Lesson 50 of Industrial Engineering ONLINE Course
Lesson 7 of Process Industrial Engineering ONLINE Course (Module)
First Lesson of Sub-module - Metal Cutting - Industrial Engineering and Productivity Aspects
Industrial engineers have to first know alternatives to produce to specification. Then ways to increase productivity of the best alternative.
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The presentation of this topic is being attempted for the first time and hence requires multiple revisions.
But this collection of notes/essays is important and it has to be done for every engineering process for effective industrial engineering. Industrial engineering is engineering practice at the core with productivity orientation. Productivity orientation covers under its scope attention to multiple areas including quality of the output and operator comfort. In the past, some promoters of techniques and methods had maligned industrial engineering with criticism that it ignored quality, human comfort etc. which is not justified and based on facts. But they popularized their argument because industrial engineering discipline and profession have not countered adequately.
The content in this collection of notes on productivity aspect of metal cutting is predominantly metal cutting theory and is taken from metal cutting textbooks. This is why the sentence was written earlier "Industrial engineering is engineering practice at the core with productivity orientation."
Taylor's first publication was on industrial engineering of belting. It was redesign of belt systems based on the cost analysis of costing records kept for many years on belt related costs.
Taylor took time taken by a machine tool and operator to complete a job as an important correlating variable to cost of machining the job. He diverted his attention to the minimization of machine time and operator time in doing a job. His complete experiments to develop productivity science of machining were presented to fellow engineers in the paper "The Art of Metal Cutting (1907)." This paper is the foundation for productivity science of metal cutting. Over the next 115 years till now (2021) many experiments were made and many ideas and formulas were developed for various metal cutting processes to gain more speed and feed and thus reduce machining time. But industrial engineering discipline failed to consolidate them and present a unified body of knowledge that is of help in industrial engineering of metal cutting processes. Such an endeavor would have resulted in similar attempts to present productivity science of many other engineering processes. Production Industrial Engineering is a popular branch in many industrial engineering departments and course offerings. But even these curricula have not covered genuine industrial engineering of production processes adequately.
In the series of lessons created by me in the module Process Industrial Engineering ONLINE Course (Module) the following lessons were on Taylor's experiments and discoveries and are part of productivity science of machining.
In this lesson a brief summary of various metal cutting processes along with variables related time taken for machining are provided to serve as an introduction to the discussion of various productivity aspects of machining covered in the latter articles.
Variables in Metal Cutting Related to Productivity
Machine tool, spindle speeds, feeds, work piece material, cutting tool material, cutting tool geometry, cutting parameters, cutting fluid, work holding device, cutting temperature, vibrations, smart machine features, cutting related software, in-process inspection features, pokayokes,
Turning
In addition to the tool geometry, the major operating parameters to be specified in turning are the cutting speed, V, feed rate, fr, and depth of cut (doc), d. The cutting speed is determined by the rotational speed of the spindle, N, and the initial and final workpiece diameters, D1 and D2.
The time taken for a cut can be calculated as length of cut divided feed per unit time. Minimizing time for cut is an important productivity aspect.
The material removal rate per unit time, Q, is given by the product of the cutting speed, feed, and
depth of cut:
Q = Vfd
Hard Turning
A special case of turning is hard turning, in which hard metals (45–65 HRc) are machined using ceramic or polycrystalline tool . This process is substitute for for rough turning, hardening, and finish grinding for parts made of tool steels, alloy steels, case-hardened steels, and various hard irons. Very fine finishes and tolerances can be produced by this process, and in some cases part quality is better than that can be obtained with grinding because intermediate chucking operations and associated setup errors are eliminated.
Hard turning produces a different surface topography compared to grinding and better surface integrity due to reduced thermal damage in many applications. Hard turning is a more efficient process than grinding where appropriate.
Hard turning requires high machine and toolholder rigidity and strong insert shapes (negative rakes, large wedge angles, and special edge preparations such as chamfers. Modern CNC lathes required rigidity for hard turning. Hard turning is generally performed dry. Typical depth of cut ranges from 0.08 to 0.5 mm, with speeds between 50 and 150 m/min. Size tolerances of ±0.005 mm or better are achievable with surface finish better than 0.3 μm Ra. Typical applications are gears, and axles.
Boring is equivalent to turning and its time cut also depends on the cutting speed, depth of cut, and feed rate. The equations relating these parameters to time for cut given for turning are also applicable to boring. Traditionally, moderate cutting speeds and small depths of cut and feed rates are used in boring to ensure accuracy. But in recent practice, higher cutting speeds have been successfully used. The higher speeds are experimented to reduce errors due to mechanical and thermal distortion. Heavier depths of cut are used when multipoint boring tools are employed.
Deep-Hole Drilling
A hole with a depth-to-diameter ratio of more than 5:1 requires special machines to drill holes with adequate straightness and to ensure efficient chip ejection and lubrication of the drill.
