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Answers provided by Antonio Miravete on Materials and Manufacturing

Daniel_Melo's picture

- Are we more restricted in the choice of angle with the dry ply, from a manufacturing point of view and cost? For instance with dry ply can we easily ask for a [22/30/45] laminate? Wouldn’t it be more expensive as the demand is more oriented on [0/90/45/-45]? Is it more easier with automated fiber placement for instance?

IN HAND LAY-UP PROCESSES, THERE IS NO DIFFERENCE BETWEEN DRY PLY AND PREPREG IN TERMS OF FIBER ANGLE RESTRICTIONS; IN BOTH CASES UNIDRECTIONAL PLIES (PREPREGS) AND UNIDIRECTIONAL FABRICS (DRY PLY) MAY BE PLACED OVER THE MOLD IN ANY ORIENTATION. IN AUTOMATED PROCESSES, BOTH, PREPREGS AND DRY FABRICS MAY BE ORIENTED IN ANY DIRECTION, AS WELL. TALKING ABOUT COST, DRY FABRICS ARE LESS EXPENSIVE THAN PREPREGS, ON THE OTHER HAND PREPREGS HAVE LESS POROSITY AND HIGHER FIBER FRACTION THAN DRY PLY, AND THEREFORE HIGHER PERFORMANCE.

- Hand made process gives worse property, why is that? Is it because the angle is not obtained with accuracy?

AUTOMATED PROCESSES ALLOW FINE PART-THICKNESS CONTROL AND CAN ORIENT THE PLIES MORE ACCURATELY THAN PEOPLE CAN, SO PART QUALITY IMPROVES.

- In the case of BMW i3, why the drive module has not been chosen to be made out of composites?

ONE REASON MAY BE THAT IN FRONT AND REAR COLLISIONS, CRASH-ACTIVE ALUMINUM STRUCTURES ARE VERY EFFICIENT; ACTUALY THE FRONT AND REAR ALUMINUM SECTIONS OF THE DRIVE MODULE ABSORB A LARGE PROPORTION OF THE ENERGY GENERATED. I SUSPECT THAT THE CRASH ANALYSES/TESTS GAVE THE BEST RESULTS WHEN USING A SINGLE ALUMINUM PART CONNECTING FRONT AND REAR SECTIONS. ALUMINUM MAY ALSO BE COST EFFICIENT VERSUS CARBON IN THIS PARTICULAR CASE AND HEAVIER WEIGHT IN THE DRIVE MODULE IS NOT BAD SINCE THE CENTER OF GRAVITY SHOULD BE AS LOW AS POSSIBLE TO INCREASE STABILITY WHEN THE CAR IS TAKING A CURVE.

- Can you explain why BMW has chosen to make several preformed subparts to make one final part? I suppose that the join of these different subparts is done while curing, consisting of a kind of seam, does it leads to a certain weakness on this area which is the limit between 2 subparts.

ONE REASON MAY BE THAT WE ARE DEALING WITH CARBON FIBER PARTS WITH HIGH COMPLEX GEOMETRIES. THEN, MAKING THE PREFORM OF THE WHOLE PIECE MAY NOT LEAVE THE FABRICS IN GOOD SHAPE. THEREFORE IT MAKES SENSE TO MAKE VARIOUS SUBPREFORMS, WHICH ARE EASIER TO DEAL WITH AND THEN PLACING THEM ON THE MOLD BEFORE INJECTION. SEAMS ARE AN ISSUE THAT NEEDS TO BE TAKEN ACCOUNT IN THE ANALYSIS/DESIGN PHASES. SUBPREFORM OVERLAPPING AND HIGH PRESSURE OF THE RESIN WILL HELP TO MAKE THE PART ROBUST IN THE SEAM AREAS.

- Why do we have so much different process on the same plane? Is there a kind of general guidance to associate a specific process with a typical part? For instance is it the size that mostly monitor the type of tool : small parts= hand layup, big parts = Automated lay up, very big part= infusion?

AS A RULE OF THUMB:
AEROSPACE SMALL PARTS: HAND LAY-UP
AEROSPACE LARGE FLAT PARTS: AUTOMATED TAPE LAYING
AEROSPACE LARGE COMPLEX GEOMETRY PARTS: AUTOMATED FIBER PLACEMENT
NON-AEROSPACE SMALL PARTS: RTM
NON-AEROSPACE LARGE PARTS: INFUSION
LINEAR PROFILES: PULTRUSION
BODIES OF REVOLUTION: FILAMENT WINDING

- The table in slide 9,” actual process” gives a clear view of the 4 categories : Autoclave vs OOA, pre-pred vs dry-ply fabric – can we have an idea of the gap in term of cost between the 4 categories? What is the price of an autoclave equipment + the mold? What is the price of an RTM mold…?

THE PRICE OF AN AUTOCLAVE VARIES WITH ITS DIMENSIONS, FOR INSTANCE, A 20-FT LONG, 7-FT DIAMETER MAY COST AROUND $150K. THE COST OF A MOLD FOR AUTOCLAVE ALSO VARIES WITH DIMENSIONS, AROUND $600/FT2. A RTM MOLD MAY COST AROUND $1000/FT2. THE PRICE OF A UNIDRECTIONAL HIGH STRENGTH CARBON PREPREG MAY COST AROUND $20/LB AND A UNIDRECTIONAL HIGH STRENGTH CARBON FABRIC, AROUND $12/LB.