Optimizing the Flat Pattern

Optimizing the Flat Pattern

The ExactFlat Optimize command,  optimizes the flat pattern based on material properties.  The ExactFlat optimization tools create flat patterns by seeking to minimize energy density.   An initial flat pattern is created by the intial, minimal, round, fracture or pelt algorithms.    The flat pattern piece is stretched or compressed in order that all triangles within the mesh are facing the same direction.    The spring algorithm then runs in order to allow all  of the triangle edges to relax to a low energy state.    See the video below to watch the optimizer:

Material Properties

ExactFlat Optimization Algorithms account for material properties such as Poisson ration and Young’s modulus in order to determine the optimal flat pattern shape.  For pieces with little or no strain,  these properties may have a negligible effect on the flat pattern.   Conversely, for pieces that will have high levels of strain,  these properties will have a significant effect.   In order to understand how physical properties effect the flat pattern,  the following concepts are explained below:
Young’s Modulus   is the  measure of the stiffness of an elastic material and  is also known as the tensile modulus or elastic modulus.

Poisson’s Ratio is the negative ratio of transverse to axial strain or more simply put: the tendency of a material to shrink in one direction when stretched in the other.

Flattening Metrics
A flattening metric is chosen depending on the behavior of the material.  For example, a material may be very elastic in the X direction and stiff in the Y direction.   More complex metrics require more physical property data and take longer to solve.    Below is a list of metrics:

Linear Isotropic – This metric assumes that Young’s modulus and Poisson ratio are constant throughout the stress strain curve (linear), and that the material properties are the same in all directions (isotropic).  The linear isotropic takes into account the material properties listed below:

  • Tolerance –  The tolerance value indicates to the flattening algorithm when the desired flat pattern precision has been achieved. To use a system calculated precision, enter 0 here.   The tolerance units are in energy density  (energy/unit area).
  • Young’s Modulus X – For isotropic materials, enter the Young’s modulus here.
  • Stress Limit  – The stress limit is a user defined value to provide warnings when a flat pattern result  exceeds this value.
  • Stress Units  – Units for Young’s modulus and the stress limit.
  • Poisson’s Ratio X –  The Poisson’s ratio for the material.
  • Elongation Limit –    The elongation limit is a user defined value to provide warnings when a flat pattern result exceeds this value.

Linear Orthotropic  – The linear orthotropic metric  takes into account Poisson ratio and Youn’g Modulus.  This metric assumes that Young’s modulus and Poisson ratio are constant throughout the stress strain curve (linear), and takes into account orthotropic properties (Young’s modulus and/or Poisson ratio) are different in the X and Y directions.  The Linear Orthotropic algorithm takes into account the same properties as the Linear Isotropic algorithm with the addition of the properties listed below:

  • Young’s Modulus Y –  The X and Y axis are defined on the piece using the Grain Line tool.    The grain direction for the piece  is always defined as the x-axis.  The Linear Orthotropic algorithm will require a non-zero Young’s modulus value for the y axis.
  •  Poisson’s  Ratio Y – The Linear Orthotropic algorithm will require a Poisson’s Ratio for the  y axis.
Seam Stretch
Seam Stretch allows the user to constrain the boundary of a part during optimization,  in order that the seam lines of the flat parts  remain within a tolerance of the 3D parts.
Sag Penalty
Sag Penalty allows the user to constrain a part during optimization,  in order that boundaries of the part are adjusted to preferentially eliminate sag (negative strain)  over stretch (positive strain).