Flatness Error Research Articles

Data preprocessing for flatness measurements of large precision workpieces

Abstract Measuring the flatness error of large precision workpieces quickly and accurately is a difficult problem. A new method for preprocessing flatness measurement data based on MSE (mean squared error) is proposed. A mathematical model of a new data preprocessing method was established, and the mathematical formula for model solving was derived in detail. The data were measured by digital level on the plane of the granite base with dimensions of 2340 m×1540 mm. The new method and SmartLevel (basic measurement system of the level computer) were used to calculate and process the data. The flatness errors after diagonal evaluation were 4.07 μm and 3.90 μm, respectively. The relative error of the two was 4.36%, which confirmed the reliability and accuracy of the new method. The data results show that this method can be effectively used for the engineering measurement of the flatness of large precision workpieces.

Spatial Trueness Evaluation of 3D-Printed Dental Model Made of Photopolymer Resin: Use of Special Structurized Dental Model.

(1) Background: Various 3D printers are available for dental practice; however, a comprehensive accuracy evaluation method to effectively guide practitioners is lacking. This in vitro study aimed to propose an optimized method to evaluate the spatial trueness of a 3D-printed dental model made of photopolymer resin based on a special structurized dental model, and provide the preliminary evaluation results of six 3D printers. (2) Methods: A structurized dental model comprising several geometrical configurations was designed based on dental crown and arch measurement data reported in previous studies. Ninety-six feature sizes can be directly measured on this original model with minimized manual measurement errors. Six types of photo-curing 3D printers, including Objet30 Pro using the Polyjet technique, Projet 3510 HD Plus using the Multijet technique, Perfactory DDP and DLP 800d using the DLP technique, Form2 and Form3 using the SLA technique, and each printer's respective 3D-printable dental model materials, were used to fabricate one set of physical models each. Regarding the feature sizes of the simulated dental crowns and dental arches, linear measurements were recorded. The scanned digital models were compared with the design data, and 3D form errors (including overall 3D deviation; flatness, parallelism, and perpendicularity errors) were measured. (3) Results: The lowest overall 3D deviation, flatness, parallelism, and perpendicularity errors were noted for the models printed using the Objet30 Pro (overall value: 45 μm), Form3 (0.061 ± 0.019 mm), Objet30 Pro (0.138 ± 0.068°), and Projet 3510 HD Plus (0.095 ± 0.070°), respectively. In color difference maps, different deformation patterns were observed in the printed models. The feature size proved most accurate for the Objet30 Pro fabricated models (occlusal plane error: 0.02 ± 0.36%, occlusogingival direction error: -0.06 ± 0.09%). (4) Conclusions: The authors investigated a novel evaluation approach for the spatial trueness of a 3D-printed dental model made of photopolymer resin based on a structurized dental model. This method can objectively and comprehensively evaluate the spatial trueness of 3D-printed dental models and has a good repeatability and generalizability.

Electric discharge aided surface post-treatment of laser powder bed fused non-planar metallic components for enhanced form accuracy

Laser powder bed fusion (LPBF) of metals is an advanced technology gaining popularity in the manufacturing domain for producing near net shape products. The feasibility in batch production and design freedom highlights the promising scope of LPBF over conventional fabrication methods. However, loss of geometrical and dimensional accuracy is a critical challenge in LPBF due to solidification induced volumetric shrinkage and formation of surface irregularities. The aforementioned challenge gets aggravated whenever the fabricated components are non-planar. Studies on post-processing induced modification of dimensional and form accuracy of LPBF components is limited in literature. Moreover, the existing post-treatment operations using laser source, chemicals and mechanical forces exhibit limitations in ensuring desired geometrical accuracy in LPBF components. Therefore, the feasibility evaluation of integrating an alternate post-processing method with LPBF in improving geometrical accuracy become meaningful and worth exploring. Thus, the present study investigates the efficacy of a low energy thermo-electric post-processing method called wire electrical discharge polishing (WEDP) in ensuring geometrical form and dimensional accuracy of LPBF components. The study proposes a mathematical model which discloses the factors to be considered for dimension compensation in computer aided design (CAD) model. The results of the present study indicate that the proposed approach can impart notable reduction in form deviation leading to improved geometrical accuracy. The substantial error in terms of circularity over LPBF curved specimens were drastically reduced after WEDP process. Moreover, the cylindricity of curved specimens was improved by ~80 %. Despite the reduction in flatness error to ~7 μm, the irregularities pertaining to the edges were successfully removed from inclined LPBF surfaces resulting in sharp edged profile. The polishing speed was observed to be strongly dependent on the stair-stepping effect over vertically built LPBF surface. The discharge energy in WEDP played a vital role in influencing the circularity and surface integrity of the processed surface. Furthermore, the thermal impact of WEDP process leads to microstructural modification near the surface, whereas residual stress state after WEDP remains similar to LPBF condition. In a nutshell, the WEDP method looks promising in improving the geometrical and dimensional accuracy of LPBF components thereby enhancing the acceptability of parts in industrial applications.

