Summary of Design for Manufacturing

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Summary of Design for Manufacturing

Summary of Design for Manufacturing

The past two decades have produced a wealth of research and written materials on Design for Manufacturing, Design for Assembly, Design for Maintenance, etc. These activities are frequently referred to as DFX or Design for X where X is the criteria focus of Product Engineering. Much of the research has produced a set of guidelines or rules for designers. Table 1.2 summarizes these rules for three popular systems. There are however many other DFX systems. Intuition and good judgement are the foundation for these systems.

ANDREASSEN[22]

[Andreassen, etal 1983]

LUCAS [21]
[Miles 1989]

BOOTHROYD AND DEWHURST
[Boothroyd & Dewhurst 1989]

Avoid assembly operations
Avoid orientations
Facilitate Orientation
Facilitate Transportation
Facilitate Insertion
Choose correct joining methods

Use only essential items in assembly
Check assembly sequence with a precedence diagram
Full, and correct component specifications
Minimize variation
Symmetrical components where possible
Asymmetry on asymmetric parts should be exaggerated
Minimize number of parts
Design for unidirectional assembly
Minimize assembly functions of each component
Design for machine rather than human assembly
Ensure orientation of subassembly known, and preferable throughout assembly
Subassemblies are structurally sound when being moved
Keep subassembly as far up assembly chain as possible
Ensure subassemblies and components can be handles without marring

Reduce part count and part types
Strive to eliminate human adjustments
Design parts to be self aligning and self adjusting
Assure adequate access and unrestricted vision
Ensure ease of handling from bulk
Minimize the need for reorientations during assembly
Maximize part symmetry when possible, or make part obviously asymmetrical

Table 1.2: Summary of Principle of DFM and DFA of Three Approaches to DFM/DFA

1.4.6 Group Technology (GT) for Concurrent Engineering
A great deal of research has been conducted to find ways to improve mass-production systems. The main reason for this, are the chances of obtaining substantial savings due to the large amount of products produced. This is not the case in batch-production systems, which represents the majority of the world's production capability, where the amount of products is 50 or less. To get similar improvement with this amount of products, a change of concept or idea that modifies the whole process has to be found.

The theory behind GT indicates that various situations requiring decisions, and be grouped together based on preselected, commonly shared attributes, and the decision that applies to one situation in the group will apply to all of them in that group. For this reason, the system can be looked at as a collection of batch-production systems forming a more "massive-production" type system, which can enjoy the low manufacturing cost associated with mass-production systems. The implementation of GT requires information from the manufacturing system to decide what products should belong to which group or family. This same information represents an opportunity for improving not only the manufacturing activity but also other activities such as: product design, process planning, purchasing, etc. GT is a philosophy based upon a smooth continuous and high quality flow of products and information from the initial conception of a product unit its delivery to the customer. In order to support this basis, which increases the speed of response and the productivity of a manufacturing firm with less cost and better quality.

Another important element within the GT philosophy is people. The workers should be completely involved in the process and their knowledge should be captured in databases. The concept of quality is expressed as a measure of the employee's performance. It is implemented using the notion of customer satisfaction, where the next activity in the product development process is the customer of the previous one.

To have an effective database system, it has to be consistent, structured and selective. Inconsistency is one of the most common forms of failure of data base systems. These databases contain the same data but the data is not consistent among all of them, causing mistrust among its users. The data structure is very important since it helps increase the efficiency for entering and retrieving information when large amounts of data are processed. The selectiveness of the data base comes from the fact that all the information can not be economically stored, therefore, a decision about what data to store should be made. One approach to the data base development problem is the use of Production Flow Analysis (PFA) technique, that by analyzing the similarities in the production routings of all the products, determine natural divisions among them which are used to group machines for processing groups of parts. PFA is based solely on the manufacturing process and does not take the parts characteristics into account. A modified method consisting in three parts: Data collection, data sorting and data analysis is also available. First, the minimum amount of data is collected, all the parts with identical process numbers and sequences are assigned identification numbers, and then parts and machines are grouped into families and production facilities are established/Another approach is the use of Classification and Coding (CC). Classification means to group things with the same specific characteristic, while coding permits the development of the data base since the information can be handled by computers. The data is sorted in desired groups based on the code, comparisons and syntheses of information also take place from the logic of the data.

So far GT has been described as a concept that helps simplify the manufacturing process by identifying similar characteristics in products, grouping them and establishing manufacturing machine groups or manufacturing cells to produce them. The applications of GT are separated in two groups: family formation and retrieval, and structured analysis and decision making . In the first group, design standardization is one of the most important applications. By retrieving previous design information, designers can reduce the development time, reduce the amount of designs and build a standardized design process with the use of standard components. Also in the first group the creation of manufacturing cells is present. These production units are formed based on part families and many benefits are obtained by doing so: reduced queue, reduced inventory, improved product quality, reduction in scrap, easier scheduling, etc. With the second group, the process planning process is sped up and the number of plans is reduced. Also, there is a continuous process of improvement for these plans since the previous experiences are recorded and validated over and over again. Benefits in the purchasing activities have also been reported due to the existence of products families that help obtain quantity discounts if parts are bought as families. This principle can be taken a little bit farther by organizing vendors and suppliers into families. There are many benefits that arise from having data bases to support the decision making process, such as: improvement of cost estimating, decreased time, better product-delivery performance, improved plant efficiency, etc. GT helps organize all the activities of a firm in a block form with an effective interface that makes CE (Concurrent Engineering) implementation much easier.

1.5 Implementing Concurrent Engineering
Concurrent Engineering is a very broad concept based on the integration of different disciplines in the development of a product and the control of its evolution along its life cycle. Strategies that serve as tools to CE are for example: Total Quality Control (TQC), Just in Time (JIT), Computer Integrated Manufacturing (CIM) and Human Resource. These strategies utilize some of the methods that were presented before in this chapter, which are directed toward the improvement of product quality with lower cost, better reliability and good availability (short TTM) as a means to obtain a competitive advantage in the global market. None of these CE tools represent the best solution to the transformation that manufacturing firms have to suffer to assure their survival in the marketplace, this solution has to be tailored to each firm going through a conscious analysis of its status in the market and its internal situation. In "Using Manufacturing as a Competitive Weapon: the Development of a Manufacturing Strategy" [Beckman, et al, 1990], a five step approach to manufacturing strategy development is presented. This approach can be extrapolated to CE implementation, by using the CE tools to achieve every defined task. The steps are:
1.   Start with the business strategy. More specifically, understand why customers will prefer your product or service over your competitor's. Factors that influence the customer's buying decision include: low product cost, high product quality, easy maintainability, prompt product availability, and distinguishing product features.
2.   Specify manufacturing's contribution to making customers choose your product instead of your competitor's.
3.   Identify manufacturing tactics to execute the strategy (CE tools). This requires understanding how to manage and control the people, processes, materials, and information needed to deliver products in a way that meets the objectives of the strategy.
4.   Organize for manufacturing success. Organization design, including structure and performance measurement, must match strategic needs or success will be limited.
5.   Measure the results and initiate further change. Strategies must be continually altered to meet the needs of constantly a changing environment. Feedback loops are critical to the continuous improvement process.

The steps given above are general actions that if taken will help the implementation problem. Again, it is difficult to give more detailed steps for implementing manufacturing strategies since they depend on each particular case.

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