Module 1 Introduction. IIT, Bombay

Transcription

1 Module 1 Introduction

2 Lecture 3 Embodiment Design

3 Instructional objectives It is explained in the previous two lectures how to identify the needs and define a problem based on the needs, and how to generate several concepts and evaluate the concepts in the course of a new product development. In this lecture, we will learn how to finalize the product architecture, determine the shape or form of the parts to attain the requisite functions, and quantify the important design parameters. Introduction The embodiment design phase will take the abstract design concept and mold it into a system that can actually be produced. Most of the activities in this phase are devoted to finalizing the product architecture, determining the shape and form of the parts that will satisfy the required function, and quantifying the important design parameters. The decisions during this phase should be as much as possible be justified by mathematical and physical proof or validation. Embodiment design is briefly classified into three sections. 1. Product Architecture that involves arranging physical elements to carry out functions. 2. Configuration Design that provides preliminary selection of materials and manufacturing process and modeling or sizing of parts. 3. Parametric Design that involves applying the concept and principles of design for manufacturing to finalize the dimensions and the tolerances.. Product Architecture Product architecture design is the stage when the arrangement of the physical components of a product is realized to enable the product to carry out its required function. The basic layout and the architecture of the product is established by defining the basic building blocks of the product in terms of the function of these building blocks and the nature of their interfaces. These basic building blocks are also known as chunks. Each chunk is made up of a collection of components that would carry out a specified function. Thus the architecture of the product is given by the relationships among the components in the product and the functions that the product is being made to perform as a whole. There are two different styles of product architecture. One is the modular architecture and the other is the integral architecture. In the case of modular

4 architecture, the building blocks implement only one or a few intended functions and the interactions between two building blocks are well defined. In the case of integral architecture, the implementation of a function is carried out by only one or few building blocks often leading to poorly defined interactions between the building blocks. Usually, a typical product architecture contains a combination of both the modular and the integral architecture. Figures and schematically provide typical examples of modular and complex integral architectures, respectively. For example, Figure a one to one mapping from the functional elements to the physical components and its function while Figure exhibits a complex integral mapping from functional elements to physical components Figure Schematic presentation of a modular architecture

5 Figure Schematic presentation of a complex modular architecture Three steps process for Product Architecture The product architecture design can be realized using three steps (a) defining arrangement of functional elements, (b) mapping from functional elements to physical components, and (c) defining specifications of the interfaces among interacting physical component. The process of product architecture will be explained by an example of a trailer. Arrangement of functional elements Functional elements are nothing but the functional requirements of the product. The arrangement of functional elements is referred to as functional structure. The functional elements primarily involve exchange of signals, materials, force and energy. In few instances, some elements may not interact in any form with other functional elements. Not more than 30 elements are recommended to be used to determine the initial product architecture. Figure schematically presents the functional arrangement of a trailer.

6 Figure Schematic presentation of the arrangement of functional elements in a trailer Mapping from functional elements to physical components The purpose of this step is to map the functional elements to the corresponding physical component that would implement the functional elements of the product. The mapping of the functional elements to the components can be one to one as in modular product architecture or one to many as in integral architecture. Figure depicts a typical modular trailer architecture.

7 Figure Schematic mapping of functional elements to physical components for a trailer Specifications of the interfaces among interacting physical component This step determines whether there is any possibility of geometrical, thermal and / or electrical interfaces between any two components. In many cases, a two-dimensional drawing is sufficient while a three-dimensional model may often be the requirement [Figure 1.3.5]. Creating a geometric layout forces us to decide whether the geometric interfaces between the components are feasible or not. For example, one of the interfaces for the trailer shown below is between the box and the bed. The specifications of the interface includes the dimensions of the contact surfaces between the two components, the positions and the sizes of the bolt holes and the maximum force the interface is expected to sustain.

