plastics 1

Designing of PlasticsDesigning of Plastics

Materials

Plastics (Polymers)

Thermosets Thermoplastics

Polymer Families

ThermoplasticsPlastics capable of softening and flowingwhen heated, hardening when cooled, and softening when reheated

ThermosetsPlastics which become permanently rigidwhen heated, chemically reacted or irradiated

Polymer Families

ADVANTAGES:•Recyclability•Faster Processing Time•Toughness•Assembly Options

ADVANTAGES: •High Temperature •Arc Resistance•Mechanical Rigidity•Creep Resistance•Chemical Resistance

DISADVANTAGES:•Creep•Thermal Stability•Chemical Resistance

DISADVANTAGES:•Brittle•Limited Post-Mold Assembly Options•Not Recyclable

Thermoplastics ThermosetsExamples:•Refrigeration Foam•BMC for handles•Some Coatings (Paint)•Crosslinked PE Tubing

Examples:•Refrigerator Liner•“Tails” for handles•Some Coatings (Paint)•PE Tubing

Polymers Thermoplastic vs. Thermoset

Plastic is not as stiff as metal

1040 Steel 30x106

Aluminum 10x106

Amorphous Polymer @ 0.3x106

Glass Reinforced Polymer @ 1.4x106

( psi )

Modulus of Elasticity Comparison

Polycarbonate (PC)Polybutylene terephthalate(PBT)Modified polyphenylene ether(M-PPE)Polytherimide(PEI)PC-PBT blend

Annealed Steel20

15

10

5

0

25

30

35

40

0 1 2 3 4 5 6

Mostly Linear to Yield Point

Non-linear

Non-Linear MaterialBehavior

“Stiffness Changes”

Product Information LEXAN 141

Non-halogenated, 10.5 MFR

Typical Properties Typical Value Units

MechanicalTensile StrengthTensile StrainTensile ModulusImpact Strength

ThermalHDTVicat Softening Temp.RTI

ElectricalVol Res

Everything you need to know…Everything you need to know…is is NOTNOT on the Datasheet on the Datasheet

What do you useas a material stresslimit in design?

Not on the Data Sheet

Product Information LEXAN 141

Non-halogenated, 10.5 MFR

Typical Properties Typical Value Units

MechanicalTensile StrengthTensile StrainTensile ModulusImpact Strength

ThermalHDTVicat Softening Temp.RTI

ElectricalVol Res

Everything you need to know…Everything you need to know…is is NOTNOT on the Datasheet on the Datasheet

Allowable Working Stress (Design Stress)

Allowable Working Stress

>Intermittent LoadTensile Fatique Curve - Click

>Steady LoadCreep Domain Curve

>Momentary Load70% of 0.2% strain offset

ULTEM 1000

Data sheet Tensile Strength = 15,200 PSIAllowable Working Stress

Steady load, 730 F = 3,800 PSIIntermittent Load, 730 F = 6,300 PSIMomentary Load, 730 F = 8,400 PSI

Selection Criteria

• Define criteria – Necessary

– Desirable

• Cost

• Strength / Toughness

• Dimensional stability

• Operating Temperature

• Chemical Environment

• Flammability

• Production Method

• Shrinkage

• Assembly Techniques

• Aesthetics

• Post Processing

• Rank criteria– Definite value

– Weighted opinion

• Typical Criteria

Material Selection WorksheetPart #…………………. EST Implementation Date………………………..Function…………………. REQUIREMENTS

Loading Stress…………………. Safety Factor……………… Max Temperature…………………. Impact: High Medium Low @……°C Load Type Tensile# Flexural# Shear# Compressive# Dimensional Stability: <……..% Distortion Tolerance @………. , °C…….. Rel Humidity……

STRUCTURAL

ENVIRONMENTAL Chemical exposure……… (Incidental)…………………… (Continuous)……………………. Weatherability……… (Outdoor)…………………… (Indoor)……………………. Duration………. Hrs AGENCY Flammability: V-0 V-1 V-2 5V HB @………mil

UL Temperature Rating: Others:

APPEARANCE Painted: Molded in Color: Special Surface Requirements:

ASSEMBLY Will the part need to be disassembled? Frequently…. Occasionally……. Never……..

How: Heat Staking Ultrasonic Welding Screws Adhesives Snap Fits

Plastic is melted then pushed into a mold

Plastic Flow is:

• NON - NEWTONIANNON - NEWTONIAN

• ALL FLOW IS RADIALALL FLOW IS RADIAL

• COMPRESSIBLECOMPRESSIBLE

Injection FlowInjection Flow

Injection FlowInjection Flow

Injection FlowInjection Flow

Injection FlowInjection Flow

Injection FlowInjection Flow

Plastic Flow :

Plastic will only flow so far

What is Freeze-off?

