FOCUS ON MATERIALS
After each milling run , the plate was unclamped and the flatness was assessed on the measuring tracks .
Measuring points were defined for each milling path and measured by laser . This zero measurement ‘ DG 0 ’ serves as a reference for the original state .
100 tonnes , for forging manipulators with part weights of up to 40 tonnes or for presses with part weights of up to 80 tonnes .
Pooling the benefits
There are numerous advantages to this method : while an average stress relief annealing process emits around 6.6 tonnes of CO₂ , the CO₂ emissions from vibratory stress relief are just 0.03 tonnes . The energy consumption of 32,400kWh for stress relief annealing is contrasted by only 8kWh for vibratory stress relief . Significantly less time is also required : a furnace process typically requires 72 hours , whereas vibratory stress relief for large components takes about eight hours .
In addition , vibratory stress relief does not produce a layer of scale on the component which would then be removed by sandblasting . This not only eliminates the need for costly post processing , it is also more gentle on the material . Generally , subsequent straightening is also not necessary , as no distortion occurs during vibratory stress relief . As any component size of between 100 kilograms and 200 tonnes , and even extreme component geometries , can be treated on-site , there is no need to transport them to a suitable annealing furnace .
Despite the higher labour costs during treatment , the enormous savings in energy , post-processing , transport and time make vibratory stress relief a considerably more cost-effective solution for reducing residual stresses . From Jebens ’ point of view , another argument in favour of this process was that the component dimensions produced are often so large that complete annealing is not possible or a suitable furnace can only be obtained with considerable effort .
Last , but not least , annealing is not feasible for tempered components as there would be no significant stress relief at the permissible annealing temperature .
The comparison test
Nevertheless , Jebens also has customers who have not yet authorised the process . As opposed to stress relief annealing , there is no established factor in the FKM guideline for calculating the strength of machine components as a design guideline for proving fatigue resistance . For this reason , Jebens
Jebens carried out a widely observed comparative test on deformation during the milling of stress relief-annealed and vibratory stress-relieved components
The component on the furnace cart after stress relief annealing .
The component during vibratory stress relief . carried out a widely observed comparative test on deformation during the milling of stress relief-annealed and vibratory stress-relieved components . The aim of this test was to draw conclusions on the stress status in the component .
To this end , Jebens cut two 110mm-thick plates to 800 x 800mm . It then applied a welding seam preparation for a V 110 seam on one side and tacked the components by hand . They were then welded together using a welding robot . Both welds were carried out with the same parameters . The parameters were also selected to maximise residual stresses in the welding seam area .
One set of plates then underwent stress relief annealing , the other was subjected to vibratory stress relief . Milling in the welding seam area should then cause a change in the residual stresses in the components and lead to deformation of the workpieces . Unlike deformation , residual stress cannot be measured in a component , so three measuring grooves were milled into the back of each set of plates . The respective flatness deviations in these grooves had to be measured by laser after each milling run . An initial measurement was carried out as a zero measurement in this state .
A wide milling path was machined on the top of the welding seam to mill off weld material and the heat-affected zone completely . Three millimetres were fed in per milling run . A total of three milling processes were carried out with a chip thickness of three millimetres . The first two runs were milled with cooling lubricant , the third without . The individual milling runs were always carried out with the same parameters . After each run , the flatness of the measuring grooves was measured
98 | ismr . net | ISMR October 2024