Form Deviation Research Articles

Improvement of NC Program Quality based on Shape Generation Motions and Feed Drives for Five-Axis CNC Machine Tools

Five-axis Computer Numerical Control (CNC) machine tools, integrated with Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) systems, are used to machine complex parts and reduce trials and errors. However, these machine tools still rely on Numerical Control (NC) programs and often lack accuracy and precision due to poor quality when implemented in the machine. This research aims to enhance the quality of NC programs for five-axis CNC machine tools by focusing on shape generation motions and a closed-loop feed drive system with Proportional-Integral-Derivative (PID) control. The individual motions were mathematically described using 4x4 transformation matrices, incorporating kinematic motion deviations, end mill geometry, machining parameters, and cutting forces derived from virtual machining. Additionally, a closed-loop feed drive system with PID control was integrated with the new position and angular data of each axis from the shape generation motions model. The new NC programs were validated by machining an S-shaped part and measuring dimensional errors at 64 points before and after using a Coordinate Measuring Machine (CMM). The results indicate a substantial reduction in the standard deviations of form and angular errors within the NC program quality, totaling approximately 80.73%. Reductions are demonstrated in the standard deviations for the X, Y, A, and B axes, with decreases of 76.83%, 95%, 82.40%, and 68.72%, respectively indicating a significant improvement in the overall quality of the NC program.

Form Deviation Uncertainty and Conformity Assessment on a Coordinate Measuring Machine

Coordinate measuring machines are widely used in the industrial field due to their ease of automation. However, estimating the measurement uncertainty is a delicate task, especially when controlling for deviation, given the large number of factors that influence the measurement. A precise estimate of the uncertainty is crucial to avoid incorrect conformity assessments. The purpose of this study is to control geometrical-form tolerance specifications, taking into consideration their associated uncertainty. A surface fitting model based on the least squares criterion is proposed, allowing one to obtain the variance–covariance matrix by iterative calculation according to the Levenberg–Marquard optimization method. The form deviation is then evaluated following the Geometrical Product Specifications (GPS) Standard, and its associated uncertainty is estimated using the guide to the expression of uncertainty in measurement (GUM) propagation of the uncertainty law. Finally, the conformity assessment is performed based on the measured deviation and its associated uncertainty. Different results for the measurement of straightness, flatness, circularity, roundness, and cylindricity are presented and detailed. This model is thereafter validated by a Monte Carlo simulation, and interlaboratory comparisons of the obtained results were performed, which showed satisfactory outcome. This contribution is of great use to manufacturing companies and metrology laboratories, allowing them to meet the normative guidelines, which stipulates that each measurement result must be accompanied by its associated uncertainty.

Accuracy of the geometric shape of the hole in the longitudinal section during honing

The wide application of honing as a finishing treatment of internal cylindrical surfaces for cylinder-piston systems, used in some structures, is caused by high accuracy measured in tenths of a micrometer, and high productivity of the process. The most important indicator of reliable operation of cylinder-piston systems are high requirements for the geometric accuracy of holes. Due to the lack of sufficient theoretical justification for the selection of honing parameters ensuring the accuracy of the geometric shape of the hole in the longitudinal section, the authors proposed a model for the formation of errors in the geometric shape of the hole. The model is built on the kinematic characteristics of the process including the ratio of the honing stone dimensions, the length of the hole, the stroke of the honing head, the ratio of the speeds of translational and rotational movements, and the force action in the processing zone, which changed due to the presence of an overrun of the honing stone. To obtain analytical dependencies ensuring the minimisation of form deviations, the conditions for stock removal for the points of the machined surface were considered, the value of which was taken proportional to the path of movement, and the pressure value. For this purpose, graphs of the distribution functions of displacements and pressure changes were constructed depending on the coordinate of the point location on the generating line of the hole being machined. Using the obtained analytical dependencies, the potential occurrence of a shape error in the form of a saddle shape was found, the dominant factor influencing the value of which is the value of the honing stone overrun. At the same time, it was identified that the ratio of the speeds of translational and rotational movements has an insignificant effect on the violation of the form in the longitudinal section.

