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The spider chart shows the relative strengths of each additive manufacturing deposition process based on the results in this study for five categories: deposit density, elongation, yield strength, tensile strength, and Charpy v-notched toughness.
This project seeks to develop, evaluate, and qualify novel methods of rejuvenating and repurposing die cast tooling using additive manufacturing (AM).
High pressure die casting is a secondary manufacturing process in which molten metal is formed into a desired shape by allowing it to flow into a mold under externally applied pressure. The most common materials for manufacturing die casting tooling are AISI grade H13, H11, and modified versions of these steels. Maraging steels provide alternatives to medium- and high-carbon tool steels because they reduce the occurrence of quench cracking, while the high nickel content provides corrosion resistance. Maraging steels have a higher cost; however when applied as a low volume cladded layer, the higher cost is justified by improved performance.
The objective of this project was to develop, evaluate, and qualify novel methods of rejuvenating and repurposing die cast tooling using additive manufacturing (AM). The goal was to determine the best method or combination of methods for reconstructive repair, selected on a case-by-case basis, yielding detailed documentation regarding the selection criteria and rationale.
The project team was led by Case Western Reserve University and included Dante Solutions, Benet Laboratories, Delaware Dynamics, General Die Casters, Keystone Synergistic Enterprises, Lincoln Electric Company, Magma Foundry Technology, Nebraska Aluminum Casting, North American Die Casting Association, Sciaky, and Twin City Die Casting.
The testing for this study was conducted using H13 base metal blocks with varied deposition patterns. Tension testing, Charpy v-notched toughness testing, hardness testing, X-ray radiography, and metallography were performed on each sample. The following additive manufacturing processes were evaluated:
Data collected was used to develop computer models for comparison.
Based on the depositions conducted in this study, there are many acceptable deposition processes for additive tool repair and repurposing. From the mechanical testing, it appeared that additively manufactured maraging structures have sufficient hardness, toughness, and strength for use in die cast tooling repair and repurposing. The hardness of the deposit generally matched the hardness of tempered H13, which is the workhorse of the industry currently, while having higher strength, provided by the martensitic microstructure of maraging steels.
The CMM conducted on blocks post-deposition showed little distortion in the base material, even on an annealed H13 base plate. This is promising, since distortion in these experiments could have indicated the presence of residual stresses in the deposit which could increase the likelihood of cracking, especially during the thermal cycling of die casting.
For evaluating the deposit for structural integrity, the biggest factor was macroscopic voids and/or inclusions. The X–ray images showed that many of the deposition processes had some amount of porosity present. Since the surface of the deposit would be machined away to the final geometry, it is recommended to use this process as an opportunity to inspect each surface for porosity during and after machining.