STRUCTURAL FOAM MOLDING

AND SANDWICH MOLDING

INJECTION MOLDING

To produce the parts by injecting a material.

Performed with metals, , thermoplastic and thermosetting polymer.

STRUCTURAL FOAM MOULDING

Definition.

Process

WHAT IS STRUCTURAL FOAM MOLDING? Low pressure injection moulding process. Inert gas is introduced into molten polymer for reducing

density and weight. Used in mass production of large parts or multiple parts

produced in single machine. It requires less pressure than other moulding process so

parts are likely to have thicker wall section.

PROCESS Molten resin is injected with Nitrogen gas or chemical

blowing agent. The mixture is injected into the mould. The gas expands and fills the mold with foam. As the foam flows through the mould ,the surface cells

collapse. Solid skins are formed against the walls of mold while

core remains structurally foamed.

PROCESS. The outer skin is solid and the centre of the wall is foam. The part weight is reduced upto 20%. Part densities are as low as 40% of density of solid

plastic. Thermoplastic material used in structural foam

applications include polycarbonate,ABS.

APPLICATIONS

•Tool boxes•Trash cans•Commercial laundry bins•Pallets•Replace wood,concrete,metals,fiberglass

ADVANTAGES OF STRUCTURAL FOAM MOLDING

ADVANTAGES Low cost tooling Different materials can be run simultaneously Low pressure process for optimum product quality Large parts can be produced Superior design flexibility High strength to weight (specific strength) ratio Reduced part weight with high stiffness to weight

(specific modulus) ratio

ADVANTAGES Can achieve between 10% to 30% weight reduction

without affecting structural integrity Finished products is glossier than other low pressure

methods Less energy and materials are used , resulting in energy

savings Superior impact resistance Dimensional accuracy over the entire production run

STRUCTURAL FOAM MOLDING

DISADVANTAGES OF STRUCTURAL FOAM MOLDING

DISADVANTAGES Air trapped in mold causing the burning Bubbles are showing in the finished part due to the

moisture Shrinkage occurs due to not enough plastic for molding In the product surface , there are some marks due to

unbalanced flow of mold in the gates and runners

SANDWICH MOLDING

SANDWICH MOULDING

Two or more polymers are injected one after another through the same gate in one or more cavities.Core and skin material different or same.Also called as co-injection molding

PROCESS

INJECTION 1-FORM THE SKIN MATERIAL

INJECTION 2- FORM THE CORE

INJECTON 3-TO SEAL THE GATE AND FINISH THE PART

PROPERTIES OF SKIN MATERIAL

Will be thin Surface structure of the material.Transparent materialPaintable surfaceE.g.: glass, thermoplastics,

thermosets , sheet material , plywood

PROPERTIES OF CORE MATERIAL

Thick but will be lightweight.Low density materialHigh bending stiffness.Recycled material.E.g. :PVC, polyethylene ,polystyrene ,

metal foams.

METHODS:

Autoclave molding Adhesive bonding Liquid molding Continuous lamination Compression molding

APPLICATIONS OF SANDWICH MOLDING

APPLICATIONS

Door handles in car industryElectronic housingsDecks in shipsIn aerospace, making doors in

airplaneAntennas

ADVANTAGES AND DISADVANTAGES OF

SANDWICH MOLDING

BENEFITS OF CO INJECTION MOULDINGRECYCLED CORE REDUCES COSTS RECYCLED CORE REUSES WASTE

ENGINEERING CORE STRUCTURE.EG.FIBER FOAMING,ENHANCES PRODUCT STRENGTH OR PERFORMANCE.

VIRGIN SKIN PROVIDES QUALITY AESTHETIC FINISH FOR RECYCLED OR ENGINEERING CORE.

ELASTOMER SKIN IMPROVES SURFACE TOUCH.

STRUCTURAL PRODUCT:

CO INJECTION IS PREFERRED TO CONVENTIONAL STRUCTURAL FOAM OR FIBER REINFORCED PLASTICS BECAUSE OF ITS SUPERIOR SURFACE FINISH.

A SOLID SKIN COMBINED WITH A STRUCTURAL FOAM CORE PROVIDES THE ADVANTAGES SUCH AS LOW MOLDED IN STRESS,SKIN FREE PARTS WITHOUT THE SKIN SURFACE DEFECTS.

QUALITY SURFACE IS OBTAINED IN FIBER REINFORCED PLASTICS SINCE THE FIBER LOADED MATERIAL IS RESTRICTED IN THE CORE OF THE PART.

EXCELLENT BONDING between components.

DESIGN (colour combinations,information brokerage,marketing possibilities)

SOFT TOUCH or NON SLIP COVERAGE (to obtain certain grip control or for ergonomical reasons)

SEALING FUNCTIONS (closens against dust and condensation water).

RIGIDE/FLEXIBLE COMPOSITES ( with good damping characteristics).

LESS PRODUCTION STEPS

Shorter period between order and delivery of parts

Higher reproducibility and increased productivity

High reliability of production process

Simplified logistics

VISCOSITIES

LESS

HIGH

VISCOSITY LIMITATION OF 2 MATERIALS

TWO MATERIALS CAN ONLY BE PROCESSED SUCCESSFULLY BY CO INJECTION MOULDING IF THEIR PROCESSING PROPERTIES MATCH.

THAT IS THE VISCOSITY RATIO OF CORE/SKIN SHOULD BE BETWEEN 0.5 AND 5.

LOWER VISCOSITY RATIOS WOULD LEAD TO BREAK THROUGH OF CORE MATERIAL.

HIGHER VISCOSITY RATIOS WOULD LEAD TO POOR MOLD FILLING, FINGER LIKE DEFECTS AND VARIABLE CORE THICKNESS THROUGH THE PART

ADVANTAGES DISADVANTAGES

MATERIALS COST SAVING AND LIGHTER WEIGHT PARTS

MACHINE COSTS ARE 25 TO 30 % HIGHER THAN FOR STANDARD INJECTION EQUIPMENT

2 DIFFERENT OR ALIKE MATERIALS CAN BE SHOT SIMULTANEOUSLY INTO MOULD

GOOD TOOL MAKERS FAMILIAR WITH TOOLING REQUIREMENTS ARE DIFFICULT TO FIND IN SOME AREAS.

SOME CO INJECTION MACHINES CAN BE ADAPTED FOR GAS ASSIST,WHICH ALLOWS THE MACHINE TO PERFORM DUAL FUNCTIONS

MATERIAL VISCOSITIES MUST BE VERY SIMILAR OR PART CAN EASILY BE CORE RICH OR SKIN POOR.

ALLOW AN OUTLET FOR REGRIND USAGE ON INTERNAL CORE

SOMETIMES DIFFICULT TO OBTAIN TECHNICAL SUPPORT FOR EQUIPMENT PROBLEMS.