Sheet-bulk Metal Forming Research Articles

Numerical and experimental investigation of extrusion processes from coil

The use of coil material as semi-finished product in sheet-bulk metal forming (SBMF), offers the possibility to use high-speed presses and thus to achieve high output quantities. However, compared to industrially established forming of pre-cut blanks, the reduced geometric accuracy of the parts due to the asymmetrical material flow represents a challenge. Against this background, the aim of this study is to gain an in-depth knowledge on the influence of the process setup on the material flow direction and on the forming of geared functional parts. A combined numerical-experimental approach of each a lateral and a backward extrusion process of a DC04 sheet metal ( t0 = 2 mm) is applied for a fundamental process analysis. For this purpose, process-dependent causes for the asymmetric part forming are analyzed by means of material flow simulations. Subsequently, the numerical results are verified experimentally in terms of the part geometry, the process force and grain structural changes. Based on the numerical and experimental results, cause-effect relations between material flow, part accuracy and tool load are derived. In addition, the transferability of the causes of the asymmetric material flow to processes with different primary material flow directions and part geometries is verified. The findings facilitate the future counteraction of asymmetrical material flow in SBMF from coil, which in turn leads to enhanced component quality.

Correlating Ultrasonic Velocity in DC04 with Microstructure for Quantification of Ductile Damage

The detection of ductile damage by image-based methods is time-consuming and typically probes only small areas. It is therefore of great interest for various cold forming processes, such as sheet-bulk metal forming, to develop new methods that can be used during the forming process and that enable an efficient detection of ductile damage. In the present study, ductile damage in DC04 was examined using ultrasonic testing. First, different grain sizes were set by heat treatment. Subsequently, the sheet metal was formed by cold rolling. A clear correlation between the average void diameter and the measured ultrasonic velocity could be shown. The ultrasonic velocity showed a clear decrease when the average void size increased because of the increasing forming degree. The ultrasonic measurements were finally employed to calculate a damage parameter D to determine the amount of ductile damage in the microstructure for different grain sizes after cold rolling.

Micro structuring tool steel components using Precise Electrochemical Machining (PECM)

Surface structuring offers great potential for modifying frictional properties for various applications, such as complex forming processes like sheet-bulk metal forming. The production of surface structures in micrometre range is challenging for manufacturing processes in particular when machining hard-to-cut materials like hardened tool steels. Precise electrochemical machining (PECM) has great potential for surface structuring and shaping of metallic materials regardless of their hardness with high surface quality and comparatively very short process times, especially when structuring large areas and batches. Micro structuring of hardened tool steel surfaces using PECM is investigated in this paper. Surfaces of high-speed tool steel and hot-work tool steel are structured using a commercial PECM machine with neutral solution of NaNO_3 as electrolyte. In a process sequence, PECM tools were manufactured in a first step producing selected structures by high-feed milling (HFM) and micromilling (MM). In a further process step, the negative shape of these complex structures was machined using the PECM process. Through this process chain, new types of structures can be generated which have different tribological properties than their corresponding negative shapes of HFM and MM structures. Tribological behaviour and wear properties of the structured surfaces are investigated through ring compression test (RCT).

Investigation on micro-textured tappets from design and production to the application properties

In industrial sectors like medical and automotive engineering, the demand for metal components with a high function integration brings conventional production technologies to their limits. This motivates research on innovative processes, which can meet the present requirements on fabricated parts and consequently also the demands on the applied manufacturing process. Part-sided, a high strength, narrow dimensional tolerances and a large functionality is often desired. In addition, an economical component production calls for processes with high material utilization as well as the achievement of short cycle times. The process class of sheet-bulk metal forming, characterized by the application of bulk forming operations on sheet metal, offers the potential to meet these requirements. Currently, sheet-bulk metal forming is mainly used for the fabrication of components with functional elements of macroscopic size. However, microscopic elements and micro-textured surfaces are of high interest for applications in prosthetics and automotive engineering. The objective of this study is therefore to develop an application-oriented method for the design, production and testing of 16MnCr5 metal components, manufactured by a combined process of sheet-bulk metal forming, creating a defined microstructure on the surface. Since the selection of a suitable texture layout and geometry is crucial for tribological optimization, these are designed for their application using numerical elastohydrodynamic lubricant simulations. The contact conditions occurring in the application are modelled as realistically as possible so that texture designs suitable for production can subsequently be compared in test bench trials. It is shown that the tappets produced by forming technology can be efficiently investigated with the test rig presented.

