Winning with silent tools

[microcnc]

I was cleaning out pictures on my phone tonight and found a few old ones so I thought I'd share.

I'm an aerospace pattern maker and my main job is as a CNC programmer/operator. I have the privilege of working on many of our countries cutting edge missiles,jets, and rockets, both private and government. So it's a little frustrating not being able to show off my work, but obviously I don't want to give the other side any ideas and would be too much red tape to ask.

I would like to share my experience with tooling my shop purchased for a custom job. A couple years ago a client had a rush job to create five, 5 axis trim fixtures for some aircraft parts. There were five pieces that would make an entire fixture so twenty parts total.

Composite parts would be place on this fixture in a monster 5 axis mill and they would trim the excess from the part and cut location holes. My boss came to me and asked how long I thought it would take and if I could do it in less than two months. The parts were all a minimum of 145 to 155” long by 16 to 20” wide and heights were 15 to 35 inches tall.This is all off the top of my memory. The material was M1 mold aluminum and the weight of each part was between 4,000lbs to 12,500lbs. The finished parts all had to be 850 lbs. so the entire part had large pockets on both sides and cut through the center. Basically they were completely ribbed out similar to a casting with the largest wall thickness was 1” and smallest at 1/2” thick. So the largest parts I would be removing about 11,500lbs.

The challenge was that I needed to rough one part a day so I could put the parts on the vibration stress relieve machine so we could finish the top of the part in the shortened time frame of two months.

Our largest bridge mill is a SNK RB-150F 5 Axis machine 50 taper. We have Capto tooling ranging from 2” to 3” for our shop. My boss said any tooling I needed he'd order it. So off to the races...

The M1 mold aluminum is a cast tooling aluminum like MIC 6 Jig plate so two of the sides came milled parallel and the other sides were sawed. The parts were so large and thin walled I figure the fastest way and safest would be to machine it standing up so my Z was 35” X was 155” and Y was 16”.

I had to hold the part on knees on the mill so I could bring the head in from the side 90deg to the Y axis on both sides. I was not allowed to machine any hold down holes for clamps . So I took some scrap aluminum and made parallels 1 X 4 X 25 I would weld these on the bottom of the part centered with two holes through the parallels to attach to the knees. As one part was being machined I used a plywood jig to align the parallels to the next part and weld them on.

Before I could weld the parallels on I would lay each part down on the milled face of the M1, and turn the head 90deg to machine the bottom surface. I was working 10 to 12hrs a day 6 days a week. The first 1.5 days I spent laying the M1 down to mill the bottom square so all I had to do was weld the parallels on pick the part up and go.

Some of these parts looked like a triangle so half of part had to be milled completely away before I could mill the side pockets as the part would not support the weight on top otherwise. I started with a 6 flute 3” sandvik shell mill sticking out 12”. I had to cut all the excess material from the top and I had to reach it from both sides. To avoid leaving a thin wall I would cut a full cutter pass half way through the part and then repeat that on the other side. That way the thin material was only 3” thick cutting from the other side. I used this method all the way down till I was ready to cut the pockets.

The pockets I used and adaptive clearing program (mastercam) and kept it conservative at .25 DOC and %40 step over so 1.2” moving at 160IPM, I can't remember RPM. This seemed to be the sweet spot with the tool so I let it run. So in 10 hours I welded on parallels set up the part and machined the top and got ready for the pockets. I cleaned the machine out, it has two conveyers on each side and that filled up to hoppers. I don't like roughing at night but I didn't have a choice in our time frame so I let the pockets run on both sides. I hooked up a wifi web cam so I could watch the machine on my phone that night to check on the coolant level. Much nail biting time for bed and say a prayer.

The next morning... I still had my tool, my part, and the machine, but a hell of a lot of cleanup. Chips in the machine were two feet thick and well the hoppers... I knew I had to produce a larger chip but the tools I had were reaching their max so it's time to call sandvik.


The engineer there told me about their silent tool line. Our distributor came out and an application engineer. They brought a 3” silent tool shaft and shell mill. Now my cutter was 14.5” out so I was like how the heck will this be better for rigidity.

But I loaded it up and spent the next couple hours tuning the speeds and feeds. Now completely throw out any speed feed calc. 9,900RPM 400IPM 1/2” DOC and 2.25” step over.

Normally my wife is the only thing that gets me excited but HOLLY COW! Now I was able to rough the whole part in one 10 hour shift and run a finish pass over night in the pockets. The larger chip also produced half the amount of chips eliminating the volume it took up in the machine and hoppers.

Word to the wise when pushing this hard, doors closed, all safty gear on and finger on the stop button. This is what happens when you loose a insert, it's like a bullet clean through the enclosure.



In the end we spend 10k on tooling and made $175 shop rate. Just another day of fun.

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[1Jumper10]

Wow! That's pretty cool.

[microcnc]

Yeah it was one of those fun/scary jobs. I've been doing this for 18 years using conventional CNC tooling. It really was amazing to be able to push the machine to it's max. The spindle load on that 50 taper machine ran at %100, I had to pay attention to the way I programmed it making sure there were no tight shifts in direction or it would spike way into the red. I used dynamic roughing in mastercam adding large radius to the tool path and trochoidal motion to keep it from spiking. The nice thing was because the parts were so large it only started using trochoidal motion in the last two passes in the pockets to clean the corners. Everything used a helix ramp in the center and spiraled out. It was a fun learning to use the new technology in tooling.

Funny thing was that the machine was fully enclosed except where the head moves around in the Y axis. The ceiling over the machine is about 20 feet because we have a hoist over the machine to feed it. Chips were coming off that so fast and hard they would hit the ceiling and would rain down on me at the control. I had to get a large piece of cardboard to place over the control and the enclosure to keep from getting burnt.