Lecture 4 Flashcards
What is a Preform?
- A preform is an assembly of materials that are cut and placed over a tool surface
- Preforming converts 2D intermediates into a 3D form
Name some characteristics of Hand Layup 3D Preforming:
- Only suitable for low production volumes ~ 1,000ppa
- Expensive at high volumes
- Requires skilled labour, Down to experience of operator
- Poor repeatability
- Requires multiple parallel tools
- High material wastage ~ 40%
Name the pros and cons of Human operators:
Advantages
* Highly dexterous (Can take action when spotting errors)
* Good at visually spotting errors
* Adaptive – can perform multiple roles
Disadvantages
* Expensive, skilled labour
* Variable skill
* Take short cuts
* Require motivation - Repetitive tasks are tedious
Name the pros and cons of Robot operators:
Advantages
* Strong
* Fast
* Cheap
* High precision
* Repeatable and more consistent
* Work in dangerous/harsh environments
Disadvantages
* Limited feedback
* Limited movement envelope
* Dedicated to one role
* Cannot take corrective action if there’s a problem
* Not as fast as expected
* Require skilled programmers
Name some characteristics of Automated Tape Laying:
- Wide carbon fibre prepreg tapes robotically placed on tool surface
- Use continuous unidirectional tapes
- Exclusively used for Aerospace
- Most effective over long courses
- Enables more intelligent use of materials
- Wastage is dependent on size/shape of component and fibre orientations
Name some disadvantages of Automated Tape laying:
- Expensive feedstock materials
- High capital equipment costs – Machines cost
£2m + - Inflexible machines – tend to be dedicated to producing one component
- Limited to simple geometries
- Lack of CAE design tools
- Long machine set up times
- Layup quality depends on humidity – hard to control, age of prepreg – variable tack
Name some characteristics of Automated Fibre Placement:
- Similar to ATL but individual tows rather than tapes.
- AFP is more precise than ATL
- Lower material wastage than ATL
- Similar challenges to ATL
Name the characteristics of Matched Tool (Press) Forming
- High CAPEX
- Non-isostatic pressure – problems for near vertical faces
- High material wastage – additional blank material required for gripping
- Blank holder controls material draw-in and tension
- Blank holder used to locate/hold preform prior to
forming - Preforms can be formed using multiple operations
Name the characteristics of Single Diaphragm Forming (SDF)
- Low CAPEX
- Isostatic pressure
- Net-shape
- Limited control over material draw-in or fabric wrinkling
- Preforms can be formed using multiple operations
- Intensifiers can be placed inside (or incorporated within) the diaphragm
- Minimal spring-back – depends on release agent/film
- Difficult to locate preforms prior to forming
Name the characteristics of Double Diaphragm Forming (DDF)
- Low CAPEX
- Isostatic pressure
- Net-shape
- Pressure between diaphragms can be regulated to control tension
- Lower membrane prevents multiple forming operations
- Difficult to incorporate intensifiers
- Problems removing preform – spring back of lower diaphragm
- Lower diaphragm used to transport preforms
Name some characteristics of Braiding (Direct textile preforming)
- Displacers can be used to create holes
- Strength can be 1.8 times higher than a cut hole due to fibre continuity
- Superior fatigue performance compared to filament winding due interlacing
- Low wastage (<10%)
- High degree of automation
- Batch process – limited mass of fibre on bobbins
- Long set up times and machine downtime
- Cycle time is dependent on mandrel complexity
- Most efficient when braiding straight sections
- Suitable for structural applications (bending, torsion, crash)
Name some other Direct Textile Preforming methods
- 3D Weaving
- Embroidery
- Filament winding
