By Zachi Fizik, ZF Consulting
Throughout this series, I have focused on plastic parts used in your medical device and the associated mold production process. I began with the fundamentals needed to define and design a plastic part, then suggested a methodology of transferring this design into production, and then I guided you, step by step, through the procedure of starting a mold production.
At this point of the process, we’ve released our designs to our vendor and molds build has started. The time we have now could vary from 3–4 weeks to 20 weeks or more, depending on the mold and part. During this time, there are two things we should do:
- Time control. It is quite common that the mold maker will send a bi-weekly report with detailed progress regarding the mold manufacturing. You may want to look only that the first trial, T1, is as promised, but you may also want to monitor the progress to predict delays. For that, you may need a professional who has a deep understanding of the steps of mold manufacturing.
- Regroup and start preparing for T1. We have the time to look back into our plans and check if we covered all bases, if we defined all we wanted to, and if we covered operation issues such as raw materials for the testing, as well as double checking that the mold maker has the latest part drawings, etc.
I’ll explain how I see the difference between T0 and T1.
The first stage before injection of the plastic that will form into parts is to see that the mold works. This is what I call T0. This is the first time the mold maker mounts the mold on the injection machine and sees that the moving elements move well, that the plastic melt flows well, that the cooling performs, and more. Just like every car manufacturer will have a “dry run” of the car before it is driven out of the assembly hanger, the mold maker should ensure this machine performs its basic functions before handing samples for examining.
If the mold performs well in T0, then this test can be called T1 because we have samples. However, T1 samples might not (or, in some predefined cases, should not) be within the final dimensions; the surface finish is not final; and we may have visual marks, flashes, and mismatches. That being said, the samples are a milestone with two main aspects: one is that the mold maker delivered a mold — a tool, a machine — that can produce the parts we had up until now only as a CAD file, 2D drawings, and models. The other is that the developer gets the queue to initiate the final stage of the product development, what we call the “T1 to T-final” (the well-known Tf) phase, which is the “money time” of our project.
To clarify, this stage is not a mold process validation (installation qualification, operational qualification, performance qualification). This is the stage in which we aim to achieve a verified, stable part that will qualify our definitions. Once we get that, we may initiate mold performance validation.
T1 samples are pre-matured for our keen quality control teams and the ones to handle them are the engineers and designers. Since injected plastic part quality and mechanical behavior depends on the material preparation and the injection parameters, I recommend that you answer the following questions prior to making any decision regarding the T1 samples:
- Has the mold maker (or injection company) confirmed that the defined material was used for these samples? This becomes extremely critical since these grades were chosen to meet certain certifications that in most cases need to be verified and validated. Some of these tests that take a long time, so having these samples verified to be from the correct grade will enable commencing these tests. Best if the confirmation is in form of an official curriculum of compliance (COC) but in any case, ensure you have the full grade name and the LOT number logged for this test and each one of the following tests.
- Has the drying procedure regarding the materials used to produce the samples been logged and documented by the vendor, and then reviewed by you? Most injected materials need drying, and some are more sensitive to that than others.
- Has the mold maker submitted an injection report that includes an injection machine data, short shot review and balance test results, injection parameters, mold steel temperature (measured on the steel) and part(s) weight? This report should be reviewed by a professional to verify the part has been injected properly.
- If the above conditions have been fulfilled, has the mold maker performed a first article inspection (FAI)? An FAI is basically a dimension report of all the dimensions and all the instruction that are in the drawing that was submitted at the mold approval stage.
Even though we are in the digital era, sometimes good old-fashioned clips and pictures of the workstation and injection machine, a mold injection cycle, part handling from the moment the mold opened and until it gets into packing, etc., are more illustrative than all the reports.
Also, remember that an injected plastic part could be an open book to professionals. Flow marks, weight, surface finish, gate appearance, deformations and flashes can all tell the story of the injected part. Include your vendor’s and your plastics expert’s reviews and recommendations in your gathered data. Some of these remarks may not influence part performance but could improve mold and part performance and reduce risk to mass production.
T1 samples usually look great when they are taken out of the delivery parcel, or if you view them near the injection machine, but the trouble starts emerging only after we dive into the details. We need to be sure that the samples are what we intended them to be. Here are some example scenarios:
- Your device is a closure that was defined to be from a polycarbonate (PC) and polybutylene terephthalate (PBT) polymer blend (PC/PBT) because of the high resistance this material has to disinfection materials used in hospitals. Imagine that wrong injection conditions have resulted in internal stress in the part and it consistently fails under the main bleach wet towels that are to be used by your client.
- The same closure operates in the operating room under neon lights and was defined to be UV-stabilized. You chose the proper grade, but another grade was used for the tests. This wastes valuable lab time and human resources trying to understand where your engineers went wrong.
