1. Plastic Mold & Part Design Guideline

2. Design Guideline Mold Design Process Filling System Design
Venting System Design
Cooling System Design
Ejecting System Design

3. Priorities of Filling System Design
Part Design
Cavity Design
Gate Design
Runner Design
Nozzle Design

4. Typical Filling System
Filling System Design
Typical Filling System
主流道
Sprue
分流道
Main Runner 产品
Part 浇口
Gate
冷料井
Cold Slug Well
次分流道
Branch Runner

5. Gate Design The Number of Gates
Once a gate is added, at least one weld line, one gate mark, more air traps and more runner volume will be added.
As long as the cavity is able to be filled, as expected, gates are the less the better.
In order to reduce the number of gates, each gate shall be located at where the melt is able to cover maximum part area based on the largest melt flow length/thickness ratio .

6. Ratio of Max. Runner Length /Wall thickness
Gate Design
L/t t (mm)
ABS PA PC PE
PMMA
POM PP
PVC(Rigid)
Ratio of Max. Runner Length /Wall thickness

7. L/t will be changed as per the Gate location
Gate Design
L/t will be changed as per the Gate location
235 mm
132 mm
70 mm
0.6t Ｌ
Gate
165 mm
Short Side
Long Side
10 mm
(87 mm)
35 mm
Even the size and wall thickness are the same, L/t will much different when gate location is different!

8. Comparison between 5 Gate and 3 Gate Designs
Case (5 Gates)
Case (3 Gates)
Inject. Pressure (MPa)
86.17
83.98
Clamp Force (m ton）
2,598
2,295
Weld Lines
Strength Concern
Less Strength Concern
Air Traps
Vent is not easy
Vent is easier

9. Gate Design
Filling patterns, air-traps and weld lines location needs to be adjusted to less sensitive areas for mechanical strength and cosmetic surfaces

10. Gate Design for Flat Part
Center Gate
Fan Gate
Worst
Worse
Better
Best
Edge Gate
Film Gate

11. Gate Design to Avoid Hesitation
thin
thick
Poor
Good
Gate location will be the furthest place from hesitation

12. Gate Design to avoid Sink Mark & Void
Poor
Good
Gate location suggest to be on thick wall
gate: 1t
Void
max. thick.: 6
max. thick.: 6

13. Avoid Jetting by Using Impingement Gate
Gate Design
Avoid Jetting by Using Impingement Gate
Jetting starting at the gate, spreading over the entire molded part
Poor
Good
Jetting Mark
Poor
Good

14. Profiling Gate Properly
Gate Design
Avoid Jetting by
using Tab Gate
Avoid Jetting by
Profiling Gate Properly
Poor
Good

15. Rectangular Edge Gate Design
L = 0.5 ~ mm
h = n t W
When W < 2h, use W= 2h.
h =gate thickness (mm) t =wall thickness (mm)
W =gate width (mm)
A =surface area of cavity (mm2)
n =material constant
0.5 for TPU
0.6 for PE, PS
0.7 for POM,PP
0.75 for ABS, SAN, SBC(K-RESIN)
0.8 for PA , PBT, PC, PMMA
0.9 for PPO, PVC, +GF t L h

16. Gate Design Fan Gate Design L= 1.3mm W= When W < 2h, use W= 2h.
w=gate width (mm)
A=surface area of cavity (mm2)
n=material constant
0.5 for TPU
0.6 for PE, PS
0.7 for POM, PP
0.75 for ABS, SAN, SBC(K-RESIN)
0.8 for CA, PA , PC, PBT, PMMA
0.9 for PPO, PVC, +GF
gate thickness (mm) h1 = n t ; h2 = wh1/D
t= wall thickness (mm)
When W < 2h, use W= 2h.

17. Gate Design Pin Gate Design t (mm) 0.75 1.00 1.25 1.50 1.75 2.00 C
0.178
0.206
0.230
0.242
0.272
0.294
When d < nt, use d = nt
d :gate diameter (mm)
t :wall thickness (mm) (
(applied to thickness of: 0.75~2.5 mm)
C : a function of t, see the
table below
A : surface area of cavity (mm2)
n : material constant
0.5 for TPU
0.6 for PE, PS
0.7 for POM, PP
0.75 for ABS, SAN, SBC(K-RESIN)
0.8 for CA, PA, PBT, PC, PMMA
0.9 for PPO, PVC, +GF
L = 0.5 ~ 0.75 mm t d

18. Gate Design Dimple d : 4～10 h= 0.75 (t<0.75) =t (0.75≤t≤1.5)

19. Gate Design Sub gate Design h= gate thickness (mm) = nt W=
30 ~
15º ~ 25º
h= gate thickness (mm) = nt W=
t = wall thickness (mm)
W = gate width (mm)
A = surface area of cavity (mm2)
n = material constant
0.5 for TPU
0.6 for PE, PS
0.7 for POM, PP
0.75 for ABS, SAN, SBC(K-RESIN)
0.8 for PA, PBT, PC, PMMA
0.9 for PPO, PVC, +GF
When W < 2h, use W= 2h.

