Basics of Metal Cutting Process

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Metal cutting process is like cutting out an Image -Monument from rock. The process is to remove all the material that is not required, and in the end, you get a form or an object of your expectation.  In metal cutting process you take a piece of metal – called raw material, and remove metal with the help of an equipment / machine to get the part that you call a finished part. But in doing so the not required material that you removed remains with you as trash – scrap- generally in the form of chips/strands/powder. It is important that we take a look at all these while we decide the process and equipment for machining.

Metal cutting formula in simple language is:

Finished Component = Raw material – Scrap

This also means
Component as comes to machine – Material to be removed = Component as goes out of machine.

For every process of a component two types of drawings are made, namely Drawing for Part as comes to the machine(input component)and Drawing for Part as comes out of machine(output component).

 

The process of manufacture is dependent on various characteristics and conditions in which the component is coming to the machine. This generally consists of

  • Material Condition

Type of material – such as steel, copper, aluminum, brass etc.
Hardness of the raw material – This will make us understand the type of cutting tools to be usedand their grades. Tools used for Hard and Soft material will differ. The power required for metal cutting depends a lot on the hardness of the material. It will be good to have material inspection data. Material condition also tells us the type of chips likely to come out as we remove material and also the metal cutting behavior – ease of cutting.

 

  • Form of the raw material as presented to the machine

Complete dimensional details of the raw material are necessary. The component form may be made by castings or it may be a bar or a welded construction. The form provides input for deciding the holding arrangement (Jigs/Fixture) during metal cutting and also enables to understand requirements of supports during machining if needed, such as steady or supporting jacks. The drawing for input component provides dimensional details of various portions of the component and their relationship.

 

  • Form of the component as it comes out of the machine

It includes complete dimensional details of the component after machining. This is nothing but a machining drawing. Dimensional details of various portions of the component and their relationship like positions, concentricity, etc. Details like Surface Finish, dimensional tolerances etc. The details from the input component drawing and output component drawing tell you the material to be removed.

 

  • Weight of the component as comes to the machine

Many a time, this element is missed out. Material and size decide weight. While handling the component manually, one needs to understand the fatigue that the loading unloading is going to cause to the operator. How often the component loading unloading on machine is to be done is dependent on the machining cycle time. Heavy component with less machining time can cause a lot of fatigue if a full shift quantity is to be machined. There are ILO (International Labour Organization) recommendations to understand the fatigue factors and calculate them. This study can also help to know if anything to ease out loading and unloading can be provided or a fully automatic loading and unloading arrangement becomes useful.

To be continued…

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Shrikrishna Prabhakar Vaidya
shyam

Mechanical & Electrical engineer with 33+ years experience in manufacturing engineering, particularly in metal cutting processes and machine tools.

Working as a freelance consultant in manufacturing for last 15 years.

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