The Flatness Error Evaluation of Metal Workpieces Based on Line Laser Scanning Digital Imaging Technology

With the development of intelligent manufacturing, the production and assembly accuracy of components in factories is increasing in line with growing demand. However, the traditional manual quality inspection is inefficient, inaccurate, and costly. To this end, digital and optical imaging techniques are used to achieve intelligent quality inspection. However, during the reconstruction process, the high reflectivity of object materials affects the speed and accuracy of reconstruction results. To overcome these problems, this study investigated the three-dimensional (3D) digital imaging techniques based on line laser scanning. It advances a novel methodology for image segmentation, underpinned by deep learning algorithms, to augment the precision of the reconstruction results while simultaneously enhancing processing velocity. After the reconstruction phase, the research assesses flatness tolerance using point cloud registration technology. Finally, we constructed a measurement platform with a cost of less than CNY 100,000 (about USD 14,000) and obtained a measurement accuracy of 30 microns.

Research and Development of a Multi-Point High-Precision Displacement Measuring System for the Installation Space of Vibration Isolation on Submarine Raft Structures

The well installed status of raft vibration isolation is undoubtedly of great significance in marine engineering, especially for submarines. To achieve this, the accurate measurement of the installation space of the vibration isolation is necessary. The traditional measuring technique has many drawbacks. Therefore, simultaneously measuring the multi-point spacing with high precision between two metal surfaces is the focus of this work. Based on eddy current sensing principle, a multi-point spacing measuring system with a simple structure and good measurement accuracy has been developed and reported. The system includes a sensor array component, an integrated controlling component, and a calibration platform. The measured data from multiple points are obtained at the same time through the sensor array and are uploaded to the host computer and a corresponding LabVIEW program was exploited to display, process, and store the spacing results. Furthermore, the least square algorithm has been employed to calculate the flatness of the measured metal surfaces, and the GUM (guide to the expression of uncertainty in measurement) method has been applied to evaluate the flatness error uncertainty. The experimental tests show that each measuring duration only lasts for seconds to get results and the error uncertainty of the measured surface flatness could reduce to less than 1.0 μm. The developed measuring system has better efficiency and higher precision compared to traditionally manual operations. The measuring and analysis method could also be applied to other related situations.

Design and Fabrication of a New Filament, PLA with PTFE as Fillers, for Water Repellent Surfaces

The use of additive manufacturing by fused deposition is a versatile, cost-effective and simple prototyping and manufacturing technique that is generating and accelerating a revolution in equipment and filaments. However, materials are limited to a small number of polymers. It is a scientific challenge to bring new characteristics and properties to the parts obtained. In this work, a new filament has been designed with the combination of PLA (poly lactic acid) as matrix and PTFE (polytetrafluoroethylene) as filler. This filament has improved the water repellency of the parts obtained. Cleaning, demoulding, anti-adherence, anti-frost, anti-humidity and anti-bacterial applications can be deployed with this new filament. Extruded filaments have been obtained with PLA beads and PTFE micropowder. Flat test tubes have been produced with this filament. The experiments included PTFE fillers (1% to 40% by weight). The surfaces have been characterised by sliding angle (SA) and static contact angle (CA) tests, surface roughness (Sa and Sz), flatness error and % water adsorption. The results indicate, as expected, that the higher the fluoropolymer content, the higher the hydrophobicity, reaching values of 125° for CA and 9° for SA, and the % adsorption decreases. In terms of roughness, the surfaces are less rough when the PTFE load increases. On the other hand, the flatness is a property strongly affected by the % PTFE load and at values higher than 15% it produces intense warping and deformation of the specimens. Finally, the PTFE loading thresholds in the PLA matrix have been obtained below which the wettability and dimensional reproduction properties are balanced and optimal.

