ccf_fabrication_techniques

A survey of fabrication techniques

-Analogue fabrication for limited space and tooling
oversized pattern transfer was expedited using digital projection onto wall hung material. This increased allowable design time before “design freeze” for export, removed outsourcing time and costs. A jigsaw power tool was used to “rough cut” the boundary curves freeing the template shape from the stock.
The creases themselves were routed manually with a steady eye and hand ona horizontal surface, with continuous arm body motion along the patterns. The mountain creases were routed on one surface face while the valley creases were routed from the reverse face, tending toward a cleaner visual expression of the different direction folds in aggregate when the pattern was folded.
Where the pattern symmetry axis occurs, two separate sheets abut without visible lapping. Surface continuity on the wearing surfaces and in-plane structure integrity is maintained via a concealed continuous overlay patch. Two surfaces are thermofused together utilising a lapping strip covering the entire butt joint of the symmetry axis remaining discontinuous only at perpendivular creases. A soldering iron is used and a stippling pattern implemented to locally fuse sufficient depth and density to bond the layers of material. This resulted in some surface penetration on the flush wearing surfaces in the prototpye, however this could be removed through automation.
Despite manual deviation due to distortion and errors during transfer or cutting, the technique is useful to facilitate design iteration and prototype concepts quickly with minimal access or time available with digital fabrication tools. (fig process)

process 01

process 02

 

-material resilience “memory”
sheet sizes of roughly 3m x 3m could be designed as a continuous roll delivered in a shipping tube, stacked in discrete pre patterned sheets, or preassembled as the final product design for delivery. We worked with Forbo and their London supplier DeBruyn to test vinyl roll flooring for structural resiliency under load, finding the material to slump over time resulting in deformation of the design under self load, and collapse under loading.
(Figure XYZ – Forbo roll flooring studies)

forbo roll material studies
However, discrete sheet stock of polypropylene plastics of equal thickness retained the geometry under self load of the material and subsequent performance loading tests. The internal rigidity and “memory” of the sheets to spring back to flat plays a vital role in the chair design to maintain a stable form.
(fig load test)

LOUTH_ABRIDGED v11 A4Llores 12 - WEB

 

-digital fabrication approaching zero thickness (polypropylene, paper, metal)
Among the foremost challenges of translating folding techniques between micron thin to 2-3mm thick materials, is maintaining surface continuity across the fold itself. A number of strategies are possible including perforations via rotary cutter, local compression of fibers via stamping (resch, pattato ), local material excavation via milling or etching, and compositing via adhered laminars. Local material excavation was selected due to the desire for the purity of a homogenous material solution and a limitation in digitally tooling available at university at the time.

we tested groove types in 3mm polypropylene and checking for deformations resulting in the groove, including a performance test of one’s ability actuate the crease by hand. Variations included “V” and “U” bits, differing bit widths and routing depths.

We learned:
1. slower tooling speeds build up heat at the bit which smear the grooves in plastics creating inconsistent depths. Speeding up tooling resolved this
2. intersecting grooves or grooves intersecting a perimeter edge of the sheet resulted in material fracturing upon folding. offsetting the termination of grooves a few mm resolved this.
(Figure XYZ – Milling Depth Studies)

Crease Grooves-WEB
Another challenge in 1:1 prototyping is transcending the standard sizes of available sheet stock without exposed or mechanical fastening. in early concept studies, sizes such as A4, and A3 expedite iteration using traditional office copier scanning functions and tape. However scale studies approach zero thickness and therefore are more amenable to various joining and lapping techniques witjout discernable material buildup .However in the chair, folded dimensions in 1:1 scale resulted in a 2.6m x 2.6m flat pattern. The largest available polypropylene sheet at the time in the UK was 1.2 m x 3m. This dictated a multisheet joining strategy.

As a result we discretised the design into symmetric halves on facing sheets that would join together.For smaller sheet sizes we explored a series of mechanical interlacing zippers which fastened halves together be means of tabs and slots. Variations included tabs scaled to estimated loading at that point in the design, square and arrow type tabs, as well as partial weaving. Firstly, these failed under loading. The tabs tended to buckle and surfaces abruptly splay apart. Secondly, the zippers did not maintain the design surface curvature across the zipper fastening developing kinks locally. Thirdly the lapping of straps through slots proved unmanageable at 1:1 scale due to workability and thickness buildup of laps.
(Fig Zipper Details)

fasteners-WEB

Results were more promising when thermal fusing (plastic welding) was explored. Using a flat tipped soldering iron, we set out exploring variants in joining 3mm plastic sheets as butt joined on the design wearing surface, but overlay on the concealed faces. The combination proved sufficient in maintaining geometric curvature continuity and structural rigidity in plane across the crease. In addition, this method allowed the finish face of the chair to remain visually uninterrupted, shiny and glossy reducing the material sheet seam line to a mere hairline in the prototype.
(Figure XYZ – Plastic Fusion Studies).

Fusing-WEB
-digital cfabrication toward solid thickness (timber, solid surface, foam) Odico, Icd,