- Your polyphenylsulfone (PPSU) disposable air connector fails autoclave tests after two rounds, but you were told that the chosen grade will last more than three rounds. Your specialist will find out that it happened because the material was not dried well, or mold temperature was not adequate.
- You have sent the samples you received to receive an urgent and costly biotest. The part fails. Do you have a way to figure out why?
- You are using a glass-reinforced polyamide, carefully calculated by your engineers, as a chassis in your hand-held device. The part fails the drop test. Before your engineers lose their confidence in their design, maybe you’ll discover that the material was not dried, mold temperature was not adequate, and the part did not reach maximum weight.
The extent of testing and analysis done on the T1 samples depends on sample quality, project complexity, and timetable. In either case, you should issue a report to the mold maker with instructions. I tend to classify these remarks as follows:
- Corrections are points issues in which the part does not follow the 2D/3D data. Our responsibility is to identify them to the mold maker and ensure we understand the cause and the way the correction is done.
- Calibrations are locations where a small tweak is needed to refine a dimension to meet the final demand. In some cases, these locations are predefined as steel safe deliberate mistakes in the parts that enable correction by removing steel (machining, eroding, grinding, etc.) rather than steel addition (welding). In other cases, they are results of fine-tuning part engineering based on functional and performance testing we conducted on the samples we get from the injection trials. The mold maker might institute limitations in certain cases. Understanding mold making restrictions, mold design, and plastic injection will minimize the number of tweaks and the improve the collaboration with the mold maker to achieve the demands with minimum tweaks.
- Modifications are requests to modify the part design from our original design. No matter what the reason is, modifications should take into account the fact that we have a mold and that might limit our options. Understanding mold engineering and injection molding when defining our modifications will make this less “painful.”
Once you send your T1 remarks to the mold maker, we will be able to set up T2. We hope that this will be the last test, but it might not be because the part has still not reached its final dimensions and performance. Even if we have T2 samples, we can approve, they will not have the final surface finish, which will only be added after dimensions and performance are confirmed. Beware of that and plan accordingly. Texturing or polishing followed by injection trial can take as long as a week. Only after these samples are approved can we declare we have reached the destination of Tf.
To sum up, a proper basic Tf and mold certification should include the following:
- The final test should be done in conditions that will simulate the mass production.
- The injection machine and the working environment should be verified.
- Injection conditions and a "working window" should be identified and documented.
- Material preparation, storage, and traceability should be checked and confirmed.
- The mold will be injected for a preset number of hours during which the parts’ quality will be controlled according to the define quality level and procedure.
- After the injection test, the mold will be disassembled and checked by a mold engineer.
- In case the production was successful in terms of parts quality and the mold passed its assembly check, the test is declared as Tf.
- The injected samples from the Tf can go to verification and validation (V&V) for final approval.
Especially in cases where we have more than a few molds and parts, each with its own demands, this phase of mold production has a high potential of causing serious and expansive delays to the project. If you designed and planned well, if you choose your vendor well, and if your data and expectations were clear, you will save time. However, there are also factors that are beyond your control. This phase is where you need a combination of experience and agility. Assign a trusted point person on your team to this phase, and do not hesitate on using several “navigation systems” consultants.
This article concludes a series of articles that encompass the path of an injected plastic part for your medical device from design to manufacturing. The path is based on the following principles:
- Plastic material is unique. Understanding the material and the injection process is vital for having a feasible, durable, quality part in an unbreeched budget and delivery time. If you do not want to get into the details, get professional support.
- Take material selection seriously because it is not only a cost issue. You can work on the edge of the material performance envelope, but do take the time to calculate the risks. Be sure you covered all bases when regarding regulatory certifications.
- Bear in mind that even though your part design looks great on your monitor, its printed model performs well, and the rendering presented by marketing looks realistic, the final test is the part’s behavior in the injection molding and its quality.
- Even though you know so much about your product, that does not mean your vendor does. The quality of the information, deliverables, and expectations are your responsibility, and you will be surprised how much this affects the success of your project.
- Be aware and respect your company’s culture, vision, and dreams, for they are the cornerstone of your success. Take that into account with your planning, commitments, deliverables, and choice of vendors, consultants, and supply chain. Define your level of involvement in the procedure based on a realistic ability of your organization to control the project at large.
There is no one way of doing things, but this one methodology will increase your chances to reach success.
About The Author:
Zachi Fizik specializes in all aspects of plastics engineering with particular expertise in injection molding tooling and supply chain strategy. He has more than three decades of experience supporting both startups and well-known brands in the medical, military, telecom, and consumer industries throughout the entire plastics lifecycle, 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 startups whose novel devices reached regulatory approvals. You can reach him at firstname.lastname@example.org and connect with him on LinkedIn.