Machining Structural Steel 1

[Wganders]

We are machining some bushings made from S355J0, a structural steel, and having some problems. Here's the deal:

Material: 125mm hot-rolled bar stock
Part: 121mm OD, 106mm ID (+.0016) x 35mm long
Prep: Saw-cut with 3/16" stock on length and pre-drilling a 1-5/16 hole.

We machined one part and it went out-of-round over night!

Does this material need to be normalized before machining? Should we rough it out, normalize, and then finish?

Any help would be most appreciated!!

Thanks,
Wganders

 

[MikeHalloran]

Clearly, the material is telling you that it's going to move around when you remove some internal stresses. Consider how it's made and how it's intended to be used.



Mike Halloran
Pembroke Pines, FL, USA

 

[TVP]

You probably don't have to normalize the steel (~ 900 C followed by slow cooling), although this may improve the machinability over the hot-rolled condition. Stress relief annealing may be sufficient: try 595 C for 1 hour on the bar prior to machining.

 

[ornerynorsk]

Anything considered structural or CQ is horrendous for machining purposes. You truly never know what you're getting. With the added uncertainties and possible additional cost of annealing, you may want to just upgrade to a better material, if you're allowed.

 

[Wganders]

Thanks for all the info. I finally found a solution:

1. Rough part leaving .05/side
2. Sub-critical anneal (1250F for 2 hours followed by air cooling)
3. Finish machine

The 2 samples I did still moved a little, .001 out-of-round, but I can live with that!

Now we need to get approval from the customer and bump up the price!!

Wganders

 

[silveringchap]

I'm assuming you are holding on the bar end and parting off the component when you've finished machining the outside/inside and the end. During the machining, just keep it nice and cool with the coolant.You may need to invest in a coolant cooler if you intend to do this as a regular job.Take the skin off out/inside before finishing!

 

[desertfox]

Hi Wganders

Might it be more economical in this case to use say a cold drawn bar it might eliminate having to heat treat.

desertfox

 

[mfgenggear]

I would do as you are planning

rough machine then anneal or stress relieve then finish machine.