Fourier Features and Machine Learning for Contour Profile Inspection in CNC Milling Parts: A Novel Intelligent Inspection Method (NIIM)

Form deviation generated during the milling profile process challenges the precision and functionality of industrial fixtures and product manufacturing across various sectors. Inspecting contour profile quality relies on commonly employed contact methods for measuring form deviation. However, the methods employed frequently face limitations that can impact the reliability and overall accuracy of the inspection process. This paper introduces a novel approach, the novel intelligent inspection method (NIIM), developed to accurately inspect and categorize contour profiles in machined parts manufactured through the milling process by computer numerical control (CNC) machines. The NIIM integrates a calibration piece, a vision system (RAM-StarliteTM), and machine learning techniques to analyze the line profile and classify the quality of contour profile deformation generated during CNC milling. The calibration piece is specifically designed to identify form deviations in the contour profile during the milling process. The RAM-StarliteTM vision system captures contour profile images corresponding to curves, lines, and slopes. An algorithm generates a profile signature, extracting Fourier descriptor features from the contour profile to analyze form deviations compared to an image reference. A feed-forward neural network is employed to classify contour profiles based on quality properties. Experimental evaluations involving 60 machined calibration pieces, resulting in 356 images for training and testing, demonstrate the accuracy and computational efficiency of the proposed NIIM for profile line tolerance inspection. The results demonstrate that the NIIM offers 96.99% accuracy, low computational requirements, 100% inspection capability, and valuable information to improve machining parameters, as well as quality classification.

AscentAM: A Software Tool for the Thermo-Mechanical Process Simulation of Form Deviations and Residual Stresses in Powder Bed Fusion of Metals Using a Laser Beam

Due to the tool-less fabrication of parts and the high degree of geometric design freedom, additive manufacturing is experiencing increasing relevance for various industrial applications. In particular, the powder bed fusion of metals using a laser beam (PBF-LB/M) process allows for the metal-based manufacturing of complex parts with high mechanical properties. However, residual stresses form during PBF-LB/M due to high thermal gradients and a non-uniform cooling. These lead to a distortion of the parts, which reduces the dimensional accuracy and increases the amount of post-processing necessary to meet the defined requirements. To predict the resulting residual stress state and distortion prior to the actual PBF-LB/M process, this paper presents the finite-element-based simulation tool AscentAM with its core module and several sub-modules. The tool is based on open-source programs and utilizes a sequentially coupled thermo-mechanical simulation, in which the significant influences of the manufacturing process are considered by their physical relations. The simulation entirely emulates the PBF-LB/M process chain including the heat treatment. In addition, algorithms for the part pre-deformation and the export of a machine-specific file format were implemented. The simulation results were verified, and an experimental validation was performed for two benchmark geometries with regard to their distortion. The application of the optimization sub-module significantly minimized the form deviation from the nominal geometry. A high level of accuracy was observed for the prediction of the distortion at different manufacturing states. The process simulation provides an important contribution to the first-time-right manufacturing of parts fabricated by the PBF-LB/M process.

A new approach to identify wear regions on bearing surfaces of retrieved endoprostheses

