How to ensure repeatability with design for manufacturing.
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On the topic of design for manufacturability (DFM), a rarely discussed element is designing parts to ensure precision in manufacturing. So, how can you ensure your parts can be made to your requirements repeatedly? We often only consider accuracy and tolerance requirements when designing but repeatability is also critical.
In this article, Fictiv’s machining experts discuss precision machining and share some insights on saving time and money during machining projects. Read on to learn the top three tips to ensure you get precision parts every time.
Precision vs. Accuracy
As a quick refresher, let’s review the difference between precision and accuracy, which are often confused. Precision is repeatability; the ability to replicate consistent attributes across many produced units (for example, hitting the same dimension when machining 200 parts). Accuracy means how close to the targeted values something is; for example, how close the measurement is to the dimension.
What Does Precision Machining Mean?
“Precision machining” is a catchy marketing term used by many companies that may or may not be excellent at achieving precision. A machine shop should strive to achieve precision, but it requires more than just purchasing state-of-the-art machinery.
Christian Gilroy represents Fictiv on social media and has extensive experience operating CNC machines, leading computer aided manufacturing (CAM) programming and machining and has worked as a shop foreman. His goal in the machine shop was to “make the parts look like jewelry” — which meant not just meeting the specifications for the parts but also producing parts that looked, felt and appeared to be perfect.
Samson Olanrewaju, a Senior Technical Applications Engineer for CNC at Fictiv, has a degree in aerospace engineering and spent years working as an aerospace design engineer. For him, the true test of precision machining is the ability to achieve extremely tight tolerances when manufacturing highly complex parts. According to Olanrewaju, precision machining produces the highest consistency and accuracy by utilizing high-end technology, skilled craftsmanship and stringent quality control measures to exceed customer expectations.
Tip One: To Increase Precision, Go Back to Basics (GD&T/DFM)
Riley Hall, Fictiv’s Director of Product Marketing, has a mechanical engineering degree from the University of Michigan and has worked with engineers from various industries. A common issue he’s seen repeatedly in his years of experience is the practice of over-engineering.
To address the issue, Hall advises engineers to always be mindful of the design intent of their project, and the stage of product development they are in at the time. Using that lens, you can find opportunities to save money and make precision easier to achieve with simpler production methods or looser tolerances. Also, a solid foundational understanding of geometric dimensioning and tolerancing (GD&T) is critical to ensuring achievable precision targets.
Tip Two: Cross-functional Collaboration is a Must for Precision Parts
Design engineers are commonly seen as ‘divas’ with stringent and difficult-to-achieve expectations. Olanrewaju says that a foolproof way to avoid mistakes that cause precision issues is for designers, engineers and machinists to collaborate. Lines of communication must remain open for a design to be effective and manufacturable, and manufacturability is key to ensuring precision.
He says that an easy way to foster such collaboration is to hold regular meetings — designers and engineers should get together to discuss the design and ensure that it’s both functional and manufacturable with precision. They should also consider factors like tool access, material selection and machining processes during these discussions.
Collaborative design review meetings with designers, engineers and machinists are also helpful. That way, as the proposed design is evaluated for manufacturability, the machinists can provide feedback on tool selection, setup considerations and any potential machining challenges that could affect precision.
After a prototype of the component is manufactured, it’s used as a test case to validate the design’s precision and functionality. Since machinists play a crucial role in producing prototypes, maintaining open-loop communications lets them provide real-time feedback on any issues they encounter during machining. If precision issues do occur, the feedback loop makes it easy for designers, engineers and machinists to discuss and identify the root cause and then make necessary design changes and or process improvements.
Gilroy’s experience also taught him the importance of open communication between designers and machinists. He still recalls the stress from his time as a machinist that came from inexperienced engineers specifying impossible machining requirements.
He recalled a particular order where an engineer designed a part with a â…› in. radius all for all corners — but that engineer didn’t know that the material (a hard grade of titanium) was difficult to machine, and Gilroy’s shop broke multiple small diameter tools in the process. It turned out that the small radius wasn’t even necessary; better up-front communication could have prevented the issue entirely.
Tip Three: For Precision, Prioritize Requirements
Hall also mentioned something that might seem obvious but is often forgotten: keep your application in mind when designing precision machined parts. That means only applying precision requirements when they’re necessary for the part’s application.
This concept also resonates with Gilroy, who said that holding every single dimension to super-tight tolerances is unrealistic. Doing so can also cause a machinist to focus on less critical — but perhaps more difficult to machine — design features. For the best results, designers should prioritize requirements and only call out precision requirements where they matter. Doing so ensures your machinist will focus their efforts on the right features.
Ultimately, precision is an important design goal that ensures that your parts are repeatable. Precision mitigates assembly issues and helps to reduce safety concerns with the end-use of your parts.
Gilroy said it well: “Getting your parts precision-made is kind of like going to a fine dining restaurant. You pay for exceptional food, presentation, etcetera. Otherwise, you can go to McDonalds and save money. If you do things cheaply, it can end up poorly for your product, the same way fast food can cause indigestion in your stomach.”
To learn more about precision vs. accuracy and how to improve the precision of your parts, check out Precision Machined Parts: Fictiv’s Comprehensive Guide.
