Progress Update

WEEK 1: 13-20th May

  • Delegation of roles
  • Decision on work distribution
  • Settling of administrative deliverables

WEEK 2: 20-27th May

  • Mathematical modelling of folding mechanism
  • Research about possible materials

WEEK 3: 27-2nd June

  • Compare and contrast about different folding mechanisms and different materials
  • Decide on the structure and additional features of the lunchbox

WEEK 4: 3-9th June

  • Progress meeting 1

WEEK 5: 10-16th June

  • Finalised prototype design

WEEK 6: 17-23rd June

Monday, 17th June

  • 3D printed mould (to cast silicone in)
  • Duration of printing: ~13h in total
  • Settings used: 20% infill

Exploring print preview of lower mould

In the midst of printing upper mould (red)

In the midst of printing upper mould (red)

 

Tuesday, 18th June

  • Collected the printed moulds
  • Outcome: moulds are generally in good condition. However, there are areas for improvement which we will incorporate into our next round of printing:
    • The lower mould (black) had holes at the bottom which will cause the silicone to leak into
    • The fineness of the PLA material might not be watertight enough
    • The thickness of the groove (1mm) in the lower mould is not significant enough to make a visible impact on the silicone after casting

Black: lower mould, Red: upper mould

Close up of grooves for folding

Close up of grooves in the middle portion

  • Collected silicone mould rubber for casting moulding
  • Manufactured first prototype sample
  • Cast a sample of silicone to test its properties using Room Temperature Vulcanization (RTV)

Left: platinum catalyst (A), right: silicone rubber (B)

Equipment set up

  • 20g of material A and B were first mixed for 5 minutes in the mixing bowl
  • Following which, the mixture was transferred to the red mould
  • The sample was then left in the open for ~6h to cast.
  • Result: clear, flexible and smooth silicone rubber was obtained

Front view of the silicone sample

Side view of the silicone sample

Testing the flexibility of the silicone sample

 

Wednesday, 19th June

  • Progress Meeting 2
  • 3D printed moulds of 2mm and 1mm thickness to create prototype and gauge our preferred thickness for the lunchbox, as well as to test the preferred groove thickness.

2mm thickness

1mm thickness


Flat plate to seal

  • Purchased acrylic spray, rods, and syringes
    • Acrylic spray was intended to smoothen out the surface of the moulds by spraying several layers
    • Acrylic spray was also intended to patch any holes in the mould due to printing defect
    • However, we soon realized that spraying acrylic did not help much as we tested it on the previous black mould and the effect was negligible

Acrylic spray we used

Spraying the acrylic on the black mould

Black mould after spraying and letting dry. Layer was inhomogenous and still rough

  • Sourcing for polypropylene plates
  • Sourcing for adhesives to stick the pp plates to the silicone

 

  • Attempted to iron the PLA surface (3D printed material) with a glass slide heated to 75 degrees but to no avail

 

Thursday, 20th June

  • Collected the 3D printed samples

Left: 2mm thick plate (red) with 0.5mm and 1mm scoring (grooves), Right: flat plate (black) used for sealing

  • The silicone cast is then poured into the red plate and will then be covered by the flat plate
  • The four holes at the corner are then used to align the plates together by inserting a piece of rod at each corner
  • Note that 1mm thick plate was not printed due to resource limitation
  • Silicone casting was then obtained after letting it sit for ~6h

First attempt of silicone casting on plate moulds. Presence of many air bubbles.

Second attempt, after spraying the moulds with acrylic. Still presence of many air bubbles.

 

  • 3D printed a mini-box that is used to test out actual prototype, except that it is scaled down to save cost and time. Once the main mechanism works, we will then print in full scale.
  • Also 3D printed the 1mm thick plate that was previously not printed to test the thickness as well
  • Duration for mini-box: ~13h
  • Settings: 40% infill, upper/lower/shell layer on 5/5/3

Design for lower mould with grooves

Design for upper mould. Holes within cavity are for leakage compensation

  • Plan for next week:
    • Cast 1mm plate
    • Cast minibox
    • Source for acrylic mould from external vendor (acrylic mould preferred over 3D-printed ones)
    • Source for pp plates
    • Purchase sil-poxy as the adhesive
    • Stock up on sandpaper and gloves

 

