Mareile Kriwall

Graduation:
Dipl.-Ing.
Function:
Manager process technology
Phone:
+49 (0)511 279 76-330
E-Mail:
kriwall@iph-hannover.de
vCard:
vCard

Publications

Process monitoring strategies allow wear-related conditions of forging dies to be detected and predicted. The prediction of the wear condition allows intelligent maintenance strategies. This allows residual tool life to be fully utilized, scrap to be reduced and downtime to be calculated. The content of this article is an economic analysis for calculating the payback period of a process monitoring system.

forging, process monitoring, economic efficiency

In manual solid forming, hand-guided forging tongs are used when processing forged parts. During the forging process, employees are physically stressed by high forging part weights and transmitted impacts. This physical stress leads to employee health limitations and increases absenteeism rates. Ergonomic forging tongs have been developed at IPH that lead to a relief of the forging employees.

ergonomics, forging tongs, forming technology, prevention

The results of the wear investigations will allow multidirectional processes in hot forging to be optimized in the future in a low-wear and economical manner. The determined, wear-inducing process parameters within the design guideline represent elementary basic knowledge which can be applied in a process-specific manner. In principle, the economic potential of multi-directional forging processes using of multi-directional forging processes using sliding dies depends on the application and the desired component geometries. Multi-directional forging processes forging processes offer great potential for savings and can be process design using the results obtained, they can achieve high tool life and have a positive influence on the competitive situation of companies. As a result costs for explicitly selected niche components with significantly higher with significantly increased complexity can be reduced in the future with manageable investment costs in the future. In addition to the process-specific optimization of the process parameters, in the future options for mold design adaptation with regard to local cooling or local cooling or thermal insulation of the slide-wedge wedge mechanics, in order to be able to use the systems in automated series automated series production.

Slide tools, process design, economic efficiency, solid forming

Tailored forming is used to produce hybrid components in which the materials used are locally adapted to the diferent types of physical, chemical and tribological requirements. In this paper, a Tailored Forming process chain for the production of a hybrid shaft with a bearing seat is investigated. The process chain consists of the manufacturing steps laser hot-wire cladding, cross-wedge rolling, turning and deep rolling. A cylindrical bar made of mild steel C22.8 is used as the base material, and a cladding of the martensitic valve steel X45CrSi9-3 is applied in the area of the bearing seat to achieve the strength and hardness required. It is investigated how the surface and subsurface properties of the hybrid component, such as hardness, microstructure and residual stress state, change within the process chain. The results are compared with a previous study in which the austenitic stainless steel X2CrNiMo19-12 was investigated as a cladding material. It is shown that the residual stress state after hot forming depends on the thermal expansion coefcients of the cladding material.

Tailored forming, Residual stress, Laser hot-wire cladding, Deep rolling, Hybrid Components

The Tailored Forming process chain is used to manufacture hybrid components and consists of a joining process or Additive
Manufacturing for various materials (e.g. deposition welding), subsequent hot forming, machining and heat treatment. In
this way, components can be produced with materials adapted to the load case. For this paper, hybrid shafts are produced by
deposition welding of a cladding made of X45CrSi9-3 onto a workpiece made from 20MnCr5. The hybrid shafts are then
formed by means of cross-wedge rolling. It is investigated, how the thickness of the cladding and the type of cooling after
hot forming (in air or in water) afect the properties of the cladding. The hybrid shafts are formed without layer separation.
However, slight core loosening occurres in the area of the bearing seat due to the Mannesmann efect. The microhardness
of the cladding is only slightly efected by the cooling strategy, while the microhardness of the base material is signifcantly
higher in water cooled shafts. The microstructure of the cladding after both cooling strategies consists mainly of martensite.
In the base material, air cooling results in a mainly ferritic microstructure with grains of ferrite-pearlite. Quenching in water
results in a microstructure containing mainly martensite.

laser hot-wire cladding, cross-wedge rolling, hybrid components, cladding

The manual handling of forged parts is physically demanding for forging employees. These physical stresses are reflected in damage to the hand-arm system and back and lead to forging employee absenteeism. In order to protect the health of forging employees, the aim is to reduce the basic stress caused by the dead weight of the forging tongs by using lightweight forging tongs.

forging tongs, ergonomics, lightweight design

Flat die rolling is a solid forming operation, in which two engraved tool plates run past each other and thereby form a cylindrical semi-finished product. The non-circular rolling can be used as a preform optimising process, where it should be possible to form local non-circular sections, for example ellipses or eccentrics, into a cylindrical semi-finished product. The material flow should be exclusively in radial direction. Initial simulations show that the requirements can be met.

