Case study

Inspection Fixtures — Traditional Machining vs Additive Manufacturing



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In this post, we delve into inspection fixtures and the struggles many face when creating them using traditional methods.

Traditionally manufacturing inspection fixtures

Inspection is a routine component of the manufacturing process; as parts come off of the production line, some are examined to ensure accurate dimensions. This process requires specialized workholding. Two examples include CMM fixtures and check gauges.

A coordinate-measuring machine (CMM) is a precision tool that probes multiple points on a part to determine if the geometry is within specification. Check gauges are another form of inspection fixture used to quickly and accurately determine if parts are satisfying basic tolerances. If the part fits into the gauge, the part is within specification.

These fixtures need to satisfy stiffness and precision requirements, which traditionally would mean they would be custom-machined out of aluminum. However, the process is expensive and depletes valuable shop time. As the effort increases with the complexity of machined parts, it becomes even more cumbersome to manufacture inspection fixtures that must contain intricate geometries.

Check gauges that include complex surfaces like this one for a French horn part are difficult and time-consuming to machine

Why machining complex parts is hard

With 3-axis mills, complexity is already restricted by machine-specific limitations, such as the inability to perform undercuts. This renders certain geometries unproducible and forces you to constrain the complexity of your design to those restrictions.

After your part is designed for traditional manufacturing, it’s not ready to be fabricated quite yet. If a fixture is to be machined, it must be prepared in CAM beforehand. This process involves selecting which tools will be used to cut the stock and planning out the paths for each of those tools. Because more complex geometries often require a higher number of cutting operations, more intricate parts make for more work in CAM, and more skilled labor spent on fabricating the part. Alternatively, utilizing composite 3D printing to manufacture fixtures allows you to produce stiff, precise workholding while cutting out the expensive, time-consuming CAM process. Eiger, Markforged’s slicing software, takes care of all of the preparation; so all you have to do is design, then start the print. Higher geometric complexity can be printed with no extra effort, allowing for intricate, form-fitting fixtures to be produced at a lower cost.


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