WEEK 7: 24 – 30th JUNE

Monday, 24th June

  • Collected the 3D prints from the lab: 1x 1mm plate, 1x mini-box lower mould, 1x mini-box upper mould

Lower mould (with grooves)

Upper mould (flipped around)

1mm plate

  • Smoothed out the edges of the rough sides of the moulds with penknife
  • Sprayed the surface of the prints with one coat of acrylic

 

Bottom mould before smoothing

Mould after smoothing with penknife

  • Casted the 1mm plate (w/o sealing plate)
    • No air bubbles
    • Scrape out the excess layer and let it dry

1mm with silicone cast

  • Casted the minibox
  • Used rods and syringes to assist in improved casting

Rods used to put the lower and upper mould in line and place

Syringes used to insert silicone cast into the sides of the minibox

  • Sourcing updates:
    • Acyrlic – no response from manufacturers and companies
    • Pp plates – pending reply from monotaro.sg
    • Metal – asking Mr. Abdul Rahman for advise

 

Tuesday, 25th June

  • Obtained the silicone casting from the mould: 1mm and mini-box
  • Conclusion:
    • Acrylic spray does not make the surface smooth
    • Either we have to source for another spray that is silicone-phobic, or we will need to sand the surface of the mould
    • We decided to sand the surface of the mould for future printing

Initial prototype of the minibox (2mm thickness)

1mm thick silicone plate

 

  • Due to the flaws of the previous design – that is, the silicone casting will be stuck to the mould due to obstruction from the holes, a redesign was called

Updated design of the upper mould

Lower mould remains unchanged

  • Decided to reduce thickness of the mini-box from 2mm to 1.5mm for future printing after taking into account the overall thickness of the collapsed lunchbox after attaching the pp plates
  • Placed orders for adhesives from Amazon and pp plates from Monotaro
    • Adhesives arriving this Friday
    • Pp plates arriving this Friday (pending confirmation from supplier)
  • Headed down to mechanical workshop to discuss potential of printing 3D metal moulds
    • Conclusion: the size of metal printing allowed is not big enough to accommodate for our size of lunch box. Hence, we will stick to 3D printing the mould and sanding
    • Also obtained some sandpaper from the Mechanical Workshop to assist in sanding
  • Printed the new upper mould as well as the lid mould

 

Wednesday, 26th June

  • Collected the various 3D prints and sanded the contact surfaces
  • Sanding the surface produced a much smoother surface which will assist us in casting later
  • Concluded that sanding is our preferred method over spraying acrylic

Upper mould after sanding (top view)

Upper mould after sanding (bottom view)

 

Bottom mould after sanding (top view)

Bottom mould after sanding (bottom view)

 

Thursday, 27th June

  • Casted the silicone mini-box in the morning
  • Removed the casting at night, obtaining our second prototype

 

The upper mould’s surface broke off due to insufficient support in its structure

After removing the mould, the silicone casting was taken out

Second prototype of mini-box

Second prototype of mini-box (ctd’)

From left to right: first prototype (2mm thickness), second prototype (1.5mm thickness) and mould

Folding mechanism of the mini-box

 

Friday, 28th June

  • Sil-poxy adhesive arrived
  • Printed a new design for the mini-box after considering the difficulty in removing the mould to obtain the silicone casting of the minibox
  • L-shaped sides and grooves are for ease of removing mould to obtain casting.
  • Settings used: 30% infill, 5/5/4 upper/lower/shell, Primary Layer thickness 0.15mm

Design of the new mould for the mini-box (expanded view)

Design of the new mould for the mini-box (assembled view)

 

Saturday, 29th June

  • Finalised the tentative design of the lid
  • The lid is split into three parts:
    • Left PLA component (in grey)
    • Right PLA component (in grey)
    • Middle silicone casting (transparent, below)

Current design of the lid (front view)

Current design of the lid (bottom view). The lighter shade of gray represents the cavity to attach the silicone casting in.

  • Printed the PLA component of the lid

The PLA component of the lid attached to the mini-box (1.5mm thickness). Note that the silicone component has not been attached to the PLA component yet.

  • We then casted the silicone component of the lid for the mini-box – the hinges fit perfectly on top of the silicone mini-box and also fit in the two PLA parts.

Silicone component of the lid

  • The two parts of the lid are then connected via silicone casting in the middle such that when folded, the lid is watertight and takes up less space.

