Computational Fluid Dynamics (CFD) is used to better understand the performance of a wide range of industrial and commercial applications, as diverse as the flow of ink in a ball point pen, combustion efficiency of gas turbines, bread baking in industrial oven, and the comfort level in winter gardens. CFD is a specialist engineering tool which affords a greater level of insight and understanding than is possible through experimentation alone. Metro SMT apply CFD during the design process for their range of nozzles, resulting in improved vacuum formation and stability and reduced pressure loss and contamination.

CFD is a technique to solve the fundamental transport equation for the transient conservation of mass, momentum, energy, and turbulence, in three-dimensions in an arbitrary domain. The domain would be the air flow inside the nozzle, around the machine head, and over the circuit board, and the solution to the equations tracks the path that the air takes between the nozzle tip and the component, and through the nozzle tip as the component is being picked and placed. The following examples how how CFD is applied to nozzle design:

Figure 1: Internal Air Flow

Figure 1 shows the results of CFD highlighting the flow inside the nozzle as the nozzle tip approaches the component prior to picking. The path that the air flow takes from outside to inside the nozzle is depicted by the coloured ‘pathlines’. While most of the pathlines pass through the nozzle, some form closed loops or recirculations. This highlights a problem with the nozzle design because dust and other contaminants could migrate into the recirculation where they would be trapped and build up over time, causing the nozzle to clog, lose vacuum pressure, and fail prematurely. Additional CFD can be developed to explore the effect of changes to the internal nozzle profile, and the pathlines can be compared to identify the optimum design by minimising or irradicating the recirculations.

Figure 2: External Air Flow

Figure 2 shows another set of pathlines, showing the air diverting over and around the nozzle and component as they traverse along the tool path. As the air changes direction and speed (accelerates) it imparts a force on the component, which, if it is greater than the holding force of the vacuum pressure, may displace the component.