DFMXpress is the smaller brother of the full blown version DFMPro by HCL Technologies, LTD and is included in each level of SOLIDWORKS. DFM stands for Design For Manufacturability. This is a tool we can use to improve our designs by ferreting out those difficult, impossible or expensive to manufacture features we add to our designs. DFMXpress also helps us conform not only to good manufacturing guidelines but also company standards for best machining practices.
I certainly could have used a tool like DFMXpress when I started my career as a design engineer at Xerox. During the prototype stages of the product design process we had parts made in the Model Shop. The Model Shop was manned by a dozen or so Journeymen who knew how to make parts. Every now and then one of the Model Makers would appear at my desk and ask me “son, how would you make this part?” When that happened you wanted to crawl under your desk because the next thing you heard was all the reasons why my beautifully design part couldn’t be made in the shop and some exotic expensive process like EDM had to be used to make it. I took those episodes as learning experiences because there’s nothing like learning from a highly experienced model maker on how to design and manufacture parts.
DFMXpress uses a set of rules we establish for the following types of machining:
1) Drill Rules for various types of holes.
Holes with flat bottoms
Hole entry and exit surfaces
Holes intersecting cavities
Linear and angular tolerances
Standard drill or punch size check
2) Mill Rules for general types of milling operations such as:
Deep pockets and slots
Sharp internal corners
Fillets on outside edges
3) Turn Rules
Minimum corner radii
4) Sheet Metal Rules
Hole diameter to thickness ratio
Hole to edge distance
i. For most materials the bend radius should be at least equal to the material thickness
5) Injection Molding Rules
Minimum and Maximum wall thickness
Let’s go through setting up rules in DFMXpress to check these parts:
This is the setup page for Mill/Drill processes. We’ll use the defaults for our example.
Here are the results. As you can see there are a number of problems with this part. 2 holes violate the hole depth to diameter ratio, there are internal sharp corners in the rectangular slot, a hole with flat bottom, fillets on the outside edge, deep pockets and so on. These violations drive up the cost of the part. Removing these violations the part can be made cheaper and faster.
The sheet metal part faired a bit better than the machined part. Most of the violations have to do with hole to edge and standard hole size violations.
As you can see DFMXpress is a handy tool to use to make sure your designs can be easily machined at the lowest cost possible.