The drilling operation, using standard or parabolic-flute twist drills, is used for deep-hole drilling using “pecking” (drilling to intermediate depths and periodically withdrawing the tool to clear chips) Using a high pressure coolant may help in the process.
Three deep-hole drilling methods are solid drilling, trepanning, and counterboring. Solid drilling is used more popularly, and it has four approaches: conventional twist drilling, gun drilling, ejector drilling, and BTA (STS) drilling.
Deep-hole drilling machines are always equipped with high pressure, high volume coolant systems.
The best hole quality is obtained when both the tool and workpiece rotate.
Microdrilling
Boring
Boring is equivalent to turning and its time cut also depends on the cutting speed, depth of cut, and feed rate. The equations relating these parameters to time for cut given for turning are also applicable to boring. Traditionally, moderate cutting speeds and small depths of cut and feed rates are used in boring to ensure accuracy. But in recent practice, higher cutting speeds have been successfully used. The higher speeds are experimented to reduce errors due to mechanical and thermal distortion. Heavier depths of cut are used when multipoint boring tools are employed.
Deep-Hole Drilling
A hole with a depth-to-diameter ratio of more than 5:1 requires special machines to drill holes with adequate straightness and to ensure efficient chip ejection and lubrication of the drill.
The drilling operation, using standard or parabolic-flute twist drills, is used for deep-hole drilling using “pecking” (drilling to intermediate depths and periodically withdrawing the tool to clear chips) Using a high pressure coolant may help in the process.
Three deep-hole drilling methods are solid drilling, trepanning, and counterboring. Solid drilling is used more popularly, and it has four approaches: conventional twist drilling, gun drilling, ejector drilling, and BTA (STS) drilling.
Deep-hole drilling machines are always equipped with high pressure, high volume coolant systems.
The best hole quality is obtained when both the tool and workpiece rotate.
Microdrilling
Microdrilling is the drilling of small diameter (less than 0.5 mm) holes with a depth-to diameter ratio greater than 10. Holes as small as 0.0025 mm have been successfully drilled. Microdrilling presents special, since coolant fed drills cannot be used. High spindle speeds are required to generate sufficient cutting speed. Feed rates also are low, in the range of 0.00005–0.0005 mm/rev.
The performance can sometimes be improved by supplying ultrasonic energy to the cutting zone. High-frequency forced vibrations at frequencies between 15 and 30 kHz allow increased material removal rates. The vibrations tend to break chips into smaller sections while lowering forces. They can increase throughput by a factor of two while improving tool life and hole quality. The vibration frequency must be carefully determined and controlled.
Peck drilling (frequent withdrawals of the drill) is used to clear chips from the hole and to permit intermittent cooling of the drill. But peck drilling increases cycle time. Precise feed control is necessary to avoid excessive dwelling of drill. Peck drilling may not be necessary if high spindle speeds can be utilized.
Thread Cutting
(Need to rewrite the content)Thread turning is a process for producing external or internal threads, using a single point tool. This process is traditionally used on soft materials, is now also used when turning hardened steels using PCBN tools.. The tool may be fed into the workpiece either radially or axially. Radial feed cutting generates higher cutting forces and leads to greater difficulty in chip disposal and is used mainly on materials that produce short chips or with multi-toothed inserts. In flank-infeed cutting (in which the tool is fed axially) the cutting action is more like conventional turning. There are many different flank-infeed sequences, which distribute the thread form between passes. The infeed sequence can be optimized to reduce the number of passes while keeping the chip load constant between passes. The optimum number of passes depends on the tool geometry and edge strength. In some cases, the center portion of the thread is removed using radial infeed while the remaining stock is removed using flank infeed. In other cases a significant amount of material is removed with a grooving tool, leaving only a small amount to be cut with a threading tool.
Multi-toothed full-profile indexable inserts are also used to turn threads. Such inserts generate the full thread profile including the crest in a single pass, eliminating the multiple passes required to produce threads with a single point tool.
Thread milling is used to generate internal or external threads using a milling cutter. The cutter is fed along the axis of the workpiece as in thread turning to generate the threads in a single pass. With a stationary workpiece, a rotating tool moves simultaneously along three axes to generate the helical thread (as compared to the two-axis motion used in circular interpolation). When cutting an external thread, the tool moves along the part’s outside diameter; when cutting an internal thread, the tool moves inside a previously drilled hole. As in cut tapping, the feed rate is determined by the workpiece speed in a turning machine or by the helical path speed in NC machining centers or special machines. The accuracy of the thread is controlled by the accuracy of the axial and circular feed mechanisms of the machine, not by the cutting tool. It is preferable to start the thread-milling operation at the bottom of blind hole so that the tool moves outward to avoid chip recutting at the bottom of the hole. In thread milling, the tool rotates at higher speeds and lower feeds than in tapping or thread turning; the feed can be adjusted to generate the desired surface finish and is not constrained by the desired thread pitch as in other threading operations.
