Guest Column | September 21, 2020

A Methodology For Developing Injection-Molded Plastic Parts For Your Medical Device

By Zachi Fizik, ZF Consulting

Medical devices are usually practical. They are engineered and designed to provide a solution to a specific need and to be used by the user that needs the product. So when it comes to specifying a product, we usually can pinpoint with pretty high confidence the need, the functionality required to respond to that need, and the certifications and regulations applicable to bring this product to the market.

Medical device developers tend to focus on the above since this is where the “dreams” are and because this is what is visualized on their CAD monitors or materialized by 3D printers. This is what is shown to investors, marketers, doctors, and potential users. And that’s the way it should be done. However, developing plastic parts is not only about the WHAT, it is quite significantly about the HOW.

In this article, I will suggest a methodology that will incorporate questions that have a reputation for being “troublemakers” into the process of injected plastic product development, without compromising innovation and creativity. For example, finding the right time to start thinking about manufacturability of the plastic parts in our bill of materials (BOM) is disputable and depends on who you ask. But I think that all will agree that at some stage we will not be able to ignore it. Knowing the right time depends a lot on experience and the developing company’s culture. It lies in the organization’s ability to create an environment and methodology that balances the “thinkers,” e.g., developers, researchers, engineers, and designers and the “executioners,” e.g., operations, mold and injection specialists, assembly, and QC/QA. It is like accepting that a “devil’s advocate” during the development of the plastic parts  could only contribute to and refine the development by clarifying feasibility of the plastic material manufacturability, cost, delivery time, etc.

Development Stage

Since we do want our engineers and designers to be free spirits in the pursuit of their directives, we could “keep an eye” on their outcomes if we execute prescheduled design reviews (DR) throughout the parts design process. These DRs should monitor the evolution of the parts’ designs in the following ways:

  • Reassuring that ALL specifications (including operational and regulatory) are determined and considered when choosing the raw material, engineering solutions, and production technologies.
  • Ensuring compatibility with injection molding technology. If needed, give online guidance and support.
  • Debating between different assembly options, such as how would snaps, screws, glue, or ultrasonic welding affect the function, cost, availability, delivery, and QC.
  • Incorporating industrial design, marketing, and operations into the design, e.g., colors, surface finish, writing, special finishes and secondary operations, packaging, storage, transportation, etc.
  • Updating realistic production forecasts. From my experience, this has a significant effect on the boundaries of the injected parts design.
  • Understanding, from QA, the AQL (assurance quality level). Special care should be given in cleanroom production or when process validation is needed.
  • Monitoring the budget by checking that the cost of goods (COG) is within targets and that the molds budget is not breached.
  • Controlling the flow of information within the organization. Be strict on data management, file naming systems, meetings summaries, and planning.
  • Checking and monitoring the progress and setting forth the next steps.

Transfer To Production

The development stage should give us confidence that the product has attained its objectives, but it is still mostly based on what we see on our monitors as CAD files, tables and presentations, and tests using machined or 3D printed models and prototypes. Yet we introduce the products to market, promote business contracts, get funding, and take commitments.

Now we start thinking of how and where we transform this promise into a product. The risk is that we could find ourselves facing an expensive product, high investments in molds, a limited list of qualified suppliers, and longer deliveries.

The approach of letting the designers have free hand is not straightforward anymore. The tendency is to apply stricter and well-defined limits with respect to part cost and the supply strategy. This could slow down development a bit and even increase development costs, but the notion that parts design will define mold and product cost is important and should be balanced only by innovation and time to market.

Here are some actions you can incorporate at this stage:

  • Meticulously control and manage product BOM. Visualize the scale of the expected plastic parts production by having the information arranged for each part: part name, part number, quantity in the assembly, material definition (material grade), color, secondary operations (e.g., insert stacking, painting, printing, labeling), and projected supply quantities. A well-kept and updated Excel table could do wonders.
  • Set up a strategy based on values, ambitions, and ability. For example, do you wish to produce the product or are you looking at an exit strategy, do you produce and assemble in-house or use an external vendor, where on the globe will you produce, etc.
  • Refine your material list. Check possible suppliers based on your strategy to ensure that chosen grades’ availability, delivery time, and minimum order quantity (MOQ) meet your plans.
  • Identify the parts that should undergo flow analysis in order to predict deformation after injection and integrate the results back to part design, gate design, and location definition and production data that could be very helpful in injection machine and mold specifications as well as valuable information that can help predict part performance and cost.
  • Start working on parts drawings. You can define them as “for inquiry/quotation/development use only,” but since the drawing eventually will be the basis of your contract with the manufacturing body, it should have time to be developed as well. There is no place for procrastination with the drawings.
  • Set rules, known to all, about data control since you will start outgoing data transfer. Use generic 3D formats and PDFs only. Make sure your data defines your identity and its purpose. The level and quality of the data you release will set the “first impression” that will define your relationship with the “outside world.”
  • Assemble a professional team (two or three mold and injection experts) that will define, review, and advise on all topics related to molds, injection, and the designated supply chain.

Readiness For Molds

Producing injected plastic parts is unique in the sense that they are based on molds (tooling) and in some cases on secondary operations, both often executed by subcontractors. In practice, choosing the supplier will have significant impact on the part’s quality, cost, and delivery.

I cannot convey strongly enough the importance of choosing the RIGHT supplier. It should not be necessary to explain the extent to which this decision could influence all aspects of product success. A future article will be dedicated to choosing a supplier.

But with respect to product development, here are some points to consider:

  • Fine-tuning the design in parallel to the mold approval phase (T1 to Tf) is becoming more common as time to market shortens. In practice, it means we could predesign our “mistakes” and prepare the mold accordingly with steel safe or changeable inserts, get samples, check their performance and measurements, and make the needed tweaks to reach the final design. This is a valuable tool for the injected part designer and if it is available, design should exploit it.
  • Mold makers have CAD tools that can analyze the part from a mold and injection perspective. Having these tools available will give the designer more confidence in making decisions and maintaining the design within manufacturability boundaries.
  • Start preparing your mold’s scope. Based on your strategy, different tactics for arranging the molds could be set. This phase is worth a lot of money, since a bird’s-eye perspective will enable building an efficient mold arrangement. Sometimes, changing a material or color of a component can save a mold and a part design change can reduce mold size – all of these parameters affect the investment as well as part cost.
  • Keep your hands on the mold’s specifications and scope. Prepare mold specifications and a request for quotation (RFQ) that detail what you would like to have and, more important, how you would like to have it. This will also serve as a common base for all quotations, which will enable you to establish a correct benchmark to make your choice of supplier.
  • Build a basis of trust with your suppliers, but if you feel you do not speak the same language, use mold mold/injection experts and specialists to bridge the gaps.

There is no single way to do it right. Business culture, financial availability, geography, and timing will define many of our decisions. However, the questions we don’t ask are the ones to worry about. By achieving the right balance between design and execution early in the process, we can significantly minimize the need to deal with those questions after the device has reached a functional probability, has been certified by the regulators, and is promised to a client with a certain design, specifications, cost, and date.

About The Author:

ZachiZachi Fizik specializes in all aspects of plastics engineering with particular expertise in injection molding tooling and supply chain strategy. He has over three decades of experience supporting both startups and well-known brands in the medical, military, telecom, and consumer industries throughout the entire plastics life cycle, from the early design phase through the engineering phases and into mass production. He holds a BSc. in mechanical engineering from the Technion Israel Institute of Technology. Recently he served as consultant to several promising innovative Israeli medical start-ups whose novel devices reached regulatory approvals. You can reach him at and connect with him on LinkedIn.