Intelligent Computation in Manufacturing Engineering - 4

ADVANCED PROCESS CHAINS FOR TOOL AND DIE MANUFACTURING

R. Neugebauer, A. Schlegel

Fraunhofer Institute for Machine Tools and Forming Technology IWU, Reichenhainer Str. 88, D-09126 Chemnitz, Germany

Abstract New trends and demands of the automotive industry have dramatically influenced the requirements and processes of tool and die manufacturing over the last years and have led to new, serious and often incoherent challenges for the tool and die makers which have to rethink and redefine their concepts for manufacturing, machinery and production management. To assist in establishing advanced process chains for tool and die manufacturing, problem-adapted solutions and services, based on competences on the relevant field of forming technology, precision technology and machine tools construction plus the incorporation of digital development tools such as CAD, CAM, Simulation and Virtual Reality, are provided.

Keywords: forming technology, tool and die making, machine tools construction, machining strategies, virtual design

1 INTRODUCTION

1.1 Initial situation, Objectives

The tool and die construction branch as problem solver and system supplier for the automotive industry is subject to a permanent pressure of change and innovation by its very nature. Over the last few years however, processes and requirements have changed dramatically due to a series of influences [1][2]. Especially the following developments are of highest importance and have lead to new demands on products and manufacturing processes:

(1) Use of new materials in sheet-metal forming. In addition to geometric optimization of the components (p. e. hollow parts in the automotive powertrain) also new construction materials are used for realising the principle of light-weight construction. Car body parts are manufactured more and more by high-tensile steel [3], aluminium or magnesium alloys [4]. While the tool and die makers can count on their experience and on precise simulation results for traditional sheet metal components, there is a lack in mathematic models and practical experience, especially concerning the resilience behaviour of new materials.

(2) Platform concepts: In order to reduce the variety of components, the automotive industry introduced the platform strategy in the 90´s of the last century. Not only various automobile models but also different models of different brands are based on a defined group-wide platform whose components are nearly the same. This strategy permits the exploitation of enormous cost-efficient potentials in the fields of production and development through an increase in the number of pieces coming along with an increasing proportion of equal components. A differentiation mainly becomes visible by the different car body parts.[5]

These changes, combined with the increased competitive pressure of a globalised market, shortened product life cycles, reduced lot sizes and a rising diversity of products, are leading to new, serious and often incoherent challenges for the tool and die makers. For example, the shorter product life cycles and increased product diversity require simple, cost-efficient tools with reduced durability for car-body parts, but for the automotive power-train, new forging dies with extended durability are needed due to platform concepts.

Tool and die makers have to meet these challenges and they have to implement optimal concepts for

manufacturing, machinery and for production manage-ment.[6] In this process, the existing expert knowledge must also be worked up, renewed and sometimes be queried, taking into consideration new aspects of tool and die manufacturing. The Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz, Germany assists in these tasks by following the holistic approach of “advanced process chains for tool and die manufacturing”. Within this concept, solutions and services for technology, process and machinery design as well as production and knowledge management are provided.

1.2 Approach

The concept of “advanced process chains for tool and die manufacturing” is based on distinctive competences on the various fields of work plus the incorporation of digital development tools such as CAD, CAM, simulation and virtual reality (VR) for the design and evaluation of problem-adapted services and solutions. The following approach is principally pursued:

1. Starting from the manufacturing tasks of production for the components, which (besides geometry and material) especially are determined by manufacturing amounts and target costs, manufacturing concepts are designed and assessed. Often a process simulation decides on the technical realisability and provides important process parameters such as tool geometry and pressure pad forces for drawing operations. The definition of technology and forming stages is followed by the development of forming tools from which other tasks of production are derived.

2. Manufacturing concepts for forming tools are mostly based on cutting processes. Important aspects are the choice of the individual manufacturing processes and decisions for handling and transport devices. To create an optimal manufacturing concept for the given manufacturing tasks, all of these elements are combined to a host of concept variants promising to be successful and are assessed by simulation.

3. The decision for a manufacturing concept leads to specific input parameters and optimisation emphasis for a specific machinery concept. Such input includes technological parameters like cutting, positioning or feed rates, type and number of spindles required, the capabilities of the machine control unit (such as 5-axis machining), the clamping equipment to be used and

information on the concatenation of the machines (transport, material flow intensity, the order of various arrangements, functionalities, etc.). The development of machine concepts is supported by virtual design tools.

