Product Design Intro

8/17/2019 Product Design Intro

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Plastic Product Design

• Product should meet design requirement

• Economical Process

• Quality should be built into the system

• Should be flexible and responsive to new technology• High productivity: est utili!ation of man" material"

machine" capital and available resources#


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Steps in $odern $anufacturing

Production drawings;

Instruction manuals

Conceptual design and

evaluation Feasibility study

Design

analysis;codes/standards

review; physical and

analytical models

Prototype production

testing and evaluation

Definition of product need,

marketing information

aterial !pecification;process

and e"uipment selection;

safety review

Pilot Production

Production

Inspection and "uality

assurance

Packaging; marketing and

sales literature

Product

C#D

C# and C#PP


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$

Introduction % Concept is simple

• Melt plastic, fow into mold and take part shape, cool, demold

% Injection molding makes parts in discrete (discontinuous) process % More injection molding machines used or plastic processing than

any other equipment

% Almost all thermoplastic and some thermosets materials can einjection molded

% !rocess is automated and highly repeatale parts % Injection molding parts are "nished with little post molding

operations

% #ery comple$ parts can e made

% Machines are e$pensi%e

% Molds are e$pensi%e, usually !&' steel


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Ad%antages o !lastic

• ow Cost

• *asily made into any +hape

•ight weight• ecyclale

• -ide range o color

• Comple$ .esign can e made• /nreakale

• 0on&erosi%e


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imitations o !lastic

• ow +trength

• 1igh initial cost

• 0on&thermal staility• 2rittle at ow temperature

• ow 3hermal and *lectrical

conductors• It destroys soil source 4 not eco

riendly


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!lastic !roduct 5eatures

Corners and *dges is

2oss

1oles

+trengthening the parts

.rats

&ny automobile interior ' exterior thermoplastic partcomes across different types of design features# Some

of the most important design features are below#


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Corners and *dges

In the design o injection moldedparts, sharp corners should ea%oided6

+harp corners act as stress risersor concentrators, reducing partstrength and causing prematureailures6 +harp corners may alsoe7ect plastic fow, producingparts with ojectionale suracefow patterns6

3he inside radius should e atleast hal the part wall thickness

3he outside radius should equalthe inside radius plus the partthickness

(i6e6 68 wall and inside radius o69 equals outside radius o689


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Corners and *dges

As seen in the chart, thestress concentration actoris quite high or :3 %aluesless than 696 5or %alues o

:3 o%er 69 the stressconcentration actor getslower6

3he stress concentrationactor is a multiplier actor,

it increases the stress6Actual +tress ; +tressConcentration

5actor < $ +tress Calculated


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is

Many times the sti7ness o a part mustincrease ecause o the load applied to thepart design6 -ithout ris, the thickness has

to e increased to increase the endingsti7ness =ne o the easiest ways to cure thisprolem is change the part geometry yadding ris6

3he use o ris is a practical way andeconomical means o increasing the endingsti7ness i6e6 the structural strength o a part6


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is

i thickness should eless than wallthickness6

A ri thickness o >?to @? o nominalwall thickness isrecommended6

i should e attached

to the ase withgenerous radiusing atthe corners6


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is

5or a gi%en sti7ness, itis etter to increase

the numer o ris,not the height6

3he height o the ri

should e limited toless than $thickness


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is

3he ri orientation isased on pro%idingma$imum endingsti7ness6

.epending on orientationo the ending load, withrespect to the partgeometry, ris oriented

one way increase

sti7ness6I oriented the wrong way

there is no increase insti7ness6

2 i l i i


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%$

2oosting structural integritywith ris

• +tructural integrityB the goal o e%ery design % 3he major component o designing or structural integrity,

in many cases, is to design the structure to e sti7 enoughto withstand e$pected loads6 Increasing the thickness toachie%e this is sel&deeating, since it willB

• Increase part weight and cost proportional to the increase inthickness6

• Increase molding cycle time required to cool the larger mass omaterial6

• Increase the proaility o sink marks6

% -ell&designed ris can o%ercome these disad%antages with only amarginal increase in part weight6

2 i l i i


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%&

2oosting structural integritywith ris

• 3ypical uses or ris % Co%ers, cainets and ody components with long, wide suraces

that must ha%e good appearance with low weight6

% ollers and guides or paper handling, where the surace muste cylindrical6

% ear odies, where the design calls or wide earing suraceson the center shat and on the gear teeth6

