Investigation into Non-Conventional Mold Designs using 3D Sand-Printing in Castings

Open Access
Author:
Sama, Santosh Reddy
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 02, 2018
Committee Members:
  • Guhaprasanna Manogharan, Thesis Advisor
  • Robert Carl Voigt, Committee Member
  • Paul Carl Lynch, Committee Member
Keywords:
  • 3D Sand-Printing
  • Sand Casting
  • Additive Manufacturing
  • Gating System
  • Process Monitoring
  • Internet of Things
  • Conical-Helix Sprue
Abstract:
In recent years, Additive Manufacturing (AM) technologies are fueling a paradigm shift in the advanced manufacturing landscape across all industrial sectors. The metal casting industry is also taking advantage of the wide variety of rapid manufacturing solutions offered by AM processes. The metal casting industry supports about 90% of total manufactured goods and is expected to reach a market size of about 40 billion USD by 2025. Sand casting is the most widely used metal casting process and utilizes expendable molds that demand expensive tooling, high lead time and limited flexibility in their fabrication. In addition, limitations in process control and feasible gating and feeding systems, traditional sand casting experiences higher scrap rates. AM offers an alternative mold fabrication technology known as 3D Sand-Printing (3DSP) process that enables direct digital manufacturing of complex expendable sand molds and cores without any tooling requirements. Ever-growing interest in this indirect metal AM process is attributed to its ability to rapidly produce cores and molds for complex metal castings that are otherwise impossible to manufacture using conventional techniques. Knowledge-based design rules for this process are currently very limited and are progressively realized in an ad-hoc basis to produce economic low-volume castings. Despite the wealth of knowledge in metal AM, no work to date has been reported to take advantage of design complexity offered by 3DSP in developing optimal gating and feeding designs to mitigate casting defects. This thesis provides the first known investigation into the application of design freedom offered by 3DSP to transform and monitor sand casting performance. Non-conventional design rules for gating and risering (also known as rigging) systems are developed to reduce surface turbulence, oxide films, air entrapment, bubble damage and several other casting defects, and improved metallic yield. Several case studies are presented to illustrate the improved casting performance through systematically reengineering elements of the rigging system viz. pouring basin, sprue, runners and risers. Their efficacy is validated through computational simulations and experimental procedures. Of the various components of gating system, innovative sprue design provides the highest opportunity to improve casting quality. Numerical models for novel parabolic and conical-helix sprue profiles can be developed through constrained optimization algorithm based on principles of casting hydrodynamics to reduce surface turbulence. Computational flow simulations, computed tomography scanning, microstructure and mechanical characterization experiments are performed to validate that incorporation of 3D Sand-Printing featured mathematically optimized gating systems (particularly conical-helix sprues) to significantly improve the performance of sand castings. Finally, existing foundry technologies have very limited capabilities to monitor real-time flow conditions of liquid metal during mold filling. Two approaches for novel non-intrusive real-time mold fill monitoring by embedding inexpensive miniature Internet of Things (IoT) sensors into 3d sand-printed molds are proposed. These sensor technologies are based on the electrical properties of molten metals, the former measuring the magnetic flux generated by the conductive liquid and the latter measuring the interference of electric fields by modifying dielectric near the sensor. Experiments are conducted to evaluate the efficacy of both these concepts. Results from experiments validate that IoT sensors can be embedded into 3DSP molds to successfully monitor flow fields that can be used to benchmark simulation results and optimize gating systems.