Journal of Theoretics Vol.2-3

A DECISION SUPPORT SYSTEM FOR ADVANCE COMPOSITE MANUFACTURING COST ESTIMATION

Authors: Zaki NM zaki97@hotmail.com, Daud N

FIST, Multimedia University (MMU), Ayer Keroh 75450 Melaka, Malaysia

Abstract: The increased use of advanced composites in aerospace manufacturing has led to the development of new production processes and technology The implementation of advanced composites manufacturing technology is poorly served by traditional cost accounting methods, which distort costs by using inappropriate volume-based allocations of overhead. Activity-based costing has emerged as a methodology, which provides accurate allocation of costs to products or activities by their usage of company resources. Better designs may also be produced if designers could evaluate the cost implications of their choices early in the design process. This paper describes a methodology whereby companies can improve the quality of product cost estimation at the conceptual design phase using intelligent searching and arrangement of existing accounting data enabling designers to access the activity cost information more readily. This concept has a considerable scope for application in industry because it will allow companies, to make better use of the said information already recorded in their information system. 
 
Keywords: computer programming, engineering, methodology, cost analysis, computer aided design (CAD), Computer Integrated Manufacturing (CIM), Decision Support System.

INTRODUCTION

The growing use of advanced composites in the aerospace industry has led to the development of new methods and equipment for manufacturing materials and structures. In this relatively new field of design, the behavior of production costs relative to the different design variables, is not the way defined it is done in the more established aircraft manufacturing industry, especially in fields of sheet metal forming and fabrication. Engineering models traditionally used for aircraft cost estimation, may not be valid for composite materials. For example, the cost of graphite composite parts may be higher than a similar glass composite part, but substantially lighter in weight, and having enhanced structural properties. The trade-off between weight, performance, and cost is of interest to designers, but is difficult to assess, given the lack of accurate cost information that is currently available.

The primary goal of this study is to analyze the integration of information concerning these various domains that provide information to designers on the cost impact of their design choices. This work assumes that Computer Integrated Manufacturing (CIM) methods will be used in this environment, from computer aided design (CAD) and drafting, through computer aided process planning (CAPP), along with production scheduling and computer controlled/assisted manufacturing processing. The principles of Design for Manufacturability provide a core philosophy for the achievement of design and manufacturing cost reductions. Existing cost estimation techniques provide some ready tools and models for comparison and evaluation. The shortfalls of these methods provide the impetus for this work.

COMPUTER INTEGRATED MANUFACTURING (CIM)

CIM is the integration of the whole manufacturing process through the use of integrated systems twined with new managerial philosophies that improve organizational and personnel efficiency. The goal of CIM is the integration of all enterprise operations and activities around common data repositories. (Computer and Automated Systems Association of SME, 1993)

This study is grounded in the philosophy of sharing common data resources, requiring access to knowledge sources in manufacturing, production control, accounting, and design systems. The challenge is to integrate this information in new ways to provide increased value to the design activities of the enterprise, and thereby improve the competitive advantage of the company. The SME’s use of efficiency as a goal is unfortunate because effectiveness would have been a more far-reaching goal. 

Effectiveness implies that one seeks to improve the position of the company by deciding its activities, rather than just improving the efficiency of whatever activities it is doing.

RESEARCH HYPOTHESIS

In this paper we hope to discover whether this framework as outlined can be constructed in the manner envisaged, and if so then what benefits can be achieved by the proposed design decision support system. This hypothesis could be more specifically stated with the question, “How can product cost estimates be modeled using the existing information sources within the advanced composites manufacturing environment?” 

METHODOLOGY

This study is meant to show how product cost estimates could be modeled using the existing information sources in the advanced composites manufacturing environment. The overriding reason and purpose for this study is to provide decision making environment to product designers (or managers) enabling them to make informed design choices, thereby gaining the most value from their production resources at the least cost. The following sections outline the basis of a methodology for a design decision support system (DDSS) that actively seeks out costs related to a product or function, by intelligently searching the existing accounting, production and engineering data sources.

DESIGN DECISION SUPPORT SYSTEM MODEL

The conceptual model of the Design Decision Support System methodology includes the following sub-systems: the manufacturing system, the design information system, the accounting information system, the production planning system, the Design Decision Support System itself, and the interfaces thereof. In order to capture the complexity of the methodology in a graphic model, it is helpful to consider separate flowcharts for the different levels of the system. Each sub-system is described as a separate entity, and the relationships between the systems are defined.

The DDSS model is discussed in three levels. The first model depicts the top-level interactions between major components that affect the Design Decision Support System, the second model depicts the iterative cost estimation loop within the Design Decision Support System, and the third level details the search methods and calculations for each cost category within the DDSS methodology. 

TOP LEVEL MODEL

The focus of the top-level model is on describing the key components of the Design Decision Support System, and how they interact with the other systems. The underlying manufacturing system is the basis around which all the other systems function. The manufacturing system is defined as the facilities, labor resources, equipment resources, and materials used in the production process. In addition to the basic production resources, the maintenance support sub-system is considered, as it is an important part of the ownership cost of production equipment in the facility. The key objective of the DDSS is to capture all of the costs of the manufacturing resources as described here, and to correctly allocate these costs to the production processes consuming these resources. The information systems are described in the order of logical flow of information through the production process. The Design Information System is the starting point for each cost estimate as it is the point at which designers interact with the rest of the system. This Design Information System is modeled on the Design Methodology for Composite Aircraft Components. This DDSS is intended to provide decision support for designers at the conceptual design stage, by providing cost information to designers in order to evaluate the effect of alternative design choices for them. The Process Plans and Bills of Materials produced in the Detailed Design stage are through conventional inputs to the Production Planning System.

