Workpiece Clamping Research Articles

Effect of the Axial Profile of a Ceramic Grinding Wheel on Selected Roughness Parameters of Shaped Surfaces Obtained in the Grinding Process with a Dual-Tool Grinding Head.

The use of CNC equipment that integrates several machining operations eliminates downtime due to changes in setup and clamping of workpieces in more than one machining device. A review of CNC equipment and tools known from the literature and from manufacturers' offerings indicates that new technical solutions are being developed to integrate two or more technological operations. However, these examples have numerous limitations and are mostly not suitable for machining surfaces with complex shapes. An example of such solutions is the use of a dual-tool grinding head, which integrates the process of rough grinding with a ceramic grinding wheel and finish grinding with a flexible grinding wheel. Unfortunately, it has the disadvantage of being limited by the angular shape of the ceramic grinding wheel, making it unable to adapt to the complex geometries of the shaped surfaces being ground. The need to overcome this limitation became the motivation for the research work described in this article. By means of experimental research, it was verified what effect the radial outline on the periphery of a ceramic grinding wheel realized by rough grinding would have on the surface roughness parameters obtained in the process of grinding shaped surfaces. For this purpose, grinding processes using a ceramic wheel with a conical and radial outline were compared. The result of the study was a summary of the surface roughness parameters Sa, St, Sq, Spk, Str, and Sds obtained after two-stage machining (rough and finish grinding). The obtained analysis results showed that changing the axial outline of the ceramic grinding wheel makes it possible to significantly expand the range of applications of the dual-tool head without negatively affecting the quality of the machined surface. Thus, such an improvement will make it possible to increase the applicability of the head by grinding shaped surfaces with a radial profile of curvature.

Reducing Cycle Time in the Manufacturing Process of Circular Pattern Interpolar Products (CPIP) Using Special Fixtures on a 3-Axis CNC Machine

This research focuses on the design of fixture aids to support the manufacturing process of Circular Pattern Interpolation Products (CPIP), such as disk brake components, flanges, turbine disk runners, and other plate components with circular feeding patterns in the 3-Axis CNC machining process. The objective of this study is to achieve more efficient CPIP production times on 3-Axis CNC machines. The research methodology employed a design and build approach, involving the design of fixture aids, fabrication, and testing during the production of turbine disk runners on a 3-Axis CNC machine. This was done by comparing the initial workpiece setup time and the workpiece clamping transfer time using CPIP production aids versus not using CPIP production aids. The results showed that the designed CPIP Fixture significantly reduced the CPIP manufacturing Cycle Time, with a reduction of 63.11% in the initial workpiece setup time and 83.55% during the clamping transfer process.

Study on milling flatness control method for TC4 titanium alloy thin-walled parts under ice fixation

Thin-walled parts are characterized by weak rigidity and are very prone to deformation during machining, which directly affects the machining accuracy and performance of the parts, so controlling the machining deformation of thin-walled parts is an urgent process problem to be solved. To address such problems, this paper proposes a flatness control machining method based on ice holding of workpieces. The method uses frozen suction cups to solidify liquid water to achieve stress-free clamping of workpieces. We conducted a low-temperature tensile test to investigate the low-temperature mechanical properties of the material. Comparative tests of ice-free and low-temperature ice-fixed milling were conducted to compare and analyze the changes of flatness and milling force in the two working conditions, to investigate the influence of machining parameters on the flatness of thin-walled parts, and to reveal the mechanism of low-temperature milling of ice-fixed workpieces. In addition, the low-temperature milling performance of titanium/aluminum alloy based on ice-fixation was compared. The results show that TC4 has good plasticity, high flexural strength ratio and strong resistance to deformation at low temperatures. Compared with no ice-holding, ice-holding machining effectively improves the flatness of the workpiece, and the order of the machining parameters affecting flatness is: feed rate > milling depth > spindle speed. The milling forces under ice-holding conditions were all greater than those without ice holding. The stiffness and hardness, resistance to damage and deformation of titanium alloy at low temperature are greater than those of aluminum alloy. This method provides a new method for high-precision machining of thin-walled parts.

