Post on 16-Jul-2015
INTRODUCTION
INJECTION MOLDING MATERIALS
INJECTION MOLDING SYSTEM
WORKING OF INJECTION MOLDING
SCREW AND MOLD DESIGN
THE MOLDING CYCLE
ADVANTAGE & LIMITATION OF INJECTION
MOLDING
REFERENCES
Injection molding is a manufacturing process for
forming objects as of plastic, metals, rubbers by
heating the molding material to a fluid state and
injecting it into a mold.
Polymers that are capable of being brought to a state
of fluidity can be injection molded.
Injection molding is suitable processing method for
following materials:
Thermoplastics
Elastomers
Rubbers
Thermosets
Composites
The injection unit has two functions:
1. to melt pellets or powder
2. to inject the melt into a mold.
Most widely used types of injection units:
1. conventional units: consists of a cylinder and a plunger.
2. reciprocating screw units: a barrel and a screw that rotates to melt & pump the plastic mix from hopper to end of screw and then moves forward to push the melt into mold.
Clamp unit has three functions:
1. open and close mold halves
2. eject the part
3. After closing hold mold with sufficient force to resist melt pressure inside mold as it is filled
Magnitude of initial opening force required depends on:
1. packing pressure
2. Material
3. part geometry (depth and draft)
Functions of a mold:
1. impart the desired shape to the plasticized
polymer
2. cool the molded part
A mold is made up of:
1. the cavities and cores
2. The material used for making mold is either
steel or aluminium
Mold basically consists of two parts:
1. a stationary half (cavity plate)
2. a moving half (core plate)
Parting line: separating line between the two
mold halves
The injected material is transferred through a
central feed channel, called the sprue.
Order data: Part design,quantity,molding material,
tolerance etc.
Molding machine ---number of cavities
Type of mold ----selection of parting surface
Incorporation of feed system (sprue, runner, gate)
Incorporation of ejection system
Alignment of mold
Arrangement for mold lifting & clamping
Shrinkage factor
Parts can be produced at high production rates.
Parts require little or no finishing.
Close dimensional tolerances can be maintained.
Parts can be molded with metallic and non metallic
inserts.
The inherent properties of the material give many
advantages such as high strength-weight rates,corrosion
resistance.
Mold costs are high.
Molding machinery and auxiliary equipment
costs are high.
Lack of knowledge about the fundamentals of
the process causes problems.
Injection Molding Technology & fundamental-by
James L.white,4th edition,2009,ISBN-978-3446-4185-7
Technical manual on Plastics Processing-by
CIPET,Chennai,1st edition,2007
Technical manual on Plastics Mold design-by
CIPET,Chennai,1st edition,2007