This article will touch on three (3) areas:
1.0 Driving Forces Behind Technological Developments in Production Engineering
1.0 Driving forces behind technological developments in production engineering.
2.0 Current statistics and trends - Cutting tools and Machine tools.
3.0 Emerging trends and technologies.
In today’s fast paced, ever changing global manufacturing environment, the Management of the worlds production engineering and manufacturing resources are driven by several key forces:
1.1 Increased Production Demand.
Without a doubt, the requirement to deliver more, in less time is present in most, if not all, manufacturing environments. From computer hardware to jetliners, to automobiles, to construction equipment, the overall global manufacturing environment is strong with all indications pointing to sustainable growth into the year 2000 and beyond.
As a result of this increased demand, the "farming out" or "outsourcing" of the excess manufacturing load of larger manufacturing corporations has led to the growth of existing primary (tier I) and secondary (tier II) suppliers, some small in size, yet large in capability. In a previous survey of USA metalworking manufacturing companies conducted by Kennametal, Inc., it was predicted from the data that greater than 50% of the machine tool base in the USA was located in companies of 100 or less employees. This trend was expected to continue with the percentage approaching 65% by 2005.
This trend represents a growing market in need of new machine tools and cutting tools and newer, more cost effective concepts and processes. In many cases the younger, smaller manufacturing companies, not slowed down by existing infrastructure, can be quicker to implement newer technology and gain from the benefits of today’s leading manufacturing concepts and communication tools.
1.2 Shorter Production Lead-times:
A key support strategy in achieving higher output in less time is to drive production lead-times lower. When looking at some of the demands placed on some of the worlds largest manufacturing companies and their supporting suppliers...
1. Increase from 20 to 40 widebody jetliners per month...
2. New car models in months not years...
3. Machine tool deliveries in weeks not months...
4. Special tooling solutions in days not weeks...
5. Demands for information & answers in minutes not hours or days...
It becomes evident that efforts and programs directed at the research and utilization of available technologies and processes to reduce production lead-times can pay great dividends in production output and customer satisfaction.
1.3 Increased Machine Tool Utilization:
One key contributing factor in achieving reduced manufacturing lead-times is getting more production out of existing machine tools by increasing their "uptime" or "chip making" time or "utilization".
Through surveys of several US based manufacturing organizations it was determined that the average machine tool "Uptime" (time in-process producing workpieces) was still below 60% and in several cases as low as 40%. This would imply that, on average, a manufacturer could reduce that portion of the total manufacturing lead-time associated with "chip making" by 50% if they could more effectively utilize their machine tools. Stating it another way, they could increase their "chip making" capacity by 100%, eliminating the need for additional machine tools and associated tooling, fixturing, and manpower to operate it. Several machine tool utilization improvement strategies and real-world applications will be presented later in this paper.
1.4 Continuously Improved Product Quality:
Global competition demands ultimate product quality. Once considered a competitive advantage, quality is now considered a given, a "must have" in order to be considered a competitor in today’s global manufacturing environment. As machining accuracy continues to improve, product designers will continue to shrink tolerances, improving fits, which in turn increase product life span, performance, and efficiency.
As new quality milestones are achieved, customer expectations will increase. There will be no end to continuously improving product quality. Customer expectations will not only be related to physical product specifications but to product availability, packaging, warranty, real-time application support, on demand service calls, and proactive contact with information related to product improvements and the expected performance benefits obtainable as a result of those improvements.
1.5 Environmental Issues / Dry Machining:
The health and environmental concerns related to the use of metalcutting fluids in manufacturing facilities are becoming more and more prevalent around the world. The use of these fluids in day to day machining operations expose machine operators to potential health hazards.
There are large and increasing costs associated with the disposal and / or pre-treatment required prior to the disposal of these fluids back into the environment. This issue is most prevalent in Europe with increasing attention being paid to this issue in the USA. It is expected that there will come a time when the costs associated with the purchase, maintenance, and disposal of cutting fluids will exceed that of the metalcutting benefits gained by their use.
For tooling suppliers and machine tool builders the reliance on cutting fluids to remove heat, provide lubricity, reduce wear, provide chip evacuation, act as a rust preventative, and keep dust to a minimum, must be replaced by some other cost effective technology or process to keep the metalcutting application personally and environmentally safe and productive.
1.6 More Difficult to Machine Materials:
If higher production rates in shorter lead-times with continuous quality improvement and the need to actively pursue more challenging dry machining techniques weren’t enough, there is the constant demand for increased performance from manufactured products that can only be met through the utilization of more difficult to machine workpiece materials!
