Design for Manufacturing: Concept to Reality
- Saturday, 01 December 2012
Design for Manufacturability (DFM) is a well-established practice, essential in realizing the transformation of new product concepts into mass-produced medical devices. And yet, all too often issues that could have been avoided are identified very late in the process and impact production costs and schedules. This suggests that key DFM principles are often underutilized in practice and not applied consistently, or to the degree necessary, to avoid these negative implications.
This article discusses three DFM-based best practices that help create conditions for success as manufacturing partners work with device designers towards a common goal. Engaging key stakeholders in an organized team from the very start of a project, conducting a thorough feasibility study, and implementing the proper quality tools will ensure that a device design is reliable, manufacturable, and acceptable to the physician or end user.
Integrated Product Development: One Team, Multiple Disciplines
The first and most important element of DFM is a truly integrated multi-disciplinary product and design development team. Good collaboration here can help ensure that elegant engineering solutions are practical to manufacture from a cost or materials standpoint, and suit the end user. An integrated team also helps reduce the risk of a “silo” approach and an overemphasis of any one element, while other design considerations are overlooked.
A senior staff engineer from one device manufacturer said the level and degree of the DFM teams vary, but may involve representatives from product management, quality and design engineering, regulatory, packaging, purchasing, calibration, prototyping, post-market, and others as required. He added, “We have a strict procedure in place based on the product and production line. The team must be approved at the project charter stage.”
All critical customer requirements must be clearly established during initial team meetings, as total project lifecycle costs and speed to market are often dictated early on in the process. A good interdisciplinary team considers important details such as performance characteristics, cost, timeline, clinical needs, and regulatory requirements. (See Figure 1)
“From the design phase, suppliers who are critical to the project’s success should be included in the discussions, and the sooner the better,” said a senior staff engineer. “We receive great input from our suppliers in their fields of expertise and having a good partnership with the supplier ensures the launch is successful.”
Consulting with key suppliers early can avoid costly rework later down the line. For example, Precipart recently prepared a feasibility study for a tight tolerance gear assembly that identified an opportunity for performance im provement of a medical imaging device by recommending bench assembly and light run-in to create the contact pattern on a helical gear. Improving gear backlash by approximately .002" would significantly improve the durability and performance of the device. (See Figure 2)
The Feasibility Study: Charting the Course for Success
A comprehensive feasibility study examines the key specifications throughout the life of a project and requires the team to thoroughly review and consider all potential design issues from the project’s beginning. A thorough feasibility study will provide information on a number of aspects crucial to the success of a product. Some aspects to consider include:
Materials Selection: This is crucial because biocompatibility issues often combine with metallurgical and process challenges to impact manufacturing techniques downstream. The need for biocom patible materials may require changes in manufacturing approaches. For example, titanium screws for a prosthesis, while biocompatible, are difficult to injection mold and may require machining that adds complexity and cost. Hip and knee replacements require both costly highgrade materials and complex post-machining processes such as coatings or polishing. Ceramics are biocompatible but may be more expensive in high volumes. The grade of ceramics can also make a difference, as in the recent case of a cardiac rhythm management device that had a high failure rate because cracks appeared during post-fabrication brazing. Substituting a higher, more heat-tolerant grade proved to be more cost-effective in the long run because of higher throughput.
A feasibility study should also consider the tolerance of materials for post-fabrication treatments, such as deburring and brazing. Materials, such as titanium, can cause laser markings on surgical instruments to smear or be rubbed off. Keeping them legible may require additional processes, such as coating or embossing. Choosing the right material can also reduce fabrication steps.
Manufacturing Processes: Alternative manufacturing processes are almost always available but the trade-offs need to be weighed between speed and cost. For example, multiple machining steps might be replaced by ceramic or metal injection molding for some components. Ma chined components can be used for initial design and the proof of concept phase, with injection molding substituted during production.
Application demands often determine the processes used. Injection molding may be the most economical way to produce gears in volume, but if the device requires high torque, machined gears may be required to maximize durability. Similarly, designs can be changed early in the process so that parts are produced by off-the-shelf tooling instead of using more costly specialized machinery or tools.
Finishing Processes: A component’s finish can have a substantial impact on durability, service life, and clinical performance. Poorly finished parts are a frequent cause of rejection and production delays. Some clinicians demand a pristine- looking reflective mirror finish, which may require specialized metals, surface treatments, polishing, or blasting. Other instruments need duller finishes to reduce glare during surgical procedures.
The need for easy sterilization is another design factor that often guides DFM teams in selecting materials and processes. Where instrument life and durability is an issue, the team may recommend electropolishing or the use of anodized metal. The look and feel of a device or instrument may make the difference in acceptance by end users.