Machining Time Reduction - Machining Cost Reduction - Machine Productivity Improvement - Taylor - Narayana Rao
Taylor - Narayana Rao Principles of Industrial Engineering
Proportion is as 1 in the case of semi-hardened steel or chilled iron to 100 in the case of very soft low carbon steel.
Proportion is as 1 in tools made from tempered carbon steel to 7 in the best high speed tools.
Proportion is as 1 with thickness of shaving 3/16 of an inch to 3.5 with thickness of shaving 1/64 of an inch.
Proportion is as 1 in a thread tool to 6 in a broad nosed cutting tool. ,
Proportion is as 1 for tool running dry to 1.41 for tool cooled by a copious stream of water.
Proportion is as 1 with 1/2 inch depth of cut to 1.36 with 1/8 inch depth of cut.
Proportion is as 1 when tool is to be ground every 1.5 hour to 1.207 when tool is to be ground every 20 minutes.
Proportion is as 1 with lip angle of 68 degrees to 1.023 with lip angle of 61 degrees.
Proportion is as 1 with tool chattering to 1.15 with tool running smoothly.
Taylor's Contribution to Machining Time Reduction and Machining Science/Productivity Science
Taylor also established that the power required to feed the tool could equal the power required to drive the spindle, especially when worn tools were used. Machine tools of the day were underpowered in the feed direction, and he had to modify all the machines at the Midvale plant to eliminate this flaw. He also demonstrated the value of coolants in metal cutting and fitted his machines with recirculating fluid systems fed from a central pump. Finally, he developed a special slide rule for determining feeds and speeds for various materials.
Taylor summarized his research results in the landmark paper On the Art of Cutting Metals, which was published in the ASME Transactions in 1907. The results were based on 50,000 cutting tests conducted over a period of 26 years. Taylor's also indicated the importance of tool temperatures in tool life and developed the famous tool life equation. His writings clearly indicate that he was most interested in efficiency and economy in his experiments and writings.
Machine tools built after 1900 utilized Taylor's discoveries and inventions. They were designed to run at much higher speeds to take advantage of high speed steel tools. This required the use hardened steel gears, improved bearings and improved bearing lubrication systems. They were fitted with more powerful motors and feed drives and with recirculating coolant systems.
The automotive industry had become the largest market for machine tools by World War I and it has consequently had a great influence on machine tool design. Due to accuracy requirements grinding machines were particularly critical, and a number of specialized machines were developed for specific operations. Engine manufacture also required rapid production of flat surfaces, leading to the development of flat milling and broaching machines in place of shapers and planers. The development of the automobile also greatly improved gear design and manufacture, and machine tools were soon fitted with quick-change gearing systems. The automotive industry also encouraged the development of dedicated or single purpose tools. Early examples included crankshaft grinding machines and large gear cutting machines. It led to the development of transfer machine. An in-line transfer machine typically consists of roughly thirty highly specialized tools (or stations) connected by an automated materials handling system for moving parts between stations. The first was built at Henry Ford's Model T plant in Detroit. . Transfer machines required very large capital investments but the cost per piece was lower than for general purpose machines for the production volumes of hundreds of thousands required in auto industry.
In the 1930's a German company introduced sintered tungsten carbide cutting tools, first in brazed form and later as a detachable insert. This material is superior to high speed steel for general purpose machining and has become the industry standard.
A great deal of research in metal cutting has been conducted since 1900. A bibliography of work published prior to 1943 was compiled by Boston, Shaw and King. The shear plane theory of metal cutting was developed by Ernst and Merchant and provided a physical understanding of cutting processes which was at least qualitatively accurate for many conditions. Trigger and Chao and Loewen and Shaw developed accurate steady-state models for cutting temperatures. A number of researchers studied the dynamic stability of machine tools, which had become an issue as cutting speeds had increased. This resulted in the development of a fairly complete linear theory of machine tool vibrations. Research in all of these areas continues to this day, particularly numerical analysis work made possible by advances in computing. All these discoveries and their implementation in machine tools gives higher productivity in machining.
One of the most important innovations in machine tools was the introduction of numerical control. Today CNC machine tools are the most used ones.
New tool materials were invented. A variety of ceramics are currently used for cutting tools, especially for hardened or difficult-to-machine work materials. Ceramic and diamond tools have replaced carbides in a number of high volume applications, especially in the automotive industry. Carbides (often coated with ceramic layers) have remained the tool of choice for general purpose machining. There has been a proliferation of grades and coatings available for all materials, with each grade containing additives to increase chemical stability in a relatively narrow range of operating conditions. For many work materials cutting speeds are currently limited by spindle and material handling limitations rather than tool material considerations. Dozens of insert shapes with hundreds of integral chip breaking patterns are available now.
Chapter 13. Machining Economics and Optimizationin Metal Cutting Theory and Practice - Stephenson - Agapiou, 2nd Edition
Economic Considerations are important in designing the machining process of a component. Each operation done on a machine involved number of decisions. There is more than one approach for doing an operation and each approach will have as associated machining time, part quality and cost of machining. An effective and efficient methodology is to be employed to attain the specified quality of the operation with the least cost.
The machining cost of an operation on a component is made of several components. They include machine cost, tool cost, tool change cost (includes set up), handling cost, coolant cost etc. Some of these costs vary significantly with the cutting speed is different directions. At a certain cutting speed we get the minimum cost and at certain other cutting speed we get the least machining time. There is a need to calculate these minimum point cutting speeds for each work material, tool material and machine tool combinations. F.W. Taylor developed slide rules for this purpose. Now those slide rules are not in place, but machining handbooks and machine tool/cutting tool manufacturers provide guidance. Process planners and industrial engineers need to do the required calculations depending on the trial production within their plans.
Time Estimates Required
Total Production Time for an Operation, TTO =
Tr = Approach time
Tp = Table index time
Ta = Acceleration time
Td = Deceleration time
Tx = Tool rapid travel time
Time study used for machine work study has to determine these time times from formulas as well as time study observations for the existing way and proposed way to validate the time reduced by the operation analysis based on operation study and time data.
Constraints for Minimizing the Machining Time - Cost
Allowable maximum cutting force, cutting temperature, depth of cut, spindle speed, feed, machine power, vibration and chatter limits, and party quality requirement.
Industrial engineers must have knowledge of maximum permissible depth of cut. feed and cutting speed.
Industrial engineers have to monitor research and continuously update their understanding of limit to the constraints. Developments in engineering and industrial engineering keep increasing the quantity of limits in favor of more productivity.
The cutting parameters of various work materials will be covered in Machinability of Metals - Machine Work Study Topic
Machining Operation Analysis and Improvement - Bibliography
Developments in Manufacturing Processes for Operation Analysis - Value Engineering - Product/Process Industrial Engineering
Manufacturing Processes - Book Information and Important Points - Under Collection
Updated on 30 July 2021, 2 April 2020
26 March 2020