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Hybrid manufacturing - in-situ printing-casting


Why
What
How
      Design
            OpenSCAD file
      Printing
      Casting
      Assembly

Why

Often an elastomer part needs to be combined with a rigid part. Silentblocks, bushings and other vibration suppression devices are typical examples. Without multimaterial 3d-printing such parts are difficult to produce and require assembling from multiple parts.


What

A 3d printer filament extruder actuator stepper motor was held in place with a rigid mount printed from PLA. The printout also undergone deformation from the heat of the motor. PLA is just a suboptimal structural material.

A replacement mount had to be printed. It was decided to include vibration suppressors, elastomer blocks, into the design.

Low-stakes projects without deadlines are excellent for testing of new technologies. Here, it was decided to try out hybrid manufacturing method: 3d-print a part with pockets for casting, casting in a two-component silicone rubber, then cut out the external parts of the pockets.


How

A motor mount was designed, a modified variant of the earlier design.

Design


Design

Design

Design

Bottom view

Bottom view

Cut view

Cut view

Cut view

Cut, pocket profiles

Cut

OpenSCAD file

Printing

The two parts of the motor mount were printed at once, from colorless ABS. Hexagonal lightening holes were included in the design, to save material and to make the printing slightly more difficult, to expose eventual issues. Pockets with mechanical interlock shape were cut out into the top and bottom sections of the parts. The external areas, where the rubber has to protrude from the parts, were realized as thin-walled pockets. Roughly 45-degree slopes were used to mitigate issues with overhangs.


Printout of clamp

Printout of clamp

Printout of clamp

Printout of clamp

Printout of clamp

Printout of clamp

Printout of clamp

Printout of clamp

Casting

Small cups were printed from PETG, to avoid having to look up bottle caps.


Mixing cups

Mixing cups

Mixing cups

Two-component silicone rubber, Raytech Magic Rubber, was mixed in a cup. The liquid was transferred with a screwdriver to the pockets in the printouts. Excess rubber was placed to the back side of the printout, where it meets the vertical rail of the printer frame, to further suppress the vibration transfer.


Cast rubber

Cast rubber

Cast rubber

Cast rubber

Cast rubber, painted backside

Cast rubber

Cast rubber

Cast rubber

The material was left to set, using a bed printer heated to 60°C to accelerate the curing.

After curing, the excess rubber was peeled from the part; the low adherence of the silicone to ABS made the task easy. It also illustrated the need for the mechanical interlocks to hold the rubber pads in.

The external parts of the pockets were cut with a sharp knife. Despite the single layer thickness this turned out to be rather difficult, the knife occasionally slipping into the silicone and cutting it with ease. A hot blade should have been used instead.

M3 threads were cut into the plastic of the frame-side half of the holder.


Cut off trays

Cut off trays

Exposed rubber pads

Exposed rubber pads

Exposed rubber pads

Exposed rubber pads

Exposed rubber pads

Assembly

One half of the motor holder was attached to the printer frame, using two M3 screws. The motor was inserted to the holder, and the outer clamp was screwed in place.


Back side mounted to frame

Back side mounted to frame

Back side mounted to frame

Motor holder assembly

Motor holder assembly

Motor holder assembly

Motor holder assembly

Motor holder assembly

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