Accessibility analysis for automatic inspection in CMMs by using bounding volume hierarchies

Accessibility analysis represents one of the most critical tasks in inspection planning. This analysis determines those probe orientations that can touch an inspection point without collision. This paper presents a methodology based on part discretization and the application of space partitioning techniques (kd-tree) in order to reduce the number of intersection tests between probe and part. A STL model has been used for discretizing the inspection part in a set of triangles, which permits the application of the developed system to any type of part, regardless of its shape and its complexity. Likewise, a recursive ray traversal algorithm has been used in order to speed up the traversal of the kd-tree hierarchical structure and to calculate exclusively the intersection of each probe orientation with those part triangles that can potentially interfere with it. In a further step of the analysis, the real geometry of the probe has been considered. Hence, a simplified model has been developed for each probe component (column, head, touch probe, stylus and tip) using different basic geometrical shapes. Finally, collision-free probe orientations are clustered for minimizing the orientation changes during the inspection process. Furthermore, the applied algorithm allows for determining different valid combinations of clusters. The developed system was applied to two example parts in order to prove that this methodology is adequate for the solution of real cases.     

Development of a Thermophysical Handy Tester for Non-Destructive Evaluation of Engineering Materials

Techniques of quality inspection and non-destructive diagnosis of engineering materials have been developed as procedures for determining various physical properties. The diagnostic techniques are usually based on detecting a very delicate signal concerned with changeable properties, and therefore detecting such a signal requires a great deal of experience in the procedures. In situ measurement for thermophysical properties of engineering parts is also important for judgment of the intrinsic soundness of the parts or for distinction between similar materials. The purpose of this study is the development of a thermophysical properties handy tester that can be used to simultaneously measure thermal conductivity and thermal effusivity and can be applied to the non-destructive diagnosis of numerous engineering materials. The tester consists of a portable data-acquisition unit, a probe holder equipped with a thermal probe, and a notebook computer. Measurements can be carried out by merely bringing the probe into point contact with a testing body for a period of 10 s. The thermal probe is constructed from a thin thermocouple in order to satisfy conditions based on the measurement principle. Materials that can be measured include polymeric resins, glasses, ceramics, alloys, and pure metals, among others.     

Relative positioning of toleranced polyhedral parts in an assembly

Parts with geometric (size and shape) variations generate uncertainties in every assembly configuration. The resultant uncertain assemblies are far more complicated than the nominal assembly configurations. To perform tolerance analysis, the real positions of variant parts in a variant assembly configuration need to be investigated. In this paper, a relative positioning scheme is proposed to determine the optimal configuration of variant parts in an assembly. A method of calculating and representing positions of 3D polyhedral parts in assembly has been presented. Translational and rotational constraints, which are developed corresponding to the extra degrees of freedom caused by the shape and size variation of parts, have been formulated. By computing translational and rotational constraints, the allowed motion space for each mating pair is obtained. Assembly configuration uncertainties caused by part variations are clarified by realizing the transformation of the object part according to the objective function, A 3D example is given to explain how the proposed relative positioning scheme is used in tolerance analysis of assemblies.     

Methodology for set-up planning automation of turned parts

This paper presents an automatic set-up planning module integrated in a CAPP system for rotational parts to be machined on a lathe. The developed system determines the possible set-up combinations that are necessary for a complete machining of the part as well as the order of each set-up and the surfaces to be used for clamping the part. The applied methodology takes into consideration constraints such as the geometry of both the stock and the final part, the geometry and the capacity of the chuck, and the part tolerances. In general, these constraints allow the system to obtain several valid solutions for clamping the part. Some criteria based on the clamping force and the value of tolerances have been considered in order to establish a preference order among these solutions. Finally, the analysis of linked tolerances and the tool approach direction to each surface determine the sets of surfaces to be machined within each set-up. An example part is used in the course of the paper to illustrate conveniently the methodology, and two additional case studies prove that this methodology is adequate for the solution of real cases.     

Constitutive relations for a planar,simple shear flow of rough disks

Stresses developed in a rapid simple shear flow of disks are quantified. Collisional momentum transfer is considered to be the dominant stress generating mechanism. The disks are inelastic and frictional. The restitution coefficient and the coefficient of friction together determine the transfer of momentum and dissipation of energy during a collision. The frictional coefficient generates and maintains a rotational motion of disks. The total fluctuation motion of disks consists of two translational modes and one rotational mode. The rotational mode is found to depend on both the restitution and the friction coefficient. Equipartition of energy among all modes of motion is absent. The mean rotation depends only on the mean flow gradient. The analysis assumes fluctuation modes all have constant magnitudes. Comparison with a computer simulated disk flow shows good agreement. This implies that the distribution of velocity magnitude may not be crucial to the quantification of stresses.     

