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  5. Abrasive Processes and Gear Technology
Foto einer lächelnden Frau, die eine rote Maschine bedient.

Against the background of constantly increasing demands on materials and machining processes, the department Grinding and Gear Cutting is concerned with the further development of grinding applications for machining mainly metallic materials and components. The scientific penetration of the mechanisms of action in machining with geometrically undefined cutting edges requires a holistic approach that takes into account specific material properties as well as process kinematics, tool development or the application of process aids.

Simulation as a means of improving process understanding is an indispensable tool in our work. In addition to basic research work, which is funded by the German Research Foundation (DFG), for example, a large part of our research and development work is based on industrial cooperation projects. Scientifically trained and motivated personnel, a modern machine tool park and extensive laboratory facilities form the basis for successful project work.

As often the last step in a longer value-added chain for the production of high-quality components, high demands are placed on the grinding process in terms of processing quality and productivity. In addition, there are demands on the energy and resource efficiency of the processes used. Only through a profound analysis can the interactions between the process design, the material to be machined, the tools used and process auxiliaries be mastered.

In the grinding and gear cutting department, grinding technology research work is concentrated in the Production Engineering department. Basic and applied research work is carried out here with the focus on material-oriented, productive and resource-efficient design of process chains. In this area of conflict, the research and development work combines the materials and process engineering know-how available at the Leibniz Institute for Materials-oriented Technologies. The mature developments are applied in the automotive industry and its suppliers, in aerospace technology and other key industries. In addition, innovations are realized in tool technology, medical technology and machine tool construction.

  • Soft and hard machining of gears
  • Machining of difficult to machine materials
  • Evaluation of cooling lubricants
  • Optimized coolant supply
  • Resource and energy consumption in grinding technology
  • Process development and optimization
  • Tool development
  • Tool Grinding

Projects of Abrasive Processes and Gear Technology

Integral Coupled Simulation of the Fluid Dynamics of the Coolant and the Machining Process in Vibration Drilling – ViBohr

The FluSimPro priority program focuses on the development of advanced simulation techniques that couple mechanical and fluid-dynamic processes for efficient cooling, lubrication, and transport in machining processes. In the ViBohr subproject at Leibniz-IWT VT/FT, this is being implemented for vibration drilling.

Transregional CRC 136 „Process Signatures“ – Transfer project T05: Detection and avoidance of undesirable surface layer modifications during surface and profile grinding considering the process signature concept

Based on the process signature concept of the transregional CRC 136, this project aims to develop an assistance system for the detection of undesirable material modifications during surface and profile grinding of hardened steels.

The main objective is to create the basic principles and the subsequent development and testing of a prototype with the industrial partner Blohm Jung GmbH. The assistance system is intended to enable in-process detection of grinding burn and thus of undesirable surface-layer modifications such as tempering zones during surface and profile grinding.

Cooperation: Blohm Jung GmbH
Funding: DFG

Schleifprozessparameter und thermische Prozessgrenzen beim Profilschleifen. Links oben: Schleifscheibe (ds = 400 mm) mit Parametern: vc = 35 m/min, vf = 2983 mm/min, ae = 0,05 mm, ap = 26,15 mm. Links unten: Diagramm zeigt spezifische Wärmestromdichte εP' über Kontaktzeit Δt mit kritischen Grenzen (~20 W/mm² und ~17 W/mm² mit TGT), Toleranzband und aktueller Schleifleistung unterhalb der thermischen Prozessgrenze. Rechts: Werkstückzeichnung (Meldefenster) mit Abmessungen B = 30 mm, L = 160 mm, H = 30 mm, φ = 35°. Hinweis: Keine Schleifbrandgefahr.
Performance comparison of metal working fluids for discontinuous profile grinding

The use of oil as a metal working fluid for gear grinding is indispensable. The chemical and physical properties of the oil influence the grinding process and thus the productivity.

The main objective of this project is to investigate the influence of three different grinding oils during discontinuous profile grinding of gears. A suitable oil is to be identified in which the thermal load during the grinding process is as low as possible despite an increasing machined volume. With the help of such an oil, significantly more gears can be ground before thermal damage occurs and the grinding wheel has to be dressed.

