Browse Topic: Geometric design and tolerancing (GD&T)
Additive manufacturing (AM) is currently being used to produce many aerospace components, with its inherent design flexibility enabling an array of unique and novel possibilities. But, in order to grow the application space of polymer AM, the industry has to provide an offering with improved mechanical properties. Several entities are working toward introducing continuous fibers embedded into either a thermoplastic or thermoset resin system. This approach can enable significant improvement in mechanical properties and could be what is needed to open new and exciting applications within the aerospace industry. However, as the technology begins to mature, there are a couple of unsettled issues that are beginning to come to light. The most common question raised is whether composite AM can achieve the performance of traditional composite manufacturing. If AM cannot reach this level, is there enough application potential to warrant the development investment? The answers are highly dependent on the individual processors and will require significant research. Yet, there are still other common challenges that are not isolated to a singular processor. The focuses of this chapter are the capability to design and provide robust structural analysis for continuous fiber-reinforced polymer AM—two unsung aspects that can make or break this new technology as it finds its way into the aerospace market. These two unsettled issues, out of many, may require fundamental changes to the design, analysis, and manufacturing process. Without solutions to them, adoption by the aerospace industry will be limited to point design applications, thus constraining the technology to being nothing more than a specialized tool.
In the 1990s and early 2000s, the field of parallel kinematics was viewed as being potentially transformational in manufacturing, having multiple potential advantages over conventional serial machine tools and robots. Many prototypes were developed, and some reached commercial production and implementation in areas such as hard material machining and particularly in aerospace manufacturing and assembly. There is some activity limited to niche and specialist applications; however, the technology never quite achieved the market penetration and success envisaged. Yet, many of the inherent advantages still exist in terms of stiffness, force capability, and flexibility when compared to more conventional machine structures. This chapter will attempt to identify why parallel kinematic machines (PKMs) have not lived up to the original excitement and market interest and what needs to be done to rekindle that interest. In support of this, a number of key questions and issues have been identified which need to be explored to advance the technology further. In this chapter, we establish the history and current state of the art of PKMs and identify key issues that unlock the technology’s potential. We have sought the views of recognized thought leaders to understand the practical limitations that have hindered deployment and what, if anything, can be done to move the technology forward given the prospective advantages.
The dimensional quality of the car body is built on quality management of form, fitment, and functional requirements. Each of these attributes reflects the final product quality and, therefore, needs to be ascertained quantitatively. Design intent and functionality conformance with specifications are paramount to performance, and thus quality. It is accomplished through optimal Geometric Dimensioning and Tolerancing of parts (GD&T), datum/Primary Locating Points (PLP) strategy, tricks/levers, and assembly design. Challenges stem from the complexity involved in the datum layout strategy and its optimization for desired deviations. Incorrect datum schemes in design prompt underconstrained fixtures, redundant datum, the sensitivity of datum layout, etc. and induce defects in later stages. The end effect is smoothing out the variation issues leading to compromise in quality. Hence, robust datum schemes and checks become imperative for high-quality standards, and keep components within tolerance. The article presented here provides a design aid for quality assurance of datum and assembly dimensional quality targets at the early stages of design. The methodology will be supported through the design and development of a knowledge-based tool containing the creation and validation of datum design parameters for manufacture and assembly for the first-time-right design itself. Based on the analysis, minimizing errors in the datum scheme in the design process such as underconstrained fixture, redundant datum, and inefficient datum layout and defects are contained effectively without affecting development cycle time, cost, and quality.
To provide the curved hose industry and their customers with a recommended practice for applying GD&T procedures to curved hoses and to provide generic curved hose drawings that represent the application of GD&T to typical curved hose parts. Dimensioning and Tolerancing will be in accordance with ASME Y14.5M.
As the brake industry moves completely into globalization, a standardized method to define and validate the dimensions of backing plates, in a way that is both clear and feasible, is of critical importance for manufacturers at all tiers. The plate drawing not only defines the component as it fits into a brake assembly; it is also what the plate supplier relies on to define the plate for manufacture. If a drawing does not define every dimensional aspect of the product with perfect clarity, in ways that are easily measured, loss of time and resources will result from questions and/or mistakes. This paper proposes an SAE standard for defining the dimensional requirements of backing plates on the drawings themselves, and defining the measuring procedures used to validate those dimensions. The proposed standard employs already established methods such as geometric dimensioning and tolerancing (GD&T), including instruction on its proper application to features specific to backing plates. Current ‘best practices’ of design and drafting in our industry are similarly highlighted; drawing clarity, revision control, and dimensioning for both function and manufacturability. Generic examples are used to illustrate both the advantages of best drafting practices, and the potential failure modes that can result from poor drafting practices. The standard also proposes the best methods of measurement required to properly validate requirements such as feature size and location, surface roughness, plate flatness and bow shape. Most importantly; this paper invites the industry professionals responsible for both creating and using backing plate drawings, to join or collaborate with the SAE Brake Linings Standards Committee and help grow this paper from a proposal to a globally accepted engineering standard.
