Mating Parts Research Articles

Nonlinear Variation Analysis of Compliant Sheet Metal Assemblies Including Effect of Surface Continuity in Components

Assembly processes are often complex and highly nonlinear. In sheet metal assemblies, the most important factor that makes the process nonlinear is the contact interaction between mating parts during the assembly process. This paper focuses on developing a methodology for nonlinear variation analysis of compliant sheet metal assemblies which also includes the effect of surface continuity of components. The proposed methodology integrates a nonlinear finite element analysis with an improved sensitivity-free probability analysis in order to predict the final assembly variation. The efficiency of the developed approach is evaluated by an experimental case study as well as Monte Carlo simulation.

A Bernoulli Model of Selective Assembly Systems

In many assembly systems, components may exhibit different quality behaviors. By selecting the mating part whose characteristics match with those of the main part, high precision assemblies can be achieved. Such a process is referred to as selective assembly. Most of the studies on selective assembly only consider the case where machines are reliable and the buffer capacity is infinite. However, unreliable machines and finite buffers are commonly observed in many assembly systems. This paper studies a two-component assembly system with unreliable Bernoulli machines and finite buffers. Analytical methods based on a two-level decomposition procedure are developed to analyze the system performance. The convergence of the procedure is justified analytically. Numerical study shows that such a method provides a high accuracy in performance evaluation.

English

The paper predicts the exceptional extreme pressure properties of multi walled carbon nano tube as compared with traditional mineral oil which also contained some additives and graphite. The extreme pressure property was predicted by four ball tester. In the test the load bearing capacity of the newly developed nano oil was predicted to have a better value than the commercial available mineral oil. The weld load of the nanolubricant was found to be 200 kgf as compared with the base mineral oil which got welded at 160 kgf. Thus, the finding would be helpful in developing new nanolubricants which would increase the life of the mating parts, reducing the chances of failure of machine and increasing the productivity. Key words: Mineral oil, multi walled carbon nano tube (MWCNT), pass load, weld load, load bearing capacity, Carbon Nano Tubes (CNT).

Wear and Sliding-Friction Characteristics of Stainless Steel SS316LN Without a Coating and With a CrN Coating at Elevated Temperatures and in a Vacuum

Stainless steel of type AISI 316LN - one of the structural materials of fast neutron reactors - must have a long service life under conditions that subject it to different types of wear (galling, adhesion, fretting, and abrasion). Cobalt-based hard facings are generally avoided due to induced radioactivity. Nickel-based hard facings are strongly preferred instead. One alternative to both types of coatings is a hard-alloy coating of CrN. This article examines wear and friction characteristics during the sliding of uncoated steel SS316LN and the same steel with a CrN coating. In addition, a specially designed pin-on-disk tribometer is used to perform tests in a vacuum at temperatures of up to 1000 degrees C in order to study the effect of oxygen on the wear of these materials. The morphology of the wear surface and the structure of the subsurface were studied by scanning electron microscopy. The formation of an adhesion layer and the self-welding of mating parts are seen to take place in the microstructure at temperatures above 500 degrees C. It is also found that steel SS316LN undergoes shear strain during sliding wear. The friction coefficient depends on the oxygen content, load, and temperature, while the wear rate depends on the strain-hardening of the surface of the material being tested.

Effect of sandblasting and residual stress on strength of zirconia for restorative dentistry applications

Sandblasting is a commonly used surface treatment technique for dental crowns to improve the adhesion of the mating parts of a restoration. The goal of this work is to study the effect of different sandblasting conditions on the mechanical properties of 3mol% yttria stabilized tetragonal zirconia (3Y-TZP), such as biaxial strength, surface elastic modulus, contact hardness and residual stresses induced by sandblasting. The specimens were sandblasted considering two different particle sizes (110, 250μm), two pressures (2 and 4bar) and two impact angles (30° and 90°). Biaxial strength of 3Y-TZP increases when sandblasted with 110µm particles while its decreases with 250µm particles for impact angle of 90°. Strength increases slightly when sandblasting with 30° impact angle regardless of the size of the particle. Elastic modulus and contact hardness were not affected by sandblasting with 110µm particles, and compressive residual stresses are produced down to a depth of ~10µm.

