With today’s complicated medical regulations,  many clients do not have the expertise for optimizing the manufacturing processes. Recently, while joking with a customer, we found that one interpretation of our quality agreement can be likened to: “if we change the toilet paper brand, we need to put in a change request.” However, when there are changes that need to be completed in a timely manner—such as qualifying a new supplier to keep the supply chain moving—it can take up to two years to complete. It seems the medical manufacturing industry does not allow for easy changes.   

When setting up new processes, it is essential that the Technical Data Package (TDP), prints, and specs target both the function of the medical device/implant, as well as the manufacturing and inspection criteria. Triangle’s Product Realization Process allows for Design for Manufacturing (DFM) and Design for Inspection (DFI), which optimize the TDP for production. This process has proven to minimize change requests and production issues.   

DFM is the engineering art of designing products for ease of manufacture. There are multiple levels of DFM, but the one that affects our company the most is DFM for CNC machining.

DFI, a related discipline, involves engaging designers and quality engineers to ensure that the print portrays the proper callouts to help streamline inspection techniques with current advanced metrology equipment. With growing quality controls in the medical industry, inspection becomes a big challenge, especially when the print is not clearly defined.

Our Approach to DFM/DFI

The Problem

There are many ways to approach the DFM/DFI process. Medical device engineers put hundreds of hours into designing an assembly and are justifiably proud of their new product. Eventually, they share their hard work with a manufacturer for a quote. After the quote is accepted, placing a production order kicks off the DFM/DFI process.

When the manufacturer approaches the OEM with a DFM/DFI activity, the team must know its audience. After spending hundreds of hours on their design and TDP, most engineers think their work is just about done—or even 100% complete. But most of the time, that’s not the case. Design engineers piggyback off of what works in the industry. Most of the time, they use tolerancing that worked on a similar component. This enables them to leverage previous data, but it sometimes adds cost and/or lead time for production parts.  

Triangle’s Solution

Approaching a new client or design engineer is one of our greatest challenges. Everyone is different. At Triangle, we have found success with the following approach:

First, conduct a meeting to fully understand the assembly and function of the manufactured part or set of parts. If it’s an implant, we ask the engineers to review the risks of the implant. For example, an edge round may be a simple break-edge to the manufacturer, but for an implant, it may mean that tissue gets snagged on that sharp edge which can cause irritation to the patient.

Second, information from the first meeting allows the manufacturer to better understand the critical dimensions and start making a list of design details that may have to be held close. The manufacturing team also gets an idea of how to work with the design engineer. A positive sign is when the design team asks for feedback regarding the drawings.

The prints should be reviewed in light of using standard tooling, paying special attention to the following:

• Fillet radii should be large enough so a standard end mill or boring bar can be used to cut the part.

• Fillet radii should be large enough so a standard end mill or boring bar can be used to cut the part.

Design out costly manufacturing steps, such as die-sinking EDM, where you use a custom electrode to burn the shape into each part. Typically, you need to make or purchase the electrode, inspect it and then use the custom electrode to burn the feature in the part.

In parallel, the prints should be reviewed so that everything is dimensioned (not double-dimensioned), features are clear, and the Geometric Dimension and Tolerance (GD&T) is correct. All runouts should be in true position, if possible. With the understanding of the assembly, the manufacturer should request modifiers, such as Max Material Condition (MMC) and Least Material Condition (LMC), where appropriate. When used properly, these modifiers give the manufacturer more tolerance to make the part without changing the design intent.

A bolt-hole pattern demonstrates a useful example of MMC use. For instance, if you have a plate with six dowel pins pressed into it, and it is designated to mate with another plate with corresponding holes, a true-position callout with MMC would be helpful for the plate with holes. With larger holes, the manufacturer gets more true position tolerance and the assembly will still go together.  LMC and MMC are tools that are often overlooked but they provide great value to the manufacturer.

­For DFI, the manufacturer should gauge the print callouts to make shop floor inspection techniques quick and effective. The industry has moved toward Coordinate Measuring Machines (CMMs) for repeatability and automation. There are times when you need a Subject Matter Expert, or SME, to understand how to interpret how a hole should be measured, and mutually agreed upon by the customer. 

Here is an example of measuring a circle. The “form,” or roundness, is exaggerated for understanding this difference. Below is a .500” diameter that is out of round by .020”.

Typically, CMMs default to LSQ, but that may not agree with the design intent. In fact, most of our clients do not verify parts to the design intent. There are times when we need to pull in the designer for inspection techniques during inspection correlation exercises. 

For a hole that gets a pin placed in it, the “go-member” of the plug gauge would represent the inscribed diameter. 

For a shaft, the “go-member” may be a ring gauge, representing the circumscribed diameter.

Automation, such as CMM and vision systems, is great, but it’s costly and cannot be at every work center. GD&T callouts must be straightforward, and both parties should have the capability to capture this data correctly and consistently. From the above example, it is easy to get into a correlation issue with clients depending on how they analyze the feature.

Proven Methods

Unless you have a great working relationship with the design engineers, the manufacturer should not push the boundaries by going overboard with constructive criticism. An example would be redlining all features and wanting changes to everything, even when the print is not that good.

Instead, we like to organize design details into three categories for manufacturing and inspection. The designer should be able to identify each detail one of the following:

• Must-Have 

Something that needs to be changed that cannot be manufactured.

• Needs Clarification

A good example of a “clarification” is when a designer puts a datum on a centerline of multiple features, not one. This leaves the datum axis open for interpretation and needs clarification.

• Nice-to-Have

It’s possible, for example, to produce a 0.003-in.-max radius described on a print. However, there are benefits on tool wear, feeds, and speeds if the radius is increased to a 0.018-in. max.

Start with the “must-haves” for print updates. Afterward, and judging how well identifying the “must-haves” went, follow with clarifications. These need not be print updates. But follow up with an email summary to document the discussion. Identify the “nice-to-haves” design details only when things are going well. Most of the time, the “nice-to-haves” should be left off.

In one of our most successful DFM applications, we had sufficient time and got paid for experimenting with questionable drawing callouts. We experimented with a hard coat anodize thickness to get an exact deviation in both its size and color. Soon after, this project went into production with minimal issues.

Meetings that discuss and resolve these matters can make or break a project, sometimes even a customer. The customer can either appreciate the service, find it distracting to the project’s time constraints, or even interpret the effort as an insult. It is imperative to correctly judge customer reactions and act appropriately. If such discussions go negatively, the customer may want to end the business relationship. When they go positively, money will be saved for both the manufacturer and the designer.

The Payoff

A few benefits to a productive design and manufacturing discussion include cost reductions that come from:

• Reducing or eliminating expensive manufacturing techniques
• Reducing scrap because of optimized print callouts
• Streamlining inspection techniques
• Standardized tooling allows using off-the-shelf versus custom
• A manufacturable design and shorter lead times and minimal changes.

DFM/DFI meetings are excellent catalysts for getting projects started on the right foot and building your team. The key is to get involved as early as possible in the design stage. Having a collaborative relationship and positive line of communication with the customer always helps the process go smoother and leads to a lasting impact on the business.