Help - Mild Steel Plate CR4

[Ewok]

Can anybody advise me please?

I got some 2mm steel plate from a local supplier (he’s on his holls at the mo) to make some prototype hinges. Did that worked fine, so drew them up and got a batch laser cut buy my local supplier in MS CR4.

The laser cut ones are a soft as poo. You can bend them in your fingers. The ones I made are MUCH stronger – exactly the same size. I don't understand.

Are there different grades of mild steel plate – do I need to specify something different?

Any advice / comments would be gratefully received...

 

[Iain Westland]

you need to know what the plate that you got from the suppier was/is. CR4 is a grade, but you might have speced differently to the delivered material.

did you take the hinges in to the laser guys or just the cad? maybe they could help

Iain

 

[Ewok]

Just back from town and my metal bending guy who supplied the plate for my prototypes was back. His plate was CR4 as well. Showed him the hinge I had done and he could not understand either. I think I need to get back to my laser cutting people.

Are there actually different grades? As far as I understand the CR is cold rolled and the 4 is the grade.

 

[Ewok]

Thinking on...

The hinge component is quite small - most of its length it is 15mm wide. Would the heat build up from the laser slightly have annealed the plate? – is that why it is so soft by comparison?

 

[bigbadbugga]

How did you make the prototype?

Is it possible that you work hardened the steel?

 

[Arsonista]

CR4 is the 'mothers pride' of sheet steel and at 2mm thick should be quite sturdy. Maybe the laser people got a bit of CR3 mixed up with it. It's softer but not as common.

 

[scott0031]

Thinking on...

The hinge component is quite small - most of its length it is 15mm wide. Would the heat build up from the laser slightly have annealed the plate? – is that why it is so soft by comparison?

Would suggest its a mix up somewhere down the line, But depends on the use i guess as i don't find any of the cr's have that much strength compared to a bit of proper steel.


It shouldn't be affected at all by the heat from the laser, those softer types of material are generally 'non heat treatable', hence why certain materials are used for their heat treatable properties to suit a certain application. Nearly all softer types of mild steels including mild steel can only be heat treated with the introduction of another material such as 'carbon' as in case hardening. The only other process that could occur is 'normalising' this effectively only stress reliefs the material, but does not alter the materials mechanical properties'


Kind regards,


Scott (ward eng)

 

[Ewok]

How did you make the prototype?

Is it possible that you work hardened the steel?

No. I just traced the drawing out onto the sheet and cut / ground it to shape with a griderette (and a file and a dremmel and my finger - still hurts)

 

[Ewok]

Ummm - I think I'll take it up with the laser people. It really is a soft as ...

 

[Paul.]

It could just be that the grain is running in a different direction to the original, It can also make a noticeable difference when bending on a press, parts bent across the grain will spring back differently to parts bent along the grain, sheet is also more likely to crack if the bend is in line with the grain rather than across it.

 

[Ewok]

Hinge part in question. You can hold the straight part at the top and easily bend the metal between your thumbs between the holes.

and in use...

these are my "hand made" ones and really are MUCH more rigid. The hinge on the right looks thicker - but it's 2mm the same - just the camera angle.

 

[Ewok]

It could just be that the grain is running in a different direction to the original, It can also make a noticeable difference when bending on a press, parts bent across the grain will spring back differently to parts bent along the grain, sheet is also more likely to crack if the bend is in line with the grain rather than across it.

Don't think so - it's universally "soft" throughout it's shape.

 

[Arsonista]

I'd have used about 6mm for that.

 

[Ewok]

I'd have used about 6mm for that.

Nooo, way OTT

 

[busa]

I'd have used about 6mm for that.

I'd have used stainless!

 

[Ewok]

I think I will use stainless next time - would this be "stiffer" ?