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Euro-directions: Germans share their technology.

Euro-directions: Germans share their technology

GAMMATEC II, the second German American Forum on Manufacturing Technology, was held May 8-9, 1991, at the Institute of Advanced Manufacturing Sciences Inc (IAMS), Cincinnati, OH. It was an opportunity for domestic manufacturers and researchers to learn about developments at one of Germany's leading manufacturing-research institutes, the Laboratory for Machine Tools and Industrial Management (WZL), Technical University, Aachen, Germany. Topics presented ranged from management strategies to specifics on cutting-tool research, machine-tool technologies, and computer integration.

Spokesperson for the group of presenters was Dr Walter Eversheim, Chair of Production Engineering and a director of WZL.

In Germany and Europe, as in the US, concern for the environment is impacting on manufacturing.

"Germany and all of Europe are more and more concerned with ecological questions," Eversheim reported, "both in how our products are used and the effects of our manufacturing technologies. It is interesting to note that both BMW and Mercedes Benz are doing major tests of disassembly of their cars (for recycling) with a high level of automation. There's also a lot of ecological concern about using plastics in certain combinations. At the same time, we are looking at technologies to get rid of the use of certain machining coolants through dry cutting.

"When we examine these new dimensions of ecological quality, we must also think about the costs involved. We must ask: 'Who pays for this?' The microeconomics in the factory must be broadened to include the macroeconomics of the whole marketplace."

Cultural differences

Eversheim acknowledges the big difference in reputation the engineer enjoys in Germany versus here in the US or elsewhere--the issue of whether it is more desirable for the young to become lawyers or engineers.

"In our country, the engineer's office is well respected. They have a good social status, and mix well with the society of upper management."

Machine operators also have more status and a more significant role there. The operator closes the control loop and provides important feedback to the NC programmer.

Investment differences

There are also differences in governmental influences on manufacturing R&D. "This technology is driven by DOD in your country," he notes. "The Department of Defense pushes through new materials, technologies, and the transfer of research from institutes or universities to industry. In contrast, in Germany, the Ministry of Defense is of nearly no importance--it has very little research money to spend. Instead, this is done by our Ministry of Research & Technology, and is more concentrated in the public domain and primarily fundamental research. The universities do applied research, and are heavily funded by industry." (Whereas the German R&D budget in the public domain is 4% of GNP/year, private industry spent an estimated 47 billion Dm on research last year. The US R&D estimate for '91 is $150 billion, evenly split between federal and industry funding.)

Another important point is that their universities work closely with industry on these programs, using students pursuing engineering theses on these large, publicly funded projects. "These students train on the job, go out from the universities to the companies, get in touch with the unions, and learn the labor environment first-hand, which is very important. When they come later to their white-collar jobs, they will not have these (informal) discussions. So, these approaches are quite different from your system. But this is West Germany. It is not the same in France, for example.

"Also, our R&D institutes are kept well informed in the very early proposal stages about what is going on in other major institutes in Munich, Stuttgart, Berlin, etc. We don't do duplicate work! Or, if we quit a project, that is also known, and the way is opened for others to try a different approach."

Improving delivery time

A bigger competitive factor than a product's price today is its delivery time, says a survey of leading machine-tool manufacturers in Germany. When asked about their goals and how well they were meeting them, the highest discrepancy was minimizing lead time. While 59% said it was their most important goal, only 19% had reached it, whereas, minimizing inventory, a goal of 68%, was already achieved by 45%.

In production control, they see a need for decentralized tools to make the order-processing process more flexible and reactive to changing customer requirements. Instead of centralized control, order processing must be broken down into control of manufacturing assembly, planning, logistics, and storage using control stations at the operational level. This is being helped by PC software tools now available and relational databases and networks to exchange information. (WZL is coming out soon with production-management software.)

WZL engineer Gerald Muller described their use of simultaneous engineering, but acknowledged that this approach takes more total engineering time. Yet, they can show examples where this investment of a few million extra deutsche marks produced savings of ten to fifteen times that amount. More importantly, these examples have made a convincing impression on their bean counters and affected how they justify technology investments.

