Volumes of production

The process involves no tooling and is therefore equally suitable for one-off jobs and large production runs.

Unit price vs. capital investment

Because there is no tooling, and designs are taken from CAD files, setup costs are low, and there is no consequent hike in unit price. Shapes can also be “nested”—laid out in a clever way to maximize the surface area of the sheet (as you would when cutting out cookies from rolled dough).

Speed

An abrasive jet can cut a ½-inch-thick titanium sheet at the rate of 6¼ inches per minute.

Surface

The cut edge has the same sort of edge as if it had been sand-blasted, but without any of the burring that you may get with laser cutting (see p.46).

Types/complexity of shape

Because the cutter works like a plotting machine or a CNC router, it is possible to cut fine and intricate shapes. However, due to the high pressure of the water, thin sheet material may distort or bend. Processes such as laser cutting avoid this problem due to the lack of such pressure.

Scale

Most industrial cutting takes place on a cutting bed, which restricts the size of the material that can be used. Standard sizes extend up to a maximum of 10 by 10 feet. The upper limit for thickness varies with the material.

Tolerances

The jet can be accurate to 1/250 inch. Particularly thick materials may result in the jet “wandering” slightly from its point of entry.

Relevant materials

Water-jet cutting offers a huge range of possibilities in terms of materials—you can choose from glass, steel, wood, plastic, ceramics, stone, marble, and even paper. It is also used for cutting sandwiches and other food. Having said that, it is worth bearing in mind that materials that are particularly prone to absorbing water are not suited to this process.

Typical products

Decorative architectural panels and stones. The process works very well under water, and it was used in the rescue operation of the Russian Kursk submarine in 2000.

Similar methods

The process can be used as an alternative to die cutting (p.40), and as a cold alternative to laser cutting (p.46).

Sustainability issues

The water used for cutting can be recycled back into the process to form a closed loop cycle, which reduces water consumption and resources. Additionally, with no tool contact, maintenance and material use through replacement parts is reduced. No heat is required so energy use is fairly low while no fumes, toxins, or contaminants are released during cutting. The nature of the material determines whether waste (of which there will be a considerable amount) can be reheated and recycled.

Further information

www.wjta.org

www.tmcwaterjet.co.uk

www.waterjets.org

www.hay.dk

Wire EDM (Electrical Discharge Machining) and Cutting with Ram EDM

Designers are rediscovering the use of surface decoration as a valid form of design expression. Industrial techniques have been borrowed from engineering applications and are used to create highly intricate patterns, as decorative as if they have been abstracted from nature or fairy-tale narratives.

Many unusual methods have been invented for cutting complex patterns into difficult materials. Dating back to when the phenomenon was first observed in the 1770s, electricity has been harnessed by scientists for use in cutting and machining materials. Wire EDM (electrical discharge machining) is one of the latest processes to exploit electricity for cutting intricate patterns.

Since its commercial development in the 1970s, wire EDM has become an increasingly popular method of machining metals. Together with processes such as water-jet cutting (see p.42) and laser cutting (see p.46), Wire EDM is a noncontact method of cutting materials. Less commonly used than the other two and more suited to extremely hard steels and other hard-to-cut metals such as high-performance alloys, carbides, and titanium, it is, nevertheless, able to achieve the same level of intricacy.

Based on a type of spark-erosion (it is sometimes also referred to as spark machining or spark eroding), wire EDM is used to cut very hard, conductive metals by using sparks to melt away the material. The spark is generated by a thin wire—the electrode—which follows a programmed cutting path (determined by a CAD file). There is no contact between the electrode and the material, so the spark jumps across the gap and melts the material. Deionized water is simultaneously jetted toward the melting point, cooling the material and washing the waste away.

There is another sort of EDM machine, the “ram.” As the name suggests, the ram method involves a machined graphite electrode mounted on the end of an arm (the ram) being pushed onto the surface of the material to be cut.

–  Ideal for cutting intricate shapes from metals that would be difficult to machine.

–  The process cuts without force.

–  No flushing.

–  Time-consuming.

–  Limited to electrically conductive materials.