Production of a Strain-Measuring Device with an Improved 3D Printer

The two-phase solid-liquid fabrication can also be applied to the manufacturing of structural microsphere materials in various field of study, including the electronics, biopharmaceutical, energy, and defense sectors. This system does not require wires or electrical connection and allows a wide range of applications related to microstructure deformation to be measured. Before beginning the procedure, construct an experimental platform that includes a modified 3-D printer, a strain gauge indicator, a driving device, a support frame, an aluminum bar, a PDMS lens, a smartphone, weights, a printed amplifier, and a strain gauge.

Set the height of the nylon layer in the printer to 0.05 millimeters. Set the diameter of the printing head to 0.2 millimeters, and set the nozzle temperature to 220 degrees Celsius. Set the printing speed to 2000 millimeters per minute.

Adjust the orientation of the spherical extrusion head so that the metal nozzle faces the low temperature platform and print a contour to ensure a normal extrusion. Then hang the nylon on the column. The front end must enter the printing coil container to be melted by the metal nozzle.

To assemble the PDMS microscope, use a magnetic stirrer to mix a 10 to one weight ratio of PDMS precursor to curing agent solution and de-gas the mixture for 40 minutes. When all of the bubbles have been removed, pour the mixture into the PDMS container of the spherical extrusion head and rotate the spherical extrusion head and platform so that the plastic nozzle faces the high temperature platform. Set the plastic nozzle increment to 50 microliters and use the nozzle rotation and the stepper motor in the Z-axis to place the bottom end of the pipette device 20 millimeters away from the mold.

Then heat the high temperature platform and squeeze the PDMS container to print the PDMS lens. When the printed PDMS lens has cooled to room temperature, use rubber tweezers to remove it from the printer. To perform a loading test strain measurement, use nuts and bolts to fix one end of a 380 by 51 by 3.8 millimeter aluminum 6063-T83 bar to the operating table and draw a cross at the center and 160 millimeters from the free end of the cantilever beam.

To remove the oxide layer on the beam, polish the surface with fine sandpaper at an about 45 degree angle from the direction of the strain gauge wire grid. Use cotton wool soaked in acetone to wipe the surface of the sanded cantilever beam and the surface of the strain gauge paste. Then connect the driving device and the strain gauge indicator and turn on the power.

Next, mount a strain gauge onto the center surface of the aluminum bar at its fixed end and fix a standard weight to the free end of the cantilever beam to control the concentrated force input. Record a baseline read-out using a conventional strain gauge indicator with a quarter bridge connection method before replacing the strain gauge with a nylon amplifier. Attach the PDMS lens onto a smartphone camera with an eight megapixel sensor at a focus distance of 29 millimeters and adjust the focal length of the camera until a clear image is obtained.

Then use the PDMS microscope to read the displacement of the pointer. To perform a finite element analysis, import the cantilever beam and the amplifying mechanism into the material library of the software and simulate their placement positions. Analyze the mechanical properties of the amplifying mechanism pointer under the action of a cantilever beam and use tetrahedral elements with a fine element size to generate meshes for use in 3-D geometric models.

Then refine the flexure hinges, especially the hinge between the pointer and the other bodies, and apply a concentrated force of one newton to the center of the free end of the cantilever beam. As the platform temperature is increased, the droplet diameter and curvature radius decrease, and the contact angle increases. Here a comparison of the experimental displacement measurement with the FEA simulations for nylon is shown, while this graph illustrates the minimum and maximum discrepancies between the slopes for ABS.

In this representative experiment, the measurement sensitivities for nylon and ABS were determined. Controlling the molding temperature of the PDMS lens is difficult. We use a non-contact infrared radiation thermometer and high-temperature platform to ensure that the temperature changes are within tolerance.

This solid-liquid manufacturing method can also be applied to studies in the biopharmaceuticals field, particularly for the preparation of microsphere structures.