1. High temperature aerospace alloy development...
2. Replacement of aluminum with higher strength alloys in airframe fabrication...
3. Higher strength ductile iron usage in automotive...
4. Silicon Aluminum usage...
5. Magnesium usage...
6. Composite materials...
The use of these new materials will increase over time and the development of new cutting tools, machine tools, and metalcutting processes, under dry machining conditions will offer many opportunities to tooling and machine tool manufacturers in the years to come.
2.0 Current Statistics and Trends - Cutting Tools and Machine Tools
With the above forces at work on the metalcutting manufacturing community, there are several current trends that merit review. Following this review, we’ll take a look at some emerging trends and the technologies that are enabling concepts that will shape the future of metalcutting.
2.1 Cutting Tool Material Trends
FIGURE 1 shows the estimated usage of the main cutting tool materials in use today in the USA and on a global basis.
FIGURE 2 shows the estimated shift of material type in the year 2005. It’s clear that the CVD coated carbides will retain the highest share while PVD coated carbides reflect the largest growth. The advancement of coating technologies will continue to drive major performance gains especially in the super-hard coatings (Diamond and CBN) and extremely lubricious coatings (MoS2). Both the high hardness and high lubricity coating technologies are enablers of the transition to dry machining.
3a, 3b, & 3c shows the relationship between cutting tool material and cutting speed when machining various workpiece materials. In 1995 Kennametal commissioned a "Technology Forecast 2005" in which predictions were made regarding cutting speeds in the year 2005. The graphs shown indicate 1995 predictions made for 2005 and compare those predictions to what currently exist in 1998. It can be see that in some cases, today’s current speeds already exceed the 2005 predictions.
2.3 Workpiece Material Trends:
General workpiece material trends are as follows:
1. Alloy Steels and Grey Cast Irons will be the primary materials machined into 2005. There is a trend towards higher strength irons with the increased usage of nodular and compacted graphite irons.
2. Aluminum and Magnesium usage will increase in Automotive applications as Steel and Cast Iron usage declines. Aluminum continues to expand beyond engine and wheel applications to more structural frame, suspension and body panel applications.
3. More plastics "under the hood" will be utilized in support of lower vehicle weights, reduction in component parts, less manufacturing expense and, in Europe, auto recycling mandates.
4. Within the aerospace industry Aluminum volume continues to grow rapidly due to the shear volume of aircraft production though Aluminum is being replaced by higher strength Titanium alloys in some structural airframe components in new and / or updated aircraft designs.
2.4 Quick Change Tooling Trends:
Again related to the need for increased machine tool utilization, there is a continuing trend to utilize quick-change tooling and fixturing to reduce machine downtime and increase productive "Chipmaking" hours. On lathes the use of quick change tooling, and to some extent, chucking concepts, has continued to increase over the recent past though there is considerable room for expanded growth and utilization of this concept. Many lathe producers offer "quick change" tooling packages as a standard feature on new machines. Though this technology is available from various tooling providers, less than 10% of the machines capable of utilizing this technology (when purchased new or via retrofitting) are actually tooled up to take advantage of the technology and the "Increased Uptime" benefits achievable.
2.5 Proper Application of Existing Tooling Solutions:
As indicated by the above limited usage of quick change tooling (a known productivity improvement technology) it has become evident, and confirmed by further survey findings, that the end user of metalcutting tools does not always utilize the technology to their best advantage. See FIGURE 4 for an example of this as it relates to indexable insert selection, application, and tool life criteria in the USA, Germany, and Japan.
Whether this is due to limited technical support by the tooling providers or roadblocks at end user facilities due to existing machine tool capability, unavailable resources to make program and process changes, or just reluctance on the part of the users to push tooling and processes to their ultimate limits, there are, in many cases, productivity gains left untapped by global metalcutting users.
2.6 Current Machine Tool Trends:
Some general trends evident in the 90’s:
1. Decrease in fixed / hard transfer lines...
2. Increase in Machining Centers in support of Cellular and Agile machining concepts...
3. Turning Centers offer driven tooling (milling capabilities) greater than 50% of the time...
4. Flexibility and "Maximum Uptime" are becoming key requirements to capture the order...
2.6.1 Declining Cost of Machine Tools
When adjusted for inflation, the selling price of machine tools has declined over the last two decades while the productivity of the machines has increased dramatically. As a result, the cost of machine tools per unit of productive capacity has declined. This reduction in effective cost has led some to incorrectly conclude that most manufacturers are making inadequate investments in capital equipment simply because the investments in machine tools have declined. In fact the reductions in investment are appropriate due to the increased productivity of the tools, and the machine tool industry should not expect to see a return to the investment levels of the past within its current customer base. Growth will come from new customers in new markets.