% 5rames and supports6


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%'

is .esign• .esign ules• i geometry

% i thickness, height, and drat angle are relatedB e$cessi%e thickness willproduce sinks on the opposite surace whereas small thickness and too greata drat will thin the ri tip too much or acceptale "lling6

% is should e tapered (drated) at one degree per side6

• ess drat can e used, to one&hal degree per side, i the steel that ormsthe sides o the ri is careully polished6

• 3he drat will increase the ri thickness rom the tip to the root, y aout68D9 mm per centimeter o ri height, or each degree o drat angle6

• 3he ma$imum recommended ri thickness, at the root, is 6@ times thethickness o the ase to which it is attached6

• 3he typical root thickness ranges rom 69 to 6@ times the ase thickness6


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%(

is .esign

• .esign ules•


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%)

ecommended .esign !arameters6• +ee 5igure 8 or recommended design parameters6

i i l


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%*

is .esign ules• ocation o ris, osses, and gussets

% is aligned in the direction o the mold opening are the least e$pensi%e design option totool6

% As illustrated in 5igure 8, a oss should not e placed ne$t to a parallel wallE instead, o7set

the oss and use gussets to strengthen it6 % ussets can e used to support osses that are away rom the walls6 3he same design rules

that apply or ris also apply or gussets6

• Alternati%e con"gurations % As shown in 2elow, ris can take the shape o corrugations6

% 3he ad%antage is that the wall thickness will e uniorm and the drat angle can e placed

on the opposite side o the mold, therey a%oiding the prolem o the thinning ri tip6 % 1oneycom riing attached to a fat surace pro%ides e$cellent resistance to ending in all

directions6

% A he$agonal array o interconnected ris will e more e7ecti%e than a square array,with the

same %olume o material in the ris6


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2osses

2osses are used or locating, mounting,and assemly purposes6 3here are ossdesign guidelines that must e ollowed

to insure the highest quality in moldedparts6 3he wall thicknesses should e less than

> ? o nominal wall to minimiFe sinking6

1owe%er, i the oss is not in a %isilearea, then the wall thickness can eincreased to allow or increased stressesimposed y sel&tapping screws6


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2osses

+ule of thumb the wall thickness around a boss design feature -t.

should be (0 of the nominal part thickness -1. if that thickness is

less than %/*23

If the nominal part thickness is greater than %/*2 the boss wall

thickness should be &0 of the nominal wall3


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2osses

3he oss can estrengthened y

gussets at thease, and yattaching it toneary walls with

connecting ris6


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1oles

1oles are easy to produce in molded parts6Core pins that protrude into the mold

ca%ity make the holes when the part is

molded6 3hrough holes in the moldedparts are easier to produce than lindholes, which do not go all the waythrough a part6

2lind holes are made y core pinssupported on one end only6


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1oles

A good rule o thumB thedepth o the lind holeshould e aout twice thediameter o core pins upto :8>G,and up to ourtimes the diameter ocore pins o%er:8>G6 3heguidelines or lind andthrough holes are seenelow6

2lind 1ole (shown withdrat)B

; '. or .iameters essthan :8>G dia6 core pins

; H. or .iameters Morethan :8>G dia6 core pins


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1oles

As shown the distancerom the edge o a holeto a %ertical surace(i6e6 ri) or the edge o

a part should e twicethe part thickness (ormore), or at least onediameter o the hole6

3his same rule appliesetween holes & at leasttwo part thicknesses orone hole diametershould e speci"ed6


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1oles

5or e%ery cored or molded hole there wille a weld line6 3he weld lines are causedy the fow o the melted plastic around

the core pins6 3hese weld lines are not asstrong as the surrounding plasticmaterial, and also may detract rom theo%erall appearance o the molded part6

3he part designer should consider thesepoints when designing holes in a moldedpart6


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+trengthening the !art

In the design o injectionmolded parts, sharpcorners should e a%oided6

+harp corners act as stressrisers or concentrators,

reducing part strength andcausing premature ailures6+harp corners may alsoe7ect plastic fow,producing parts withojectionale surace fowpatterns6

In addition to reducingstresses, "llet radiusespro%ide streamline fow!aths or the molten plasticresulting in easier "lls6


