Eric U
Hot Rolled
- Joined
- Feb 26, 2003
- Location
- Eastern AL
Long story, sorry in advance...
I'm a 99% aluminum one-person shop, mostly making my own products. I've got a buddy who has a much larger shop and is swamped. He asked me if I'd be interested in making some overflow parts for him. They are a family of bushings, with very tight tolerances on the bore (+/- .0001"). Originally it was going to be a one-time 1800 piece order for him. I've already made over 3000, and am booked solid for then next few months. The part is very profitable for me, but frustrating as you'll see below.
Material is 4140HT. My machine is a Doosan Lynx 220 LYA. The part is .5" OD and the ID varies from .221" up to .375", with about 130 sku's total. Because of the number of sku's the bores are made by boring. I'm using a 5mm SCLCR carbide boring bar held in an ER16 collet. Stick-out is about .8". The inserts are Mitsubishi CCGT03S102L-F in VP15TF. I initially ran the same program and tooling as my buddy did.
Originally I'd get 60-80 good parts before I had to switch insert edges. Good part to me meant shiny bore (no profilometer here) and within +/- .00005". The problem is in between those good parts were about 15-25% scrap. Suddenly a bushing would have a rough bore and be undersize by .0005"-.001" or so. Next one would be good to go. The scrap rate usually went up the more parts there were on the insert edge. My inexperienced steel machining gut was telling me its probably BUE.
A Mitsubishi rep came by and suggested the same insert but with the MS6015 coating (supposed to be slicker). They left a worse finish and didn't last as long, with the same suspected BUE scrap issues. I went back to the original insert.
I was using Qualichem Xtreme Cut 250c, which works great in aluminum, and was passible in the very little steel work I did before. My Qualichem rep said that I probably needed chlorinated paraffins to help eliminate the BUE so he sent me a pail of 251c to try. It was the only pail available at the time, so after I filled the sump and my coalescer it was at about 8% concentration. He had suggested 7-10%. I ran the 250c at 10%+ concentration on my aluminum parts. Now my bore finish is worse. The bushing bores look like glass for the first 8-10 parts, but after that the bores have a more matte finish, and things start to go out of spec by about 40 bushings. The scrap rate for the bue/size issue has gone down (now 8-12%), but I'm getting even less parts per insert edge. I can't increase the coolant concentration until either some water evaporates off or I get more 251c. Two other pails of 251c will be here mid-month.
About 200 parts before the coolant swap I went from my buddy supplied material (Ryerson) to my own supplied material (Speedy Metals). I did get about the same finish (and issues) as before the coolant swap, near as I can remember, but I'm getting forgetful in my old age. I checked hardness on both the Ryerson material and the Speedy material and they are about the same, RC 25 or so. I know that's lower than what's expected for 4140HT, but that could be my hardness tester being uncalibrated. Could material selection cause my new finish issue?
Getting this boring bar aligned is a royal PITA. The reason I've got a .8" stickout when I only need to bore .450" deep is I'm trying to hold a parallel on the end of the tiny flat of the boring bar while tightening the collet nut...all while trying to keep things from rotating out of alignment. Not enough hands and not exactly precise. I found and tried a 5mm to 3/4" boring bar sleeve. That was worse. I'm not sure if there was some kind of chatter due to the slight amount of clearance there has to be between the bore of the sleeve and the shank of the boring bar? How critical is it for the insert tip to be on centerline? I've got a y-axis so I can fudge it up and down, but I didn't notice any change with +/- .005" or so. I'm boring .450" deep on a .375" deep part because I had some chip packing issues that would occasionally leave a step in the bore the last .050" or so. I try my best to get coolant shooting down the bore to keep the chips clear but it isn't perfect.
Generally I run these bushings with a feed rate of .003" roughing and .001" for the finish pass. I rough at .003" per side and finish at about .002" per side. Surface speed is about 330FPM. I've tried all kinds of variations of speeds/feeds/DOC, but nothing really seems to help. Remember this is a 5mm boring bar so I can't really push it much.
I'm running out of ideas. Is there anything glaringly wrong with what I've tried so far? What can I do to keep my surface finish good and lower my scrap rate?