3.0 Emerging Trends and Technologies
3.1 Metalcutting Manufacturing Industry Trends
1. Skilled Manufacturing shop floor labor force is diminishing in the larger, established manufacturing giants. Some have set their focus on assembly and integration efforts and no longer consider manufacturing to be a core competency...
2. Technological advancements in machine tools, machine tool controls, and cutting tools are advancing at rapid rates. Sometimes more rapidly than larger end users can adapt, accept, and incorporate the new capabilities...
3. Small "Upstart" manufacturing companies can "jump in" with today’s available technologies and match or exceed the quality and productivity of the established giants, faster and cheaper. This trend continues to be fueled by the growing move towards outsourcing and the pressure, and opportunity, global competition brings to the manufacturing environment and chip making entrepreneurs.
3.2 Cutting Tool Material Advancements:
With respect to the main cutting tool materials (carbides, their related coatings, cermets, and ceramics) the following trends are predictable.
1. Carbides: Development is mature. Progress does continue in binder enrichment techniques which result in increased cutting edge security and wider range of application.
2. Hard Coatings: Progressing from CVD (approximately 50% of the coatings in use today) to PVD (most rapidly growing coating) which offers the ability to coat a sharp edge. New coating materials include TiAlN and TiB2 by PVD techniques, and application of soft lubricious coatings such as MoS2 and WC/C over PVD TiN or TiAlN mostly for drilling & dry drilling applications.
3. Development continues on advanced coatings such as cBN, which will offer the same increases in productivity in ferrous machining as already commercially available diamond coatings have provided in non-ferrous applications.
4. Cermets: Newer developments combine excellent resistance to deformation and chemical wear with a degree of toughness that enables them to be used in semi-finishing as well as finishing operations. Coatings further enhance the performance of these modern day cermets.
5. Ceramics: Advances in silicon-nitride ceramics have expanded their application range from nickel-base alloys to cast irons. CVD coatings on these materials have expanded their application to ductile iron workpieces. In the aerospace industry a new breed of alumina ceramics strengthened by silicon-carbide whiskers is significantly enhancing productivity in the machining of Inconel and similar high strength high temperature alloys.
3.3 Cutting Tool Geometry Advancements:
The relationship between cutting tool Micro (cutting edge preparation) and Macro (rake face topography) geometry is becoming more and more understood as a competitive advantage by tooling manufacturers. Chip control, tool life, workpiece finish and accuracy can be greatly improved by applying the proper combination of Micro and Macro geometries in conjunction with the proper substrate and coating.
Control of the chip, dissipation or deflection of heat via restricted contact topographies, reduced cutting forces as a result of positive rake surfaces incorporated in the insert rake face itself all lead to the improved performance of today’s modern molded cutting insert geometries.
The growing trend toward maximizing productivity and higher material removal rates has generated the need for developing very accurate and reliable machining processes. Traditionally, the techniques used in industry are based on previous experience, extensive experimentation, empirical techniques and trial and error. While academic knowledge tries to catch up with new emerging trends in machining, the industry practitioners are left with no choice but to resort to the old habits of experimentation and trial and error.
The lack of fundamental understanding of the material behavior has also resulted in a lot of frustration in the machining industry. The term "machinability" is historically understood to be a property of the work material alone. There are several machinability database systems that are built on extensive experimental data and would provide guidelines on selection of cutting conditions. A lot of these databases have presently been integrated into commercial CAPP (computer aided process planning) systems. However, with the development of new cutting tool materials, coatings and chip-groove styles, these databases become "obsolete" within a very short time. Also, the experiments rely heavily on predicting machining performance based on one or two of the machining parameters instead of assessing the cumulative effect of all parameters.
Another area of concern for the industry is the slowness of the international governing bodies (e.g., ISO and ANSI) in updating standards. A clear example is the tool wear standards, last updated in 1993. The tool wear criterion is either the flank or crater wear, based on flat-faced tools. However, most chip-groove inserts do not fail in either mode. In many cases, the tool fails due to back wall wear of the groove or nose wear. In fact, in a recent study, 11 different modes of tool wear in grooved tools have been identified . The tool wear standards need to be updated to accommodate these new changes.
3.3.1 Challenges for the Academic and Industrial Research Community
The industrial landscape is changing very rapidly due to new technological advancements in the areas of improved cutting tool materials, tougher and more wear-resistant tool coatings as well as faster machine tools, all directed toward achieving higher productivity. The issues facing both industry and academics are summarized below together with possible future directions.
