Dimensional Tolerances Research Articles

COMPARISON OF FORGING LOAD, MATERIAL FLOW AND PRESSURE DISTRIBUTION OF THE UNI-DIRECTIONAL, BI- DIRECTIONAL AND TWO-STEP FORGING PROCESSES

Because of high productivity, closer dimensional tolerances, and minimal material waste precision forging (net or near net shape) processes have been used for manufacturing automobile components. The primary disadvantage of precision forging is the encountered higher tool stresses due to applied higher forging loads. Thus, forging load reduction is a higher priority in precision forging in terms of energy consumption and cost because higher loads required higher investment and higher energy consumption. Forging load is affected by several parameters such as temperature, material flow, the geometry of the billet, and punch movement. In this study, forging load, material flow, and normal pressure distribution in the forged part were investigated considering uni-directional, bi-directional, and two-step forging processes. FEM simulations were performed by using a solid cylindrical billet. To perform FEM simulations, the finite element analysis package (DEFORM 2D) was used. Also, experimental studies of the FEM models were performed. For bi-directional and step-forging experimental studies, a double-acting servo press was used because the movement of the top and bottom punch can be controlled accurately. Then the results of FEM and experimental studies were compared with each other. The results of the FEM simulations and experimental studies show two-step forging offers lower forging load and energy consumption whereas the uni-directional closed die forging process needs higher load and energy consumption

Calculation and selection of interference fits for restoring the shaft surface under the sealing ring by pressing thin-walled bushings

Methods for restoring shaft surfaces to nominal sizes are analyzed. It is recommended to use the thin-walled bushing method. The research used the principles of the theory of accuracy, interchangeability, and the theory of strength of materials. The input shaft of the ЯМЗ-239 engine gearbox was studied. As a result of research, a technique is developed that allows one to determine the interferences and select fits that guarantee clear fixation of pressed-in thin-walled bushings on the shaft. Keywords fit, cup-type seal, reliability, durability, interference, dimension tolerance, fit tolerance

Effects of milling parameters on roughness and burr formation in 3D- printed PLA components

This study investigated the 3D-printed PLA (Polylactic Acid) workability during the operation of milling. It is difficult to obtain as a result of a Fused Deposition Modeling (FDM) 3D printing a very strict tolerance, and a good roughness surface. A possible solution can be the usage of the last milling operation that can complete the workpiece in terms of desired roughness and dimension tolerances. A design of experiments (DOE) analysis has been applied to observe the optimizing result. Three factors have been analyzed: feed rate, depth of cut, and rotational speed. Two responses were investigated: roughness (Ra) and burr height. The results show that these two parameters present optimum results in two different values of the process parameters: the Ra is better at a higher feed rate and low depth cut, but the situation reverses for the burr height, for which lower heights are obtained when using higher feed rate and depth cut.

Единая система отсчета геометрических характеристик размерных элементов деталей. Часть I. Теория двух размеров максимума и минимума

A unified reference system for geometric characteristics is based on the classification of joints of applied mechanics, in which the class number is determined by the number of degrees of freedom limited by mating elements of parts and has received the short term «informativeness». Different information content of the bases of elements that materialize coordinate systems determines different information content of the coordinate axes – four, two, zero and different information content of design planes – three, two, one. The paper shows that the information content of elements in the functions of auxiliary bases and executive elements determines the number and type of coordinates (linear and angular), with the help of which it is necessary to set their position in the generalized coordinate system of the part. It is shown that the accuracy of coordinating dimensions should be specified by symmetrical tolerances for linear and angular dimensions.

Fully automated tool path planning for turbine blade repair

The recontouring process of aircraft engine parts like turbine blades is a manual or in best-case semi-automated process due to high individuality of the workpiece. This leads to in-process scrap because of low process stability and high process times. An automation of process planning reduces both. This paper introduces a method for a fully automated and individual tool path planning using 3D-scan data. Geometric parameters of the degenerated blade were considered to find best-suitable target geometry in a robust way. For turbine blade repair, the process stability is increased while meeting the dimensional tolerances required for the international aviation certifications.

