Machining Tolerances Research Articles

Three-Dimensional Synthesis of Manufacturing Tolerances Based on Analysis Using the Ascending Approach

The present paper develops a new approach for manufacturing tolerances synthesis to allow the distribution of these tolerances over the different phases concerned in machining processes using relationships written in the tolerance analysis phase that have been well developed in our previous works. The novelty of the proposed approach is that the treatment of non-conventional surfaces does not pose a particular problem, since the toleranced surface is discretized. Thus, it is possible to study the feasibility of a single critical requirement as an example. During the present approach, we only look for variables that influence the requirements and the others are noted F (Free). These variables can be perfectly identified on the machine, which can be applied for known and unknown machining fixtures; this can be the base for proposing a normalized ISO specification used in the different machining phases of a mechanical part. The synthesis of machining tolerances takes place in three steps: (1) Analysis of the relationship’s terms, which include the influence of three main defects; the deviation on the machined surface, defects in the machining set-up, and the influence of positioning dispersions; then (2) optimization of machining tolerance through a precise evaluation of these effects; and finally (3) the optimization of the precision of the workpiece fixture, which will give the dimensioning of the machining assembly for the tooling and will allow the machining assembly to be qualified. The approach used proved its efficiency in the end by presenting the optimal machining process drawing that explains the ordered phases needed to process the workpiece object of the case study.

Validation of spine SBRT using a 3D printed Anthropomorphic phantom

A segment of a spine was 3D-printed based on real patient anatomy, using metal-doped high density plastic to radiographically mimic bone. This spine was submerged in a water tank to create an anthropomorphic phantom. The spine print incorporated a slot for Gafchromic EBT3 film dosimeters and fiducials for alignment of measured and calculated dose distributions. Spine SBRT treatment plans were generated for both 6 MV and 10FFF energies based on oncologist-drawn contours transferred from real anatomy. Plans were delivered under image guidance using our clinical procedures, to evaluate the dosimetric accuracy of our planning system in high density inhomogeneities and the geometric accuracy of delivery. Results show that the Acuros XB algorithm (dose-to-water) agrees well with film measurements throughout the measured region, including within the bone substitute material. Alignment of the steep dose gradients in planned and measured doses was within 0.5 mm in the ANT-POST direction and within 0.9 mm in the SUP-INF direction, both within machine tolerances. Our results give us confidence in our ability to plan and accurately deliver spinal SBRT treatments.

Development of an End-Toothed Disc-Based Quick-Change Fixture for Ultra-Precision Diamond Cutting

With its standardized and unified interface, the quick-change fixture is an important part for maintaining high efficiency without compensation of precision in the metal-turning process because it can conveniently realize high-precision repeated clamping and multi-station conversion without complex positioning and adjustment steps. However, the existing quick-change fixture products and related research cannot fully meet the needs of repeatability and applicability raised from ultra-precision, single-point diamond turning with ultra-high accuracy and ultra-small depth of cut. In this paper, we develop a quick-change fixture for ultra-precision diamond turning, in which the end-toothed disc acts as the positioning element. Specifically, the main parameters of two key components of the end-toothed disc and slotted disc spring are calculated analytically to ensure the positioning accuracy of the designed fixture used in the rotation condition, which is further ensured by controlling the machining tolerance of the tooth profile of the end-toothed disc. Additionally, finite element simulations are performed to investigate the static and modal states of the quick-change fixture, which demonstrate a maximum deformation of about 0.9 μm and a minimum natural frequency of 5655.9 Hz for the designed fixture. Two high-precision sensors are used to detect the radial jump and end run-out values after repeated clamping actions, which are employed to verify the repetitive positioning accuracy of the fixture. Subsequent finite-element simulation of the clamping of small-diameter copper bar, as well as the diamond turning experiment, jointly demonstrate that the designed fixture can achieve a precision of 1 μm. Current work provides an effective quick-change fixture to reduce the deformation of a weak-stiffness workpiece caused by clamping deformation in ultra-precision diamond cutting.