Solid

Melt

Freeze-off

Cooled Part

Plastic Flow :

Does not like to change direction

Uniform wall thickness promotes better flow

Uniform Wall Thickness

Minimizes:

• Molded-in Stress

• Warpage

• Voids

• Sink Marks

Sink Marks VoidsLow mold in stress

High mold in stress

Warpage

Improved Design

Poor Design

Efficient Wall Design

Minimum Wall Thickness Increases Productivity:• Reduce Cycle Time• Reduce Material Consumption

Limits to Minimum Wall Thickness:• Flow Length - Click• Structural Stiffness & Strength• Flammability Rating• Uniform Thickness

Flow Length Requirements on a Material can be Reduced by Adding Gates

Increasing the Number of Gates Increase the Number of Knitlines

For Best Aesthetics: Use Higher Flow Material with a Single Gate

Reduced Flow Length vs. Knitlines

Gate selection will impact ease of processing as well as aesthetics.

Click

Plastic Flow :

will flow around holes and cut-outsto form weld lines

Flow Direction

Flammability Limitations

UL Flammability Requirements:If a flammability rating is required for an application, the resin’s minimum thickness to pass the flammability test isthe part’s minimum wall thickness.

Example:A NORYL® resin has a UL 94 V-0 rating at .060”.An application requiring a V-0 rating will requirea .060” minimum wall thickness.

Recommended Wall Thickness

Non uniform thickness builds stresses near the boundary of the thin section to thick section.

The thin section does not yield because it is freeze-off, the thick section (which is still liquid) must yield. Often this leads to warping or twisting. If this is severe enough, the part could even crack.

Why Warpage?

Factors Affecting Warp:

(Uneven Shrinkage Causes Warp)

• Uneven Wall Thickness

• Unequal Cooling Rate

• Unequal Pressure

• Anisotropy

Warpage

h

h

h

3h

Poor

Good

Best

What if you cannot have uniform walls, (due to design limitations) ?

Wall Thickness

When uniform walls are not possible, then the change in section should be as gradual as possible

Warpage Due to Uneven Thickness

Alternatives

Molded in stress can reduce the load bearing capability of my part

Molded-in Stress

Mold-in

Mold-in

Assembly

Assembly

Application

Application

LowMolded-in

Stress

HighMolded-in

Stress

HighPerformance

LowPerformance

Molded-in Stress

•Overpacking

•Uneven Shrinkage

Causes:

Overpacking

•More Material than Required in the Mold Cavity•Results in Molded in Stresses

Shrinkage

• Decreased spacing between polymer chains at cooler temperatures

• Must be accommodated in tooling design

I can’t define tolerances the sameway as with metal

Moldability

ShrinkagePost-Mold Dimensions of Plastic Parts Differ From Mold

Cavity Dimensions

VpartVmold

lpart

lmold

Sl = lmold - lpart

lmold

Sv = vmold - vpart

vmold

or

Moldability

Factors Affecting Shrinkage:

•Material Properties

•Part Geometry

•Manufacturing

Material Considerations

Some materials shrink differently than othersand require different part & tool

design considerations

Crystalline Amorphous Filled Amorphous

- - -Part

Shrinkage and Materials

Amorphous Typical ShrinkageLEXAN® (PC) 5-7 mm/mNORYL® (PPO)CYCOLAC® (ABS)

Semi-crystallineVALOX® (PET/PBT) 5-25

BlendsXENOY® (PBT/PC) 5-10NORYL® GTX (PPO/Nylon)CYCOLOY® (PC/ABS)

Shrinkage and Part Geometry(Stress Due to Uneven Shrinkage)

Non-Uniform Part Thickness Cools UnevenlyCausing High Molded-in Stress

Uneven Shrinkage Defects

VoidsAlready Cooled Surface

Will Not Yield to ShrinkingInterior

Sink MarksSurface Yields to the

Still Shrinking Interior Mass

Click

Reinforcements are better than thicker walls

Reinforcement Structures

GussetRibbing

Boss

Rigidity Balance

E1X I1 = E2X I2

Two parts with equivalent RIGIDITY

I bh3

= Modulus of Elasticity

= Moment ofInertia

(E) (I)

Equivalent Rigidity12” x 24” Plate

Thickness (in.) 0.040 0.182 0.196 0.125

E (psi) 3.0 x 107 3.2 x 105 2.58 x 105 3.20 x 105

I (in.4) 0.000064 0.006 0.0075 0.006

Exl (Rigidity) 1920 1920 1920 1920

Solid Structural Ribbed*Plastic Foam SolidSteel

2” .270”.065”

Equivalent Rigidity12” x 24” Plate

Solid Structural Ribbed*Plastic Foam SolidSteel

Thickness (in.) 0.040 0.182 0.196 0.125

E (psi) 3.0 x 107 3.2 x 105 2.58 x 105 3.20 x 105

I (in.4) 0.000064 0.006 0.0075 0.006

Exl (Rigidity) 1920 1920 1920 1920

Weight (lbs) 3.24 1.88 1.78 1.601.60

Rib Thickness

In structural parts where sink marks are of no concern, rib base thickness can be 85% of the wall thickness

