Task: DDM Chassis Construction Techniques
Background info: Create a structural chassis using DDM techniques that will minimize the use of tooling/tooling changes. These techniques should use FDM printing in some aspect of it's manufacturing
Objectives: This design is intended to be used to test chassis construction techniques, and manufacturing techniques. The final design of this mule should be/have the following.
- Be quick to design/manufacture
- Use RFEV drivetrain (unless another drivetrain is chosen by 07/20/2015)
- Use T-Bird suspension components (excluding metallic subframes)
- Use DDM Subframes
- Have easy to replace modules
- Be able to survive road loads, but not necessarily crash loads
- Have a wheelbase of approximately 105”
- Have a trackwidth of approximately 60”
- Ideas or concepts that can be used to create a structurally sound chassis, that is manufactured using DDM technologies
Will you help with this task?
A possibility of spring loaded bracketing throughout the chassis. A benefit will include vibration dampening throughout the body resulting in material longevity.
The DDM structure should be a lightweight hollow framework that creates the shape of the vehicle and includes reinforcing and stiffening shapes such as ribs and webs. Single extrusion paths of large scale FDM material should be used in most places to minimize weight and an average thickness of 1" between walls to form a sandwich structure that will be filled with a low density expanding foam. Carbon fabric will then be placed over the DDM material using spray tack adhesive and layered depending on the thickness necessary as determined by a test verified finite element model. Only the required amount of carbon should be used, but this could be as much as 10 layers in areas of high stress such as suspension mounting points. It would taper to an average of one or two layers of fabric over most of the surfaces. The structure will then be envelope bagged with a vacuum bag and properly ported after placing infusion flow mesh and flow channel materials optimally as determined by an infusion design software such as Polyworx or PAM-RTM. A room temperature infusion will be performed to fill the fabric with epoxy resin, it will also penetrate the surface texture of the DDM material and fill voids to improve interlayer adhesion. The closed cell foam will prevent resin from filling the large cavities of the hollow DDM structure. After removal of the vacuum bags, flow mesh and release film, the epoxy may require abrasive smoothing in some areas where large winkles or bridging of the bagging material had occurred before overspraying with a Line-X textured rubber coating to provide a finished look and feel.
The first set of three images here show how to mount the T-bird front suspension using inter-changable stainless steel brackets. A hexagonal cross section frame rail is printable due to the 45-degree overhang limit and these may be supported by single bead sections that are cut away after printing. This is illustrated in the SECTION A and FRONT views with light lines. The hexagonal sections will widen and curve into the tub or bulkhead to enable distribution of loads. Cross-members will also widen at the intersections with the rails and curve to form large fillets. The sections will all be 0.22 single bead hollow forms which will be foam filled, over-wrapped with carbon fabric and resin infused. Sizing to take all loads will be accommodated by adding layers of carbon fabric. This enables tool-less composite manufacture, but also the possibility of shapes that could not be made with conventional tooling. Brackets may be attached by match drilling and bolting through completed rails, or placed onto the printed preform, laid-up over with fabric and embedded into the composite. The first approach is allows them to be serviced and re-used, the second is lighter weight and higher stiffness.
The bottom images show how this concept evolved and how the rail chassis concept could apply to a body on frame design approach. The chassis structure would be the same across many models and the various over-bodies could be printed as part of the chassis. Alternatively, the body could be fastened to an all composite rolling chassis so that it could be quickly and easily changed. The chassis itself would contain the primary structure of the crush tubes and rollover protection for crash performance while the body would be secondary structure that would only need to be self-supporting through driving loads. This may help allow certification of many vehicle styles on a single base platform by similarity.
A 3D printed upper chassis wrapped & strengthened by materials such as carbon fiber would provide an excellent solution, Consider the shock/strut support already in production by Xtreme Racing.