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.rat

.rats (or taper) in a mold,acilitates part remo%alrom the mold6 3he amounto drat angle depends onthe depth o the part in the

mold, and its required enduse unction6

It is est to allow or as muchdrat as possile or easyrelease rom the mold6

As a nominalrecommendation, it is estto allow 8 to ' degrees odrat6


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!lastic !roduct .esign

Apart rom the earlier discussion.esigners should ha%e to consider

ate .esign

unner +ystem .esign

Cooling +ystem .esign

+hrinkage and -arpage .esign

+ t


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45

unner +ystem

• +e%eral types o runners

% single part runner % multiple part runner

• symmetrical runner

• non&symetrical runner

% runner&less designs with hot maniolds

+ t


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$

unner +ystem

• unner siFe considerations

% Although properly siFing a runner to a gi%en part and molddesign has a tremendous pay&o7, it is oten o%erlooked sincethe asic principles are not widely understood6

• !ros and cons o large runners % -hile large runners acilitate the fow o material at relati%ely

low pressure requirements, they

% require a longer cooling time, more material consumption andscrap, and more clamping orce6

• !ros and cons o small runners

% .esigning the smallest adequate runner system will ma$imiFeeciency in oth raw material use and energy consumption inmolding6 At the same time, howe%er, runner siFe reduction isconstrained y the molding machineJs injection pressurecapaility6

+ t


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$%

unner +ystem

• unner 2alancing is an essential or a alanced

"lling pattern with a reasonale pressure drop6• !ayo7s o good runner design

% A runner system that has een designed correctlywillB

• Achie%e the optimal numer o ca%ities

• .eli%er melt to the ca%ities

• 2alance "lling o multiple ca%ities

• 2alance "lling o multi&gate ca%ities

• MinimiFe scrap

• *ject easily

• Ma$imiFe eciency in energy consumption

• Control the "lling:packing:cycle time6

1 t + t


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$4

1ot unner +ystem• 3he ideal injection molding system deli%ers molded parts o

uniorm density, and ree rom all runners, fash, and gate stus6

• 3o achie%e this, a hot runner system, in contrast to a cold runnersystem, is employed6 3he material in the hot runners ismaintained in a molten state and is not ejected with the moldedpart6 1ot runner systems are also reerred to as hot&maniold

systems, or runnerless molding6

FI67+8 %3 9ot runner system types -a. the insulated hot runner, -b. the internally heated hot:runnersystem, and -c. the eternally heated hot:runner system


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$$

unner uidelines• Common runners

% 5ull&round runner

% 3rapeFoidal runner

% Modi"ed trapeFoidal runner (a comination o roundand trapeFoidal runner)

% 1al&round runner

% ectangular runner


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$&

ate .esign

• ate .esign =%er%iew % +ingle %s6 multiple gates

• +ingle gate is usually desirale ecause multiple gates ha%eweld lines

% ate dimension• 3he gate thickness is usually two&thirds the part thickness6

• 3he gate thickness controls packing time

• Chose a larger gate i youJre aiming or appearance, lowresidual stress, and etter dimensional staility6

% ate location• !osition the gate away rom load&earing areas6

• !osition the gate away rom the thin section areas, orregions o sudden thickness change to a%oid hesitation and

sink marks


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$'

ate .esignate .esign =%er%iew

% ate 3ypes• Manually trimmed

% equires an operator to separate parts rom runnersduring a secondary operation

% 3ypes include sprue, ta, edge, o%erlap, an, disk, ring,"lm, diaphragm, spider

• Automatically trimmed gates % Automatically trimmed gates incorporate eatures in the

tool to reak or shear the gate % +hould e used to

( A%oid gate remo%al as a secondary operation

( Maintain consistent cycle times or all shots

( MinimiFe gate scars

% 3ypes include !in, +umarine, hot&runner, and %al%e


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$)

ate .esign• .esign ules

% ate ength• ate length should e as short as possile to

reduce an e$cessi%e pressure drop across thegate6 anges rom 8 to 869 mm (6H to 6>

inches)

• 3he gate thickness is normally 9 to @ percent othe gated wall section thickness6 !in andsumarine gates range rom 6'9& '6 mm (68K&

6@K)• 3he reeFe&o7 time at the gate is the ma$ e7ecti%e

ca%ity packing time6

• 5ier&"lled materials require larger gates to

i i i k th "

Product Design Intro

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