced and analyzed particularly for kinematical performance using kinematical analysis software. The new linkage drive turns out to be effective in terms of load and velocity characteristics and productivity. Kinematical performance also provides a basis for the proper selection of mechanical presses.

Effect of size of the cylindrical workpiece on the cold rotary-forging process

Cold rotary forging is an advanced but much complex incremental metal forming process with multi-factors coupling interactive effects. The size of the workpiece has a significant effect on the cold rotary-forging process. In the current work, a reliable 3D elastic–plastic dynamic explicit FE model of cold rotary forging of a cylindrical workpiece is established under the ABAQUS software environment. Based on the valid 3D FE model, the effect laws of size of the cylindrical workpiece on metal flow, degree of inhomogeneous deformation of workpiece and force and power parameters in the cold rotary-forging process have been investigated. The research results show the following: (1) With increasing the initial diameter of the cylindrical workpiece D 0, the “mushroom” effect of the deformed cylindrical workpiece becomes less obvious and the deformation becomes more homogeneous, while the maximum axial forging force and forging moment gradually increase. (2) With increasing the initial height of the cylindrical workpiece H 0, the “mushroom” effect of the deformed cylindrical workpiece becomes more obvious and the deformation becomes more inhomogeneous. Meanwhile, the maximum axial forging force and forging moment increase slowly. (3) The effect of the height to diameter ratio H 0 /D 0 by changing D 0 on the cold rotary-forging process is different from that by changing H 0. The above results have been explained by the critical parameter affecting the cold rotary-forging process significantly, namely the length to height ratio of the plastic deformation zone K ¯ .

Study on Edge Contact Area and Surface Integrity of Workpiece in Point Grinding Process

During cylindrical grinding process, the geometric configuration and size of the edge contact area between the grinding wheel and workpiece have the heavy effects on the workpiece surface integrity. In consideration of the differences between the point grinding and the conventional high speed cylindrical grinding, the geometric and mathematic models of the edge contact area in point grinding were established. Based on the models, the numerical simulation for the edge contact area was performed. By means of the point grinding experiment, the effect mechanism of the edge contact area on the ground surface integrity was investigated. These will offer the applied theoretic foundations for optimizing the point grinding angles, depth of cut, wheel and workpiece speed, geometrical configuration and size of CBN wheel and some other grinding parameters in point grinding process.

AZ31 마그네슘 합금의 온간 후방압출에서 변형특성과 결함성장에 관한 유한요소해석

Deformation characteristics and damage evolution during warm backward extrusion of bulk AZ31 Mg alloy were investigated using finite element analyses. AZ31 Mg alloy was assumed as a hardening viscoplastic material. The tensile tests of AZ31 Mg alloy in previous experimental works showed the ductile fracture even at the warm temperature of <TEX>$175^{\circ}C$</TEX>. In this study, damage evolution model proposed by Lee and Dawson, which was developed based on the growth of micro voids in hardening viscoplastic materials, was combined into DEFORM 2D. Effects of forming temperature, punch speed, extrusion ratio and size of work piece on formability in warm backward extrusion as well as on mechanical properties of extruded products were examined. In general, finite element predictions matched the experimental observations and supported the analyses based on experiments. Distributions of accumulated damage predicted by the finite element simulations were effective to identify the locations of possible fracture. Finally, it was concluded that the process model, DEFORM2D combined with Lee & Dawson#s damage evolution model, was effective for the analysis of warm backward extrusion of AZ31 Mg alloys.

Study of Intelligent Prediction and Control of Workpiece Size in Traverse Grinding

A size intelligent prediction control model during traverse grinding is constructed. The model is composed of the neural network prediction model, the deformation optimal adaptive control system and fuzzy control model. Dynamic Elman network is used in the prediction model. The first and the second derivative of the actual amount removed from the workpiece are added into the network input, which can greatly improve the prediction accuracy. The flexible factor is introduced to the fuzzy control model, which can self-adapt and adjust the quantification factor and scale factor in the fuzzy control. Simulation and experiment verify that the developed prediction control model is feasible and has high prediction and control precision.

