Predicting Pattern Tooling

1
Predicting Pattern Tooling Casting
Dimensions for Investment Casting - Phase
I Srinath Viswanathan Adrian Sabau Oak Ridge
National Laboratory

• Objectives Determine constitutive
  equations and develop software tools for
  accurately and efficiently predicting pattern
  tooling and casting dimensions for all types of
  investment castings. Key program considerations
  include
• Thermal expansion
• Mold restraint on the wax and alloy
• Thermo-mechanical behavior, such as plastic,
  creep, and elastic deformation of wax, shell, and
  alloy materials during solidification and
  subsequent cooling.
• The computational models also will take into
  account the solidification and crystallization
  characteristics of the alloy wax and alloy,
  respectively.
• Sponsors
• American Foundry Society Des Plaines, IL
• Accu-Cast, Inc., Chattanooga, TN
• DOE Office of Industrial Technology
• Howmet Corp., Whitehall, MI
• Johnson Johnson, Inc. Raynham, MA
• M. Argueso Co. Mamaroneck, NY
• MINCO, Inc., Midway, TN
• PED Manufacturing Ltd. Oregon City, OR
• Precision Metalsmiths, Inc. Cleveland, OH
• Spokane Industries Spokane, WA
• UES, Inc., Annapolis, MD
• Problem/Opportunity
• As tools for predicting pattern tooling to
  achieve casting dimensions are very limited,
  trial and error approaches during the first
  article production is used. Pattern
  modifications required to tune the process
  increase lead times and raise costs. To date,
  technical literature has been limited to
  experimental, phenomenological studies aimed at
  obtaining empirical correlations for application
  in industry. In this project will develop
  standardized material property measurement tests
  and computational methodologies for accurately
  predicting pattern tooling and casting
  dimensions, taking into account the
  characteristics of the pattern wax, shell mold,
  and alloy solidification.

2

• Action/Implementation
• Guidelines for pattern handling are currently
  available but cannot be used to predict wax
  deformation. Phase I focuses on measuring wax
  properties and predicting wax pattern dimensions
  based on thermal expansion/contraction and
  viscoelastic properties of the wax during its
  crystallization and subsequent cooling.
• Models that seek to predict investment casting
  and tooling dimensions must include heat
  transfer, solidification, stress build-up due to
  the restraint of wax and alloy geometrical
  features. Thermo-mechanical properties of the
  alloy (elastic, viscoplastic) and wax
  (viscoelastic) must be considered.
• Pressure and temperature measurements can be used
  to determine the maximum dwell time and the onset
  of gate freezing.
• Temperature data near the die interface was used
  to estimate the heat transfer coefficient

Test methods used to characterize polymeric
materials were used to quantify wax deformation
properties. Stepped wax patterns, with and
without mold restraint, were made. Analysis
procedures for computing the wax dimensions were
developed.
Shrinkage cm

• The shrinkage factor is dimension dependent.
• Shrinkage of the pattern length is larger for the
  restrained pattern.
• There is a good agreement between experimental
  data and numerical simulation results of wax
  pattern distortion.

Future Potential The development of constitutive
equations for wax, shell, and alloy materials
based on experimental measurements will provide a
sound base for casting packages. Future efforts
will focus on filled waxes, shell, and alloy
materials. To facilitate adoption by industry,
tutorials on the use of investment casting models
for production castings will be developed.
Workshops will be conducted for industry sponsors
and the results will be disseminated through
trade press and industry conferences. For more
information visit http//www.ms.ornl.gov/research
groups/process/PROCESS.HTM