This document discusses different molding processes including structural foam molding, sandwich molding, and their advantages and disadvantages. Structural foam molding is a low pressure injection molding process where gas is introduced into molten polymer to reduce density and weight. It requires less pressure than other molding processes. Sandwich molding involves injecting two or more polymers one after another through the same gate to form a layered part with different materials for the core and skin. This allows for weight reduction and various material combinations. Advantages of these processes include lower costs, weight reduction, design flexibility, and strength to weight ratios. Disadvantages include potential for air bubbles or shrinkage.

1. STRUCTURAL FOAM
MOLDING
AND
SANDWICH MOLDING

2. INJECTION MOLDING
To produce the parts by injecting a
material.
Performed with metals, ,
thermoplastic and thermosetting
polymer.

3. STRUCTURAL FOAM MOULDING
Definition.
Process

4. 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.

5. 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.

6. 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.

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

13. ADVANTAGES OF STRUCTURAL FOAM
MOLDING

14. 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

15. 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

16. STRUCTURAL FOAM MOLDING

17. DISADVANTAGES OF STRUCTURAL
FOAM MOLDING

18. 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

19. SANDWICH MOLDING

20. 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

21. PROCESS
INJECTION 1-FORM THE
SKIN MATERIAL
INJECTION 2- FORM THE
CORE
INJECTON 3-TO SEAL THE
GATE AND FINISH THE PART

22. PROPERTIES OF SKIN MATERIAL
Will be thin
Surface structure of the material.
Transparent material
Paintable surface
E.g.: glass, thermoplastics,
thermosets , sheet material ,
plywood

23. PROPERTIES OF CORE MATERIAL
Thick but will be lightweight.
Low density material
High bending stiffness.
Recycled material.
E.g. :PVC, polyethylene ,polystyrene ,
metal foams.

25. METHODS:
 Autoclave molding
 Adhesive bonding
 Liquid molding
 Continuous lamination
 Compression molding

26. APPLICATIONS OF SANDWICH
MOLDING

27. APPLICATIONS
Door handles in car industry
Electronic housings
Decks in ships
In aerospace, making doors in
airplane
Antennas

32. ADVANTAGES AND
DISADVANTAGES OF
SANDWICH MOLDING

33. BENEFITS OF CO INJECTION MOULDING

34. STRUCTURAL PRODUCT:

35.  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).

36. LESS PRODUCTION STEPS
Shorter period between order and delivery of parts
Higher reproducibility and increased productivity
High reliability of production process
Simplified logistics

37. VISCOSITIES
LESS
HI
GH

38. 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

39. 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.