The Production Planning System captures information about production orders, materials, human resources, and equipment resources, as required to control the production process. The Production Planning System is by necessity, somewhat integrated with the Accounting Information System. The description of the Production Planning System should therefore be read as put in association with the description of the Accounting Information System. Although separate systems, there are several points where information exchanges take place between the two systems. 

The model developed for this study uses descriptions of conventional production planning systems, and accounting information systems for production processes, with specific reference to the Integrated Production Information System developed by Gelinas and Oram (1996). Other sources include Murtuza (1995), Nash (1989), and Wilkinson (1993). While specific to this DDSS model, the information flows described here are common to most production and accounting information systems. Example formats of the documents relating to these accounting and manufacturing information flows were also taken from sources in production planning and accounting information texts.

An important feature of DDSS methodology is that it does not disturb the existing information flows in the company's production system it acts rather independently of the design, planning, and accounting information systems. It interacts only with replicated copies of the information systems databases, thereby avoiding the inherent problems and expenses of reconfiguring the existing systems to specifically serve the DDSS.

DATA SEARCH AND ANALYSIS MODEL 

The second level of the DDSS model describes the iterative procedure followed by designers, in developing cost estimates for the designs they wish to analyze. The cost estimation procedure involves first looking for a prior history of making the same or similar products in this enterprise. A product description is entered, and the DDSS searches the Production Planning System databases and returns the closest match to the product that has been made previously by the firm. The order number of that production job defines this product order. Based upon that order number, the DDSS then searches the Production Planning System for the detailed information on that particular product order. 

It returns the records of all the processes involved in making the product, identifying all the materials used for each process, and the human resources and the equipment resources used to carry out the processes. The DDSS then uses these process details to create a fully worked process plan, including the costs of labor, materials, and equipment usage. Details are then extracted from predetermined fields in the process plan; these pieces of information then drive a further search for cost information, using structured searches through the Accounting Information System databases. The said costs are then calculated by DDSS, and inserted back into a newly created process plan spreadsheet. 

ACTIVITY-BASED COST CALCULATIONS IN THE DDSS

The third level of the DDSS model describes in detail the methods for calculating costs for labor, materials and equipment resources used in the composite part manufacturing processes. The cost calculations are driven by the information extracted from defined fields in the process plan. 

The DDSS uses the fields from each row of the process plan, in this case, the material description and size parameter to drive the search process. For each item of material listed in the process plan/bill of materials for a product, the DDSS searches through the inventory master file, and the unit cost of the item is returned. The material cost for each item is calculated as the quantity (number of units) multiplied by the size and then multiplied by the unit cost for that item. The material cost for that process activity is then inserted back into the newly created process plan spreadsheet for the product. 

In a similar fashion, the DDSS searches for labor costs and equipment costs associated with each process activity to make the product. Calculating the cost of equipment first involves creating a separate worksheet to collect all of the costs associated with each equipment asset used in the manufacturing process to make the given product. 

The DDSS program then steps into the next process activity and calculates all of the costs for that activity. For each process, a new structured search routine is created, and the cost information is extracted from the Accounting Information System databases. The cost information is used in the calculation routines, and inserted back into the process plan spreadsheet. In this way the spreadsheet is built up, activity-row by activity-row. 

RESULTS AND DISCUSSION

This initial study identified a need for better methods to evaluate the cost of newly developed manufacturing methods and to make better-informed decisions on designs using these processes and materials. Concurrent engineering techniques and computer integrated manufacturing developments provide the thrust for the study effort. The concepts of Design for Manufacturability target costing, and the strategic use of cost information to compete in the global market all contribute to the usefulness of improved cost-benefit information. Specifically, the design decision needs of aircraft designers were evaluated, especially with regard to providing the necessary information to conduct trade studies and overcoming some of the barriers that have been identified with introduction of composite structures in aircraft designs.

The approach to designing the DDSS was to use commonly used business software as the framework, which would make the system more accessible to users across different functional disciplines. The methods used here compared favorably to the methods using exponential equations and scaling factors as used in COSTADE (Mabson et al., 1994). These cost scaling functions were modeled using the paradigm of Hooke's Law spring equations and thermodynamic entropy, which may make sense to engineers, but might be difficult to fathom for production staff and accountants.

The cost to implement such a system in any given production environment is small when compared to other activity-based cost systems, or parametric costing systems. The system has the additional advantage that it does not require any re-design of the existing accounting information system or production information system. This helps to reduce the barriers of organizational resistance against implementing any new decision support system. The simplicity of explanation and use may also enable organizations take over the system without continued support from (expensive) systems design consultants.

The portability of the system is assured by virtue of combination of a widely used office software package together with the Visual Basic programming language, which allows for easy encapsulation into object-oriented code modules. The databases used for the prototype were constructed using Microsoft Access, but the program would be compatible with a number of major database formats. (e.g. Paradox, FoxPro, Dbase, Lotus). The search routines use SQL (Structured Query Language) syntax, which is an industry standard for Database Management Software. This would allow compatibility with some of the mainframe DBMS and databases (e.g. Oracle). The use of Microsoft Excel spreadsheets as the main input and output interface, provide an easy to understand (and explain) paradigm for engineers, accountants and other managers.

CONCLUSION

This tool could be of a considerable value to industry, in that it may provide a means to access the information that companies already have, but have found difficulty in using it in a meaningful ways to help the design process. The system aims to use the existing information systems as data sources, rather than advocating replacement information systems which would entail considerably more expense and overhead to implement. One of the major barriers to implementing large scope activity-based costing systems has been the high threshold cost to implement these systems, and the heavy investment of skills and resources required to maintain them. 
 
 
REFERENCES:
 
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