Folding capabilities of the lid. The two PLA components are connected via the silicone casting glued in the middle (sil-poxy was used as the adhesive).

Folded view (side view)

Folded view (front view)

Folding mechanism of the lid

 

Sunday, 30th June

  • Tested the adhesive, sil-poxy on different combinations of surfaces
    • Silicone, in general, does not adhere well to other surfaces using sil-poxy as an adhesive. Even after spraying acrylic, it did not work
    • Silicone-PLA was moderately strong but peelable
    • Silicone-Polypropylene did not adhere

 

Week 8: 1st – 7th July

Monday, 1st July

  • Collected the 3D print of the new mould design
  • Sanded down relevant surfaces and hinges to ensure that they fit the holes

Mould for mini-box (expanded)

Mould for mini-box (assembled view). The spacing between the exterior and the interior allows for a silicone casting of 1.5mm thick box.

  • Continued testing different combination of surfaces for epoxy
    • Silicone – PET: Slightly OK
    • Silicone – Polypropylene (tupperware box surface): Does not adhere
  • Conclusion: sil-poxy is not very effective in bonding silicone to other materials.
  • Considering using epoxy and PET plates rather than sil-poxy and PP plates.

 

Tuesday, 2nd July

  • Progress meeting feedback:
    • Can consider pouring hot water on silicone mini-box to demonstrate thermal capabilities both chemically and physically
  • Assembled the most recent mould and plugged in any holes to ensure that the silicone casting does not leak out during casting using masking tape. The mould was the secured using rubber bands to ensure watertightness between the two L-plates at the sides
  • Sanded the relevant surfaces of the upper and lower mould for smoother surfaces
  • Casted the new mini-box using the new mould design

Compared to the previous designs, the current mould design enables our mini-box base to be exposed to air, allowing for a smoother base surface

Securing the casting using rubber bands and masking tapes

  • Polypropylene (pp) plates from Monotaro.sg arrived
  • A small piece was cut and glued to casted silicone to test the adhesive strength between pp and silicone surfaced

 

Wednesday, 3rd July

  • Removed the silicone mini-box cast from the mould
  • Obtained the silicone mini-box
  • Conclusion: Pp plates do not adhere to silicone using the adhesive
  • Plan: Test other methods of gluing
    • Sandwich method
    • Rivet method
  • Not going with PET plates because they have low temperature tolerance

The current design allows for easier removal of the mould as compared to previous ones

Casting was removed relatively easily

Casted mini-box (top view)

Casted mini-box

Casted mini-box (downside up – the clear layer is the base)

 

Thursday, 4th July

  • As most adhesives used were unable to glue pp plates to silicone, a revamp of the current design was called for
  • Future plans:
    • Redesign the current mould design to be 5 pieces instead of 2 L-shaped pieces
    • Source for an adhesive that works
    • Otherwise, revamp the current design and implement a caveat or sandwich method to encompass the pp plates within the silicone without relying on adhesives

 

Friday, 5th July

  • Found and bought several other sources of adhesives that will hopefully stick pp to silicone: epoxy and silicone sealant

 

Week 9: 8th – 14th July

Monday, 8th July

  • As the adhesive did not work, we decided to go with the caveat and sandwich method, as illustrated below:

Box design. The white part represents the silicone while the red color part represents the pp plates. The short side refers to the side with the sliding piece and three pieces of triangular pp plates while the longer side refers to the side with two pieces of rectangular pp plates.

Redesign for bottom layer

Redesign for short side

Redesign for long side

 

  • With reference to the box design above, we decided to go with the method of casting one side one at a time, then gluing everything together with silicone to form the box
  • We will first cast a layer of silicone on the short, long and bottom side (refer above)
  • The resultant cast will then consist of depressions to insert the corresponding pp plates, as shown below:

Short side silicone cast

Long side silicone cast

 

Tuesday, 9th July

  • The pp plates were then cut accordingly and inserted into the depressions of the cast. Furthermore, small holes were punched into the pp plates for increased contact area (caveat method) between the first and second layer of silicone to “sandwich” the pp plates between:

Silicone cast of long and short side fitted with pp plates. Note that the design allows for an additional layer of silicone to be filled on top of the pp plates such that the height would just reach the perimeter height of the cast.