Optimized Design of Flexible Quick-Change System Based on Genetic Algorithm and Monte Carlo Method

In order to realize the high efficiency and precision clamping of large workpieces with several processes and multiple species processing, the distribution number and position of the zero point clamping unit in the flexible quick-change process system for big thin-walled cylindrical structural parts are presented. The error model of the flexible quick-change process system is established by the Monte Carlo method, which is used to optimize the system structure design. The error variation of the flexible quick-change process system under the action of transposition and extreme working conditions such as cutting force is revealed, and further analysis on the sensitivity of the workpiece’s global displacement error and global attitude error to each error source is carried out. After the optimization, a high-quality, cost-effective, flexible quick-change clamping system is created. The three-coordinate measurement experiment is used to test the functionality and accuracy of the flexible quick-change process system. A significantly improved level of the system’s repetitive positioning accuracy (less than 0.01 mm) is detected. Importantly, the flexible quick-change system obtained by the combinatorial optimal design method has been successfully applied to the production of aerospace components with improved quality and efficiency.

Optimization of the Clamping Layout of Thin-walled Parts with Partition Frame

When the thin-walled parts are machined, they need to be clamped and positioned. By using finite element method (FEM), the deformation law of workpiece clamping caused by single clamping layout parameter can be gained. However, it is impossible to express the relationship between the clamping deformation and the clamping layout parameter by FEM when multiple clamping layout parameters are taken into account simultaneously. Therefore, ABAQUS is used to establish a three-dimensional finite element model for the clamping layout of thin-walled part. And by combining the milling force and the static balance equation, the appropriate clamping force value can be obtained. Then it is convenient to obtain the initial data sample of genetic algorithm. Genetic algorithm is used to optimize the clamping layout of frame type of thin-walled part and obtains the optimal layout. The minimum value of maximum clamping deformation is 15.50 µm. In the field of thin-walled part machining, the research results of this paper have an important guiding role in the rational design of the clamping layout scheme.

Feasibility Study of Integrated Precision Abrasive Machining of Shaped Surfaces

The use of CNC equipment that integrates several machining operations allows the elimination of downtime resulting from setup changeovers and the clamping of workpieces in several different machine tools. More and more CNC machines and tools that allow the integration of several machining operations are appearing on the market, but there are only a few examples of these and many solutions that allow such integration for more complex operations are still missing. The aforementioned factors motivated the research work described in this paper. The purpose of the present study was to develop an innovative grinding head with different functional features for use in the process of shaped surfaces face grinding, the use of which will enable complete abrasive machining in a single mounting. The conducted tests of the grinding process showed a reduction in the values of the roughness parameters Sa (5.30, 1.12, 0.63 μm), St (31.8, 14.4, 6.72 μm), Sq (6.39, 1.46, 0.81 μm) and Spk (6.16, 0.77, 0.33 μm) and an increase in the value of the parameter Sds (393, 563, 1203 pks/mm2) on the surface after machining in two stages, first for rough grinding and then for finishing relative to the surface after the shaped milling process.

Detection and Identification of Nonlinear Contact Dynamics at Workpiece Clamping Positions

1. HESSE S., KRAHN H., EH D., 2012, Betriebsmittel Vorrichtung - Grundlagen und kommentierte Beispiele, Carl Hanser Verlag, München. Google Scholar

Structural Design of a Special Machine Tool for Internal Cylindrical Ultrasonic-Assisted Electrochemical Grinding.

