Efficiency of nested-based manufacturing

      How much time can be saved? January 16, 2002

While I am not immediately looking at NBM, I am considering upgrading my machining centre to a flat bed machine and wondering if you need 5' capacity to make the nesting work efficiently. I use my CNC too much currently to consider dedicating more time to panel processing, but I hate to cut off any potential for future NBM. How long does it take to router out the average kitchen using NBM?

Forum Responses
We were using the cab to CAM link from Alphacam linked to Cabinetvision. The result was machining a 30 cab kitchen in about 8 hours. This seems like a long time, but remember all the holes are in the sides when it is finished and the panels are cut to size.

From contributor M:
Nesting is a bit more efficient in both material yield and time savings for obvious reasons. As for the time to route an average kitchen, count how many sheets of 5 x 8 material it will take to do your average kitchen. Multiply this number times 10 minutes and you will be close. 20 sheets x 10 minutes = 200 minutes or 3 hours and 20 minutes.

From the original questioner:
So does this mean that 5x8 is the material of choice? It takes considerably more machine to have that depth.

From contributor L:
The larger the table, the more efficient your NBM operation will be. If the average kitchen takes 800 square feet of material, as in the above example, using 4x8's you will nest 25 sheets; with 5x9's you will nest 18 sheets. With an average sheet change of 5 minutes, including spoilboard cleaning, the savings is 35 minutes per kitchen. At 3 kitchens/day that's over 1 1/2 hours. $60/hour for router time=$90/day plus the savings from better yield that the larger sheet will give you.

Check to see if ALL your tooling will reach full travel on the X and Y axes--this is important.

Contributor M, how is the nesting going, feed speeds, tool life, software? We have pushed our 1/2 melamine to 2000 inches/min. and the 5/8" and 3/4" to 1600 inches/min. Average bit life is 150-200 sheets.

From the original questioner:
How are you guys generally assembling your cabinets? Are you doweling or are you using the blind dado method? If you are doweling, are you doing the horizontal holes on another machine or putting the parts back on the CNC for a secondary operation?

From contributor M:
Everything is going well. Now that the dust has cleared, the facts surrounding nesting are a little bit clearer. With my router the limitation became the router rpm’s. Mine is an 18000 rpm 15 hp motor. Talk about a mismatch. I am sure there is some application where the bit needed to turn at 18000 rpm’s or less and at the same time would use the full 15hp, but I don’t know what it is.

After I figured out this limitation I did some tests to see what all the "bigger is better" was about when it came to routers and nesting. I took an average pattern of cabinet parts. It was a 5 x 8 of 3\4” melamine. The yield was around 87 percent. The pattern was made up of a good mix of drilling, grooving and cutting. It really was just a good average panel. I posted and cut it at what I found was the top speed I could run my 3\8” 2 flute Vortex bits. This speed is 925 inches per minute and I will cut 60 sheets between bit changes. The time to cut this pattern at 925 IPM was 6 minutes and 48 seconds.

I then re-posted this pattern at 1625 IPM. This time the pattern ran in 6 minutes and 36 seconds. This over 50 percent increase in feed speed achieved a whopping 12 seconds or 3 percent reduction in cycle time. If you get a chance run your router through the same test and see what your results are.

To the original questioner: In the nested machining process, I pre-drill several 1.5 mm pilot holes on all cabinet side panels for screws. We staple and screw our boxes together. No horizontal hole drilling is happening on my router.

The reason the 5' material works best in the cabinet business is due to the fairly standard sizes that used to produce a base end and bottom, a wall end and bottom and so forth. There is nothing really special about it--it just happens to work the best. As a further point, I have nested on all sizes from 4x8 up to 5x10 and once you get to the 5' dimension, the length effects the yield in only very small ways. My preference was 5'x10'. I used the 10' stock only to increase the cycle time and therefore allow us to run two nested machines facing each other with only one operator. Yes, he was busy, but when I offered a $2/hour raise to the best candidate, what do you think he said?

As to contributor M's experiment with feed rates, this is absolutely the truth. In nested, the idea that faster feedrates rule is simply ignorant. An average machine needs approximately 12" to ramp up to full feed speed and then obviously 12" to ramp back down in order to take the corner effectively. If one analyzes the average lineal inches in the cabinet parts they run, they find that their machine will only be at full speed less than 10% of the cutting cycle. This is evidenced by contributor M's results.

Also, when going faster than contributor M's results, you begin to lose the other major benefit of NBM and that is the "free labor" that you get with a longer internal cycle time (10-15 minutes). Much faster than 6 minutes and the operator will be too busy to edgeband, drill, sand or assemble.

From contributor L:
To the original questioner: We use a combination of 8mm plastic dowels plus 5mm wooden dowels for finished ends. We use confirmat screws for the unfinished ends. Horizontal boring is done on a separate machine. The router operator has time to horizontal bore while the router is running.

Contributor M, I ran those tests you suggested. My test feedrates were 975 IPM and 1950 IPM. We ran a complete job, which consisted of 3 different sizes of material, 18 sheets in all. The higher feed rate yielded a 15% decrease in time, or dropped the overall 69 min. in cycle time down to 59 min. At first glance, this does not seem significant, however, in an 8 hour shift, saving 10 min/hour adds up. We have also found, (after first sharpening) that the 2000 IPM feedrate has significantly extended tool life.

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