Determination of the Feasibility of Using Eco-Friendly Walnut Shell Abrasive Particles for Pocket Milling of Titanium Workpieces by Abrasive Waterjet Technology

Abrasive waterjet technology is nowadays a well established non-conventional method with significant capabilities for material removal with high productivity and minimum environmental impact compared to other processes. However, in order to be in line with the green transition directives, further steps are required to ensure the sustainability of manufacturing processes and reduce the risk of material depletion by employing recyclable materials. For this purpose, an eco-friendly abrasive material such as walnut shell is employed for pocket machining of a titanium alloy workpiece. Due to the relatively low hardness of this material, compared to common abrasive materials such as garnet or alumina, it is required to determine the appropriate range of process parameters in order to obtain high-quality pockets with high productivity. Thus, in this work, a comprehensive experimental study is conducted in order to determine the effect of various process parameters on pocket depth, pocket width, material removal rate, flatness and parallelism error of produced pockets. The results prove the feasibility of using walnut shell as abrasive material for pocket milling, although MRR is almost an order of magnitude lower than the values commonly obtained for usual abrasives. Moreover, it is not recommended to use jet pressure values over 250 MPa so dimensional accuracy, flatness and parallelism error are maintained in acceptable values.

Splicing Measurement and Compensation of Straightness Errors for Ultra-Precision Guideways.

The straightness error of guideways is one of the key indicators of an ultra-precision machine, which plays an important role in the machining accuracy of a workpiece. In order to measure the straightness error of a long-distance ultra-precision guideway accurately, a splicing measurement for the straightness error of a guideway using a high-precision flat mirror and displacement sensor was proposed in this paper, and the data splicing processing algorithm based on coordinate transformation was studied. Then, comparative experiments on a splicing measurement and direct measurement of the straightness error were carried out on a hydrostatic guideway grinder. The maximum difference between the two measurements was 0.3 μm, which was far less than the straightness error of 5.8 μm. The experiment demonstrated the correctness of the proposed splicing measurement method and data processing algorithm. To suppress the influence of the straightness error on machining accuracy, a straightness error compensation algorithm based on error rotation transformation and vertical axis position correction was proposed, and the grinding experiment of a plane optics with a size of 1400 mm × 500 mm was carried out. Without error compensation grinding, the flatness error of the element was 7.54 μm. After error compensation grinding, the flatness error was significantly reduced to 2.98 μm, which was less than the straightness errors of the guideways. These results demonstrated that the straightness error of the grinding machine had been well suppressed.

The level measuring method of machine tool flatness and its data processing of three far point method and least square method

The flatness error of the machine tool worktable is an important index to evaluate the worktable. The measurement process of flatness error is complex, and data processing is difficult. Aiming at the indirect method of flatness using the level, this paper introduces in detail the grid method path planning method, the original data recording method, the calculation method of local data conversion, and the calculation method of global coordinate sorting, conversion, and verification. On this basis, the three distant point method and the least square method are used to process the original data respectively, and the least square method is solved by MATLAB to obtain the flatness error. Through the example of flatness measurement of rectangular worktable of machining center, the path planning method, original data processing, three far point method, and least square method are further introduced. The research of this paper standardizes the flatness measurement method and data processing method of the level in detail, which can improve detection efficiency and data accuracy.