non-circular rolling, cross wedge rolling, flat dies, preforms and intermediate forms, FEM

Multi-stage forging process chains are often used for the efficient production of complex geometries. Typically, these consist of homogeneous heating, one or more preform stages, and the final forging step. By inhomogeneously heated billets, the process chains can be simplified or shortened. This shall be achieved by setting various temperature fields within a billet, resulting in different yield stresses. These can influence the material flow, leading to easier production of complex parts. In this study, the influence of inhomogeneously heated billets on the forming process is investigated by means of FEA. For this purpose, two process chains including inhomogeneous heating and three homogeneously heated reference process chains are developed and compared. Each process chain is optimized until form filling and no defects occur. Target figures for the assessment are necessary forming force, the amount of material necessary to achieve form filling and die abrasion wear. For process chains with inhomogeneously heated billets, the results showed a small time window of about 5 s for a successful forming in terms of form filling. Forming forces and die abrasion wear increase for inhomogeneously heated billets due to higher initial flow stresses. However, the flash ratio decreases when billets are heated inhomogeneously. Depending on their size, inhomogeneously heated billets show up to 11.8% less flash than homogeneously heated billets. This shows a potential for the use of inhomogeneous heating to make forging processes more efficient. Subsequently, experimental tests will be carried out to verify the results of the simulations.

Inhomogeneous heating, Forging, FEA, Resource efficiency, Preform operation

To increase the economic efficiency in the production of geometrically complicated forgings, material efficiency is a determining factor. In this study, a method is being validated to automatically design a multi-staged forging sequence initially based on the CAD file of the forging. The method is intended to generate material-efficient forging sequences and reduce development time and dependence on reference processes in the design of forging sequences. Artificial neural networks are used to analyze the geometry of the forging and classify it into a shape class. Result of the analysis is information on component characteristics, such as bending and holes. From this, special operations such as a bending process in the forging sequence can be derived. A slicer algorithm is used to divide the CAD file of the forging into cutting planes and calculate the mass distribution around the center of gravity line of the forging. An algorithm approaches the mass distribution and cross-sectional contour step by step from the forging to the semi-finished product. Each intermediate form is exported as a CAD file. The algorithm takes less than 10 min to design a four-stage forging sequence. The designed forging sequences are checked by FE simulations. Quality criteria that are evaluated and investigated are form filling and folds. First FE simulations show that the automatically generated forging sequences allow the production of different forgings. In an iterative adaptation process, the results of the FE simulations are used to adjust the method to ensure material-efficient and process-reliable forging sequences.

Automatic process design, Forging, FEA, Resource efficiency, CAD

A method is presented that enables the complexity of a forging to be determined automatically on the basis of the CAD file of the forging. An automated evaluation of the forging complexity is necessary for a digitized and automated design of stage sequences in order to be able to determine important design parameters such as the flash ratio or the number of stages.

CAD, forming technology, algorithms

Solid formed components are subject to ever higher load requirements while at the same time striving for resource efficiency.
ciency at the same time. An ultrafine-grained microstructure can improve the strength and ductility of the component. This makes it possible to design smaller and lighter components and to exploit lightweight construction potential. One possibility
process for producing an ultrafine-grained microstructure is cross wedge rolling.

 

Cross wedge rolling, Fine-grained structure, Lightweight construction

This paper presents concepts for shock and vibration reduction of a forging tongs. In the forging industry, hand-operated forging tongs are often used for the machining of forged parts. Here, the employees are exposed to high loads from shocks and vibrations of the forming machines. A simulation model that has been created evaluates concepts for reducing the shocks and vibrations during forging

Ergonomics, forging, shock and vibration reduction

Hybrid compound forging of aluminum bulk parts and steel sheet metals is a combination of material lightweight design and structural lightweight design. During this process, an aluminum bulk part and a steel sheet metal are combined and formed simultaneously. A material joint is generated by deforming, using zinc as solder material. This prevents the generation of brittle intermetallic Fe-Al-Phases as well as contact corrosion. The zinc layer is applied to the aluminum bulk part by hot dipping. To create a material locking connection by forming, suitable parameters such as the forming temperature are identified in first experimental trials. Microsections showed that the zinc layer is still intact after forming. In this paper the investigation of the effects of different steps of forming and different geometries of the aluminum bulk part surface on the joint strength are described. The forming tests show that a further forming of the aluminum part, resulting in a bigger deformation, leads to a stronger connection between both joining partners. But there is a limit to the forming since the applied forces can transfer to the steel sheet leading to an unintended deformation. The generated hybrid parts are tested for their ability for further forming. Therefore, the joined hybrid parts are undertaken a deep drawing process to see if the joint withstands further forming of the hybrid part.

