Themadag Mikrocentrum Verbinden van Kunststoffen24 April 2012

Dirk Noordegraaf

Mechanical Assembly of Plastic Components

No. 1

Assembly Methods

ScrewsBolt and nutsNailsSnapfitsInsertsRivetsHeat/sonic inserts

hot plateultrasonicvibrationlaserelectromagnetic

Cyanoacrylates 2K, UV Acrylates hot melt1K, 2K epoxy1K, 2K Polyurethane1K, 2K Silicone

Mechanical Adhesives Welding

No. 2

Time

Deformation = Constant

Mechanical Fixing = Managing Stress and Stress relaxation

Inserts, Screws, Snapfits all introduce local permanent stress and/or elongation

No. 3

Relaxation modulusRelaxation modulus

Rela

xati

on

s m

od

ulu

s E r

Time

= 5%

No. 4

Time t (log)

εεεε

1

2

3

4

Maximum allowable elongation

No. 5

Short term longtermProduct Polymer unreinforced reinforced unreinforced reinforced

Lexan* resin PC 4 1 - 4 1) 0,8 0,4 - 0,5Noryl* resin PPO/PS 3 - 4 2) 1 - 2 1) 0,6 - 0,7 0,4Cycolac* resin ABS 2 1 - 2 1) 0,5 0,4Cycoloy* resin PC/ABS 3 0,6Ultem* resin PEI 5 0,5 - 3 1) 1 0,5Valox* resin PBT + PET 3 1 - 3 1) 2 1Xenoy* resin PC/PBT 4 1 - 3 1) 2 1Noryl GTX* resin PPE/PA 3 2 - 3 1) 2 1

Maximum allowable elongation

1) Depending nature and loading of the filler.

2) Depending ratio PPE/PS

No. 6

Stress [ h ]

σ 1

σ 2

σ 3

σ 1> σ 2> σ 3

Elon

gatio

n [ %

]

Maximum allowable stress

No. 7

Material 23 °C 50 °C 70 °C 100 °C 120 °C 175 °C

Cycolac * resin

Cycoloy * resin

Noryl * resin

Reinforced 1)

Lexan* resin

Valox* resin

Ultem* resin

12

13

8-1428

1435

1021

2643

2

5-1024

1128

-

3-721

721

3,513

-

0-312

3,514

1330

-

-

-5

-7

8

-

-

--

--

720

Maximum allowable stress

unreinforced

Reinforced 1)unreinforced

Reinforced 1)

Unreinforced 2)

Reinforced 1)unreinforced

1) Depending nature and loading of the filler.

2) Depending ratio PPE/PS

No. 8

Managing stress

Surface area

Wall thickness

No peak stresses (circular bosses, trilobal screws)

Radii everywhere

Screws

Mechanical Assembly of Plastic Components

No. 10

Screw Joints

Molded in ThreadThreadforming ScrewsThreadcutting ScrewsMetal InsertsBolt and Nut

No. 11

Screw Assembly

advantages/disadvantages

Separable Extra production stepVibration proof Extra partSelf regulating Local stress concentration

No. 12

Basic rulesBeware of sinkmark when boss is located on the backside of A surface

keep wallthickness/rib ratio

No automatic X / Y positioning by the screw. Centric boss needed.

Screw Assembly

In molded threadScrew Assembly

No. 14

In molded threadNote• use maximal radii both for external as well as internal thread • do not use tapered thread

Screw Assembly

No. 15

Threaded pipe connection

Max. torque for ¾ thread Ultem* 2400 resin 135 NmNoryl* GFN1740V resin 100 NmNoryl* GTX830 resin 90 Nm

Tensile strengthUltem* 2400 resin 180 MPaNoryl* GFN1740V resin 165 MPaNoryl* GTX830 resin 110 MPa

Maximum Torque correlated with Tensile Strenght

InsertsScrew Assembly

No. 17

Fully reversible assembly External profile determine torque and pull out forceAvoid sharp edges

Heat insert US insert Expansion insert Threadcutting insert

Inserts

Screw Assembly

No. 18

Boss Design

Boss outer diameter at least twice insert outer diameterHole ø = insert outer ø - 0.5 mmInserts should stand slightly above the surface of the plastic so that the bolt rests on the top surface of the insert and not on the plastic part.

