Why Do CNC Parts End Up as Scrap? 5 Common Reasons Manufacturers Need to Explore

For many manufacturers, scrap is often accepted as an unfortunate part of the process. Sometimes a part is sacrificed to understand if the setup has been completed correctly, or an accepted rate of scrap is built into project deliverables. Sometimes, manufacturers are in despair and repeatedly scrapping parts with no understanding of how to rectify the problem.

In a sector that promotes smart, data-driven and automated processes, scrapping parts shouldn’t be accepted as part of the process. Let’s look at what manufacturers need to fix first. 

1. Parts are being setup... But Not Accurately

Many machine shops still rely on manual alignment methods, including shimming, clocking features and manually adjusting fixtures.

While these techniques provide an adequate way of setting up simple parts, they often fail to account for several different factors when setting up complex parts. Manual setup processes struggle to create an alignment in all six degrees of freedom, therefore are unable to give a true representation of a part’s position on the machine. These processes also don’t account for any distortion, deformation or inconsistencies in the part and how it differs from the nominal CAD. Failure to do this often results in machining errors.

Often manufacturers also don’t have a way to easily verify their setup, so until a part is machined, they have no way of knowing if the setup is correct or not, only finding out when it’s too late and a part has already been scrapped.

If manufacturers are dealing with parts that are prone to distortion or complex parts that require a time-consuming setup procedure taking multiple hours or shifts, it’s likely the setup process might be part of the problem.

How can manufacturers improve part setup accuracy? 

Solutions such as MSP’s NC-PartLocator automate the alignment of complex parts, removing any manual steps and the chance for errors to occur. Using 5-axis probing, the software measures the part and compensates for any misalignment errors such as the part’s position on the machine or if the part has changed compared to the CAD nominal. 

2. The CNC Machine Is Not Performing As Intended 

Many manufacturers assume that because a machine was accurate when it was installed, it remains accurate today. Unfortunately, machine performance can change over time due to wear and tear, crashes, environmental conditions or mechanical issues.

And if these changes are not highlighted and rectified before machining begins, the more likely it is that parts will be machined out of tolerance and need to be scrapped.

Instead of monitoring machine changes, the industry’s default approach is often to assume the machine has no issue until parts start failing final inspection, relying on annual services to keep the machine steady. And this is where manufacturers have a massive opportunity for improvement.

Alternatively, if manufacturers are already conducting machine performance checks, they need to be asking if these checks are independent of the machine tool vendor tests and if their checks look at every element of the machine (e.g. rotary and linear axis, the probing system).

How can manufacturers identify CNC machine performance before machining starts?

CNC metrology software such as MSP’s NC-Checker enables manufacturers to benchmark and monitor machine tool capability, pinpointing errors before they affect part quality. If errors lie in the machine’s kinematics, the software will automatically correct these immediately. For mechanical errors, NC-Checker’s reports can be used by maintenance teams or machine OEMs to shorten investigation time and get the machine up and running faster.