JIT speed adds complexity

Dr Mathias Gross, a WZL engineer in production management, said the idea here is to combine order-planning, customer wishes, and customer-neutral planning and processing in one localized group. He cited the example of a company that introduced JIT to produce the right materials when needed and combined this with program planning of other products, using a complex mixture of push and pull mechanisms. "The result was a considerable reduction in inventory, and delivery times were reduced to two weeks. But, I must admit, the control of the process became more complex--the price you must pay for this improvement. JIT works well for simple parts with very few variances. The more variance, the more difficult and time-consuming to arrange JIT."

Intelligent sensors

WZL's Dr Schmitz-Justen reported on intelligent sensors. With the emphasis in manufacturing shifting from volume to reliability and quality, and the introduction of CNC and PC technology placing decentralized computing capacity at the machine tool, we need to exploit these tools to make our technologies a lot smarter than they are today, he says. "In conventional manufacturing, product design provides the initial information on the required machining tasks, and then we generate the machining sequence (process design). The part is machined and then inspected to see if it has been correctly machined.

"This process has two imperfections. One, is that the optimization will be done by the machine operator, usually empirically. The other is that there is no feedback from the quality criteria to process design."

So he recommends that intelligent systems use available process knowledge for process design and process control via "smart" sensors to provide feedback of real-time and recent process data to the system database. Product designers must become more aware of the actual capabilities of manufacturing technologies and specific machine tools. When they do, he feels, they might design differently.

Wherever possible, the WZL team uses force-measurement sensors, mounted as closely as possible to the cutting site, usually in the tool-holder or spindle nose, not within the spindle itself. They are less enthused about using temperature sensors for mechanical machining. They use temperature measurement only in laser welding to check the plasma temperature required for a quality weld.

Artificial intelligence

Although Schmitz-Justen admits there are no expert-systems doing tool monitoring in Germany yet, he points out that in forging, you can buy AI-framework software to which you add your own "intelligence" (i.e., company knowledge) into that framework. "You need a database with material characteristics, methods to calculate press loads in the forging preform stage, and process simulations. With these technological functions implemented, you can easily handle workpiece design variations and come up with the different contours of the forging die. To make that die, you readily convert that design to machining technology.

"One project we're working on is to do the machining of hot-forging dies out of high-strength, fully tempered material, with no further heat treatment or finishing after milling."

Some other WZL research projects:

* Machining programs that incorporate factors for the dynamic response of the machine tool.

* Tooling interchangeability--standardized tool magazines and making any tool fit any machine.

* An expert system to design fixtures.

* Modularized fixtures for robotic assembly that give the robot the ability to use these modular elements to build new fixtures on the night shift (including the ability to make microadjustments and change fingers, selecting from an array of modular grippers with built-in sensors).

The cutting edge

Dr Wilfried Konig, a WZL director and Chair of their Technology of Production Processes, is puzzled about the slow acceptance of cermets. "Why are cermets being used to the extent of 26% in Japan and only 3% to 5% in the US and Europe? New-generation cermets are complex, multiple-material systems of titanium-based hard phases with nickel binders. They belong to the carbide group just as much as the tungsten-carbide-cobalt alloys."

He cited an automotive turning example where a coated carbide produced 150 parts per insert, machined at 220 m/min at 0.25 m feed depth, whereas the cermet insert machined 240 parts at 400 m/min, 0.3 mm depth. Another example was a forged automotive part (SAE 1050 steel) that required 11 different inserts to complete the chamfering, roughing, and finishing process, whereas all that is now done with a single cermet insert with increased tool life. In gear chamfering, a cermet provided five times the cutting speed, three times the tool life, and one fourth the tool costs per part of titanium-nitride-coated high-speed steel--and twice the cutting speed and tool life and one third the tool cost of PVD-TiN-coated carbide.

Konig points out the importance here of thermal conductivity. Because turning cutting tools are more exposed to temperature effects than interrupted-cut milling, the turning cutting tool with the best thermal conductivity gives the best wear results. (Shifting the contact zone to the cutting edge is bad, he says, so you must first increase feed, and then come up with speed to get the best results, thus shifting the crater to a safer region of the workface for a more stable cutting edge.)