aluminium, hybrid forging, lightweight construction, hybrid

The aim of subproject B1 of the Collaborative Research Center (CRC) 1153 is to determine the formability of novel hybrid semi-finished products by means of incremental forming cross wedge rolling. Main aspect is the forming of hybrid semi-finished products made of steel, aluminium and hard material alloys. In order to reduce the component weight, the use of hybrid semi-finished products makes it possible to manufacture less stressed segments of a previously monolithic component from a light metal. To increase wear resistance, a component area (e.g. a bearing seat) can be coated with a hard material. In addition, process variables (e.g. temperature and force) are to be measured in contact between work piece and tool in the future. There are primarily two material arrangements for the semi-finished products used: coated (coaxial - demonstrator shaft 1) and joined at the front (serial - demonstrator shaft 3). One challenge is the heating of the semi-finished products necessary for forming, since the hybrid semi-finished product has different flow resistances due to the different materials and may have to be heated inhomogeneously in order to enable uniform forming.

cross-wedge rolling, forming, hybrid work pieces, tailored forming, hybrid semi-finished products

In order to reduce CO2 emissions, it is necessary to know the emissions of operational processes. The Institut für Integrierte Produktion Hannover gGmbH has developed a software demonstrator which shows ecological-logistic cause-effect relationships. Internal and logistical processes can be investigated with regard to CO2 emissions, costs and process duration. Comparisons of different alternatives illustrate differences and show savings potentials of CO2.

ecology, logistics, CO2

The Institute for Integrated Production Hannover develops process technologies for the simultaneous forming and joining of dissimilar materials. In the future, they should enable, for example, sheet-metal solid parts and steel-aluminum connections. This expands the possibilities for cost-efficient multi-material construction methods in the automobile.

forging, hybrid, progressive compound

The CO2 emissions of the logistics sector and the resulting environmental impact are continuously increasing. Rising costs for energy and resources, increased sensitivity of customers, changed legal bases and the impending climatic change force producing enterprises to ecologically-oriented rethink. The lack of knowledge about interdependencies, quantitative effects of actions and parameter characteristics prevents SMEs from the implementation. A holistic ecological-logistical impact model with software implementation can support SMEs reaching their potential. Requirements for the model and fundamental relationships between logistic parameters and ecological target values are presented in this publication.

SME, logistic, ecology

In lightweight automotive construction, hybrid structures made of various materials as well as solid and sheet metal elements are used. By hybrid compound forging, a sheet steel and a solid aluminium part can already be joined in a material-locking manner during the forming process. The Institut für Integrierte Produktion Hannover (IPH) gGmbH and the Institut für Schweißtechnik und Trennende Fertigungsverfahren (ISAF) of TU Clausthal are investigating how solid aluminium bolts and steel sheets can be joined in a material-locking manner. This article explains the decisive forming parameters. Furthermore, the tool design for the joining tests is presented.

lightweight construction, aluminum, compound forging

Lightweight automotive construction increasingly relies on hybrid structures made of steel and aluminium. These materials are currently joined mainly by form locking, for example by riveting. Welding and bonding are also used for joining the two materials. Hybrid composite forging allows to join the two components during the forming process. This shortens the process chain. With the help of zinc as a brazing material, the components are joined to form a material bond. This publication explains the results of the simulative parameter study. It shows how temperature, geometry and speed influence the joining result. Furthermore, first results of practical joining tests are presented.

lightweight construction, aluminum, simulative parameter study

In lightweight construction, light metals like aluminum are used in addition to high-strength steels. However, a welded joint of aluminum and steel leads to the precipitation of brittle, intermetallic phases and contact corrosion. Nevertheless, to use the advantages of this combination in terms of weight saving composite hybrid forging has been developed. In this process, an aluminum solid part and a steel sheet were formed in a single step and joined at the same time with zinc as brazing material. For this purpose, the zinc was applied by hot dipping on the aluminum in order to produce a connection via this layer in a forming process, under pressure and heat. Due to the formed intermediate layer of zinc, the formation of the Fe-Al intermetallic phases and the contact corrosion are excluded. By determining the mathematical relationships between joining parameters and the connection properties the strength of a specific joint geometry could be adjusted to reach the level of conventional joining techniques. In addition to the presentation of the joint properties, the influence of the joining process on the structure of the involved materials is also shown. Furthermore, the failure behavior under static tensile and shear stress will be shown.

lightweight construction, aluminum, joining properties

Research projects