For High appearance parts, where sink marks are objectionable, rib base thickness should not exceed

- 50% of the wall thickness if the outside surface is textured - 30% if not textured

Ribs which are too thick:•Cause sink marks•cause voids•increase cycle timet

60% t

Suggested Rib Thickness: 60% of Nominal Wall Thickness

Click

Limited By:• Thickness - Shrink and

Warp Issue• Draft - Ejection Issue

Rib Height

Suggested Height = 3 to 5t

tOriginal Design - Too High

= 2x‘t’ min.

Avoid hot blade and cooling

Stiffener Orientation

No Increase in Stiffness

Increased Stiffness

Boss Design

D

2D

W

T

R = .25 T

Strong Possibility of Sink MarksWhen W > .6 T

H = 2 to 5T

Gussets

Gussets are often placed at points of attachment, support, or contact with other components.

Effective in reducing localized regions of large deflection and in

distributing stress.

Plastic Flow :

Does not like to change direction

Rounded corners promote better melt flow

Radii, Fillets and Corners

Larger fillet radius

•Avoids stress concentration

•Provide streamlined flow paths for the molten plastic resulting in easier fills.

The stress concentration factor is a multiplier factor, it increases the stress.

Actual Stress = Stress Concentration Factor K x Stress Calculated

The stress concentration factor is very high if r/t values are less.

Radii, Fillets and Corners

A fillet radius(r) should be between 25% to 60% the nominal wall thickness or a minimum radius of 0.02 inch (0.5mm) is suggested.

The larger fillet radius suggested for load carrying features.

Break any sharp corner with at least 0.005 inch (0.13mm) radius.

The part must be able to be ejectedfrom the mold

No Draft Angle

Difficult Ejection Easier Ejection

Ejecting the Part

Generous draft angles will facilitate part ejection.

The amount of draft angle depends on the depth of the part in the mold, and its required end use function

Click

Generous Draft Angle > 1oDraft is the tapering of surfaces parallel to the line of draw (opening and

closing of the mold) for easier part removal.

The larger the draft angle, the easier the ejection.

For a Textured Sidewall

Additional 1 Degree Per 0.001 inchesin Depth of Texture

Typically draft angle is 10 with 1/20 on ribs

• Where minimum draft is desired due to design limitations, good polishing recommended and depth should not exceed 0.5 in.

• More draft aids ejection but may generate a material mass on sections contained in one side of the mold.

• The mold parting line can be relocated to split the draft in order to minimize it.

Draft leads material mass Without draft P/L relocation

• Parting line consideration depends upon shape and the function of the part. Specify the mismatch on the parting line to meet the required function.

Parting line

• Drag at shutoff will wear over time and develop flash. When a stepped parting line required allow 70 draft for shutoff . Minimum shutoff angle is 50.

Shutoff / stepped parting line

Direction of Pull

How do you stiffen the 2nd Side?(Using ribs in red?)

Mold

Mold

Part

Direction of Pull

How to Stiffen Areas Not Parallel to the Parting Plane of the Tool:•Thicken the wall and do not use ribs•Use ribs created with slides and cams in the tool (Costly)

•Often best molded as two separate ribbed parts and then assembled

Click

Click

Click

REQUIRES SLIDE IN MOLD

NO SLIDE REQUIRED

NO SLIDE REQUIRED,MOLD LESS COMPLEX

Click

Plastic Notes PDI 4.23

Material: Noryl PX1600-701 per A50LA77B. 50% regrind allowed. Wall thickness to be .060 .010 unless otherwise specified. Color White per 12H2427. Draft to be 1 max unless otherwise specified. Ejector pins, gates, and parting line locations must be approved by GEA design engineering in writing prior to initial tooling, retooling or tooling modifications. Flash not to exceed .005 height x .003 thickness. Mismatch of surface across parting line not to exceed .005. Dimensions do not include flash. All fillets, radii and edges to be .020 R .005 . GEA part number, cavity number, and proper recycling identifier (refer to PDI 5.21) must be legible And located on surface indicated.

Plastic Notes –PDI 4.23

This component (assembly) is referenced in international regulatory agency approvals. Suppliers, materials, part marking and dimensions must not be changed without prior approval of program manager international standards or designee.

Materials must be UL recognized, CSA approved (or cUL recognized). Appearance surface must have a gloss of 60 min. per test specification E9F2B. Visible surfaces to be free of sink marks and flash. Material must meet test per QCI 211112 Pt 3(heat distortion). no visible distortion. Material must meet odor and taste test per TS E8C76A SECT. ?? , less than grade 2. Max bow specification to be .010 . Max longitudinal twist specification to be 1

Thank you for your attention