Experimental and analytical evaluation of tool path error using computer integrated nonlinear kinematical modeling for a 4DOF parallel milling machine

ABSTRACT Machining errors in parallel kinematic machines primarily depend on their extent of kinematic nonlinearity. In this paper, a computer integrated model of the kinematic nonlinearity and trajectory interpolation method for a 4DOF parallel milling machine is developed. The nonlinear errors prompted during various trajectory modes are analyzed. It is proved that in order to avoid significant non-linearity, the actuator and the end-effector space must possess identical order of trajectory. The effects of tool path length, its spatial location, and the Jacobian matrix properties on the kinematic nonlinearity error, are studied. Results showed that the path length is the governing factor for the nonlinear behavior of the mechanism. Moreover, the kinematic error is illustrated to have a reverse relationship with maximum singular values of the inverse Jacobian matrix. Experiments are conducted using digital dial indicators. Experimental results verified the accuracy of the proposed mathematical approach and confirmed its applicability in actual machining processes. Moreover, the proposed interpolation algorithm successfully limits the kinematic error under the machining tolerance by minimal segmentation. Finally, it is demonstrated that the proposed method is superior in terms of accuracy, to the median osculating circle (MOC) method.

Variational simulation of Schwinger's Hamiltonian with polarization qubits

The numerical emulation of quantum physics and quantum chemistry often involves an intractable number of degrees of freedom and admits no known approximation in the general form. In practice, representing quantum-mechanical states using available numerical methods becomes exponentially more challenging with increasing system size. Recently, quantum algorithms implemented as variational models have been proposed to accelerate such simulations. Here, we study the effect of noise on the quantum phase transition in the Schwinger model within a variational framework. The experiments are built using a free space optical scheme to realize a pair of polarization qubits and enable any two-qubit state to be experimentally prepared up to machine tolerance. We specifically exploit the possibility to engineer noise and decoherence for polarization qubits to explore the limits of variational algorithms for noisy intermediate-scale quantum architectures in identifying and quantifying quantum phase transitions with noisy qubits. We find that despite the presence of noise, one can detect the phase transition of the Schwinger Hamiltonian even for a two-qubit system using variational quantum algorithms.

Improving contact resistance in metal–ceramic heat exchangers running liquid metal by additive manufacturing and ceramic tubes with electroplated films

In the search for thermal management of advanced avionics packaging, materials such as eutectic liquid metal (LM) alloys and synthetic ceramics with superior thermophysical properties offer reliable and effective solutions. Conductive ceramic tubes can be used to contain LM as a coolant for heat exchangers. However, conductive ceramics will still need to be combined with metals to provide optimal thermal and structural performances. Additive manufacturing (AM) technologies have also shown they can facilitate novel approaches for fabricating efficient multi-material structures. Recently, we developed an in situ AM approach for embedding prefabricated components, such as ceramic tubes, inside a metallic block without parting surfaces for better sealing and more intimate contact between the metal and ceramic. In this selective laser sintering (SLS) approach, metal powders are melted near embedded ceramic tubes to close interfacial gaps associated with surface roughness and machining tolerances, resulting in a contact resistance at the metal–ceramic interface that is reduced relative to conventional packaging approaches. In this paper, we demonstrate how metallic cold plates can be fabricated with improved power dissipation by encapsulating highly conductive ceramic tubes with a SLS metal structure. To optimize the adhesion of the melt pool, the surface of the ceramics is electroplated to reduce surface defects and chemistry in order to improve the wettability of the ceramic. Experimental results of the cold plate prototypes fabricated by in situ AM technique revealed up to a 1.6× improvement in heat transfer compared to cold plates packaged by a conventional assembly technique, and results are validated through further numerical and analytical approaches.

Die Placement Advancement for Prevention of Silhouetted Die Occurrence on LGA Package

In semiconductor packaging industry, silhouetted die defect is occasionally encountered in singulation process esp. on substrate land grid array (LGA) package with tight clearances. This paper is focused on the prevention of the silhouetted die occurrence as it would affect the assembly yield performance of the device. The silhouetted die is caused by the tight clearance of die edge to package edge, given the machine and process tolerances. Process enhancement and optimization were done through adjusting the die placement accordingly as per the defined measurement. Eventually, the occurrence of silhouetted die was successfully mitigated by formulating the appropriate die placement references.

Microscale flow and heat transfer between the rotor and the flank for rotary engine

This paper is to investigate microscale flow and transfer between the rotor and the flank for rotary engine. The rotor and flank are simplified to two disks in order to study flow field and temperature field conveniently. The paper takes analysis of steady laminar flow and heat transfer between two disks separated by a gas-filled gap due to machining tolerance. A 3-D multi-physical coupling model is used, involving velocity slip, temperature jump, rarefaction, and dissipation. A solution based on commercial code COMSOL is derived and the results are used to illustrate the effects to velocity field, temperature distribution, disks' torque, and Nusselt number based on the governing parameters. The paper also investigates the effects of different modified Knudsen number on flow field and temperature field.

