Adhesive Curing Fixture

Designed by: Ethan Sobkowich, Yanshen Zhou, Winnie Lin

Supervised by: Tommy Tran

Design Review by: @Tommy Tran , @kevin bui
Date: March 27, 2021

Purpose: Fixture for preparing adhesive test specimens of similar sizes (25 mm x 100 mm x 1.6 mm)

Needs statement: There exists a need to create a fixture that can hold specimens in a stationary position for adhesive curing while being able to accurately create different specimen sizes.

Constraints:

• All three adhesive joints curing at the same time

• Constrained movement in three axis

Criteria:

• Maximize number of specimens that can cure at the same time

• Can be machined in-house

• Minimize time required to manufacture

• Maximize adjustability to different size

• Minimize costs for materials and manufacturing

The idea behind this design is to create a “tray” (Fig. 1 & 2) to constrain movement in the outer edges of the specimens. Multiple specimens can be cured at the same time in this tray. The spaces between each individual specimen will be separated with rectangular 3D printed jigs (Fig. 3 & 4) as well as the spaces between each adhesive joint on a specimen (Fig. 4). A flat board/weights will be placed on top of all specimens to add pressure.

Testing between:

• Steel to steel

• Composite to composite

• Steel to composite

Open

Open

Figure 7, seen below, is a side view of one test specimen, whose material may vary depending on the test. This is how they will be aligned in the jig. The rectangular jigs will be placed in the gap spaces.

*jig can be spring with boards on either side (will remove tolerance error)

Figure 8 is an example of how the jig will clamp the test specimen. The green planks are aligned as seen in Figure 9. The main edges will be placed on a flat board or table. Then, another flat board (like a piece of plywood for example) will be placed on top of the specimens and weights will be placed on top of the board to apply downwards pressure on the z-axis (purple). When the tray is full of specimens and brown rectangular jigs, seen in Figure 9, y-axis movement will be restricted due to the packing of specimens and jigs. A sliding board will be on the edge and a pipe clamp will apply inwards pressure on the x-axis. The idea is that the blue square-shaped pieces will ensure that the test pieces line up properly under this clamping force. It is possible that more thin brown square pieces may need to be added in the middle section to ensure adequate restriction on movement. Nine of these specimens must be lined up at once inside of this tray for proper usage.

Adhesive to be Used: 3M DP 420 and Henkel EA E-120HP (both epoxy adhesives)

For Epoxy:

• Parchment Paper

• Wax Paper

• Polyethylene sheeting (saran wrap)

• Mold-release compounds for epoxy

• PTFE Tape

Anti-Stick Solution Criteria Overview:

*ranked in order of most important to least important

1. Effectiveness

• how well the solution prevents the adhesive from sticking onto the fixture

2. Ease-of-Use

• how quickly the solution can be applied and removed from the fixture

3. Feasibility

• how easy is it to obtain the solution; is it widely available?

4. Affordability

• how much the solution costs

5. Maintenance

• how often does the solution need to be replaced on the fixture

6. Degree of Obtrusion

• How much the anti-stick solution will alter the dimensions of the fixture and specimen (how thick is the solution)

Table 1: Anti-stick Solution Comparison Chart

Results:

Parchment Paper = 41 pts, Wax Paper = 38 pts, Saran Wrap = 45 pts, PFTE Tape = 27 pts

In conclusion, Saran Wrap is the best anti-stick solution because it is the most effective and easy to use, a well as being thinner than all the rest of the materials.

Source: Best Tape for Epoxy Molds!  

one design matrix per step

Assembly Procedure 

All related CAD files are found here (MSXIV->Devlopment->Materials Testing-> Adhesive Curing Fixture): https://workbench.grabcad.com/workbench/projects/gcwijX10VhtEeZ8mtyGdmiV5BQItzO7K-9PXmyIs5vRPFL#/folder/10457511

Step 1: Printing

The pieces separate individual specimens and individual components within the specimen. 3D printing was chosen as the manufacturing method as they need to be thin (<1mm) to fit under the paces of the specimen.

Use this GrabCAD file tp print the pieces:

1. Use PrusaSlicer to print an array of support pieces on the tray. Two of the “30mm mid jig” pieces are required per specimen and three of the “separating jig” pieces are required between two specimens.

