Must know question for an Interviewee.

How do you calculate Machining time?

Basically with help of feed, speed, depth of cut and number of cut you can calculate the machining time. wait is that it? yes so read this whole post to have better understanding of feed speed and machining time.

we need to get Surface speed and Feed (if it is for turning than feed will be mm per revolution) of that particular material from the standard table. The depth of cut is given or we can extract from standard table or an experienced programmer or Machinist must know the answer based on his experience. Of course Dimensions of the work piece. Finally, total number of cut to finish the part. With help of this data we will be able to find out the total machining time or ideal chip removal time. This time is ideal and can’t be achieved practically; For example in manual machining a machinist needs to load the part, adjust the part, may need to lower or increase the speed and feed of the tool and various other factors.

Anyway, let’s take an example to show you how machining time is calculated. We are going to find the turning time for the given part.

(Table for standard feed and surface speed is given below)

Turning of a Shaft : Example to find Machining time.

Let us find out spindle speed (N) from below formula:

Where, Vs = Surface speed in feet per minute or meter per minute.

D= Diameter of the work piece in inch or mm

N= Revolution per minute

(Note: here I put 12, because I am using Imperial Unit system and Vs we have is in feet per

Minute, so to convert it to inch per minute we multiplied Vs with 12 which is 12 inch = 1

Feet)

We already have Vs here so now, we need to make Spindle speed our subject and the formula will be as below.

Now, putting all the values in to the formula,

N = 12 (150) / π (2.0)

= 286.62

Spindle speed can be considered approximately 286 RPM (revolution per minute).

Now that we have got the spindle speed, we can find machining time for one minute. We have feed rate 0.01” inch per revolution. So basically, spindle rotates at 286 revolutions per minute and 0.01” inch is being cut per revolution.

So, inches is being cut per minute is = spindle speed (N) X feed rate (inch /revolution)

= (286 X 0.01)

= 2.86 inches / minute....... (1)

Now that we have found material removed per minute total machining time can be calculated as below,

2.85 inches cuts in 1 minute

:. 5.0 inches cuts in how many minutes?

So, Machining Time= total length / (feed X Spindle speed)

= 5.00 / (2.86) ........see (1)

= 1.74 minutes for one cutting pass.

Total number of pass here to finish the diameter is two.

Total Machining time = number of cutting passes X cutting time for one pass

= 2 x 1.74

= 3.508 minutes

Pretty simple right? I think now that you have gone through all this I am pretty sure that we have no Doubts. If you do have some, please do not forget to tell us in comment section.

TABLE OF FEED AND SPEED

please do not forget to watch the Video given below if you are still have some doubt!