During the process of internal cylindrical ultrasonic-assisted electrochemical grinding (ICUAECG), both the workpiece and the conductive grinding wheel are rotating, the machining space is closed and narrow, the electrolyte is difficult to spray into the machining area, and the insulation between the workpiece and the machine bed is challenging. According to the machining characteristics of ICUAECG, the structure of a special machine tool was designed to mitigate these problems. In particular, the rotation, electrolyte supply, electric connection, and insulation modes of the workpiece clamping parts were studied, yielding a novel workpiece clamping- and rotating-device design. This structure can fully use the internal space of the hollow spindle of the machine tool, effectively reduce the external moving parts, and achieve the appropriate liquid injection angle of the electrolyte. The ultrasonic vibration system and its installation mechanism, the dressing device of the conductive grinding wheel, and the electric grinding spindle-mounting and -fixing device were analyzed in detail. Then, a special machine tool for ICUAECG was designed, the operability and feasibility of which were verified by experiments involving conductive grinding wheel dressing and ICUAECG.

Nonlinear dynamic modeling and vibration analysis of whole machine tool

The machine tool structure vibration during machining operation is directly linked to machining quality, production efficiency as well as machine reliability. Hence, this research focuses on the dynamic modeling of the whole machine tool considering the milling process to predict vibration response and dynamic characteristics during machining. Applying the lumped parameter and finite element hybrid method, in order to improve virtual simulation efficiency, the analytical models of the workpiece clamping worktable system and the tool clamping column spindle system are theoretically developed considering the nonlinearity of moving joints and the position-dependent dynamics. The integrated model of the whole machine tool dynamics is established by coupling the models of two subsystems with the generated nonlinear dynamic load in the ball end milling process including the effects of vibrations and tool system errors. Subsequently, the frequency response functions and the instantaneous cutting forces and vibration responses under different cutting conditions are measured and compared with simulation results to evaluate the prediction ability of the proposed model. Finally, the experimentally confirmed model is used to carry out the parameter analysis of machine tool. The investigations reveal that the worktable system dynamic characteristics vary with the joint assembly preload, but the change becomes no longer significant when the preload increases to a certain value. Besides, cutting conditions have a significant influence on the vibration characteristics of machine tool during machining.

Friction stir welding of SS 316 LN and Nitronic 50 jacket sections for application in superconducting fusion magnet systems

This study explored the possibility of using friction stir welding (FSW) to join jacket web sections of two nitrogen-containing stainless steels for housing internally cooled superconducting cables which are utilized to generate magnetic fields in tokamak type fusion reactor systems. The two candidate materials chosen for the jacket are SS 316 LN and Nitronic – 50 owing to their desirable mechanical and physical properties at cryogenic service temperature. The current manufacturing techniques to fabricate the jackets or conduits include fusion butt welding. There are some inherent disadvantages of utilizing the fusion joining process such as the possibility of sensitization and the evolution of undesirable phases detrimental to the application. An attempt has been made to fabricate the jackets with FSW to evaluate its feasibility to obtain the desired mechanical and physical properties critical to the application. The welding parameters optimization, workpiece clamping approach, microstructure evolution, hardness line profiles, tensile properties, and magnetic properties of the jacket welds corresponding to both the materials have been discussed in the paper. It has been shown that the FSW fabricated SS 316 LN jackets possessed the required strength and magnetic properties critical to this application.

A Method and Device for Automated Grinding of Small Ceramic Elements.

The paper describes an automated method for grinding small ceramic elements using a hyperboloid wheel. The problem of automating the process of machining elements made of nonmagnetic materials with a small area and low height has been solved. Automation of the grinding process was possible thanks to automatic clamping of workpieces in the machining zone and sequential processing by a specified number of grinding wheels. The workpieces were passed through successive machining zones. The division of the allowance of individual grinding wheels was made taking into account the characteristics of the workpieces and the requirements for the results of the machining. Obtaining a long grinding zone and the effect of automatic clamping of the workpieces was possible due to the inclination of the grinding wheel axis in relation to the plane of movement of the workpieces. Innovative aggregate grinding wheels were used for grinding. The aggregates containing diamond abrasive grains, connected with a metal bond, were embedded in the porous structure of the resin bond. The aggregates ensured high efficiency of grinding, and their developed surface contributed to good holding in the resin binder. The durability of grinding wheels was 64 h, which enables the machining of 76,000 ceramic elements.