Flow-through and forming mechanism of laser shock micro-coining

Sheet-bulk metal forming (SBMF) is an advanced technology to efficiently produce high-quality parts based on high resource utilization. Coining, a kind of SBMF, can be used to fabricate functional and decorative microstructures. In this paper, a new method called laser shock micro-coining (LSMC) is proposed based on the unique advantages of intense pulsed laser of high strain rate dynamic loading characteristics and suitable for micro-forming. However, smaller sheet thickness will lead to the emergence of flow-through. In this paper, ALE model and SPH-FEM model are established for numerical simulation to study LSMC. Through numerical simulation and experiment, the forming mechanism and improvement methods of flow-through are studied, and the appropriate research parameters are determined. The material flow, forming mechanism, stress wave propagation mechanism and forming uniformity are studied. Results show that the lack of material near the projections and the unique inverse plastic deformation in dynamic forming are the important factors leading to flow-through. Suitable laser energy and large sheet thickness as well as the existence of the punch can inhibit the formation of flow-through from one or two aspects. Under dynamic forming, the material has high forming rate and good filling properties. Material deformation is related to the propagation of stress wave. The propagation of stress wave and the height of sheet metal result in a unique short rod mechanism. The process has good forming uniformity, and a more uniform forming effect can be obtained by appropriately increasing the laser energy.

Adapting the Surface Integrity of High-Speed Steel Tools for Sheet-Bulk Metal Forming

New manufacturing technologies, such as Sheet-Bulk Metal Forming, are facing the challenges of highly stressed tool surfaces which are limiting their service life. For this reason, the load-adapted design of surfaces and the subsurface region as well as the application of wear-resistant coatings for forming dies and molds made of high-speed steel has been subject to many research activities. Existing approaches in the form of grinding and conventional milling processes do not achieve the surface quality desired for the forming operations and therefore often require manual polishing strategies afterward. This might lead to an unfavorable constitution for subsequent PVD coating processes causing delamination effects or poor adhesion of the wear-resistant coatings. To overcome these restrictions, meso- and micromilling are presented as promising approaches to polishing strategies with varying grain sizes. The processed topographies are correlated with the tribological properties determined in an adapted ring compression test using the deep drawing steel DC04. Additionally, the influence of the roughness profile as well as the induced residual stresses in the subsurface region are examined with respect to their influence on the adhesion of a wear-resistant CrAlN PVD coating. The results prove the benefits of micromilling in terms of a reduced friction factor in the load spectrum of Sheet-Bulk Metal Forming as well as an improved coating adhesion in comparison to metallographic finishing strategies, which can be correlated to the processed roughness profile and induced compressive residual stresses in the subsurface region.

