Mechanical Design Pitfalls

Design pitfalls are defined as those obscure mistakes that can be attributed to negligence or ignorance of particular details and characteristics of the design and, in some cases, the manufacturing processes. This paper presents ten actual cases where a designer could be tempted or misled into design pitfalls that would create weird encounters during assembling or operating mechanical equipment. The pitfalls could have immediate, embarrassing consequences, or eventually lead to hazardous situations and failure in unexpected modes. The consequences of these pitfalls and their remedies are also discussed. The design examples lie in various areas such as gearing and planetary systems, bearings, and fluid power. They are classified under generic headings, some of which are seen to qualify, and are therefore suggested, as design principles, to be added to the repertory. It is deemed that this paper will stimulate further investigations leading to the identification of design pitfalls in these and other areas.

Download Full-text

Stress Field Around a Large Opening in a Pressure Vessel During a Major Repair

Volume 3: Design and Analysis ◽

10.1115/pvp2009-77007 ◽

2009 ◽

Author(s):

Erik Garrido ◽

Euro Casanova

Keyword(s):

Pressure Vessel ◽

New Technologies ◽

Mechanical Design ◽

General Purpose ◽

Pressure Vessels ◽

Mechanical Equipment ◽

Stress Distributions ◽

Large Opening ◽

Von Mises ◽

Case Basis

It is a regular practice in the oil industry to modify mechanical equipment to incorporate new technologies and to optimize production. In the case of pressure vessels, it is occasionally required to cut large openings in their walls in order to have access to the interior part of the equipment for executing modifications. This cutting process produces temporary loads, which were obviously not considered in the original mechanical design. Up to now, there is not a general purpose specification for approaching the assessments of stress levels once a large opening in a vertical pressure vessel has been made. Therefore stress distributions around large openings are analyzed on a case-by-case basis without a reference scheme. This work studies the distribution of the von Mises equivalent stresses around a large opening in FCC Regenerators during internal cyclone replacement, which is a frequently required practice for this kind of equipment. A finite element parametric model was developed in ANSYS, and both numerical results and illustrating figures are presented.

Download Full-text

Proving the Labeled Interval Calculus for Inferences on Catalogs

2nd International Conference on Design Theory and Methodology ◽

10.1115/detc1990-0109 ◽

1990 ◽

Author(s):

Walid Habib ◽

Allen C. Ward

Keyword(s):

Mechanical Design ◽

Formal System ◽

Constraint Propagation ◽

Operating Conditions ◽

Manufacturing Processes ◽

Entire System ◽

High Level Language ◽

Design Problems ◽

High Level ◽

Interval Constraint

Abstract The “labeled interval calculus” is a formal system that performs quantitative inferences about sets of artifacts under sets of operating conditions. It refines and extends the idea of interval constraint propagation, and has been used as the basis of a program called a “mechanical design compiler,” which provides the user with a “high level language” in which design problems for systems to be built of cataloged components can be quickly and easily formulated. The compiler then selects optimal combinations of catalog numbers. Previous work has tested the calculus empirically, but only parts of the calculus have been proven mathematically. This paper presents a new version of the calculus and shows how to extend the earlier proofs to prove the entire system. It formalizes the effects of toleranced manufacturing processes through the concept of a “selectable subset” of the artifacts under consideration. It demonstrates the utility of distinguishing between statements which are true for all artifacts under consideration, and statements which are merely true for some artifact in each selectable subset.

Download Full-text

Systematic Process Selection in Mechanical Design

Volume 1: Design for Manufacturing Conference ◽

10.1115/96-detc/dfm-1403 ◽

1996 ◽

Author(s):

Amal M. K. Esawi ◽

Michael F. Ashby

Keyword(s):

Manufacturing Process ◽

Mechanical Design ◽

Selection Procedure ◽

Manufacturing Processes ◽

Process Selection ◽

Systematic Selection ◽

Cost Penalty ◽

The Right ◽

The Cost ◽

Manufacturing Process Selection

Abstract There has been a recent awareness of the importance of making the right manufacturing decisions early in the design process before the cost penalty of making changes becomes too high. The selection of the most appropriate manufacturing process — of which there are a very large number — is one such decision. It is commonly based on human-resident experience or on established local practice. As such, some potentially-usable processes may be overlooked. This paper explores ways in which process selection might be made more systematic. It presents a procedure for manufacturing process selection which considers all manufacturing processes and eliminates the ones which cannot satisfy the design requirements. This is achieved using Process Selection Charts in which process capabilities are displayed graphically. A procedure for the ranking of the successful processes based on cost is under development. The systematic selection procedure lends itself well to computer implementation. A database of manufacturing processes and an advanced user interface thus provide ideal support for designers. Cambridge Materials Selector (CMS) software is currently being applied to manufacturing process selection.

