3.3 Optimizing process planning for HMP

be fixtured in the second and other subsequent stages of finishing. One such strategy is to create sacrificial supports that can be removed from the part once the components have been finished using CNC machining. Figure 8 shows an as-built component at the back left, a finished component with the sacrificial support still

Additionally, hybrid finishing of additive manufacturing requires considerations

in-tact in the back right, and a finished component in the front center.

Sacrificial support strategy example part (reproduced with permission from [18]).

Considerations for AM-subtractive HMP process planning.

Considerations for injection Mold-subtractive HMP process planning.

Figure 8.

Figure 9.

126

Figure 7.

Mass Production Processes

that can be grouped into three key areas: feature considerations, additive manufacturing process considerations, and finishing process considerations. Figure 9 lists key example considerations for each area. Using the strategies

When developing a process plan for any manufacturing method there are many avenues in which the plan can be developed. The most intuitive process plan can be developed from the perspective of the features themselves; this is a precedence based approach where higher precedence is given to more critical features for final part function. In this situation each feature is completely manufactured before the next feature is considered. This is the most logical method for creating a process plan.

However an optimized process plan might consider is the minimization of the number of tool changes. A tool change can occur multiple times in manufacturing a single feature. This can take a significant amount of time, especially if the tool change process is manual. In this situation the process plan is developed such that each tool is used on as many features as possible before changing tools. The drawback to this method is that multiple features may be in process at any given time. If features have critical tolerances based on each other this process plan can result in a part that does not meet standards.

Another optimized process plan may consider manufacturing parts one that reduces the number of orientation changes required. In an automated 5 axis CNC machine, orientation changes are often not a problem, however in a more manual process, changing the orientation of a part can take hours to re-fixture and re-center the part. In this scenario every feature in each orientation is machined before reorienting the part. Again, multiple features are in-process at the same time.

Even further optimized process plans can be developed combining any of the three techniques: precedence, minimizing tool change, or minimizing orientation changes. Each of these methods are important especially to HMP parts since often complex or unusual features are the driving force for choosing such complex and time consuming manufacturing methods. If the process plans are then developed manually this can take days, weeks, even months to develop an initial plan delaying a project entirely. If the plan needs to be optimized for precedence, tool changes, orientation changes, or a combination of the three the process planning phase can take an extremely lengthy amount of time delaying the project even further. Therefore, there is a considerable need for computer aided process planning software which can account for the complex geometries of such HMP parts. An Excel based prototype has been developed and is described further in the next section.