Overview on massive forming processes, future and their challenges

The massive shaping processes (forging, rolling, extrusion, wire and bar drawing) play an important role to fabricate metal products. These forming processes undergo plastic deformations of the metal and acquire required shapes and sizes by application of suitable stresses such as tension, compression and shear. Thus due to the characteristics such as cost effectiveness, good mechanical properties of the product, flexible operations, higher productivity, no wastage of the raw material and faster production rate, the work on metals in effective way becomes highly important. Bulk forming and severe deformation process result in massive shape change. The surface area-to-volume of the work is relatively small and mostly done in hot working conditions. The broad topic of bulk metal forming includes many processes both as classical and modified categories. These classical bulk metal forming processes are still in great demand in many industry sectors. It does not seem that this trend will slow down as new technologies have been developed over recent years. These technologies are continuously modified for new demands, such as higher precision (near-net shape) forming, micro-/nano-forming for micro-components, and bulk-sheet metal forming processes for complex workpieces. Thus, it is important to have a broad knowledge of the classical theories of metal forming which was mainly an overview of metal forming processes and their fundamentals. With the growing competitive industrial vibe, it is important to develop into cost-effective production processes. Especially for some automotive components, it is suggested to incorporate bulk metal forming processes into sheet metals to produce high-quality sheet metal components commercially. Sheet-bulk metal forming (SBMF) processes are defined as sheet metal forming where the flow occurs in three dimensions similar to bulk metal forming. After computer-aided design of the tool geometry, the bulk metal forming tools are usually fabricated by machining processes. The main die manufacturing process may be divided into die design, rough machining, heat treatment, finish machining, manual finishing (polishing), or benching and hard coating. The main characteristic of these processes is that the final product has the dimensions of a magnitude similar to the sheet thickness, projecting out of the plane of the sheet. Based on this characteristic, only some special bulk forming processes can be applied on sheet metals. In this review paper, the authors describe the working of various types of bulk metal forming processes, historical development, importance, future scope and challenges, so that this paper may serve as a good reference for forming process selection and identification for researchers, engineers and students.

Sheet Bulk Forming of Thin-Walled Components with External Gearing through Upsetting Using Controllable Deformation Zone Method

Sheet-bulk metal forming (SBMF) is a promising process for manufacturing complex sheet components with functional elements. In this study, the entire forming process for a typical thin-walled component with external gearing is investigated, including sheet forming and bulk forming processes. Deep drawn cups are prepared during sheet forming; subsequently, upsetting is performed on the sidewall to form external gearing. The upsetting method performed is known as upsetting with a controllable deformation zone (U-CDZ). Compared with the conventional upsetting method, a floating counter punch with a counter force is used in the U-CDZ method such that the forming mechanism is changed into the accumulation of the deformation zone instead of deformation throughout the entire sidewall. The effects of the counter force and material flow are investigated to understand the mechanism. The forming quality, i.e., the formfilling and effective strain distribution, improved, whereas a high forming load is avoided. In addition, a punch with a lock bead is used to prevent folding at the inner corner during the experiment.

SLASSY—An Assistance System for Performing Design for Manufacturing in Sheet-Bulk Metal Forming: Architecture and Self-Learning Aspects

Substantial efforts have been made to integrate manufacturing- and design-relevant knowledge into product development processes. A common approach is to provide the relevant knowledge to the design engineers using a knowledge-based system (KBS) that, in turn, becomes the engineering assistance system. Keeping the knowledge up to date is a critical issue, making knowledge acquisition a bottleneck of developing and maintaining KBS. This article presents a robust metamodel optimization and performance estimation architecture for developing and maintaining a KBS useful for design-for-manufacturing from the context of sheet-bulk metal forming. It is shown that the presented KBS or engineering assistance system helps achieve performing design-for-manufacturing, integrating both design and manufacturing knowledge. Using the presented approach helps overcome the bottleneck of knowledge acquisition and knowledge update through its self-learning component based on data mining and knowledge discovery.

Functional Analysis of Components Manufactured by a Sheet-Bulk Metal Forming Process

Due to rising demands regarding the functionality and load-bearing capacity of functional components such as synchronizer rings in gear systems, conventional forming operations are reaching their limits with respect to formability and efficiency. One way to meet these challenges is the application of the innovative process class of sheet-bulk metal forming (SBMF). By applying bulk forming operations to sheet metal, the advantages of both process classes can be combined, thus realizing an optimized part weight and an adapted load-bearing capacity. Different approaches to manufacturing relevant part geometries were presented and evaluated regarding the process properties and applicability. In this contribution, a self-learning engineering workbench was used to provide geometry-based data regarding a novel component geometry with circumferential involute gearing manufactured in an SBMF process combination of deep drawing and upsetting. Within the comprehensive investigations, the mechanical and geometrical properties of the part were analyzed. Moreover, the manufactured components were compared regarding the increased fatigue strength in cyclic load tests. With the gained experimental and numerical data, the workbench was used for the first time to generate the desired component as a CAD model, as well as to derive design guidelines referring to the investigated properties and fatigue behavior.

