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Anonymous Poster #1

Blanking / Punching of SS Coil

01/22/2017 7:13 AM

I am newbie to blanking operation.

I am manufacturing cutlery items and for the same i use blanking of SS420 coil. I do have press tools for different products with me. But i am facing one issue repeatedly. The punch gets wear out/chip off very frequently.

When consulted the tool/punch supplier, i had been informed that the higher chromium content (approx 13.5%) of SS coil causes the same.

But there are some people who are used to punch SS430 with 14-15 % Chromium so I doubt about the root cause identified by the tool/punch supplier.

Earlier i used to have SS 420 coils with 12 to 12.5 % chromium but the coils of SS420 which I have with me at present is having approx 13.5% chromium content.

Please guide me.

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#1

Re: Blanking / Punching of SS coil

01/22/2017 10:46 AM

I'd start by specifying and procuring some material with the lower Ni content.

SS is difficult to work with as you are finding. I don't know what your material requirements are but it would seem that you could use a more "punch friendly" grade of material without sacrificing any quality.

More process details would help. Do you anneal before punching?

How to Anneal Stainless Steel to Soften It - Finishing

Then temper? Stainless Steel - Heat Treatment - AZoM.com

The formula for successful punching - The Fabricator

stainless steel fabrication - SSINA

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Anonymous Poster #1
#2
In reply to #1

Re: Blanking / Punching of SS coil

01/22/2017 11:19 AM

Well, having lack of metallurgy knowledge, i will not prefer to change my product's material.

But SS420 is best suitable material for my application i.e. cutlery items.

I am facing this issue just after changing two parameters,

1) Press tool manufacturer ( I am not aware if any process/material has been changed)

2) SS coil manufacturing mill ( Both the materials which I was using earlier and currently are matching SS420 chemical composition requirements; but just chromium content of earlier coil was around 11.5 - 12% whereas current coil is having chromium content around 13- 13.5%)

The SS420 coil which I use is of cold rolled, closed annealed conditions.

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#3
In reply to #2

Re: Blanking / Punching of SS coil

01/22/2017 11:52 AM

So, you changed two parameters and now have problems?

You should be able to deduce the next steps.

1. As I said, get a material that has the lower Ni content.

2. Go back to the toolmaker that gave you satisfactory tooling.

You are beyond help, until you return to the material and tooling that gave good results.

It sounds like you are trying to operate above your level of competence. Maybe you should consider hiring someone who knows metals and tooling.

Finally, if you know nothing about metallurgy, how do you know a softer material will not give satisfactory results?

Good luck.

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Anonymous Poster #1
#4
In reply to #3

Re: Blanking / Punching of SS coil

01/22/2017 12:32 PM

Ok...thanks...i will try/ check feasibility of your suggestion but please let me know just one thing so that my doubt can be cleared..i just want to know whether the claim made by toolmaker is true or he is just trying to save his side ...he is claiming that the higher chromium content in SS coil causes the wear/chip off of punch.

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#6
In reply to #4

Re: Blanking / Punching of SS coil

01/22/2017 1:10 PM

He's probably right about higher Cr and hardness/toughness.

It also depends on the hardness/toughness/brittleness of the tooling steel.

These questions cannot be answered by this forum.

My advice to you, lacking any experience, go back to what was working.

You might also consider 410 as a material. It is lower even in Cr but still suitable for cutlery.

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#9
In reply to #4

Re: Blanking / Punching of SS coil

01/22/2017 1:29 PM

Whilst he's telling you it cannot be done, you can damn bet someone else is doing it - and doing it reliably. If he's playing CYA and you cannot trust him to work with you on this, find someone else. One monkey don't make no show.

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#5

Re: Blanking / Punching of SS Coil

01/22/2017 12:48 PM

It sounds to me like you have clearance issues....your tolerances are set too tight....here are some suggestions that may help you tweak your operation....

http://www.ssina.com/download_a_file/fabricate.pdf

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Anonymous Poster #1
#7
In reply to #5

Re: Blanking / Punching of SS Coil

01/22/2017 1:12 PM

Yes exactly, i am also having the same doubt but the tool maker is not accepting the same and instead diverting the topic to metallurgy...

That's why i just want to know whether the claim made by him about root cause of higher Cr content is true or he just don't want to accept the clearance issue.

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#8
In reply to #7

Re: Blanking / Punching of SS Coil

01/22/2017 1:17 PM

Clearance issues are part of tool design and must be suitable to produce the part. You and your tool maker must be partners with the same desire, a satisfactory end product.

Having a good relationship with your tooling supplier is critical.

Get some softer steel and see what the results are.

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#11
In reply to #7

Re: Blanking / Punching of SS Coil

01/22/2017 1:38 PM

Well what is the clearance? .025 mm should be minimum...Have you tried any lubricant, that might be an easy fix.... It's hard to figure the problem without specific details about the entire process....You just need to keep trying things until something works...It could be poor alignment in the machine for all I know....

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#10

Re: Blanking / Punching of SS Coil

01/22/2017 1:38 PM

There are two very important parameters that you do not give us. One, as SE mentioned is the punch to die clearance. The other is the type of tool steel used for the punch and any coating applied (such as TiN). In general, high Cr tool steels such as D2 are not appropriate for punching high Cr SS. They tend to gall which leads to the chipping and excessive wear you describe.

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#12

Re: Blanking / Punching of SS Coil

01/24/2017 3:34 PM

#1 then do they not meet your specification?

#2 does the other user of such equipment pre-heat and water quench to soften the coil?

#3 are you cycling your machine too fast, and heating up your punching dies, as this can soften them, or embrittle depending on how hot.

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