4. From the interaction between orders, material and machinery resources in the production system a multiplicity of diverse controlling tasks can be deduced. Examples are CNC, PLC, material flow control or order scheduling. For these tasks adequate controlling concepts must also be provided.

5. Finally, “Advanced Process Chains” implies the task of integrating these data and tools by interfaces and data bases into the company-wide or company-spanning information and communication infra-structure.

The application width of this approach shall be presented with several examples in this paper:

• Development of new tool concepts (modular drawing/cutting die for car body components; application of new materials for forging dies)

• Development of manufacturing concepts and CNC strategies plus internet-based provision of CNC programs for tool and die makers as an “e-Business” service.

• Development of innovative machinery concepts in a virtual design environment.

• Development of a web-based job shop scheduling / operating data logging system, especially designed to fulfil the demands of tool and die makers.

2 EXAMPLES

2.1 Development of new tool concepts

As previously described, new requisites on tools are resulting from the development trends in the automotive industry. Besides the already mentioned tools for reduced lot-sizes, this especially concerns forming tools for sheet metal materials difficult to form and the development of tools or dies for high volume parts which are produced as components for automotive platforms.

For the most part, necessary examinations have been effected in the course of the Fraunhofer-Demonstration-Centre for Forming and Cutting Tools “ZEUS”, which is directed by the Fraunhofer IWU.

Innovative materials and coatings for sheet-metal forming

Drawing, piercing and trimming of high-tensil materials, organic coated steel sheets or aluminium (e.g. in progressive dies or car body line dies) requires innovative tool material with adapted characteristics regarding hardness, strength and wear resistance. In a series of experiments a host of combinations of tool materials and sheet materials (see Table 1) has been evaluated using single tools.

tool material / coating sheet material Deep drawing Piercing

1.2379 (X153CrMoV12)

1.2379 (X153CrMoV12)

aluminium

CrN+W-DLC

CrN-DLC;

cemented carbide;

ZrO2;

Si3N4

Table 1: Excerpt from the material data base.

Based on the latest findings, a drawing/piercing tool has been designed and realized as demonstrator. The panel

manufactured with this tool (see Figure 1) is almost equal to an original door panel of a cabriolet.

punchings

flange crimping

trim line

recessed grip

Figure 1: Cabriolet door panel.

By designing, developing and realizing the demonstrator tool the main focus was on the application of innovative tool and work piece materials and on new technologies for complex components. [7]

Areas with high local strain gradients served as indicators for modifications in the tribological system so that findings concerning increased process security with innovative tool materials (e.g. ceramics, tools with DLC coatings) as well as results concerning the design and the stiffness behaviour of rapid and flexible manufacturable large-scale tools were deducible.

The tool (Figure 2) is designed as a welded construction in order to reach a weight advantage in comparison to the commonly used cast construction.

Figure 2: Deep drawing / piercing tool.

A specific feature is the replaceability of active components which are located in zones of high stress or with a tendency for wearing. Besides those simplification of heat treatment and replacement of active components this provides a potential for the development of flexible adaptable (prototyping) tools.

Major effects of the new tool concept were a higher die life, weight reduction of 20% and most notably improved tribologic conditions as a result of suitable coatings. Through this, the running-in behaviour could be improved and the amount of lubricant demand could be minimised.

Use of sintered carbide and coatings for forging dies

Numerous components in the automotive power train are premanufactured in bulk metal forming. Valves, connection rods, crank shafts but also steering arms, universal shafts and planetary cages are among them. Standardisation and platform concepts in automotive engineering as well as the approved potentials of near-net-shape-manufacturing lead

Intelligent Computation in Manufacturing Engineering - 4

to increased demands regarding the productivity of forging lines, the die life and the product quality, especially concerning the dimensional accuracy.

Conventional forging dies, which are made of hot-forming tool steel, are subject to thermal and mechanical forces leading to a fast wear of the lower die. Therefore, noticeable improvements shall bring new tool materials and surface coatings with them.