Force reduction by electrical assistance in incremental sheet-bulk metal forming of gears

Producing load-adapted and functionally integrated components by flexible and resource efficient processes has gained importance within industries like the automotive sector in recent years. A promising new class of processes that enables a local adaption of the sheet thickness is Sheet-Bulk Metal Forming (SBMF). While the incremental procedure (iSBMF) only requires a moderate forming force, forming of high strength steels leads to a tool load resulting in a significantly reduced tool life. One approach to reduce tool loads is the utilization of the so called electroplastic effect (EPE). This study for the first time identifies the potential of the EPE on a temporary reduction of the forming force during the iSBMF of gears targeting an improvement of the tool life. The steel grades DC04 and HSM700 HD are characterized considering the EPE under uniaxial tension. Based on the characterization, the current density and temperature increase are modelled numerically and analytically for the incremental gear forming process. Moreover, the impact of EPE on strain hardening, grain texture and forming force is determined. By a local insulation of the forming tool based on a PVD coating and the application of an electrical current, a temporary force reduction of up to 55 % is observed whereas the strain hardening effect remains almost unaffected.

Investigation of the Influence of a Superimposed Oscillated Forming Process on Forming Characteristics

The increasing demand for resource-efficient production methods is driving the development of new technologies. Sheet bulk metal forming (SBMF) offers the possibility to combine sheet metal and bulk forming operations. This allows the production of complex functional components with secondary forming elements from sheet metal. Compared to other production techniques such as machining, a more efficient use of material can be achieved. Further advantages are a near net shape production and increased strain hardening. SBMF processes are limited by forming technology boundaries. These include high forming forces, incomplete mould fillings and limited surface qualities. In this research, the possibility of enhancing the material flow, improving surface quality and reducing the tool loads in SBMF-processes is investigated by using a superimposed oscillation. The focus here is on achieving a high surface quality of components produced by forming technology and an enhanced material flow during forming. For this purpose, a forming process for ironing an axial gear geometry is superimposed with an oscillation in the main force flow.

Investigation on tailored blanks in a full forward extrusion process of sheet-bulk metal forming

Due to the ongoing technological development, the demand for geometrically complicated high performance parts with great functional density is increasing. Often, the use of sheet metal is a beneficial approach in manufacturing technology to meet the requirements on components regarding material strength and lightweight construction goals. The forming of therefore required complex sheet metal part geometries with integrated functional elements cause the need for a three dimensional material flow. Sheet-bulk metal forming, characterized by the application of bulk forming operations on sheet metals, is a suitable approach to produce such components. A challenge is the material flow control, resulting in an insufficient die filling of the functional elements. The use of tailored blanks with a defined sheet thickness distribution is an auspicious approach to face this challenge in subsequent forming processes. In the presented work, semi-finished products with a continuous thickness profile manufactured by orbital forming are applied in a full forward extrusion process. By an additional implementation of a heat treatment, the tailored blanks undergo a recrystallization process that causes a softening of the strain hardened material. In this paper, the potential of a heat treatment in the process class of sheet-bulk metal forming is shown by characterizing the geometrical and mechanical properties of the functional components by applying the mild deep drawing steel DC04 with an initial sheet thickness of t0 = 2.0 mm.

Fringe Projection Profilometry in Production Metrology: A Multi-Scale Comparison in Sheet-Bulk Metal Forming.

Fringe projection profilometry in combination with other optical measuring technologies has established itself over the last decades as an essential complement to conventional, tactile measuring devices. The non-contact, holistic reconstruction of complex geometries within fractions of a second in conjunction with the lightweight and transportable sensor design open up many fields of application in production metrology. Furthermore, triangulation-based measuring principles feature good scalability, which has led to 3D scanners for various scale ranges. Innovative and modern production processes, such as sheet-bulk metal forming, thus, utilize fringe projection profilometry in many respects to monitor the process, quantify possible wear and improve production technology. Therefore, it is essential to identify the appropriate 3D scanner for each application and to properly evaluate the acquired data. Through precise knowledge of the measurement volume and the relative uncertainty with respect to the specimen and scanner position, adapted measurement strategies and integrated production concepts can be realized. Although there are extensive industrial standards and guidelines for the quantification of sensor performance, evaluation and tolerancing is mainly global and can, therefore, neither provide assistance in the correct, application-specific positioning and alignment of the sensor nor reflect the local characteristics within the measuring volume. Therefore, this article compares fringe projection systems across various scale ranges by positioning and scanning a calibrated sphere in a high resolution grid.

