Injection moulding in footwear manufacturing

1. INDUSTRIAL TRAINING
Footwear Manufacturing by Injection Moulding
Presented By:
NASEEL IBNU AZEEZ.M.P
M-Tech Machine Design
3rd Semester
Roll No:12
AJCE-Kanjirapally

2. Company Layout
Product Design Footwear Upper
Manufacturing
Footwear Sole
Production by
Injection Moulding
Chemical
Handling
Quality Control
Heat
Treatment
Packing
&
Despatch

3. Raw Materials
Footwear Upper Materials
• Cotton
• Leather
• Rubber
Footwear Sole Materials
• Polyurethane

4. Polyol Isocyanate
Polyurethane
60-65% 35-40%
Production Of Polyurethane
Hydrolysis resistance
Microbial stability
Adhesion strength
Thermo-oxidative resistance
Low temperature flexibility
Oil and grease resistance
Injectability

5. Production Line
Releasing Agent
Injection
Moulding
Heat Treatment (40 − 50℃)
Demoulding
Cleaning
Packing Unit
Production Time
Full Cycle=180 sec.
Heating Camber=90sec.
Setting Upper

6. Injection Moulding
• Moulding material is injected into a cold mould where it solidifies and takes the
shape of the mould cavity
• Polyurethane expands on phase changing ,so the amount of polyurethane
injected is calculated based on this expansion ratio
• Polyurethane phase change starts within 10 sec.
• Polyurethane mixing occur at specially designed nozzle tip

7. Polyurethane pouring
method

8. Direct Injection Process (DIP)

9. Nozzle For Injection
Moulding
Filter
Rotating Mixer
Static Mixer
Injection Tip
CNC

10. Problems in Injection Moulding
Problem Cause Solution
Brittleness Wet-material
Overheating
Molded-in-stresses
Poor part design
Review drying procedure
Eliminate sharp corners
Increase injection pres.
Increase melt temp.
Warped parts Orientation of material
Poor part design
Ejection problem
Part temperature differential
Increase part packing
Change gate location
Add ribs or part thickness
to improve stiffness
Check for uniform wall
thickness
Flashing Inadequate clamping
High Injection Pres.
Misaligned platen
Excessive vent depth
Reduce injection pressure
Align platen
Review mould venting
Burn marks Air trapped in cavity
Barrel or nozzle overheating
Hang-up in molding machine
Improve mould venting
Check heater controls
Clean hopper dryer•
Remove and clean screw

11. Problem Cause Solution
Sticking in mold Over packing
Mold design
Reduce injection pressure
Reduce injection speed
Check for undercuts
Inspect ejector system
Increase draft
Surface imperfections
(frosty surface or white
marks)
Injection speed too low
Wet material
Increase injection speed
Increase barrel temps
Sinks or voids Insufficient feed
Gate freezing off or located
improperly
Increase shot size
Check gate dimension and
location
Gate blush Shot to Shot variation
Inadequate packing
Reduce injection speed•
Increase gate size
Add radius to gate
Dimensional inconsistency Shot to Shot variation
Melt temperature variation
Inadequate packing
Increase hold time
Enlarge gate to prevent
premature freeze-off
PU sticks on Nozzle Time delay in injection Use special designed
nozzle

12. Re-design for nozzle to improve Injection
Air Supply
• Hot air will remove the PU residuals from nozzle tip
• Hence it reduce material waste (5Kg of PU/Day)

13. Sharp Tip
Contour Tip
• Increasing degree of mixing
• Reduce centrifugal effect on of mixture , hence reduce premature solidification
• Reduce Shot-to-Shot Variation

14. Design For Injection Mould
• The basic wall of the part should be kept uniform *
• Coring should be employed where possible to reduce uniform model and avoid
sink marks*
• Provide gradual thickness transformation *
• For deep ribs and protrusions, provide knockouts *
• Provide draft angle *
• Raised or recessed letter on appearance surface should have 0.254 mm *
• Spacing between two parallel ribs should be a minimum of 2x wall thickness *
• The fillet radius should be 20-60% of wall thickness
• The outside corner thickness should be equal to inside radii plus wall thickness *

15. Improving efficiency of Heating Chamber
Working
• Heating chamber requires 45 − 55℃ heating track
• Blower placed at the centre of heating chamber
• Air is heated by heating coil placed under to blower out let & heated air
propagated towards bot ends
Problems
• Unequal temperature distribution:
High temperature at centre and low temperature at both ends
• For best result in PU phase change , it should keep at 50℃ about 60-90 sec.
• Surface imperfection in products , sticking on de-moulding etc.

16. • Provide multiple inlet for hot air
• Provide fins to improve the thermal efficiency of heating duct

17. Conclusions
1. Carried out a detailed Study about design considerations for Injection mould
design and solution for identified problems are suggested
2. Identified the problem related to injection mould nozzle design and possible
solutions are suggested
3. Identified the common manufacturing defects in the products and found
solutions to reduce manufacturing defects
4. Possible design changes are suggested to increase the efficiency of heating
chamber

18. References
1. Friedrich Johannaber ,Injection Molding Machines
ISBN-10: 3-446-22581-1
2. Gasper Gantar ,Andrej Glojek,Mitja Mori ,Resource Efficient Injection Moulding
Journal of Mechanical Engineering 59(2013)3,193-200
3. Weigang Hu , Syed Masood ,An Intelligent Cavity Layout Design System for
Injection Moulds
International Journal of CAD/CAM Vol. 2, No. 1, pp. 69~75 (2002)
4. E. Bociga, T. Jaruga,K. Lubczyñska, A. Gnatowski,Warpage of injection moulded
parts as the result of mould temperature difference
International Scientific Journal -Volume 44 Issue 1-July 2010
5. David O. Kazmer, Russell G. Speight,Polymer Injection Molding Technology for
the Next Millennium
Journal of Injection Molding Technology-University of Massachusetts