Page 37 - MetalForming Magazine April 2023

loads to reduce delamina- tion, cracking or other fail- ure modes.
“With shrinkage com- pensated for (as the tool cools after deposition and heat treatment),” he says, “such a tool would be capable of withstanding typical impact loads and thermal shock loads found in the hot stamping tooling business. But while deposition rates are improving, these rates still are far short of what’s required economically to produce large-scale tools.”
While Austin also sees R&D improvements that allow for viable printing of conformal-cooling tool segments, “cross-drilling will be cheaper for the bal- ance of a tool that features somewhat straight holes in the channels.”
ORNL officials in a presentation last fall at MetalForming’s Hot Stamping Experience and Tech Tour touted improved cooling effects and reduced lead time in AM test tooling, specifically a 400-lb. 5-ft.- long full-scale automotive B-pillar hot stamping die, as compared to a fully machined tool with machined channels. Using AM, ORNL officials cited tool-build lead reduction from 20 days down to eight with 20- percent cooling improvement in selected tool regions. Photo courtesy of U.S. Department of Energy Oak Ridge National Laboratory.
metallurgical issues related to what happens when addi- tively building a tool and not being able to keep it at an elevated temperature.”
All of the heating and cooling experienced when adding material brings undesirable stresses, accord- ing to Austin.
All of this said, Austin remains happy with the results during DTG’s first go- round with wire-fed AM, and with recent improvements he remains optimistic on its future use for hot stamping tooling, with qualifications. One qualification: issues with locating metal when performing high-speed fin- ish-cut machining.
“A cutter flying around and suddenly hitting metal at high speed can break the cutter,” he says. “Shrinkage or metal movement after
Segmented Tooling,
Heat Cycles Also Challenge AM
The hot stamping industry’s interest in segmented tooling when compared to large one-piece tools also affects the choice of AM or machining.
“The industry wants segmented tooling that allows for repair or replace- ment of portions of the tool,” he says. “An A-pillar or B-pillar part features some areas at the ends that benefit from conformal cooling, but the center of the part has some long, relatively straight holes that
need for conformal or any cooling channels. This precludes the need for AM, Austin reports.
Progress as to pre- and post-heating during wire-fed AM also must be made to make it more viable for hot stamping tooling, according to Austin.
“We see the need for a process to preheat the tool before we feed the wire into it and strike the arc,” he says. “Then after the arc leaves, we need to slow the cooling—a post-heating process. A head that combines wire feed with pre- imposed laser heating would address
printing makes it difficult to locate metal accurately and program the machining accordingly. Surface scan- ning can resolve this challenge in cut- ter-path programming.”
An alternative of drastically slowing machining would extend lead time and add costs.
Opportunities
in Die Repair: Tailored Surfacing
Shifting to die repair, AM again holds promise, according to Austin,
can be drilled more cheaply. As long as I’m producing seg- ments and tying them together, I’m better off drilling.”
As for prototyp- ing hot stamping dies, these often can be produced in one large piece and, being proto- types, without the
The CAD model (left) shows a hat-shaped hot stamping tool with four cooling lines. ORNL, as part of a project with Diversified Tooling Group, printed the R&D part (right) via wire-fed AM.
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