By Omar Ahmed
The prototyping process is inherently tedious. Devices that made it to market likely went through dozens, perhaps even hundreds, of iterative builds and rebuilds. Luckily, that process is made exponentially easier through the use of computer aided design, or CAD. CAD software allows a user to make 2D and 3D models of anything, from rocket engines to bicycles to balloon dilation catheters, with extreme precision and accuracy. These electronic models can then be used as a blueprint for the creation of physical prototypes. In this article, we will discuss the basics of CAD and highlight a variety of tools that can help you create your novel medical device.
Computer-Aided Design (CAD)
CAD software provides anyone with the ability to model both simple and complex hardware devices and is an invaluable tool for those involved in biodesign. Whether you are attempting to design a novel device from scratch or implementing a minor structural change to an existing device, CAD software allows you to electronically construct and visualize your ideas. As an example, assume you are an interventional radiologist interested in designing a new balloon catheter. First, you are going to open up a CAD program. Below, we can see the interface for SketchUp, a free and simple CAD program you can use on your web browser. While each CAD program has a unique interface, most have the same general appearance.
Learning how to construct 3D models in CAD can be challenging, but there are dozens of free resources online that can help you become proficient. Once a prototype is completely designed on a CAD program, the file can easily be converted into a format suitable for 3D printing. For more information on this topic, check out our article on 3D printing. Additionally, there are open-source design concepts for many medical and non-medical devices that can be found online and imported into a CAD program for editing. For those looking to make minor tweaks to existing concepts, this technique can save a lot of time. In SketchUp, this tool is called the 3D warehouse. The following design was found by searching for “catheter” in the 3D warehouse. The file can be downloaded and used as a launch pad by anyone who is interested in modifying the standard design of an existing medical device.
Most CAD programs also allow a user to construct multiple components in the same workspace and model how each piece could/would interact with the others. For instance, if one were to design an interlocking catheter-sheath system, he or she could construct each component and modify the size and structure of each until they slide into place as desired. With CAD, the possibilities are only limited by your own imagination.
Choosing a CAD Software
Commonly used CAD software programs include: SOLIDWORKS, AutoCAD, FreeCAD, CATIA, Oneshape, SketchUp, Autodesk Fusion 360, Solid Edge, and many more. Some of these programs, such as SketchUp or FreeCad, offer free software, while others such as Autodesk Fusion 360 have special offers for students and instructors. We recommend contacting your IT department to inquire whether any specific CAD programs have a licensing deal with your institution.
SketchUp and FreeCAD are both relatively simple programs that are great for beginners. SOLIDWORKS, Autodesk Fusion 360, and other complex programs offer a much more versatile and expansive toolkit, but may be daunting for beginners. We recommend starting with a simpler software and transitioning into a more comprehensive program once you have mastered the basics.
Once you have chosen a CAD software, you should be able to find countless free resources on how to start using the program, its capabilities and limits, how to navigate its interface, and other helpful information. It is important to note that each CAD program functions slightly differently, so we will not go into detail on how to use any particular program.
Engineering Workshop Machines
As you make the transition from computer models to physical models, you may find yourself needing to manually create components for your device in an engineering workshop. Walking into a machine shop for the first time can be intimidating. Machine shops are the places where the physical construction of a device or prototype takes place. The term “machining” refers to the cutting and shaping of raw materials into a desired size and form. The machines found in these shops are designed to cut and manipulate metal, wood, plastic, ceramic, and various other composite materials. There are seven basic types of machines at a machinist’s disposal: turners, shapers, drillers, millers, grinders, power saws, and presses. Hundreds of additional specialized variations exist, but in this article, we are going to cover the seven machine types you will most likely encounter.
- Turning Machines – The most useful and commonly used tool in any engineering shop is the engine lathe, a type of turning machine. This machine utilizes a single-point cutting tool to shave excess metal off of an object that is being rotated at high speeds. This is an efficient and highly effective way to create an object with a specific shape. The major function of turning machines is to change the size, shape, or finish of a revolving work piece. A video demonstration of the engine lathe can be found below.
2. Shapers – The cutting tool on a shaping machine oscillates but only cuts on the forward motion. This results in a repetitive, evenly spaced cutting motion that follows a linear toolpath. This is most commonly used to put lines, grooves, ridges, or teeth on a flat surface of an object. An example is found below.
3. Drilling machines – Also called a drill press, drilling machines are heavy duty drills that cut holes or bore into objects using a rotating, customizable drill head.
4. Milling machines – To cut using a milling machine, a user feeds an object against a rotating cutting tool. This is a useful way to construct smooth flat surfaces or grooves, inclined surfaces, shoulder edges, and angles.
5. Grinding machines – Grinding machines are the most accurate of all the basic machine types. These machines use an abrasive belt or wheel to precisely shave away material, particularly metal, in order to form the desired shape. By changing the shape of the abrasive belt, a user can cut nearly any shape. A video example of a grinder is linked below.
6. Power Saws – Power saws are the most recognizable machine in the shop. A motorized, toothed blade cuts material at angles designated by the user. There are three basic types of power saws: power hacksaws, band saws, and circular saws. Band saws are best with irregular or curved lines while circular saws are better with straight lines, but generally cut smaller cross sections than band saws. Power hacksaws have great durability but have much lengthier cutting times.
7. Presses – Pressing machines are the most diverse category with widespread functional capabilities. Hydraulic or mechanical presses use force to shear, form, bend, forge, squeeze, or hammer material into a specific shape. Most shops will have some form of a hydraulic press, which uses immense force to compress material. A video demonstration of a hydraulic press can be found below.
All of the machines mentioned should be used with extreme caution and safety should be a top priority. Remember to always wear eye protection and closed toe shoes while operating heavy machinery. Many shops will prohibit the direct use of machinery without proper certification and safety training. Machine shop safety classes are usually offered by the Environmental Health and Safety department at academic institutions. We recommend contacting your local machine shop to learn about their specific safety protocols.
We hope you found this introductory article informative and that it was able to point you in the right direction. Detailed instructional videos on any of the machines mentioned can readily be found online, but we welcome you to contact the SIR Tools of Biodesign committee for any further questions.