Volumes of production

Plasma-arc cutting is an economical process for small-batch quantities because it can be performed without tooling.

Unit price vs. capital investment

Unless a cutting template is introduced, the process does not require tooling. In the automated process, the information for the shape is provided by CAD files.

Speed

There is generally very little setup time involved, but the speed is greatly affected by the type of material and its thickness. For example, to cut a 1-inch chunk of steel, 12 inches long, will take about 1 minute, whereas a 1/12 -inch piece can be cut at a rate of 94 inches per minute.

Surface

Even when hard stainless steel is used, the process provides smooth, clean edges with better results than those produced by oxyacetylene cutting (see p.48). The cutting can also be controlled to produce different grades of surface, depending on the cost versus the edge quality—that is, longer cutting times equal better edge finish.

Types/complexity of shape

The process is best suited to heavy-gauge materials. Thin-gauge metals of below 3/8 inch may distort as a result of the process, as may thin and narrow sections. As in all sheet-cutting operations, nesting one shape within another (as when you make cookies and cut them as close as possible to make the most of the rolled dough) results in an economical use of the material.

Scale

Handheld cutting means there is no maximum size. Sheets thinner than about 3/8 inch may distort.

Tolerances

Depend on the thickness of the material, but, to give a basic idea, it is possible to keep tolerance to ±1/17 inch for sheet materials ¼–13/8 inch thick.

Relevant materials

Any electrically conductive metallic material, but most commonly stainless steel and aluminum. The process becomes more difficult the higher the carbon content of the steel.

Typical products

Heavy construction, including shipbuilding and machine components.

Similar methods

Electron-beam machining (EBM) (p.24), oxyacetylene cutting (p.48), and laser (p.46) and water-jet cutting (p.42).

Sustainability issues

One of the most energy-intensive processes around, plasma-arc cutting requires extreme heat and pressure for the gas to achieve cutting strength. Because shapes can sometimes be cut from sheets there is also a high amount of material wastage.

Further information

www.aws.org

www.twi.org.uk/j32k/index.xtp

www.iiw-iis.org

www.hypertherm.com

www.centricut.com

2: Sheet

Chemical Milling

Die Cutting

Water-Jet Cutting

Wire EDM (Electrical Discharge Machining) and Cutting

Laser Cutting

Oxyacetylene Cutting

Sheet-Metal Forming

Slumping Glass

Electromagnetic Steel Forming

Metal Spinning

Metal Cutting

Industrial Origami®

Thermoforming

Explosive Forming

Superforming Aluminum

Free Internal Pressure-Formed Steel

Inflating Metal

Pulp Paper

Bending Plywood

Deep Three-Dimensional Forming in Plywood

Pressing Plywood

Components that start life as a sheet of material

Within the last fifteen years or so, there has been a surge in the number of products made from sheet material. Maybe this is because the starting point is a preprepared material, which goes some way in reducing the production costs. Maybe it is also the cost-effectiveness of die-cutting tools, or even the absence of any tooling costs for processes such as chemical milling. But, on a mass-market level, the die cutting of a plastic such as polypropylene has led to a wealth of new packaging, lighting, and even larger-scale furniture. Perhaps it is also the ability of these materials to be cut by a manufacturer and handfolded and assembled by the consumer that has created an appeal.

Chemical Milling

AKA Photoetching

Product	Mikroman business card
Designer	Sam Buxton
Materials	stainless steel
Date	2003

The fine, intricate details of these cleverly designed business cards, which unfold to show a man on a bicycle and one in an office environment, are an excellent example of the ability of chemical milling to offer a highly decorative and ultrafine method of cutting metals.

Chemical milling, also known as photoetching, is a great method for producing intricate patterns on thin, flat metal sheets by using corrosive acids in a process similar to that used for developing photographs.

Chemical milling involves a resist being printed onto the surface of the material to be treated. This resist works by providing a protective layer against the corrosive action of the acid, and it can be applied in the form of a linear pattern or a photographic image. When the part is sprayed with an acid on both sides, the exposed metal (without the resist) is eaten away by the chemical. As in the die-cutting process (see p.40) used for plastics, crease lines can be “half-etched” into the pattern, which allow the sheet to have foldable crease lines for the creation of three-dimensional structures.

–  No tooling.

–  Highly flexible process for creating surface detail.

–  The image is laser-plotted onto film from a CAD file, so designs can easily be modified.

–  Fine tolerances.

–  Suitable for thin sheets.

–  Can only be used for metals.