The coupling thermal–mechanical and microstructural model for the FEM simulation of cross wedge rolling

The microstructural evolution models on AISI 5140 were obtained using the Gleeble-3500 thermo-mechanical simulator. Simulation on the cross wedge rolling (CWR) process has been carried out on the platform of finite element software DEFROM-3D with thermo-mechanic and microstructural evolution coupled. And distributions of the different field-variables during the whole rolling process from the knifing, guiding, stretching to sizing stage, such as effective strain, effective strain rate and temperature, were obtained. Meanwhile, three-dimensional (3D) distribution of austenite grain size of workpiece was also achieved. It is significant to understand the net-shaped mechanism and optimize CWR technology.

ＪＩＳ ＳＫＤ６１の焼入れ変形の数値解析による予測

The strongly commercial interests have been focused on avoid distortion and attain higher toughness of quenched JIS SKD61 die block. FE (Finite Element) analyses before practical trials that can visualize local distribution of temperature or stress are available to complete these requests. In order to establish the basics of simulation technique, stress-strain behavior is derived from tensile tests and also boundary condition data is generated through quenching tests in compressed N2 gas. It's obvious that the elastic/plastic boundary stress which to be treated as yield point in FE analyses is from 35 to 80 % for 0.2 % proof stress. And the influence of gas pressure P on heat transfer coefficient h is defined for material surface temperature. Given h is approximately 250 W/m2/K for P equals to 4700 torr. Then the validity of database is verified on quenching of die-block-like two types of 4 kg work-pieces. Predicted transformation temperature is agreed well with that in experiments. And also the tendency of change in work-piece size is represented by FE analyses. Moreover the difference of distortion between shapes of work-pieces during quenching is shown. These results suggest that the recommended process could be designed for each die shape and it's expected through numerical simulation.

2912 6 軸超精密複雑形状金型加工機の開発とその加工効果

We have developed a "Nano-Precision Machining System" which machines have produced metal die for ultra precision micro lens and liquid crystal optical wave guides etc. The developed machine is mainly composed of the high stiffness machine frame, NC controller, air hydrostatic spindles and supporting devices such as oil tanks and temperature control units. The machine has 6 axes. Three linear axes (X, Y and Z-axes) can be controlled at a feeding resolution of 1 nm under full closed feedback. The maximum workpiece size is 220 mm × 170 mm along the X and Y axes. In this paper, the concept of the "Nano-Precision Machining -System" are proposed and introduced. The system configuration, features, and specifications were described.

New approach to determination of maximum temperatures in welding using travelling heat sources

The present paper considers methods of calculation of maximum temperatures in welding using a constant welding speed and a point heat energy source. A comparison of theoretically obtained times for the occurrence of maximum temperatures with those obtained experimentally shows slight deviations. The latter are dependent only on the accuracy of temperature measurements and the workpiece size (i.e. plate size in the present work). In the present case, the limitations refer only to the workpiece size. The advantage of this new approach is in the determination of a plane curve which is an envelope of all the points in the workpiece that are simultaneously at the maximum temperature in arc welding.

1015 遠心力による研削砥石の弾性変形に関する研究

The elasticity of grinding wheels has been analyzed depending on a mathematical model so far. As the results of analytical and experimental evaluations, it is confirmed that the model we proposed can be useful for analyzing the elastic phenomena of grinding wheel. In this paper, the effect of centrifugal force on the size of grinding wheel is evaluated by using our model. According to the evaluation, it is clarified that the rotating wheels radius change due to the effect of centrifugal force and then the finishing workpiece size may be influenced by the rotating speed.

機械加工バリ取り作業を対象とした力制御の迫従性向上

Force control of a manipulator is essential in a finishing robot system. But, there is not an effective force control method and a manipulator mechanism for every finishing task because finishing processes are different in individual tasks. In this paper, examination for deburring of machined tasted iron parts using a force controlled robot with a conic mill was performed. We have proposed a reference trajectory generate function (ROUND function). The ROUND function inserts an arc in the reference trajectory for the two straight edge parts. Thus the press direction changes continuously, and the robot can follow the edges. It is useful when a workpiece position and/or size is different from the taught one. Also, we have developed a new force control method and a tool hold mechanism for deburring of machined casted iron parts. In the force control method, a force feedback gain is proportional to force error. The tool hold mechanism make equalized compliance of the tool center point. The force feedback gain in the new method and the new tool hold mechanism was three times the gain in the conventional method and mechanism.

