Predictor
Prediction of Distortion Control and Techniques to avoid Rework

Project Background

This project is intended and designed to develop, prove and pilot in shipyard conditions, a method for the Prediction and Management of the Distortions of Steel Plates during assembly, due in the large part to welding induced distortion and shrinkage.

The need for this project can be demonstrated by consideration of the re-work, both recognised and hidden, which forms part of the total steelwork man-hours in ship production.  The re-work inherent in steel assembly is only partly recognised by the recording of man-hours spent rectifying deformed plates.  From a review of the partner shipyards and other, a conservative estimate of the recognised and recorded re-work due to distortion is 5% of total steelwork hours.

However, there is also unrecognised re-work hidden in the steelwork productivity norms which are used for estimating and planning purposes.  Built in re-work, that is part of the normal hours, is a major element in the overall steel work hours in many shipyards and includes routine processes.  Examples are fairing and alignment of steel structures using hydraulic jacks or welded attachments and their removal.

The difference in man-hours for a specific task between the best and worst productivity shipyards can primarily be accounted for by the accuracy with which the assemblies are produced.  Weld induced distortion is a major component in inaccuracy and therefore in additional man-hours.  If international comparisons are made, productivity figures for poor and good performance shipyards show that the best use only half ( or sometimes less than half ) of the man-hours of the worst.  That is to say, by eliminating the work content ( whether recorded as re-work or not ) which is associated with aligning structures which do not immediately fit together, a significant reduction in overall steel man-hours is possible.

The costs of the re-work can be broadly estimated.  There are around 2,000 steel workers in UK ship construction in all sectors.  This represents in excess of 3,000,000 annual man-hours.  Of these abut 1,200,000 are in large unit / block assembly and ship construction, and are most affected by distortion.  The typical productivity figure across sectors is around 100 man-hours per tonne, and the UK shipbuilders are anticipated to produce some 30,000 tonnes of steel annually in the next few years.

The potential saving, assuming a conservative reduction in man-hours of 30% of the hours spent after the unit assembly stage of production is 360,000 man-hours annually at a cost of some £3,600,000.

As important is the potential effect on speed of construction.  Avoiding re-work will make planning more reliable and the availability of completed steelwork will make outfitting at an early stage easier.  A reduction in time of 10% is potentially feasible, and this may be greater on closer examination.

Partners

The project is being led by BAE Systems ( BAE ) through the Clyde shipyards at Scotstoun and Govan.  The project manager is Norrie McPherson who is the Welding Engineering Manager.  BAE Systems Clyde shipyards are lead UK producers of surface warships, auxiliary ships and commercial vessels.

BAE are providing the facilities where controlled experimental work will be carried out in support of the project.  BAE is a major centre of shipbuilding welding expertise.

The technology is being provided by the School of Marine Science and Technology of the University of Newcastle, ( DMT ).  The Department is a leading European and World department in its field, the largest such in the UK.  The project manager is George Bruce who is a Senior Lecturer in Marine Production Technology.  Recent PhD work has led to the development of a methodology to predict weld deformation which shows considerable promise and which will be developed and fully trialled in this project.

Corus is a leading steel producer and supplier to the marine industry.  The company has made major developments in steel quality improvements, to support the use of novel production techniques ( e.g. laser cutting and welding ) and is keen to extend this work to new areas.

Objectives and Success Criteria

The objectives of this project are to :

•  Fully identify and classify the causes of welding distortion

•  Identify and make readily accessible procedures for steelwork alignment and welding which will minimise deformation due to distortion and shrinkage.

• Develop and prove a predictive method for welding shrinkage

• Develop a software tool which will allow the distortion due to a particular welding set up to be predicted

The over-riding aim is to use the procedures developed during the project to reduce the man-hours associated with steelwork alignment, welding and deformation correction.

On the basis of the man-hours expected in the UK shipbuilding sector, the savings can be expressed in terms of man-hours per unit of steelwork and also as a cost.

The man-hours per tonne for the UK as a whole is around 100.  This would reduce as a result of the project to 98 by eliminating only the typically 5% recorded re-work at block and construction stages.  Taking into consideration the hidden re-work, the potential is to reduce the man-hours per tonne to 88, a 12% overall reduction.

The total man-hours which would be saved are around 60,000 from recorded re-work, with a cost saving estimated at £600,000 per annum.  Up to £3,600,000 could be saved if the full savings from hidden re-work are realised.  The impact of shorter construction times has not been estimated but is potentially greater.