When designing a new part, you have the liberty to add as much complexity as your heart desires. But when it comes to machining, a complex design could cost you more time and money than you have to spend—especially if you need production quantities.
It’s ideal to design your part for machinability from the beginning, so set yourself up for success with Ketchie’s Design for Manufacturing (DFM) tips to optimize precision machining.
DFM tip #1: Consolidate multiple parts into a single machined casting
Welding a single machined casting is challenging enough as it is, so naturally it’s even more challenging to weld multiple castings together. When a customer needed our help deciding between a three-piece welded casting or one solid cast unit, we helped them understand the pitfalls of multi-part casting and welding.
This option would have involved casting a multi-piece yoke support, welding the parts together, and then machining them. Although it’s possible to weld cast iron, welding multiple castings accurately is extremely difficult.
During the welding process, carbon migrates into the metal, which leads to brittleness and cracking. Introducing heat also causes the metal to warp. Welding can also result in internal voids and porosity, creating part weakness. We determined that after welding, our customer’s parts would have been so far out of spec that they would be unusable.
Casting the part in one piece would eliminate each of these issues. This option required a bigger upfront investment, but it meant only having to develop one fixture instead of several—and ensuring the quality of their parts. Ultimately, this solution saved the customer time and money on their project.
DFM tip #2: Reduce the number of machined features in a design
When designing for manufacturing, only add features that are necessary for the function of the part.
A locomotive builder wanted us to machine a basic cast part and then have it welded into place. The customer wasn’t sure which surfaces to cut, so we talked to them about functionality and installation to determine how the part was located. Based on that information, we determined that we needed to machine fewer surfaces than the original design indicated.
By limiting machined features, we helped the customer reduce costs and got the part into their hands faster.
DFM tip #3: Update designs to work within standard tooling capabilities
Custom tooling is expensive—and doesn’t always produce the desired results. Whenever possible, we recommend designing parts that can work within standard tooling capabilities.
One of our customers was developing a new iteration of a large casting. When they showed us their design, we could tell right away that it wasn’t machinable—but our customer didn’t fully understand why.
We explained that standard CNC milling tools wouldn’t be able to reach the features as designed. Even custom tooling wouldn’t necessarily solve the problem: the tool would have to be so long that it would never cut properly. When long tools don’t have enough support, they are unsteady and produce chatter, machining vibrations that leave visible waves on the part surface.
We shared with them a basic rule of thumb in metal cutting known as the 4:1 ratio, which refers to the length and diameter of a tool. If a tool is 1” in diameter, for instance, it must be no longer than 4” for it to be steady enough to cut properly.
With this new information, the customer took the design back to their engineering team and changed how the part needed to be cut. Using the updated design, we were able to turn the part on its side and enter from a different angle, allowing us to use shorter tools that wouldn’t produce chatter.
In each of these scenarios, communicating early in the design process was key to the success of the project. Our team is always ready to share our manufacturing knowledge to help save our customers time and money on machining. It’s just one of the ways we’re committed to your success.
Let’s work together to optimize your part for machining. Request a quote from Ketchie today!
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