Materials & Manufacturing update

Owned by Sheila Afros
Last updated: May 01, 2021
8 min read

Manufacturing detailed steps

Seats Cushions:

Materials:

·        Neoprene 1/2 in thickness foam

·        Polyethylene open cell high density 1 in foam

·        Meidong Nano Tape Double Sided Super High Viscosity Tape Roll or Polystyrene Foam Insulation 78 Spray Adhesive

·        Scissors

·        2 part epoxy (DP-420)

·        3M SJ3550 Dual Lock Recloseable Fastener

Manufacturing:

  1. Using the 2 part epoxy (DP-420) (making sure to pull the neoprene over the edges of the seat back) adhere to seat back and seat pan

  2. Adhere the polyethylene closed cell to the neoprene with the tape/spray (the foam will need to be pressed down with a weight and left for 1-3 hours to dry). The tape/spray should be applied to both sides of the cushioning.

  3. Place the open cell on the areas that need to be padded based on the mockup (again use the tape/cement to secure the soft open cell to the closed cell)

  4. The contouring of the foam will need a jig

Seat Pan:

Materials:

·        Carbon fiber flat panel from the flat panel (2 layer carbon fiber each side)

·        DP-420 Black

·        Neoprene foam

·        Polyethylene foam

·        ¾ inch divinycell foam

Manufacturing:

  1. Infusion process using the flat panel (glass sheet will work)

  2. Cut from the panel into the shape needed with cnc

  3. Cut foam to fit inside the seatback (please see assembly doc)

  4. Adhere foam together with the tape/spray (will need to be clamped down)

  5. After the foam has uncompressed adhere it to the seat back with DP-420 (the carbon fiber will need to be cleaned with acetone and sandpaper before using the adhesive)

  6. Adhere extra support to the foam with the tape/spray (side cushioning for butt and legs)

  7. Make sure the edges are covered (either with tape or foam so there is no carbon fiber to person contact)

Seat back:

Materials:

·        Carbon fiber 6.2oz x 50” Twill Carbon

·        MDF mold from wood

·        Cnc routed for the cuts (cnc for the mold and the cutting of the hole for the inserts)

·        Peel/wax

·        Divinycell foam core (1/4 in)

·        Tacky tape

·        Vacuum bag

·        Resin

·        Neoprene foam

·        Polyethylene foam

·        90 degree brackets

·        Rivets or Fujilok

Manufacturing:

  1. Take CAD mold and CNC them

  2. Line mold with wax (anti-peeler)

  3. Take the carbon fiber (2 layers) take the divinycell foam and poke holes about an inch apart then place another 2 layers of carbon fiber on top and cut a section of Kevlar to place in the shoulder region

  4. Set up vacuum and resin infuse

  5. Remove from the mold

  6. Cut foam to fit inside the seatback (please see assembly doc)

  7. Adhere foam together with the tape/spray (will need to be clamped down)

  8. After the foam has uncompressed adhere it to the seat back with DP-420 (the carbon fiber will need to be cleaned with acetone and sandpaper before using the adhesive)

  9. Adhere extra support to the foam with the tape/spray (side cushioning, bolsters, lumbar, and headrest)

10.   The seatback will be attached to the chassis using 90 degree brackets and rivets (drill through the C bulkhead and attach to the chassis)

Seat Supports:

Materials:

·        Carbon fiber flat panel

·        DP-420

·        Foam mold

·        Divinycell foam core (3/4 inch)

·        90 degree brackets

·        Highlock or fujilock or rivets

·        Filet support marterial (to support the 90 degree panel)

·        Rivets and washers

Manufacturing:

  1. Use the foam mold with 90 degree edge to manufacture the panel

  2. Cut holes for chassis (using a machine)

  3. Adhere all flat panels to each other using DP-420

  4. Attach to the bottom panel using DP-420

  5. Attach rivets to the seat pan and the edge of the seat supports in a single lap joint

Ballast:

Materials:

·        Carbon fiber flat panels (1 layer of cf per side for the ballast)

·        DP-420 for cf to cf adhesive

·        90 degree angle brackets

·        Locks

·        Highlock or fujilock or rivets

·        SmartStraps 14 ft. 1500 lb RatchetX Ratchet Tie Down

Manufacturing:

  1. Cut from the flat panel into sections (see CAD for dimensions)

  2. Adhere all cf panels with DP-420

  3. Drill holes in the side panel and in the lid

  4. Align 90 degree brackets and attach to chassis

  5. Adhere lock onto the ballast lid

Inserts:

·        3D printer

·        PC-ABS plastic with solid fill and standard should be ok

Manufacturing:

  1. Take mold from CAD

  2. Put into machine

 

Seats Fastening Research and Proposal

OVERVIEW

The purpose of this document is to serve as documentation for the decision making process behind the choice of fasteners and how the seats would be installed in MS XIV

CONTEXT

It is important to note that this was not originally considered in the design / manufacturing of the seats for MS XIV. This was due to an oversight in looking through the regulations, not having been fully aware of specific best practices and changes to the bottom panel (which was integral to the original plan)

Original Plan

The original plan was to have the seats (and ballast) attach solely via adhesives. 