Intelligent jamming region division with machine learning and fuzzy optimization for control of robot’s part micro-manipulative task

An algorithm for an intelligent jamming region division with machine learning and fuzzy optimization for the control of a robot’s part micro-manipulative task is introduced. A comparison with existing works and the advantages of the proposed algorithm in this paper are described. A quasi-static part mating (micro-assembly) is accomplished using a fuzzy coordinator combined with a learning algorithm of the jamming region division while avoiding jamming. Depending on the positional relationships between a part and an assembly hole (target) in a workspace, a specific rule base for avoiding jamming is activated. The region division algorithm merges all adjoining subregions, of which the quad-tuple control values describe similar jamming states, into one region and the weights of the subregions are adjusted. A fuzzy entropy, which is a useful tool for measuring variability and information in terms of uncertainty, is used to measure the degree of uncertainty related to an execution of the part micro-assembly task. A degree of uncertainty associated with a task execution of the part micro-assembly is used as a criterion of optimality, e.g. minimum fuzzy entropy. Through a decision-making procedure, the most appropriate quad-tuple control value with the lowest fuzzy entropy in each region is chosen as a final control value to carry out an assigned task. The proposed technique is applicable to a wide range of the robot’s tasks, including choosing and placing operations, manufacturing tasks, part mating with various shaped parts, etc.

Generic face adjacency graph for automatic common design structure discovery in assembly models

Common Design Structure Discovery (CDSD) is to identify local structures shared by multiple models. Nowadays it is mainly restricted to part models. Extending it to assembly models can produce a significant value for assembly design reuse. However, current descriptions of assembly models usually capture topological information qualitatively, considering little geometric information, and thus are not suitable for CDSD in assembly models (CDSDA). To counter this problem, this paper proposes a generic face adjacency graph (GFAG) which is extended from the face adjacency graph for B-Rep part model description. GFAG can transform abstract relationships in assembly models into measurable entities by introducing a concept of mating face pair (MFP), thus facilitating a more quantitative and consistent description of parts and relationships in assembly models. Corresponding to geometric faces and edges in a part model, GFAG treats parts and relationships in an assembly model as generic faces and generic edges respectively. To make GFAG have a higher discrimination capability, a node in GFAG captures the geometric information of a part together with its mating parts by shape parameters and also quantitatively incorporates a relationship between parts by shape parameters of an MFP. By doing so, GFAG can take more geometric information, together with topological information, into account quantitatively, and thus can be mapped into a 2D coordinate system for easy validation. We also extend a discovery algorithm to validate the feasibility of GFAG for CDSDA, and the results demonstrate the expected effectiveness.

Evaluation of Thermal Contact Resistance at the Interface of Dissimilar Materials

When jointed portions of structures and machines are subjected to thermal loads, various problems and troubles occur due to the difference in thermal expansions between mating parts. In order to accurately analyze thermal and mechanical behaviors of the joints, the effect of thermal contact resistance must be taken into account. In this paper, thermal contact coefficient, which is the reciprocal of thermal contact resistance, at the interface of dissimilar materials is quantitatively measured by infrared thermography. The target materials are common engineering materials such as carbon steel, stainless steel and aluminum alloy. It has been shown in the previous papers that there exists a significant directional effect in thermal contact coefficients when the mating surface is composed of different materials. That is, thermal contact coefficient has a larger value when the heat flows from the material with lower thermal conductivity to the one with higher thermal conductivity. The effects of contact pressure and surface roughness on the coefficient are also evaluated in this work. Using the measured data, an empirical equation to estimate thermal contact coefficient is proposed, for the purpose of engineering applications, which correlates closely with the experimental data.

