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Insert mill tooling cost calculation

starlays

Plastic
Hello.

We are a small and new workshop and we recently have been asked for a quote on a relatively high number of steel parts to do some operations on them.

I have found some formulas on internet to be able to determine the operation costs that takes in account a solid carbide end mill that gives good results.

My question is, when doing operation cost calculation, in the case of an end mill with inserts what is to be taken in consideration on cost calculation? Is it enough to take in consideration the cost of one insert or I should take in consideration the total cost for all the inserts that equips the insert end mill?

The situation is that I'm using an end mill for planar milling that has 7 inserts (each insert has 14 indexable cutting edges) and I want to know how can I make the operation cost calculation. One insert costs around 10e, for per operation cost calculator should I take the tool cost as 10e/14(cutting edges) or should I take 10e/14 X 7 inserts and use this value in operation cost calculation? What should be the correct way on doing this?

Thank you.

EMTech

Aluminum
Hello,

Cost of insert / # of cutting edges × number of inserts in the cutter body.

This will give you the price per tool or "endmill" based on the consumable inserts, but doesn't take into account the cost of the cutter body itself.

Then you will need to take into account the number of parts that you will be able to cut with that tool to be able to figure tooling cost per part.

Keep learning and enjoy the journey!

mhajicek

Titanium
Yup, figure the total insert cost per number of parts. Count the price of the body once, plus however often you guess it'll get crashed. If someone tries to push insert life past the safe point, you can sometimes get catastrophic insert failure that damages or destroys the body. Determining how far you can safely push the inserts requires a bunch of trial and error. Then there's operator error, forgetting to clamp the vise, not clamping it tight enough, putting the part in the wrong orientation, etc. that can all destroy a body, so to be accurate you have to estimate how often your operator will screw up. Some of this can be mitigated with probing checks, at the cost of cycle time.

CarbideBob

Diamond
Then you will need to take into account the number of parts that you will be able to cut with that tool to be able to figure tooling cost per part.

Therein lies the trick.
How long or how much cutting per edge.
How to know that with no actual use numbers to back it up?
What if I change surface footage for shorter or longer insert life?
Bob

Booze Daily

Titanium
Do you really want to do this on every job? My perishable tooling is built into the shop rate.

Are you trying to quote this at such a razor thin margin that if the operator has to take a shit you lose money on the job?

plastikdreams

Diamond
Figuring it per indexable side is flawed...what if some jabrony blows 2 or 3 up?

EMTech

Aluminum
Therein lies the trick.
How long or how much cutting per edge.
How to know that with no actual use numbers to back it up?
What if I change surface footage for shorter or longer insert life?
Bob

You bet it is a trick! Particularly when it is a new job, and you don't have a known baseline for tool life.

If it is an existing job, then all the changes you mentioned can be compared to the standard and kept or discarded based upon the results.

For new jobs, it comes down to a guess. The better the guess, the more profitable you will be. There are just to many variables for tool life (and thereby tool cost) to be anything other than an educated guess on a new job. The exception to this would be if the new job is extremely similar to an existing known job for which you have good data.

EMTech

Aluminum
Do you really want to do this on every job? My perishable tooling is built into the shop rate.

Are you trying to quote this at such a razor thin margin that if the operator has to take a shit you lose money on the job?

I like your idea of building perishable tooling into the shop rate. I personally do the same based on an average (guessed) tooling cost. I do add a line item in my quoting for when a part comes along that I know will involve much higher tooling cost.

The parts I make (and the tools required) vary so much that I don't think it makes sense to try to capture all tooling in shop rate, but that will probably vary based on preference and type of parts being run.

Kalispel

Aluminum
Make your best estimate and multiply by three. If it runs better, you will have extra inserts for next time.

We learned machining by trial and error. At first we relied on calculators and spec sheets. Those things are essential guidelines but the real world has chatter, hard spots, programming nuisances, etc.

We learned the manufacturers generally exaggerate a bit. The inserts will run about 15 minutes at the maximum quoted SFM. Be a little on the conservative side. Slow the SFM down 25 percent from the maximum possible and they will last lot longer.

Cut with air blast instead of coolant when milling steels. Again, counterintuitive but the rapid thermal cycling kills the inserts. All the fancy coatings will do very little good when cutting steel in coolant (drilling and turning are different because the cutting edge is always in contact with the part).

Insert details matter a lot - some slice and some shear. Insert quality varies greatly between manufacturers. Carefully observe your chips, the wear on the inserts and the sounds the setup is making. Think about how the tool and insert are working. You will figure out what to try next.

If you wear a cutting edge out, rotate the inserts. They should all be similar if things are right.

If you push too hard and wreck an insert (crack, break, destroy), change all of them because one or more of the others will fail. If you don’t catch the failure quickly, your tool body will get mangled beyond repair.

Get religious about tightening the inserts. Put some grease on the screws - counterintuitive but it makes a difference in consistency. Buy good screws. Chinese screws are apparently made from laughy taffy. Buy tools that accept substantial inserts (thick) and have robust clamping screws / clamps.

Orange Vise

Titanium
Do you really want to do this on every job? My perishable tooling is built into the shop rate.

+1

You could have a base shop rate + a multiplier based on the material being cut. Aluminum could have a 1.0 multiplier, i.e. no surcharge. Steel would not. This is for internal use only - your customers don't need to know your base shop rate nor your adjusted shop rate, just the quoted cost per part.

Also, don't forget to account for the labor involved in changing tools: cleaning, changing inserts, touching off, and spindle downtime during this process.

Did you know that Inconel is really easy to cut with fresh tooling? But changing out inserts every 10 minutes gets real old, real fast.

Clive603

Titanium
Building insert costs into the shop rate along with all the other consumables is the sensible way of going about things.

But..

You need some numbers to start with. Once you have been running a fair while you will have the experience to assess whether or not you need to add a bit to shop rate to cover expensive inserts et al. Lacking that experience you make your best guess and run some numbers.

On a side note also need to watch out for consumables and other "its not much" costings. Over a year significant under-estimation can nickel and dime your profits down to a lot less than you expected. General tendency is always to under-estimate such things along with lost 5 minutes there, 10 minutes here, in between management crap et al time. Trouble is full on "Mighty Great Big Company" practices that can track this stuff accurately are too complex and time consuming for little guys

It always takes longer and costs more. Always. As a one man band on repair and onesy - twosey work I calibrated my initial estimate error, that x3 multiplier from Kalispel sounds familiar, and saved a lot of figuring. At year end I'd always made a fair return so I called it good.

Clive

Milling man

Cast Iron
Regarding the relationship between tool life and cutting speed.
As a rule, tool life is proportional to the cutting speed to the third power.
That is, with a decrease in cutting speed by 2 times, durability will increase by 8 times. Of course, this simplest ratio does not take into account the influence of metal heating in the cutting zone, build-up on the tool, and other similar factors. But, if the base speed is about 2/3 of the manufacturer's recommended, then this formula will work.
In my opinion, an accurate calculation of resistance for a small production with a variety of nomenclature makes little sense. You can simply record how much material your cutter cuts before changing and then build on that when working with similar materials.

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