Nickel shells bring shorter lead times and faster cycles to blow molding. (Blow Molding Close-Up).

* Two Canadian tool builders have formed an alliance to introduce the first blow molds made by nickel-vapor deposition (NVD). The partners are the Nickel Tooling Technology div. of Weber Manufacturing Ltd. in Midland, Ont., and Ryka Blow Molds Ltd. of Mississauga, Ont. For more than a decade, Weber has used NVD to make large, complex injection, compression, and RIM molds. Until now, however, NVD has not been used to make blow molds.

"A key benefit of NVD technology is the ability to achieve precise surface detail and easy reproducibility of mold cavities and other mold components at relatively low cost," says Michael Ryan, president of Ryka Blow Molds. Weber's NTT group will provide know-how and form the nickel shells for molds. Ryka will design and build the holders for the NVD shells and incorporate cooling channels into the tools. Ryka also is marketing this new tooling approach.

The alliance's initial commercial focus is on multi-cavity extrusion blow molds for HDPE containers and on stretch-blow molds for PET bottles. Customers are already testing NVD molds in both applications. Down the road, Ryka also envisions NVD tooling for industrial blow molding, such as large automotive parts like roofs, dashboards, and consoles.

Precise but low-cost

The first step in building an NVD blow mold is CNC machining (by Ryka) of a mandrel or pattern that includes precise cavity details. The mandrel is heated and placed in the deposition chamber where it attracts vaporized nickel powder, creating a thin (5-mm) but strong shell on the mandrel surface. Weber's process allows deposition of a shell in about 20 hr. The shell is removed by Ryka from the mandrel and fastened into a holder.

The mandrel is reused to replicate as many cavities as required without further machining or polishing. According to Ryka, the cost benefit of NVD typically is realized with as few as three cavities and increases as cavitation goes up. NVD blow molds reportedly can be delivered at least 30% faster than conventionally machined and polished multi-cavity tools.

What's more, Brinell hardness of an NVD nickel shell is 195, versus 167 for the QC-7 aluminum commonly used in blow molds. Another patented technology allows Ryka to harden NVD shells or inserts to a level equal to beryllium copper tooling.

NVD tools are also about 25% lighter than aluminum versions. Ryka is designing new lightweight holder for NVD shells to further reduce over tool weight.

"We are also able to apply advanced cooling technologies for NVD tooling, resulting in significant increases in the heat-transfer rate versus conventional blow molding tools," states Scott Covey, a Ryka official. He says Ryka incorporates copper tubing behind the shell, shaped to hug the shell's contours. Subsequently, these cooling channels are encapsulated and secured to the shell by means of a second NVD step. This "conformal cooling" approach reportedly provides more efficient cooling than is possible by gun-drilled straight channels. 53