Residual brake torque (RBT) is generated in disc brakes as a result of contact between brake disc and brake pads when the braking pressure is not applied. Among the negative implications of RBT are, notably, dispensable additional fuel consumption as well as increased pad (taper) wear. Several properties of the brake system have a direct influence on the level of residual torque [1]. A major effect is connected to the caliper properties determining the clearance gap. This is characterized by the default air gap between pads and disc and its distribution regarding vehicle inner and outer sides (piston and fist sides for floating type calipers). Initial air gap is mainly influenced by the sealing grove design (between piston and housing, where the sealing ring is positioned). The retraction of the piston due to the sealing ring, also called rollback, mainly depends on the load case (e.g. applied pressure and temperature). Insufficient air gap will lead to residual clamping forces between pads and rotor and thus the friction coefficient itself influences residual brake torque directly. In addition, there are also parameters which can exert influence on the residual brake torque, which are not caliper, but primarily rotor-related. These include axial thermal deformation, thermal coning effects, lateral runout (LRO) of the rotor due to geometrical tolerances and also LRO excited by tensioning the rotor to the wheel hub. These influences on caliper drag are typically well known and understood at least qualitatively. To accomplish customer’s requirements according to RBT, the calipers are extensively tested (e.g. NEDC/WLTP, coast down, ATE) in different test procedures on dynamometers. Some test specifications contain ambitious requirements on the intended drag torque (e.g. less than 0.1 Nm). In contrast to the requirements, other possible influencing parameters, e.g. disc deflection, caused by vehicle dynamics, is currently not included in any RBT-test on dynamometer. During e.g. curve driving, the lateral forces are generated between tire and road and can also be transferred into the rim/rotor/hub/bearing contact at the knuckle. Additionally this is overlain by the wheel load. It must be assumed that the side forces and wheel load affect the deflection of the disc. Thus, this may also influence residual brake torque. This paper shows Continental’s setup for application of wheel load and side forces on dynamometer. Based on previous results from vehicle test, the disc deflection during dynamic driving is characterized and the wheel load setup was enhanced to apply side forces. Different positions of side force and wheel load induction are compared. Furthermore the setup is used to identify the influence of dynamic disc deflection on caliper drag. This is done with an exemplarily floating-type caliper (FN). Dedicated measurements illustrate the influence of left and right curve driving on the level of RBT.
Conventionally, the engines are calibrated under the assumption that engines will be made exactly to the prints, and all the engines from the same batch will be identical. However, engine-to-engine variations do exist which will affect the engine performances, and part-to-part variations, i.e., the tolerance, is an important factor leading to engine-to-engine variations. There are researches conducted on the influence of dimensional tolerances on engine performance, however, the impact of straightness, which is an important geometric tolerance, on lubrication is an unsolved issue. This study presents a systematic method to model the straightness and to analyze its effects on the friction loss. The bearing model is built based on elastohydrodynamic (EHD) theory. Meanwhile a novel modeling method to represent any form of straightness in three-dimensional space is proposed. Then the meta-model with straightness as the input and friction loss as the output is built based on Kriging interpolation theory. Genetic algorithm (GA) is utilized to search for the straightness forms that lead to the best and worst lubricating conditions, respectively. Results show that straightness of the U-shape could lead to an increase or decrease of friction loss and this is mainly determined by the straightness phase. It is also shown that the degree of friction variation at a certain straightness phase is determined by the shape and amplitude of straightness.