Funding: Kooperationsprojekt mit Fa. Master Fluid Solutions WDG GmbH

Verlauf der Schleifleistung über die Anzahl geschliffener Zahnlücken bei drei verschiedenen Kühlschmierstoffen. Das Diagramm zeigt die Schleifleistung P (kW) auf der y-Achse über die Anzahl geschliffener Zahnlücken (0-100) auf der x-Achse. Drei Messkurven repräsentieren unterschiedliche Öle: Öl 1 (blaue Rauten), Öl 2 (rote Dreiecke) und Öl 3 (grüne Kreise). Der Prozess ist in drei Phasen unterteilt (1., 2. und 3. Zahnrad). Die Schleifleistung steigt von etwa 5,5-6 kW zu Beginn auf 7,5-8,5 kW am Ende an. Öl 3 zeigt die höchsten Leistungswerte, während Öl 2 die niedrigsten Werte aufweist.
FVA 758 IV “Effect of alloy-specific surface layer formation on grindability”

The objective of the project is a systematic investigation of the gear grindability of various case hardening steels. The results offer the potential to coordinate the choice of alloy system and case hardening steel as well as the process design during heat treatment and grinding process in a productivity-optimized manner.

This research project confirmed the significant influence of the material and, in particular, the outermost surface layer. This was illustrated, among other things, by the significantly better grindability (up to a factor of 11) of the low-pressure heat-treated variants without a surface oxide layer, which were additionally considered in this study. Furthermore, for the first time, clear correlations were identified between the alloy system, the formation of the outermost surface layer after case hardening, and the resulting gear-grinding performance. Of particular importance here is the manganese content of the raw material, taking into account the total oxidation potential (PIGO) of the alloy system.

Processing: Leibniz-IWT FT/WT
Funding: FVA Eigenmittel

Korrelation zwischen Manganoxid-Typ und Oxidausmaß verschiedener Stahllegierungen. Links: Mikroskopaufnahmen zeigen Oxidformationen bei 18CrNiMo7-6 (globuläre Oxide) und SAE9310 (linienförmige Oxide) mit 10 µm Maßstäben. Mitte: Streudiagramm zeigt linearen Zusammenhang zwischen Mangangehalt (Ma.-%) und Oxidausmaß (µm/mm²) mit R² = 0,99. Verschiedene Legierungen (18CrNiMo7-6, 20CrMnMoH, 25MoCr4, 26MnCrNiMo6-5-4, 17NiCrMo6-4, SAE9310) sind als Datenpunkte dargestellt. Zwei Oxidtypen werden unterschieden: Ni ≥ PBD > 0 (globuläre Oxide) und Ni ≤ PBD < 0 (linienförmige Oxide). Unten: Mikroskopaufnahmen verschiedener Manganstähle zeigen die morphologische Variation der Oxidbildung. Formel: V'VM(Mn, Ni) mit Bedingungen für Ni- und PBD-Werte. Rechts: Validierung mit V'VM(Mn): R² = 0,99 und V'VM(Mn, Ni)?.
Integral coupled simulation of the fluid dynamics of the cooling lubricant and the cutting process during vibration-assisted drilling – ViBohr

This project aims to develop an in-depth understanding of the dynamics, resulting effects, and interactions of minimal quantity lubrication (MQL) in vibration-assisted drilling by numerically modelling the interactions between flow dynamics and chip formation.

This results in comparatively small, funnel-shaped chips, which is particularly helpful when machining ductile materials that produce long chips. As part of this research project, in addition to the aforementioned vibration-assisted drilling, minimum quantity lubrication and its interactions will also be investigated. To gain detailed insights into the behavior, as well as the resulting effects and interactions of minimum quantity lubrication (MQL) during vibration-assisted drilling, this project employs a variety of measurement techniques and, in particular, numerical simulation methods. The goal is to achieve a comprehensive coupling of the flow behavior of MMS with the chip formation of the vibration-assisted drilling process. From this, design recommendations for the process and tool design recommendations will be derived in the future.