Although total hip replacements (THR) can be considered one of the most successful implantable medical devices in history, wear remains the ultimate challenge in order to further increase clinical success. Wear assessment on retrieved implants is the most reliable way to perform research into failure mechanisms. Therefor the bearing surface of the explant is measured geometrically by coordinate measuring machine (CMM).Wear determination in geometrical data is carried out in 3 steps: (1) identifying the worn area, (2) reconstructing the pre-wear geometry and (3) quantify wear as the difference between worn area and pre-wear geometry. In previous studies, assumptions to pre-wear geometry had been made for wear determination (step 2) and the worn area was identified by deviations between measured data and assumed form. Thus, the original form of the retrieved endoprostheses, including form deviations due to the manufacturing process and implantation, was not considered which leads to uncertainties in the wear computed.This work introduces a method which allows to identify the wear area without making assumptions to the original form. Instead, the curvature of the bearing surface obtained by simple computations on the measurement data is analysed and the edge of the wear region is recognized by its deviation in curvature.The method is applied to a retrieved Metal-on-Metal prosthetic head and the results are compared to those of the well-known method introduced by Jaeger et al., in 2013. With the new approach the wear region is identified more accurately.

An improved tolerance analysis method for gear mechanisms considering form deviations and elastic-plastic contact behaviors

The contact quality between geometric features significantly affects the assembly accuracy and dynamic performance of mechanical products. However, accurate and efficient contact problem solving is currently a common challenge in the fields of tolerance analysis and tooth contact analysis (TCA). In this paper, a tolerance analysis method for gear mechanisms considering form deviations and elastic-plastic contact behaviors is proposed. Specifically, tolerance modeling of systematic and random deviations on tooth surfaces is represented by skin model shapes (SMS). Elastic-plastic contact behaviors including contact deformation, status, and stress distribution are modeled and calculated by a modified boundary element method (BEM). The accuracy and efficiency of this BEM algorithm are verified by comparing with the finite element method (FEM), indicating that the BEM can greatly improve the computational efficiency while maintaining high solution accuracy. A case study for a pair of spur gears demonstrates the significant effects of contact behaviors on transmission performance. This research provides an effective method to introduce mechanical contact behaviors in tolerance analysis of gear mechanisms. In addition, the contact simulation results can also be adopted in the analysis of vibration, reliability, and other aspects.

Incident angle optimization with multiple conflicting objectives based on BP-MOPSO in oblique laser interferometry

The oblique incident phase-shifting interferometric measurement method is an effective technique for assessing gear tooth form deviation. In the measurement process, the tooth flank incident angle is a crucial factor determining the quality of interferograms. Addressing the challenge in traditional optical path design, where the selection of the tooth flank incident angle encounters a trade-off among quality features such as measurable tooth area (MTA), interference fringe density (IFD) and interferogram compression ratio (ICR), this paper proposes an optimized method for the tooth flank incident angle. Firstly, a comprehensive evaluation model is established to calculate and analyze the MTA, IFD and ICR of the helical gear. Secondly, by integrating BP neural network and Multi-Objective Particle Swarm Optimization (MOPSO) algorithm, a tooth flank incident angle optimization method is devised to simultaneously optimize the measurement light incident angle γ and the rotation angle of the gear axis β. Finally, simulation analyses and physical experiments are employed to demonstrate the feasibility of the proposed method, compared to before optimization, the pseudocorrelation (PSD) value has increased by an average of 34%, and the residual points have decreased by an average of 80%, confirming its capability to improve quality interferogram and measurement accuracy.

Endoscopic self-expandable metal stent versus endoscopy vacuum therapy for traumatic esophageal perforations: a retrospective cohort study