1. The development of more reliable constitutive material models utilizing work material flow stress data at elevated temperatures, strains and strain rates remains a major goal. Attempts should be made to use process parameters that are easily obtainable (e.g., cutting forces) into finite element models and fine-tune flow stress data and material behavior. We also need to work very closely with commercial research laboratories in order to improve experimental data collection of flow stress properties.
2. Computational tools (e.g., finite element modeling techniques) need to be used, wherever applicable, in order to reduce extensive experimentation. FE models, verified by limited experimental results offer a reliable, cost-effective approach to the design of new products.
3. Reliable tool life prediction remains a priority for chip-groove inserts. Again, establishing a relationship between the cutting forces and tool wear offers a promising approach. Initial work in this regard has achieved highly encouraging results .
4. More awareness and research in the area of grooved tools is necessary to move toward a reliable, predictive modeling approach and understanding of the complex tool/chip interaction. Again, this FEA approach offers a very promising solution. However, as a stopgap measure, empirical testing, and the resulting experimental databases, should be encouraged to achieve a preliminary understanding of the complex process behavior.
5. Lastly, the industry and the universities need to work very closely to understand each others’ views and to utilize their respective strengths to move toward a more predictive modeling approach. Sharing of important test data and experimental information would avoid costly duplication of efforts on both sides and would eventually lead to improved, reliable and predictable cutting processes.
3.4 Innovative Tooling and Part Processing Techniques:
As the demand for increased productivity at lower cost continues to challenge manufacturing companies it becomes vitally important to develop and implement innovative manufacturing techniques. Working together with machine tool builders and tooling providers, end users can achieve some valuable production advantages. The following examples relate to automotive engine component manufacturing on a machining center as opposed to traditional transfer line manufacturing methodology. The Machining Center approach provides added flexibility or, to use today’s term, "agility", to the process. Agility can take a number of forms, and has meant different things to different people. First is the agility to change cutting conditions, including tool path and spindle speed. Second is agility in tooling, the ability to automatically change tools, or actuate tools. Third is agility in deployment so that machines can be incrementally added to a line as requirements increase, or re-deployed as requirements decline. The tooling concepts developed to address the requirements for "agility" fall into three categories:
1. Combination tools which can generate various forms with a single tool, reducing tool changes and other parasitic time.
2. Special actuated tools such as "squirt" (axially extending) reamers or generating heads, which have been associated with special equipment and were not supported by agile machines.
3. Tools which can be automatically adjusted, to support closed loop size control.
Specific examples are:
3.4.1 Combination Hole Making and Threading Tools
The Tornado® & Typhoon® Thread Milling tools are good examples of combination tools that have been developed to perform multiple operations without a tool change. They can produce holes, counterbores, chamfers, back chamfers, and threads with helical interpolation. The depth and diameter of features machined can be changed with a change in tool path. For example, a single tool could be used to mill holes and thread M8x2 and M10x2 threads, with or without chamfers, and with or without counterbores of various sizes. The same tool can be utilized to produce O.D. threads, multi start threads or tapered threads.
3.4.2 Line Boring Tools (See FIGURE 5a)
Line boring, associated with crank and cam bores, has been performed on special machines with outboard bearings to support the end of the boring bars. Two developments have supported the transition of this operation from dedicated to agile machines. First is the development of hydrostatic water bearings to support the long tools. Second is the development of automatic tool changers which can support the long tools or, in other applications, the development of exceptionally accurate rotary tables to support bore-index-bore operations.
3.4.3 Generating Heads
Generating heads are now available for agile machines and can be actuated by fluid pressure (through spindle coolant) or electric servo (mechanical connection to traditional servo or inductive power driving an internal servo).
3.4.4 Closed Loop Control of Coolant Activated Tools (See FIGURE 5b)
Fluids have been used to actuate tools in response to gauging information. This allows automatic compensation for tool wear without operator intervention. More recently, Makino has introduced a system in which the fluid control is a simultaneous servo. This allows for correction of more complex errors. For example, if taper in a bore violates the cylindrically tolerance, the pressure can be modulated during the boring cycle to compensate.
3.4.5 Closed Loop Control of Fine Precision Boring Tools
When it is not necessary to change the diameter of the bar while it is cutting, simpler tools are available to support closed loop control. For example, fine precision boring tools such as Romicron boring heads, which are adjusted by rotating a ring in the head, can be modified so that the ring is held stationary by the fixture while the bar is rotated by the machine tool spindle. Therefore any agile machine with programmable spindle orientation can be utilized to adjust the diameter of the bar.
