Nereth1
Mechanical
- Feb 2, 2014
- 136
Hi all,
Our production engineering has designed a hand tool that significantly improves a process speed, but by its design, it has an 0.8mm thick x 5mm long cantilevered section with a stress raiser on one side, placed under unidrectional bending. Sketch attached.
The stress raiser is on the compressive side, so I'm not sure if it's actually an issue. Arguably it is drawing stress away from the tensile side I suppose, and we should consider making it even worse.
In any case, we can't find a material suitable to make this work for more than a few weeks. Money is effectively no object due to the amount of time this tool saves, versus the frustration of remaking them every week as they fail with what we have attempted thus far:
1) K1045 at around 400MPa yield, visibly bends after a dozen uses.
2) 4140 at around 900MPa, lasts a good few hundred uses.
3) Bohler K245, ( heat treated professionally to around 58 Rc. Lasted a few thousand uses. This was not heat treated in a vaccuum furnace.
Next, we have been given a handful of tool steel options from the local Bohler rep, and were going to send the lot interstate for a more precise, cleaner heat treatment in a vaccuum furnace. Hopefully one of those works. If they end up failing in a month, I want to be prepared to get a little more exotic, for which I was hoping for the help of the experts here. What are everyone's thoughts on:
1) Other, non tool-steels for this application. I was thinking a lot of these hard tool steels are not designed for this kind of fatigue, so I was looking at other UHS steels e.g. Ferrium M54, but I don't know how they would compare.
2) What do we need to watch out for in the heat treat - e.g. as we are going up to high 50 Rc, I assume we are quenching pretty aggressively and not doing a lot of tempering - but would such a thin section attached to such a thick section be subject to massive internal stresses that would be counter productive in that case? How do we control that?
3) I have been thinking about secondary processes like nitriding to put a compressive preload in the tensile surface, but with such a thin section, would there be issues with us just accidentally nitriding most of the section depth, and having the centre of it go too far tensile and thus being counterproductive?
Thanks.
Our production engineering has designed a hand tool that significantly improves a process speed, but by its design, it has an 0.8mm thick x 5mm long cantilevered section with a stress raiser on one side, placed under unidrectional bending. Sketch attached.
The stress raiser is on the compressive side, so I'm not sure if it's actually an issue. Arguably it is drawing stress away from the tensile side I suppose, and we should consider making it even worse.
In any case, we can't find a material suitable to make this work for more than a few weeks. Money is effectively no object due to the amount of time this tool saves, versus the frustration of remaking them every week as they fail with what we have attempted thus far:
1) K1045 at around 400MPa yield, visibly bends after a dozen uses.
2) 4140 at around 900MPa, lasts a good few hundred uses.
3) Bohler K245, ( heat treated professionally to around 58 Rc. Lasted a few thousand uses. This was not heat treated in a vaccuum furnace.
Next, we have been given a handful of tool steel options from the local Bohler rep, and were going to send the lot interstate for a more precise, cleaner heat treatment in a vaccuum furnace. Hopefully one of those works. If they end up failing in a month, I want to be prepared to get a little more exotic, for which I was hoping for the help of the experts here. What are everyone's thoughts on:
1) Other, non tool-steels for this application. I was thinking a lot of these hard tool steels are not designed for this kind of fatigue, so I was looking at other UHS steels e.g. Ferrium M54, but I don't know how they would compare.
2) What do we need to watch out for in the heat treat - e.g. as we are going up to high 50 Rc, I assume we are quenching pretty aggressively and not doing a lot of tempering - but would such a thin section attached to such a thick section be subject to massive internal stresses that would be counter productive in that case? How do we control that?
3) I have been thinking about secondary processes like nitriding to put a compressive preload in the tensile surface, but with such a thin section, would there be issues with us just accidentally nitriding most of the section depth, and having the centre of it go too far tensile and thus being counterproductive?
Thanks.
