Making a Replacement Cooling Impeller

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EricPeterson
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Making a Replacement Cooling Impeller

Post by EricPeterson » Wed May 04, 2016 7:42 pm

One of the pieces of equipment on our lines is a large ground lug welder that clamps things like battery lugs over heavy cables between great big electrodes and zaps them with very high currents to fuse the lugs to the cable. The welding heads -- the big conductive ceramic blocks that actually contact and clamp the lugs -- are water cooled.

Yesterday this machine went down because the cooling water pump overheated. The cooling water pump overheated because the cheap plastic centrifugal impeller used to provide air cooling to the motor started to slip on the motor's shaft, at which point the hub quickly melted and the fan jammed into its housing.

Here's the old plastic impeller:

Image

The pump is made in Germany. The chance of getting a replacement fan quickly was nil, and getting a new pump would require modifying the enclosure and mountings for a different motor frame.

After examining the motor shaft and impeller housing, this took about 45 minutes:

Image

The flat disk under the impeller is a geometry raft, an adhesion platform. For precision components I always use them, sized for only upper and lower solid layers, no partial fill, and placed under the actual component. The adhesion platform adheres to the build plate and covers up any bubbles, creases, or tears on the tape, and the part is built up entirely on support laid down on the adhesion platform. I get much improved first layers topological consistency this way, no spread, no flow, no warp. I increased blade count to move more air, reduce noise, and avoid harmonics with the supply power frequency. I swept the blades back to reduce noise and to improve discharge, and I twisted the blades because the housing provides for only axial discharge as opposed to radial discharge, so my new blade is part radial impeller, part axial fan.

M2 print settings were 85% infill -- any more than that and I find I get bad distortion -- with a very small support angle limit and a very small support granularity. I run the extruder at 240 and keep the plate at 100 the whole print. Support is twenty layers at 0 degrees followed by one layer at 90, 30%, .3 mm horizontal sep, no dense layers. I find using the twenty layers at 0 and one layer at 90 support gets me very dimensionally stable non-sagging, non-warping support -- but it's still as easy to pull out as if it were purely webs at 0 degrees.

Here's the new blade assembly on the pump motor six hours later:

Image

The pump shaft has splines intended to cut into the force-fit impeller hub, but they displace material rather than increasing the shaft diameter. I sized the bore nominal .010" smaller than the shaft diameter, which together with the standard over extrude at that diameter and density yields about a .015 total interference, so it was a nice tight fit going on with a block and mallet.

The failure occurred near an end of shift. The printer ran during plant shutdown. Installation took only a few minutes in the morning, so there was precious little actual downtime. The pump runs cooler now than it ever has, and is much quieter!

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Jules
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Re: Making a Replacement Cooling Impeller

Post by Jules » Wed May 04, 2016 8:55 pm

Now that's a success story! :D

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zemlin
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Re: Making a Replacement Cooling Impeller

Post by zemlin » Thu May 05, 2016 5:28 pm

Nice work

Bratag
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Re: Making a Replacement Cooling Impeller

Post by Bratag » Thu May 05, 2016 7:37 pm

Looks like you took the opportunity to improve greatly on the blade design compared to the original fan.

This is where I see a real strength for 3d printing. To get a replacement part could have taken days (I assume). You were able to solve a problem immediately and that's money.

I think too often people look to 3d printing expecting it to be a replacement for large scale manufacturing and thats obviously not viable. This is a great example of what it can be extremely useful for.

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pyronaught
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Re: Making a Replacement Cooling Impeller

Post by pyronaught » Thu May 12, 2016 3:51 am

Bratag wrote:Looks like you took the opportunity to improve greatly on the blade design compared to the original fan.

This is where I see a real strength for 3d printing. To get a replacement part could have taken days (I assume). You were able to solve a problem immediately and that's money.

I think too often people look to 3d printing expecting it to be a replacement for large scale manufacturing and thats obviously not viable. This is a great example of what it can be extremely useful for.

The media dopes who don't even understand 3D printing are always the ones who try and portray it as a mass production method that could "compete with China." Prototyping is the #1 application, with in-house custom jig making right behind it. Just those two things alone are extremely valuable. I was working with a team of areospace engineers recently on a large RC airship project and 3D printing was absolutely crucial in getting the job done. The high strength to weight ratio resulting from partial infills and the ability to make complex custom shapes quickly without getting a machine shop involved really cut down on development time and resulted in an awesome final product ( I'd post pictures of it on this forum but unfortunately I'm not allowed to ). If courses on 3D printing are not a mandatory staple in most college engineering programs then they should be, or they should at least be incorporated into the CAD courses.
Experience is what you get when you didn't get what you wanted.

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ednisley
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Re: Making a Replacement Cooling Impeller

Post by ednisley » Thu May 12, 2016 1:26 pm

pyronaught wrote:courses on 3D printing ... in most college engineering programs
Our EE-flavored Larval Engineer reports that the show-n-tell bag she brought to her co-op job interviews gave her immense credibility compared to her video-game-wizard compadres. Handing the interviewer a 3D printed object from one of her projects worked wonderfully well to convince him (it's always a him) that a girl in a hard-as-nails tech program knows what she's doing.