Cooperation: Leibniz-IWT FT/VT
Funding: DFG (SPP 2231)

Optimierungskreislauf für die Schleifscheibenauslegung mittels Multi-Skalen-Simulation (MMS). Das Flussdiagramm zeigt drei Haupteingänge oben: MMS-Formulierung, Stellgrößen und Werkzeuggeometrie. Links: Spantransport-Modell mit Spanverweilauer und Belastungskollektiv (Spanbildungsmodell, thermomechanische Belastung). Zentral: 3D-Modell einer Schleifscheibe mit konischem Profil. Rechts: MMS-Zufuhr mit Kühlkanal- und Benetzungsmodell, einschließlich Volumenanteil, Aerosolströmung und Ölbenetzung der Schneiden, sowie KSS-Formulierung. Alle Inputs fließen in AP5: Optimierung (zentral, rosa Box). Unten: Optimierte Ausgänge für MMS-Formulierung, Stellgrößen und Werkzeuggeometrie. Pfeile zeigen den iterativen Optimierungsprozess.
Analyzing the process effects when grinding with elastic grinding wheels

In this practice-oriented study, the question of the correlation between the process parameters as well as the system parameters and the residual stresses that occur after fine machining is systematically analyzed. Using different grinding wheel specifications with an elastic bond system, the limits of machining for the surface integrity properties are analyzed.

Funding: FGS – Forschungsgemeinschaft Schleiftechnik e. V.

Vergleich der Eigenspannungsverläufe nach verschiedenen Bearbeitungsverfahren. Das Diagramm zeigt Eigenspannungen σ1 (MPa) über den Abstand zur Oberfläche z (µm). Drei Kurven werden verglichen: konventionelles Schleifen (grün), Feinschleifen (blau) und Wärmebehandlung (rot). Der graue Bereich markiert den Anstieg der Druckeigenspannungen (0-100 µm). Konventionelles Schleifen zeigt moderate Druckspannungen (200 MPa), Feinschleifen erreicht höhere Druckspannungen (-350 MPa) mit anschließendem Übergang zu leichten Zugspannungen, während Wärmebehandlung die höchsten Druckeigenspannungen (~-900 MPa) erzeugt. Standardabweichung σ = ± 30 MPa ist angegeben. Alle Kurven nähern sich bei größerer Tiefe dem Nullniveau.
Transregional CRC 136 “Process Signatures” – Transfer project T07: Exploiting the potential of mechanical material stress during grinding using a novel tool concept

In the transfer project T07, an increase in the mechanical load in the process is to be achieved by adjusting the grinding wheel.

As a grain shape with the largest possible rake angle, it was shown that with a spherical grain there is potential for subsurface layer strengthening by setting favorable residual compressive stresses. In addition to the surface and subsurface properties, the roughness of the components is also considered, as this also significantly determines the functional properties. The theoretical considerations are supported by simulation models and grinding tests.

Cooperation: Artifex Dr. Lohmann GmbH & Co. KG
Funding: DFG

Schematische Gegenüberstellung zweier Schleifprozesse: Links zeigt ein konventionelles Schleifwerkzeug mit scharfkantigem, starr gebundenem Korn die Spanbildung an der Werkstückoberfläche. Rechts ist ein elastisch gebundenes Werkzeug mit sphärischen Körnern dargestellt, das eine geschliffene und zugleich verfestigte Oberfläche erzeugt. Ein Pfeil markiert den Übergang vom starren zum elastischen System.
Targeted adjustment of surface layer modification through stock-oriented grinding process design

When designing the process cycle for a multi-stage grinding process, thermal damage in the surface layer is always avoided, as it can negatively affect functional performance.

However, this approach generally fails to take into account that damage to the surface layer caused by the roughing process can be removed to a certain depth in the subsequent process steps (finishing and superfinishing), as long as the required final contour of the workpiece still lies within the remaining grinding allowance. The goal of this project is to develop a model that systematically integrates the influence of upstream process steps on edge zone depth into the design of the grinding process cycle. This should contribute to an optimized cutting sequence and, consequently, to increased productivity through reduced direct processing times.

