Scan Pattern–Mesh Intersection

A scan pattern is a representation of the movements of a tool that is moving or scanning regions of a cutting plane or slice.

Some additive manufacturing processes are characterized by a tool trajectory that follows a repetitive pattern in space; for example, powder bed fusion with the laser beam following a predefined island scanning strategy. In such cases, instead of describing individual trajectories of a toolpath, it is more effective to define a scan pattern that represents the idealized motion of a tool inside a part. The part being printed is divided into equally spaced (uniform thickness, h) slices or cutting planes that are perpendicular to the build axis, K (see Figure 1(a) and Figure 1(b)). The build axis system IJK is a user-defined coordinate system that indicates the printing direction, K.

A scan pattern with four pattern patches.

The scan pattern consists of a rectangular unit cell (see Figure 2). The rectangular unit cell is repeated to cover the cutting plane. The rectangular unit cell consists of a number of smaller rectangular patches. Each patch can define a local angle, φ, between the direction of the scanning motion of the tool and the I-axis. You can assign an eigenstrain tensor to each of the pattern patches representing the inelastic deformation induced by the process. You can define a scan pattern by defining extents of individual patches (xmin, ymin) and (xmax, ymax). All patches together must form a rectangular unit cell that must be situated entirely in the first quadrant of the IJ plane, and one corner of the cell must be at (0, 0).

A scan pattern with four patches with local orientations rotated by 90°, 0°, 135°, and 45° with respect to the I-axis of the build axis system.

A scan pattern is active inside a scanning region. A scanning region is a build axis–oriented bounding box defined by its extent (xmin, ymin, zmin) and (xmax, ymax, zmax) (see Figure 1(a)). The height of a scanning region (zmaxzmin) must be an integral multiple of the thickness, h, of a slice. Multiple nonoverlapping scanning regions can be defined to cover the entire part. A different scan pattern can be active inside each scanning region. All scanning regions share the same build axis system. A layer-to-layer or slice-to-slice rotation angle, θ, can be defined. The scan pattern is rotated by (i1)θ on the ith slice for layer i>1 (see Figure 1(c)).

For a given element, the toolpath-mesh intersection module computes the number of slices, m, inside the element in a given increment (see Figure 3). It finds which pattern patch contains the center of each slice in that element and the local orientation of that patch considering the layer-to-layer rotation, θ, and the local rotation, φ, of the scanning direction in that patch. The module also computes the partial volumes, vf, of the element below each slice.

Scan pattern overlaid on an element.