How a 3D Printer Can Identify Its Own Mistakes (Part II)

November 10, 2015 | Author: Donald Godfrey

As I stated in the last blog posting, normally our blog posts have been a short explanation consisting of a few hundred words describing what Honeywell is doing in the area of additive manufacturing.  However, Honeywell is developing two system approaches on the topic of “Objective Evidence of Compliance to Design Intent” and will use two blog postings to describe this technology and the Honeywell effort.

As 3D printing technology moves closer to production application, the manufacturer must verify that the part meets the geometrical, metallurgical and mechanical property requirements identified by the design engineer.  Today in most industrial markets, inspection is completed after the part is produced. Mechanical technologies such as coordinate measuring machines (CMM), and X-Ray inspect for internal defects. CT Scanning looks deep beneath the surface of a part.  However, all of these technologies are subject to human error. 

This is why objective evidence of compliance to design intent is important.  Objective evidence is captured when no human is involved.  Therefore, an in-situ (in process) method of sensing and monitoring build parameters and part geometry is preferred.  Honeywell is working with Sigma Labs to develop two separate quality systems that will help make this possible.  Read or re-read the previous blog posting to understand the first system, how software slices a CAD file into multiple layers and how this technology is used to inspect each machine pass during the build. 

The above photo shows how part geometry can be digitally sliced into multiple layers by the build software.  Using the PrintRite3D® CONTOURTM software a JPEG of the build slice is compared to the CAD slice for geometric accuracy.

Now lets learn a second method for developing objective evidence of compliance to design intent.

SYSTEM 2: PrintRite3D® INSPECT TM

This software is being demonstrated as part of a DARPA funded effort in which Honeywell is the contract lead and Sigma Labs is a supplier to the program.  The technology behind this system utilizes pyrometers and photodiodes to monitor the temperature of the molten weld pool, where three process variables are recorded: 1) the “rate” the temperature increases when being melted; 2) how “long” the molten weld pool stays at maximum temperature; and 3) the “rate” the weld pool cools.  By capturing these three variables, the system generates an “electronic fingerprint or signature” of the weld pool and thus an “electronic signature” of the micro-structure of the part for each slice (layer) of the part in the X, Y and Z orientation.

The logic is based on the premise that when a good part is produced in the 3D printer, the PrintRite3D® INSPECT TM generates an electronic signature of each slice of the part. That signature becomes a slice by slice comparison to an already established baseline for what a quality part would look like when looking at the part from an electronic perspective.  It should be noted that this electronic signature is of little to no value unless it is correlated to mechanical and metallurgical property data.  This means the user must produce numerous test specimens to generate this property data AND correlate that property data back to the electronic signature data.  The goal of this software is to have an electronic signature (objective evidence of compliance) of the mechanical properties of the part by slice.

The above photo shows pyrometers installed in one of the Honeywell 3D Printing machines.

Summary:

The ability to generate objective evidence of compliance to design intent is possible with the correct technology and correct data gathering techniques.  This system is being developed via cooperation between two companies and will help Honeywell maintain its position as one of the global leaders in this area of research and application to insure the path to “Objective Evidence of Compliance to Design Intent” moves forward.

Donald Godfrey

Donald Godfrey

Donald Godfrey is an engineering fellow at Honeywell Aerospace.

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