Download Full-text

Quantifying Design Feasibility Using Probabilistic Feasibility Analysis

17th Design Automation Conference: Volume 1 — Design Automation and Design Optimization ◽

10.1115/detc1991-0092 ◽

1991 ◽

Author(s):

R. J. Eggert

Keyword(s):

Design Space ◽

Mechanical Design ◽

Three Dimensional ◽

Feasibility Analysis ◽

Manufacturing Processes ◽

Moment Matching ◽

Probabilistic Constraint ◽

Constraint Equations ◽

Design Specifications ◽

Variation Propagation

Abstract Engineered products are designed for manufacture using nominal values and tolerances. As such, finished products will more or less satisfy design specifications depending on the actual materials and manufacturing processes used. Design feasibility, therefore, depends on how these variations impact specified constraints. Probabilistic feasibility analysis can be used to extend conventional feasibility analysis. By using moment matching and simulation, the probability of points occurring in the design space can be evaluated. The resulting values establish the limits of feasibility and the amount of feasibility in between. The nature of variation in mechanical design is introduced along with concepts of variation propagation in functions of random variables. Moment matching methods are applied to illustrative cases consisting of deterministic and probabilistic constraint equations, resulting in three dimensional feasibility mappings of each design space.

Download Full-text

Analysis of Equipment for Testing the Processability by Injection Molding of Plastics on the Basis of Axiomatic Design Principles

Materials Science Forum ◽

10.4028/www.scientific.net/msf.957.437 ◽

2019 ◽

Vol 957 ◽

pp. 437-444

Author(s):

Adelina Hriţuc ◽

Margareta Coteaţă ◽

Oana Dodun ◽

Gheorghe Nagîţ ◽

Laurenţiu Slătineanu

Keyword(s):

Injection Molding ◽

Axiomatic Design ◽

Design Principles ◽

The Other ◽

Manufacturing Processes ◽

Functional Requirements ◽

Constructive Solution ◽

Other Hand ◽

Design Activities

The obtaining of information concerning the processability by injection of plastics could facilitate a better design of injection manufacturing processes of parts made of such materials. With this aim in view, equipment for testing the processability by injection of plastics was designed. On the other hand, there are known the possibilities of using the axiomatic design principles to solve equipment or various design activities problems. Within this paper, an evaluation of the complying with the requests of the axiomatic design by the designed equipment was developed. The axiom of independence of the functional requirements necessary to be achieved by the equipment was applied. The analysis allowed the formulation of some remarks concerning the fulfillment of some principles of axiomatic design by the constructive solution proposed for the equipment for testing the processability by injection of plastics.

Download Full-text

Exploring the Retention of Sustainable Design Principles in Engineering Practice Through Design Education

Volume 3: 17th International Conference on Advanced Vehicle Technologies; 12th International Conference on Design Education; 8th Frontiers in Biomedical Devices ◽

10.1115/detc2015-46778 ◽

2015 ◽

Cited By ~ 2

Author(s):

Bryony DuPont ◽

Addison Wisthoff

Keyword(s):

Product Development ◽

Design Education ◽

Online Survey ◽

Expert Knowledge ◽

Mechanical Design ◽

Sustainable Design ◽

Design Principles ◽

Design Guidelines ◽

Engineering Practice ◽

Graduate Level

The School of Mechanical, Industrial, and Manufacturing Engineering at Oregon State University is home to one of the largest academic Mechanical Design groups in the country. As a leader in undergraduate design education, we have been able to keep in touch with a large group of mechanical design graduates, and as such are capable of assessing how students retain information learned in undergraduate coursework to see how this understanding is employed in real-world engineering practice. However, the principles governing the design of sustainable products and processes are relatively novel and are only now being integrated into the undergraduate and graduate mechanical design curriculum. It is our hypothesis that particular means of learning and understanding sustainable design — via lectures, homework assignments, design projects, and the use of various sustainability-related LCA tools — will enable the highest retention of sustainable design understanding, and a higher likelihood that this sustainable design knowledge will be propagated into design practice in industry. Multiple curricular studies that explore dissemination and retention of sustainable design skills are being explored, including a junior-level introductory mechanical design course and a graduate level sustainable product development course. In the junior-level course, baseline sustainability knowledge is tested by allowing students to make sustainable design decisions by applying varied skill sets, including general principles, a list of sustainable design guidelines, and an innovative online survey (The GREEn Quiz). The graduate-level course, which employs sustainable design principles within a larger product development architecture, will capitalize on more “expert” knowledge. Future work will also be discussed, including planned validation studies and curriculum improvements, as well as the means of quantifying the retention of sustainable design information.

Download Full-text

Overview of the opto-mechanical design of the 2-5 micron arm of the Thirty Meter Telescope planetary systems imager

Ground-based and Airborne Instrumentation for Astronomy VII ◽

10.1117/12.2313767 ◽

2018 ◽

Author(s):

R. Deno Stelter ◽

Andrew J. Skemer ◽

Renate Kupke

Keyword(s):

Mechanical Design ◽

Planetary Systems

Download Full-text

Advances in the design of optical see-through displays

Advanced Optical Technologies ◽

10.1515/aot-2020-0005 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Yao Zhou ◽

Jufan Zhang ◽

Fengzhou Fang

Keyword(s):

Design Principles ◽

Manufacturing Processes ◽

Performance Parameters ◽

Innovative Technologies ◽

Potential Applications ◽

Future Potential ◽

Systematical Review ◽

Physical Principles

AbstractDriven by greatly increased applications, the optical see-through displays have been developing rapidly in recent decades. As a result, some innovative technologies have emerged toward making the display more compact and lighter with better performance. This paper serves as a systematical review on the advances in developing optical see-through displays, including the physical principles, optical configurations, performance parameters and manufacturing processes. The design principles, current challenges, possible solutions and future potential applications are also discussed in the paper.

Download Full-text