How to Create a Contoured Fixture for a Medical Device. Step-by-Step.

Background info: For medical devices to be launched in the marketplace, they need to be approved by the FDA. That requires countless tests for characterization, functionality, and durability. To conduct these tests as accurately as possible, the medical device often must be fixtured so that its position and/or orientation is repeatable. One way of doing that is by making use of a contoured nested fixture.

Below is a step-by-step guide on how to create a contoured nest in your holding fixture to ensure maximum repeatability in the position and orientation of your next medical device, tool, or implement.

If you prefer video, we created one which covers the same content:

Download SolidWorks files HERE for free if you wish to follow along:

These are the SolidWorks features we will use:

1) Create Your assembly as a Part

You can only create your contoured medical device holder after finishing your medical device. Hence, you first need to model the medical device or get a file that can be used for the process. Your medical device file will probably be a complex assembly file with several components. We will use this device as an example:

2) Save Medical Device Assy as a Single Part File

To make the development of the holder easier, we will start with: Suppress all the bodies that will not affect the design of the fixture itself. What this usually means is that we only need to keep the bodies that make up the outside surfaces of the medical device.

Change “File Type” to Part, Change “Geometry to save” to All Components, and then click Save.

3) Find part file you created and open it

4) Let’s begin the process of fusing the parts.

Start by using Isolate to get largest body of the device by itself. In this case, we will isolate the white handle body.

5) With the handle body isolated, create a copy of external surfaces: Open offset surface command and select all external surfaces.

Tip: In many cases you can right-click and select tangency to get most surfaces.

6) Now that we have a copy of the external surface, hide the solid body.

You should only have the surface body visible now.

7) We can now manipulate the new surface body to make it airtight.

This will be the most laborious effort, but we have some great tips to save you significant time.

Tip: An easy way to identify open edges is to change their color in options. Select Tools->Options and follow the steps in the image below. It’s highly recommended you implement these settings before getting started in the process. We changed the color to fuchsia.

Utilize two main features to enclose the volume.

Option A: Delete hole

Delete hole is preferred when you have a hole in a single surface because it deletes the hole and automatically knits it together, all in one step.

Option B: Fill surfaces

Select Open Loop is huge time saver when doing this manual work.

Some open surfaces may not be so obvious to detect. Therefore, use the check feature to find any remaining open surfaces.

Knit all surfaces into one solid body.

8) While still in isolate view, “show” another body and then we will turn it into a surface body.

We’ll choose to hide the Trigger body in this example.

Summary: Right-click on trigger body -> Select Tangency -> Offset surfaces (zero value). You now have created a surface body, so hide the trigger solid body.

9) Let’s create a continuous airtight surface. We will use Trim Surface to remove the internal portion of the trigger.

Use Trim Surface to remove internal surfaces we don’t need.

Note: Take your time with the trim feature. Make sure to hover your mouse over every item to understand what the program is asking you so that you don’t get confused and struggle.

10) Repeat steps 7-8 for other bodies that are intersecting the main body want to make airtight.

We’ll do the tail cable body sticking out of the end of the device next. 

11) Extrude the block of material that will have the medical device’s contour in it.

First, use the medical device surfaces as references for where you want the block to start and end. We chose to create two planes to be these references. Create a rectangular sketch on the top plane and use the references to define the size. Make sure not to merge the bodies when you create this new solid. You will need two separate bodies to do the “indent” feature, which will be next.

12) Create the contour using Indent.

To prevent the part from getting stuck in the fixture, the contour needs a little extra clearance. We will use a .005” offset. 

 13) With the contoured nest completed, you can continue adding features to the fixture for your application.

ARTICLE SPONSORED BY: Pipeline Design & Engineering. We partner with medical device engineering teams who need turnkey equipment such as cycle test machines, custom test fixtures, or automation equipment but don’t have the bandwidth or resources internally to develop that equipment. You can find us on the web at www.testfixturedesign.com . Examples of our fixtures below: 

ABOUT THE AUTHOR: My name is Rafael Testai, I’m a mechanical designer at TestFixtureDesign.com

Thank you Mark Downey from GoEngineer for helping me troubleshoot obstacles.