A Data-Driven Machining Error Analysis Method for Finish Machining of Assembly Interfaces of Large-Scale Components

Abstract To guarantee the final assembly quality of the large-scale components, the assembly interfaces of large components need to be finish-machined on site. Such assembly interfaces are often in low-stiffness structure and made of difficult-to-cut materials, which makes it hard to fulfill machining tolerance. To solve this issue, a data-driven adaptive machining error analysis and compensation method is proposed based on on-machine measurement. Within this context, an initial definite plane is fitted via an improved robust iterating least-squares plane-fitting method based on the spatial statistical analysis result of machining errors of the key measurement points. Then, the parameters of the definite plane are solved by a simulated annealing-particle swarm optimization (SA-PSO) algorithm to determine the optimal definite plane; it effectively decomposes the machining error into systematic error and process error. To reduce these errors, compensation methods, tool-path adjustment method, and an optimized group of cutting parameters are proposed. The proposed method is validated by a set of cutting tests of an assembly interface of a large-scale aircraft vertical tail. The results indicate that the machining errors are successfully separated, and each type of error has been reduced by the proposed method. A 0.017 mm machining accuracy of the wall-thickness of the assembly interface has been achieved, well fulfilling the requirement of 0.05 mm tolerance.

Leakage study of a lubricant-free revolving vane compressor

• Analytical model for leakage paths in a lubricant-free revolving vane compressor. • CFD studies were used to obtain correlations for equivalent leakage channel widths. • 3D leakage flow model developed with one-directional Fanno flow model. • Analytical leakage model is accurate with discrepancies at ±15% This study presents an approach to study the three-dimensional internal leakage gas flow occurring in a lubricant-free revolving vane compressor. In this study, the two-dimensional analytical analysis was first carried out using Fanno flow through the leakage paths. This is then expanded by computing the equivalent width of the leakage path which was obtained from a comprehensive three-dimensional computational fluid dynamics model, to form a three-dimensional analytical leakage flow model. Thereafter, measured data from the physical prototype was collected and used to formulate a set of effective leakage flow coefficients. The resultant three-dimensional leakage model was then used to predict the internal leakage flow in the lubricant-free compressor. The results show that the proposed three-dimensional internal leakage model was able to predict the internal leakage of the compressor within discrepancies of ±15%. Subsequent studies show that with better machining tolerance control, a practical volumetric efficiency above 90% can be achieved by the lubricant-free revolving vane compressor.

Kinematic error analysis of the rotor vector gear reducer with machining tolerances

The rotor vector (RV) gear reducer is a mechanism used for motion and torque transmission. With characteristics similar to a traditional cycloidal gear drive, it has been popularly applied in precision machinery because of its high-speed reduction ratio, large torque capacity, and high efficiency. In this work, we aim to analyze the kinematic error (transmission error) of the RV reducer with manufacturing and/or assembly tolerances. Formulae for the kinematic error are established by using the theory of gearing as well as tooth contact analysis. Subsequently, sensitivities of the kinematic error with respect to various design parameters are investigated. Lastly, a process to simulate the distribution of maximum kinematic errors of the gear reducer with various tolerance grades of the parts is developed via Monte Carlo method. It is shown that through selected tolerance control on the machine parts, the accuracy of the gear drive can be retained. The results of this work can be useful for controlling the manufacturing precision on the machine parts and assessing the overall accuracy of the mechanism in the design phase.

FEM-based optimization approach to machining strategy for thin-walled parts made of hard and brittle materials

Thin-walled parts are widely used in the aerospace, automotive, and medical industries. High machining efficiency is desired as much of the material needs to be removed. The aggressive machining strategies are often applied but tend to cause poor surface finish, inadequate machining tolerance, and even fracture of workpiece. Thus, it is of vital importance to adopt reasonable machining strategy and choose accurate machining parameters considering of both the machining efficiency and quality. In this paper, an optimization approach to enhance machining efficiency for thin-walled parts made of hard and brittle material without compromising machining quality was proposed. The core idea of the proposed approach is to minimize the maximum stress of the thin-walled part during machining by optimizing the workpiece shape based on finite element method (FEM). The stiffness of the thin-walled parts during machining retains high while the machining induced deformation is small. The optimization approach was experimentally validated on K9 glass, and the maximum deformation of the thin-walled part for the optimal machining strategy decreases significantly compared with that of traditional machining strategy and the total machining time is reduced by 44%.