8 Box Fairing Bed Hitch Wheels Springs Figure Schematic three-dimensional drawing of a trailer to aid to specification of interfaces between components Configuration Design In configuration design we tend to realize the shape and the general dimensions of components although the exact dimensions and tolerances would be finally established during parametric design in later stages. The configuration design is developed from the functions and it strongly depends on the availability of the materials and production techniques that would be used to create the form from the material. Usually the decisions about the design of a component cannot proceed further without making the decisions about the material from which the product (or the components) will be made and the manufacturing process that will convert a raw material to a functional part of component or product. There is a close interrelationship among the functions and from and the dependency between the material and the method of production which is schematically shown below [Figure 1.3.6]. The configuration design should involve the following steps. [1] Review the product design specifications and any subassembly specifications developed.

9 [2] Determine the spatial constraints that are related to the product and the subassembly being designed. Most of these constrains would have been addressed in the product architecture. In addition to the physical spatial constraints, the constraints pertaining to the human interaction with the product, products life cycle, and the constraints related to providing access for maintenance and repair should also be addressed at this stage. [3] Create and refine the interfaces and connections between the components. Special design efforts are required at the point of connection between the components. It is necessary to identify and offer special attention to interfaces where the most critical functions would finally be carried out. [4] It is quite essential to maintain functional independence in the design of an assembly or the components. It means that changing of a critical dimension should affect only a single function. [5] Following questions should be answered before the initiation of the configuration design, [a] can some parts be eliminated or combined to give fewer parts and components? [b] can a standard part, assembly or module be used? Figure Interrelationship among material, form or shape, intended function and the manufacturing processes

10 Parametric Design The parametric design is primarily concerned with the specific values and attributes of various design elements that are found in the configuration design. These are also known as design variables. The design variable is an attribute of a part whose value is under the control of the designer. These typically include dimensions or tolerances, material, shape, manufacturing processes, assembly and finishing processes, and so on that must be undertaken to create the part. The objective of parametric design is setting values for the design variables that will produce the best possible design considering both the performance and the manufacturability. Parametric design is also about setting the dimensions and tolerances so as to maximize quality and performance and minimizing the cost. Various steps are undertaken in parametric design procedure. Failure mode and Effects Analysis (FMEA) By performing FMEA we can determine all possible ways by which the components can possibly fail in service and establish the effects of the failure on the system thus improving the performance and quality of the product. Design for Reliability By designing for reliability the capacity for the product to operate without failure in the service environment increases. Robust Design By performing the process of robust design high quality in product can be assured as it reduces the variability in performance and manufacture over a wide range of operating conditions. The following are typical steps undertaken towards the approach for robust design. (1) System design: This relates to what we have referred to as the product architecture where the engineering principles are used to determine the basic configuration of the system. (2) Parametric design: Statistical methods and techniques are used to set nominal values for the design variables that minimize the variability from uncontrollable variables in the environment. (3) Tolerance design: Extensive statistical methods are used to set the widest required tolerance s on the design variables without increasing their variability

11 Tolerance Permissible tolerances must be placed on dimensions of a part to limit the acceptable variations in the size of a part. A small tolerance means greater ease of interchangeability of parts and less play or vibration but this obviously leads to increased cost in manufacturing. Dimensions are used to specify the size and locations of the features. Tolerances determine the acceptable variations to the ideal or nominal dimensions. The above were some of the methods by which the quality and performance can be improved. The second goal of the parametric design is to reduce the manufacturing cost. This essentially required close attention to design for manufacturability to understanding the various design features affecting the manufacturing cost. By performing the parametric design we conclude the embodiment design and a prototype of the product can be constructed. A prototype is a full-scale working model, technically and visually complete. The main purpose of the prototype is to confirm that the design satisfies all the customer requirements and performance criteria. Extensive testing of this prototype gives the necessary information for reliability and robustness of design. It will also verify whether the environmental, safety and other legal requirements have been met.

12 Exercise 1. Distinguish between modular and integral product architecture References 1. G Dieter, Engineering Design - a materials and processing approach, McGraw Hill, NY, K.T. Ulrich, The role of product architecture in the manufacturing firm, Dec 1993,