Computer-aided Fixture Design Research Articles

Intelligent design of reconfigurable flexible assembly fixture for aircraft panels based on smart composite jig model and knowledge graph

The current demand for aircraft panel assembly fixtures necessitates agile manufacturing solutions. Traditional welding fixtures struggle to meet diverse panel types, high quantities, and short manufacturing cycles. Conversely, reconfigurable flexible assembly fixtures offer universality, efficiency and ease of maintenance but heavily rely on designers' experience, hindering knowledge reuse. Existing research on computer-aided fixture design (CAFD) primarily addresses specialized fixtures, neglecting reconfigurable flexible ones, lacking fixture design knowledge systems. Aiming at the above problems, the study proposes an intelligent design method for the reconfigurable flexible assembly fixture for aircraft panels based on the smart composite jig model (SCJM) and knowledge graph (KG). Firstly, based on the SCJM of the aircraft panel type assembly fixture (PSCJM), a configuration design method is proposed to carry out the multi-level design of reconfigurable assembly fixture to instantiate PSCJM containing fixture configuration rules and a module library based on model definition (MBD). Then, a knowledge retrieval method is proposed to search the suitable fixture design knowledge based on KG, assisting designers in achieving the flexible design of aircraft panel reconfigurable assembly fixtures. Finally, practical engineering design validation confirms the method's feasibility and effectiveness in obtaining the reconfigurable flexible assembly fixture design scheme for aircraft panels.

Computer aided machining fixture design algorithm and software based on case learning for near-net-shaped jet engine blade

In the blade computer numerical control (CNC) machining process, the machining fixture design for each type of blade will be a very difficult task due to the large variety and quantity of blades. This study proposes a computer-aided machining fixture design algorithm and software based on case learning. The three-dimensional model of the case learning blade and the target blade is firstly projected into a cylinder surface based on the projection algorithm, and the cylinder surface is expanded into a two-dimensional plane based on expansion algorithm. Then, the matching machining fixture layout of the target blade relative to the case learning blade is obtained in two-dimensional space by the mesh affine transformation algorithm according to the geometric edge constraints and the matching relationship of the case learning blade and target blade. At last, the inverse transformations of projection and expansion are used to obtain the final fixture layout of the target blade three-dimensional model based on the previous projection and expansion relationship. The special computer-aided fixture design software of near-net shaped blade is developed, and the machining fixture design and CNC machining experiment based on two typical near-net-shaped blades proved that the computer-aided fixture design algorithm based on case learning is feasible and can be used to realize the intelligent design of near-net-shaped blade machining fixture.

Investigate on computer-aided fixture design and evaluation algorithm for near-net-shaped jet engine blade

Abstract This study proposes a computerized framework for computer-aided fixture design and evaluation for near-net-shaped jet engine blades. First, the manufacturing process of near-net-shaped jet engine blades and requirements for the fixture design and evaluation were analyzed. Second, a numerical model of the positioning error and the corresponding experimental platform were established. Third, a mechanical model of the blade under cutting conditions was analyzed, a finite element model (FEM) was established. Fourth, a mathematical model of the machining fixture layout optimization was established, and the positioning clamping points of the machining fixture were optimized by the combination of finite element analysis (FEA) and genetic algorithm. Finally, the corresponding algorithm verification was carried out by positioning error and cutting experiments. The results showed that the proposed computerized framework could evaluate and optimize the fixture of the same type blade to obtain the positioning and mechanical behavior of the fixture, and can realize high-precision manufacturing of near-net-shaped jet engine blades.

Brief review of methodologies for creation of cohesive fixture design

Abstract Fixture design is manual process and requires heuristic knowledge and skill. As the product varieties increases and lifecycles of product shortens, different development approaches needs to be adapted for the survive in market. Computer aided fixture design has constituents in four areas like Setup planning, Fixture Planning, Unit Design and Verification. Different methodologies were developed for each of these area. In this paper, the authors integrate the different methodologies established in fixture design area. These methodologies are segmented in nature hence the effectiveness is not gained for fixture design. Hence the primary aim of this research work is to integrate the segmented methodologies into one integrated methodology for cohesive fixture design.

