Tue, 01 November, 2022
(Written by Dr Abbasi Gandhi and Kandarp Amin)
With the increasing focus on renewable energy generation there has been a significant change in the automotive industry with a drive towards electrification and EVs. Recent European Union targets propose a ban on the sale of new cars with internal combustion engines by 2035 (and 2030 in the UK). As a result of the current surge in targets for EV manufacturing, significant challenges are being placed on the supply chain in terms of design requirements, inspection, testing and validation (inc. electrical testing) and, most importantly, joining and manufacturing technologies.
TWI Members’ Core Research Programme (CRP) aims to provide a comprehensive assessment of battery joining options for electric vehicle (EV) battery pack manufacture. Our literature review report [1] has highlighted that the focus of this CRP project should be on laser and ultrasonic bonding (such as wire bonding) methods, as these are the leading methods for joining battery packs. Furthermore, the literature review has shown that there is limited directly comparable data between the mechanical and electrical performance of cell to busbar joints manufactured using these two joining techniques. Therefore, this CRP will aim to develop the best processing parameters for joining, then compare, and contrast laser welding against wire bonding to generate directly comparable data sets for different bus bar materials.
Objectives:
- To identify and develop the best processing parameters for wire bonding and laser welding using Design of Experiment (DoE) methods.
- To directly compare the joint strength of laser welding joints to the wire bonding process.
Summary of DoE study:
- The materials down selected to represent the battery tabs were commercially pure Al and nickel-plated stainless steel (NiP-SS).
- The wire bonding was conducted using a Hesse Bondjet BJ985 ultrasonic wide wire bonder and the laser welding was conducted using a G4 pulsed fibre laser (nanosecond pulse, Ep-Z, Class A1) with 50W power.
- In order to characterise, the joints were subjected to mechanical pull-out using Nordson Dage Bond Tester 4000Plus and electrical contact resistance (ECR) testing using 4-point resistance methods with bespoke probes.
- DoE software MINITAB-14 was used to identify the parameters to be trialled with a view to finding the best processing parameter set for the material combination, for the joining equipment used.
- Successfully conducted DOE on the joints and the most significant factors effecting the pull-out force and ECR for wire bonded and laser welded Al on NiP-SS sheet were identified.
- The results from this study will assist in process selection for tab-to-busbar joints and module design, which is not readily available in the public domain.
[1] https://www.twi-global.com/what-we-do/research-and-technology/research-programmes/core-research-programme/technical-literature-reviews/33559-2021-review-of-electric-vehicle-battery-joining-methods-and-testing
More information
For more information on Wire Bonding at TWI, visit here
For more information on Laser Welding at TWI, visit here