A method of predicting the best conditions for large-size workpiece clamping to reduce vibration in the face milling process

The paper presents an innovative method of solving the problem of vibration suppression during milling of large-size details. It consists in searching for the best conditions for clamping the workpiece based on a rapid modal identification of the dominant natural frequencies only and requires repetitive changes in the tightening torque of the clamping screws. Then, by estimating the minimum work of the cutting forces acting in the direction of the width of the cutting layer, it is possible to predict the best fixing of the workpiece. Application of the method does not require the creation and identification of a computational model of the process or preliminary numerical simulations. The effectiveness of this method was confirmed by the evaluation of the Root Mean Square (RMS) of the vibration level in the time domain observed during the actual face milling process. The worst results were obtained for the configuration of supports tightened with a torque of 90–110 Nm, and the best—with a torque of 50 Nm.

Identification of Analytical Dependencies of the Operational Characteristics of the Workpiece Clamping Mechanisms with the Rotary Movement of the Input Link

Abstract The research is devoted to the problem of determining the efficiency of the workpiece fixing mechanism operation. Improving characteristics of workpiece fixing is one of the required conditions to increase the cutting modes, which may help to enhance the machining productivity. The study investigates the main characteristics and general features of a new structure of clamping mechanisms with electromechanical actuators for fixation of rotation bodies. The main advantages of using electromechanical clamping actuators with self-braking gear are presented. Two simplified dynamical models for the description of different stages of the clamping process are developed. The calculation scheme was formulated to find out how the mass-geometric parameters of mechanism elements should influence the main characteristics of the clamping mechanisms of this type.

Витягування циліндричних деталей із не суцільного матеріалу

A new method for drawing cylindrical parts from a flat metal mesh netting with square openings has been proposed, developed and investigated. According to this method, drawing is carried out from a square workpiece, whose sides are parallel to the diagonals of the netting mesh. A new method of drawing parts with flange clamping of a sheet workpiece has been proposed and experimentally tested, which differs in that the workpiece is pre-perforated; perforation of the workpiece is performed only in the flange area, whose inner diameter is equal to the average diameter dc of the cylindrical part obtained; perforation of the workpiece is performed so that the sum  of all jumpers by the width ai on each concentric circle of the location of the perforation holes is equal to the circumference at the average diameter dc of the cylindrical part obtained, i.e. formula is valid. The use of the proposed method, in comparison with the known one, creates such conditions for drawing, under which the limiting drawing ratio becomes significantly lower (< 0,46), which makes it possible to conduct a deeper drawing of parts in one press run. The scientific novelty of this research is as follows. Usually, when manufacturing parts such as caps or box shapes, stamping is used in several runs to avoid the phenomenon of tearing- off of the bottoОдержаноm. However, the use of stamping in several runs leads to a complication of the process equipment and an increase in the cost of the product, which is justified only for cases of obtaining a high-quality product and provided that the integrity of the part is intact at a considerable depth. When trying to draw parts of considerable depth, objective difficulties arise associated with breaking-off of the bottom, which are due to exceeding by the tensile stresses in the critical section of the workpiece (between the bottom and lateral surfaces) of the ultimate tensile strength в of the latter. As part of the research described in this article, a way to overcome those difficulties has been proposed. It is based on the fact that when implementing the stamping process at lower values of the drawing ratio than the critical one, a metal mesh netting or perforated workpiece is used, and tearing-off of the bottom is therefore no longer observed. This method made it possible to obtain an integral shape of the part while using a significant depth of drawing due to the prior perforation of the workpiece, which significantly reduces the cost of the product. That means that the obtained scientific result in the form of a proposed kinetic description of the stamping process compared to the known one creates such drawing conditions, under which the unevenness of the height of the cylindrical portion of the part is significantly reduced, which in turn reduces by 35-40% the cost of stamping cylindrical parts from a flat metal mesh netting with square openings. This result is interesting from a theoretical point of view. As far as the practical point of view is concerned, a mechanism of transition of plastic bending of netting meshes into cold volumetric expanding of its constituent wires has been revealed, which makes it possible to determine the conditions for using the process of manufacturing parts from metal mesh netting or perforated workpieces. Consequently, an applied aspect of using the scientific result obtained is the possibility of improving the typical technological process of stamping, where the stamping force will be significantly reduced and hence the stress in the critical section, which will make it possible to reduce significantly the limiting drawing ratio and increase the depth of stamping. This constitutes prerequisites for the transfer of the obtained technological solutions of the process of drawing from a metal mesh netting or a perforated workpiece.