D

2*D

D+0.5 mm

R=0.25W

W

D ~ 0.5W for reduced sink mark

0.5-1.5°Draft angle

Reduce mass

2 mm for flash

0.05 –0.2 mmD

2*D

D+0.5 mm

R=0.25W

W

D ~ 0.5W for reduced sink mark

0.5-1.5°Draft angle

Reduce mass

2 mm for flash

0.05 –0.2 mm

ScrewsScrew Assembly

No. 20

Threadcutting Screws

Use only for rigid plastics to avoid high stresses

45°±5°

Thread forming

Generally used for plastics

Screw Assembly

No. 21

Diameter screw is determined by the maximum stress at stripping

Unreinforced resinsdhole = 0,8 x dscrew

Reinforced resins dhole = 0,88 x dscrew

Lead-in counterbore to reduce radial edge stresses

outer d1.7-2.5*d

Hole d

d

0.3-0.5d

ThreadEngagement

1.7-2.2*d

s

A

R

R

detail A

d+0.2mm

Wallthickness

Boss design

Screw Assembly

No. 22

30°

Frad

Fax F

Frad = 0.26FFax = 0.97F

Flank angle • 30° for low radial stresses

Thread pitch• max. 8° for vibration

resistance

Core diameter• small to enable material flow• enough space for displaced

material

Tolerances• only + tool to reduce

thread stripping

Screw Design

Screw Assembly

No. 23

Screw installation process

Positioning and fixation

Alignment

Installation• torque• speed

Screw Assembly

No. 24

Installation torque

Thread engagement

torque

threadforming

Thread friction

Clamp force

Stripping torque

Screw headin contact with boss

thread forming

head in contact without clamp load

(installation torque Ti)

destruction of the joint

(stripping torque Ts)

Screw Assembly

No. 25

Torque versus hole diameter

Torque versus hole diameter

0

0.5

1

1.5

2

3 3.2 3.4 3.6 3.8

diameter mm

torq

ue N

m

installation torquestrip torque

Material Lexan* resin 161Screw PT K40 Depth 6 mmSpeed 400 RPM

Largest difference between installation and strip torque is at 3.4 mm

No. 26

Torque versus installation speed

Cycolac* resin4.0 mm hole5.0 mm screw8.0 mm depth

heat generationweakens andmelts boss athigh speed

torque and flankstress decrease 0

1

2

3

0 500 1000 1500 2000 2500

driver speed (rpm)to

rque

(Nm

)

installation torque

stripping torque

optimal driver speed

SnapfitsScrew Assembly

No. 28

Strain in constant width and thickness beamStrain in constant width and thickness beam

3 * f * h2 * l2

=

h

f

l

x 100%max = 93,2 MPa (103,5) max = 3,7 % (4,5)F = 20,1 N (20,7)

Nonlinear FE analysis

l = 10 mmh = 2 mmf = 1,5 mmb = 3 mmE = 2.300 N/mm2 (manual

calculation)

max

Fbending =f*E*b*h3

4*l3

3 *E* f * h2 * l2

=max Length is a dominant factor in the snapfit

max

No. 29

Conical SnapfitsConical Snapfits

0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

R = ho hs/

1,0

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9

2,0

2,1

2,2

Ks

h0

hs

f

max=3 *f * hs

2 * l2 * Ks100 %

Ks = Geometry factor

max = 58,7 MPa max = 2,3 %F = 12,3 N

l = 10 mmh1 = 2 mmh2 = 1 (0.8) mmf = 1,5 mmb = 3 mmE = 2.300 N/mm2

max = 52,4 MPa max = 2,0 %F = 10,8 N

No. 30

Insertion and Pull-out Forces

h

f

l c

F

FF2 12 1

F : deflection forceF1 : insertion forceF2 : pull-out force1 : insertion angle: pull out anglef : deflection