During an extensive material screening with five ceramics, three sintered carbide materials, two hot-forming steels and six coating systems as main friction body (pin) and 1.1191 (Ck45) as secondary friction body (disc) at an pin-on-disc tribometer, basic findings for the decision of a special material have been determined. While the pin-on-disc experiment at 1040 °C doesn’t indicate an improved wear resistance for CrN coated test pieces of 1.2365 (X32CrMoV33), for CrVN coatings a lower coefficient of friction can be expected due to the formation of vanadium pentoxide V2O5 above 650 °C, which acts like a lubricant.

For defining the thermo shock and wear conduct under close-to-use conditions, forging elements for the eye of the connection rod of a passenger car motor have been manufactured and tested. Special piercing mandrel elements of different materials have been contracted thermically into the experimental forging die (Figure 3) whose geometry corresponds to those of a big eye of a connection rod. Taking the volume wear and the coefficient of friction into consideration, silicon nitride and a CrVN coating on steel substrate - still being in the development phase – has been chosen for manufacturing and testing of the mandrel elements.

Figure 3: Forging die with coated mandrel inserts (left: upper die, CrVN; right: lower die, CrN).

Experiments with a monolithic forging die showed striking wear at the flash line and the edge radius of the mandrels. Not all of the coatings chosen showed satisfying results. The microscopic analysis of the mandrel’s edge radii, where there is only a slight relative movement between die and forged piece, evidenced grooves deeper than the coating thickness after only fifty strokes. In addition to this, adhesion of forging piece material could be detected.

Better results could be achieved with CrVN coatings. An extraordinary potential of this coating can be expected especially in warm forming.

Further investigations were conducted using a forging die with a cemented carbide (CC) insert (see Figure 4). The experimental results of the hot forming of automobile engine valves convinced the industrial partner of the advantages of this tool concept: the die life exceeded 10.000 valves, compared to 200…300 valves using a monolithic hot-forming tool steel forging die.

Figure 4: Forging die with shrinkage-fitted CC insert.

By reducing the tool wear, not only productivity and safety could be increased, but also subsequent machining time could be reduced by virtue of higher precision.

2.2 Developing Strategies for NC Machining

When manufacturing those drop-forge dies or for example, hydroform tools, it is often necessary to generate very high volumes of chips (for instance, machining deep pockets, clearing away in the basic form of the tool or engraving processing three-dimensional components running in space). The machining techniques most frequently applied are milling (approximately 75% of production time) and drilling. Extensive analyses in tool and die construction indicate that milling takes up 70% to 80% of the main time for roughing down operations. This is the reason why innovative tool designs give hope for enhancing the roughing down technique to tap this time and cost potential.

Plunge milling (also known as “Bore-Jet”) is a machining strategy that can be used for machining deep engravings on high-performance tool machines. Here, the engraving is made using a drilling pattern developed from CAD data with forward feed in the Z-direction and by shifting the tool to the side for feeding on the XY-level. As a measure of how neighbouring areas are covered, the radial contact width determines the number of holes that have to be drilled. Tools with a centre tool tip have greater radial coverage, meaning that they provide axial restraint that reduces one-sided stress.

We analyzed drilling roughing by comparing the machining strategies currently in use in tool and mold construction:

• Plunge milling with a center tool tip + residual material processing,

• Plunge milling without a center tool tip + residual material processing,

• blank roughening with a toric tool (an end milling cutter with a corner radius)

• blank roughening with new types of tool geometry (for preventing vibrations) including subsequent residual material processing)

for roughing down an engraving (refer to diagram 1) depending upon the engraving depth.

0

20

40

60

80

100

120

0 20 40 60 80 100

Gravurtiefe [mm]

Bearb

eit

un

gszeit

[m

in]

Bohrschruppen (Werkzeugtyp I)

Bohrschruppen (Werkzeugtyp II)

Rohteilschruppen mit torischemWerkzeug

Rohteilschruppen mit neuartigerWerkzeuggeometrie

Diagram 1: Machining times (engraving 125 mm x 250 mm; diameter range 30-35 mm).

Type I plunge milling effected the shortest machining times while the percentage benefits with blank roughening and new types of tool geometry peaked at greater engraving depths. The difference between scenarios I and II is the fact that that 65 percent is covered and the fact that non-productive time for positioning and return stroke is scaled back. We machined a reference component on a PC 130 horizontal boring machine from the Chemnitz-based UNION Werkzeugmaschinen GmbH for verifying our preliminary theoretical deliberations.