Sensory zero-point clamping system for condition and process monitoring

Zero-point clamping systems are used for safe and reproducible clamping of workpieces and workpiece pallets in machine tools. Due to the high geometric repeatability of the clamping process, re-clamping errors are avoided and thus high accuracy is achieved when machining workpieces on multiple machine tools. In order to avoid errors during clamping, e.g. due to chips between the clamping surfaces, the clamping force as well as the clamping condition must be checked manually. However, this time-consuming work cannot be carried out simultaneously. In order to reduce non-productive times and to increase the process reliability, a sensory zero-point clamping system was developed. The use of sensory zero-point clamping systems enables process-parallel measurement of clamping and process forces as well as the evaluation of the clamping condition. In this paper, a method for the design and integration of strain sensors in zero-point clamping systems is presented and evaluated. For the experimental validation, four sensory zero-point clamping systems are used to clamp a workpiece pallet. The sensory zero-point clamping system is used for process as well as condition monitoring. As an example of process monitoring, the determination of clamping and process forces that occur during milling is presented. Within the scope of the experimental investigations, a clamping force resolution of 32 N and a process forces resolution of 2 N was achieved. Furthermore, the monitoring of different clamping conditions is shown on the basis of the detection of erroneously missing pallets in the machine tool and the existence of foreign objects between the clamping surfaces. It is shown that deviations from the target states of these conditions can be detected. This offers potential to avoid non-productive times and geometry errors of the workpieces.

Selection of a workpiece clamping system for computer-aided subtractive manufacturing of geometrically complex medical models

Abstract Physical models of anatomical structures can be made using Additive Manufacturing (AM) or Subtractive Manufacturing (SM). The advantage of subtractive techniques over additive ones is the possibility of maintaining the homogeneity and consistency of the processed material, which is extremely important in the case of medical devices. Currently, a geometrically complex medical model can be made even on a simple, 3-axis CNC machine tool. However, often the semi-finished product must be machined in at least two clamping configurations. The aim of the work is to present the method of fixing a workpiece in the process of subtractive production of geometrically complex medical objects on the example of skull bone prostheses. The paper discusses the use of two clamping systems for machining such models. It presents the process of subtractive production of bone prostheses models fitted to the defect of the skull bone with the use of the proposed methods of fixing the workpiece. The result of the work are two models of the skull bone prosthesis. A more complex model was analysed in terms of the accuracy of geometry reproduction. The research confirmed the usefulness of the proposed clamping systems for the preparation of medical models of geometrically complex anatomical structures.