Low-Cost Real-Time Automated Optical Inspection Using Deep Learning and Attention Map

The recent trends in Industry 4.0 and Internet of Things have encouraged many factory managers to improve inspection processes to achieve automation and high detection rates. However, the corresponding cost results of sample tests are still used for quality control. A low-cost automated optical inspection system that can be integrated with production lines to fully inspect products without adjustments is introduced herein. The corresponding mechanism design enables each product to maintain a fixed position and orientation during inspection to accelerate the inspection process. The proposed system combines image recognition and deep learning to measure the dimensions of the thread and identify its defects within 20 s, which is lower than the production-line productivity per 30 s. In addition, the system is designed to be used for monitoring production lines and equipment status. The dimensional tolerance of the proposed system reaches 0.012 mm, and a 100% accuracy is achieved in terms of the defect resolution. In addition, an attention-based visualization approach is utilized to verify the rationale for the use of the convolutional neural network model and identify the location of thread defects.

Medical Device Hybrid Manufacturing: Translating the Coordinate System From Metal Additive Manufacturing to Subtractive Post-Processing

Abstract Additive manufacturing (AM) has transformed not only how parts can be realized but also their design. Metal additive manufacturing (MAM) has increased AM’s utility toward the manufacture of functional products. This has been seen in several industries including medical device, aerospace, and the automotive industries. The main limitation of MAM continues to be the part dimensional tolerances that can be achieved, and the respective surface finish produced. Hybrid manufacturing processes have been used to address these limitations; however, there remain challenges of how to translate the component’s coordinate system from AM to subtractive post-processes. This paper explores this topic through a medical device case study. A translatable coordinate system was produced by first designing features to serve as a datum reference frame (DRF). These features were introduced by MAM and then finalized with wire-electrical discharge machining (EDM). The produced DRF features successfully prepared the component for translation from the MAM to subtractive post-process. The completed medical device component met the expected requirements with a less than 1% difference on key part nominal dimensions. In addition, the hybrid process exhibited a potential for sustainable manufacturing with a buy-to-fly ratio of 6:1. The study demonstrated that a coordinate system can be translated effectively in hybrid manufacturing by designing part features informed by both AM and wire-EDM processes.

Experimental investigation of hole geometry during electric discharge drilling of aerospace material sheet

In this research paper experimental investigation of hole geometry during electric discharge drilling (EDD) is reported on Arial material Inconel-718. Electric discharge drilling is extensively used for aerospace equipment and component manufacturing. Proper geometry and close dimensional tolerance play a very important role during operations and functioning of aerospace parts. One of the important application of electric discharge drilling is in creating cooling hole in gas channels of gas turbine engines and similar other high temperature applications. In order to understand the parametric effect on hole geometry during electrical discharge drilling on Inconel-718, experiments are conducted according to the Box-behnken design of experiments. Four main electric discharge drilling parameters considered: Flushing pressure, Discharge current, Pulse on time and Duty cycle factor. Parametric effects and their interactive influence on hole geometry are studied by plotting contour plots. Favourable range of process parameter: Flushing pressure (kPa): 26 – 30, Discharge current (amp): 2–2.5, Pulse on time (µs): 6 – 6.5, Duty cycle factor (%): 50 – 55. After validating the established favourable range, improved hole geometry in term of better circular hole is observed in range of 0.989 to 0.992. Reported results can be useful to aerospace equipment manufacturers for getting improved geometry of drilled hole and also main recommendation is useful developing efficient automation of EDD process for quality production.

Experimental characterization of the nonlinear thermomechanical behaviour of refractory masonry with dry joints

Refractory linings can withstand severe working conditions and are widely used for the linings of many high temperature applications, such as steel ladles. Some of these linings are built with dry joints. These structures undergo very complex responses in service conditions, making the prediction of its behaviour a challenging task. To develop robust numerical prediction tools, experimental validation is necessary. The present paper gathers a considerable database on the mechanical and thermomechanical characterization of refractory masonry with dry joints (up to 1500 °C). The test setups, measurement techniques, specimens, test procedures, and results of the large-scale experimental campaign are presented. The results of the tests help in understanding the complex thermomechanical behaviour of refractory linings. Aspect such as joints closure and reopening, dimensional and shape tolerances of the bricks, creep and stress relaxation are investigated. The results of these tests are essential for developing, calibrating, and validating efficient numerical models for the design and optimization of refractory masonry linings.

