working times

[yudansha]

Good morning to all, I am a student of ing.mechanics.
I'm interested in "production processes" that lead from the crude to the finished piece. in particular of the estimate of the "working processes".
from the text of "mechanical production" (secciani-villani) I have identified the passages for the calculation of such times differentiated according to the technology (fresatura, broccia, etc.etc.)
at this point my question is addressed to you that you have more practical experience than what can be a workmanship with a modern "work center" (5 axes, etc. etc. ):
according to you these formulas can still be useful to the purpose or in practice you prefer to make chronometer detections to the hand; or further manufacturers of machine tools provide graphs/tables/programmes, for a rapid estimate of the "working processes"?

Thank you very much
Edoardo

 

[Perfection Lab]

Hi, Edward.

I try to answer your question, which is not very simple as regards milling.

many variables come into play, especially when talking about multiaxial processing.

if you have to calculate the working time of a single processing, for example a simple pavement, it is "sufficient" to calculate the path that the tool will have to follow (considering its center) and divide it for the set advance. the result is reliable if the path is straight, because if the curves come into play, obviously the machine will slow down, making a very precise calculation rather difficult.

machine tool manufacturers do not provide any chart or table that allows a quick estimate of machining times. However some controls, after planning a processing phase (e.g. a profile roughing) prevent the cycle time with a good approximation.

the fastest way to calculate a cycle time and maybe choose between 2-3 alternatives the most convenient is currently to use a cam. Those I have seen carry out the calculation by measuring the tool paths and dividing the length for the advancement, therefore continue not to consider the slowing and accelerations that the cnc control will do in reality (variable from machine to machine).

then sum the cycle time of each processing at the time of tool change set (the time that the machine uses to stop the spindle, replace the tool and return the spindle to regime) multiplied by the number of tools used. thus obtain the total working time for the realization of a resumption of the piece.

The table positioning times are still lacking (in the case of 4 or 5 axes machines), gaps and various returns in the home, accelerations and slowdowns in the case of complex 4-5 simultaneous axes and negligible plc calculation times.

Currently, from what I know, it seems to me that the most advanced solution at this point of view is represented by the virtual machine that offers dmg. a program that once obtained the data related to tools and paths, can calculate a cycle time with a 99% accuracy. the program is made expressly on the customer machine, complete with all the options actually installed.