The scope and purpose of this paper is to give input and propose solutions to the creation of an efficient and productive geometrical measurement planning process. The case study outline what is important and how to identify and determine the preconditions and input data which is required to start the preparation and planning activities of geometrical measurements. That is why the following three main research and development questions should be answered: Firstly; What is the need and why does an efficient and productive geometrical measurement planning process contribute to decrease cost upstream as well as downstream in terms of reduced lead times in measurement planning process work? Secondly; Why are reduced uncertainties related to geometrical; functionality, specification and verification, important? And how are they linked to each other and how can they be theoretically modeled and defined in terms of uncertainties? The last question is; How is the current geometrical measurement planning process constructed and what does it contain and how is it functioning? By applying a more systematic and holistic approach in product realization and measurement planning activities, the accomplished study indicates improvements and high potential for cost savings, from 3 up to 12 times. Hence the improvement potential is strongly dependent of the actual geometrical complexity level of the airframe assembly being studied. Results from this study will further improve and develop current applied geometrical measurement planning process and will contribute to a more effective and productive working methodology and process.
3D digitalization and modeling is very popular in industrial applications such as metrology, geometric dimensioning and tolerancing (GD&T) and tridimensional object inspection. The 3D captured data can be used for the inspection of object surfaces. However, hidden defects cannot be detected with this technology. In order to get this kind of information, NDT/E (Non-Destructive Testing/Examination) approaches are used (ultrasounds, infrared imaging, etc.). These two types of information are very important in aerospace products inspection (e.g. composite materials). The two modalities (3D Vision and NDT) are still used separately. In this work, we present a new multi-modal fusion framework for combining these two data types. The fusion scheme works on 3D image data and temporal thermal images in order to obtain a hybrid model for simultaneously inspecting the 3D surface and the hidden sub-surface defects. The proposed system permits an augmented visualization of structural non visible defects in a three-dimensional space.
The parabolic leaf spring plays a vital role in suspension systems, since it has an effect on ride comfort and vehicle dynamics. Primarily, leaf spring endurance must be ensured. Presently, there are two approaches to designing a leaf spring. In the traditional method, fatigue tests should be repeated for each case, considering different material, geometry and suspension hard points. However, it takes a long time and requires a heavy budget to get the optimized solution. In the contemporary method, a numerical approach is used to obtain the fatigue life and the leaf geometry against the environmental condition on the basis of material properties. This paper presents a more precise method based on non-linear finite element solutions by evaluating the effects of the production parameters, the geometrical tolerances and the variations in the characteristics of the material. In other words, it is a hybrid method, a blend of the traditional and the recent ones, which correlates the real life conditions and the results of computer aided engineering. Leaf springs of different characteristics were produced and tested in the plant of OlgunCelik plant. The design methodology of this paper also offers a practical approach to industry professionals. The aim was to create a design tool with 2D FEA which is well correlated with 3D.The correlation of 3D and simple 2D methods with experiments are validated through a design of experiment (DOE) study.
The automotive industry is one of the drivers of CAE-based virtual product development. Due to a highly competitive market, development of innovative, high quality products within a short time is necessary and it is only possible by using virtual prototyping. It is important to note that increased application of virtual prototyping itself increases the necessity to perform robustness studies. If the number of hardware tests has to be reduced, it is essential to implement the scatter, which is always present in these tests (such as loads, material, geometry), into the computational model. Consequently, probabilistic methods using CAE-based stochastic analysis have to be utilized in order to quantify robustness, safety and serviceability. Brake noise is one of the most important problems in the automobile industry due to the high warranty costs. The generation of brake noise is due to the development of instabilities in the brake system. The analysis of brake squeal is highly complex and it is also very sensitive to the operation conditions. Therefore, the scope of this work is to carry out a robustness analysis for analyzing the behaviour of the system due to a change in the above-mentioned parameters. Robustness analysis is primarily carried out to determine the variation range of significant response variables and their evaluation by using definitions of system robustness due to the unavoidable scatter of design parameters. The imperfections of the design parameters are usually modelled by either random variables that are constant in space or random fields that vary in space. In this paper, material and geometrical tolerances are considered. Material tolerances are modelled using random variables which have been in existence for long time, but the geometrical tolerances are modelled using the random field, which has been used in this field recently. From robustness analysis, the transfer behaviour of design parameter dispersion to important NVH performance criteria is investigated. As a result, the design parameters responsible for the main scatter of responses are identified, which in turn leads to the information regarding the improvement of design. The probabilistic and structural analyses are performed with optiSLang and Nastran software programs.
To provide the curved hose industry and their customers with a recommended practice for applying GD&T procedures to curved hoses and to provide generic curved hose drawings that represent the application of GD&T to typical curved hose parts. Dimensioning and Tolerancing will be in accordance with ASME Y14.5M.
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