Increasing Yield on Sheet Metal Remnants
Sheet metal remnants (a usable piece of material remaining after parts are cut from the sheet, often referred to as “drop”) are the bane of every programmer and shop’s existence. They are a pain to inventory, difficult to handle because of their odd shape, and a constant reminder that they need to be used or wasted.
This article offers some hope to the beleaguered programmer and operator. There are ways to avoid having remnants in the first place, and if all else fails there are tools to help quickly dispose of them with little effort.
Here we go.
How to Avoid Creating Sheet Metal Remnants
As we all know the best remnant is no remnant. In a perfect world all the parts would fill every sheet completely, and we wouldn’t have to deal with this challenge. A zero-remnant reality may not always be possible, but there are two strategies that help avoid creating remnants in the first place.
1. Using Filler Parts to Manage Sheet Yield and Reduce Remnants
Filler parts are parts with a less than urgent priority. They are parts that can be made now but are made from scrap or material that would be a remnant. There are three strategies commonly used to manage filler parts.
Filler Part Strategy #1 – Part Inventory
Creating part inventories from scrap or remnant material is the first strategy for filler parts.
Sometimes manufacturers carry part inventories of stock items to reduce setup costs or order response times. Alternatively, their production line may integrate a Kan-ban system, where part orders are cued when the part “card” indicates a need to replenish the stock.
In either approach, these parts are ideal filler parts. When a nest has unused material, extra space on the nest or material that would otherwise be a remnant can now be filled in with parts that will be used for inventory without preventing urgent parts being produced first.
Intelligent nesting software will report back to the order or scheduling system the number of parts created for each stock item. The scheduling system will then update the “quantity needed” before any additional parts are ordered to avoid overproduction.
Filler Part Strategy #2 – Higher & Lesser Grade Materials
Many manufacturers use multiple grades of material; some more costly than others. In the case of a manufacturer of industrial kitchen equipment, he may use brushed stainless steel for the exterior, visible surfaces of the cabinets and a plain finished stainless for the unseen back panels and interior parts. The brushed stainless is more expensive, but it has the same structural properties as the plain finish, so it is more than adequate as a replacement (filler) material for the plain finished stainless.
The second filler part strategy is to make good use of all of the higher grade material scrap whenever possible. To do this the manufacturer can use the scrap or remnants of the higher grade material to make parts that would otherwise be made of a lower grade stock by treating them as filler parts for the higher grade stock. In the case of the kitchen equipment manufacturer, he would make back panels and interior parts out of the brushed stainless – only when the material would otherwise be a remnant or scrapped – to prevent the expensive material from being wasted. At the end of the nesting process, the nesting software would know how many of the secondary filler parts were and were not nested. It would return the remaining quantity to their normal, not filler, order status on the plain material.
Expensive, high grade material destined for the scrap bin has been salvaged and made into usable product components. And expensive, high grade material remnants have been avoided.
Filler Part Strategy 3 – Future Orders
Consider a nesting environment where the engineer wishes to produce all of the parts due today only. In the case of batch nesting (creating a series of nests for multiple sheets of material from one set of part orders), as nests are built, the number of parts remaining gets smaller and smaller. Toward the end of this nesting process there will be fewer parts to nest and the nest efficiency will decrease; this is known as tail-off. It’s also where remnants are created.
To increase the material efficiency, the programmer can allow the nesting software to look ahead at tomorrow’s orders and treat them as filler parts. The nesting software will only include the filler orders in locations in the nest where material would otherwise be scrapped, such as a remnant. Today’s orders will be the priority and will be nested first, and tomorrow’s orders will fill in the scrap areas. This strategy blends the end of today’s production with the beginning of tomorrow’s production in a smooth and material efficient series of nests. And the opportunity for remnants is minimized.
2. Using JIT (Just-in-Time) Nesting to Avoid Remnants
JIT Nesting is all about creating nests just as the machine that will produce the parts is ready for them – just in time. The architecture behind this process is a never ending, always filling, real time order bucket reflecting the most current production demand. As new orders come in they fill the order bucket. As the machine (punch, laser, plasma, etc.) is ready to produce, the nesting software empties the bucket. Orders and products are coming in and out in a constant flow of production – meeting needs just-in-time.
How this helps minimize or avoid remnant production may not be self-evident. The secret is constantly keeping the orders coming in so that there is never a tail-off of orders, which usually creates a remnant.
JIT nesting in practice is similar to the Future Order Filler Part strategy when used with batch nesting. The difference is the “future orders” for JIT nesting are the orders needed for the very next nest. Whereas the “future orders” for batch nesting may be the 2nd shift production or tomorrow’s orders. The window for “future” with JIT nesting is a very tight single machine cycle.
Therefore, each nest will have the advantage of pulling from the greatest pool of orders to provide the optimal sheet material efficiency.
How to Optimize Sheet Metal Remnants
As mentioned earlier, it’s hard to imagine a zero-remnant world. So, in those cases where remnants are inevitable, here are two strategies to best manage them and make the most of this extra material.
3. Automatic Remnant Management
Advanced nesting software has the ability to automatically manage remnant creation, nesting, and use for the programmers and machine operators. The process starts when a sheet is identified by the software user as having sufficient material to create a remnant. The user can tell the nesting software to then generate an electronic remnant with a straight edge cut or a stepped-edge cut (see image above) to free it from the consumed, nested material. The software then creates a unique material ID for storage among the material available to nest on. When more parts are ordered the user or the software can “call down” the remnant by its ID, nest parts on it and send the finished nest to the machine operator as normal.
With this approach remnants aren’t lost in the system and risk damage or being scrapped.
4. Irregular Remnant Management
Not every remnant can be squared-off to a rectangular or stepped-rectangular shape. Sometimes there are irregular-shaped remnants that result from a very large, odd-shaped part being extracted. In these circumstances, automatic nesting software can treat the irregular shaped remnant in the same manner as a regular-shaped remnant by storing it, labeling it, and retrieving it when needed for use. For more on irregular-shaped remnant management, see this article.
In Conclusion…
There is no reason remnants should present the problem that they often do. There are sizable material efficiency gains to be had with effective remnant management and the application of dynamic nesting software.
How about you?
Are remnants an issue in your shop? How do you manage them? What’s working, and what isn’t? Do you have any creative solutions?
If you’d like to talk more about the remnant strategies discussed here, contact Optimation.