A part-feature recognition system for rotational parts

In this paper, a part-feature recognition system for the conversion of a CAD language to a CAM language is developed. The parts of interest are rotational without deviation. The recognized part information is posted into a part-definition data structure, which many manufacturing functions such as computer-aided process planning, group technology coding, NC program generation, and inspection can access to. A part-feature recognition algorithm, the ‘intelligente’ of the system, is discussed in great detail. Finally, an example is evaluated to demonstrate the success of the system.     

Haptic modeling for a virtual coordinate measuring machine

Introducing a haptic device into coordinate measuring machine (CMM) inspection path planning leads to the proposal of a novel CMM off-line inspection path planning environment, a haptic virtual coordinate measuring machine (HVCMM), which makes use of the haptic modeling technique for CMM off-line programming. The HVCMM is an accurate model of a real CMM, which simulates a CMM's operation and its measurement process in a virtual environment with haptic perception. In this paper, a simple and effective mechanics model is implemented for the proposed HVCMM. The HVCMM enables CMM off-line programming to take place exactly as if an operator were in front of a real CMM and moving a real CMM probe. Even more, operators can feel the collision between the CMM and a part. Since there is a force feedback when the probe reaches the surface of the part, besides showing the contact in the HVCMM environment, it is much easier to generate a collision-free probe path than using other off-line inspection planning methods. The HVCMM not only facilitates inspection path planning, but also speeds it up because the operator does not need to slow the probe down when it is approaching an object. Combined visual and force feedback is the best indicator for selecting measurement points.     

The criterion for the unstable failure of cracked stainless steel piping subject to a combination of applied loadings

For extreme accident conditions, the applied loadings on a cracked piping system are complex and can be a combination of loads and displacements applied to various parts of the system. In investigating the problem of crack instability for such conditions, this paper analyses the model where a straight pipe, containing a circumferential through-wall crack at its mid-length position, is subject to bending deformation as a result of rotations applied at its built-in ends through rotational springs and a transverse load applied at an intermediate position along the pipe, again through an appropriate spring system. It is thereby possible to examine the effect of a wide range of loading combinations on the crack instability criterion, as derived using the tearing modulus methodology. One important conclusion is the underscoring of the view that the loading characteristics at the pipe-ends have a very important effect on crack instability.     

Detecting and locating burrs of industrial parts

Burrs (excess material) are usually squeezed out around the periphery of the mould, and are irregular and vary considerably between parts. This paper aims at the development of a machine vision system for automatic detection of burrs and peripheral defects of casting parts. This non-contact detection result can be applied to automatic deburring systems and used for automatic inspection of peripheral breakdown.

This research concentrates on flat casting parts comprising piecewise smooth curves on the boundaries. The detection procedure is based on the fact that the irregular burrs show high curvature changes in a small segment of the boundary, whereas a smooth segment without burrs presents a succession of low curvature points. Given a casting part with burrs, we arbitrarily select a few boundary points from the smooth segments and connect these points to form a polygon. The matching process then finds a corresponding polygon from the model part. The transformation parameters of rotational angle and translation between the part in the image and the model part are evaluated from these two equivalent polygons. The proposed matching algorithm is computationally fast and the time complexity is bounded by O(m), where m is the number of points on the digital boundary of the model part.     

Scanning Near-Field Millimeter-Wave Microscope: Application to a Vector-Coding Technique

The purpose of this paper is to propose an evanescent field-scanning millimeter-wave microscope to bridge the frequency gap that currently exists in probe microscopy. The method is supported by the use of a six-port-based reflectometer operating at 35 GHz in association with a microfabricated resonant micro stripline probe. The simplicity of the method makes it suitable for an industrial context and offers integration possibilities to gain in compacity, reliability, and time operation, in particular. This millimeter-wave microscope is well suited for the characterization of conductors and local electromagnetic properties of dielectrics. The resolution of the probe is experimentally verified by scanning gold lines deposited on a silicon substrate. In addition to the demonstration of the system, we propose to discuss various probe parameters that can be considered to design evanescent millimeter-wave probes (EMPs) for different applications. An original use of the system is suggested through a vector-coding technique of digital information that makes use of the real and imaginary parts of the reflection coefficient.     