   1. You may need to change the dimensioning of the support beams to customize it to the dimension your specimen.

   2. Print according to the number of specimens that are cured.

2. Remove the printed pieces.

Table 2: Support Component Manufacturing Decision Matrix

*Feasibility for laser cutting is -1 because the Rapid Prototyping Centre does not machine parts that are thin enough for this application.

Step 2: Machining Cover

This component is placed on top of all the specimens after they are placed correctly. The purpose of this cover is to restrain joints with epoxy from lifting.

1. Measure and mark the area to be cut on the 3mm birch plywood. Ideally, each length and width should be 0.5cm less than the inner dimensions of the tray. For example, if the inner dimensions of the tray are 19cm by 24cm, then the dimensions cut from the plywood should be 18.5cm by 23.5cm.

2. Use a band saw in the design center machine shop to cut out measured dimensions.

Step 3: Laser Cut Tray

Laser cutting was chosen as the manufacturing method as it provides more cut precision when compared to manufacturing by hand. It is also faster.

1. Use AutoCAD to create layout of pieces that need to be laser cut. In total, this needs to include 4 copies of each component of the tray. There is an AutoCAD .dwg file on the GrabCAD- use this template as a base for your dimensions. Change accordingly so the fixture can cure the desired number of specimens.

   1. Ensure that your dimensions for the inner length and width of the tray is equal to the width of all the support pieces and the specimens.

   2. The idea behind this is to stack four 1/8 inch thick pieces of fiberboard to create a 1/2 inch tall tray. Ensure that each part in the .dwg file is quadrupled. Please minimize space taken up by the drawing (this minimizes cost).

   3. Minimize the area occupied by the pieces. This is because the 3D Print Centre charges per square foot.

   4. All vector cut lines should be 0.00 units line thickness.

2. Submit a laser cutting request: https://uwaterloo.ca/3d-print-centre/laser-cutting-request-form

   1. Turnaround time is 2-3 days.

3. Use wood glue to bond two copies of the same part.

   1. Apply a thin strip of wood glue along the entire piece.

   2. Clamp down both pairs of fiberboard pieces for curing. This takes 24 hours according to the glue manufacturer instructions.

   3. After the pairs of fiber board have fully cured, repeat steps a-b to bond the two pairs of fiberboard. This creates four stacked layers of fiberboard.

   4. After curing, use sand paper to sand off any excess glue.

   5. Note: it is important to cure the layers as aligned as possible to create a flat edge.

Table 3: Curing Tray Manufacturing Decision Matrix

3D printing such a large part would take a significant amount of time. It is also a simpler shape, so the complex structure capabilities of the 3D printer are not required.

Step 4: Anti-stick Solution

This is to prevent the epoxy from curing to the fixture. Ideally, we should aim for no epoxy bonding to the fixture.

Tray

1. Cover the inside of the tray with saran wrap

2. Press down on the inside edges and corners to try and flatten the wrap as much as possible

3. Trim excess saran wrap off the sides of the tray if needed

4. Tape down sides of saran wrap to the outside of the tray to prevent movement of the wrap

5. Place saran wrap on the flat surface where the curing fixture will sit. Tape down saran wrap to surface.

Spacing supports

1. Double wrap supports with saran wrap

2. Tape off loose ends 

Step 5: Placing Specimens in Place

This fixture is designed to restrain the curing specimens from movement in three axis. Proper placement of the support pieces and specimens are required to cure specimens properly.

1. Align first specimen in a corner with the longer side of the specimen touching the shorter side of the curing fixture.

2. Wedge a support fixture along the specimen to hold the individual pieces in place. Correct placement shown in fig. 5.

    

   Figure 5: The adhesive specimen is shown in blue. The support material is coloured in orange and labelled. They hold pieces on the same level in place.

3. Place three support pieces perpendicular to the first specimen at each joint to provide support for the next one (fig. 6). Continue placing specimens down until the tray is full or until you are satisfied with the number of specimens. If the tray is not full, wrap a flat piece of wood in saran wrap and place it flat against the last specimen. Put a weight behind the piece for support (i.e. a piece of steel, a block of MDF, a rock, etc.)
   
   

   Figure 6: Two specimens (blue) with support pieces (red) restraining movement at each joint.

4. Place a flat board on top of the tray and specimens. The flat board should also be wrapped in saran wrap. Place a weight on top of the board.

Bill of Materials

generally less walls of text. pictures explain for you, just use the right pictures.