Technical Tip: Increasing Waterjet Profitability

There exists several cutting techniques that can lead to an increase in the profitability of your waterjet.

The profit margin of the goods sold by a company can be a good indication of the efficiency of their production process. Higher profit margins equate to more money in the company's pocket at the end of the fiscal year. Two ways to increase profit margins include reducing production costs and increasing part output. 

Reducing physical production costs will lower the average part cost and add to your profit margin.

A significant portion of your part cost and profitability is related to your fixed costs. Increasing output allows you to spread the cost of your machine, overhead, and interest across more parts per day, lowering average part cost.

In this week's Technical Tip, we will discuss several waterjet cutting techniques that can trim production costs and grow total output, increasing the profitability of your waterjet.

Common Line Cutting

It is possible to reduce the total amount of cuts needed to complete a project by utilizing common line cutting. By overlapping the cut lines of two parts, the cutting stream cuts an edge on both parts at the same time. The common line cutting method can reduce overall cut time, decrease abrasive consumption, and maximize material usage. Utilizing this technique also minimizes wear on the waterjet’s on/off valve due to the reduction in the number of pierce points. Most waterjet software is capable of automating the common line cutting process, but this technique can also be programmed manually.

270" cut, 27 minutes, 27 parts, 1 part per minute.


810" cut, 81 minutes, 27 parts, .33 parts per minute.


552" cut, 55.2 minutes, 32 parts, .58 parts per minute.

In this example of common line cutting, the red lines represent the toolpath. In the left photo, assuming part sizes of 3” x 12” and a cut speed of 10 ipm, the yield is 27 parts with 27 overall cuts. In the right example, given the same part size and cut speed, the yield is 32 parts in 11 cuts - 3 vertical, 7 horizontal, and 1 perimeter. As you can see, using common line cutting resulted in an increase in part production while decreasing job time, material waste, and abrasive usage.

Note: There are several things to keep in mind when utilizing common line cutting. The first is to be sure that parts are large enough to span at least three grates or slats so that parts will not tip up or fall through the grates. Tipped up parts can result in broken nozzles, far outweighing the savings in material and time. Secondly, keep tolerances in mind. As a nozzle wears and the stream width widens, parts will become smaller. You cannot add additional tool offset to common line cuts, so tolerances for the parts should be taken into account.

Stacking

The benefits of stacking are going to be more evident on thinner material (less than 11 ga.). More of the energy of the waterjet stream goes straight into the tank on thinner materials. This can be seen when you compare actual speeds on thin materials versus the theoretical speeds shown in cut speed calculators. For example, for 0.050” thick steel, a cut speed calculator will estimate 175 ipm for an “average” edge quality. Realistically you probably can’t cut this material faster than around 100 ipm. Machine acceleration and part geometry could also limit your actual average inches per minute to something even lower than that. In this scenario, cutting three or four sheets of 0.050” could be more cost effective. Four x 0.050” is the equivalent of 0.2” thick material. 0.2” thick material with an “average” edge quality is around 20 inches per minute times four sheets at one time equates to 80 inches per minute.

One interesting application for stacking is companies that waterjet cut laminated shims. In this application, 25, 50 or 100 sheets of material .001 to .005” thick will be tightly clamped together and waterjet cut.

As you go thicker and the efficiency of the waterjet process increases, the benefits of stacking decrease. For example, 0.125” steel for an average edge quality is around 40 inches per minute. Three sheets of 0.125” stacked equals 0.375” thick. 0.375” for average edge quality is 9.4 inches per minutes. 9.4 x 3 = 28.2 inches per minutes. In this case you might be better off cutting one sheet of 1/8” thick at a time.

Note: Avoid stacking parts that require many pierce points. Frequent pierces can cause water and abrasive to accumulate between sheets, pushing them apart.

Nesting

Nesting maximizes material usage by strategically placing parts on the workpiece. This both minimizes the amount of scrap material left behind and maximizes the total number of parts per cut. Software is available that will automatically nest parts, but it is possible to manually nest as well.

270" cut, 27 minutes, 27 parts, 1 part per minute.


Un-nested parts


Nested Parts

In the example above, 21 parts can fit onto the sheet. After nesting, 30 parts can fit onto the sheet while the amount of scrap material is minimized. Below, both the nesting and common line cutting methods are used.


Nesting & Common Line Cutting

Cutting with Multiple Heads

If you have a machine with multiple heads and an appropriately sized pump, on thinner materials it can be more cost-effective to cut with two heads with a smaller nozzle orifice combination (one x 0.014/0.040 versus two x 0.010/0.030). This is related to the surface area of the waterjet stream that is doing the work versus the exponential increase in cross-sectional area of the stream that needs to be filled with abrasive. If we look at 1/8” thick steel again, where the 14/40 nozzle combination can cut it at 39 inches per minute, a 10-30 nozzle combination can cut it at 26 inches per minute. Two x 26 ipm = 52 inches per minute. As the graph below shows, the difference becomes less significant as thickness increases.


Cut Speed vs. Material Thickness

Running Multiple Jobs at Once

The great thing about waterjet cutting systems is that no change of tooling is needed when switching from one material to the next. The same abrasive nozzle can go from cutting drywall to titanium without ever stopping the cutting stream. Consider programming multiple jobs into one cut and utilize the space that you have. The cutting table can usually accommodate more than one workpiece; multiple smaller jobs can be completed in one go if there is ample space. If different cut speeds or abrasive feed rates are needed, ensure that the adjustments are programmed at the correct point in the cut.

When starting a job on your waterjet cutting system, always ask yourself if you are maximizing the efficiency of the machine. Sometimes all it takes is a simple adjustment of the toolpath or alignment of parts on the workpiece to make a huge difference in machine profitability.



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