A complex approach to the development of the method and equipment for thermal nondestructive testing of CFRP cylindrical parts

Composite materials are being increasingly used in high-tech industries, such as aerospace, automotive manufacture and building inspection. Thermal nondestructive testing (TNDT) has become an accepted method for composite inspection. However, the majority of investigations have dealt with flat or slightly-curved composite components with a thickness of up to 5 mm. Particular studies have been devoted either to NDT modeling with an emphasis on some theoretical issues, or they have been based exclusively on experimental results. There has been some recent interest in the use of composite materials in the nuclear industry. Some critical parts, including centrifuge components, have been made of carbon fiber reinforced polymer (CFRP) composites. The working conditions in a centrifuge include radioactivity and high rotational speed, and the composites used in centrifuges must have very uniform thermal properties and must be free of defects.This paper describes a complex approach to the TNDT of cylindrical parts made of CFRP by starting from thermal properties measurement, theoretical modeling and preliminary experiments, and finishing with the technical requirements for the development of practical equipment capable of operating in both laboratory and industrial conditions.The objects tested were CFRP cylinders with a diameter of 150 mm and a wall thickness of 4–6 mm, and they contained some artificial defects of varying size and depth. Both one- and two-sided test procedures have been analyzed for spot, line and uniform heating. Ultrasonic excitation has also been used as an alternative stimulation technique.In a one-sided test, the depth detection limit has been about 4 mm. Similar results have been observed in the case of ultrasonic stimulation, but the practical implementation of ultrasonic IR thermography to the inspection of cylindrical parts requires further exploration.In a two-sided test, even fairly mild heating resulted in the reliable detection of all defects independent of their size and depth.In all test cases, the highest signal-to-noise ratio occurred after applying the technique of principal component analysis.     

Investigation into the causes of fracture in railway freight car axle

Railway axles are vital parts of railway. Their failure in the form of dynamic fracture is commonly of disastrous outcomes for railway vehicles. Accordingly, railway axles are designed to be highly reliable, while the maintenance system requires regular inspection in terms of crack initiation. However, due to complex exploitation conditions, complex stress state and multiple stress concentration, railway axles often experience fatigue failures. This occurrence has been studied in a large number of papers. This paper too sheds light on the causes of fracture occurrence in the axle of railway freight car for coal transport in a thermal power plant. Detailed analyses were conducted on the axle fracture surface and mechanical properties. Also, microstructure of the axle material, as well as on exploitation conditions and stress state was examined. Calculations indicated that, apart from working load impact, the influence of press fit joints, especially of the one between the labyrinth seal and the axle is of crucial importance for the analysis of railway axle stress state. The entire numerical–experimental analysis has shown that the considered axle failure was caused by inadequate maintenance, insufficient axle strength and adverse stress state in the railway axle critical cross-sections.     

Estimating manufacturing cycle time and throughput in flow shops with process drift and inspection

Process drift is a common occurrence in many manufacturing processes where machines become dirty (leading to more contamination) or processing parameters degrade, negatively affecting system performance. Statistical process control tracks process quality to determine when the process has gone out of control (has drifted beyond its specifications). This paper considers the case where parts examined at a downstream inspection station are used to determine when the upstream process is out of control. The manufacturing cycle time from the out of control process to the downstream inspection process influences the detection time that elapses until the out of control process is noticed and repaired. Because an out of control process produces more bad parts, the detection time affects the number of good parts produced and the throughput of the manufacturing system. This situation is common in many industries but no models of the phenomena exist. This paper presents a novel manufacturing system model based on queueing network approximations for estimating the manufacturing cycle time and throughput of such systems. These are important performance measures since they influence economic measures such as inventory costs and revenue. The model can be used for a variety of system design and analysis tasks. In particular, the model can be used to evaluate the placement of inspection stations in a process flow.     

Least in-sequence probability heuristic for mixed-volume production lines

The paper focuses on the sequencing aspects of a stochastic hybrid flexible assembly system (FAS) operating in a build-to-order environment. In such a system, although the flow of parts is unidirectional, parallel paths can exist for accommodating different types of parts produced and potential rework of the parts that fail inspection at a given production stage. As a result, the original sequential order of parts can become distorted, resulting in an exit demand sequence which is at variance with the input sequence. To compensate for such sequence disturbances, an adequately sized buffer is installed at the exit end of the FAS. From a practical viewpoint, the study is relevant to the sequencing of upstream operations in an automotive assembly plant functioning in an in-line vehicle sequencing mode. An important feature of the FAS considered in this study is that the demand sequence of part types is known and fixed for a given period of time. Further, the different part types that constitute the demand sequence can have different frequencies of occurrence in a range specified from low to high. We exploit this property of the demand sequence in the development of the least in-sequence probability (LISP) algorithm. The development of LISP is based on the trade-off of pulling low-volume parts ahead in the input sequence while delaying the high-volume parts. We propose the use of the heuristic as a means to achieve both of the following: (a) to improve customer service levels in terms of the number of in-sequence parts output from the system, given a fixed size for the re-sequencing buffers; and (b) to reduce re-sequencing buffer sizes given target levels of customer service.     