Sheet-bulk metal forming of copper heat spreader with controllable deformation zone

In this paper a novel precision forging process for the manufacture of CPU heat spreaders is presented. The study included numerical and simulation verification and the purpose was to replace the commonly used forging methods used for heat spreader manufacture with sheet-bulk metal forming (SBMF). The process includes roughing, finishing and trimming from a pre-formed shape. The finite element method (FEM) was used to optimize the design of the width and variable flash controllable deformation zones (W-CDZ/VF-CDZ) to ensure the dimensions were within the 0.1 mm critical specifications for flatness and parallelism. Simulation analysis took into account all the related microscopic phenomena: forming, material flow, flow velocity and strain distribution. The simulations and experiments showed that the occurrence of SBMF overlapping defects could be successfully avoided by the proper design of W-CDZ and VF-CDZ. The forming load, material flow, flow velocity and strain related distribution were thoroughly investigated within the controllable and stable deformation zones. It was found that the forming sequence and filling ratio could be improved, and uniform distributed cross-sectional hardness could be attained which augmented uniform heat dissipation.

Additive Manufacturing of Tailored Blank for Sheet-Bulk Metal Forming Processes

Functional integration and lightweight construction pose increasing demands on manufacturing processes and require innovative approaches. In this context, sheet-bulk metal forming combines the advantages of conventional sheet and bulk forming processes expanding the limitations of these particular processes. However, the intended three-dimensional material flow contains major challenges regarding the material flow control. To enhance material flow control and part quality the application of process-adapted semi-finished products is an expedient approach for sheet-bulk metal forming processes. So-called Tailored Blanks have a process-adapted sheet thickness profile or combine different mechanical properties within a single blank and were applied in the 1980s for the first time. Since then tailored approaches gained in importance and find broad application in research and industry. At present, various technologies are used to manufacture Tailored Blanks. The Tailored Blanks applied in sheet-bulk metal forming are often manufactured by sheet-bulk metal forming processes themselves. The achievable gradient in thickness depends on various factors but is eventually constraint by the material volume of the initial blank. In this regard, Additive Manufacturing offers new possibilities to overcome those limitations and to expand the limits of sheet-bulk metal forming processes further. Additional material can be allocated with high geometric flexibility. Besides the allocation of additional material, this technology allows the manufacturing of discrete functional elements within the production of Tailored Blanks. In this investigation, Tailored Blanks made out of stainless steel are produced using sheet material and additively manufactured elements. These Tailored Blanks are processed in a deep drawing and a subsequent upsetting operation to manufacture a functional component with an external gearing. Conventional sheet material is also processed to compare the resulting part properties and to evaluate the different semi-finished product strategies. For this purpose, an analysis of geometrical as well as mechanical Tailored Blank properties is conducted. Furthermore, the part properties after deep drawing and upsetting are analysed. The investigation evaluates the potential for Tailored Blanks consisting of sheet metal with additively manufactured elements in sheet-bulk metal forming and conclusively points out the need for further research in this field.

Numerical study of sheet-bulk forming process of high strength steel 16MnCr5

The sheet-bulk metal forming (SBMF) technology provides a new processing method for gears. This manufacturing technology is greatly affected by process parameters, deformation conditions and material properties. Defects such as holes, tearing and insufficient filling of materials are easy to occur during forming process. In order to understand the mechanism of this process, finite element modelling and simulations are carried out on the sheet-bulk forming of gears. Equivalent stress and material flow are analyzed by combining point tracking method. The mechanism of incremental sheet-bulk forming of gears technology is clarified. The phenomenon of insufficient filling of initial teeth caused by restricting material flow is emphatically explained.