Any help is appreciated!
I'm a 99% aluminum one-person shop, mostly making my own products. I've got a buddy who has a much larger shop and is swamped. He asked me if I'd be interested in making some overflow parts for him. They are a family of bushings, with very tight tolerances on the bore (+/- .0001"). Originally it was going to be a one-time 1800 piece order for him. I've already made over 3000, and am booked solid for then next few months. The part is very profitable for me, but frustrating as you'll see below.
Material is 4140HT. My machine is a Doosan Lynx 220 LYA. The part is .5" OD and the ID varies from .221" up to .375", with about 130 sku's total. Because of the number of sku's the bores are made by boring. I'm using a 5mm SCLCR carbide boring bar held in an ER16 collet. Stick-out is about .8". The inserts are Mitsubishi CCGT03S102L-F in VP15TF. I initially ran the same program and tooling as my buddy did.
Originally I'd get 60-80 good parts before I had to switch insert edges. Good part to me meant shiny bore (no profilometer here) and within +/- .00005". The problem is in between those good parts were about 15-25% scrap. Suddenly a bushing would have a rough bore and be undersize by .0005"-.001" or so. Next one would be good to go. The scrap rate usually went up the more parts there were on the insert edge. My inexperienced steel machining gut was telling me its probably BUE.
A Mitsubishi rep came by and suggested the same insert but with the MS6015 coating (supposed to be slicker). They left a worse finish and didn't last as long, with the same suspected BUE scrap issues. I went back to the original insert.
I was using Qualichem Xtreme Cut 250c, which works great in aluminum, and was passible in the very little steel work I did before. My Qualichem rep said that I probably needed chlorinated paraffins to help eliminate the BUE so he sent me a pail of 251c to try. It was the only pail available at the time, so after I filled the sump and my coalescer it was at about 8% concentration. He had suggested 7-10%. I ran the 250c at 10%+ concentration on my aluminum parts. Now my bore finish is worse. The bushing bores look like glass for the first 8-10 parts, but after that the bores have a more matte finish, and things start to go out of spec by about 40 bushings. The scrap rate for the bue/size issue has gone down (now 8-12%), but I'm getting even less parts per insert edge. I can't increase the coolant concentration until either some water evaporates off or I get more 251c. Two other pails of 251c will be here mid-month.
About 200 parts before the coolant swap I went from my buddy supplied material (Ryerson) to my own supplied material (Speedy Metals). I did get about the same finish (and issues) as before the coolant swap, near as I can remember, but I'm getting forgetful in my old age. I checked hardness on both the Ryerson material and the Speedy material and they are about the same, RC 25 or so. I know that's lower than what's expected for 4140HT, but that could be my hardness tester being uncalibrated. Could material selection cause my new finish issue?
Getting this boring bar aligned is a royal PITA. The reason I've got a .8" stickout when I only need to bore .450" deep is I'm trying to hold a parallel on the end of the tiny flat of the boring bar while tightening the collet nut...all while trying to keep things from rotating out of alignment. Not enough hands and not exactly precise. I found and tried a 5mm to 3/4" boring bar sleeve. That was worse. I'm not sure if there was some kind of chatter due to the slight amount of clearance there has to be between the bore of the sleeve and the shank of the boring bar? How critical is it for the insert tip to be on centerline? I've got a y-axis so I can fudge it up and down, but I didn't notice any change with +/- .005" or so. I'm boring .450" deep on a .375" deep part because I had some chip packing issues that would occasionally leave a step in the bore the last .050" or so. I try my best to get coolant shooting down the bore to keep the chips clear but it isn't perfect.
Generally I run these bushings with a feed rate of .003" roughing and .001" for the finish pass. I rough at .003" per side and finish at about .002" per side. Surface speed is about 330FPM. I've tried all kinds of variations of speeds/feeds/DOC, but nothing really seems to help. Remember this is a 5mm boring bar so I can't really push it much.
I'm running out of ideas. Is there anything glaringly wrong with what I've tried so far? What can I do to keep my surface finish good and lower my scrap rate?
Any help is appreciated!