Question
We have had our machine since February and have made great improvements. We cut out parts for sofa frames from a sheet of plywood. At first, to get the machine quickly in production with minimum knowledge, all we did was nest parts and cut them out. As you know from reading our posts, we are rookies in CNC and we had to overcome obstacles such as fires, tool slippage, loss of vacuum air and so on. Now we have conquered and overcome many of those obstacles and have learned how to nest using one line cuts and other techniques.
What tips can you give us from your experience with NBM (nested based manufacturing)? How do you save time, clean the dust off the spoilboard, place the skid of plywood, speed up production?
Right now we have two guys on. One operates the machine, the other helps out - brushes off the table, puts the parts away. The first guy sets up the programs, starts up the machine, then they both put on the sheet of plywood and wait. While one guy stands and waits, the other is putting parts away and the operator is trying to turn the very little waste from the last cut into something useful or cutting the waste up and disposing of it.
I know some of us do simple 2D plywood cutting and some of us do more advanced cutting and some are doing cabinet cutting, but in general, what are some techniques to speed things up?
Forum Responses
(CNC Forum)
From contributor D:
Typically, when nesting parts, we place the material to be cut to the right of the machine on a scissors lift. This allows a single operator to slide the sheet onto the machine. Also, in addition to the spoil board on the machine, we use a removable 1/4" spoil board. When the program is complete, the operator slides the spoil board along with all the cut parts onto a cart. He then blows what little dust is on the table off, places another 1/4" spoil board on the machine along with the next sheet to be cut and starts the cycle. While the next program is running, parts are sorted and the spoil board on the cart is cleaned for the next pattern. Note this is all done with a single operator.
As for programming parts and creating nests, this is all done in the office. Programs are sent to the machine on the network. This allows the operator to concentrate on running the programs and generating parts.
You say you want tips on speeding up production. What are you doing now? 10 sofas per shift, 30, 100? And how many do you want to be able to produce? Double? Or are you happy with the output and just want to make the operation more cost effective?
I can say this: two people per one router is one too many. I never run the router so a person is waiting. With what you are doing, one person could run two routers (once he/she knows what they're doing). Or better yet, have the operator assemble the sofa frames while waiting on the cycle to finish.
We use a Vac hoist to assist the operator loading of the sheet. Once the parts are cut, he unloads them manually. We use the router to cut in break points in the scrap (similar to crack lines in concrete) if a piece of scrap is longer than we want. A cut is made across it and the operator can easily snap it in two.
We have vacuum lift but switched to scissors lift because sliding material across the table was easier and faster. Also, vacuum lift may not be as effective in your operation involving plywood due to rough surface of material.
Another area of improvement is having the operator be productive while the machine is cutting. In my shop we process melamine and p lam. Recently we switched to 5x8 sheets because it gave us better yield and, more importantly, longer cycle time for the operator to complete the task of edgebanding parts from the previous sheet.
Contributor L, I would like to hear more about your conveyor setup. I'm in the process of moving to a new shop and contemplating installing a conveyor system between machines. I sure would like to see your layout.
I will probably load the skid on with a forklift, rest it in front of the machine, and every time I'm done with a nest, collect the pieces, salvage the scrap, clean off the MDF spoilboard, slide on the next plywood sheet, and keep going from there. I will probably have the skid resting at the end of the machine so I can slide it in from the side, because if it's in the front, it's going to cause us problems - we need that room for safety reasons and for bringing in supplies (lumber, forklift, etc.). What might be a reasonable setup?
This can be accomplished with a thin secondary spoilboard on top of the main one. When the machining cycle is completed, slide all of the parts off on the thin spoilboard to an unloading table or look at a sweeper unit.
These systems can range from sweeping the cut parts to a table to a fully automatic one which sweeps the parts off, vacuums the spoilboard and loads a new panel, with a total cycle time of under 30 seconds.
If you are labeling, there are systems available which allow for the uncut sheet to be accurately labeled before the parts are cut by use of an overhead laser. This eliminates the time for labeling.
Lastly, software is available which will actually nest parts inside cutouts. This will increase your yield and reduce the amount of waste.
Can you explain more on unloading and loading parts? What is a sweeper unit?
