Offcuts and scrap are inevitable in metal fabrication. Handled right, (which means with gloves,) they’re worth money. Handle them the wrong way and we’d be throwing money away, and who likes doing that? So for anyone interested in controlling manufacturing costs, here’s a little dumpster dive into the topic of scrap metal.
The Origins of Scrap
Bar, tube, and extrusion arrive on-site in long lengths, and sheet comes in, well, sheet form. Every job that hits our factory floor starts with cutting these materials to size and shape, and inevitably there are leftovers. Then, as the job moves through the shop, pieces are sacrificed for setup. This is especially common at bending and welding. Then, just occasionally, someone will make a mistake or a piece will get damaged and it has to be discarded.
This means we have a lot of scrap and offcuts in our shop. Technically, they’re two different things. Offcuts are pieces of bar, tube, or sheet leftover from one job that we might be able to use elsewhere. Scrap on the other hand refers to pieces that we’re not going to use anywhere else.
The pack rats among us would gladly save every offcut, but that’s not really practical. If we’re going to make use of them on another job we have to know exactly what each piece is, we have to store it somewhere, and we have to keep a record of where we put it. So only the larger, more valuable offcuts get saved. The rest go in the scrap bin.
Maximizing Utilization to Minimize Waste
The best way of managing scrap is not to make any. Yes, some of it has some value, (more on that in a moment,) but we only get back a few cents on the dollar for what we paid.
Maximizing material utilization is largely about planning each job, and even goes back to the design stage. We try to ensure bar, tube, and extrusion parts are dimensioned to leave the minimum over from the length of raw material.
When cutting sheet we try to nest pieces in a way that maximizes what we get from the sheet. (This is why we try to keep the kerf width — the thickness of the material that gets cut away — as thin as possible and keep distortion-inducing heat to a minimum.)
Inevitably though, material is left over. Turret punches, lasers, and waterjet cutters all leave lacy webs of sheet metal that the parts we needed were cut from. And these leftovers go in the scrap bin.
The Value of Scrap
Scrap metal isn’t worthless, most of the time anyway, and this is something we like to remind our people about. Scrap metal prices go up and down all the time but at the time of writing copper is worth around $3/lb and aluminum $0.40/lb. Steel and cast iron aren’t nearly so sought after and fetch around $220/ton. Actually getting these prices for our scrap metal does require us to take care of it though.
First, it must be separated by type. Copper in the copper bin, aluminum in the aluminum bin, and so on. If we don’t do that the scrap metal dealer has to sort it. That’s why mixed scrap metal is nearly worthless.
If you think about it, this should just be part of keeping the shop organized, just as we do with our fab shop 5S activities.
Second, the scrap should be clean and uncoated. Metal that’s painted or sheathed in insulation, like electrical cable, has little value because it needs preparation before it can be melted down. The same applies to chips from milling and turning, (which we do very little of.) If they’re wet with coolant and/or mixed, recycling is more trouble than it’s worth.
Scrap Metal Recycling
Recycling is of course a good thing to do. It avoids having to mine more metal ore and turn it into the materials we use, but it’s also good economics. Aluminum is the best example.
According to the Aluminum Association remelting needs one-tenth of the energy used to produce aluminum from bauxite. This is why there’s a market for recycled aluminum: because remelting is cheaper than processing the raw material. The figures are similar for remelting copper and the same applies to other metals, although to a lesser extent.
Scrap Handling Precautions
If we’ve motivated you to take a closer look at how you handle scrap metal, good. But do it carefully. Offcuts of metal can have wicked burrs that will gouge the hands of the unwary. Always wear sturdy gloves when moving scrap metal with your hands. In fact, that’s good advice for handling any metal that’s being worked on, so be careful!
Taking Care of Business
In the metal fabrication business, we’re always going to have scrap, no matter how hard we try to reduce it. At Wiley though, we try to minimize what it costs us, by collecting, sorting, and selling it for recycling. We’re not perfect, but we do see this as one more aspect of running an efficient shop. And if we’ve inspired you to do something similar, great!