For the seatback, the rear of the seat would be attached to the bulkheads they would be laying on (either the B Panel for the Front Seat, or C Panel for the Rear Seat)

For the seat pan, they would be attached along the bottom edge that interfaces with the bottom panel as well as the edge of the seat pan supports.

The seat pan supports would be attached along the bottom edge that interfaces with the bottom panel

Regulations

While regulations within the Seats and Ballast specific sections were met, there were regulations within the fastener section that affected the seats and ballast. They pertained to how certain components (designated “critical areas”) could not be solely attached via adhesives.

Thus, our previous fastening plan was in direct violation of this regulation and had to be modified.

Best Practices

When coming up with designs it is important to keep in mind best practices or guidelines regarding components, fasteners or designs in general. In this case, with adhesives, it would be best to adhere to design guidelines regarding these in order for them to perform their function (securing the seat) to the best of its ability.

When designing a joint using adhesives, it is best to minimize any tensile loading as it will cause cleavage stress to develop. This is “highly unfavourable for adhesive bonding” [Remove Stress from Adhesive Joints for a Stronger Bond]. 

With the previous fastening plan, in the event of any impact from the rear (e.g. a rear collision), some of the adhesive joints (such as the seatback to the bulkhead) would be under a tensile loading as the seatback is trying to pull away from the bulkhead.

Thus, it was evident that either a new geometry for these adhesive joints would need to be made, or another fastening method (besides adhesives) should also be utilized in order to prevent high levels of cleavage stress developing within the adhesive joint.

Note: While implementing other design guidelines for adhesives (such as increasing the bond area between for the adhesive) could minimize the effect of cleavage stress, this would still be putting the adhesive in its least favourable loading condition and may cause a larger bonding area to be required (increasing material usage)

 

 

Manufacturing Changes

Due to manufacturing constraints / issues, the bottom panel would no longer have a layer of core material. This greatly reduces the load bearing properties of the bottom panel. Read this confluence page on Composites for more background info about this: Basic Composites Knowledge  

Originally, the weight of the occupant would be transferred via the seat pan, to the seat pan supports and to the structural bottom panel. However, with the bottom panel no longer being structural, transferring the loading of the occupant’s weight onto this panel is risky and may result in failure of the panel.

Instead, transferring the loading of the occupant’s weight onto the chassis or another structural member is a much safer avenue to pursue. In addition, to provide a further safety factor a new structural bottom panel will be laid over the chassis tubes. This will help take some of the loading from the occupant’s weight and transfer loading to the chassis.



Revised Plan

Based on the regulations, design for adhesive best practices and manufacturing changes, it was ultimately decided that an additional means of attaching the seats (likely fasteners) would be used. In addition, the seats would also have to be attached to structural members such as chassis tubes along with the previously chosen mounting points (e.g. bulkheads)

Front Seatback

In addition to being adhered to the B Panel Bulkhead, it was determined that the front seat back should be attached to the chassis tube that intersects near the shoulder level. 

This was chosen as it is easily accessible to the existing front seat design and it also provides an additional mounting point/area higher up on the seat. This helps prevent lateral movement of the seat and further fixes it in place

 

Seat Pan Supports (Front and Rear)

The seat pan supports will still remain adhered to the seat pan panel itself but instead of resting (and adhering) to the bottom panel, it would rest on top of the new structural bottom panel.

In addition, the seat pan supports will be attached to the anti-sub chassis tube via a bracket and fasteners and flanges will be added preferably to both the top and bottom to either increase bond area (attaching to new structural bottom panel) or to provide a surface for fasteners and the aforementioned reason (attaching to seat pan panel)



Seat Pan (Front and Rear)

The seat pan will largely remain unchanged, save for any mounting holes that may be needed to attach to the seat pan supports.



Rear Seatback

In addition to being adhered to the C Panel Bulkhead, it was determined that the front seat back should be attached to the chassis tube that intersects near the shoulder level. 

This was chosen as it is the most accessible chassis tube available for us to connect the rear seat to. That being said, the rear seat is curved at this height and this may pose some challenges to fastening. If needed design changes to the rear seatback may be done to overcome / mitigate this challenge.

FASTENING SOLUTIONS

This section will cover how various fastener types may be applied to help fasten the seatback, seat pan and seat pan supports.

The list of fastening solutions comes from this Confluence page: https://uwmidsun.atlassian.net/wiki/spaces/MECH/pages/2085257229  

In addition to this video: Assembly Solutions for Honeycomb Composite Panels: Surface Mounted Fasteners and Deform-nut Inserts

And finally this product: Composi-Lok® | Monogram Aerospace Fasteners | Composi Lok 

List of Fastening Solutions:

  • ASP (Adjustable Sustained Preload) Fastening System

    • Composi-Lok (seems to be a derivative of the ASP system)

  • Lockbolt Fasteners

    • May be known as the trade name “Hi-Lok”

  • Eddie-Bolt Fasteners

  • Embedded Fasteners

    • bigHead is one such example

  • Surface Mounted Fasteners

    • Note: Loading would still have to go through an adhesive, not sure if this is still considered an adhesive mounting method as per ASC regulations

  • Deform-Nut Inserts

  • Rivets

    • Based on the Confluence page however, it seems this would require special riveting equipment (not your standard rivet gun)



MILESTONES