Applying Regression Model to Predict the Effects of Shaft and Bearing Deviations on the Clearance of the Assembly of Mating Parts

This work presents formulation of linear regression model for the effect of shaft and bearing deviations on the clearance of the assembly of mating parts. The model validation confirmed the existence of statistical relationships between clearance and shaft and bearing deviations. Applying data collected from direct measurement of shafts and bearings produced in the workshop, R values of 99.7% was obtained for assembly of mating parts model ; thus, indicating that about 99.7% of the parts produced are interchangeable, thus reducing the probability of producing scraps to the barest minimum. The results obtained using critical parameters of assembly of mating parts and multiple linear regression models give good estimation and are validated with experimental values with an error much lesser than 4% error. The regression model also showed that given the shaft and bearing deviations, the expected clearance can be determined, thus, enabling the quality control personnel to significantly monitor and reduce variation in the assembly of mating parts.

Passive Precise Assembly Algorithm for Ring Assembly

This paper proposes the method for assembling a ring into a shaft with the clearance of several micrometers by using a robot manipulator. Assembly by a robot manipulator is difficult compared with other production processes in a factory. This is because there are some problems of the robot positional accuracy, the size tolerance and the deformation of mating parts. The purpose of the proposed method in this paper is to resolve these problems. The features of the method is to utilize the characteristic finger shape and the method is suitable for high-speed assembly because complicated robot control method is not required. Finally, the availability of the method is verified by the experimental results.

SCARA based peg-in-hole assembly using compliant IPMC micro gripper

Robotic assembly is difficult as there always exist position errors between two mating parts. Compliance is added in a selective compliant assembly robot arm (SCARA) in the form of a two ionic polymer metal composite (IPMC) fingers based micro gripper. This micro gripper is integrated at the end effector position of a SCARA robot. Peg-hole interaction is analytically modeled and based on it the force required to correct the lateral and angular errors by IPMC is calculated. A proportional-derivative (PD) controller is designed to actuate the IPMC to get the desired force for correcting the peg position before assembly. Simulations and experiments were carried out by developing an IPMC micro gripper and using it to analyze various cases of peg in hole assembly. The experimental results prove that adding compliance through IPMC helps in peg-in-hole assembly.

Minimizing Surplus Parts in Selective Assembly Using GA

Selective assembly is a method of obtaining high-precision assemblies from relatively low-precision components. In selective assembly, the mating parts are manufactured with wide tolerances. It is impossible that the number of components in the selective group will be the same, and a large number of surplus parts exist according to the difference in the standard deviations of the mating parts. A method with new grouping method and chromosome structure is proposed to minimize surplus parts by using genetic algorithm.

Fuzzy inference mechanism for recognition of contact states in intelligent robotic assembly

This paper presents a methodology for generating a fuzzy inference mechanism (FIM) for recognizing contact states within robotic part mating using active compliant motion. In the part mating process, significant uncertainties are inherently present. As a result it is pertinent that contact states recognition systems operating in such environment be able to make decisions on the contact state currently present in the process, based on data full of uncertainties and imprecision. In such conditions, implementation of fuzzy logic and interval inference brings significant robustness to the system. As a starting point for FIM generation, we use a quasi-static model of the mating force between objects. By applying Discrete Wavelet Transform to the signal generated using this model, we extract qualitative and representative features for classification into contact states. Thus, the obtained patterns are optimally classified using support vector machines (SVM). We exploit the equivalence of SVM and Takagi---Sugeno fuzzy rules based systems for generation of FIM for classification into contact states. In this way, crisp granulation of the feature space obtained using SVM is replaced by optimal fuzzy granulation and robustness of the recognition system is significantly increased. The information machine for contact states recognition that is designed using the given methodology simultaneously uses the advantages of creation of machine based on the process model and the advantages of application of FIM. Unlike the common methods, our approach for creating a knowledge base for the inference machine is neither heuristic, intuitive nor empirical. The proposed methodology was elaborated and experimentally tested using an example of a cylindrical peg in hole as a typical benchmark test.