Ultra-precision time-controlled grinding for flat mechanical parts with weak stiffness

High-precision flat mechanical parts are widely used, such as in aerostatic bearing, which requires a rather high machining precision. Due to large size, low stiffness and other machining problems, traditional ultra-precision grinding machine tool cannot directly achieve the final precision, so manual grinding is necessary to meet the manufacturing requirements, resulting in low efficiency. Based on the computer-controlled optical surfacing (CCOS) method and the flexible grinding process, the time-controlled grinding method (TCG) is proposed to achieve quantitative material removal at each position on the workpiece. Combined with the material removal mechanism, the removal function with good linearity and stability is extracted by controlling corresponding parameters. By applying a novel measuring and processing method of surface data with high precision and high efficiency, the flatness error and parallelism error are accurately obtained and used as grinding reference to carry out the time-controlled grinding experiment on one spacer ring with a diameter of 190 mm. The final flatness error converges from 1.5–2 μm to 0.6–0.7 μm and parallelism error converges from ~2 μm to ~0.6 μm, while the roughness converges from 273 nm Ra to 65 nm Ra, achieving the goal of ultra-precision digital machining of submicron level. The machining precision is better than traditional ultra-precision grinding machine tool, and the potential for time-controlled grinding method of ultra-precision machining in flat mechanical parts especially with low stiffness is verified.

Intelligent Assembly Method of the Profiled Thermal Battery Pack Based on Improved DE Algorithm

An intelligent assembly method was designed to realize the intelligent assembly of the profiled thermal battery pack and improve its assembly accuracy. Firstly, as the number and size of different monomer batteries vary, this paper takes the monomer thermal battery assembly as the object, with a common shape circle assembly screw arrangement and an established process model. Then, the assembly also has an improved differential evolution algorithm for assembly arrangement and process on the number, location, tightening of the screw assembly, torque, and the order of solutions. According to this scheme, the assembly and the flatness test were carried out. The results showed that the bottom plate of the assembly frame was “concave in the middle and warped around”, and the flatness error was large. The scheme was optimized by numerical simulation analysis. After optimization, the average offset of the floor plane was 0.04 mm, and the offset accounted for 0.028% of the overall height; the maximum offset was 0.094 mm and the offset was reduced by 0.312%.

Five-degrees-of-freedom error motion measurement method of precision rotary table based on BMPES

It is essential to obtain the five-degrees-of-freedom (5-DOF) error motion of a rotary table to reconstructthe real trajectory of the rotating shaft, but there are many error coupling problems when measuring the error motion of a rotary table. In order to improve the measurement accuracy of the 5-DOF error motion of the rotary table, a method of measuring the error motions based on bidirectional multi-point error separation (BMPES) is proposed. First, by analyzing the motion characteristics of the rotary table with multiple degrees of freedom error during the rotation, a detection system with a double-layer structure probe arrangement is designed. Then, the three-point method is used in the radial direction to separate the roundness error of the measuring disk, which improves the measurement accuracy of radial error. Finally, the coupling relationship between the mixing errors collected by the axial probes is researched, and a face-four-point error separation method is proposed, which can separate the flatness error of the lower surface of the measuring disk and complete the decoupling of the tilt error and the axial runout error. Simulation results show that for the measurement of radial, tilt and axial errors, the measurement errors of the BMPES method proposed in this paper are reduced by 97.89%, 68.40% and 99.99%, respectively, compared with the five-point method, and when eccentricity errors exist, the measurement errors of the radial and tilt errors are reduced by 99.06% and 85.67%, which verifies that the method can accurately obtain the 5-DOF motion of the rotary table errors.

