Wednesday, November 3, 2010

Iterative Design - As Easy As 1, 2, 3D Print

This week’s guest post is by Leo Kiefer, Z Corporation Mechanical Engineer

I found a good definition on the other day:

Iterative design is a design methodology based on a cyclic process of prototyping, testing, analyzing, and refining a product or process.

This could not have described my recent design exercise better.

In an effort to minimize the number of molded parts on a particular 3D printer, I was tasked with the redesign of one of the service stations used in this printer. During the printing process, powder and binder gradually build up on the face of the print head. The role of this particular station is to keep print heads clean by periodically “servicing” or removing the build-up. It is a simple, yet important, process that requires the print head assembly to push down on a spring-loaded cam, set the correct height, and then slide along the cam to perform the proper cleaning procedure.

I was able to consolidate the design into a single injection molded part. I wanted to print a prototype to ensure the design was correct before investing in a molding tool. Due to some design limitations for molding, I was not able to achieve a tight interface between this base part and my cam part. This caused the parts to bind, and not return to their original position in certain scenarios.

Figure 1 - Original model - Shown exhibiting the racking problem and without the rubber wiper.

After some testing and analyzing the cam action, I decided to change the interface to a 2-post and 2-collar design. Essentially the posts would act as guides for 2 collars on the cam part. Since I no longer had to deal with tooling shut-offs in the interface areas, I was able to minimize the draft angles and reduce the amount of clearance between the parts. I retained the single base part requirement, but had to add 2 plastic screws in exchange.

So I printed another model on our ZPrinter® 650. The new iteration did achieve a slight performance increase, but not enough. So, back to the drawing board. I decided to move the bosses further apart, assuming that wider is better, and quickly made yet another 3D printed model. This time I almost had it, but I wanted to make a small tweak in order to get it to be 100% perfect. The binding was completely eliminated in the back to forth direction, yet it still caused problems left to right. Instead of increasing the clearance between my boss and sleeve, I decided to make the holes slightly oval in the left to right direction. Another 3D printed model fresh from the printer proved to have all the requirements I was looking for.

Figure 2 – Cross-sectioned SolidWorks CAD model of final assembly

Admittedly CAD software is a good tool for getting parts to fit together, but when it comes to moving components, nothing beats a good physical prototype. The whole design process could have taken a single day if that was all I was working on, but I was able to cut considerable time off the design process by 3D printing models along the way, versus machining the prototypes. With the help of a ZPrinter, the Iterative Design process is a fast and extremely useful tool in any designer’s bag of tricks.

Figure 3 – Iterative Design summarized in one image

CAD Software: SolidWorks 2010
Printed On: ZPrinter® 650 using zp150 powder
Print Job: 432 layers, approx 2.5hrs


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