Fabrication is the act of taking raw stock material and turning it into a part for use in an assembly process. There are many different types of fabrication processes. The most common are
Cutting. There are many ways to cut nowadays. The old standby is the saw. Others now include plasma torches, water jets, and lasers. There is a wide range of complexity and price, with some machines costing in the millions.
Folding. Some parts need to be bent. The most common method is a press brake (or brake press). It has a set of dies that pinches the metal to form a crease. This operation can only be performed in very specific cases due to the movement of the part and the possible shape of the dies. Designing for Lean manufacturing, though, can help prevent complex shapes that slow down production. Sometimes using two different types of fabrication processes or two different pieces fastened together work better than one complicated piece.
Machining. This is the process of removing metal from a piece of material. It might be done on a lathe, where the material rotates against a cutting tool, or in some other cutting machine where a rotating tool is moved in a variety of ways against a stationary piece. Drills fall into this latter category. The range of motion of the cutting head is defined by the number of axes (i.e. a 3-axis machine).
Punching. Punching is the act of a punch and a die forming a ‘scissor’ effect on a piece of metal to make a hole in it. Obviously, the punch and die must be the same shape and size of the desired hole. In some cases, the main piece of material is kept, as in when holes are added for fasteners. In other cases, the piece that is removed is the desired product-this is called ‘blanking’.
Shearing. Shearing is the process of making a long cut on a piece of metal. It is, in effect, just like the action of one of those paper cutters with the long chop-handle. This is done on sheet metal.
Stamping. Stamping is very similar to punching, except the material is not cut. The die is shaped to make a raised portion of material rather than penetrating.
Welding. Welding is the act of joining two pieces of metal together. A variety of types of welding exist for use in different applications and for the range of metals used in manufacturing.
But there is one area where Lean can struggle. Some extremely large machines are well matched to the products they are making. But far too many big machines with too long of a changeover time drive up inventory and promote overproduction. It is best to ‘right-size’ machines and put them into work cells if possible. That helps create flow.
The biggest impediment to making flow in a fabrication shop is the preponderance of large, multi-function machines that take a long time to change between parts. This drives up the lot size, creating inventory. It also means that a machine may be used to produce many different components for several product lines. Deciding where to put it is a challenge. If you include it in flow of one line, even the biggest line, it would be a problem for all the other lines.
The task in this case is first and foremost to reduce the changeover time so that the machine does not run large lots. At that point, you can keep reducing the amount of inventory that the machine creates. The second task is to get away from buying large, expensive machines when smaller, dedicated ones will suffice. In many cases, a small machine can be automated with jidoka and hanedashi to make their efficiency rival that of large CNC machines.
One challenge with linking fabrication and assembly processes tends to be the painting process. In many cases, parts leave the fabrication shop to go out for painting, or go right to an in-house paint center. In either case, the flow is disrupted, and the delays cause more inventory. Again, use the CI tools at your disposal to minimize this impact—reduce cure time, reduce the changeover, make smaller batches, go to smaller, dedicated paint booths. Do what you can to keep coming closer to flow.