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Plastics Lightweighting Saviour
Best Practice & Assessment of Joint Integrity
of Welded Moulded Plastics Components
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Dr Farshad Salamat-Zadeh
TWI, Cambridge, UK
LIGHTer International Conference Gothenburge, 17-18 November 2015
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Introduction
Plastics in Automotive Sector
Assembly of Plastics
Case Studies
Vapour Separator
Standards on Thermoplastics Welding
TWI Services
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Content
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Plastics in Automotive Sector
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During the oil crisis of the '70s, automakers realised that plastics could make cars more energy efficient by reducing weight
Advantages: Light weight
Durable
Corrosion resistance
Tough
Resilience
Ease of colouring and finishing
Applications include: Cabin console , door assemblies, headlight and sideview mirror
housings, air intake manifold, fuel tanks, fluid reservoirs such as; windscreen washer, power steering, brake and clutch fluid
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Plastics in Automotive
Oil Prices: http://www.huffingtonpost.com
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Engine Coolant Expansion Tank
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Plastics in Automotive
Fuel Tank - Internals
Engine Manifold
Throttle Manifold
Steering Fluid Reservoir
Key Fob
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Plastics reduced the weight of the average passenger car built in 1988 by 66 kg Saves millions of gallons of petrol each year Will save the energy equivalent of 21 million barrels of oil over
the average lifetime of those cars
By the 1993 model year, over 114 kg of plastics were used in the average vehicle
By 2020 plastic will account for 18% of average vehicle weight
Global trends are pushing automakers to reinvent their product and manufacturing processes
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Plastics in Automotive
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Automakers face challenging new fuel-economy and greenhouse-gas emissions regulations
In North America passenger cars must meet corporate-average fuel economy (CAFE) standards of 54.5 m/g (4.32 l/100 km) by 2025
In EU, light-duty vehicles will be required to reduce CO2 emissions on new cars to 95 g/km by 2021
Lightweighting in part, requires replacing conventional metals with polymers and hybrid materials
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Plastics in Automotive
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Replacement of engine components such as the engine manifold requires advanced engineering thermoplastic materials, which need to be moulded into a complex 3D structure
Such structures will often be designed and moulded in two halves
Advanced new-materials with complex designs demand suitable joining solutions
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Plastics in Automotive
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Assembly of Plastic Components
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There are currently 16 different welding techniques available for assembly of plastic parts
Ultrasonic
Spin
Vibration
Orbital
Friction stir
Heated tool
Hot gas
Extrusion
Resistive implant
Heat sealing
Flash-free
Infrared
Laser
Induction
Radio frequency
Microwave
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Assembly of Plastics
Friction Direct Heat Source Electromagnetic
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Weld quality of plastics is very much dependent on both the material and the joint design for the specific welding process
Companies have their own internal specifications for Welding of Plastic Parts which dictates both design and welding/joining aspects of plastic components
Verification of weld quality has been a challenging task:
− Visual inspection
− Pressure / burst test
− Microtoming
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The Need
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Case Studies
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Part
Material
Process
Post process
Issue
Vapour separator
Hostaform® C13031 (POM)
Injection moulding
Linear vibration welding
Leakage at weld
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Vapour Separator
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Design Rule
A tongue and groove joint for linear vibration welding (image courtesy of JLR).
A tongue and groove joint showing melt-down region prior to welding (View B), and after welding View-C (image courtesy of JLR).
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General quality test
Some components failed within the warranty period whilst in service
Failure at weld is not unique to this component
On average such premature failures are costing automakers between €4M to €7M to investigate and rectify
Visual inspection
Pressure / Burst test
Leak test
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Vapour Separator (POM)
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Failure Investigation Visual Inspection
Uneven weld gaps
General defects witnessed included: Surface detects
Low melt temperature
Inhomogeneous melt
Weld misalignment
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General defects witnessed that resulted from the welding process included: Voids
Crack at the edge of the weld-line
Poor weld penetration
Misalignment
Excessive loading
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Failure Investigation Microscopy
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(b)
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Failure Investigation
X-ray Radiography & Computed Tomography
HMXCT 225 X-ray Micro-focus machine
CT images of a welded vapour separator: a) complete component with the six critical locations (1-6) marked b) a slice through the part exposing the weld interface and weld-flash
(a)
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“Design Rules” for vibration welding dictate critical dimensions which should be adhered to if a good weld is to be expected
In most investigations the unwelded parts of the component are not available to measure and compare against the “Design Rules”
One major advantage of CT is that the joint design dimensions of the welded part under investigation can be measured on the CT images using software which allows live measurement analysis of the weld-lines
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Failure Investigation
Computed Tomography
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Computed Tomography
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Computed Tomography
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Computed Tomography
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Thermograph Inspection of Tooling & Packaging
On tool core
On tool cavity
Part on conveyer belt
Part in box (packaging)
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Standards on Thermoplastics Welding
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Many national and international standards on the welding and testing of plastics pipes and geomembranes
Some European standards on manual plastics welding techniques
Hot gas, extrusion, etc.
