Plastic Mold & Part Design Guideline

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

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

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

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 .

Ratio of Max. Runner Length /Wall thickness Gate Design L/t t (mm) ABS 160-280 1.5-4.0 PA 200-320 0.8-3.0 PC 100-150 1.5-5.0 PE 200-280 0.3-3.0 PMMA 100-150 1.5-5.0 POM 150-250 1.5-5.0 PP 160-280 0.6-3.0 PVC(Rigid) 100-150 1.5-5.0 Ratio of Max. Runner Length /Wall thickness

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!

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

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

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

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

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

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

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

Rectangular Edge Gate Design L = 0.5 ~ 0.75 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

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.

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

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

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.

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

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

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%.

Runner Design Runner Sizing

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

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

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.

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

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

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

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

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

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

Venting System Design Runner Vent Depth: 1. 0.075 mm (easy-flow mat.) 2. 0.125 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)

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

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

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.

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

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

Cooling System Design Mold Cooling System

Cooling System Design Inlet Outlet Cooling Channels

Cooling System Design Baffle Bubbler

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.

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

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

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.

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)

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.

Heat Transfer Coefficient Cooling System Design Heat Transfer Coefficient

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.

Cooling System Design Unbalanced Design

Cooling System Design Balanced Design

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

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

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

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

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.

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

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.

Cooling System Design Poor Design Better Design

Cooling System Design Poor Design Poor Baffle Better Design

Cooling System Design Poor Design Better Design

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

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

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.

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

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 0.5- 1° 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

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 0.5-1 degree, if the polishing surface lines is on the direction of pulling mold, the draft angle can be smaller. PP: 0.5-1 degree PC: 1.5-2 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 1.5-3 degree PA: Good moisturizing, the angle can be 0.5-1 degrees.

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: 0.5-1.5 degrees. POM: The self adjustment is good, the shrinkage rate is large, draft angle can be between 0.5-1.5 degrees PVC: The mosaic coefficient is large, suggested draft angle: between 1.5-3 degrees PMMA: The stress concentration point is fragile, suggested draft angle: between 1.5-3.

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