BackgroundTraumatic esophageal perforations (TEP) are a grave medical condition and require immediate intervention. Techniques such as Esophageal Self-Expandable Metal Stent (E-SEMS) and Endoscopic Vacuum Therapy (EVT) show promise in reducing tissue damage and controlling esophageal leakage. The present study aims to compare the application of EVT to E-SEMS placement in TEP.MethodsRetrospective cohort study valuated 30 patients with TEP. The E-SEMS and EVT groups were assessed for time of hospitalization, treatment duration, costs, and clinical outcome.ResultsPatients treated with EVT (24.4 ± 13.2) demonstrated significantly shorter treatment duration (p < 0.005) compared to the group treated with E-SEMS (45.8 ± 12.9) and patients submitted to E-SEMS demonstrated a significant reduction (p = 0.02) in the time of hospitalization compared to the EVT (34 ± 2 vs 82 ± 5 days). Both groups demonstrated a satisfactory discharge rate (E-SEMS 93.7% vs EVT 71.4%) but did not show statistically significant difference (p = 0.3155). E-SEMS treatment had a lower mean cost than EVT (p < 0.05). Descriptive statistics were utilized, arranged in table form, where frequencies, percentages, mean, median, and standard deviation of the study variables were calculated and counted. The Fisher's Exact Test was used to evaluate the relationship between two categorical variables. To evaluate differences between means and central points, the parametric t-test was utilized. Comparisons with p value up to 0.05 were considered significant.ConclusionE-SEMS showed a shorter time of hospitalization, but a longer duration of treatment compared to EVT. The placement of E-SEMS and EVT had the same clinical outcome. Treatment with E-SEMS had a lower cost compared with EVT.

Precision of diamond turning sinusoidal structures as measurement standards used to assess topography fidelity

In optical surface metrology, it is crucial to assess the fidelity of the topography measuring signals. One parameter to quantify this is the small-scale fidelity limit T FIL defined in ISO 25 178-600:2019. To determine this parameter, sinusoidal structures are generated, where the wavelengths are modulated according to a discrete chirp series. The objects are produced by means of ultra-precision diamond face turning. Planar areas and regions with slopes below 4° could be produced with form deviations of ≲10 nm. An initial estimate of the cutting tool’s nose radius resulted in a deviation that caused the ridges of the structures to be too narrow by approximately 150 nm, while the trenches were too wide. At the bottom of narrow trenches, deviations are observed in the form of elevations with heights of about 20 to 100 nm. The measurement standard investigated in this study has also been used to characterise optical instruments in a round-robin test within the European project TracOptic, which requires precise knowledge of the geometry of all structures. The geometry of the topography, cosine structures superimposed with form deviations, was measured using the Met. LR-AFM metrological long-range atomic force microscope of the German National Metrology Institute.

A Comprehensive Study on the Challenges of Using Pure Water Jet as Post-Treatment of Abrasive Water Jet Milled Pockets in Titanium Alloy

Abrasive waterjet (AWJ) machining offers the possibility of creating a wide range of features on mechanical parts with different degrees of complexity with a relatively high efficiency. However, after the roughing passes, the surface quality of features such as blind pockets is rather low, with unfavorable implications for surface waviness and form deviations apart from high surface roughness. Apart from the traditional methods for finishing, such as grinding or lapping, it is worth attempting either to improve the surface quality obtained during roughing by an AWJ or to integrate a post-processing step by using a pure WJ in the existing process in order to ameliorate the surface quality. Thus, in the current study, the effect of pure waterjet (WJ) post-processing of machined pockets by AWJ milling on a Ti-6Al-4V workpiece using recycled glass beads was investigated under different conditions. The findings indicate that although the different post-processing treatments by a pure WJ can affect the surface quality on average, these differences are not considerably important, probably due to an insufficient capability of material removal, which hinders the smoothing effect on machined surfaces. Thus, it was indicated that a higher number of post-processing passes under different conditions than those of the roughing pass can be more favorable for efficient post-treatment by a pure WJ.

G-code generation for deposition of continuous glass fibers on curved surfaces using material extrusion-based 3D printing

Improving the mechanical properties of 3D printed parts produced through a material extrusion-based 3D printer with continuous fibers (carbon, glass, and aramid) has been a focal point for numerous researchers. Given the layered nature of additive manufacturing (AM) processes, wherein parts are built up layer by layer, most studies involve the deposition of continuous fibers onto a 2D surface. Cases involving curved surfaces have employed robots with high degrees of freedom. This research introduces a method for depositing continuous glass fibers onto curved surfaces, implemented on a cost-effective material extrusion-based 3D printer. The presented approach involves G-code modification, the incorporation of a rotating axis for the nozzle, and the application of computer-aided design and manufacturing techniques. Experimental results affirm the efficacy of this method for depositing continuous fibers onto curved surfaces. The developed technique enables the production of free-form composite shells with a thermoplastic matrix and continuous fiber reinforcement. Lastly, through 3D scanning of the printed sample and subsequent comparison with the 3D model, the degree of surface form deviation and tolerance is determined. The maximum deviation identified in this study is 0.1 mm, a tolerable amount considering the inherent characteristics and behaviors of thermoplastic materials (shrinkage and warpage) during production processes.

