In the medical device industry, plastic components are used in joint replacements, implant trials, interbody cages and instruments. The machining and molding of medical grade polymers can pose different challenges than the manufacturing of metal, particularly with the quality and cosmetic requirements of products that will be used in the human body.When machining polymers, one main challenge is implementing proper part holding techniques. The part holding fixtures are made of metal, which is harder than the plastic they are holding, and can create surface imperfections if fixtures are not made exactly right and maintained with a very smooth finish.
Another challenge is to find the proper chip load for each cutting tool based on finish requirements. Each chip load is contingent on the geometry, feeds and speeds of each cutting tool.
To minimize time and cost, there are some important factors for OEMs to keep in mind when designing plastic components such as:
- Raw material specifications: Customer designed raw material specifications can create very low production quantity needs for specific sizes and colors, which can force a minimum lot buy and/or cause a significant increase in cost to manufacture the raw material
- Surface finish requirements: Surface finishes of machined product must be created while cutting each feature. Finishes of molded product is closely related to the finish of each feature of the mold tool. The typical surface finish of articulating feature of machined product is 32Ra. While finishes less than 10Ra can be achieved on molded product.
- Tolerances: We can, and do, hold very tight tolerances on parts. Our goal is to develop production and measurement processes to meet or exceed a 1.33 Cpk value. This reduces the need to perform 100% dimensional inspection of product features and reduces the cost of manufacturing the product. Where tolerance requirements are so tight this cannot be done, increased inspection requirements must be agreed upon to ensure 100% quality.
- Measurement: Though we can make almost anything that can be designed, the design must consider how the feature will be measured and if that feature is important enough to drive up time and cost
With any medical device project, it is beneficial for OEMs to involve the contract manufacturer early in the design transfer process. This allows the engineers to talk about different ways to achieve certain part features without inducing unnecessary time and cost in manufacturing and to ensure design for manufacturability (DFM).
To improve the development process for injection molding, we are using a 3D printer to produce temporary plastic molds. This allows customers in the development stage to iterate their design while still receiving molded parts. The quick lead times (only a few weeks) and low cost (only a couple thousand dollars) of these tools makes for a new approach to part development through molding – where molded parts have significantly different mechanical properties that machined ones.
Partnering with an experienced contract manufacturer that will help guide you through the right questions during the design transfer process in order to reduce cost and increase time-to-market is key.
Orchid has been machining and molding plastics for five decades and we understand the intricate interplay between part holding pressure, spindle speeds, feed rates and chip load. We know how to combine the required unique part holding techniques to be aggressive in our machining approach (to reduce time and cost), while controlling both the surface finish where the cutting tools are removing plastic as well as the surfaces where the part is being held in the unique fixtures.
We believe that one thing that sets us apart is our team. People throughout the facility can be seen every day helping out in other areas of the business. This allows Orchid to be extremely agile and customer focused, while enhancing teamwork and a family feel. We always encourage people to come visit us. When you meet the people at Orchid and see the capabilities we possess, you will understand why it is an enviable environment in which to do business.
For your next medical device plastic project it is important to address these challenges at the beginning of the project whether it is machining or molding considerations, design requirements or selecting a proper manufacturing partner. These challenges have the potential to cause serious delays with your project so it is critical to address these early on.
By Patrick Davidson, General Manager, Orchid Chelsea and Orchid Memphis
Mr. Davidson joined Orchid in February 2012 as General Manager of Orchid Chelsea. He is a leadership and continuous improvement expert with more than 15 years of experience in industry. He has been an educator, full-time Continuous Improvement consultant, Value Stream Manager, Lean Six Sigma Engineer, Materials Manager, Operations Manager, Assistant General Manager and now a General Manager. He has worked in the automotive, education, healthcare, aerospace and orthopedic industries. He is also a professor at Villanova University in their Lean Six Sigma online programs. He holds a Bachelor of Science degree from Xavier University in Mathematics and a Master of Arts degree in Educational Leadership from Eastern Michigan University.
Post Author: Erin Berard