Near-Net-Shape Trimming Process by Abrasive Water Jet Cutting of High-Performance Workpieces for the Aerospace Industry

High-performance materials offer enormous potential for increasing the efficiency of many complex and highly stressed systems in the aerospace industry. However, due to their special material properties, most of these materials are very difficult to machine using conventional machining processes such as turning, milling and drilling. In comparison, water jet cutting technology offers all the prerequisites to bring high-performance materials to their final contour and to efficiently realize a large portion of the material removal. Because of the complex geometry of 3D components used in the aerospace industry, a further development of existing system technology as well as the generation of cutting paths, which are usually designed for pure 2D machining, is required. The aim of the study is the implementation of an automated pre-contouring for difficult to machine materials using abrasive water jet cutting for industrial 3D applications. This is achieved by using an innovative workpiece clamping as well as a new cutting technology, the trimming, in order to reduce the costs of the pre-contouring process as well as the time and resource consumption of the entire process chain. During trimming, a continuous cut takes place and the semi-finished product is brought closer and closer to the required component geometry by cutting off the outer material areas. For this purpose, tests were carried out on workpieces made of stainless steel X5CrNi18 (EN 1.4301) with cutting conditions that are demanding for the abrasive water jet cutting process, such as high cutting depths with simultaneously low cutting angles. It was possible to use these findings to extend existing material models and thus ensure an error-free path generation for cutting processes. The investigations are the basis for the future use of waterjet cutting for near-net-shape machining of workpieces with complex 3D geometry. The experiments showed promising results in terms of the economic efficiency of the trimming process and provide a basis for subsequent investigations with difficult-to-machine workpieces for the aerospace industry.

The use of finite element analysis in studying deformations of parts clamped in machine tool devices

Increasing the productivity and quality of products while reducing production costs are the main objectives of manufacturing companies in the market economy. For companies that produce parts using cutting processes, these objectives are strongly influenced, among other factors,by the devices used during the manufacturing process. Devices must allow the clamping of workpieces to be done in a short period of time, to have simple construction, to be cheap while positioning and installing errors to be minimal to ensure that the parts correspond to the manufacturing documentation. The calculation of clamping errors of workpieces and devices involves complex analysis, therefore in order to accurately determine these errors, data obtained from experiments, sometimes costly and difficult to be done, are used. This paper presents the clamping force calculation of a prismatic part, as well as the study of elastic deformations that appear by clamping it in the device, using finite element analysis.

Experiment and simulation analysis on the mechanism of the spindle barrel finishing

The spindle barrel finishing is commonly used to improve the surface integrity of the important parts of the high-end equipment while it is difficult to provide enough test artifacts for the traditional trial and error experiment to obtain the desirable processing technology. The EDEM simulation of the spindle barrel finishing can provide effective help for the process design. In this paper, simulations and experiments are conducted based on the identical apparatus and conditions to facilitate the comparison and validation between each other. The parameters required in the simulation are determined based on reliable experiments. In order to explain the interaction of ceramic media and metal workpieces in the finishing barrel, firstly, the depth of material wear on the surface of the workpiece is obtained, and the amount of material removal is calculated in conjunction with Archard wear theory based on the Hertz-Mindlin with Archard wear model in EDEM. The relationship between the amount of material removed and the time and position of workpiece clamping is quantified. It is in good agreement with the experimental results; the maximum deviation is 20.14%. The finishing mechanism is analyzed based on the motion trajectory of the barrel finishing media that are in contact with the workpiece observed in the simulation and the corresponding contact forces obtained from both the simulation and the experiment. Furthermore, the machining effect of the workpieces after the finishing process is discussed considering the analysis of the motion trajectory and the contact force. The achieved trajectories permit to calculate the active working time. This work provides an understanding of spindle barrel finishing process fundamentals and guidelines for optimal operating conditions.

Improving Clamping Accuracy of Thin-walled Workpiece in Turning Operation

This study presents theoretical and experimental error analysis and avoidance which results from the fixation of a thin-walled metal disk workpiece on a duplex turning machine. The distance between the rotating workpiece surface and a fixed datum point is measured using a laser displacement sensor (LDS). The measured data are analyzed numerically to get the error in the fixation system in terms of Euler angles. Then the workpiece clamping points are axially adjusted according to the calculated angles. Moreover, the problem formulation and the solution procedures are presented in details. Finally, a case study has been used to verify the proposed approach. The results indicate that the proposed technique can be used to decrease the fixation error to a reasonable range.