1. PLASTICS
PRODUCT DESIGN

2. PLASTICS PRODUCT DESIGN
PART DESIGN
MAIN FACTORS –
END USE
MATERIAL PROPERY
MANUFACTURING PROCESS

3. PLASTICS PRODUCT DESIGN
PRIME CONSIDERATION OF A PART DESIGN –
BASED ON END USE
i. SHAPE – SIMPLE/COMPLEX, HOLLOW/ SOLID,FLAT/ROUND
ii. SIZE – LARGE / SMALL , THICK / THIN &
iii. PART FEATURES

4. PLASTICS PRODUCT DESIGN
PART FEATURES
DETAILS TO BE CONSIDERED IN A PART
WALL THICKNESS
CORNERS
RIBS
BOSSES
WELD LINES
DRAFT
PARTING PLANE
UNDERCUT
INSERTS
TOLERANCES
LOAD & STRENGTH
HINGES & SNAP FIT
THREAD

5. PLASTICS PRODUCT DESIGN
WALL THICKNESS
PLASTIC MATERIAL PROPERTIES GOVERNING WALL THICKNESS OF PLASTICS PART –
MATERIAL STRUCTURE – PARTLY AMOURPHOS, PARTLY CRYSTALLINE & VISCOSITY.
PROCESS – THE NATURE OF PLASTIC PRODUCT MANUFACTURING IS MATERIAL ADDITION.
THERMAL CONDUCTION – PLASTICS IS BAD CONDUCTOR OF HEAT , HENCE SOLIDIFICATION PROCESS VARIES WITH THICKNESS.
THERMAL EXPANSION / SHRINKAGE –
ABOVE FACTORS INDICATE , WALL THICKNESS SHOULD BE UNIFORM AND THIN.

6. PLASTICS PRODUCT DESIGN
WALL THICKNESS
WALL THICKNESS SHOULD BE AS UNIFORM AS POSSIBLE TO ELIMINATE INTERNAL STRESSES, PART DISTORTION, AND CRACKING.

7. WALL THICKNESS

8. PLASTICS PRODUCT DESIGN
WALL THICKNESS
If two different wall thickness is join , blending should be Gradual

9. PLASTICS PRODUCT DESIGN

10. PLASTICS PRODUCT DESIGN
WALL THICKNESS

11. PLASTICS PRODUCT DESIGN
WALL THICKNESS
GOOD DESIGN BAD DESIGN
UNIFORM WALL THICKNESS IS DESIRABLE

12. PLASTICS PRODUCT DESIGN
CORNERS
GOOD DESIGN BAD DESIGN
SHARP CORNERS SHOULD BE AVOIDED

13. PLASTICS PRODUCT DESIGN
RIBS –
PURPOSE – IT HAS TWO PURPOSE
A) TO IMPROVE MELT FLOW IN THE SECTION
B) TO INCREASE FLEXURAL STIFFNESS

14. If a part has wall thickness W, and thickness W is added as follows –
Case (a) Parallel Along thickness &
Case (b) perpendicular to wall , then
Comparing Case (a) and Case (b)
Section Modulus - is proportional to Square of thickness.
Weight is proportional to thickness
Cooling Time is proportional to Square of thickness
Increasing Stiffness – Reduce
Deflection
Reduce Creep Strain
Natural Frequency
Impact Resistance

15. PLASTICS PRODUCT DESIGN
RIBS -
The Rib design and proportions used in most thermoplastic materials
Note : If thickness “C” is more than 0.8A, Sink mark will appear.

16. PLASTICS PRODUCT DESIGN
RIBS -
A uniform wall thickness can be maintained in a rib if it is hollowed or cored out from the back

17. PLASTICS PRODUCT DESIGN
RIBS -
A Rib should be located in the corner or side of a moled part. This will lower the mold cost and allow easier filling of the plastic part

18. PLASTICS PRODUCT DESIGN
RIBS -
IF THE RIB IS TO BE EXTREMELY THIN AND AWAY FROM SIDES OF PART, FILLING MAY BE HELPED BY ADDING INTERMITTENT HEAVY SECTION ON WHICH VENT PIN CAN BE PLACED.

19. PLASTICS PRODUCT DESIGN
BOSSES –
It is protruding studs on a part that assist in assembly of the plastic parts and also bear stress and strain therein.

20. PLASTICS PRODUCT DESIGN
BOSSES
Design and proportions of boss at a wall, it is used in most thermoplastic materials

21. PLASTICS PRODUCT DESIGN
BOSSES
Design and proportions of boss away from a wall, it is used in most thermoplastic materials
Note : If thickness “C”
is more than 0.8

22. PLASTICS PRODUCT DESIGN
BOSSES
Ribs on the side of long bosses will aid in filling them

23. PLASTICS PRODUCT DESIGN
BOSSES
Recommended proportions for Boss on the outside of a moulded part
B = A or 2A max.

24. PLASTICS PRODUCT DESIGN
Gusset Design
RIM DESIGN –
It is an undercut in the part and is used to give added strength and support.
GUSSETS –
These are supporting arrangements for an edge. For additional support, two or more gussets do the job better than increasing height or width .

