3D printed molds can be used to cast parts with many different materials. The molds can be simple one part molds or more complicated two part molds. Inner Void spaces like the one for the inside of this silicone rubber "boot" can be achieved by using a removable inner "form" that fits between the two outer halves of the mold.
This 3D printed injection mold can be use to make a Flexible Silicone rubber "boot" for a solenoid actuated lift arm, for a slide rack, on an automated stainer. Add some pigment to color the end product. Add a rigidizer or use different kinds of silicone rubber to get different tensil strenghts for the boot.
The design can be modified to shape many different kinds of outer contour and inner void space. You can match the inner and outer contours by copying the outer, reducing its size and then subtracting it form the original outer object. Subtract a cylinder form the top and bottom surfaces and you've got a perfect match for the inner and outer contours.
Using One-to-One mix silicone rubber ( https://www.micromark.com/One-To-One-Rapid-Mold-Rubber ) and a 10 ml syringe (without the needle) the holes on the top can be used as a fill and vent hole.
Allow bubbles to rise in the syringe before injecting the mold, cover the inside of the mold with talc or brush crevices with liquid silicone rubber, then assemble and clamp the the mold. The mold is held together with two small clamps. One clamp holds the inner stem down against the bottom of the outer mold, the other holds the two halves together. The inner form aligns the outer parts.
Clean and coat surfaces with talc.