Investigation on extrusion processes in sheet-bulk metal forming from coil

The increasing demand for functional-integrated lightweight components is bringing established manufacturing technologies to their limits and motivates research into the innovative process class of sheet-bulk metal forming (SBMF). By applying bulk forming operations to sheet metal, thin-walled components with integrated functional elements can be produced in short process chains by a three dimensional material flow. Currently, pre-cut blanks are frequently used for this purpose. Manufacturing components from coil would combine the advantages of SBMF with those of production from coil regarding high output quantities. Therefore, the objective of the present research is to develop a fundamental process understanding for SBMF of parts from coil. For this purpose, a lateral and a backward extrusion process are set up and numerically mapped for a process analysis. Known challenges in SBMF of pre-cut blanks are a limited component accuracy due to a partly uncontrolled material flow and high tool loads. Consequently, both are addressed in context of a production from coil in a combined numerical-experimental approach. An anisotropic material flow is identified as a coil-specific challenge and fundamental difference to the SBMF of blanks. It causes an unequal forming of the components. The sheet geometry as well as a local pre-hardening induced by the forming of previous parts are found to determine the anisotropic material flow. In addition, an understanding of the effects of anisotropic material flow on tool loads is developed. An unequal deflection of tools is found as a tool-specific challenge. The obtained process knowledge provides a basis for research into measures to counteract the anisotropic material flow as a central challenge of SBMF of coils in future work.

Lightweight in Automotive Components by Forming Technology

Lightweight design is one of the current key drivers to reduce the energy consumption of vehicles. Design methodologies for lightweight components, strategies utilizing materials with favorable specific properties and hybrid materials are used to increase the performance of parts for automotive applications. In this paper, various forming processes to produce light parts are described. Material lightweight design is discussed, covering the manufacturing processes to produce hybrid components like fiber–metal, polymer–metal and metal–metal composites, which can be used in subsequent deep drawing or combined forming processes. Approaches to increasing the specific strength and stiffness with thermomechanical forming processes as well as the in situ control of the microstructure of such components are presented. Structure lightweight design discusses possibilities to plastically form high-strength or high-performance materials like magnesium or titanium in sheet, profile and tube forming operations. To join those materials and/or dissimilar materials, new joining by forming technologies are shown. To economically produce lightweight parts with gears or functional elements, incremental sheet-bulk metal forming is presented. As an important part property, the damage evolution during the forming operations will be discussed to enable even lighter parts through a more reliable design. New methods for predicting and tailoring the mechanical properties like strength and residual stresses will be shown. The possibilities of system lightweight design with forming technologies are presented. A combination of additive manufacturing and forming to produce highly complex parts with integrated functions will be shown. The integration of functions by a hot extrusion process for the manufacturing of shape memory alloys is presented. An in-depth understanding of the newly developed processes, methodologies and effects allows for a more accurate dimensioning of components. This facilitates a reduction in the total mass and an increasing performance of vehicle components.

Investigation of a tailored blank for the elimination of forging laps during cup sidewall upsetting

In this study, sheet bulk metal forming (SBMF) processes for manufacturing sidewall-thickened cups were explored, including sheet forming processes for the preparation of cup billets and bulk forming processes for sidewall thickening. To avoid forging laps caused by the clearance between the cup corner and die during sidewall upsetting, a locally thickened tailored blank was designed and produced. To form tailored blanks, coining and orbital forming were compared, and a strategy based on a coining process with different lubrication conditions was analyzed. The tailored blanks were drawn to cups, which had sharp corners and were used as billets for the final upsetting operation to avoid the clearance and thus eliminate forging laps. Adopting upsetting with controllable deformation zone (U-CDZ) method, the cup sidewall was thickened. During forming, the buckling on the sidewall and laps on the corner were prevented. The numerical and experimental results indicate that sheet parts with complex sections can be formed using a tailored blank with the U-CDZ method.