Automotive Design Guidelines for Composite Manufacturing

Techniques

Andy Rich

Background

42 kg body on 200kg chassis695 kg car

68 kg BIW

300 kg car 900 kg car

Consulier 1990

890 kg complete carGlass Fibre Monocoque$60,000

Mosler MT900

900 kg carAll- Carbon Fiber$180,000

Déjà vu all over again

The Problem:

How to get modern composites to work cost-effectively as both primary structure and/or class-A surfaces.

Do Not:

Repeat the same mistakes that were done in the past.

10 Common Mistakes

1. Part thickness needs to be uniform.2. Component fiber layers must be quasi-isotropic.3. All fiber layers need to be stitched or woven.4. Every layer needs to be carbon. 5. Ribs add stiffness, and carefully considered holes in

the inner panels will reduce weight.6. Assume that it is possible to make any shape.7. Assume that there will always be a lot of scrap and

nothing can be done about it.8. Allow the number of subcomponent pre-forms to

escalate out of control. Assembly of the final part wet-out/ cure stage should be as simple as possible.

9. Part integration can go too far; there is an inherent limit to the advantages of part integration.

10.Assume suppliers already make all possible fiber architectures, and you can already buy what you need out of existing catalogs.

10 Manufacturing Principles to Design in Engineered Composites-

1. Use nest-able shapes – Whenever possible: Rectangles and trapezoids

2. Consider the materials like they were Gold; - not to be wasted.

3. Consider drape, and roll-width as design restrictions.4. Consider the pre-forming function to be as important, if

not more important, than the final wet-out/ cure station.5. Use fibers only where needed; use anisotropy as an

advantage.6. Not every layer needs to be carbon. 7. Final part thickness does not need to be uniform; it may

incorporate overlaps. Consider single sided tooling. - at least in lower volumes.

8. Find a way to incorporate scrap into the finished part or final assembly. Plan early to utilize scrap.

9. Minimize the number of subcomponent pre-forms necessary.

10.Work with suppliers to provide pre-layered multi-material stacks.

Most Important Manufacturing Principles:Multiple Processes for Multiple Applications1. RTM should be used where it works the best,

pre-pregs can be used where it makes the most sense, but braiding, and wet-compression, and thermoplastics will make sense in other applications.

2. Plan for disposable consumption of certain waste materials needed for the removal of air /voids.

3. Composite manufacturing systems in which a thermoset resin wets out a dry pre-form, will always benefit from having off-part edges. STOP TRYING TO MAKE NET SHAPE PARTS.

#1 Part Thickness1. Part thickness DOES NOT need to be uniform. This

is especially true for structural components.

In fact, as layers are built up, if one layer cannot be contiguous, it is far better to overlap the abutting pre-forms than to create a butt joint, which will inevitably be a weakness in the structure.

#2. All Composites DO NOT need to be Isotropic, or “Act like” quasi-isotropic materials

0º 90º

Laminates need to be balanced about the neutral axis, but that does not mean you need to add extra layers to create quasi-isotropic properties with respect to X and Y

#3 & 4 – All layers do not need to be the same weave, or even the same fibers

8 layers Innegra 4/4 Innegra/Carbon

Innegra S Carbon Fiber

8 layers Carbon6/2 Innegra/carbon

#3 & 4 – All layers do not need to be the same weave, or even the same fibers

8 layers Biomid 4/4 Biomid/Carbon

Biomid Cellulosic Fiber Carbon Fiber

8 layers Carbon6/2 Biomid/carbon

5a Ribs are not needed to add stiffness

Ribs add stiffness to sheet metal, but just make composites more complicated and difficult to mold5b - Holes in the inner panels will not save much weight and will significantly increase manufacturing complications which will introduce flaws.5c - Minimum Radius of the panels edges will always tend to introduce flaws, if too tight.

Rule #5 – Stop Making Your Own Life Difficult

6 - Choose shapes carefullyConsider the drape of the fabric, and the width of the rolls, as well as the darts and overlaps that will be necessary.

Think in terms of Nesting Shapes

Maximize material usage

6 - Choose shapes carefully

Think in Terms of Draping Fabrics

7 – Consider the Incorporation of Scrap and Re-GrindMany steps may be taken to minimize scrap

by design. However, assume that you will have between 5% and 10% scrap rates depending on the processes used, and there are several uses for regrind - plan for it. 1. Tooling2. Edge filling3. Filleting4. Bonding5. Hiding read-through6. Non-critical components7. Impact Absorption

8 – Minimize the number of parts, but, . . .

Part Integration can go too far

9 – Minimize the number of subcomponent pre-forms;

A 3-minute wet-out cycle isn’t worth much if it takes 30 minutes to load the tool with 90 pre-forms

10 – Work with Suppliers to Minimize System Costs => Stop thinking in Euros/Kg. or $/lb. 1. Weavers

2. Multiple Fiber Suppliers 3. Resin manufacturers & pre-preg suppliers4. Pre-Form Machinery Suppliers5. Reclaiming and Recycling Suppliers6. FEA Experts7. Crash and Repair-ability Experts8. Process Consultants

1.Pre-Form Machinery Suppliers2.Reclaiming and Recycling Strategies3.FEA Expertise4.Crash and Repair-ability 5.Process Consultancy

We can provide impartial advice:

1. Composite Vehicle Design 2. CAD Design for Composites3. Drape and Formability of Fabrics4. Pre-Form Machinery 5. Assembly Strategies and Part Count6. Recycling Strategies7. FEA Expertise8. Crash and Repair-ability 9. Process Choices and Applicability10.Achieving Class-A surface Finish

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