In hard machining--materials case-hardened to over 60 Rc--coating effects are very powerful. In hard-broaching of a sliding gear with a PVD-coated tool of micrograined carbide, the previous operation sequence was to size the part by broaching in the annealed condition, and then case hardening it to 62 Rc. In the new approach, the part is broached after case hardening at cutting speeds of 66 m/min. After 3000 pieces, tool wear was only 20 microns, even though cutting was done dry. The ultimate result is improved material content of the gearing and enhanced shifting properties, because dimensional and form errors from hardening are eliminated.

In the cold extrusion of a helical gear, a PVD coating of titanium nitride reduced the pressing force from 250 kN to 210 kN and boosted the parts per die from 1500 to 40,000.

These kinds of results, Konig explains, imply major future benefits in reducing or eliminating the use of coolants and their attendant disposal problems. "We are now discussing the possibility of tools able to machine gears without any application of lubricants. Indeed, we have them now in the form of carbides, submicrograin tools, hydrostatically pressed. Our research clearly shows that we can apply these tools, and that it is possible to regrind them.

"The only problem is heat flow affecting the accuracy of the machined part. Our present work is trying to determine this heat flow, and look for ways to compensate for it. In hard machining, you must diminish the surface conductivity of the material so that heat flows into the chip. By using different heat-conductivity methods, you control to some extent where the heat is flowing, whether into the tool or the chip. You look for clever ways to get rid of this hot chip immediately. So far, different coatings give us the potential to control this heat flow."

Layered coatings

In milling and interrupted-cut work, the coating's wear resistance must be augmented by the substrate's impact strength and stability under temperature change. The cutting tool's resistance to mechanical or thermal stress cracking depends both on the properties of the substrate and the bond of the hard-phase coating to that substrate.

One solution WZL has found is the use of intermediate layers of titanium nitride or titanium carbonitride. These layers act as a buffer between the comparatively soft and tough substrate and the substantially harder and more brittle carbides, nitrides, or oxides of the coating. Some examples: In a milling application, a multilayer coating provided a 37% improvement in tool life over a titanium-carbide, aluminum-oxide coating; and in a turning-with-interrupted-cut application, a multilayered coating with a boundary-free zone of tungsten carbide and cobalt boosted tool life 52% over a single titanium carbonitride coating.

Although the cutting-tool material and its properties are often the focus, they note, optimum performance depends also on choosing the right tool geometry for the task, along with the right fixturing of the tool and a high-grade tooling system to deliver it to the workpiece.

Similarly, PVD coatings with hard phases are excellent for boosting the performance of forming tools by a factor of four or more. However, they warn, this increase in load cycles can mean the tool material fails in fatigue rather than wear. Although the hard-phase coating reduces the forces and stresses in the tool, this is not sufficient to compensate for the increase in number of load cycles.

Other trends

Expansion of near-net-shape technology is increasing the demand for highly wear-resistant cutting tools for fine finishing. Because the cermets are particularly suitable for such machining tasks, they are expected to increase their market share in Europe from 5% to 15% at the expense of tungsten-based carbides and oxide ceramics. As coating techniques get more complex and multi-element, they will become even more customized to specific applications, WZL feels.

With the production of diamond and CBN materials in less expensive, low-pressure processes, WZL predicts their use will expand, and they will be used more in grinding and polishing, for coating components and tools exposed to wear, and in the machining of aluminum-silicon alloys, ceramics, composites, and graphite.

Improved cutting tools and coating techniques, particularly turning with diamond-tipped tools, will provide dimensional and form accuracies and surface finishes that challenge conventional grinding for finishing. This suggests improved flexibility in tackling contours, shorter throughput times, and the reduction in the generation of pollutants by increasing the use of dry cutting. A finer and more process-oriented graduation of tool properties will be possible. Tool design and selection will become even more important. Computer-aided and expert systems for tool selection will become increasingly important.

PHOTO : Paralleling the work of the WZL group in Aachen, Germany, is the research at IAMS' Metcut Machining Laboratory in Cincinnati, OH. Both are constructing predictive tool-life and machinability models for use in cost, operational, and process-improvement analyses; for example, to use in comparative ranking of tools, materials, fluids, and related machining factors.

Eugene E Sprow Special Projects Editor
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Author:Sprow, Eugene E.
Publication:Tooling & Production
Date:Jul 1, 1991
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