Application of fuzzy logic in the selection of part orientation and probe orientation sequencing for prismatic parts

With an increase in complex designs and tighter tolerances, the Coordinate Measuring Machine inspection process has become increasingly more advanced. By inspection planning, design data can be transferred to an inspection system and an entire inspection operation can be carried out with a minimum of time and with reduced uncertainty. The current need is to automate this process completely so that the inspection plan can be generated directly from the design information. Two modules of inspection planning, i.e. selection of part orientation and probe orientation sequencing, have not been dealt with properly. Also, some important factors for the selection of part orientation have been neglected and proper weights have not been given to the probe-orientation sequencing criteria. An attempt was made to overcome these limitations. Both problems have been approached as the ranking of a number of alternatives based on multiple criteria, where each criterion has unequal importance. To get the optimum probe-orientation sequence and stable part orientation, fuzzy logic was applied. Fuzzy sets were obtained and combined using a suitable methodology. To explain and validate the proposed methodology, an example part was taken. As a practical case, an engine block was considered and the results presented.     

清洗时间对钛合金铸件荧光渗透检测的影响

在钛合金铸件荧光渗透检测以浸涂方式施加渗透液时,渗透剂去除时的清洗时间对荧光渗透检测结果有重要影响。以不同清洗时间条件下的PSM-5标准试块渗透检测结果为依据,结合不同清洗时间下钛合金铸板的荧光渗透检测实验结果,研究确定了钛合金铸件荧光渗透检测允许最长清洗时间和单次渗透检测最大检测铸件数量。结果表明,为得到可靠的荧光渗透检测结果,在荧光渗透检测系统各参数满足标准要求的前提下,最长清洗时间不宜超过15 min。结合最长清洗时间,确定某铸件进行荧光渗透检测时的单次最大检测数量为20件。对大型复杂结构铸件进行荧光渗透检测时,可通过增加清洗人员数量的方法控制清洗时间,确保荧光渗透检测结果的可靠性。     

Homogeneous cooling of hard ellipsoids

We study the homogeneous cooling of hard, smooth ellipsoids in three dimensions using event driven numerical simulation. The elongation of the particle has a strong effect on the cooling behavior. Weakly elongated ellipsoids display two distinct cooling regimes. For small times, the translational and rotational energy decay at a different rates. Once their ratio reaches a time-independent value (different from equipartition), the overall temperature of the system decays like t ^?2, as predicted by Haff??s law. For more elongated ellipsoids the translational and rotational temperatures rapidly reach a constant ratio near unity. The cooling behavior in the homogeneous state can be predicted from Haff??s law and the equilibrium collision rate.     

气体水合物超声结晶实验

实验中将15kHz超声波引入R141b和水体系,反应过程在恒温水浴中进行,对超声探头处于不同位置、不同过冷度情况下分别研究.结果表明在超声启动后5秒内就出现大量水合物浆,成核对过冷度的依赖程度降低,但结晶完成时间随过冷度的增加而减少.在同样条件下,探头位于两相界面处,消耗的能量较低.分析结果认为这可能与超声空化产生的一系列效应有关.     

A study of the optimal production strategy for hybrid production systems

Due to increased environmental awareness, the issue of recycling and disassembling damaged or malfunctioning products after consumption to obtain useable parts for remanufacturing has become essential. This study considers a hybrid production system with both external and internal reverse logistics in which the external recycled products are utilised for remanufacturing to satisfy demand first, and then the ordinary manufacturing process may supplement this if there is any shortage in production. In addition, the defective items produced internally by either the manufacturing or the remanufacturing process can also be repaired by a remediation process. The objective of this study is to determine the optimal strategy for the manufacturing, remanufacturing, disposal, and remediation rates. Three conditions are considered in which the production strategy varies with different yield rates and capacity limits. The impacts of related factors on the production strategy are investigated to probe the trade-offs between product consumption and environmental protection.     

Comparative analysis of vision systems for electroplating surface quality inspection

In industrial practice, a human operator establishes the surface quality of an electroplated deposit through a subjective visual inspection, and this tends to be the immediate indicator of a quality defect. Electroplating in connector manufacture is a continuous process yet the quality inspection is an offline, operator-dependent process. The goal of this research was to automate the inspection of surface quality through the application of inline vision systems. Three vision system types were evaluated: a high-speed greyscale system, a standard colour system and a high-speed colour system. The efficacy of each approach was evaluated using attribute repeatability and reproducibility analysis (ARR); other factors considered were throughput, ease of operation and cost. The results proved that the high-speed colour system achieved the highest resolution reliability output for defect identification. Using key factor analysis and designed experiments, the optimum factor conditions were established for the high-speed colour system. To determine the practical implications such as false-positive and -negative results, the work was applied to a high-volume connector manufacturer. The overall benefit of such an implementation is an improvement in the defect rate and a reduction in risk priority number on the failure, modes and effects analysis of the process.