PROBLEMS OF MEASUREMENTS OF ROUNDNESS DEVIATIONS WITH THE USE OF COORDINATE MEASURING MACHINES

This work deals with the problem the measuring of form deviations of rotating parts with the use of coordinate measuring machines equipped with a scanning probehead. The authors investigated the influence of the measurement speed and the number of sampling points on the results of the roundness deviation assessment. The experiments were carried out on a Prismo Navigator coordinate measuring machine (Zeiss) equipped with a VAST GOLD XXL head for a scanning speed range of 10 to 60 mm/s and for three different values of sampling points on the roundness profile. The results were compared with reference values obtained from the Taylor Hobson Talyrond 365 instrument. The measurements results were compared both quantitatively (by means of roundness parameter compliance analysis) and qualitatively (by visual analysis of profiles obtained at different scanning speeds). The research showed that the scanning speed can significantly affect the result of the roundness deviation measurement with the use of CMMs.

Kinematic accuracy analysis for cam mechanism considering dynamic behavior and form deviations

Previous research on tolerance analysis has primarily overlooked the influence of mechanical vibration on the accuracy of motion, neglecting its significance in systems with moving components. To bridge this research gap, we propose an innovative tolerance analysis framework that combines the theories of skin model shapes and system dynamics. The skin model shapes are employed to represent the form deviations of the workpiece, while the principles of system dynamics are utilized to describe and analyze dynamic behavior. Then, we conduct simulation studies on cam mechanisms to show tolerance analysis outcomes with the consideration of mechanical vibration. This study also defines an index to measure the impact of internal mechanical system components on tolerance analysis. Our findings indicate that the presence of dampers reduces the effect of surface deviation of parts on kinematic accuracy, which is associated with the value of damping coefficient. Therefore, when the internal damping effect of the system is considered in the tolerance analysis, the tolerance design requirements of the parts can be appropriately relaxed, thereby reducing the cost.

A layerwise geometric error compensation procedure for additive manufacturing

PurposeThe purpose of this paper is to provide a new procedure for in-plane compensation of geometric errors that often appear in the layers deposited by an additive manufacturing (AM) process when building a part, regardless of the complexity of the layer geometry.Design/methodology/approachThe procedure is based on comparing the real layer contours to the nominal ones extracted from the STL model of the part. Considering alignment and form deviations, the compensation algorithm generates new compensated contours that match the nominal ones as closely as possible. To assess the compensation effectiveness, two case studies were analysed. In the first case, the parts were not manufactured, but the distortions were simulated using a predictive model. In the second example, the test part was actually manufactured, and the distortions were measured on a coordinate measuring machine.FindingsThe geometric deviations detected in both case studies, as evaluated by various quality indicators, reduced significantly after applying the compensation procedure, meaning that the compensated and nominal contours were better matched both in shape and size.Research limitations/implicationsAlthough large contours showed deviations close to zero, dimensional overcompensation was observed when applied to small contours. The compensation procedure could be enhanced if the applied compensation factor took into account the contour size of the analysed layer and other geometric parameters that could have an influence.Originality/valueThe presented method of compensation is applicable to layers of any shape obtained in any AM process.

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.