Funding: DFG

Diagramm zur Einordnung thermischer Effekte beim Schleifen: Die x-Achse zeigt die Schnittgeschwindigkeit, die y-Achse die spezifische Wärmestromdichte. Verschiedene Messpunkte (unterschiedliche Symbolformen) sind über farbige Zonen verteilt, die Bereiche unterschiedlicher thermischer Beeinflussung kennzeichnen: von „kein thermischer Effekt“ (grün) bis hin zu fünf Stufen steigender Randschichtvertiefung Δz (hellrot bis dunkelrot, >400 µm). Rechts ist ein Mikrostruktur-Bild einer geschliffenen Oberfläche integriert, in dem Δz anhand eines Pfeils visualisiert ist. Darunter stehen Prozessparameter (vₜ = 2.000 mm/min, aₑ = 200 µm), die gemessene Zeit Δt und die Wärmestromdichte P꜀.
Impact of machining-related surface layer changes on the nitriding response of forging tools

Nitriding is a thermochemical heat treatment in which nitrogen diffuses into the surface layer of a component to improve its surface properties. At temperatures below 600 °C, a nitrided layer forms on the component’s surface, consisting of nitrides and/or carbonitrides, depending on the process variant and the alloy being treated.

Since these strength-enhancing precipitates remain stable up to the nitriding temperature, nitriding is used, among other things, to improve the heat resistance of forging dies. Due to the low process temperatures, no phase transformation or martensitic hardening of the components occurs during heating. As a result, final machining close to the component can take place even before heat treatment. This eliminates one manufacturing step in the process chain. The components are typically machined using cutting processes with the aid of cooling lubricants. In this process, interactions between the tool’s surface layer, the component, the cooling fluid, and the thermal load lead to the formation of surface layer conditions that negatively affect the nitriding result. The figure shows examples of surface conditions after grinding with different process parameters. This research project investigates the conditions under which surface layer changes occur during fine hard machining and how these affect nitriding, in order to enable optimal coordination of the individual steps in the process chain for nitrided tools and components.

Cooperation: Leibniz-IWT WT/FT
Funding: BMWK-AiF/IGF (AWT)

Vergleich von Schleifproben aus dem Stahl X38CrMoV5-3: Im Bild sind zwei Gruppen von je drei Proben nebeneinander angeordnet. Oben sind die Härte der jeweiligen Gruppe angegeben – links „55 HRC“, rechts „41 HRC“. Jede Probe zeigt eine Farbskala von hell (oben) zu dunkler (unten), was wahrscheinlich unterschiedliche Oberflächenzustände oder Tiefen von Randschichtveränderungen darstellt. Der Vergleich illustriert, wie sich unterschiedliche Härtegrade des Stahls auf das Schleifergebnis bzw. die Oberflächenverfärbung auswirken.
Non-destructive characterization of grinding-generated surface-layer modifications depending on the material condition using micromagnetic testing methods (FVA 723 III)

Aim of this project is the investigation of so far unknown effects on the micromagnetic detection of thermo-mechanical surface damages at ground gear flanks. Based on previous projects, investigations are carried out on profile and generating ground gears from case-hardening steel 20MnCr5 in different heat treatment conditions.

Building on previously completed projects, investigations are being conducted on profile-ground and gear-ground gears made of 20MnCr5 case-hardened steel in various heat-treated conditions. Various surface layer conditions were created and thoroughly characterized by progressively increasing the buildup on the grinding wheel (profile grinding) or by varying the grinding parameters (gear grinding). In addition to Barkhausen noise measurements and Nital etching, the radiographic half-width was determined for several flanks on each gear. Representative flanks, based on the Nital etching classes, were characterized using metallographic sections, hardness measurements, and residual stress depth profiles.

Cooperation: Leibniz-IWT WT/FT
Funding: BMWi-AiF/IGF (FVA)