WR-3 Band Waveguide Filter Tolerance Analysis and Surface Metallization Comparison

In this paper, a fifth-order WR-3 band waveguide filter with two transmission zeros (TZs) is presented. The design process is described and manufacturing issues are addressed. The filter is designed to fulfill a center frequency of 237.9 GHz and a fractional bandwidth of 2.64%. Three identical filters are manufactured with the classical computerized numerical control (CNC) milling technique in order to obtain information about the manufacturing repeatability for filter structures in the WR-3 band. The comparison shows that even in very high frequency regions a good repeatability can be achieved, if modern high-speed cutting (HSC) CNC milling machines are used. A comprehensive tolerance analysis is accomplished to classify the obtained results. The filters were manufactured from brass to ensure a meaningful comparability and due to the good machining qualities in CNC machines. In order to reduce the losses, the filters are afterwards sputtered with different materials (gold, silver, copper) to evaluate the effect on the insertion loss at very high frequencies. In comparison with the literature, it is shown that even narrow-band filters, which show a high sensitivity to machining tolerances, can be manufactured with high reliability and manufacturing repeatability in modern CNC milling machines. One of the measured filters shows a return loss higher than 20 dB over the whole passband.

Multioutput Circuit for Low Voltage Ultracompact W-Band Klystron

In this article, the design, characterization, and manufacture of a circuit for a ${W}$ -band, ultracompact continuous wave sheet beam klystron are described. This klystron, aiming to produce more than 1.5-kW output power, operates at a comparatively low voltage benefiting the device size and extending its application space. However, a lower operation voltage adversely affects the beam-gap interaction efficiency. Two multigap output cavities have been employed to achieve a higher beam interaction efficiency without introducing additional competing modes or shrinking the interval between the operation mode and competing mode. Inspired by the resynchronization technology, the second output cavity can be optimized for the spent beam from the first output cavity. Comprising a single cavity output structure, the circuit efficiency of this double output cavity circuit is increased from 2.37% to 4.96%. In this circuit, electromagnetic modeling and design have been optimized to avoid complicated structures which are constrained by current mechanical design and manufacturing techniques. The MAGIC simulation shows that, driven by a 1-W RF signal, this circuit can extract more than 1.7-kW output power from a 35-kV, 1-A beam. A prototype single output cavity circuit has been designed and manufactured to determine the required machining tolerances for the final double output cavity circuit.

Комплексне технологічне оснащення адаптивного типу для токарної обробки кільцевих деталей

The main problem of dimensional ring parts turning is insufficient rigidity of work piece and technological system at all. In many cases due to the ring parts clamping their deformations are proportionate to the machining tolerance. In this way the achievement of the given parameters of ring work pieces machining surface shape accuracy is a complicated technological and production task. The machining error minimization is possible only with correctly selected machining methods and tooling equipment. Using the developed complex technological equipment comprises multi-tool devices of adaptive type as well as corresponding clamping devices with equilibrium distribution of clamping force and its regulation possibility. This is an effective technique of minimization of elastic strains as well as deformations due to the cutting forces in the machining the ring parts inner surfaces. The recommendations justification was provided for use of double tool equipment of adaptive type in ring parts machining. The method of these parts shape errors determination is proposed taking into account the influence of clamping loads and cutting forces in the machining with the double tool equipment. The developed technique allows determining minimal quantity of clamping elements and acceptable clamping forces range by the final profile of machining. This guaranties the necessary roundness tolerance of ring cylindrical parts providing their reliable clamp during machining.

On the stability of well-type ionization chamber source strength calibration coefficients.

To investigate the variability and stability of brachytherapy source strength calibration coefficients for air-communicating and pressurized well-type ionization chambers among high-dose rate (HDR), low-dose rate (LDR), and electronic brachytherapy (EBT) source qualities. These qualities of an ionization chamber are important features to assess given their role in maintaining traceability to a primary national standards laboratory and facilitating efficacious patient care in brachytherapy. The calibration records from the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) customer well-type ionization chamber database were retrospectively analyzed for calibrations performed between 1996 and 2019. A statistical analysis was performed and differentiated among calibration type to quantify the distribution of chamber calibration coefficients among several chamber models. Distributions were quantified based on their moments and by quantile analysis. For LDR calibrations, chamber response was further differentiated by seed type to study the variability in seed dependence within and across chamber models. In addition to these metrics, the calibration lineage at the UWADCL was used to assess the stability of these calibration coefficients among chamber model and source type based on the ratio of subsequent calibration coefficients. The distribution of brachytherapy source strength calibration coefficients for a particular chamber model is not necessarily normally distributed and is sensitive to changes in the machining tolerances or design of the chamber model. Calibration source quality also influenced the distributions of calibration coefficients for a chamber model; the air-kerma rate calibration coefficients for EBT sources were the most variable followed by LDR and then HDR source types. The stability of a chamber's source strength calibration coefficient exhibited a similar dependence on the source quality. Air-communicating and pressurized chambers exhibited an average stability between subsequent calibrations of 0.2% and 3.0%, respectively, for HDR calibrations, but could exhibit more than double this variability characteristic of their leptokurtic distributions. For LDR calibrations, the spread and stability in a model's calibration ratio toward another seed type is extensive and notable. For some seed types and chamber models exhibit variations of <0.5% while others exceeded 2.0%. Furthermore, the magnitude of this dependence is outside the variability of the source's source strength due to manufacturing, which was determined from the manufacturer and NIST source strength intercomparison records at the UWADCL. As a result, establishing and disseminating calibration conversion factors among different source and chamber models is not advised as it would substantially increase the uncertainty in a clinical user's determination of source strength. The calibration of a well-type ionization chamber is unique to the chamber, source, and source holder. Attempting to generalize source strength calibration coefficients among chambers of the same model or source type is impractical given the variation in response observed across the calibration history of the UWADCL. Attempting to quantitate and transfer calibration coefficients in such a relative sense may significantly degrade the uncertainty relative to specifically calibrating a chamber for an individual source.