No international standards on the welding and testing of moulded plastics components
DVS guidelines for heated tool, ultrasonic, vibration and spin welding
Need to determine and promote best practice for the welding and testing of moulded plastics components
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Available Standards
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TWI was invited to review the internal welding guides and procedures of a major automotive company
TWI helped to set up a new Working Group within BSI committee WEE/3 “Welding of Thermoplastic Moulded Components”
Aim is to assist Design engineers and Tier-1 suppliers to design correct joints for welding of injection moulded components
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Approach
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Overcoming Barriers OEMs
Standard Bodies
TWI and others
Tier-1
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Subject: Materials
Sector: Manufacturing & Services
Scope Under the direction of WEE/3 is responsible for the preparation of
British Standards specifically in the welding of thermoplastics materials using the following processes: laser, linear vibration, spin, hot plate, infrared, hot ’convection’ gas and ultrasonic welding. The group also provides the UK input into CEN/TC249/WG16
Who is currently involved
BSI Secretary - PRI/-1
TWI Ltd
Jaguar Cars
Ford Motor Company
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Committee: WEE/3 Welding of thermoplastic moulded components
Rofin-Baasel UK
Mergon International
Telsonic UK Ltd
Cikautxo Group
British Plastics Federation
Emerson
JCB Research
Branson
Dyson
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Development of a Bespoke Course
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Three-day training course and assessment, including practical demonstrations, to improve understanding of material selection,
design and fabrication of moulded plastic components.
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Plastic Welding Training Course
Day – 1 Introduction to plastics & welding principles Heated tool, infrared & hot gas convection welding Vibration welding Demonstrations of heated tool & vibration welding Tour of the facilities
Day – 2 Ultrasonic welding Laser welding Spin welding Ultrasonic & hot air stacking Vibration welding Demonstrations of ultrasonic & laser
welding
Day – 3 Mechanical & non-destructive testing
of plastics welds Design Rules Other welding techniques for plastics Adhesive bonding Multiple-choice examination Feedback & discussion
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Joining processes
Vibration welding
Spin welding
Hot plate welding
Ultrasonic welding
Infrared welding
Laser welding
Hot air and ultrasonic staking
Adhesive bonding
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TWI Services - Polymer Division
Services offered
Process selection and optimisation
Mechanical testing
Failure investigation
Joint design
Materials analysis
Training and assessment
Standards development
Non-destructive inspection
Materials selection
Prototype equipment and part development
Pre-production welding
Welding
Mechanical testing
Tensile
Flexural
Flower test
Compressive
Creep
Peel
Fatigue
Impact
Pressure/burst test
Nano-indentation
Inspection techniques
Visual
Microtoming
SEM/EDX
Ultrasonic
X-ray radiography
Thermography
Optical microscopy
Analytical testing
DSC
TGA
DMTA
FTIR
GC-MS
Rheometry
Permeation
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All current investigative techniques are valid
X-ray Radiography & CT:
CT has proved to be an impressive tool which provides a non-destructive test of welded parts
Enables direct comparison against “Design Rule”
X-ray, CT highlighted:
Non-uniform weld flash around the perimeter of the weld
The weld step-H (tongue and groove), weld-flash created and the weld-gauge were inconsistent and did not pass the criteria set by automotive company’s Design Rules
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Summary
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Enables detection of defects and voids in the parts
Packing pressure
Holding pressure
Gate choice
Tool temperature
Thermography inspection identifies
Heat signature
Uneven cooling
Uneven tool tolerances/pressure
Resulting in unacceptable changes to crystallinity
Recommendation for regular QA checks and components qualification using these technique.
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Summary
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Thank you for your attention …
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