20. Coss-sectional area of the flow
Runner Design
Hydraulic Diameter
DH : hydraulic diameter
A : cross-sectional area of the flow
P : wetted perimeter
Coss-sectional area of the flow
DH=
0.8771D
0.8642D
0.8356D
0.7090D
10o H P L D
R=D/2 S 2S 4S

21. Coss-sectional area of the flow
Runner Design
Hydraulic Diameter
DH : hydraulic diameter
A : cross-sectional area of the flow
P : wetted perimeter
Coss-sectional area of the flow
DH= D
0.9523D
0.9116D
0.8862D D P L S H
10o
R=H/2

22. Runner Design Runner Sizing Note :
D : runner diameter in mm
W : downstream plastic weight
L : runner length in mm
Note :
The above-mentioned empirical formula is suggested as a guide to the size of the runner or branch runner for mouldings weighting up to 200 g, and with wall sections less than 3 mm. For the rigid PVCs and the acrylics, increase the calculated diameter by 25%.

23. Runner Design
Runner Sizing

24. Runner Design Runner Sizing
2mm (part thickness) x 1.5 (2.25 if amorphous) = 3.00mm > 2.38mm, so D1=3.00mm

25. Tungsten Steel Ball Cutter (mm)(2 Blades)
Runner Design
Tungsten Steel Ball Cutter (mm)(2 Blades)
Radius
Handle Length
Blade Length
Total Length
R0.5 4 2 50
R0.75 3 R1
R1.25 5
R1.5 6 R2 8
R2.5 10 R3 12 R4 16 60 R5 20 75 R6 24
Suggest to use 1.5mm Tungsten steel ball cutter

26. Runner Design Runner Sizing
D2 is calculated as 4.33mm, Tungsten Steel Ball Cutter (mm)(2 Blades radius available: 2mm and 2.5mm, Diameter is 4mm and 5mm, so suggest to choose R=2.5mm , Tungsten Steel Ball Cutter.

27. Tungsten Steel Ball Cutter (mm)(2 Blades)
Runner Design
Tungsten Steel Ball Cutter (mm)(2 Blades)
Radius
Handle Length
Blade Length
Total Length
R0.5 4 2 50
R0.75 3 R1
R1.25 5
R1.5 6 R2 8
R2.5 10 R3 12 R4 16 60 R5 20 75 R6 24
Suggest to use 2.5mm Tungsten steel ball cutter

28. Runner Design PS, ABS W (g) W :weight S : thickness
D': reference diameter
D’ (mm)

29. Runner Design PE, PP, PA, PC, POM W (g) W :weight S : thickness
D': reference diameter
D’ (mm)

30. Runner Design L : length of runner fL : correction factor
D': reference
diameter
D： diameter of runner
D = D’ x fL

31. Cold Slug Well Design Cold slug well 2d secondary runner d Gate
primary runner
Gate
cavity

32. Runner Design Sprue Bushing Sizing
Dave :Average diameter of sprue in mm
W :Downstream plastic weight in g
L :Sprue length in mm, the shorter the better

33. Venting System Design Runner Vent Depth: 1. 0.075 mm (easy-flow mat.)
mm (stiffer-flow mat.)
3. Deep enough to feel flash at runner end
Width:
- as wide as runner dia.
- vent lip: 1.5mm A1 (finish)
(SPI Finish Designations：A-1 Grade #3 Diamond Buff)
vent channel to atmosphere: 1mm (deep)

34. Venting System Design Parting Line Vent Depth: Check case by case
Width: 5mm/25mm or whole perimeter
Length: 1 mm or 1.5 mm A1 finish
(SPI Finish Designations：A-1 Grade #3 Diamond Buff)
Vent channel to atmosphere:1mm deep
Injection Vent

35. Venting Guidelines for fully optimized molds polymer
Venting System Design
Venting Guidelines for fully optimized molds polymer
Material
Depth of Vent (mm)
EASY FLOW
STIFF FLOW GLASS FILLED
ABS, SAN, HIPS
0.0508
0.0762
Acrylic
Nylon 6/6
0.0127 —
Nylon 6/6 – 13% Glass
0.0381
Polyallomers
0.0254
Polycarbonate
Polyethylene
Polypropylene
TPE
0.025

36. Purposes of Mold Cooling Design
Cooling System Design
Purposes of Mold Cooling Design
1. Even Cooling (Improve Part Quality)
Efficient Cooling (Increase Productivity)
Thin-wall part can not afford as much thermal induced bending moment as the conventional one does. An even cooling design becomes very important to control the warpage at an acceptable level.

