Machining end of long hard bar

[Pattnmaker]

I have a job coming up we have been forging for years but the customer has made a major change to the end that we Forge. Typically we are making 10 or 20 of these every few months however the volume has gone down over the last few years and due to upcoming process changes in a few years they may or may need them after their process changes.

I made some samples of the new design a year ago. I forge (flatten) the end of a 12ft long bar of 4340. When we're done forging the bar Hardness could be as high as low 50s rc. but will likely be mid 40s especially if I normalize the end. When finished the end of the bar gets hardened to low 50s. I then have to cut out a spear shape from the flattened end and chamfer both sides. Spear shape tolerances are pretty loose, for the samples we made a template zip wheeled and ground to shape with an angle grinder. I had considered making a really quick and dirty shearing die to shear them hot which I have done before but it's an expensive option for a job with an uncertain future.

It occurred to me this morning machining the ends might be a good option. On my mill the table moves in and out in y but the head is on a gantry for x so sticking out the front of the machine the bar would only be moving in and out. Even so a lot of x moves make me nervous. What would your approach be to machine the spear shape out of 1/4 4340 on the end of a long 1" bar? Slow full width cut with one endmill. Slow full width roughing cut with rougher then finish cut. Or just go at it with an adaptive and live with all the in and out of the 12ft bar. Rough out the 3/32 chamfer or just cut in one go?

Workholding easiest would be to clamp on the round but it leaves the spear unsupported. If I clamp on the spear the clamp would be in the way and require a longer tool.

 

[implmex]

Hi Pattnmaker:
Have you considered making the heads as separate pieces and welding them on?

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[michiganbuck]

Is the spear end faceted or round?

 

[Pattnmaker]

Its a faceted spear end. Funny enough the ultimate customers drawing calls for a 2" deep by 1/4" slot machined into the end of the 12' bar and then the flat slid into the slot and welded. Just as bad or worse to machine the slot in the end of the bar of 4340 pre hard. I have 3 other products I make for this customer and another in the same industry that the drawing calls for a machined and welded tool all made of 4340. They all were failing in use they came to me and I now forge the parts and they stand up. I quoted the parts as forged out of a single bar and I would feel more comfortable forging them rather than welding them.

 

[gbent]

How do you forge the ends? Could you hobb a die?

 

[Pattnmaker]

The samples I just forged the width out holding the part diagonal on my power hammer dies and flipping it between blows. But this time I plan on making a simple die that will shape the center rib and give me stock to cut the outside from. The die won't give me the outside shape however. Like I mentioned I could make a shear to trim the outside and may still go that way but I was trying to save myself tooling time and costs.

 

[memphisjed]

A leaf shape? You can rough out a near net shape then final shape with a flapper wheel faster than squishing then getting in a mill.
Leaf/spear is a shape steel wants to go into.

 

[Pattnmaker]

Not just a leaf shape a specific profile. With a heavy rib down the middle. Yes we could pre taper the bar and get a leaf shape but I need a consistent faceted shape 1/4 thick. This is not my first forging. We do a lot of specialized forged tools on open dies. Edging 2" wide by 1/4 thick almost at a 45 degree per side angle is going to be tricky especially on the end of a 12 foot 1 Inch alloy steel bar.
A few years ago I did some similar shaped bars 5/8" diameter 20 ft long no welding allowed. They required upsetting first, flattening and then a hot shearing die under the hammer. I now have a hydraulic press strong enough to do the hot shearing which will be easier than doing it under the hammer but if I can machine it as fast as zip wheeling it or even close I will get a more consistent part and it’s a much more pleasant job for my employee than grinding it to size.

 

[L Vanice]

Without a picture, I may not be understanding what needs to be done. But, if a shear can do the trimming job, then I have to wonder whether a bandsaw can do it, faster than a disc grinder and with no special tooling.

Larry

 

[gbent]

Curiosity. What size, brand hammer?

 

[Rickyb]

A word of caution if you do decide to shear the ends. Any heating you might do must remain 50°F below the original tempering temp that got the parts to Rc50. That will be fairly low. This will prevent the parts from further tempering and keep them at Rc50.

 

[Pattnmaker]

Curiosity. What size, brand hammer?

5cwt Massey

 

[gbent]

Cool! Thats plenty big enough. I'd love to work with it for a while.

 

[Pattnmaker]

Yes it handles 1" pretty easily. We just finished a shackle that we had to start with 4" round. That was heavier than I want to work regularly, especially in the summer heat.

 

[DDoug]

CellCon machine moves only the head.

 

[Superbowl]

Can you use a cut off saw to cut the shape close enough so grinding is minimal?