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August 4, 1998

4 Min Read
Thin-shell nickel tooling seals up time savings

Testing real parts during product development often ensures success during mold sampling and production phases. But the expense and time required to create prototype tooling can deter even the most diligent of product designers. A new twist on "bridge" tooling, developed jointly by Tupperware (Orlando, FL) and electroforming specialists at Vintage Industries (Longwood, FL), may be the answer. It is based on nickel electroforming (a process used to make U.S. currency as well as CD and DVD masters), capable of accuracies down to .001 inch and details of .0002 inch.

When Tupperware designers came up with a spillproof seal concept for children's beverage containers, they couldn't accurately test the nonspill mechanism without building a tool and running it with the correct material and cycle times. Building prototype tool inserts for the two-part Sipper Seal in several days rather than several weeks was the challenge posed by Tupperware's Bill Morgan, product development engineer, and Brent D'Alessio, project engineer.

"The outer seal was a single-cavity insert," Morgan says, "while the nonspill component required a family insert to allow us to test three unique designs." Both inserts were fairly straightforward from a mold design standpoint. Each had a planar parting line and a small shutoff area located on the neck. But complications arose--the outer seal required an undercut on the outside to create sealing action. And the family insert needed to be balanced properly. Morgan decided to try thin-shell nickel tooling using SLA masters.

"I had become familiar with the DirectAim process for bridge tooling (from 3D Systems) after seeing how a low-melt alloy could significantly improve results," he recalls. (For this project, he won second place in the '97 North America stereolithography users group awards.) Working with Joe Vallone, president of Vintage Industries, Morgan attempted to break through previous limitations using the Sipper Seal project.

Table 1. Sipper Seal Specifics

Part name

Tooling

Part dimensions

Material

Inner seal

Family insert

.75 by 1.5 by 1 inches

TPE

Outer seal

Single-cavity insert

3 by 1.5 inches

LLDPE

Vintage developed and patented a proprietary electroforming process to create prototype tooling, a process it has used for six years. Its original procedure: start with an SLA master pattern, go through the reversal process, electroform a .125-inch-thick shell (a 10-day process), then backfill the shell with aluminum-filled epoxy. Morgan's challenge: apply Vintage's expertise toward creating a uniform shell within three days.

After several tries, Morgan and Vintage engineer Jay Wells produced a core and cavity set in less than five days using the following process:
1. Create part in CAD using a surface or solid modeler.
2. Address design for moldability issues.
3. Create core and cavity inserts in CAD--scale part surfaces for shrinkage, add runner and gates.
4. Produce core and cavity--the team used an SLA250-50 with SL5170 epoxy.
5. Sand and polish areas of concern with Micromesh.
6. Perform reversal process (Vintage uses a proprietary material) (3 to 4 hours). Producing a reversal part allows greater surface duplication accuracies as well more uniform shell thicknesses.
7. Electroform the thin nickel shell over the reversal product (three to four days), then backfill with a low-melt tin-bismuth alloy (3 hours)--remember the opportunity to design conformal cooling lines at this stage.

Morgan notes that the coefficient of thermal expansion for the low-melt alloy and nickel are similar, which ensures that the thin shell will not separate from the backing. Thermal conductivity comparisons to stainless steel (Table II) indicate that cycle times, even without conformal cooling, average about 20 percent lower with nickel tooling. On the other hand, compressive strength is much less, so tools made of standard electroform nickel tend to be less robust than stainless. "Vintage's proprietary alloy has significantly greater strength, though," Morgan says, "and it is currently analyzing the material to determine how it retains greater compressive strength."

With the success of this technology, Vintage has created a division called Nickel Composite Tooling, which produces thin-shell nickel mold inserts for custom and captive molding operations. These can be production or prototype tooling depending on volume levels. Morgan estimates that a .600-inch-thin nickel shell tool can maintain dimensional stability in production runs up to 500,000 parts.

Table II.
Nickel Performance Compared to 420 Stainless Steel

Thermal conductivity

Four to six times higher

Hardness

Equivalent

Yield strength

1.75 times higher

Compressive strength

50 percent lower

Operating temperature

500F, higher

Contact information
Vintage Nickel Composite
Tooling
Longwood, FL
Phone: (407) 831-8949
Fax: (407) 831-5346

Contact information
3D Systems
Valencia, CA
Gary Sande
Phone: (805) 295-5600, Ext. 2234
Fax: (805) 257-1200
Website: www.3dsystems.com

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