The sweeper unit can be a basic unit which mounts to the gantry arm. At the conclusion of the machining cycle, a M code is fired, the arm which extends across the Y axis on pneumatic cylinders comes down and the gantry moves in X to "sweep" the parts off. This system would run in the $10,000 usd range.
A more automated system can push the parts off the spoilboard in the Y axis, vacuum the spoilboard and load a new sheet in less than 30 seconds and all automatically. This unit would run in the $50-$60,000 usd range.
I thought that since you were cutting plywood frame parts, you had a CNC flat bed router. It sounds like you are talking about a point to point.
What is the purpose of a 9.5 mm hardboard with a 19mm LDF on top? If the LDF is 19mm and you want it thinner, just use a flycutter and machine it down to whatever thickness you want. It will take about 10 minutes.
We don't use a scissors lift, just a vac hoist because of similar problems like you mention. It's hard for one person to drag a sheet and locate it properly on the bed. With the hoist, it becomes very easy with no strain on the operator.
Let's back up to your original question about speeding up production. You really haven't said if it's just the router operation you want to speed up, or your total output through the facility.
If you are just looking at router output, there are 3 or 4 things that you have to look at.
1. Machine time.
a. Is every path optimized?
b. Are you using the fastest speeds with the proper tooling?
c. Are you doing extra work on the CNC that would be better done off the router? For example, the cutting of the scrap might be better for your operator to do on a small bandsaw next to the machine during the cycle time, as opposed to having the cuts done on the router.
d. Are the parts being cut appropriate for the router or should they be done on another machine? Again, if you are cutting rectangles, maybe you should just take a chunk of plywood off the bed and let the operators cut it up on a tablesaw.
I am not suggesting you do any of this, you just need to go through the analysis.
2. Load and unload time.
a. You need to study this operation, time it and see if there are ways to speed it up. Better team work, scissors lift, vac hoist, movable pallets, etc.
3. Changeover.
a. Again, time study the operation, and see what takes the longest. Are the tool lengths preset, is the program debugged and ready to run? Are your spoilboards cut and ready to go?
All these things should be done no matter what, but what you should be looking at is the overall impact of the CNC on the plant. If you are simply cutting parts and then sticking them in the warehouse for future pulling for assembly, you are really missing the competitive advantage of the CNC router.
I suggest you get a copy of the book, "Furniture Manufacturing in the New Millenium" (or something like that) published by Thermwood. Whether or not you use their machinery or agree with everything in the book, it is full of great information about looking at the factory as a whole and how the CNC fits in.
Can you guys explain more about the vacuum hoist?
Yes, I do have a flatbed router.
To answer all the other questions on speeding up production:
1. Machine time
It takes me under two minutes to cut out all the major parts that I need cut from my Rover 24. I run it at a feed rate of 30 and spindle speed of 15000.
a. Is every path optimized?
Yes, every path is. We use Mastercam v9.1. The nesting program is good but we usually just go in there and nest it manually. We always do one line cuts (2 parts share the same line, 1 cut only) and we barely have waste except for the surrounding 25 mm in the ply.
b. Are you using the fastest speeds with the proper tooling?
We did have a problem that has been well documented on this message board. The feed rate we use currently is 30 and speed is 15000, so I think that is fairly good.
c. Are you doing extra work on the CNC that would be better done off the router?
No, on a sofa frame we have a few long rectangular panels we put on the front. We cut those out on other machines, and the waste material is very little - we just break it off by hand and cut a 2" to 5 1/2" piece depending upon the waste, and that is material that we use on other pieces, so it works good for us.
d. Are the parts being cut appropriate for the router or should they be done on another machine?
I think the answer can be found above.
2. Load and unload time
That's where we have a major problem and I am asking for tips.
Again, we just got the machine and we are still trying out new tools and such here and there. We got a few good ones, our programs are good to go, and we got our spoilboard skid in the back 19mm thick.
At IWF2004 there were several solutions to handling at the CNC. There were machines that use the traveling gantry to push the load off. Komo had a separate machine displayed that pushed the load off, vacuumed the table and loaded another sheet, all in one motion, 40 second cycle time. They had a nice dust collection table that the load was pushed onto. There were several displays of ball roller tables, not automated but relatively cheap.