25. PLASTICS PRODUCT DESIGN
DRAFT –
TAPER IS PROVIDED IN A MOLD WALL TO FACILITATE EASY EJECTION. Also HELPS IN STACKING

26. PLASTICS PRODUCT DESIGN
MOULDED HOLE -
Holes should be Parallel to Draw of mold
as it opens. Oblique angle hole are
expensive to manufacture.
ii) Strength of PIN forming the moulded hole is influenced by ratio of Diameter to Length called Slenderness Ratio.

28. PLASTICS PRODUCT DESIGN
MOULDED HOLE -

29. PLASTICS PRODUCT DESIGN
MOULDED HOLE
HOLES OF VERY SMALL DIAMETER IN CASE OF COMPRESSION MOLDING

30. PLASTICS PRODUCT DESIGN
UNDERCUTS

31. PLASTICS PRODUCT DESIGN
THREADS -

32. PLASTICS PRODUCT DESIGN
Metal INSERTS -
FACTORS TO BE CONSIDERED WITH MOLDED IN INSERTS
It should provide required mechanical strength. Sufficient anchorage must be provided to prevent insert from pulling out of the plastic.
Some plastic material will crack around the insert as it ages.
Flow of plastic material should not dislodge the insert.
Plastics has higher co efficient of thermal expansion and contraction than metal.
Insert may be pre heated prior to molding to avoid cracks around insert.

33. PLASTICS PRODUCT DESIGN
INSERT -
A ROUND SHOULDER ON THE TOP PART OF A HEXAGONAL INSERT ELIMINATETHE NECESSITY TO MACHINE A HEXAGONAL HOLE IN THE METAL MOLD.

34. PLASTICS PRODUCT DESIGN
NOT PREFERRED
PREFERRED
WHEN STRESSES ARE ENCOUNTERED , INSERT AND NOT PLASTIC SHOULD BEAR THE LOAD

35. PLASTICS PRODUCT DESIGN
INSERT -
INCORRECT
CORRECT
METAL INSERT IN BOSSES SHOULD EXTEND TO WITHIN ONE MATERIAL THICKNESS OF OPPOSITE WALL AND RIBS CAN BE ADDED FOR ADDITIONAL SUPPORT

36. PLASTICS PRODUCT DESIGN
INSERT
MALE INSERT SHOULD HAVE SHOULDER IN ORDER TO SEAL OUT PLASTIC MATERIAL THAT MIGHT BE FORCED AROUND THE INSERT
BETTER DESIGN
HORIZONTAL &
VERTICAL SEAL
BEST DESIGN
HORIZONTAL &
VERTICAL SEAL
POOR DESIGN
NO SHOULDER OR SEAL
GOOD DESIGN
HORIZONTAL SEAL

37. PLASTICS PRODUCT DESIGN
HINGES IN PLASTICS PRODUCT -
TYPES OF HINGE –
RATHBUN HINGE – IT USES ELLIPTICAL SHAPED STEEL SPRING CLIPS TO HOLD A BOX LID TIGHTLY CLOSED OR WIDE OPEN. CLIP ARE PLACED IN SMALL UNDERCUTS OR SLOT . PROVIDES STURDY SPRING ACTION AND HOLDS COVER TIGHTLY
PIANO HINGE – MADE OF METAL , SAME AS USED FOR HINGE COVER OF PIANO. HINGE RIVETTED OR FIX BY SELF TAPPING SCREW.
LUG & PIN HINGE – LEAST EXPESIVE . RECESS DRILLED IN SIDE OF BOX & COVER IS PROVIDE. METAL PIN IS DRIVEN THRO’ HOLE
STANDARD PIN HINGE – Molded HOLES ARE EXPENSIVE FOR CAM OPERATION IN MOLD.
INEXPENSIVE PIN HINGE – ELIMINATES DRILLING OR CAM OPERATION
HEAT SEALED HINGE – VERY STRONG AND DURABLE. AFTER ASSEMBLY, TWO TABS ARE HEATED AND BENT PERMANENTLY AROUND TWO PINS.
BALL GRIP HINGE – USED IN SMALL BOXES. BALL SNAPS INTO TWO DEPRESSION .
INTEGRAL HINGE

38. PLASTICS PRODUCT DESIGN
HINGES IN PLASTICS PRODUCT
STANDARD PIN HINGE INEXPENSIVE PIN HINGE

39. PLASTICS PRODUCT DESIGN
HINGES IN PLASTICS PRODUCT -
RATHBUN HINGE PIANO HINGE LUG & PIN HINGE

40. PLASTICS PRODUCT DESIGN
HINGES IN PLASTICS PRODUCT -
HEAT SEALED HINGE –
VERY STRONG AND DURABLE. AFTER ASSEMBLY, TWO TABS ARE HEATED AND BENT PERMANENTLY AROUND TWO PINS.

41. PLASTICS PRODUCT DESIGN
CLASPS –
MOSTLY WORKS ON FRICTION HOOK PRINCIPLE

42. PLASTICS PRODUCT DESIGN
SNAP ON FIT SNAP IN FIT

43. PLASTICS PRODUCT DESIGN
SNAP FITS

44. PLASTICS PRODUCT DESIGN
SNAP ON FIT & SNAP IN FIT