3.4.6 Honing (See FIGURE 5c)
At IMTS ’98 machine tool builder Makino, Inc. introduced a coolant actuated, cylinder bore honing tool. Actuated by pressurized coolant, the tool incorporates a thin walled, CBN plated membrane that can be expanded to micron accuracy. The coolant pressure is controlled by a fluid servo for precise size control. Both traditional "crosshatch" and "plateau" finishes can be produced.
3.4.7 Grinding (See FIGURE 5d)
Agile machines are now performing a wide variety of grinding operations. The materials ground include ferrous, nonferrous, combinations (iron sleeves in aluminum blocks), and high temperature alloys. The abrasives utilized include both conventional and superabrasive in friable, metal, and plated bonds. Planer, cylindrical, and complex geometries are ground. The processes applied have included creep feed, surface, orbital, and High Efficiency Grinding (HEG) with high velocity, super abrasives.
3.4.8 "Squirt" (axially extending) Reamers (See FIGURE 5e)
"Squirt" reamers have traditionally been used on special machines to produce valve guides and seats for internal combustion engines. The tools have been actuated / extended with drawbars which were not available on agile equipment. In the past two years, "squirt" reamers have been introduced on agile machines. Designs incorporating coolant pressure or centrifugal force for tool actuation now exist.
3.4.9 Gun Drilling
Gun drilling and reaming is being performed on agile machines with the availability of high pressure through spindle coolant, and appropriate processing techniques. The guide bushings associated with traditional gun drilling machines have been replaced with witness bores produced in the work.
3.5 High Velocity & Machine Spindle Trends
In addition to innovative tooling concepts which increase productivity, the increase in spindle speeds and the gains associated with those increases will continue to impact metal removal rates. FIGURE 6illustrates the growth of high speed capable spindles (by tool shank connection) as previewed in IMTS and EMO International Machine Tool Shows since 1990. As can be seen by this information, the availability of high velocity capable machine tools is on a strong growth curve. Cutting tool manufacturers will put high velocity tooling development activities on a supportive growth curve as well.
3.5.1 High Velocity Tooling Concepts:
FIGURES 7a & 7b represent one such high velocity concept where the cutter body design reflects the need for less mass at the outer periphery of the body to reduce the inherent centrifugal forces acting on those outer elements. Use of finite element analysis, empirical testing, and spin-to-destruction testing of such high velocity designs will be required to ensure user safety and practical application of these high velocity concepts in the future.
3.5.2 Chip Disposal Issues at High Velocity
As cutting speeds increase and chips are produced more rapidly, the disposal of chips in a quick and efficient manner is also a requirement. Vacuum systems that remove chips and airborne dust particles form the work area and deliver same to recycling containers seem the obvious choice but come with their own set of limitations related to the size of the chip they can adequately handle, noise restrictions, and cost to operate. As a result, the machine tool builders must consider chip removal features key in the design and implementation of new high velocity machining concepts. Tooling producers must always consider features of the tool design that reach a balance between the most appropriate sized chip, the lowest cutting forces, reduced cutting temperature, extended tool life and adequate workpiece surface finish.
3.6 Balanceable Tooling Concepts:
With the increase of high RPM machine spindles and high velocity rotating tool applications, balanced and balanceable tooling is becoming a critical requirement to ensure satisfactory performance, operator safety, and machine longevity. Several balanceable concepts exist including adjustable rings which are themselves unbalanced and can be manually rotated about the axis of the holder to create a balanced result within certain limitations. Other systems incorporate radially located screws, which can be manually adjusted closer or farther from the centerline of the rotating tool to affect balance. In all cases these concepts must be used in conjunction with a balancing machine which indicates to the operator where the imbalance is and when the adjustments being made have corrected the imbalance problem within the limits deemed acceptable.
Future approaches will incorporate balancing devices directly on the cutting tool and machine tool that will automatically balance the "spindle and rotating toolholder assembly" as the spindle ramps up from zero to its programmed high RPM. This will be performed automatically, either in the machine spindle by moving the tool assembly into a balancing position within the "balancing device" or off-line on instrumented balancing machines that determine the imbalance and send the proper signals to the balancing components to properly adjust the tool within appropriate limits.
FIGURE 8 shows a rotating tool complete with Electro-Magnetically positioned rotors that can be rotated automatically to achieve required balance conditions. In cases where the length of the tool is such that dual plane balancing is required, tool holders incorporating the automated balancing components will be balanced in multiple planes, automatically.
In addition to balance requirements, the structural design of the tooling that will operate at ultra high cutting velocities must be carefully considered. As this higher velocity machining trend continues, the cutting tool providers must keep pace by providing cutting tool materials that can operate at the elevated cutting speeds in addition to robust balanced and/or balanceable tooling concepts which can withstand the forces related to high rotational speeds.