Development of locating system design module for freeform workpieces in computer-aided fixture design platform

Abstract Development of an efficient computer-aided platform for fixture design requires intelligent algorithms to be developed as decision making tools for different designing functions. Locating system design is among the representative fixture design functions which are in need of such intelligent algorithms to implement their complicated roles. This rather unmet need has already hampered the development of automated computer-aided fixture design systems. The authors have proposed an analytical and algorithmic locating system design procedure as a part of their continuous effort to establish a PythonOCC-based platform, which is the subject of the present paper. In order to surmount the geometrical restrictions, workpieces with freeform geometries of NURBS types have been taken into consideration for locating system design. Constraining workpiece’s degrees of freedom, capacity of locating surfaces in bearing the machining loads, and ease of workpiece loading and unloading into and from the fixture together with some other checking rules constitute the characteristic criteria of the proposed analytic procedure. The proposed procedure has been employed for several workpieces with freeform geometries to evaluate its efficacy.

A Fixture Design Retrieving Method Based on Constrained Maximum Common Subgraph

Fixtures are widely used in almost any modern manufacturing. They add directly to the cost base, impact manufacturing firms’ responsiveness and contribute to the overall product quality. Computer-aided intelligent fixture design was developed over the years to give a competitive edge to the manufacturing firms who are facing unprecedented competition and challenges. Among the techniques, case-based reasoning (CBR) method leverages previous design experience and emerged as one of the most popular methods. However, existing CBR methods are more focused on frame work building and less on detailed techniques on case retrieving, which is the central part of any CBR methods. This would inevitably impose negative impact on the overall efficiency of any CBR-based methods. In light of this, this paper presents a new case retrieving method based on a constrained common subgraph technique. This technique tracks down similar cases from a case library through comparing the maximal common subgraphs constrained by meeting fixturing functional requirement. Efficient and robust algorithms have been developed subsequently to implement this technique. The developed method can be highly effective for retrieving cases related to some manufacturing parts with complex geometry. An illustrative example, combined with other key fixture design factors, demonstrates the effectiveness of the proposed method. The presented method is intuitive and can be used in combination with existing CBR methods and well positioned for the upcoming “big data” manufacturing. Note to Practitioners —Providing capability for rapid responsiveness, enhancement of product quality, and production at low cost are the three main objectives for the wide manufacturing firms. Fixtures are widely used across manufacturing and assembly processes, and they are closely linked to all these three objectives. Today’s manufacturing enterprises face unprecedented challenges to control costs and to deal with an ever increasing number of product variants and smaller lot sizes. All these facts raise high demands on computer-aided intelligent fixture design. Case-based reasoning (CBR) method, tackling new problem by using the solution of similar past problems or through revising the previous solution, gains popularity among researchers and practitioners. However, existing CBR methods put more focus on CBR framework design while the case retrieving, the key process of any CBR methods, still relies on some basic feature attributes comparison. This would inevitably reduce the overall effectiveness of the CBR method. In view of that, this paper proposed a graph method for case retrieval based on comparing maximal common subgraphs (MCSs). Dictated by fixture functional requirement, a constraint (to match machining features and/or other user defined requirement) has been imposed during the MCS search process. This constraint turns out to be quite useful in term of reducing search space and increasing computation efficiency. Robust algorithms have been subsequently developed to implement this technique. Graph is a powerful tool to analyze structured object, the proposed method can handle some bespoke and complex fixture design cases. The presented method is intuitive and flexible and can be integrated into existing CBR frameworks to improve the allover effectiveness of current intelligent fixture design.

