Volumes of production

Jigs can be made up for single profiles in a small workshop. Industrial production setups can produce hundreds of thousands of units.

Unit price vs. capital investment

Jigs for low-volume production can be expensive due to the labor costs involved. However, depending on the design, simple molds can be made that are still economical for small production runs or even one-offs. At the industrial end of the scale, as with most other manufacturing processes, higher tooling costs are balanced by low unit costs.

Speed

Cycle times are fairly long because the glued veneers have to dry inside the mold before they can be taken out, and the parts need subsequent finishing, including edge trimming, surface treatments, or painting.

Surface

Dependent on the type of wood.

Types/complexity of shape

Restricted to simple bends in a single direction. The inherent flexibility of the material can allow for slight undercuts when removing pieces from the molds.

Scale

The scale is generally suited to furniture and accessories (such as magazine racks). The restriction on size is determined by the size of the molds and the ability to exert the degree of pressure needed to compact the layers.

Tolerances

Rather low because of the flexibility of the material.

Relevant materials

Birch is used in the majority of mass-produced furniture, but many other types of wood, including oak and maple, can be used. Burly woods (the outgrowth of a tree, also known as the burr), including pine, are not to be recommended, because it is difficult to produce plywood of consistent quality from them.

Typical products

Furniture, interiors, and architectural cladding. Aircraft frames were made from bent plywood during the two World Wars.

Similar methods

Inflating wood (p.184) and pressing plywood (p.86).

Sustainability issues

Wood is a natural resource that is renewable when controlled by a sustainable forestry. However, the production of the plywood, and additional forming, is quite energy intensive as the wood undergoes extensive processing. At the end of its lifespan the plywood can be recycled.

Further information

www.woodweb.com

www.woodforgood.com

www.artek.fi

www.vitra.com

www.lapalma.it

Deep Three-Dimensional Forming in Plywood

Product	Gubi chair
Designer	Komplot
Materials	Walnut veneer
Manufacturer	Gubi using Reholz® deep 3-D forming technology
Country	Germany (process) Denmark (chair)
Date	2003

The apparently simple curves of the Gubi chair mask the sophistication of this completely new method of forming wood. The compound curves (the seat passes through an almost 90-degree angle) are a result of the ability of this treated ply to conform to far more complex shapes than, for example, the pressed plywood tray (see p.86).

This book features a number of new and radical ways to process plywood into ever more complicated and curved forms. One of these is deep three-dimensional forming in plywood, a combination of a production method and a material specifically developed for the purpose. Using an innovative treatment in which the wood fibers are relaxed, it is now possible to bend plywood into wavy shapes that were once unthinkable.

The technology for preparing the plywood was developed by the German manufacturer Reholz^®, and it enables the plywood to be molded into a deep, three-dimensional compound curve, which is capable of producing forms that resemble molded plastic rather than a piece of wood.

The key to this process, and the first stage in achieving the complex curves, is a series of closely cut, parallel lines, so deeply cut into the individual veneers that the wood itself almost falls apart. This gives the veneers the elasticity to be bent in different directions without breaking, which is particularly important when bending them against the direction of the grain. The individual sheets of veneer are glued together in a way that is similar to the bent wood process (see p.80), in order to achieve stiffness and strength.

1 The stack of prepared sheets of veneer assembled with the grain running in alternate directions.

2 The stack of veneers before the male and female molds are brought together.

3 The seat for the Gubi chair, post forming.

4 The seat is ready for the final shaping process, which involves the excess material around the seat being cut away.

–  Permits new forms to be produced from plywood.

–  Allows wood to enter markets normally reserved for metals and plastics.

–  Enhances the structural strength of plywood.

–  There are some limitations with regard to small radii and other sharp bends.

–  Since this is a wood process, moldings will never be as accurate as, for example, plastic components.

–  Available only from Reholz^®, the originator of the technology.