Cooling improvement for the machining process with the inclusion of nanoparticles using the experimental approach

Machining of hard materials has always experienced challenges in their production process owing to several elements such as surface roughness, dimensional and geometrical tolerances, machining forces, longevity of the tools, and the generated heat during the operation. In order to tackle these technical problems, cutting tools, cutting fluids, and chipping strategies have undergone precise evaluation to facilitate the machining challenges. The current study is fixated on the assessment of cutting fluids and their significant efficacy on turning process. The desirable quality of a production part in machining processes is contingent upon the effectiveness of lubrication and cooling process during the turning operation. Hence, the tests have been done under various conditions regarding the cutting fluid for the cooling purpose. This study evaluates the efficacy of dispersion in the base fluid with volume fractions of 1.5 % and 3 % on temperature of the cutting tool in Mo40 steel turning operation, compared to the conditions utilizing coolant oil and conventional dry condition. Nanofluid minimum quantity lubrication (NMQL) strategy, as the main hindrance for immoderate use of cutting fluid, has been applied within the machining phenomena of Mo40 steel. Cutting speed and feed rates have been selected as the variable input parameters, for which the tests were performed and compared. The obtained results of this work revealed that employing nanofluid in machining operation led the cutting tool to experience an average reduction of about 60 % in the temperature range. Notable to mention, the growth in concnetration of the nanofluid intensifies temperature decrement of the cutting tool. In detail, the cutting zone temperature for 3 % volume concentration found to be 2 °C less than that of 1.5 %. Furthermore, using nanoparticles improved the roughness quality of the workpiece, and tool wear. Tool geometry, tool coating, along with various nanofluids are other factors, for which the experiment can be implemented as the future study.

Multi-Ion-Based Modelling and Experimental Investigations on Consistent and High-Throughput Generation of a Micro Cavity Array by Mask Electrolyte Jet Machining.

The controllability and consistency in the fabrication of micro-textures on large-scale remains a challenge for existing production processes. Mask electrolyte jet machining (MEJM) is an alternative to Jet-ECM for controllable and high-throughput surface microfabrication with more consistency of dimensional tolerances. This hybrid configuration combines the high-throughput of masked-ECM and the adjustable flow-field of jet-ECM. In this work, a duckbill jet nozzle was introduced to make MEJM more capable of batch micro-structuring. A multiphysics model was built to simulate the distribution of electrochemical reaction ions, the current density distribution, and the evolution of the shape of the machined cavity. Experimental investigations are presented showing the influence of the machining voltage and nozzle moving speed on the micro cavity. Several 35×35 micro cavity arrays with a diameter of 11.73-24.92 μm and depth of 7.24-15.86 μm are generated on 304 stainless steel.

Optimization of the radial bearing geometry by the dimensional analysis

In order to improve the working capacity and life of bearing units, the dimensional analysis of the inner geometry of a cylindrical radial bearing was carried out. The assembly component, composed by the outer diameter dimensions of the raceway of the inner race, the inner diameter of the outer race and the two diameters of the rollers, was considered as a dimension chain. It is recommended, in order to reduce wear and friction losses, to produce the diametrical dimensions of the roller according to the fifth accuracy degree. It is established that the cause of the axial clearance between the roller and the double-flanged race is the distance between the contact points on the right and left flanges with the horizontal position of the roller, as well as the diagonal distance. Tolerances for ring dimensions, for such a combination, are recommended to accept with respect to accuracy degree 6.

Tolerance analysis method considering multifactor coupling based on the Jacobian–torsor model

Assembly quality affects the performance of mechanical products and reasonable tolerance designs are central to assembly quality. Unreasonable tolerance design leads to the mechanical equipment performance degradation under complex operating conditions. This study developed a novel tolerance analysis method that considers the influence of temperature, load, and other environmental factors based on the Jacobian–torsor and skin models. First, the deformation caused by multifactor coupling was analyzed using the finite element method, and the feature surface of deformation is extracted. Second, the deformation extraction and tolerance conversion based on the new generation geometrical product specification theory was used to convert the deformation of the feature into the dimension, orientation, and form tolerance. Third, the modified Jacobian–torsor model considering multifactor coupling was constructed by superimposing the converted tolerance with the design tolerances. Finally, the abrasion problem of the airborne actuator was considered as an example to verify the effectiveness and accuracy of the novel method. Through the accurate calculation of tolerances, it accurately analyzes the assembly state of the product under the influence of environmental factors, and provides more accurate guidance for the design and optimization of product tolerance in complex working conditions.

