Manufacturing processes PRIMAs

The principal intention is that the candidate processes are selected before the component design is finalized, so that any specific constraints and/or opportunities may be borne in mind. To this end, the manufacturing process PRIMA selection matrix (see Figure 2.2) has been devised based on two basic variables ... 

Consider the problem of specifying a manufacturing process for a chemical tank made from thermoplastic with major dimensions - 1 m length, and 0.5 m in depth and width. A uniform thickness of 2 mm is considered initially with the requirement of a thicker section if needed. The likely annual requirement is 5000 units, but this may increase over time. The manufacturing process PRIMA selection matrix in Figure 2.2 shows that there are four possible processes considered economically viable for a thermoplastic material with a production volume of 1000-10000. These are ... 

With reference to the manufacturing process PRIMA selection matrix in Figure 2.2, it can be seen that the requirement to process carbon steel in low to medium volumes (1000-10000) returns thirteen candidate processes. This is a large number of processes from which to select a frontrunner. However, some processes can be eliminated very quickly, for example, those that are on the border of economic viability for the production volume requested. The process of elimination is also aided by the consideration of several of the key process selection drivers (as shown in Figure 1.11) in parallel. For example ... 

To provide for the first point, a set of so-called manufacturing PRocess Information MAps (PRIMAs) have been developed. In a standard format for each process, the PRIMAs present knowledge and data on areas including material suitability, design considerations, quality issues, economics and process fundamentals and process variants. The information includes... 

A key feature of the PRIMAs is the inclusion of process capability charts for the majority of the manufacturing processes. Tolerances tend to be dependent on the overall dimension of the component characteristic, and the relationship is specific and largely nonlinear. The charts have been developed to provide a simple means of understanding the influence of dimension on tolerance capabUity. The regions of the charts are divided by two contours. The region bounded by these two contours represents a spectrum of tolerance-dimension combinations where Cpt>1.33 is achievable. Below this region, tolerance-dimension combinations are likely to require special control or secondary processing if Cpk= 1.33 is to be realized. 

The work is presented in three main parts. Part I addresses the background to the problem and puts process selection and costing into the context of modern product introduction processes and the application of techniques in design for manufacture. Part II presents the manufacturing process information maps (PRIMAs) and their selection. Part III is concerned with methods and data for costing design solutions. 

In the development of the assembly variability risks analysis, expert knowledge, data found in many engineering references and information drawn from the CSC DFA/MA practitioner s manual (CSC Manufacturing, 1995) were collated and issues related to variability converged on. Much of the knowledge for the additional assembly variability risks analysis was reviewed from the fabrication and joining data sheets called PRocess Information MAps (PRIMAs) as given in Swift and Booker (1997). 

Next we proceed to compare relatively the data in each PRIMA for the candidate processes against product requirements. Figure 2.8 provides a summary of the key data for each process upon which a decision for final selection should be based. An X next to certain process data indicates that they should be eliminated as candidates. Vacuum forming is found to be the prime candidate as it is suitable for the manufacture of tub-shaped parts of uniform thickness within the size range required. Vacuum forming is also relatively inexpensive compared to the other processes and has low to moderate tooling, equipment and labor costs, with a reasonably high production rate achievable. Production volumes over 10 000 make it a very competitive process. 

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