Left: after punching holes, Right: before punching holes

 

  • The second layer of silicone was then castes on top of the pp plates, and the resultant product is as illustrated below:

Short side folding mechanism

Long side folding mechanism

 

  • We realised that the first cast was not tall enough for the second layer to be casted, hence we re-printed the mould to be slightly taller than the previous one
  • Also re-casted the first layer for the bottom base because the previous one failed

 

Wednesday, 10th July

  • 3D printed the same designs except at a higher height to accommodate for the second layer of silicone casting
  • The process of building the prototype will therefore be as follows:
    1. Cast the first layer of silicone on the mould with grooves
    2. After casting, fill in the pp plates in the depression at their respective slots
    3. Cast a second layer of silicone on top of the pp plates
    4. After casting, the pp plates will then be sandwiched between both casts

From top to bottom (long side): first mould, second mould, silicone cast after first mould

From top to bottom (short side): first mould, second mould, silicone cast after first mould

The cast is then placed in the second mould and pp plates are then inserted in the grooves of the cast. A second layer of casting will then be applied on top of the current casting to sandwich the pp plates

 

 

Thursday, 11th July

  • Printed the bottom layer of the mould
  • Printed the second bottom layer of the mould

 

Friday, 12th July

  • Purchased more silicone for casting

 

Week 10: 15th – 21st July

Monday, 15th July

  • Connected the long sides and short sides together using silicone as a casting glue. The general perimeter of the prototype for the lunchbox is thus done.

Prototype of the lunchbox perimeter

Folding mechanism of the current prototype of the box

  • Subsequent plans:
    • Cast the bottom layer of the lunchbox –> Insert the pp plates inside the first cast layer –> cast a second layer for the bottom layer of the lunchbox whilst connecting it to the perimeter shown above
    • 3D print the two parts of the lid and cast the flexible middle part on the lid
    • Combine the parts into one full lunchbox
    • Laser cut the pp plates

 

Tuesday, 16th July

  • Progress meeting
  • Collected the 3D printed bottom piece (first and second layer mould for the bottom piece of the lunchbox)
  • Designed the .DXF file used for laser cutting tomorrow

.DXF file used for laser cutting

 

Wednesday, 17th July

  • Laser cut the pp plates

In the process of laser cutting pp plates

Pp plates after laser cutting. Corners are smooth and holes are consistent.

 

  • Collected the remaining 3D printed pieces:

Top: mould for casting the connecting piece for the lid
Bottom: support structures for connecting the long and short sides of the lunch box

  • Casted the remaining pieces so that we can connect all the pieces together to create the lunchbox

 

Thursday, 18th July

  • Purchased two more pp plates in view of the need to laser cut more
  • Planning to outsource 3D printing for the final product

 

Week 11: 22nd – 28th July

Wednesday, 24th July 

  • Casted the bottom piece

Casting of the bottom piece (first and second layer)

  • Casted the connecting piece for the lid

The lid is represented by the pink component shown above. The silicone in the middle allows for flexibility to fold the lid into a half.

Folding capabilities of the lid

  • Combined the bottom to the perimeter from the previous prototype to obtain the full box (refer to 15th & 17th July)


First prototype of the lunchbox

  • Tested the folding properties of the lunchbox (shown below)

Lunchbox folds properly. The thickness after folding is as shown in the video.

 

Week 12: 29th July – 4th August

Monday, 29th July

  • Casted a second prototype of the lunchbox using a three-step sequence:
    1. The first layer of silicone is casted as per usual
    2. The pp plate is then pressed down using weights, and a thin layer of silicone is applied to the pp plate.
    3. After approximately 2h of casting, the remaining silicone is then applied to the mixture to ‘sandwich’ it and left to cast.
  • The reason for the additional step (2) is to ensure that the plate sticks to the bottom of the first cast. This is because we faced a problem from the previous prototype whereby if we poured the silicone straight into the pp plate, the plate will float atop the silicone due to lower density which then eventually results in an uneven casting and improper sandwiching and riveting. Furthermore, the improper sandwiching also results in a thicker wall than we envisioned.

Final prototype of the box (without the lid)

  • Also casted a second prototype of the lid as the grooves for the previous design was not deep enough to encase the box perimeter. As shown below, the grooves are significantly deeper for better watertightness.

Final prototype of the lid

  • Combined both to obtain the final prototype of the lunchbox

Our final prototype of the lunchbox