Spray formed tooling for rapid manufacture

Spray form tooling technology marries conventional electric arc spraying, usually used for producing coatings, with freeze casting, robot manipulation and thermal process control to produce dimensionally accurate sprayed tools suitable for production applications.

The spray form tool process offers the potential to manufacture tools of sufficient quality and robustness for production applications, at reduced time and cost in comparison with current machining routes.

Read more about this work in an Ingenia article, published by the Royal Academy of Engineering.

An overview of our work in this area is described in: doi:10.1361/105996306X1468794

The process step by step

The spray form tool process starts with a pattern or "master" which can produced in a number of ways:

  • an artist's model
  • a UV cured model produced directly from a CAD file using stereo-lithography
  • a silicone rubber impression of the component to be produced by the tooling
  • a master produced by machining epoxy bonded ceramic powder filled board on a low stiffness router

A silica sol slurry is then cast against the boxed-in pattern, and then frozen to produce a solid. On thawing, the resulting ceramic remains solid due to a freeze-gelation process occurring in the sol. It is then dried and is ready for use as the substrate for the sprayform tool process. Because no firing is required to produce the ceramic, freeze casting is a low cost process that replicates the pattern with high accuracy.

Freeze cast ceramics offer the key attributes:

  • low cost
  • little or no dimensional change during freezing and any changes are isotropic
  • excellent thermal shock properties
  • excellent surface properties

The pictures above show the spray cell.

 

Some complex topographic features of the freeze cast ceramic cannot be accurately replicated by the sprayform tool process. In these cases, the original CAD file can be modified or inserts used that blank off these features. The detail is then restored by post-spray EDM operations.

The freeze cast master is then sprayed using four electric arc spray guns mounted on a 6-axis programmable robot (right). The robot manipulates the guns and the metal spray in a controlled way, over the surface of the shaped freeze cast substrate to be sprayed. The equipment is housed in a dust proof, acoustic chamber, complete with a dust and fume extraction system, as shown above.

By careful control of the spraying process, the solidification and thermal contraction stresses that are normally an inherent feature of sprayed metal coatings and products are eliminated. This stress control enables thick tooling to be produced without distortion and loss of dimensional accuracy in steels suitable for production applications.

After spraying, the tool preform undergoes a variety of finishing procedures before entering production service (left).

 

 

Processing of Advanced Materials