Final Flashcards
What are several Liquid Transfer Molding Techniques?
Resin Transfer Molding; Vacuum-Assisted Resin Injection; Vacuum Assisted RTM;
Thermal-Expansion RTM; Rubber-Assisted RTM; Resin Injection Recirculation Molding; Continuous
RTM; Co-injection Resin Transfer Molding; Resin Liquid Infusion;
Resin Film Infusion; Seeman’s Composite Resin Infusion Molding Process;
Ultra-Violet (Cure) RTM.
What is Resin Transfer Molding?
The impregnating of preformed dry reinforcement in a closed mold with wet thermosetting resin under
pressure
What must be kept in mind when performing a RTM Process.
Resin Viscosity; volume fraction of fibers; fiber porosity; race-tracking of resin; dry spots by air
entrapment; resin rich area do to geometry; mold integrity.
What are the advantages of Liquid Molding like RTM?
• Low capital investment
• Good surface quality
• Tooling flexibility and range of options–can use a cost-effective tooling for prototyping and a
more expensive and durable tooling for production
• Large, complex shapes are possible
• Ribs, cores, and inserts can be included in structure
• Parts integration–several parts can be replaced with a single liquid molded part
• Range of available resin systems
• Range of reinforcements can be used
• Fiber orientation is controllable
• Controllable and predictable fiber volume fraction
• Closed mold process = lower emissions + both sides of part have tool surface finish
• No air entrapment if properly designed (tooling, preform, and resin)
• Once process established very repeatable and predictable
• Permits relatively high fiber volume (40% - 50%)
• Preform design can incorporate damage tolerant features
• Close dimensional tolerances can be maintained
• significant part consolidation - ability to incorporate cores, ribs, and inserts
• low tooling cost/short tooling lead times
• versatile - prototype or high production rate (tooling)
• fast part production: 2 - 8 pph (parts per hour) spray-up @ 0.5 pph
What are several desirable resin characteristics?
must remain liquid as it is held in the reservoir prior to injection
• must impregnate fiber preform quickly and uniformly without voids
• must gel as quickly as possible once impregnation occurs (fast cycle time)
• must possess sufficient hardness to be demolded without distortion
• Low viscosity critical (< 1,000 cps to impregnate preform loading of 50%)
What are several Disadvantages of RTM Process?
• Preform process - preparation can be labor intensive, process waste may be high, because
preform lacks strength may have to be assembled in mold (tying up mold)
• Preforms may be oversized in order to pultrude from tool edge to provide escape route for
displaced air and excess resin
• Oversized preforms will have to be trimmed (sealing or close-out will be required over exposed
reinforcement to prevent potential path for moisture ingress)
• Movement of reinforcement during injection (fiber wash)
• Control of resin uniformity difficult - radii and edges tend to be resin rich
• Higher speed versions of process undeveloped - still problems filling large parts with high
reinforcement content at low pressure
• As part consolidation increases high losses for manufacturer if part scrapped and replacement
cost to consumer can be significant
What are several RTM Process Issues?
May or may not take place under vacuum (assists in minimizing air entrapment)
• Mixer/injection head is inserted into mold
• Injection pressure pushes check valve off its seat and allows resin to begin filling
• Air is pushed ahead of resin
• Resin will begin flowing from vent ports if part design is simple may be full and if part design
complex, may require slight overfill to vent all air
• Vent ports are pinched off and internal pressure causes inlet check valve to close.
• Critical to control infusion rate and flow front of resin so that it infiltrates fiber preform evenly
and completely, but quickly before gelling
• Resin is injected in center of part to guard against formation of air pockets and minimize distance
resin must travel
• Care must be exercised to insure reinforcement does not move during injection (fiber wash).
What is RIM?
Two highly reactive liquid monomers that are carefully metered, brought together in a mix head, and
immediately injected into a heated mold under low pressure.
What are the variations of resin types,
Neat resin
Reinforced reaction injection molding (RRIM) - fillers (including chopped glass, carbon/graphite fibers,
calcium carbonate and other type of fillers) can be incorporated into one or both monomers
Structural reaction injection molding (SRIM) - reinforcement placed in mold before injecting the
reactive liquid monomers
What are the advantages and disadvantages of RIM?
many of the same advantages/disadvantages as RTM process, differences with RTM process is that
resin builds viscosity rapidly (higher average viscosity during mold filling), applications must be simple
geometries, SRIM preform must be less complex and lower in reinforcement content, parts do not
normally flash out of mold parting line sufficiently to require sealing beyond metal land area or a pinch
off around perimeter of part (low viscosity of RTM resin requires gasket or O-ring)
What is Additive Manufacturing?
A process for making 3D products by primarily adding material rather than removing it.
which layers of material are successively built up under computer control to create an object
What are the various technologies under Additive Manufacturing?
Vat Photopolymerization, Material Extrusion, Materials Jetting, Binder Jetting, Powder Bed Fusion,
Direct Energy Deposition.
Stereo lithography is:
a form of 3-D printing technology used for creating models, prototypes, patterns,
and production parts in a layer by layer fashion using photopolymerization, a process by which light
causes chains of molecules to link, forming polymers
Advantages: wide range of material; good accuracy, surface finish; possible build larger parts.
Disadvantages: Only photopolymers; mechanical properties are not stable; materials are
expensive; build process is slow
Laser Sintering is
: a form of 3-D printing technology that uses a focused laser to sinter powdered
material (typically metal), at points in space defined by a 3D model, binding the material together to
create a solid structure.
Advantages: Manufacture parts in standard metals high density; a wide set of materials is
available; parts can be further processed; flame retardants and chemical resistant.
Disadvantages: technology is slow and expensive, tolerances and finish limited.
Material Jetting (PolyJet) is
a form of 3-D printing technology that jet drops of liquid photopolymer
onto the build tray, similar to an inkjet document printing, Multiple print heads jet material
simultaneously to create each layer, and UV light is then used to cure the layers. These layers build up
one at a time in an additive process to create a 3D model.
Advantages: Good accuracy and surface finish; multiples materials in a single build, Digital
materials for customized properties; intricate and accurate parts.
Disadvantages: Fragile parts; Slow build process.