37. Injection Molding Cycle Time
Cooling System Design
Injection Molding Cycle Time
Fill Time
Open Time
Post-fill Time

38. Typical Cooling System
Cooling System Design
Typical Cooling System 1
Temperature controlling unit
Cooling Circuit 1
Hoses
Pump
Collection manifold
Supply manifold
Cooling Circuit 2

39. Cooling System Design
Mold Cooling System

40. Cooling System Design
Inlet
Outlet
Cooling Channels

41. Cooling System Design
Baffle
Bubbler

42. Min. Possible Cooling Time
Cooling System Design
Min. Possible Cooling Time
the min. possible cooling time
the max. part thickness
thermal diffusivity of the melt
injection temp.
coolant temp.
ejection temp.

43. Cooling Time and Thickness Profile
Cooling System Design
Cooling Time and Thickness Profile
Bad Design
Good Design

44. Diameter, Depth & Pitch of Cooling Channel
Cooling System Design
Diameter, Depth & Pitch of Cooling Channel
D : Diameter of Cooling Channel, 10 to 14 mm
d : Depth, D to 3D
P : Pitch, 3D to 5D

45. Cooling System Design
The cooling rate is not only in proportion of Temperature Difference, but also in proportion of 0.8s of the flow Velocity.

46. Cooling System Design Newton's law of cooling
The cooling rate of the cooling body is in proportion to the temperature difference between the substance and the cooling medium
Heat taken from mold by cooling medium
Heat transfer coefficient between mold and cooling medium(W/m2-°K)
Heat transfer area of cooling channel (M2)
Temperature difference between die and cooling medium (degree K)
Cooling time (SEC)

47. Forced Convention Heat Transfer Inside Tubes and ducts
Cooling System Design
Forced Convention Heat Transfer Inside Tubes and ducts
Long Ducts, Liquids and Gases in Turbulent Flow (Re > 6,000, Pr > 0.7)
Notes:
Re is Reynolds number.
Pr is Prandtl number.
Nu is Nusselt number.
Re, Pr and Nu are all dimensionless.

48. Heat Transfer Coefficient
Cooling System Design
Heat Transfer Coefficient

49. Cooling System Design
Relationship between cooling rate and temperature difference and velocity
The cooling rate of the mold is not only proportional to the temperature difference between the mold and the water, but also proportional to the 0.8 power of the water flow rate.

50. Cooling System Design
Unbalanced Design

51. Cooling System Design
Balanced Design

52. Internal Manifold Design
Cooling System Design
Internal Manifold Design
without Using Frop's

53. Internal Manifold Design
Cooling System Design
Internal Manifold Design
Using Frop's

54. Flow Resistance Orifice Pin
Cooling System Design
Flow Resistance Orifice Pin
(FROP)

55. Turbulent and Laminar Flows
Cooling System Design
Turbulent and Laminar Flows
Turbulent Flow
Laminar Flow

56. Cooling System Design Reynolds Number Reynolds number (dimensionless)
density (g/cm3)
diameter (cm)
velocity (cm/sec)
viscosity (poise or dyne-sec/cm2 or g/cm-sec)
The flow is laminar when the Reynolds number is below 2,100. In the range of Reynolds numbers between 2,100 and 10,000, the transition from laminar to turbulent flow takes place. At a Reynolds number of about 10,000, the flow becomes fully turbulent.

57. Nusselt No vs. Reynolds No
Cooling System Design
Nusselt No vs. Reynolds No
Laminar
Turbulent

58. Forced Convention Heat Transfer Inside Tubes and ducts
Cooling System Design
Forced Convention Heat Transfer Inside Tubes and ducts
Long Ducts, Liquids and Gases in Turbulent Flow (Re > 6,000, Pr > 0.7)
Notes:
Re is Reynolds number.
Pr is Prandtl number.
Nu is Nusselt number.
Re, Pr and Nu are all dimensionless.

