Component life extended at lower cost

An automotive transmission component often failed prematurely in service. The problem was solved by conversion to manufacture by low pressure die casting – and production costs were cut as well.

Transmission life extended and waste reduced by conversion to Low Pressure Die Casting

An automotive transmission component often failed prematurely in service. The problem was solved by conversion to manufacture by low pressure die casting – and production costs were cut as well.

The challenge: Keeping your taxis on the road

An Australian-made transmission found in most taxis had a reputation for not going the distance. The problem was at the heart of the unit – an aluminium alloy casting known as the ‘clutch cylinder’. The unit would suffer a fatigue failure at about half its rated lifetime – the taxi would be off the road, and the transmission would need a rebuild. Many casting companies had unsuccessfully attempted to make a better version of the part without success – and the transmission was getting a bad reputation.

Our response: Working with industry as part of a new casting development team

The CSIRO worked with Nissan Casting Australia to redesign the part and tooling to make it suited to their Low Pressure Die Casting (LPDC) process. With this approach, the part could be made to solidify in the axially-symmetrical manner seen as the key to improving the part’s service fatigue life. CSIRO used its knowledge of the LPDC process to propose various designs that were then analysed with the MAGMAsoft flow and solidification simulation program. With the predictions looking good, the investment was made in the new tooling and ancillary equipment. CSIRO then worked as part of the in–plant team during the commissioning phase, collecting data and reconciling it with the simulation model – all with the aim of tuning the process to get the best result.

The results: A new casting process, a fundamental fix

The results for the LPDC version of the clutch cylinder casting were excellent. Not only did the finished components meet the required fatigue life for the first time, but the wastage due to production of reject parts was much reduced. Another benefit was the very high as-cast yield. This means that much less metal needs to be poured to produce the component, with the result that less energy is consumed. With an annual production in excess of 200,000 parts, the conversion to LPDC made a substantial positive benefit to the triple-bottom-line: for both the caster and the transmission maker.

Table: Comparison of clutch cylinder performance from two different casting processes

Process Reject rate(%) Individual part weight (kg) As-cast weight (kg) As-cast yield (%) Typical fatigue life (cycles)
Gravity Die Casting 20 2.025 4.132 49 < 600,000
Low Pressure Die Casting 3 1.803 1.898 95 > 1,000,000

 

Two metal like objects. First image cylinder like ovject with several spiraling levels with metal arm attachment. Second image same size as the first but without arm attachment and has a smother surface area
At left is the previous ‘as-cast’ version of the component that had a relatively short service life and was more expensive to manufacture. At right is the improved version of the component in the form in which it is taken out of the casting die.

At left is the previous ‘as-cast’ version of the component that had a relatively short service life and was more expensive to manufacture. At right is the improved version of the component in the form in which it is taken out of the casting die.

Diagram with several layers indicating the temperatures within an object through the various layers

A ‘temperature map’ from the process simulation model that was used to help develop the new version of the casting

Large piece of machinery with three rows of intertwining slabs of metal and an overhanging sheet of metal pressing down

Two new clutch cylinder castings (upper centre of picture) emerge from the new LPDC die

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