Welding & Joining Technology
Welding research with AMAP focuses on the methods of predicting, overcoming and controlling the weld distortion associated with the fabrication of sheet metal products in the automotive supply industry, as well as the associated welding process development.
The subject of welding and distortion has been investigated extensively, however, there is still significant scope for improved methods for predicting and controlling distortion from the welding process to ensure this does not have a detrimental effect on the product in terms of cost, dimensional conformance or technical specification.
Welding is the primary method of joining used for part assembly in the automobile and ship industry, and, increasingly for aerospace applications.
One major industrial concern is that welding distortion often results in problems such as dimensional inaccuracies during the assembly and increased fabrication costs. Optimisation of the welding sequence and process is one way to reduce the costs and effort associated with rework.
Welding distortion is the result of the non-uniform thermal expansion and contraction of the weld and surrounding base material caused by the heating and cooling cycle of the welding process.
Tensile stresses are generated around the weld combined with compressive stresses in the rest of the plate due to the expansion and subsequent contraction of the yielded material which is restrained by the surrounding colder material.
Distortion occurs when the stresses exceed a certain level. With increasing competition in the manufacturing sector in the global market, the quantification of the level of distortion from welding processes is crucial to meet the increasingly stringent accuracy requirements.
Clearly, there is a strong need for a fabricator to develop the capability to design and manufacture innovative, large and complex welded products at competitive rates with manageable levels of technological and financial risk.
It is known that a number of factors affect welding distortion and these are:
- Material properties of base material.
- Residual stresses induced from shape changing, e.g. rolling, bending, forming, etc.
- Joint design.
- Accuracy of manufacture.
- Welding procedure e.g. heat input and welding sequences.
One approach to reduce distortion, that is being pioneered for industrial readiness in AMAP, is the application of local cooling near to a weld during the welding process, referred to as Dynamically Controlled Low Stress No Distortion, DC-LSND, welding is known to reduce distortion. However, this process is yet to be established in industry due to a range of practical issues.
To promote adoption of the approach then it is desirable to have both the welding process and cooling on the same side of the joint. However, in bringing the cooling to the same side as the welding process then, in the case of Gas Metal Arc Welding, GMAW, the cooling must not interfere with the welding arc and shielding gases to ensure the quality of the weld is maintained. Configurations to overcome such challenges and establish weld process conditions for low distortion welding in sheet metal have been investigated.
A prototype industrial LSND welding system has been manufactured and integrated into a robotic welding system, which has allowed single sided, high quality, reduced distortion welding in a production environment when applied to both sample and real component geometries.
Within AMAP there has been significant work carried out on the modelling of welds to simulate distortion and mechanical properties, using a variety of CAE tools as well as development of some knowledge based prediction methods.
In addition work has been carried out previously on industrial laser welding, including remote laser welding, in conjunction with other academic partners, and this is an area that AMAP are currently looking to develop further, with technology partners.