Verlauf der Schleifleistung über die Lückennummer bei verschiedenen Prozessparametern. Das Diagramm zeigt die Schleifleistung P (kW) auf der y-Achse (0-7 kW) über die Lückennummer (0-310) auf der x-Achse. Acht verschiedene Parameterkombinationen sind dargestellt, kodiert als Vorschub/Schnittgeschwindigkeit/Kühlschmierstoff (z.B. 0,7/0,65/160). Die Kurven zeigen nach einem initialen Anstieg (bis ~Lücke 93) unterschiedliche Verläufe: einige steigen kontinuierlich an (blaue, orange Kurven bis ~4,5 kW), während andere nach anfänglichem Peak abfallen und dann moderat steigen (grüne Kurven bei ~3-4 kW). Die Parametervariationen umfassen Vorschübe von 0,7 und 1,2 mm, Schnittgeschwindigkeiten von 65 und 85 m/s sowie verschiedene KSS-Typen (160, 200, Ch2).
FVA 1023 I “CoolToolGrind” – Analysis and optimization of the interaction between metal working fluid and grinding tool for gear grinding

Compared to conventionally case-hardened gears, carbonitrided gears with a high residual austenite content offer improved mechanical properties. Consequently, in the interest of conserving resources, the size and mass of the gears can be reduced while simultaneously increasing the transmissible operating loads.

However, cost-effective grinding of such surface-layer structures is currently not feasible due to severe clogging and wear of the grinding wheels. This project aims to demonstrate that the technological process window for discontinuous profile grinding of load-capacity-optimized gears can be expanded by using a coolant supply tailored to the grinding wheel structure. To this end, the influence of different grinding wheel structures on the grindability of load-capacity-optimized gears and their interaction with the coolant jet will be systematically investigated, and the coolant supply will be optimized based on the results obtained.

Funding: BMWK-DLR/IGF 23195 N/FVA 1023 I

Mikroskopaufnahme von Sinterkorund-Spänen nach der Zerspanung. Die hellblauen, stäbchenförmigen Späne zeigen charakteristische Aufschweißungen (rot markiert), bei denen dunkles Material an den Spanoberflächen haftet. Mehrere dunkelgraue Spannester sind zwischen den Spänen sichtbar. Die Aufnahme dokumentiert typische Phänomene bei der Bearbeitung keramischer Werkstoffe. Maßstabsbalken: 1000 µm.
Optimization of the external metal working fluid supply to save energy and CO2 in highly dynamic machining processes with geometrically indeterminate cutting edges – OdyZeuS-A

This newly launched collaborative project aims to significantly improve the energy efficiency and performance of grinding processes for materials that are difficult to machine, using higher cutting speeds. This improvement is to be achieved, among other things, through an optimized coolant supply. The project focuses on surface grinding processes for ceramics and tool grinding processes for cemented carbide.

Cooperation: QSIL Ingenieurkeramik GmbH, Lightway GmbH, Spreyer Werkzeug-Technik GmbH, Esgemo Schmierstofftechnik GmbH & Co KG, Präzisionsmaschinenbau Bobertag GmbH
Funding: BMWK, PTJ

Schematische Darstellung eines Schleifprozesses mit Projektpartnern. Die Abbildung zeigt eine Schleifscheibe auf einem Werkstück mit markierten Prozessaspekten: Schleifpartikelverarbeitung, Prozessgestaltung, Wuchtverhalten, Schleifscheibenspezifikation, KSS-Düsengestaltung, KSS-Zufuhr, KSS-Zusammensetzung und Maschinenkomponenten. Beteiligte Partner (Spreyer Grinding, Lightway, esdema, pm3, COMET, VSG, Ceramics, Schleiftechnik) sind den jeweiligen Bereichen zugeordnet.
Targeted surface layer properties by in-process-monitoring and adaptive process control during grinding

After grinding hardened components, a non-destructive inspection is usually performed to check for thermo-mechanical damage in the edge zones. In-process inspection methods, on the other hand, allow for an early response to adverse changes and save time by eliminating the need for post-process inspection.

This project demonstrated the potential of soft-sensor-based process control to prevent edge zone damage while maintaining high productivity. The soft sensor combines a thermal limit—which depends on the contact-area-related grinding power Pc'' and contact time Δt and enables the elimination of tempered zones—with the Barkhausen noise measured during the process. When CBN was used as the cutting material, a shift in the process limit determined for corundum was observed. The Barkhausen noise is influenced not only by the resulting edge zone condition but also by the mechanical effect of the grinding wheel engagement, which primarily affects the signal in the saturation region.


Cooperation: Leibniz-IWT WT/FT, Fraunhofer IWU Chemnitz
Funding: DFG (SPP 2086)