Throughout our many years of working with waterjet machines we have learned quite a few tips and tricks that help us keep costs down to an absolute minimum. There are also so great efficiencies that come along with the nature of waterjet cutting that make it extremely economical to use – for example: nesting parts, stacking up material, narrow kerf width (nozzle cut width), streamlined programming software, minimal tooling, fixturing and set-up times during production, easily saved & recycled scrap / remnant material. All of these combined - along with superior customer service and our commitment to quality help add to the bottom line of cost savings through MILCO Waterjet.
Nesting parts for waterjet is a form of tightly organizing, rearranging or situating 2D (Two Dimensional) parts on a sheet of material in one single plane. In other words, this is a way of grouping and rotating the parts in any way so that they take up the least amount of space in relation to each other so that the most parts with a given quantity can fit onto the least amount of material. From the very start of receiving our customers 2D (2 Dimensional) CAD file, MILCO will determine with our customer the quantity or how many and of which pieces they would like to manufacture. We then take our highly trained machine programmers and organize the parts so that it reduces material consumption and waste to a minimum. Below is an illustration to better show what “nesting” means and how it can help you. Typically there are automated software programs that other waterjet companies use in order to accomplish this. This creates a very robotic and generic layout and will not have the custom and specialized “feel” that a highly trained CAD Programmer could accomplish. Optimal spacing between adjacent parts is solely determined upon the overall aspects and details of each particular job, typically a .100” gap is quite common, However, we have been known to use even less spacing based upon the aspects of the job.Go to Top of the Page
Another great cost saving technique is attained by taking multiple sheets and “stacking” them on top or “sandwiching” them on to one another. This process is somewhat unique to Waterjet and cannot easily be achieved with Laser cutting. The waterjet can then cut the stack-up as if it’s cutting a normal layout – However, the settings would be increased to match the actual material thickness which is the combined height of the assorted plates or sheets. This can lead to increased productivity from 50% through 500%+ depending on the actual material thickness and how many sheets are stacked. Eventually economies of scale diminish with a stack that has the overall or combined height of .500” (1/2”) or (13mm).
MILCO will help you determine your optimum level of stacking based upon your unique job, and which is best for your particular application. We accomplish this by configuring a tool path and length of contour / cutting and multiply it by a variable times the material thickness. One drawback to stacking up numerous sheets is that precision begins to decrease as material height increases. Therefore material height and precision are inversely related.
Your parts' geometry, specifications, and tolerances have a direct effect on the level or degree it can be stacked. For example if the part has small holes on the parts on the top of the stack will tend to be cleaner and more round then the parts on the bottom of the stack to a certain degree.Another example:
If your part has a lot of corners, then stacking the material will be less advantageous compared to a part that has few corners. This is because the waterjet needs to slow down for corners, and when you increase the stack thickness, it has to slow down extra for the corners.
There is also some extra time needed in setup when stacking materials, to make the parts will not float away or the plates shift when cutting. The extra time and effort needed for fixturing stacked materials can cut into the productivity gains. Stacking is mostly useful when working with extremely thin materials such as 0.040" (1 mm) sheet or when doing large production runs with thin material.
Stack cutting with a Flow waterjet can save you time and money if the application is right.
The best range of stacking is .400 to .600 inches. The higher the stack the slower the cutting. Stacking is best for thin material - say a .125 piece can be cut in 3 minutes but stacking 4 high .5 inches it will cut in 8 minutes taking the cut time down to 2 minutes per piece. If I stack 8 high it will now take 32 minutes to cut or 4 minutes per piece. The edge quality will still stay the same as if your cutting .500 inch or 2 inch since 20% speeds will change based on thickness. At higher speeds, 60 to 80 % the bottom pieces will be rougher then the top pieces.
Although, it is certainly possible to stack 2" or even more, the effect of worse edge finish and striations become more apparent as the stack gets thicker. The only remedy to this would be to slow down the machine to help ensure that the bottom pieces of the stack have an acceptable edge finish. As a result, the overall cycle time may increase to the point where it's not worth stacking in the first place.
As mentioned before, the most effective total stack thickness would be around 0.400 - 0.600 inches. Up to this thickness, there is still significant energy available in the cut stream as the jet exits the bottom of the material, maintaining a reasonable edge finish for the whole stack. Beyond this thickness, it takes exponentially more time to maintain a consistent edge finish.