Semi-automated Thermoforming

SystemBrendan CrosbyLeon Hill

Rene Vallesteros

Jesus ToledanoSponsored by:

CalSci Inc.

Problem Statement

Build a semi automated thermoforming vacuum system for 1/16” -1/8" thick ABS and Acrylic measuring 24in. x 24in.

Requiring a uniform temperature exceeding 350℉ to be autonomously moved to a mold and pull minimum vacuum pressure of 10 psia.

Form 0.1-0.125in. thick Acrylic, and ABS plastic sheets.

Sheet dimensions: 24inx24in.Cannot heat plastic too quickly or too slowlyForming temperature: T≥ 350℉Pull vacuum pressure large enough to form plasticDepth of draw may not exceed 1/3 of smallest part width approximately 8 inches.Plastic must be formed before dropping below forming temp

Function

ConstraintsVacuum Thermoformer

● Plastic placed in machine● Heats plastic to forming

temperature● Plastic placed on mold● Vacuum pulls plastic

tightly around moldAutomated System

● Loads plastic into machine● Controls heat rate● Maintains constant

vacuum● Releases part from

machine

Systems

1

34

1.Structural Frame2.Oven3.Plastic Holding

Frame4.Drive System5.Vacuum System

2

5

Fig 1. System Model

Figure 2 (a): System in up position Figure 2 (b): System in up position

Structural Frame

● Comprised of 2”x2”x1/8” aluminum angles and particle board and sheet steel

● Will have to support weight of the oven, drive system, and vacuum system.

● System weighs 58 lbs22 lbs oven21 lbs pump12 lbs frame & plastic

Figure 3(a):Premade materials

Figure 3(b):Assembly

Figure 3(c):Completed

OvenManufacturing

• The oven is comprised of an internal and external cover.

• Internal cover housed the heating elements.

• Fiberglass insulation is covered by an external cover.

Figure 4(b): Fiberglass insulation in between internal and external covers

Figure 4(c): Two 725 watt heating elements

Figure 4(d): Oven shield comprised of wooden board covered in aluminum foil to help reflect and store heatFigure 4(a): Sheet metal oven sidings

Oven Analysis

Figure 5(b): Oven Circuit

1st law of Heat Transfer

Oven Differential Equation Matrix

Steady State Convection and Radiation

Figure 5(a): Transient Oven Response

Oven Air Temperature

Testing Results

Will put excel plot here

Testing by using an analog air thermometer taking measurements at 2 minute intervals. Will do several runs and to create a general trend that will be compared to theoretical values

Figure(s) 6() will go here.

Plastic holding Frame

• Frame moves plastic up to be heated then down to vacuum platen for forming

• The frame wanted to tip and bind inside the structural frame

• Bearing sliders had to be redesigned to prevent tipping and binding

• Weighs roughly 12 lbs Figure 7(c): Plastic holding frame clamped to a piece of acrylic

Figure 7(a): Visiting Japanese ME student Kyosuke Kurokawa assembling plastic holding frame

Figure 7(b): Bearing sliders

Plastic Analysis

Figure 8(b) Testing results plot

Figure 8(a) Transient Plastic Heating

1D Conductive Heat Transfer

Nodal Numerical Analysis

Resulting Plot

Plastic Results

Drive System

● Comprised of laser cut ABS, ½” aluminum driveshaft, DC motor, and coil springs

● Coil springs offset the weight of plastic frame reducing motor size

● Arms are glued together and interference fit onto drive shaft

Figure 9(a) Drive shaft and controls table

Figure 9(b) Laser cut ABS for drive arms

Drive System Analysis

● F is weight of frame, F=12lbf● T = F*L*cos(Ө)

Where L = 9” ; Ө = Ang Position● Worst case Ө = 23°● T = 99.4 in-lbf● This model assumes frictionless

bearings

Results● Measured with torque wrench on the

end of drive shaft

Tactual = 110 in-lbf

Figure 10 GIF of torque wrench testing drive system

Vacuum System

● Vacuum below part allows pressure of atmosphere to form heated material onto mold

● Plastic must seal to vacuum platen

● With 1mm plastic 3.5 inHg vacuum will form part

● High CFM pulls heated plastic over platen more efficentily than low CFM with high vacuum pressure.

Figure 11(a): Part to be formed laying on vacuum platen

Figure 11(b): Part formed over using 1mm ABS sheet

Overall System

Comment: GIF of system -->

Figure 12 complete system in operation (GIF)

Special Thanks to:

• Sponsor:Mark Lawrence|CalSci Inc. • Professor: Dr. Vogt• Assistant professor:

Efrain Garcia• Professor: Dr. Zhou• James Mullinix (SDSU)

Questions?

ReferencesRosato, Donald, Ph.D, Marlene Rosato, PE, and Nich

Schott, Ph.D. "3G Thermoforming." Plastics Institute of America: Plastics Engineering, Manufacturing & Data Handbook. By Dominick Rosato. Vol. 1. Boston: Kluwer, 2002. 886-977. Print.

Ogorkiewcz, R. M., ed. Engineering Properties of Thermoplastics. Bristol: Wiley-Interscience, 1970. Print.

Mizra, Sohail. "Overview of Industrial Motor Control Systems." Design Support. Maxim Integrated, May 2010. Web. 15 Feb. 2016.

“Vacuum Forming Tutorial.” Massachusetts Institute of Technology, Web. 15 Feb. 2016.

Taylor, C. A., Delorenzi, H. G. and Kazmer, D. O. (1992), “Experimental and numerical investigations of the vacuum-forming process”. Polym Eng Sci, 32: 1163–1173. doi: 10.1002/pen.760321613