Teach your kids to think that way until the schools catch up! [grin]

(She also brought some knitted projects that clinched a gig at a toy manufacturer: "Great, you understand electronics and soft goods!")

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Jules
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Re: Making a Replacement Cooling Impeller

Post by Jules » Thu May 12, 2016 4:37 pm

ednisley wrote:
pyronaught wrote:courses on 3D printing ... in most college engineering programs
Our EE-flavored Larval Engineer reports that the show-n-tell bag she brought to her co-op job interviews gave her immense credibility compared to her video-game-wizard compadres. Handing the interviewer a 3D printed object from one of her projects worked wonderfully well to convince him (it's always a him) that a girl in a hard-as-nails tech program knows what she's doing.

Teach your kids to think that way until the schools catch up! [grin]

(She also brought some knitted projects that clinched a gig at a toy manufacturer: "Great, you understand electronics and soft goods!")

:D

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pyronaught
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Re: Making a Replacement Cooling Impeller

Post by pyronaught » Fri May 13, 2016 2:34 pm

Jules wrote:
ednisley wrote:
pyronaught wrote:courses on 3D printing ... in most college engineering programs
Our EE-flavored Larval Engineer reports that the show-n-tell bag she brought to her co-op job interviews gave her immense credibility compared to her video-game-wizard compadres. Handing the interviewer a 3D printed object from one of her projects worked wonderfully well to convince him (it's always a him) that a girl in a hard-as-nails tech program knows what she's doing.

Teach your kids to think that way until the schools catch up! [grin]

(She also brought some knitted projects that clinched a gig at a toy manufacturer: "Great, you understand electronics and soft goods!")

:D
Yep. Unless the guy who posted the cooling fan here is the owner of the company, you can bet he just increased his job security by being competent with 3D printing. On my airship project we had a number of college interns helping out and they all seemed to be familiar with 3D printing. There was one young guy who was hired on without a degree just because he was working at a Maker Space in Palo Alto and was familiar with all the 3D printing machines, laser cutters and other CNC tools they had there. When I toured some NASA offices there I noticed that 3D printers were almost standard equipment on every desk. My role in the project would have been much more limited than it was if I didn't have the 3D printing skills, or at best the items I made for them would have been inferior had they been fabricated by other means. It really makes you look like a pro to be able to deliver cleanly designed, solid parts with no compromises due to limited metal working tools or skills.
Experience is what you get when you didn't get what you wanted.

EricPeterson
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Re: Making a Replacement Cooling Impeller

Post by EricPeterson » Mon Jun 27, 2016 8:17 pm

I hadn't seen that this discussion went on after the first few responses. And thanks for the kind words, folks!

Bratag, yes, I improved the design considerably. The original straight-bladed soft plastic impeller was really only appropriate for radial discharge, whereas the fan housing only allowed for axial discharge near the outer rim of the impeller. That makes for extra noise and poor efficiency, and it's why I twisted and furled the blades. Furthermore, the stock impeller had a dozen blades in a neat, easy-to-design simplistic arrangement. Not a good idea when you've got 60 hz power. Anyone who's ever built rotating machinery understands that you avoid harmonic relationships -- easy multiples of feature counts and drive frequency -- whenever possible -- just to avoid the possibility of a harmonic noise or vibration issue.

Getting an original part from Germany would have taken weeks, not days. It simply wasn't an option. Using the printer reduced the repair to hours.

And as for your comment about the uses of the printer -- prototyping and custom fixture building -- that is exactly what we do. One printer sits in my office and is used primarily for prototyping. The other sits on the production floor with a flat panel. The cell leads pick what they need from the SD card menu when assembly a new set of tooling, and the printer makes them overnight, and in the morning he's ready to put together another cell.

pyronaught, we're in a business here that uses tons of little custom plastic tools and fixtures, many hundreds to thousands of little fixtures, all different and used in small quantities. Traditionally our competitors and/or tool suppliers used acetyl or laminate epoxy resin wood stock and NC mills to churn out tools. Using the printer is not as fast as the NC mills, but of course requires a tiny fraction of the capital investment -- and offers more flexible design options to boot. Only our largest global competitors - and we're smaller and regional -- have their own shops. Building our own tooling has given us a huge advantage over other smaller competing firms who don't have the engineering know-how to support their own tool building needs.

We were faced with a large traditional project early last year and were putting the tool requirements in the cost spreadsheets when the light bulb went off. A day of research later I had the M2 on order, and three days after it arrived we were building useful tools. Given that the entire printer cost what we would have sent the machine shops in a week to cut delrin, it was a no-brainer.

The two printers are now central and key to our tool building process.

Being able to churn out fast fixes and repairs to equipment is a bonus. It wasn't on the radar originally. This is not the first equipment fix, but it's the most interesting by far.

We have two interns this summer, both mechanical engineers. Neither had ever played with a 3D printer before, but both are CAD-literate, and I think both have The Knack. The first tools designed by the students are coming off the production floor printer later today. I have no doubts that closing that loop -- idea to design to tool to cell to production to improvements -- is going to be a huge, huge, huge benefit to the students and make them far more valuable than they already would have been.

- ep

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