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MICRO MOULDING FEATURE


moulders have been defying these “suggestions” for more than 30 years. If there seems to be a casual response to a moulding project the part is either simple or the moulder does not appreciate all of the subtle complexities of the process. So what does it take? And, what does this DFM conversation sound like? Here are four main conversation topics every DFM should include for micro moulded projects:


GEOMETRY & MATERIAL SELECTION The primary discussion for any micro moulded DFM starts with the geometry and material selection. As with any sized part, it is possible to draw a part that isn’t producible. Even micro moulding can’t defy the laws of physics. That being said, there is also a geometric limit to any design. It can be too thin, too long, to deep, etc. The discussion with the moulder at this point is to finesse those limits. As a general rule, start with the ideal


design for the situation keeping in mind that the general moulding rules apply. For example, there needs to be a gate, a way to eject the part and draft, even at micro sizes, is still welcome. Then let the micro moulder suggest where the design may need to be altered to be successful. This assessment is based often on the experiences of the moulder rather than relying on some piece of software to dictate success. It’s this experience that separates a general moulder with a small moulding press from a micro moulder with years of successful tool building and moulding. Press manufactures don’t typically sell 30 years of experience with each machine. The second major part of the discussion


is material selection. This is important because at typical micro moulded feature sizes the material selected can have a profound effect on the success of the project. Again, an experienced micro moulder can usually look at the geometry and the material selected and give an idea of what the outcome would be. There are many situations where the geometry is manufacturable but the chosen material dictates otherwise. This can be a particular difficult obstacle to overcome. Material is typically chosen for its inherent properties like strength, heat resistance, bio-compatibility, etc. The data sheets can also be misleading since much of their moulding suggestions (i.e. gate size, flow capability) are based on much larger sample mouldings. Trust the experience of the moulder to help lend some direction here but keep in mind that the ultimate decision for the material choice is not the moulder. The designer will have to choose how to navigate this important step given all the advice offered. Talk it through.


components needed should take place. Sometimes the moulder can source everything and sometimes it’s the designer’s company. Figure that out now.


TIME AND COST Rounding off the DFM is typically a circle back to the initial quote and time line. The common practice is a design is sent in for a quote, as much critical detail is collected as possible and the moulder works through what they think can be done, when it can be done, and for how much. Where the situation can go array is the expectations between the RFQ and the full DFM. It’s understood that the full DFM process


QUALITY & CRITICAL FEATURES After there is agreement on the geometry and the material the conversation should next move to quality. Often the tolerances on critical dimensions related to micro moulded projects are set at 25µm or less. It’s not uncommon, especially with micro optics, for dimensional tolerances to be ± 2-3µm. In this part of the discussion it’s important to understand that a true 0 tolerance is probably not realistic, and neither is putting tight constraints on every feature. The discussion should flow around the


critical tolerances as well as any other quality related requirements. Having the conversation about important surface areas, cosmetics and other geometric concerns at this stage is a must. The tool builder will make hard steel decisions based on this part of the conversation. Mould design, parting line, gating and ejection are just a few of the items that will need to be ticked off the list. Another important part of this too is the annual unit demand. The moulder must understand what kind of volume must be produced off this tool for the mould design to be robust. Quality requirements like CPK expectations, SPC, part handling and/or packaging are also extremely valuable details to the mould designer. With these type of projects, these seemly mundane details can have huge positive or negative effects down the line. Somewhere along the line in discussions, there should be opportunity to describe any extra or special items necessary for a successful project. These can be items that are to be over-moulded or encapsulated. They could also be any special handling, packaging or automation requirements. It is crucial anything of this nature be included in the DFM, again, for many of the same tool building considerations. This is also where discussion about any sourced materials or


/ MICROMATTERS


Figure 2: The challenge with micro moulding begins when the project moves from the digital to the physical stage


“One


of the key enabling technologies in the miniaturisation


phenomenon is micro- injection moulding. Electronics and plastics go hand-in-hand these days.”


can be lengthy and require multiple team members from both the designer and the moulder. Most moulders can’t do a full DFM with every quote thus leaving the potential for new details to come out after the quote has been submitted. It’s very important to understand this part of the sequence so that expectations can be met by all. An experienced micro moulder will ascertain what it typically needed for a quote but make sure the Sales Engineer working up the initial details has everything they need. Lastly as it relates to time and cost, keep in mind, because micro moulding is not a run-of-the-mill process the tool build efforts can take time and the costs can be significant. Don’t fall into thinking that because it’s small it must be cheap. Of course, as with any sourced component, the lead time to market and costs associated have to make sense. Going into a DFM with all eyes open will help everyone involved and will help make the experience successful. The challenges that exist for OEMs to develop the “next big thing” in microelectronics are huge, and in order to fully realise this potential, it is important to engage a micro moulding partner that can not only assist in the design of smaller plastic components, but, which is also aware of the particular contingencies and issues that apply when manufacturing such components. Opportunities exist to make smaller and lighter parts, to add micro features to existing parts, or even to add new micro features to micro parts but knowing how to approach such an opportunity will help aid success and ultimately help achieve the “impossible.”


Accumold www.accu-mold.com 1-515-964-5741


MICROMATTERS | SUMMER 2015 21


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