Microstructure and properties of laser-borided 41Cr4 steel

Laser-boriding, instead of diffusion-boriding, was applied to formation of boride layers on 41Cr4 steel. The microstructure and properties of these layers were compared to those obtained after typical diffusion-boriding. Three zones characterized the microstructure of laser-borided layer: laser-borided zone, hardened medium-carbon zone (heat affected zone) and medium-carbon substrate without heat treatment. The through-hardened laser-borided steel was also analyzed. In this case two zones characterized the microstructure: laser-borided zone and hardened medium-carbon substrate. The microstructure of laser-borided zone consisted of eutectic mixture of borides and martensite. This phase composition (especially martensite presence) was the reason for microhardness decrease at the surface in comparison with diffusion-borided steel. However, the use of laser-boriding causes the decrease in microhardness gradient between the surface and the substrate in comparison with typical diffusion-boriding process. The value of mass wear intensity factor of the hardened laser-borided layer was comparable to that obtained in case of diffusion-boriding and through-hardening. The use of laser-borided layers instead of typical diffusion-borided layers may be advantageous under conditions of high abrasive wear of mating parts. For the experimental condition used, the laser-boriding process presented worst results concerning the fatigue strength. The cracks formed on the surface during laser re-melting were the reason for relatively quick first fatigue crack. In case of elements, which require high fatigue strength, the use of modified laser processing parameters would be necessary. The better results should be obtained by increasing of tracks overlapping. Although the cohesion of laser-borided layer was sufficient, the diffusion-borided layer showed a better cohesion.

The influence of assembly clearance on the deformation and stress of an assembly structure through FEA simulation

In order to facilitate parts assembly in a product structure, different clearances are provided in mating parts. The aim of this research is to investigate role of certain clearances in an assembly structure. These clearances are not part of tolerance stack but still can impart significant impact on product functional performance. Their influence on the product functional parameters like different stresses and deformation is studied in this research. A structure from automotive spot welding equipment is considered for this study. The effect of these clearances is determined using finite element analysis (FEA) simulations for process model of the product. It is found that some clearances are more critical for certain parameters. The results show that the product design can be improved by taking such clearances into consideration during design phase.

Response of shrink fitted assemblies to the dynamic torsion

Product design is mostly centered around design of different contact pairs. Among contact pairs, interference fit pair is widely used. Design of interference fits, involves not only dimensional interference, but also condition of interface between mating surfaces. Factors such as texture of interface, hardness of interface material and also physical properties of contacting materials influence the functional characteristics of interference shrink fitted assemblies. In actual practice most of such joints are subjected to dynamic loading. Data on torsion response is only limited. So that, detailed investigation on the influence of dimensional interference, contact length and interfacial properties (electroless nickel coating) on torsion capacity of interference fitted assemblies has been carried out. The response of interference fitted assemblies to dynamic torsion load has been evaluated, using L-9 Orthogonal array of experimental conditions to bring down the number of experiments. The results are analysed using analysis of variance (ANOVA) to find out the individual effects of parameter on dynamic loading. The Torque load carrying capacity of the shrink fitted assemblies is improved by electroless nickel coating. This could be attributed to the increase in actual contact area and tenacity of Nickel plating and presence of strong molecular bonds between the mating parts chosen for the assemblies. But the selection of interference, contact length and hardness of mating parts play a vital role in deciding the performance of these joints. The results clearly indicate that the dynamic performance of the assemblies could be improved by suitably selecting the materials keeping in mind the above factors. It is also found from the ANOVA results that the assemblies with (hardness) coated interlayer performed better. Interference and contact length also has influence on the strength but in this case their influence is not very significant. An expression is obtained using regression analysis, which gives relationship between the parameters. A result obtained from regression analysis is closer to the experimental values.

