Assembly Variability Risks Analysis

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). 

Component Assembly Variability Risks Analysis - Too often, assembly is overlooked when assessing the robustness of a design. DFA teehniques offer the opportunity for part eount reduetion through a struetured analysis of the assembly sequenee, but they do not speeifieally address variability within assembly proeesses. A eom-ponent s assembly situation involves the following proeess issues ... 

Example - Component Assembly Variability Risks Analysis... 

The CA methodology is useful in this respect. It is comprised of three sections the Component Manufacturing Variability Risks Analysis, the Component Assembly Variability Risks Analysis and the determination of the Effects of Non-conformance through the Conformability Map. 

Assembly Variability Risks Analysis is key to better understanding the effeets of a eomponent s assembly situation on variability by quantifying the risks that various assembly operations inherently exhibit. By identifying eomponents with high assembly risks and potentially high failure eosts, further design effort is highlighted and performed in order to identify the assoeiated toleranees for the eomponent s optimal fit and funetion. 

Through an assembly sequence diagram for each component in the product, the assembly variability risks highlighted by an analysis are logically mapped. An assembly sequence declaration compels the designer to focus on each stage in the assembly and therefore makes the task of identification of potential problems much easier. 

When analysing a eomponent or assembly proeess, eomplete all eolumns of the Variability Risks Results Table (see later for an example) and write additional notes and eomments in the results table whenever possible. The table is a eon-venient means of reeording the analysis for individual eomponent manufaeturing and assembly variability risks q, q ). It is reeommended that the results table provided is used every time the analysis is applied to minimize possible errors. 

A variability risk table (as shown in Figure 2.28 for the eover support leg analysis above) is a more elfieient and traeeable way of presenting the results of the first part of the analysis. A blank variability risks results table is provided in Appendix VII. It eatalogues all the important design information, sueh as the toleranee plaeed on the eharaeteristie, the eharaeteristie dimension itself, surfaee roughness value, and then allows the praetitioner to input the results determined from the variability risks analysis, both manufaeturing and assembly. 

Figure 2.42 Variability risks analysis for the solenoid end assembly initial design...

Figure 2.42 shows the variability risks analysis based on the toleranees assigned to meet the 0.2 mm toleranee for the assembly. Given that an FMEA Severity Rating (S) = 5 has been determined, whieh relates to a definite return to manufaeturer , both impaet extruded eomponents are in the unaeeeptable design region, as well as the bobbin and plunger end seal as shown on the Conformability Matrix in Figure 2.43. The toleranee for the brass tube base thiekness has no risk and is an aeeeptable design.

The doeumentation of the risks for eaeh eomponent and assembly operation follows the determination of the assembly sequenee diagram, if appropriate, when the produet eonsists of more than a single eomponent. Every eritieal eomponent eharaeteristie or assembly stage is analysed through the use of the variability risks table. An assembly risk analysis will be performed during several of the ease studies presented later. 

The final part of the analysis is based around the eompletion of a Conformability Matrix relating variability risk indiees for eomponent manufaeturing/assembly... 

The previous seetions have illustrated the use of the various proeess risk eharts and tables to obtain variability indiees assoeiated with the manufaeture and assembly of produets. It is important to be systematie with the applieation of the methodology and the reeording of any produet analyses, espeeially as produets often eontain many parts. It is also important to first deelare a sequenee of assembly for the individual eomponents before proeeeding with an analysis. 

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