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There are a lot of different aspects that play a part in the cost-efficient and timely production of parts profiled on a waterjet cutting machine.

While choosing a supplier that can offer you a competitive price is a plus, the best approach to ensure manufacturing costs are reduced and the final product is delivered within your budget and desired timescale is to get the design of your parts spot-on.

Being familiar with the most important waterjet machining features and following the specified drafting standards that permit cutting directly from the design’s CAD files will not only save production time, but also save you design time and help you avoid expensive design errors.

In this blog, we look at the most important aspects that you need to be aware of when it comes to drawing for waterjet cutting.

Technical features

Awareness of the technical features and the capabilities and limitations of waterjet technology is an essential part of being able to effectively determine firstly whether this is the right technique for your needs, and secondly how to utilise the technique for your needs while keeping costs down.

The most important things that you would need to know include:

Jet size

There are two different waterjet techniques, pure and abrasive waterjet cutting, and the latter is used for profiling hard materials such as metals, hard plastics and so on. The abrasive jet comprises a beam of water which is mixed with an abrasive, such as garnet. The garnet is actually what is doing the cutting in this technique.

The garnet is mixed with the water and exits from the equipment through a nozzle. The bigger the nozzle and garnet particles, the quicker you can cut. Most waterjets run nozzles between 1.2 and 0.9 mm, and a smaller size jet is usually used when cutting with two cutting heads at once. Single parts tend to be completed with the 1.2 mm diameter jet.

Holes

The smallest hole size available with the waterjet technique is dictated by the jet size. Holes are much more expensive than a straight-line cut, which is done on the fastest cutting speed. As the jet needs to first pierce the material and then cut the hole, it is highly unlikely that it will ever reach its fastest cutting speed. Instead, it runs at a reduced speed so that the bottom of the jet is in line with the top of the jet. However, cutting holes as part of the waterjet profiling operation will be much cheaper than drilling them manually after profiling, and the hole location will also be much more accurate.

Mesh / perforations

Profiles that require a high density of holes or cut-outs tend to be quite costly to manufacture. However, you can reduce the cost by having longer slots rather than circular holes, as this will be much easier to achieve.

Part separation / nesting

Usually you would need to leave 3.5 mm separation gap between the cut profiles. An experienced waterjet cutting company will nest your profiles into sheet layouts, while at same time maximising shield yield, ensuring the efficient use of material. Nesting has the potential to reduce material requirements by nearly 30%.

Sharp internal corners / narrow cut-outs

The waterjet cuts with a circular jet of water, therefore any internal corners can only be cut with a small radius in the corner as opposed to a perfectly straight-edged corner. A lot of the time this will not be noticeable.

Sheet size

Standard sheet sizes for metals tend to be as follows:

1 x 2 metres

1.25 x 2.5 metres

1.5 x 3 metres

2 x 4 metres

3 x 6 metres

If you need a profile that is longer than a standard sheet size, it may cost you significantly more, as use of the next largest sheet size will be required and most probably a lot of it would be wasted.

Allow 20 mm all around the edge of the sheet to enable its set up.

Drafting practices

The design of parts for waterjet cutting is usually prepared with a CAD program. Almost all abrasive waterjet systems accept CAD data, usually a 2-D .dxf file. However, if you’re drawing for a 3D waterjet cut, then 3D CAD files, such as .step files, .iges files and solid work files would be necessary. Carefully preparing an accurate CAD drawing will save time in setting the tool path and will help to prevent errors that cause scrap.

Follow these steps to ensure your designs are right the first time:

  • Produce accurate drawings and draw the part exactly to the desired size in the CAD system
  • Close the corners
  • Draw with lines and arcs
  • Set tolerances and dimensions carefully and only when necessary
  • Choose the right file format: most popular are 12 .dxf files for 2D cutting and .step files, .iges files and solid work files for 3D cutting. Avoid binary .dxf files

If you’re unsure whether waterjet cutting is the right method for you or simply want to find out more, download our free and comprehensive eBook ‘An engineer’s guide to waterjet cutting’.