http://www.sabic-ip.com/webtools/redirect?tool=snapfit

PressfitsScrew Assembly

No. 32

Press fits

Shaft/Hub Joint Bush/Housing Joint

No. 33

Key parameters for a press fitKey parameters for a press fit

Diametric Interference [ U ]Relative Diametric Interference [ U R ] Relaxationsmodulus [ E r (t) ]Coefficient of friction [µ 0 ]

http://www.sabic-ip.com/webtools/redirect?tool=bosscalc

No. 34

2

D2D1p

d = D1+ UF

D 1 = Hub inner diameter (nominal) D 2 = Hub outer diameterU = Interference (d - D1)p = Holding pressure [ MPa ]F = Assembly force

Key parameters for a press fitKey parameters for a press fit

Interference U is diameter difference between joining parts

The relative Interference is:Interference U

Nominal diameter D1x 100 %

No. 35

Maximum interferences for unreinforced Lexan* resin and Noryl* resinMaximum interferences for unreinforced Lexan* resin and Noryl* resin

Plastic shaft/Plastic hub

Metal shaft/Plastic hub

0,2 0,3 0,4 0,5 0,6 0,7

7

8

9

10

11

12

13

Max

imum

inte

rfer

ence

(μm

/mm

of t

he s

haft

Hub inner diameter / hub outerdiameter( D1 / D2)

Calculation exemple

No. 36

Calculation exampleCalculation example

D2D1p

d = D1+ U

L

D1 = 8 mmD2 = 12 mm (18 mm)

Maximum interference

D1 / D2 = 8 / 12 = 0,66= 8 / 18 = 0,44

Value 7,6 * 8 = 60,8 µ8,4 * 8 = 67,2 µ

The maximum allowable interference is

0,06 mm( 0.067 mm)

No. 37

Summary

• Mechanical fastening particularly advantageous is the assembly needs beunassembled during life time

• Managing long term lower level stresses in mechanical joint of keyimportance to prevent failure

• Performance, peak stresses and maximum allowable stresses for mostmechanical joints are very well predictable

No. 38

SABIC-IP Global Disclaimer

THE MATERIALS, PRODUCTS AND SERVICES OF SABIC INNOVATIVE PLASTICS HOLDING BV, ITS SUBSIDIARIES AND AFFILIATES (“SELLER”), ARE SOLD SUBJECT TO SELLER’S STANDARD CONDITIONS OF SALE, WHICH CAN BE FOUND AT http://www.sabic-ip.com AND ARE AVAILABLE UPON REQUEST. ALTHOUGH ANY INFORMATION OR RECOMMENDATION CONTAINED HEREIN IS GIVEN IN GOOD FAITH, SELLER MAKES NO WARRANTY OR GUARANTEE, EXPRESS OR IMPLIED, (i) THAT THE RESULTS DESCRIBED HEREIN WILL BE OBTAINED UNDER END-USE CONDITIONS, OR (ii) AS TO THE EFFECTIVENESS OR SAFETY OF ANY DESIGN INCORPORATING SELLER’S PRODUCTS, SERVICES OR RECOMMENDATIONS. EXCEPT AS PROVIDED IN SELLER’S STANDARD CONDITIONS OF SALE, SELLER SHALL NOT BE RESPONSIBLE FOR ANY LOSS RESULTING FROM ANY USE OF ITS PRODUCTS OR SERVICES DESCRIBED HEREIN. Each user is responsible for making its own determination as to the suitability of Seller’s products, services or recommendationsfor the user’s particular use through appropriate end-use testing and analysis. Nothing in any document or oral statement shall be deemed to alter or waive any provision of Seller’s Standard Conditions of Sale or this Disclaimer, unless it is specifically agreed to in a writing signed by Seller. No statement by Seller concerning a possible use of any product, service or design is intended, or should be construed, to grant any license under any patent or other intellectual property right of Seller or as a recommendation for the use of such product, service or design in a manner that infringes any patent or other intellectual property right.SABIC Innovative Plastics is a trademark of Sabic Holding Europe BV* Trademark of SABIC Innovative Plastics IP BV