Gear involute artifacts with sub-micron profile form deviations: manufacture and new design

Gear involute artifact (GIA) is a kind of calibration standard used for traceability of involute metrology. To machine GIAs with sub-micron profile form deviations, the effect on the involute profile deviations caused by the geometric deviations and 6-DoF errors of the machining tool based on the double roller-guide involute rolling generation mechanismwas analysed.At the same time, a double roller-guide involute lapping instrument and a lapping method for GIAs was proposed for lapping and in-situ measuring the gear involute artifacts. Moreover, a new GIA with three design base radii (50 mm, 100 mm, and 131 mm) was proposed for more efficient calibration and was machined with profile form deviations of 0.3 μm (within evaluation length of 38 mm, 68 mm, 80 mm, respectively, measured by the Chinese National Institute of Metrology), and the surface roughness Ra of the involute flanks was less than 0.05 μm. The research supports small-batch manufacturing for high-precision GIAs.

Lateness in production systems - In a nutshell: How to determine the causes of lateness at work systems?

Adherence to customer due dates is the yardstick for the performance of manufacturing companies. In the era of same-day delivery, consumers expect reliable delivery of ordered goods and short delivery times. Also, in the field of business-to-business supply, it is evident that adherence to delivery dates is a fundamental logistical objective for companies. Contract manufacturers, in particular, are confronted with significant challenges: strong fluctuations in customer demand, shorter requested delivery times, and high competitive pressure require appropriate organisation, planning and control of production. However, companies often miss their schedule reliability targets and fail to identify the right causes for these failures. This raises the question of what factors influence the failure to meet schedule reliability targets, how to identify such factors, and what options are available to counteract them. This contribution addresses this issue and focuses on ways to analyse the emerging lateness at work systems in production areas as a deviation of the actual form the planned throughput time. We present existing approaches to analysing the lateness behaviour at work systems and extend the current theory of logistical modelling to determine the three drivers of the so-called relative lateness – planning influences, variance of work-in-process (WIP) and sequence deviations – at work systems systematically. Through this analysis, we enable the practical applicator to initiate target-oriented countermeasures to improve the schedule reliability of their work systems with acceptable analysis expenditure.

In-situ sub-aperture stitching measurement based on monoscopic phase measuring deflectometry

This study introduces a novel sub-aperture stitching method based on monoscopic deflectometry for measuring large-aperture optical surfaces. The proposed method involves capturing sub-apertures of the surface under test (SUT) at different fields of view by rotating the SUT, and utilizing the gradient deviation and form deviation at the overlapped areas of adjacent sub-apertures as an objective optimization. This approach not only corrects the system calibration error but also improves the relative positions between sub-apertures. Then the SUT is reconstructed by integrating the global gradient to achieve full-aperture measurement of the SUT. The feasibility of the method is validated through experiments, demonstrating that the stitching accuracy is comparable to that of off-site optical measuring instruments.

Clipping in Qubadi Jalilzada's poetry

Generally speaking, literature is a rethinking of reality and the imagination, especially poetry, with its unique form and qualities such as ancient rhetoric and modern deviation devices. Any literary work must have some form deviation, in addition to creativity and poetic imagery, whether it is a change in meaning or a change in the texts structure, to be engaging for the reader, Cilliping is a bussinesing and art, we want to show all of nice art in poity. A component of structural deviation is clipping. In his poetry, jalilzada employs a variety of this approach, including the clipping of letters, words, images, half-lines( a verse), and single lines. The manipulation of this literary technique is done for both economic and aesthetic purposes, and it helps the poet stand a part from his predecessors. It implies that this device is being used as a language game and a literal device of a text. As a result, its employment demands a high level of literal quality, and a randomly selected clipping without skillful application does not always serve a texts aesthetic value. Thus, the researcher aims Because clipping affects internal and eexternal rhymes and enhances the texts aesthetic beauty, it is used to distinguish between a poetical and an unpoetical text. Thus, as a skilled poet, jalilzada has used clipping in his poetry. to illuminate the literal and aesthetical types of clipping in jalizadas poetry.