Parts Tolerance Allocation Based on Assembly Clearance Analysis and Product Functional Parameters

Geometric tolerances are assigned to avoid parts rejection in a manufacturing process while ensuring fulfillment of intended function. Selection of tolerance value is an important task which affects the overall product cost and performance both. The significance of tolerance value is more evident in case of mating parts where the dimension of more than one parts share responsibility of successful assembly and design. The objective of this research is to determine appropriate tolerance value based on assembly clearance analysis which takes into account relationship between assembly clearance and product performance parameters. The study is conducted through CAD-CAE integrated finite element analysis (FEA) simulations of the product process model. The results output help in distinguishing different tolerance levels which can be further probed for optimal, using available manufacturing resource capability data. The research output is a more practical tolerance value achieved based on product performance analysis as well as available resources and appropriate cost. The results obtained validate the utility of the approach presented in this paper.

Stabilizing slider-crank mechanism with clearance joints

In general, in dynamic analysis of mechanical systems, joints are assumed to be ideal without clearance. When joint clearance is introduced, dynamic response is considerably changed. Degradation of dynamic performance, reduction in components fatigue life and generation of undesirable vibrations result from impacts of mating parts in clearance joint. More generally, system responses tend to be chaotic and unpredictable instead of being periodic and regular. In this study, a slider-crank mechanism with a revolute clearance joint between the slider and the connecting rod is addressed. It is shown that the system may exhibit chaotic behavior under specific conditions. A control mechanism based on the Pyragas method is presented for stabilizing an unstable periodic orbit embedded in the chaotic attractor. Under a successful control, contact loss is eliminated and the system exhibits periodic motion by applying only small perturbations.

Similarity measuring strategy of image patterns based on fuzzy entropy and energy variations in intelligent robot’s manipulative task

A similarity measuring strategy of image patterns based on fuzzy entropy and energy variations, using an intelligent robot's part macro-assembly (part-bringing) as an example, is presented. A part macro-assembly, locating various shaped assembly holes (targets) in a workspace corresponding to shapes of parts and then bringing a part to a corresponding target for the purpose of part mating despite existing obstalces, is introduced. This is accomplished by cooperating a neural network system with a fuzzy optimal control. Fuzzy entropy and energy functions, which are useful measures of variability and information in terms of uncertainty, are introduced to measure its overall performance of task execution related to the part-bringing task. An interrelation among learning, fuzzy entropy, and energy variations used as a measuring tool for a degree of similarity of image patterns is described. Through variations of fuzzy entropy and energy, a degree of similarity between input and desired output image patterns of neural network can be measured. The proposed technique is not only a useful tool to measure a degree of similarity between image patterns, but applicable to a wide range of robotic tasks including motion planning, manufacturing, maneuvering around workspace, and part mating with various shaped parts and targets.

Stability of the friction stir welding process in presence of workpiece mating variations

This paper explores common process variations encountered in friction stir welding (FSW) and the limits to which acceptable joint strength is maintained while welding with a robotic FSW system. Part fit-up and mating variations are common in manufacturing, yet the limits to which a friction stir welding process can weld without major process adjustment are unclear. The effects on joint strength and mechanical properties of several of the most common mating variations (i.e., faying surface gap, misalignment, mismatch, etc.) are experimentally determined as individual effects as well as among common welding parameters. Experimental results on 5-mm-thick aluminum alloy 5083-H111 show that ultimate tensile strength, yield strength, and elongation begin to decrease from nominal weld conditions when either the tool offset distance from weld centerline or gap in abutted plates exceeds 25% of the average pin diameter (6 mm). In addition, vertical plate mismatch and lack of penetration can be tolerated up to 2.5% and 10%, respectively, before adverse effects on mechanical properties are observed. The work also indicates that of all the mating variations tested in this study, tool misalignment, followed by travel angle, has the most significant effect on the measured joint strength. Process stability testing has shown that the FSW process is able to endure part fit-up and mating variations within a defined tolerance, giving the practitioner an awareness of how well stock workpiece tolerances must be controlled before joint strength is adversely effected.