Completion of all Winding Packs for ITER Toroidal Field Coils in Japan

In Japan, National Institutes for Quantum Science and Technology (QST) has the responsibility to develop nine toroidal field (TF) coils, each of which consists of a winding pack (WP) and coil case for the ITER project. The WP consists of seven double-pancakes (DPs), which consist of conductors inserted into D-shaped radial plates (RPs). Although a WP is significantly large (14 m high and 9 m wide), the position of the current center line of the WP must be controlled within a few millimeters. Therefore, numerous technical challenges arose in DP and WP manufacturing. Herein, in the RP manufacturing, the optimization of welding and machining procedures, and accurate manufacturing techniques were established. Subsequently, all RPs were fabricated around the flatness errors of 1 mm from the nominal. In cover plate (CP) welding, the welding procedure was optimized so that a good DP flatness after CP welding was achieved. In the WP insulation, by developing a method to insulate a WP while applying compression, the dimensions within errors of a few milli-meters is achieved in all of WPs. Consequently, all nine WPs were successfully completed for TF coils in Japan in March 2022.

PRELIMINARY INVESTIGATION ON THE EFFECT OF CUTTING PARAMETERS ON SURFACE ROUGHNESS AND FLATNESS IN DRY MILLING OF PMMA

Polymethylmethacrylate (PMMA) also known as Plexiglass is a commonly used material for many applications, especially in medical industry. In some application, PMMA parts may be also used as molds for enabling fabrication of final products. Some of these parts are manufactured by injection molding, but in many cases mechanical machining of some surfaces is still required. The cutting of PMMA requires a previous optimization of the cutting parameters combination (feed rate and spindle speed). If this optimization is not carried out, the problems encountered may refer to cutting debris or material melting during machining and, consequently, the material attaches to the tool cutting edge. This will result in a surface with very poor quality, in terms of aspect and surface roughness. This paper reports on the preliminary experimental investigation of cutting parameters on the surface roughness and flatness error in dry milling of PMMA. The cutting experiments were conducted on EMCO MILL 55 CNC drilling and milling machine. The design of experiment (DOE) consists in L27 (33) design, meaning a three factorial experimental plan (3 factors on 3 levels). The cutting parameters, respectively depth of cut, feed rate and spindle speed are taken as inputs and surface roughness and flatness are taken as outputs. The surface flatness was measured with TESA Micro-Hite coordinate measuring machine. Analysis of variance (ANOVA) was adopted to identify the statistical influence of each input parameter and combination of input parameters on surface roughness. From the preliminary results, it can be observed that optimum regime is a combination of low feed rate, low depth of cut and high spindle speed. Moreover, an artificial neural model is proposed for prediction of surface roughness and flatness considering the depth of cut, feed rate and spindle speed as input variables. This approach aims to reveal the possibility of predicting the output parameters using neural network modelling, that can be further used to optimize the cutting regime.

Development and Application of Flatness Analysis System based on Coordinate Measuring Data

To realize flatness error evaluation based on coordinate measuring data, the calculation process of four evaluation methods was analyzed, and a direct calculation method of minimum zone flatness was proposed. According to the calculation process of different evaluation methods, the flatness error analysis system based on coordinate measuring data was developed, and the accuracy of the system was verified by importing the case data of related research. The practicability of the system was verified by using the developed system in the measurement task.

Formation mechanism of concave and convex surface shapes in double-sided lapping

Double-sided lapping process is a key technology for obtaining high efficiency and flatness in fabricating plane-parallel workpiece surfaces, such as wafers, optical windows, seal rings, etc. However, the formation of the concave and convex surface shapes of workpieces was rarely investigated in the previous research, and the mechanism was unknown. This paper establishes a new kinematic model to clarify the formation mechanism of concave and convex surface shapes, in which the workpiece eccentricity and rotation in the planetary wheel are considered for the first time. The measurement and control method of workpiece rotational speed in the planetary wheel is proposed. The formation of the concave and convex surface shapes is validated experimentally by adjusting the rotational speed of the workpiece, and the results show a good consistency with the calculation results. A flatness error convergency method is proposed based on the surface shape formation mechanism, and flatness superior to 5 µm is achieved on Φ200 × 2 mm thin copper substrates.