Controlling deformations of thin-walled Al 6061-T6 components by adaptive clamping

High strength, light weight, thin-walled components are gaining in importance with good market growth potential in key industries like aerospace, automotive, power generation, medical technology, etc. The challenges in machining thin-walled workpieces include static workpiece displacements and large deformations caused by local indentations at contacts and higher structural compliance, respectively. The chosen machining strategy is crucial to obtain good surface finish and fine control over dimensions and form. Owing to the limited applicability of analytical methods to standard workpiece geometries, a finite element method based numerical framework is developed in ANSYS for predicting contact and structural deformations that suits all workpiece geometries and boundary conditions. The numerical results are validated by experimental measurements using CNC-CMM on Aluminium 6061-T6 workpiece located in 3-2-1 milling fixture with two hydraulic clamps having adjustable clamping pressure. The results of static deformations match within 20%. Subsequently, clamping force-deformation characteristics are plotted for implementing corrective clamping mechanism to control workpiece deformations. This methodology will be integrated with the Computer Aided Fixture Design (CAFD) System to realize design of adaptive clamping fixtures, thereby, reducing rejections and increasing quality and productivity.

Computer aided fixture design - A case based approach

Automated fixture design plays important role in process planning and integration of CAD and CAM. An automated fixture setup design system is developed where when fixturing surfaces and points are described allowing modular fixture components to get automatically select for generating fixture units and placed into position with satisfying assembled conditions. In past, various knowledge based system have been developed to implement CAFD in practice. In this paper, to obtain an acceptable automated machining fixture design, a case-based reasoning method with developed retrieval system is proposed. Visual Basic (VB) programming language is used in integrating with SolidWorks API (Application programming interface) module for better retrieval procedure reducing computational time. These properties are incorporated in numerical simulation to determine the best fit for practical use.

Development of computer aided clamping system design for workpieces with freeform surfaces

Abstract The development of computer aided fixture design has already encountered numerous mathematical and technical challenges having hampered realization of automated design of fixturing system consisting of locating and clamping systems. This is more critical for workpieces of freeform surfaces compared with those of polyhedral geometry. In the present study, the mathematical foundation of clamping system design has been developed by using the concept of screw theory and the minimum norm principle. An algorithm has been proposed to realize the developed theory. In this algorithm, three criteria have been taken into consideration to be respected when designing the clamping system. These are minimum number of clamps, maximum contrariety of clamping force components with respect to the twists tending to break contact between the workpiece and the locators, and maintenance of workpiece’s static stability under different wrenches. The suggested theory and algorithm have been incorporated into a platform already developed by the authors in Python-OCC for computer aided fixture design. The fixturing of three different machining workpieces have been examined for evaluating the capabilities of the suggested theory and algorithm. These workpieces had freeform surfaces which were defined by NURBS formulation.

AN INTEGRATED RBR FIXTURE DESIGN SYSTEM

Traditionally fixture design processes are costly and time-consuming when carried out manually. To try to reduce the negative features, we are creating a computer-aided fixture design system, integrated in the SolidWorks’ environment. This system uses rule-based reasoning in the form of If-Then-Else rules, incorporated in its VB.NET code. This paper presents our progress in the form of an interactive add-in program for locating parts. This program generates modular fixtures for locating prismatic or cylindrical parts, using rules and mathematical equations. Its usage can shorten the time needed for determining the type and position of every module of the fixture, their assembling, and inspection.

A method for determining the degree of freedom of workpiece based on developed geometry theorem

The traditional 6-point positioning principle could not indicate the specific features of the workpiece constrained at the six locating points and could not provide the influence law of geometric relationship between each constraint and the DOF of the workpiece, which makes it difficult to adapt to various complex positioning and often mistakes DOF of workpiece to lead to fail in jig design. The normal line of the workpiece at the jig anchor point is defined as the positioning normal line in this paper. According to the number of the positioning normal lines and the geometrical relationships between them, a set of geometrical theorems on determining the DOF of the workpiece are deduced. The judgement criterion for the distribution of the normal line in over-positioning condition is also provided. The DOF of the workpiece and the solutions to the unreasonable positioning are provided by using the geometric theorems in several examples, which proves that the geometric theorems can quickly and accurately determine the DOF of the workpiece in the complex positioning. The geometrical theorems of the workpiece positioning develop and perfect the positioning theory of the workpiece and can make the method of determining DOF more precise, simple and intuitive; furthermore, the geometrical theorems are beneficial to accurately determine the DOF of the workpiece in computer-aided fixture design.

