Design for Manufacture in the Real World for SOLIDWORKS Users
Design for Manufacturability, or DFM, is an industry keyword. Add DFM to your resume and it usually brings your resume higher up on the pile to be selected for an interview. But what is DFM, and are there any tools in SOLIDWORKS that can help make it easier to implement?
There are some key principles to DFM:
- Reduce part count.
- Standardize or modularize parts.
- Design parts to be self-aligning/self-locating.
- Maximize part symmetry, if possible, or make parts obviously asymmetric.
Here we are presented with three different versions of the same design. Design 1 has the highest part count and design 3 has the lowest part count. Additionally, Design 3 has the easiest/fastest assembly method.
One way to reduce part count is to use captive fasteners.
SOLIDWORKS includes the entire catalog of PEM captive fasteners (both Imperial and metric) in the Toolbox library. If you have the toolbox installed, you have access to these parts to make it easy for you to incorporate them into your designs.
The Assembly Visualization tool (available on the Evaluate ribbon) allows you to quicky get a part count in your assembly, as well as see which parts are the heaviest.
This is a standard 4U chassis enclosure. I have designed several of these during my career. There are a lot of ways this design can be improved using DFM. One thing I have always done is meet with my preferred machine/sheet metal shop and get a list of their punch tools. That way I can design using the existing tools that are available. I normally design these using punch-outs for the different ports on the front and rear panels. Then, depending on what configuration has been ordered, the assembler punches out the desired ports. An adhesive label is then put on top of the panel which hides the unused ports. This meets DFM guidelines by:
- Reducing the part count.
- Standardizing the parts – the same front and rear panels can be used in several configurations.
- Using punch-outs, the panels are easy to use in assembly.
Because SOLIDWORKS allows you to customize your library features, you can create features for the various punch tools used by your vendors and add them to your SOLIDWORKS design library. This is especially helpful with forming tools, which create dimples or vents.
One company where I worked, the Operations Director insisted that any hardware used in a design be #6-32 size. By standardizing on a single fastener size, they only needed to keep tools for that size of fastener and it also made inventory control easier.
SOLIDWORKS comes with a free tool called DFMXpress that allows you to set rules for your designs to check that none of your designers has gone rogue and specified the wrong hardware or incorrect material for your parts.
To access the DFMXpress, you should see it listed under your Tools menu or on the Evaluate ribbon.
Once you have launched DFMXpress, select Settings.
Going back to my example of the company that decided to use one size of fastener on all their designs, you can set up a rule for standard hole sizes.
You can enable only those hole sizes that would work with a #6-32 fastener. Keep in mind that captive fasteners will use a larger hole size, so be sure to enable those hole sizes as well.
Once you have set up your rules, simply click Run.
Notice that it says my countersink holes have an issue.
If you look at the part, you can see that the countersink is located close to the edge. This could cause problems, especially if the holes become mis-aligned.
When designing parts to be self-aligning or self-locating, I had a senior engineer who provided me with some excellent guidelines. He told me that whenever you are securing two separate components, try to use only three fasteners. Make one fastener a keyway or slot as this will allow easier assembly. If you locate each fastener at 120-degree intervals around a circle, it will be easy to position the two parts.
This illustration is a simple example. Having a slot for one fastener provides some leeway for the assembly. This also ensures that you can only assemble the two parts in a specific way – meeting the alignment principle of DFM. The other two holes align with the standoffs. By using only three fasteners, I keep the part count down.
I was working as a sustaining engineer for a printer company back in the 90s and part of my job was finding ways to reduce the part count on the product design as well as improving the design for better economy. I eliminated one screw on a mounting sub-assembly using this method. Finance estimated that this one improvement saved the company almost a quarter of a million dollars that year. I got a nice bonus check at the end of the year, too.
When looking at symmetrical or asymmetrical parts, consider how they will be assembled. Many companies use robots to assemble their products and adding a keyway or some identifiable feature ensures that the robot doesn’t mis-assemble the parts. Or, using part symmetry can make the assembly “robot-proof.” Regardless, you need to consult and coordinate with any relevant team members to ensure that your design will work through the assembly process.
DFM doesn’t have to be scary or intimidating, especially if you are a SOLIDWORKS user. SOLIDWORKS comes with several helpful features to support Design for Manufacturability, including the Design Library, the Toolbox, DFMXpress and Assembly Visualization. Take these features for a test spin and add DFM to the skills in your resume.
About the Author
Elise Moss has worked in Silicon Valley for the past thirty years as a designer and mechanical engineer. She is currently traveling the United States with her husband and their two horses, exploring backroads and historical trails. She is writing about her horse travels on her blog shakespeareantrails.substack.com. Her professional website is mossdesigns.com.