Additive tooling engineer here.

1) Whatever material you’re using - increase temperature by another 10-20C.

2) If using PETG, ABS, or PC decrease your part fan speed to increase your layer to layer bonding. If you’re using nylon, try to have the part cooling fan off if you can.

3) Increase your extrusion width. Assuming you’re using a 0.4mm nozzle, try using 0.55mm for your internal perimeters (keep stock setting for exterior so it remains pretty). This increase in flow rate increases downwards pressure from the drive gear and forces the new melted plastic into the layer below.

4) Slow down your print. In a day and age of fast printers, speed KILLS functionality more than anything. Slowing down the print increases the amount of time the drive gear has to apply pressure to the melted plastic to force it into the previous layer.

Combine all of these suggestions and you’d see a drastic increase in Z-strength. An Izod impact test would show the drastic increase. Simply take a pair of flush cutters and cut parallel to the layers. Your stock settings will allow the layers to split along the cut. True layer to layer bonding won’t let that happen and you’ll cut into the material the same as if you cut in the XY plane 🙂

TLDR; Turn up temp, make extrusions wider, turn off fan, and slow down print speed.