Research on size coupling and sensitivity analysis of SAR antenna truss rod

To eliminate the influence of the size coupling of SAR antenna truss rod on assembly accuracy, this paper defines the assembly sequence, part datum, tolerance, assembly operation, and measurement operation of the model by establishing the tolerance analysis model of the assembly dimension chain and measurement target. The assembly simulation process of the deployment mechanism is simulated, the plane deviation of the antenna panel of the deployment mechanism is analyzed, and the contribution and sensitivity data of each component ring size to the closed ring size are obtained. The simulation results show that the in-plane angle error of the antenna panel is mainly affected by the length of the component ring rod. By focusing on controlling the dimensional tolerance of the truss rods with high sensitivity, the assembly accuracy of the antenna deployment system can be guaranteed. Sensitivity is the magnification of assembly deviation by the transmission of deviation source, which reflects the influence of the change of composition tolerance on the change of functional requirements. According to the sensitivity analysis, the key dimensions that affect assembly accuracy can be obtained. The assembly requirements of high-quality and low-cost products can be achieved by strictly controlling the dimensional tolerance of key components and relaxing the tolerance of non-key components.

Prediction of Machining Condition Using Time Series Imaging and Deep Learning in Slot Milling of Titanium Alloy

Low surface quality, undesired geometrical and dimensional tolerances, and product damage due to tool wear and tool breakage lead to a dramatic increase in production cost. In this regard, monitoring tool conditions and the machining process are crucial to prevent unwanted events during the process and guarantee cost-effective and high-quality production. This study aims to predict critical machining conditions concerning surface roughness and tool breakage in slot milling of titanium alloy. Using the Siemens SINUMERIK Edge Box integrated into a CNC machine tool, signals were recorded from main spindle and different axes. Instead of extraction of features from signals, the Gramian angular field (GAF) was used to encode the whole signal into an image with no loss of information. Afterwards, the images obtained from different machining conditions were used for training a convolutional neural network (CNN) as a suitable and frequently applied deep learning method for images. The combination of GAF and trained CNN model indicates good performance in predicting critical machining conditions, particularly in the case of an imbalanced dataset. The trained classification CNN model resulted in recall, precision, and accuracy with 75%, 88%, and 94% values, respectively, for the prediction of workpiece surface quality and tool breakage.

Reprocessing Zamak laryngoscope blades into new instrument parts; an ‘all-in-one’ experimental study

IntroductionDisposable instruments in healthcare have led to a significant increase of medical waste. The aim of this study is to validate the recycling of disposable Zamak laryngoscope blades into new medical components by using a new ‘all-in-one’ affordable reprocessing setup as alternative for die-casting. MethodsA n “all-in-one” casting set-up was designed and built. Laryngoscope blades, recovered from two hospitals, were disinfected, melted and cast into dog-bones and into new instrument parts. The quality of the cast material was evaluated using X-ray fluorescence spectrometry. The mechanical properties were obtained by assessing the Ultimate Tensile Strength (UTS) and tensile tests. ResultsA recovery of 93 % Zamak was obtained using a melting temperature of 420 °C for 3 h. The XRF Spectro data showed higher Zinc and silicon concentrations when compared with Virgin Zamak. The dog-bones tests resulted in an average UTS, Yield Strength (YS) and Young's Modulus (YM) of 236 ± 61 (MPa), 70 ± 43 and 9 ± 3, respectively, representing 82 %, 103 % and 64 % of the UTS, YS and YM of standard Zamak. Functional instrument parts with extensions and inner chambers were cast with a maximal shrinkage percentage of 1 ± 1 %. DiscussionThis study demonstrates that the created “all-in-one” reprocessing method can process contaminated disposable Zamak laryngoscope blades into new raw base material and new instrument parts. Although material and surface properties can deteriorate, reprocessed Zamak still has sufficient mechanical properties and can be used to cast complex parts with sufficient dimensional tolerances and minimal shrinkage. ConclusionA micro reprocessing method was designed and used to turn disposed laryngoscope blades into new basis material and semi-finished components. Follow up studies are needed to scale and optimize this process towards a functional alternative for die casting. It should be further investigated how this process can contribute to further medical waste reduction and a circular healthcare economy.

