MDDI_Medical Device & Diagnostic Industry

MDDI, June 2014

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36 | JUNE 2014 mddionline.com Molding Image courtesy of MRPC Micromolding 101: Ensuring Manufacturability As medical device parts and features shrink, the micromolding processing window narrows, creating a host of manufacturability challenges. JEFF RANDALL T he proliferation of rapid prototyp- ing and additive manufacturing has made it much easier for designers to produce prototypes or sample parts with material properties that more closely resem- ble those of production parts. In the past, the range of materials selected for rapid proto- typing applications was narrow and not very functional. But as these materials improve, designers are able to do much more testing than previously using prototypes. While this capability represents a great technological advancement, it can also pro- duce false positives during product develop- ment. It is possible to produce a rapid pro- totype, test it, and go too far in the process without realizing that the design is not man- ufacturable on a larger scale. In fact, in some cases, a design cannot be micromolded at all; it can be produced only using rapid pro- totyping. To avoid this, designers must en- sure they consider the manufacturability of a design before they become too locked into a design that may not be reversible or which is susceptible to a redesign down the road. The challenge associated with micro- molding is that as features and parts shrink, the processing windowÑor the ability to mold parts with thinner and thinner geom- etries and smaller featuresÑnarrows. Thus, the manufacturability of a micromolded component must be considered even more carefully as parts approach the micro scale. Materials One of the most important parameters designers should bear in mind when producing a micromolded part is material selection: What will the final material be? It isnÕt as simple as saying that the part should be made from PEEK, for example, because different grades of PEEK are available, some of which exhibit better flow characteristics than others. Using a certain grade of PEEK may make the part easier to mold, but it may also compromise its physical properties. Thus, when the engineer considers the design of the part, it is also necessary to consider the materialÕs processability and the design features that relate to this processability. Design for Manufacturability In addition to carefully selecting the right material for the job, design engineers should consider the features of the mold, or tooling, used to produce the component. As the component shrinks and incorporates finer and finer details, the moldÕs features tend to shrink as well, necessitating greater precision. Associated with the mold and all of its components is the need to ensure proper thermal, or temperature, control regardless of whether the material in question is a plastic, liquid silicone, or other material. Like the part itself, mold components are getting smaller and smaller, making it increasingly difficult to heat or cool them and to provide a consistent molding environment. With many medical device components, materials such as stainless steel are often used to manufacture the molds. Because such molds do not corrode or rust, they do not require the use of rust-preventive chemi- cals. This is advantageous because it elimi- nates the possibility that the chemical can leach into the part. However, a downside to using stainless-steel molds is that they do not offer good thermal conductivity, which becomes even more challenging to achieve as the part and the mold details shrink. Another consideration for designers of micromolded parts is where the part will be gated, or filled. The point at which mate- rial enters into the mold cavity is known as the gate. The gate may leave a small vestige of material on the part, which must either Micromolded parts measure less than 1 mm in length. ES451793_MD1406_036.pgs 06.05.2014 04:54 UBM black yellow magenta cyan

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