We defined an injection moulding tool as the reference component with an engraving having the approximate dimensions of 250 mm x 250 mm and a maximum depth of 90 mm. The material is a high-strength hot forming tool steel 1.2343 (X38CrMoV5.1) and the diameter of these tools ranges between 40 and 50 mm, meaning that the longitudinal diameter ratio is 2...2.5.

Figure 5: Machining the reference component.

These tests determine the impact that machining dynamics have on machining times, producing correction factors depending upon the forward feed speed. Thereupon, we calculated the actual production times for the machining strategies with the CAM systems times and the appropriate correction factors. Here, we witnessed a reduction in production time of 50% in machining time for blank roughening with the toric tool that is presently in frequent use. Admittedly, the radial contact width was no more than 50% of the effective diameter when milling with a toric tool. However, even if this were boosted to 100%, it would provide even more than 25% of the augmented efficiency of drilling roughing. Therefore, we can say that the drilling roughing strategy is superior to blank roughening with a new type of tool geometry where in particular the necessary residual material processing had a negative impact. We can summarize by saying that

drilling roughing constitutes an effective alternative to all known roughing down strategies in tool and mold construction. These insights are also applied to CNC programs featured by the service introduced below.

2.3 CNC Program Generation as an e-Service

Tool and die makers have to meet increasingly complex requirements regarding ever more sophisticated tool geometries as well as substantial growth in the diversity of cutting tools that are available on the market. Research and development in the fields of cutting tool substrate and geometry, coating materials and processes, to name only a few, can hardly be followed by most of the tool and die makers due to plain lack of time and workforce.

This is of special significance in the sector of high speed or high performance cutting where, in order to benefit from the high but narrow limits of those HSC/HPC tools, it is necessary to apply innovative processing strategies as well as to select the most appropriate cutting tools in the first place.

Lacking the appropriate technological knowledge and experience therefore leads to CNC programs that use wrong tools, inefficient processing parameters and strategies and are, as a result, inefficient in themselves.

On the other hand, there are experts with in-depth knowledge of CNC machining as well as the technology and strategies involved in generating efficient CNC programs for given tasks and who are also able to keep up-to-date with news on the market for cutting tools.

‘eNC-Programming’ is a new service that allows for an almost seamless integration of external CNC experts into the process chain of tool and die makers. Using this service, companies can have the latest processing strategies applied to their tool designs and therefore get highly efficient CNC programs. [9]

Figure 6: Architecture of eNC-Programming.

With ‘eNC-Programming’ being a centralised service, there are, apart from the actual benefit the expert knowledge is able to generate, additional ways of optimising the result, as for instance feed rate adaptation and automated selection of cutting tools most appropriate for the given tasks.

Based on a project database all information that the tool and die maker and the CNC expert interchange in the process of CNC program generation for a given tool design is stored and can later be retrieved. This facility can be used for various reasons; its main intent, however, is to fetch project information and decisions for later similar tasks and to improve the overall quality of the service by allowing for feedback from both sides to be stored and queried.

Using the service has therefore a number of advantages for tool and die making companies:

• No/less resources bound for CAM workplace and staff.

• Reduction in production time and cost.

• Creating a technology database.

• Application of latest technology and strategies for highly innovative approaches and tool designs.

engraving depth [mm]

Tim

e [

min

]

plunge milling v1

plunge milling v2

toric tool

new tool geometry

Intelligent Computation in Manufacturing Engineering - 4

2.4 Virtual Reality in the Development Process

It is necessary for tool and die makers to implement the best machine strategy in order to exploit the full potential of production strategies that are ascertained in this fashion at a high degree of process reliability. This concerns the entire production system chain including the design of individual machines. However, developing tool machines that are optimised for a given manufacturing task but can simultaneously be flexibly reconfigured would be an innovation that places supreme demands on machine element and component part engineering and testing combined with interactive communication among all of the experts involved in this intricate process of development, including the customer. Integrating virtual reality technologies (VR) into the development process would be an innovative and promising approach to this problem.[10]

Figure 7: Analyzing tool machines

with parallel kinematics in a CAVE.

