Manual work are less suitable for time predictions. You could however build yourselves a rate database for typical operations per worker. Very soon you would be able to predict machine time rather accurately.
Machine time can be calculated by logically analyzing the operation. Under CNC control the time can be estimated.
Example:
A lathe were a shaft must be machined down.
The number of revolutions per pass can be calculated by dividing the length by the federate.
The number of passes can be calculated dividing the Total depth by the depth for each cut.
By adding all of these together and add revolutions for return strokes the Total number of revolutions can be Estimated.
Dividing this total by the RPM will give you the time.
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They are many and complex due to the variety of materials and machine types, I don't have enough time to cover all the methods.
One way to approach this without formulae is to make a practice cut if the metal if it comes away cleanly with no vibration and breaks up into small chips in the case of lathe work you are probably in the ball park.
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MSJP -- Are you willing to share with us just what you plan to use such a formula for and just how accurate do you need the calculation results to be? There is a big difference in accuracy requirement between the rough number needed to give a design engineer a sanity check on his design and the number needed for a machine shop to develop a very competitive quotation in the last stages of a price negotiation.
To do the rough estimate the formula is simple but has a number of constants that vary with the material, process, and types of tooling and general part geometry.
The accurate analysis is a detailed compilation of steps in a machining process developed by a skilled process engineer or machinist for a very specific part and the specific process capabilities in the machine tools selected to do the work.
I can be of help with the "rough" formula and constants based on numbers given in Ostwald's "AM Cost Estimator" Penton Publishing Co. 1988 (book long out of print and fairly rare today) providing your materials list is short and consists of common materials. There is no easy formula for the accurate analysis unless the constants are available from the detailed process plan developed by one with the necessary skills.
Calculating Machining Time
Re: Calculating Machining Time