59. Cooling System Design
Poor Design
Better Design

60. Cooling System Design
Poor Design
Poor Baffle
Better Design

61. Cooling System Design
Poor Design
Better Design

62. Cooling System Design
The velocity and flow rate required to reach turbulent state (Re:6,000-10,000) as per different pore sizes and water temperatures
Tube Diameter mm 6 8 10
Water Temperature oC 20 60 80 Re
6,000
1.01
0.48
0.29
0.76
0.36
0.22
0.60
0.18
1.71
0.81
0.50
2.28
1.08
0.67
2.84
1.35
0.83
8,000
1.34
0.64
0.39
1.0
0.38
0.24
3.03
1.44
0.89
3.79
1.80
1.11
10,000
1.68
0.80
0.49
1.26
3.80
4.74
2.25
1.39
Upper Segment: Flow speed: m / s, Upper Segment l / min

63. The optimized cooling time for different plastic and thickness
Cooling System Design
The optimized cooling time for different plastic and thickness

64. Cooling Design Principles
Cooling System Design
Cooling Design Principles
Select Plastic Material with large thermal diffusivity.
Use a thin and uniform part thickness.
Layout cooling channels around cavities evenly.
Remove air gaps and pockets from heat transfer path.
Balance coolant flow.
Check cooling efficiency.
Make cooling evenly.
Select appropriate equipment.

65. Suggested Draft Angle for different plastic and thickness
Ejecting System Design
Suggested Draft Angle for different plastic and thickness
Material
Suggested Draft Angle
Wall thickness PP
Product with strengthen ribs
1-10mm,Big End of Rib:≤1.0: draft angle 0.5-1° for each side
≥2.0
10-30mm Big end of Rib:1.0，Small end of Rib0.8
≥2.3
30-50mm Big end of Rib: 1.2，Small end of Rib: 0.8
≥2.8
50-70mm Big end of Rib:1.3，Small end of Rib:0.8
≥3.0
Product with polished surface
30mm: draft angle ≥ 1° for each side
30-50mm: draft angle ≥ 1.5° for each side
≥50mm: draft angle ≥ 3° for each side
Product with textured surface
≤20mm: draft angle ≥ 2° for each side
>20mm: draft angle ≥ 2.5° for each side

66. Ejecting System Design
Suggested Draft Angle for different plastic and thickness
Material
Draft Angle Requirement
ABS
Product with strengthen ribs
5mm, Big End of Rib:≤1.0: draft angle ≥ 1° for each side PA
5-10mm, Big End of Rib:≤1.0: draft angle ° for each side PC
10-30mm guaranteed bottom of big end: 1.2, Small end of Rib: 0.9 AS
30-50mm, Big end of Rib:1.4，Small end of Rib: 0.9
PMMA
50-70mm Big end of Rib:1.5，Small end of Rib: 0.9
POM
Product with polished surface
≤30mm: draft angle ≥ 1° for each side
PPS
30-50mm:draft angle ≥ 1.5° for each side
PBT
>50mm: draft angle ≥ 2° for each side PE
Product with textured surface
≤20mm: draft angle ≥ 2° for each side
>20mm: draft angle ≥ 2.5° for each side

67. Draft Angle Design Principles
Ejecting System Design
Draft Angle Design Principles
There are no certain criteria for the size of draft angle, the suggestion are usually as per experience and depth of the product, the way of molding, the thickness of the wall and the choice of plastic materials. The following are suggested draft angles for some of the commonly used plastic materials:
ABS: Easy ejection, draft angle can be degree, if the polishing surface lines is on the direction of pulling mold, the draft angle can be smaller.
PP: degree
PC: degrees, because the molding is relatively large, the draft angle needs to be larger than other plastic parts.
PS: Easy to be white, angle should be bigger: between degree
PA: Good moisturizing, the angle can be degrees.

68. Draft Angle Design Principles
Ejecting System Design
Draft Angle Design Principles
PE: Soft, not easy to push out, suggested draft angle: between 3-5 degrees.
PBT: Self lubricity, but the shrinkage rate is large, suggested draft angle: degrees.
POM: The self adjustment is good, the shrinkage rate is large, draft angle can be between degrees
PVC: The mosaic coefficient is large, suggested draft angle: between degrees
PMMA: The stress concentration point is fragile, suggested draft angle: between

69. CONTACT US Website: www.pa-international.com au Hong Kong Office:
Address: Unit 2508A, 25/F, Bank of America Tower, 12 Harcourt Road, Central, Hong Kong
Mainland Office:
Address: #403, Business Center, Jing DuHui Hotel, ChangAn Town, Dong Guan City, Guangdong Province, P. R. China
Website: au