Engineering news
Energy modelling and a method for reducing the energy loss due to cutting load during machining operations
In a manufacturing system the machining operations represent a major proportion of the total energy consumption. The electrical energy consumption of a machining operation can be divided into four types i.e. standby power, operational power, cutting power and power loss due to the cutting load. Power loss due to the cutting load involves frictional power losses in the spindle bearings and also spindle motor power losses. Power loss due to the cutting load accounts for up to 20% of the cutting power consumption during machining operations.
A mathematical model was developed for the power loss in the mechanical transmission and the spindle motor separately.
The model was validated experimentally using two different NC lathes, machining workpieces of steel, aluminium and ductile iron with no coolant. This allowed conclusions to be drawn on the means of reducing the energy consumption of the machine tool. It was found that:
1. There is a positive relationship between the power loss due to the cutting load and the cutting force at the workpiece.
2. Less power is consumed when running at higher cutting speeds than at lower speeds with similar metal removal rates.
Moreover, monitoring the power used during the cutting process can be used to pinpoint impending faults in the machine tool spindle drive.
(Jingxiang Lv, Tao Peng and Renzhong Tang)
Proc IMechE Part B J Engineering Manufacture
2019. Vol 233 (Issue 3) 699-710
Mechanism and modelling of the multi-stage bending process for large-scale forgings
This work concerns the hot forging of large components. The example used was a railway coupler yoke with an unfolded length of 2030mm and 32mm thickness made from high strength low alloy steel 25MnCrNiMoA. Common faults after the bending of the component are cracks, fractures, scratches and local thinning. Moreover, expensive bending machinery is required and die wear is significant.
A three-dimensional finite element model was developed to investigate possible improvements to the process.
In order to overcome the defects a two-stage bending process was proposed with an initial V pre bend followed by the final U bend to give the required finished dimensions of the component. This was allied to the introduction of rollers in the tool in place of inlet fillets and a slight increase of the clearance between the punch and die. These changes meant that the service life of the tooling is prolonged.
Finally, the proposed bending process and tool design were validated by trial production of components.
(Lu Li and Zhi-Yuan Pan)
Proc IMechE Part B J Engineering Manufacture
2019. Vol 233 (Issue 9) 1968-1979
For a full copy of either of the papers summarised here, please visit the online IMechE library.
In case of difficulty call the library on +44(0)20 7973 1274.