Question

1) Give 3 methods to determine machining time.

2) What is the difference between process optimisation and economic.

3) From your understanding, would the costing calculation make difference from one machining process to another.Why?

Answer 1

Most commonly used machining time methods are:

1. By estimation,

2. By comparison.

3. By timing.

4. By the sum of elementary predefined times.

1. By estimation

It consists in breaking down the operation in different smaller phases, so that a rough estimation can be made based on the experience of the technicians.

It is commonly used when:

• unitary parts or small batches are required.

not enough data is available.

• delivery time is short.

As it is a estimation method, it is not very accurate.

2. By Comparison
It consists in determining the time of a specific operation by comparing it with the time consumed a previously machined similar operation.
However, it is more accurate than the estimation method.

3. By timing

It consists in measuring the time needed to manufacture the part.

Thus it is a very time consuming.

It is commonly used when:

Very stable & automatized processes are required.

4. By the sum of elementary predefined times

It consists in breaking down the execution of a part in elementary phases. The time needed to be accomplish these elementary phases are predefined in tables (machine notebooks).

It is commonly used when a fast and economic decision need to be taken.

It is an accurate time estimation method.

PART 2

Difference between process optimization and economic:-

Commonly employed optimization criteria
are:
– Max. production rate or min. production time: aims to maximize number of parts produced in a unit time interval or minimizes the time per unit part. Neglects cost and/or profit.

– Min. production cost: aims to determine the least production cost. Coincides with max. profit rate criterion for
constant unit revenue. Ignores time constraints.
• Usually one of the two criteria is used. Sometimes
both criteria are used simultaneously.

PART 3:

Yes, the costing calculation would make difference from one machining process to another because for the different machining process the cutting velocity and cutting conditions are different. Machining cost also depends on following factors:-

• Work material (type, strength, hardness etc.)
• Capacity of the machine tool (power, rigidity etc.)
• Cutting tool; material, geometry and configuration
• Cutting fluid application
• Surface finish desired
• Type of operation, for instance threading operation needs large
feed according to the lead of the thread.
• Nature of cut; continuous, shock initiated type, and intermittent
Feed, which raises cutting forces proportionally, is kept low in
shock and intermittent type cuts