The primary motivation was to make a representation of all of the development data for guaranteeing a constant and efficient exchange of data between the simulation, database and the virtual testing process. Using VR technologies provides far-reaching potential for augmenting the efficiency of the development process in particular when devising tool machines with parallel kinematics (PKM). A case in point is facilitating the selection of pivot point equipment, verifying working spaces, reviewing the mountability of the overall system, verifying CAD models as well as designing guides and linking material and power lines. Large-scale immersive visualization techniques such as CAVE or Powerwall make it possible to interactively analyze the spatial arrangements of subassemblies (such as pivots or struts) and make collision analyses of the inside of subassemblies (such as with pivot designs). This also improves the quality of visualization of the results of simulation (such as FEM or multiple-body simulation) and multiple-dimension data fields (such as of the working space, illustrating various stiffnesses and the forces exerted on the working space) or even makes them possible in the first place. Hence, integrating VR technologies can expand upon existing CAD methods and simulation strategies while enabling all persons involved in the development process to communicate interactively.

Figure 8: Using VR technologies

for developing PKM.

Unfortunately, in spite of the present development of VR technologies, the problem of integrating VR into existing system worlds has only been partially solved. In other

words, VR is still just a „one-way street", as witnessed by the fact that data on changes in the model made in VR still cannot be automatically returned to the overall process. In order to solve this problem, the Fraunhofer Institute for Machine Tools and Forming Technology is leading a research project (VRAx) centering around creating a platform for developing parallel kinematic tool machines where VR will be used for the first time as an active medium for development and engineering for immersive modelling. In other words, the basic machine model will be designed and analyzed exclusively in VR!

Storage

Application layer

User interface

Immersive Modelling

Application core

VR System

Generic building-block system

PDMCAD

FEM-Results

PDM data integration

CAM-Results

Metadata

CAM-VR FEM-VR automatic VR data generation

Method of generic modelling of machine tools

Experimental models forprocesses

and machines

CADSystem

VR-CAD interface

CAE(FEM,MBS)

VR-CAEinterface

CAMSystem

VR-CAM interface

Figure 9: VRAx - System architecture.

Figure 9 illustrates the overall architecture of the system:

• The generic building-block system facilitates a swift engineering process with parameterable elements and machine templates that can be positioned and parameterized with the appropriate metaphors. Building kit development is underway for tools, clamping equipment, components and basic structure of PKM.

• Functionalities for making expert analyses of machine models and kinematic modules are integrated into the system for virtual testing, allowing changes in components in the VR system to be examined while calculating and correctly illustrating their impact on other elements.

• Bidirectional on-line interfacing of a CAD core to a VR system are used for integrating CAD and VR combining intuitive and direct interaction of the VR user interface with the modelling potential of state-of-the-art 3-D CAD systems and wholly integrating VR into the CAx process chain.

• Generic interfaces are used to integrate CAE/CAM systems with VR while allowing simulation models to be automatically derived for multidisciplinary studies using a building-block system also containing prefabricated templates for CASE studies.

Some of the potential for this still highly-innovative VR-aided building-block application are scaling down development periods for tool machines by directly applying the customer's needs in an immersive environment with a distinctly higher degree of transparency of the development process while significantly enhancing the comfortability of using VR technologies. Furthermore, SMEs will also be offered the use of this innovative technology through regional VR development centres as run by the Fraunhofer Society all over Germany.

2.5 Production Management

Streamlining the organization of tool and die construction offers cost saving potentials other than those mentioned for technical improvements. First and foremost here are constant process transparency, downscaling lead times at a high degree of adherence to delivery dates and recording all feedback from the workshop on a near-time

basis. The traditional way of organizing work in tool and die construction resulting from the major proportion of manual labour and the focus on experienced toolmakers on process channelling makes it difficult to introduce standard applications for enterprise resource planning and job control and scheduling.

This is the reason why a multiple-stage co-operative approach is used for streamlining processes. The first step is to make an on-site analysis of the internal and external processing of orders. This process analysis results in a descriptive model for documenting the initial state, localizing weak points and discussing and designing how processes could be changed. This in turn fosters the control of activities for improvement. Illustrating it in the form of a descriptive model (refer to the figure) is also used as a basis for communicating with the company's representatives. Among other software products, the ARIS TOOLSET from IDS Scheer AG is used for modelling.

