Productivity Science of Machine - Machining - F.W. Taylor

Productivity Science - Principle of Industrial Engineering

https://nraoiekc.blogspot.com/2017/06/productivity-science-principle-of.html

F.W. Taylor is the pioneer of scientific management. He advocated strongly that science in management of work in production shops did not exist and there is an immediate need to develop science for every element of production work. He himself conducted studies and experiments to develop science of machine tool work/effort and human effort. He contributed to the development of science in both the areas. But in the area of human effort, Frank Gilbreth followed Taylor with a more elaborate framework for productivity science of human effort.

F.W. Taylor did the pioneering research study on productivity science of machines for over 30 years. He did it on machine tools. The description Taylor's work on machining is as follow.

Study of Variables that have an Effect on Cutting Speed, Feed and Time of Cutting

The productivity science problem of machine tool can be solved by a careful study of the effect each of the twelve following variable elements has upon the selection of the cutting speed and feed and therefore on the cutting time.

a. The quality of the metal which is to be cut, i. e., its hardness or other qualities which affect the cutting speed;
b. The diameter of the work;
c The depth of the cut, or one-half of the amount by which the forging or casting is being reduced in diameter in turning;
d. The thickness of the shaving, or the thickness of the spiral strip or band of metal which is to be removed by the tool, measured while the metal retains its original density ; not the thickness of the actual shaving, the - metal of which has become partly disintegrated;
e. The elasticity of the work and of the tool;
f. The shape or contour of the cutting edge of the tool, together with its clearance and lip angles;
g. The chemical composition of the steel from which the tool is made, and the heat treatment of the tool ;
h. Whether a heavy stream of water, or other cooling medium, is used on the tool;
j. The duration of the cut, i. e., the time which a tool must last under pressure of the shaving without being reground; '
k. The pressure of the chip or shaving upon the tool;
l. The changes of speed and feed possible in the lathe;
m The pulling and feeding power of the lathe at its various speeds.

The ultimate object of all experiments in this field is to learn how to remove the metal from  forgings and castings in the quickest time, and that therefore the art of cutting metals may be briefly defined as the knowledge of how, with the limitations caused by some and the opportunities offered by others of the above twelve variable elements, in each case to remove the metal with the highest appropriate cutting speed.

Before entering upon the details of  experiments, it seems necessary to again particularly call attention to the fact that “standard cutting-speed” is the true criterion by which to measure the performance of various variables like tool material, dimensions etc.

To give an illustration of the practical use of "standard cutting-speed." If, for example, we wish to determine which make of tool steel is the best, we should proceed to make from each of the two kinds to be tested a set of from four to eight tools. Each tool should be forged from tool steel, say, 5- inch x 1- inch and about 18 inches long, to exactly the same shape, and after giving the tools made from each type of steel the heat treatment appropriate to its chemical composition, they should all be ground with exactly the same shaped cutting edge and the same clearance and lip angles. One of the sets of eight tools should then be run, one tool after another, each for a period of 20 minutes, and each at a little faster cutting speed than its predecessor, until that cutting speed has been found which will cause the tool to be completely ruined‘ at the end of 20 minutes, with an allowance of a minute or two each side of the 20-minute mark.

Every precaution must be taken throughout these tests to maintain uniform all of the other elements or variables which affect the cutting speed, such as the depth of the cut and the quality of the metal being cut. The rate of the cutting speed must be frequently tested during each 20-minute run to be sure that it is uniform throughout.

Throughout this paper, “the speed at which tools” give out in 20 minutes, as described above, will be, for the sake of brevity, referred to as the “standard speed.” After having found the “standard speed” of the first type of tools, and having verified it by ruining several more of the eight tools at the same speed, we should next determine in a similar manner the exact speed at which the other make of tools will be ruined in 20 minutes; and if, for instance, one of these sets of tools exactly ruins at a cutting speed of 55 feet, while the other make ruins at 50 feet per minute, these “standard speeds," 55 to 50, constitute by far the most important criterion from which to judge the relative economic value of the two steels for a machine shop.

Productivity science related research is being carried on machining processes even now also. Only thing is that it is not being presented as part of productivity science of machines. There is a need to collect all the studies under this heading and summarize these studies and present the current guidelines for maximum productivity of each of the machines.

More Details of Taylor's Experiments on Productivity of Machine Tools and Machining

https://nraoiekc.blogspot.com/2019/06/taylor-art-of-metal-cutting-important.html


Updated on 16 November 2019, 21 September 2019