Circular saw flatness on machine measurement using a point laser displacement sensor

The flatness error is one of the critical parameters of a circular saw, which seriously affects the cutting performance. In this paper, the measurement of the circular saw flatness error based on a laser displacement sensor is proposed. For the tooth of a circular saw, the plane is discontinuous. According to the field detection demand of a circular saw, the authors collected Archimedean spiral three coordinate data of the circular saw using a laser displacement sensor. Considering the practical application of circular saw flatness detection, the authors have established an ideal plane model of the flatness based on the least-squares method to evaluate the flatness error of circular saws. The system has a maximum detection area of 400 mm × 400 mm, the measurement time is 80 s, and the measurement absolution accuracy is 10 μm.

Improving the surface integrity of additively manufactured curved and inclined metallic surfaces using thermo-electric energy assisted polishing

Laser powder bed fusion (LPBF) is an advanced layer by layer manufacturing process gaining increased interest in industrial sector owing to its complex design flexibility. However, the parts produced using LPBF are not directly used in practical applications due to the geometrical inaccuracy and poor surface quality resulting from surface irregularities and defects. The established methods for post-processing LPBF parts/components such as laser polishing, abrasive polishing, chemical polishing and conventional finishing methods have inherent limitations depending on the variation in geometric shape/profile of the components. Hence, the present study analyses the effectiveness of a low energy wire electrical discharge polishing (WEDP) method in improving the surface quality and form accuracy of curved and inclined AlSi10Mg samples fabricated using laser powder bed fusion (LPBF). A geometrical model is proposed in the study for estimating the depth of material removed in each polishing pass. The developed model is capable of predicting the number of polishing passes required for the removal of irregularities on the surface. The geometrical form accuracy of metallic AM samples was improved significantly after WEDP with more than 68 % reduction in cylindricity error and 75 % reduction in flatness error. In addition, the samples exhibited uniform surface finish after WEDP with ~50–60 % reduction in as-built roughness. The SEM analysis conducted in the study reveals that WEDP is capable of eliminating the stair stepping surface defect with enhancement in geometrical profile. Furthermore, the EDS analysis confirmed the formation of oxide layer on the LPBF surface after WEDP post-processing.

Effect of wire material and discharge energy on productivity and surface integrity of WEDM-processed Inconel 718

ABSTRACT The current work aims to study the influence of discharge energy and debris accumulation on wire break failure and surface integrity aspects like surface roughness, subsurface hardness, and geometrical errors during the wire EDM of Inconel 718. The responses considered for analysing the geometrical accuracies are flatness error, roundness error and cylindricity error. Four different wire electrodes were considered for the study based on the wire strength and coatings, namely hard zinc coated brass, half-hard zinc coated brass, hard uncoated brass, and half-hard uncoated brass wire electrodes. The geometric accuracy of the machined parts is closely related to the choice of wire electrode. High-tensile strength hard wires were observed to machine the surfaces with maximum accuracy. Also, the zinc coated wires were observed to cut faster compared to the uncoated wire electrodes. The study revealed that there exists a strong influence of discharge energy on the surface integrity of wire electric discharge machined surface. The zinc and copper elemental contamination was minimal for uncoated wire electrodes at lowest discharge energy mode. Wire wear phenomena was analysed for both coated and uncoated wires. Discharge energy had a significant impact on the electrode wear of coated and uncoated wire electrode.

Experimental Investigation of Face Milling Surface Study on AA1100 by Using VMC

Abstract: Aluminum alloys are extensively used as a main engineering material in various industries such as automotive industries, the mould and die components manufacture and the industry in which weight is the most important factor. Surface roughness is an important measurement of product quality since it greatly influences the performance of mechanical parts as well as production cost. The purpose of this research was to investigate the effect of the main factors of the surface roughness in aluminum semi-solid AA1100 face milling. The results of the research could be applied in the manufacture of automotive components and mold industries. This study was conducted by using computer numerical controlled milling machine with 40- millimeter diameters fine type carbide tool with twin cutting edge. The experimental results were evaluated using Taguchi technique. Machining timing, and Flatness were mainly influenced with feed. MRR was mainly influenced with DOC. Practically minimum flatness error obtained at low speed with maximum feed and depth of cut. During this operation very low surface finish 0.520 µm generally it can achieve cylindrical grinding process. Keywords: AA 1100, face milling, Ra, CMM, flatness error