Hard milling for tooling

[dgeesaman]

I have a component I want to have made domestically for a personal project and I have an existing version that was made overseas. That vendor has vanished just a few months after that.

I believe the existing version was made by hard milling of 440C 55HRC. It's a small split cavity mold used for cold swaging dead soft lead/lead alloys. First order will be for a quantity of two (two halves) and out of my personal pocket so I need to keep it aligned with materials and methods that are already popular with the hard milling work that's already being done.

Poking around domestic suppliers, it would seem 420 is more common for hard milling tooling than 440C. Is this the reality?

Also I see machining vendors bragging about "up to 60HRC" but I don't think my application demands very high hardness. It does benefit from high accuracy. So what material hardness would be cost effective for a hard milling and holding very tight tolerances? ('tight' being .0004 profile of surfaces extending over a 2" x 2" area)

Any guidelines for a minimum interior radius that goes with the above?

I assume the hard milled face will not be smooth and flat enough for the mold parting face so it will require separate lapping?

Thanks for any thoughts from the group before I start ringing phones of random hard milling vendors and asking really basic questions.

If there's a reference book (e.g. injection mold tooling design) that covers this well, I'll accept such recommendations.

 

[mfgenggear]

Op
Parts are normally ruffled heat treated then final machined. Depending on the configuration, milling from Solid is not normally done.

 

[DirteJoe]

The few times I have done dies from full hardness, it has always only been by grinding. Waste of time and money. It will be more beneficial to rough, heat treat, grind, and and blue - lap/polish by hand.

4340 would be a cheaper option.

 

[cnc king]

"440C stainless steel, while superior in hardness, is generally more difficult to machine, whereas 420 stainless steel typically offers better machinability due to its improved cutting performance and grindability. For applications like small split cavity molds, 420 stainless steel may be easier to work with and its performance might suffice for your needs. Considering machining performance and cost, 420 stainless steel could be a more suitable choice, especially for hard milling tools. For further details on stainless steel varieties, you can refer to this website: [https://www.want.net/materials/stainless-steel/](https://www.want.net/materials/stainless-steel/)."

I have a component I want to have made domestically for a personal project and I have an existing version that was made overseas. That vendor has vanished just a few months after that.

I believe the existing version was made by hard milling of 440C 55HRC. It's a small split cavity mold used for cold swaging dead soft lead/lead alloys. First order will be for a quantity of two (two halves) and out of my personal pocket so I need to keep it aligned with materials and methods that are already popular with the hard milling work that's already being done.

Poking around domestic suppliers, it would seem 420 is more common for hard milling tooling than 440C. Is this the reality?

Also I see machining vendors bragging about "up to 60HRC" but I don't think my application demands very high hardness. It does benefit from high accuracy. So what material hardness would be cost effective for a hard milling and holding very tight tolerances? ('tight' being .0004 profile of surfaces extending over a 2" x 2" area)

Any guidelines for a minimum interior radius that goes with the above?

I assume the hard milled face will not be smooth and flat enough for the mold parting face so it will require separate lapping?

Thanks for any thoughts from the group before I start ringing phones of random hard milling vendors and asking really basic questions.

If there's a reference book (e.g. injection mold tooling design) that covers this well, I'll accept such recommendations.