Micro molded optics are at the cutting edge of precision plastic part and component manufacturing. (Credit: Accumold)

Design for manufacturing (DfM) is a huge focus for the medical device sector today, and it becomes an ever more important consideration when production moves from time-worn and conventional manufacturing processes to more esoteric processes such as micro additive manufacturing (AM) and micro injection molding, both of which are at the cutting edge of precision plastic part and component manufacturing.

In its most general sense, DfM for medical devices means the design of parts sympathetic to the production process being used in order to make optimized outcomes in a timely fashion, and cost-effectively. The goal is 100 percent yield and zero failure rates while also taking advantage of the process being used to facilitate design opportunities that might be impossible using alternative technologies.

So, a real understanding of DfM not only saves cost and time but it can also promote medical device innovation. A proper win-win.

When applied to micro injection molding; however, the process is entering a world where the laws of manufacturing in plastics are in many instances turned on their heads. So DfM is not just a nice to have that can increase production efficiency and outcomes by a few percentage clicks, but it can be the difference between being able to make a part successfully or not being able to make a part at all.

DFM IN THE MICRO WORLD

Making smaller and smaller and often increasingly complex parts and components for medical device applications does not just mean simply scaling down macro processes. In addition, there needs to be a fundamental review of the way that a product development process is undertaken because of a disproportionate need to focus on true collaboration with production partners and a laser sharp focus on DfM.

As medical device manufacturers begin to conceive a micro molding project, it is important to bear in mind some key issues from inception. Every project should start with the end in mind. Designers need to understand the basic design approach, and really bottom out what they can and cannot do, because when micro molding, even the smallest design change can have a significant impact in terms of time and cost or product development.

DfM is a fundamental consideration when micro molding. Each micro molding project is unique in terms of geometric complexity and shape, and each can be made in a wide range of materials, all of which will ultimately affect the ability to manufacture.

Key areas of focus when considering DfM are reviewing characteristics for molding, including gating, ejection, and parting split lines, and understanding whether the part is designed for molding simplicity. As a rule of thumb, avoiding complex actions within the tool ultimately leads to a more robust, low-maintenance design that increases uptime and the chances of on-time delivery. Annual volume requirements are also important to consider because these influence cavitation requirements and directly affect complexity.

Critical to quality (CTQ) features and tolerances are just as important to project success as a robust mold design because they represent the product characteristics as defined by a customer (internal or external). CTQs drive mold design decisions by influencing manufacturing methods and a tool layout that would best achieve these critical requirements.

DESIGN AND COLLABORATION

Examples of micro molded optics. (Credit: Accumold)

DfM is vital as it truly establishes a partnership between medical device manufacturer and supplier during the product development process. When making precision plastics parts and components, micro molding per se is only one part of the product development, albeit a very important one. It is important for medical device OEMs to appreciate that various departments involved in a micro manufacturing project need to be engaged from product design inception.

Absolutely critical for success is to reassess the nature of the relationship between medical device OEM and molder in a micro molding scenario. When dealing with contract manufacturers on the macro level, the relationship can quite acceptably be that of a job shop. The design is presented, the quote is secured, and the parts are delivered. Job done.

This cannot and will not work when undertaking a micro molding project, which necessitates that the medical device OEM and the chosen micro molding company enter a fully collaborative partnership relationship. The reasons for this are numerous but begin with the fact that just as micro molding and the macro molding are completely different processes, the DfM rules are also entirely different.

DfM for micro molding is hugely important, and the expert in the room to offer advice and counseling is the expert micro molder. Very often, the less baked an idea is when the micro molder is engaged the better, as the earlier that the design of a micro product can be influenced and adjusted to optimize manufacturing outcomes, the better in terms of cost and timeliness of production.

Essentially, DfM ensures that not only will the end product be fit-for-purpose but that it is also optimized for the production processes that will be used to manufacture it — in this case micro molding and automated assembly. The micro molding team should be able to advise on such issues as material choice, draft angles and undercuts, part lines, ejector pin locations, gate locations, the likely flow of material in the mold, wall thicknesses, etc. Perhaps the key enabling technology when it comes to micro molding is micro tooling. Tooling in any manufacturing scenario is always the costliest and most time-consuming part of the product development process, but when looking at micro molding, the tolerances and complexity that is often required in micro molds make it especially critical.

Micro tooling is an art in itself, and for medical device OEMs, it is vital that they work with micro molders that are able to design, build, and maintain molds in house, and that have the expertise and experience to optimize tool fabrication.

One size does not fit all when looking at micro tooling, and it is important that medical device OEMs engage with micro molders that can work drill down into the specifics of a particular application, understand the effects of a certain material, cycle time expectations, part criteria, and expected volumes before beginning to cut steel.

In house tool fabrication — in fact, vertical integration in general ensuring that design, molding, metrology and validation, and automated micro assembly are all undertaken in the same facility with departments working collaboratively — is vital in a micro manufacturing scenario where tolerances are so tight. The probability for successful outcomes increases exponentially when the responsibility for project and production, timeline, and execution are controlled within a single entity.

The differences between macro molding and micro molding are stark when it comes to the molding process per se. Every stage of the product development process in a micro manufacturing scenario is driven by an obsession with the attainment of micron and sub-micron tolerances.

Finally, when dealing with miniaturized plastic parts and components, the assembly part of the product development process must be discussed and considered early in the design cycle. When dealing with micro scale parts and components, the cost of manual assembly is prohibitive, and often requires levels of preciseness when dealing with sub-micron tolerances that are impossible to achieve. Automated assembly is therefore a must in most micro molding scenarios.

A WORD ABOUT ADDITIVE

Micro AM technology adds a new palette of options for medical device customers. AM is an agile production technology that requires no tooling, can promote mass customization, and allows the manufacture of parts with a geometric complexity impossible using conventional production technologies. In a micro plastics part product development process, it also adds enormously at the prototyping stage, as it promotes the ability to trial multiple designs without the cost and time required to produce prototype tooling.

Design for additive manufacture (DfAM) is a subject in itself, and it effectively requires a root and branch overhaul of the way parts are designed. AM promotes design freedom, promotes innovation, promotes art consolidation. However, to achieve this, it is important to be conversant with topology optimization, multiscale structure design, multi-material design, lattice structures, and thermal issues in design.

As with design for micro molding, the key in almost all instances when considering the use of micro AM is to embrace a product development partner that has the in-house expertise to ensure the best use of technology and design optimization to promote innovation.

Article Source: Medical Design Briefs