Fast time constant estimation for plunge grinding process control

The time constant of a grinding control system indicates the speed of response to a control command and reflects variations of the wheel condition. In order to allow correct and continuous control adjustment, fast in-process estimation of the parameter is necessary. The significance of the grinding system time constant is discussed and the control system for the plunge grinding process described. An algorithm for fast time constant estimation is presented for adaptive control of the grinding process. The algorithm is useful for geometry-based grinding control systems where a workpiece size sensor is used and multiple control tasks are implemented. Experimental testing of the algorithm is explained and comparison between results from grinding and those from analysis shows that the proposed algorithm is sufficiently accurate and effective for adaptive control of the plunge grinding process.

Grinding of single crystal sapphire: workpiece roughness correlations

Experiments were performed on single crystal sapphire with a selection of bound abrasive cup tools to produce fine ground surfaces with rms roughness on the order of 1 μm. Both workpiece roughness and the ease of material removal (as quantified by Preston's coefficient or the specific grinding energy) were found to decrease with decreasing chip thickness. However, great variability was observed even for a fixed chip thickness as a result of differences in tool performance. A strong correlation was also found between Preston's coefficient and the workpiece roughness. Data for all tool bond types (resin, metal, and vitrified), abrasive sizes (2–80 μm diamond), surface conditions (as-dressed and glazed), and tool geometries fell on the same curve. This behavior has important practical effects during infeed controlled grinding. Only above a certain ‘critical roughness’, which depended on the workpiece size, was grinding able to remove the programmed infeed depth.

An optical flatness measurement system for medium-sized surface plates

This paper describes the work to develop a parallel beam scanning system (PBSS) for the noncontact measurement of surface flatness of such medium-sized surface plates, as sheet metals, sheet-moulding compound (SMC) plates, and glass plates, which are difficult to measure by traditional methods. The PBSS consists of a HeNe laser source with good pointing stability, a scanner to create divergent scanning beams, a large aplanatic meniscus lens to convert the divergent beams to parallel beams, a linear stage to drive the testpiece to each sampling position, a screen for the projection of reflected beams from the tested surface, and an image-processing unit to analyze the projected image. Because of the out-of-flatness of the surface, the straight line formed by the incident parallel beams will be distorted and magnified on the screen as it is reflected from the surface. A charge-coupled-device (CCD) camera is employed to capture the image of the distorted line each time, and proceeds in line-by-line sequence. With the proposed mathematical model, the three dimensional (3-D) flatness data of the testpiece can be converted from the input image data and analyzed by the least-squares method. Experimental results by the use of this system have shown good agreement with the results obtained from a coordinate measuring machine (CMM). Because of the limit of the meniscus lens, the workpiece size is within 200 mm in width.

A generic intelligent control system for grinding

The achievement of accuracy in precision machining depends on the ability to take account of system deflection. The application of intelligent control to grinding processes is a way to achieve a desired workpiece size and surface integrity. A generic intelligent control system for grinding has been developed based and implemented on a commercially available CNC grinding machine. The implementation has been shown to be successful. The paper describes the object-oriented development of the generic intelligent control system for grinding based on the proposed modular conceptual framework for adaptive grinding control, reviews previous work towards intelligent grinding control, summarises the previously used adaptive strategies and introduces the structure and operation of the generic intelligent control system. Finally, the problems encountered during the system development are discussed.

Measurement of Workpiece Size Errors due to Wheel Wear Using AE Signals and their Compensation in Grinding.

In this study, a method to measure workpiece size errors due to grinding wheel wear for NC grinding machines and their compensating method are proposed. In this method, workpiece size errors are measured using the contact signals between the grinding wheel peripheries and a single point diamond dresser in the dressing process, and using an NC dressing program, the worn parts of wheel peripheries can be distinguished from other parts by on/off signals of an AE sensor located behind the dresser. According to the experimental results, it is shown that workpiece size errors can be identified in the resolution corresponding to the least incremental input of NC signals using the NC machine. Furthermore, applying the relationship between AE signals and workpiece size errors, a new automatic workpiece sizing cycle is proposed, and its usefulness is experimentally confirmed.