Ressource

vorauswählenRessourcen-Filter WZB-Service

In Warteschlangeeinordnen

Jede Ressourcemöglich

WZB-Service

Ressourcefestgelegt

Mappeeingeordnet

In Warteschlangeeinordnen

Mappeeingeordnet

Prioritätsregel Prioritätsregel

nächster AGmechanische Bearbeitung

WZB-Service

Ressourceverfügbar

Figure 10: Excerpt of the business process model.

After analysis and modelling, the processes are benchmarked or reengineered consciously referring to proven solutions to the problem of labour organization to integrate them in the solution. This also encompasses mapping the new process scenarios as a model making it possible to test and analyze complex processes in a simulation for augmenting process reliability. Software tools are developed as required for facilitating the new processes to integrate them into the company's IT landscape.

An example of the latter is to be found at BROSE, an automotive supplier active on the international scene. The Fraunhofer IWU has developed a solution for planning work and machine utilization, for visualizing the production status of jobs, for channelling co-operation (for instance, in heat treatment) and recording feedback via barcode.

Figure 11: User Interface.

This software was made available to the tool and die construction personnel through the company's intranet to minimize installation and service effort allowing access to the authorized group of users with any web browser.

The application is based upon the LAMP approach (Linux with the Apache web server, MySQL databank and PHP as the programming language) has only minor hardware requirements and uses free accessible software, making it particularly interesting to small businesses as a low-cost application. Interfaces were created to CAD (to get design parts lists from PRO-ENGINEER) and to the ERP system (SAP) for integrating it into the corporate computer infrastructure.

3 SUMMARY AND OUTLOOK

It will only be possible to achieve improvements on a scale required for ensuring competitiveness by applying a holistic analysis of the process chain for tool and die construction, ranging from the manufacturing task of the forming part or casting over tool/die development, machine development to production planning and production management.

This essay described some innovative solutions to various examples of problems. These results are based on a multiplicity of different development techniques and area-specific expertise which must be integrated in order to define advanced process chains. By using virtual reality technologies, an innovative and promising integration approach is pursued.

We can rest assured, that this technology, which is at present almost exclusively being used in automotive in-dustry under the slogan of the “digital factory”, will also be a pre-eminent aid for tool and die construction in the future.

4 ACKNOWLEDGMENTS

The staff of the Fraunhofer IWU, especially named Dr. S. Kolbig, Dr. V. Kraeusel, Dr. M. Kolbe, Dr. D. Kreppenhofer, C. Hochmuth and M. Friedemann is gratefully thanked for their assistance in preparing this paper.

5 REFERENCES

[1] Fallboehmer, P., 1996, Survey of the die and mold manufacturing industry (Germany, Japan, USA), Journal of Material Processing Technology 59.

[2] Snowden, L., 1998, Tool and Die Making in an international context, Kolloquium “Werkzeugbau mit Zukunft”, Aachen.

[3] N.N., 2002, Automotive (R)Evolution in steel, Stahl-Informations-Zentrum, Duesseldorf.

[4] Kainer, K. U., 1998, Potential von Magnesium in der Karosserie, 5. Euroform, Bonn.

[5] Blanchard, O. et al., 2002, Reaching higher productivity growth in France and Germany. Sector case: Automotive, McKinsey & Company.

[6] Neugebauer, R.; Schlegel, A.; Hochmuth, C., 2003, Neue Technologie- und Maschinenkonzepte für den Werkzeugbau, VDWF aktuell 6, S. 24-29.

[7] Klose, L., Bräunlich, H., 2002, Werkzeugbeschicht-ung - Anforderungen der Umform-/Schneidtechnik, Workshop Beschichtete Werkzeuge, Chemnitz.

[8] Putz, M.; Lorenz, B.; Kolbe, M., Zukunftsträchtige Entwicklungen auf dem Gebiet der Massivumformung am Fraunhofer IWU, VDI Berichte 1766, S. 205-221

[9] Kreppenhofer, D et al., 2003, eTechnologie: Programmier- und Simulationswerkzeuge zur optimalen online NC-Programmierung, IFF-Wissenschaftstage, Magdeburg

[10] Neugebauer, R., Kolbig, S., Weidlich, D., 2002, Po-tenziale der Virtuellen Realität, ZWF Zeitschrift für wirtschaftlichen Fabrikbetrieb (97), S. 39-42.