A Method of Computer-aided Modular Fixture Design, Part 1: Creating the Feature-model Repository of Fixture Elements

Modular fixture is conventionally designed less concerning the detailed specifications of machine tool. A little of literatures involve the effectively application to the existing CAD systems in CAFD (computer-aided fixture design). The determination of the validity of modular fixture during NC machining lacks for a practical method. This paper put forward that: Firstly, the feature-model repository of elements of modular fixture can be built in CAD packages; the design of modular fixture in NC machining should be accomplished under the concept of NC Manufacturing System (NMS); the Post-NC verification can be applied to check the performance of modular fixture applied in NC machining. Part 1 of the paper focuses on the feature-model repository of the modular-fixture elements. The other jobs will be introduced in the Part 2.

TRACKING WORKPIECE STABILITY UNDER VARYING CUTTER POSITIONS, MASS AND COMPLIANCE OF WORKPIECE IN POCKET MILLING

Manufacturing accuracy and surface finish as well as productivity by way of high metal removal rates are mainly restricted by the occurrence of workpiece vibrations and loss of stability. In this paper, dynamic stability of Al-6061-T6 prismatic workpiece located in a milling fixture with 3-2-1 location principle and two hydraulically operated clamps is investigated under spatially varying cutter position and continuously decreasing mass and compliance of a workpiece during pocket milling operation. The mathematical model for the fixtureworkpiece system is based on Hertzian contact theory. The workpiece and fixture elements are considered rigid and the model takes into account the only contact stiffness. A six-dof dynamical model, that includes metal removal effect (MRE), is developed to simulate the dynamical response of the fixture workpiece system in MATLAB Simulink. Finally, the lift-off and macro-slip is calculated and the stability is determined for each contact. The effect of metal removal on the workpiece during machining is considered for 20% and 50% metal removal. For increased metal removal the measured and simulated accelerations are compared and found to have a good agreement with each other. The theoretical model thus developed for dynamic response simulation will be integrated with a Computer Aided Fixture Design (CAFD) system.

Development of an efficient method of jamming prediction for designing locating systems in computer-aided fixture design

In the present study, the mathematical theory of jamming has been developed on the basis of minimum norm principle for workpieces with free-form surfaces. This has laid the basis of a new method proposed as an efficient means of jamming prediction, which is specifically helpful when designing the locating systems in computer-aided fixture design applications. The proposed method determines the contact states between the workpiece and the fixture and checks for the contact mode to predict possible jamming when loading a workpiece into the fixture, based on which the designer can modify the designed locating system in an attempt to avoid jamming. The presented model benefits from the lower computational complexity, quicker response, and more accurate results in comparison with the previous studies in jamming prediction processes. In addition, this method does not require the contact modes to be known beforehand. This is especially crucial at the early stages of the locating system design when the contact mode is not yet clear. Three case studies have been used for evaluating the capabilities of the suggested model, including peg-in-hole, block and palm, and a typical workpiece of 3D free-form model configuration. The results have also been compared with those of previous studies.

Development of a computer-aided fixture design system for lightweight grippers in the automotive industry

The need for dedicated fixtures for flexible manufacturing systems is increasing, as dedicated fixtures are lighter, more compact, and more accurate than flexible fixtures. The main challenges are that parts and processes are becoming more and more complex, which requires designing novel or complex dedicated fixtures, and that, for one given flexible fixture to be replaced, several variants of such dedicated fixtures must be designed to hold a variety of individual parts, without causing increased costs and delays. The systematic fixture design method and computer-aided fixture design system (CAFDS) developed and applied for the presented industrial case - novel design of a lightweight (carbon fibre composite) robot gripper - is a possible approach to addressing these issues.

Fixture Design Automation and Optimization Techniques: Review and Future Trends

Fixture design is crucial part of manufacturing process. Fixture design is a critical design activity process, in which automation plays an integral role in linking computer-aided design (CAD) and computer-aided manufacturing (CAD). This paper presents a literature review in computer aided fixture design (CAFD) in terms of automation and optimization techniques over the past decades. First, the reason behind necessity of automated fixture design is stated. According to the degree of automation, fixture design methods are then categorized based on significant work done in the CAFD field. Regarding the need of automated fixture design systems, optimization techniques, which are mostly used for automated CAFD methods, are closely considered. The significant optimization techniques works are then studied in case of applications and working principle. At the end, the current weaknesses of the existing methods and the research fields, which require deeper studies as future trends, are presented as well.

