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Paul Eastburn, sales director at Wightman Stewart, explains why he believes that waterjet cutting benefits all sectors.

The applications of the waterjet cutting process are also continuing to grow as more organisations get to understand the versatility of the process.

Waterjet cutting is employed within a variety of market sectors beyond engineering subcontract work.

Conventional materials such as stainless/mild steel and aluminium through to hard, high-end materials such as titanium, inconel and hastalloy can be cut with waterjet.

Practically any non-metallic material including acrylic, polycarbonate, rubber, plastic, MDF, plasterboard, foam, glass and polystyrene can be cut, along with composite materials and carbon fibres.

Waterjet cutting lends itself to materials used in aerospace where, as a rule, heat is not acceptable as part of the cutting process.

In these applications, it is frequently used on thick materials for roughing out profiles and the edge is then finished on a machining centre.

This frees up machining centre capacity and shortens the total job duration time, as it is still quicker to use the two processes.

Customers can also obtain more efficient sheet yield as the part gap on the profile nest is smaller, equating to more parts per sheet compared to CNC machining the profile.

Customers also report that they prefer a one-operation process where they do not have to dress the edge or carry out secondary operations.

Waterjet also offers the ability to cut thick material, typically 20mm and above, cost effectively.

This capability can complement the use of lasers by freeing up capacity for the volume work – an area where lasers come into their own.

Abrasive waterjet cutting is used for any metal based application or with dense rubber, thick plastic, some composites and all brittle materials such as glass, marble and granite.

If the material is relatively soft and thin, pure-water waterjet is the preferred route.

Pure water is clean, cheaper and, with a reduction in pump pressure, it is generally a quieter process.

It is mainly used in high-volume throughput and will provide increased cut speeds in the majority of applications.

Wardjet has a dedicated J Series system with cut speeds up to 63,500mm/min and an automated change table and pinch roller.

Waterjet running costs include the power, water, cutting head and pump consumables, abrasive and replacing the worn table.

Typical running costs for a single-head machine is GBP10-12 per hour and GBP18-20 per hour for a twin-head machine.

Abrasive-removal systems are a worthy investment to remove used abrasive and offer the advantage of increasing machine uptime.

A manual clean out of abrasive can take approximately six hours, including time to drain the tank, remove the bed, dig out the abrasive and fill the tank back up.

At a cost of GBP120 per hour, this equates to GBP720 before adding labour and disposal cost and reaching a total cost of around GBP1,000-plus per clean out.

Other running costs to consider cover the wear to the high-pressure intensifier, including high-pressure seals, check valves, dump valve, water filters and hydraulic seals.

Cutting heads too are subject to wear of nozzles, orifice and on/off valves.

It is rare to have to replace worn parts on the machine’s CNC motion system.

The sizes of waterjet cutting machine available will suit all types of industry and application with typical tables starting at around a 1,270 x 1,520mm cut area and with tables such as the Wardjet Z Series going up to whatever the customer wants for a particular application, although popular sizes are 3,000 x 1,500mm and 4,000 x 2,000mm.

A positional accuracy of 0.076mm and a repeatability of 0.025mm are achievable, while speeds of cut up to 12.7m/min on abrasive machines and 63.5m/min on pure-water machines in the Wardjet ranges are available.

The hydraulic intensifier/pump provides the power behind waterjet cutting.

The majority are 30, 50 or 100HP systems and the cutting flow rates are 2.1, 3.8 and 7.4l/min.

The pump’s HP and flow rates, dictate the number of cutting heads, the orifice/nozzle combination and ultimately the cutting speed.

New developments in pump technology have seen the introduction of the 6,000 bar/90,000lb/in2 systems offering the advantage of increased cutting speeds on thick materials while reducing the abrasive flow.

The pump can be reduced to 4,000 bar for more conventional applications.

The important utility in maintaining pump pressures is a constant incoming water pressure and flow rate from the town supply.

If the incoming water pressure is below 2.5 bars then a booster pump and header tank can be added to guarantee a consistent supply to the intensifier.

Lack of power can limit the pressures that can be achieved and a lower capacity pump with a smaller electric motor that uses less power may have to be used.

A 30HP pump requires 22kw, a 50HP pump 37kW and a 100HP pump 74kW.

The amperage in the building determines the pump specification.

The cutting head has an orifice and focusing tube, with high-pressure water streamlined through the orifice.

Directly underneath is a mixing chamber where the water and abrasive meet.

The high-pressure water is directed through a focusing tube/nozzle.

Orifice/focusing tube combinations are typically 0.25/0.76mm and 0.35/1.01mm.

While there are some disadvantages with waterjet compared to other cutting methods in particular applications, these can frequently be overcome.

For example, although the speed of cut may be slower compared to laser, this can be countered by using multiple waterjet cutting heads to reduce the unit cost of production.

To assess whether waterjet is the most appropriate cutting technology for any application, it is essential that the machine supplier carries out a thorough qualification process with the client.

When it comes to making the most of a waterjet investment, engineering subcontractors offer different services.

Some focus on the higher-end aerospace market or specialist added-value applications that may be architect related and low volume.

The majority, however, offer a range of services, whether it is cutting a sophisticated and detailed ceramic mosaic layout for a hotel chain or simply cutting mild-steel manhole covers.

The key for all of them is to be proficient in the use of CAD/CAM and is a prime consideration when considering investment in waterjet cutting.

The level of CAD/CAM skills will dictate what levels of work, and therefore added value, a sub-contractor can offer.

Wightman Stewart

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