Large-volume centimeter-wave cavities for axion searches

The scan rate of an axion haloscope is proportional to the square of the cavity volume. In this paper, a new class of thin-shell cavities are proposed to search for axionic dark matter. These cavities feature active volume much larger (>20×) than that of a conventional cylindrical haloscope, comparable quality factor Q, and a similar frequency tuning range. Full 3D numerical finite-element analyses have been used to show that the TM010 eigenmodes are singly polarized throughout the volume of the cavity and can facilitate axion-photon conversion in uniform magnetic field produced by a superconducting solenoid. To mitigate spurious mode crowding and volume losses due to localization, a pre-amplification binary summing network will be used for coupling. Because of the favorable frequency-scaling, the new cavities are most suitable for centimeter-wavelength (∼ 10–100 GHz), corresponding to the promising post-inflation axion production window. In this frequency range, the tight machining tolerances required for high-Q thin-shell cavities are achievable with standard machining techniques for near-infrared mirrors.

Multi-section branch-line crossover/coupler optimization for wideband applications and higher-order harmonics suppression

In this paper, we propose an optimization-driven framework for the design of wideband multi-section branch-lines that exhibit varying branch impedances. Even-odd mode analysis is performed utilizing transmission lines theory to derive the expressions of the S-parameters. Then, an error function is developed to control the electrical characteristics of the branch-lines considering predefined physical constraints including impedance matching and machining tolerance. By modifying the error function, cascaded branch-lines can operate as crossovers or couplers. To validate the proposed concept, wideband crossover and coupler prototypes are designed, simulated and measured. Simulations and measurements agree well and show improved fractional bandwidths. Moreover, odd harmonics are suppressed in the proposed designs due to enforcing the desired electrical characteristics over a given frequency band.

Design and Analysis of the Staggered Double Grating Slow Wave Circuit for 263 GHz Sheet Beam TWT

The complete design process of a high-frequency circuit for a 263 GHz staggered double grating, sheet beam traveling wave tube is presented in this article. This device, for use in a pulsed electron paramagnetic resonance spectrometer instrument, requires >30 dB gain and a 20 GHz bandwidth centered at 263 GHz. In addition to the standard Pierce gain analysis and point by point particle in cell (PIC) simulation, a novel fast pulse response analysis technique was utilized to determine the accurate synchronization voltage and test the ``hot” feature of the high-frequency circuit. Since this new method can evaluate the entire bandwidth in a single simulation, it can significantly reduce the computational resources normally required for the conventional PIC analysis while also illustrating the potential instabilities near the band edge. Good agreement between the fast pulse response and PIC simulation results validate the accuracy of this novel method. According to the analysis results and given the manufacturing limits of nano/micro-computer numerical control (CNC) machining, an appropriate SWS, coupler, and sever designs were chosen to complement the simulated design. Finally, a prototype circuit was manufactured and cold tested to verify the design and inspect the machining tolerances.

Influence of Bearing’s Flexibility on the Working of Cycloid Drive

In this article are reviewed calculate method of force distribution with accounting bearing flexibility on cycloid reducer elements of the types KHV and 2KV. There are analyzed schemas such as gear without machining errors, with constant errors on the pins and with random errors from machining tolerance. Schemas of force distribution on the pins of the types KHV and 2KV are presented. Relation between bearings flexibility and force distribution on the pins are determined, and also relation between machining errors and force distribution on the pins. Advantages and disadvantages of various methods of load estimation in the reducer are elucidated, appliance of this methods for calculation of various types cycloid reducers are analyzed.