Locating error analysis for workpieces with general fixture layouts and parameterized tolerances

In manufacturing engineering, locating error analysis for workpieces is a common issue in predicting the quality of machined features, computer-aided fixture design and tolerance allocation. This article presents a locating error analysis approach for workpiece with general fixture layouts and parameterized tolerances. Initially, a fixture is transformed into six locating points in the space. A linearized model is then derived to convey the relationship between the errors of locating points and the locating errors, by using the implicit differentiation and the first-order Taylor expansion. Then, the tolerances for the features of plane, cylinder and free-form surface are parameterized using 4 × 4 homogeneous transformation matrices. Finally, two formulas are derived to calculate the errors in the locating points in surface-to-surface mating and hole-to-pin mating. Two workpieces are presented to demonstrate and validate the proposed method. The relative errors between the results calculated by the proposed method and the results calculated by 3DCS are less than 3%.

A methodology for applying V–blocks and clamps to non–prismatic workpart fixtures

Most research in computer–aided fixture design (CAFD) aims to develop algorithms to automatically design the fixture configuration of workpieces. Due to the complexity of non–prismatic geometry, the application domain has been mostly limited to prismatic workpiece fixturing. Moreover, based on the 3–2–1 locating principle, the locators employed are mostly restricted to the cylindrical type. This research focuses on another type of fixture configuration for non–prismatic parts that has been mostly overlooked. This is to apply V–blocks in workholding to ensure stable and efficient work setup of non–prismatic parts. The algorithm presented in this paper determines V–block locating by utilising projected geometric reasoning. The major steps of the algorithm include candidate–point generation, angle and distance checking, co–ordinate transformation, and interference analysis. Further more, this paper also explores another algorithm for determining the corresponding clamping location of the V–block. The horizontal clamp is planned based on static principles. To ensure workpiece stability, the planning procedure is classified into three distinct cases according to the force distribution and frictional conditions at the contacting regions. These two algorithms, V–block locating and clamp planning, are applied interactively to obtain the most desired fixture configuration. Finally, an example is provided to explain how these algorithms are applied.

A knowledge reuse-based computer-aided fixture design framework

Purpose – Fixture design is a complicated task requiring both intensive knowledge and experience. This paper aims to present a computer-aided fixture design (CAFD) system framework based on design reuse technology. Design/methodology/approach – Fixture design domain ontology is constructed by analyzing fixture design document corpus. A design reuse engine is proposed to realize fixture design knowledge retrieval and fixture model retrieval based on ontology and find fixture design cases similar to fixture design problem, and then use evolutionary methods to modify the retrieved model to meet the design requirements and then generate a new fixture. Findings – The paper finds that the proposed framework is an efficient tool to improve efficiency of fixture design. Practical implications – Fixture design existing experience and cases can be used efficiently reused and to advance new fixture design processes. Originality/value – This paper presents a CAFD system framework capable of carrying out fixture design through full using of the existing fixture design resource and experienced knowledge.

Recent Developments on Computer Aided Fixture Design: Case Based Reasoning Approaches

Fixture design is an important issue in the process of manufacturing. As a critical design activity process, automation in fixture design plays an integral role in linking computer aided designs and computer aided manufacturing. This paper carries out a literature review of computer aided fixture design (CAFD) developments using intelligent methods that have been commonly utilized in automation in the last two decades. The first part of this review considers the steps of fixture design along with the significant researches and requirements of fixtures over time. After that, the paper presents important and relevant research carried out in the field of CAFD using intelligent approaches and the working principles surrounding this issue. The following section concentrates on the details of case based reasoning (CBR) approach, the most successful approach in CAFD. The examination of this approach is carried out based on applications, stages of CBR based systems fixture design, working principles, and pertinent proposed approaches. Lastly, the present drawbacks of the current methods and shortfalls in research are identified for future studies.