The power required for threading can be reduced considerably using thread milling. Percent threads approaching 100% can be generated, and tapered threads can be generated easily and accurately. Thread milling is used primarily for large holes (diameter >30 mm), while tapping is used for smaller holes (diameter less than 40 mm) due to tool cost.
Threads in smaller holes can be milled using a combined short-hole drilling and thread milling operation called thrilling or drill/threadmilling. Thrilling uses a combined drill-threading tool rotating continuously at a high spindle speed to drill a blind or through hole and generates the thread through a helical retraction motion. Thread milling accuracy is dependent on the machine control system generating the helical interpolation including the machine motion accuracy. Thread milling tends to generate smoother and more accurate threads than tapping and is more efficient than thread turning. Thread milling also eliminates the spindle reversal at the bottom of the hole required in tapping. However, milled threads must typically be gauged much more carefully than tapped threads. Coolant requirements in thread milling are not as critical as those in cut tapping. Tooling costs are generally higher than for tapping.
Up-milling is used with materials that are difficult to machine (e.g., stainless steels) to improve tool life. A thread-milling tool can cut from either the entrance or exit/bottom of the hole, compared to a tap that must start at the entry. If the force in thread milling is too high for the tool L/D ratio, multiple passes can be used to avoid tool breakage. Tapping generates the full thread form and machines to final size in one pass. Thread milling can produce high tool pressures when milling at full thread length and depth, which can result in excessive tool deflection and tool breakage. Machine requirements also limit the applicability of thread milling; the proper speeds and feed rates must be available, and the machine must be capable of producing an accurate circular motion at high speeds and feeds, especially with nonferrous parts. Thread milling can also only be applied when the ratio of the thread length to the major diameter of the tool falls within relatively narrow limits.
Milling
Milling - Estimation of Machining Time
News and Information to Facilitate Productivity Analysis of Machining Elements in Milling
NPTEL DFMA Course: Module 3 - DFMA for Machining
Machining - General
https://nptel.ac.in/content/storage2/courses/107103012/module3/lec1.pdf
Turning
https://nptel.ac.in/content/storage2/courses/107103012/module3/lec2.pdf
Round Holes
https://nptel.ac.in/content/storage2/courses/107103012/module3/lec3.pdf
Milling
https://nptel.ac.in/content/storage2/courses/107103012/module3/lec4.pdf
Shaping, Planing and Slotting
https://nptel.ac.in/content/storage2/courses/107103012/module3/lec5.pdf
Broaching
https://nptel.ac.in/content/storage2/courses/107103012/module3/lec6.pdf
2022
Method for an Effective Selection of Tools and Cutting Conditions during Precise Turning of Non-Alloy Quality Steel C45
Materials (Basel). 2022 Jan; 15(2): 505.
Interesting article. Literature review gives many papers related to IoT application in machining.
2021
Research to create new sensors for cutting tools for aircraft parts begins
AI-enabled sensors for parts machining set to improve quality and help manufacturers cut costs.
Press release
Published on Tuesday 23 November 2021
Industry 4.0 – Smart cutting tools
November 10, 2021
Tools Communicating with Software
Industry 4.0 is touching the cutting tools industry from quote to delivery, according to Orris.
“Tools are becoming ‘intellectual’ because that’s what’s needed in today’s industry,” he says. “Through sophisticated technology and embedded chips, tools are communicating with software to collect data that’s critical to achieving efficient manufacturing. Understanding the data and applying what’s learned is the key to efficiency.”
“With Industry 4.0, we are creating tools that are highly connected to their applications,” Orris added. “In the field, tools are mis-applied at a rate as high as 70%. Using our digital process, we focus on reducing that 70% to – ideally, 0. We’re always looking for ways to control variables and maximize efficiency.”
Bill Orris, ARCH Cutting Tools Senior Director – Product Development and Custom Solutions, is an Industry 4.0 expert and a cutting tools industry innovation leader.
PRODUCTIVITY IMPROVEMENT IN METAL-CUTTING TECHNOLOGIES - CONVENTIONAL & UNCONVENTIONAL
Dr Nageswara Rao Posinasetti, Professor, Department of Technology, University of Northern Iowa, USA
2020
ANCA Tool of the Year 2020 – ARCH Cutting Tools
https://www.mtwmag.com/arch-cutting-tools-tops-ancas-third-tool-of-the-year-competition/
2019
What Is High-Speed Machining?
6/26/19
Grainger Editorial Staff
Revised on 31.8.2022, 19.7.2022, 18.12.2021, 20 July 2021, 4 January 2021
First published 16 September 2020
Awesome content sir
ReplyDeleteRead on 20 July 2021.
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