Large Scale Vat-Photopolymerization of Investment Casting Master Patterns: The Total Solution.

The material properties and processing of investment casting patterns manufactured using conventional wax injection Molding and those manufactured by vat photopolymerization can be substantially different in terms of thermal expansion and mechanical properties, which can generate problems with dimensional accuracy and stability before and during ceramic shelling and shell failures during the burn-out of the 3D printed casting patterns. In this paper and for the first time, the monofunctional Acryloyl morpholine monomer was used for 3D printing of casting patterns, due to its thermoplastic-like behavior, e.g., softening by heat. However, the hydrophilic behavior of this polymer led to an incorporation of up to 60 wt% of Hexanediol diacrylate, to control the water absorption of the network, which to some extent, compromised the softening feature of Acryloyl morpholine. Addition of a powdered wax filler resulted in a delayed thermal decomposition of the polymer network, however, it helped to reduce the thermal expansion of the parts. The dimensional accuracy and stability of the wax-filled formulation indicated an excellent dimensional tolerance of less than ±130 µm. Finally, the 3D printed patterns successfully went through a burn out process with no damages to the ceramic shell.

Real-Time Inspection of Rod Straightness and Appearance by Non-Telecentric Camera Array

In this paper, we propose a measurement system that employs a camera array based on a non-telecentric optical system and an accompanying measurement algorithm to measure the straightness, length, diameter, and appearance of a rod. Measurements using telecentric optical systems, which employ orthogonal projection to preserve the dimensional ratios regardless of distance, are common in image-based inspection of the dimensional or geometrical tolerances of industrial products. However, some cases depend on the size of the target or inspection item, wherein it is difficult to configure a measurement system using telecentric optical systems. As an example, this study considers the measurement of straightness of a long rod and shows that it is possible to achieve high measurement accuracy using non-telecentric optical systems by introducing methods to calibrate miniscule errors and distortions that remain uncorrected in conventional image calibration methods. We also show that the same measurement allows for the measurement of other inspection items and evaluation of their respective measurement accuracies, thereby proving that a flexible image-based inspection process can be constructed using the proposed system and method.

Mathematical Modeling and Experimental Validation of Surface Roughness in Ball Burnishing Process

Burnishing is a cold working technique used as a surface enrichment to meet the desired surface properties of the workpiece. It improves the visual properties, dimensional tolerances, fatigue strength, surface roughness, and hardness of the work material by applying appropriate pressure through a complex ball burnishing tool to cause plastic deformation. In the current work, the mathematical modeling of the burnishing process was carried out to predict surface roughness by considering the process parameters such as contact radius, penetration depth, and elastic rebound. Further, a customized tungsten carbide (W.C.) insert having a hardness of 80 HRC was developed for the burnishing operation. The micro-hardness of the resulting burnished surface improved from 44 to 48 HRC. The surface quality of the tungsten carbide insert improved by up to 17.1 nm through polishing. Several experiments were performed by selecting appropriate process parameters using developed model feedback. The surface quality of the workpiece improved by up to 45 nm, which resulted in automatic improvements in fatigue strength up to seven times that of the virgin material. The results predicted from the mathematical model were in good agreement (less than 5% deviation) with the experimental results. This study helps to understand the surface formation mechanism in the burnishing process in more detail. Additionally, the achieved results show a significant improvement in the surface finish (~95%), indicating the potential of the burnishing process and how fast and cost-effective it is. The novelty of this paper lies in the improvement in surface roughness and the validation of our mathematical model results with the experimental results.

Tolerance analysis by static analogy: numerical and experimental results

Industrial requirements to design high quality products in shorter and shorter times impose the use of numerical models to estimate the geometrical deviations of these products, which are assemblies, starting from the geometrical deviations of their components. Numerical models may support this estimation activity, thus reducing the time to market and the design costs. The free-body model is an interesting numerical method to translate the tolerance chain into a static problem solved by algebraic or graphical procedures by using the free-body diagrams of force analysis. This work presents a free-body model that is able to deal with dimensional and geometrical tolerances that involve translations of the features to which the tolerances are applied. Moreover, it validates the free-body model for tolerance analysis of rigid parts by defining and solving a case study through numerical and experimental activities. The present work uses a case study to demonstrate the effectiveness of the free-body model by underlining that the experimental results obtained are very close to those from the numerical model.