Research Papers

Improved Sheet Bulk Metal Forming Processes by Local Adjustment of Tribological Properties

[+] Author and Article Information
H. Hetzner

Chair of Engineering Design,  Friedrich-Alexander-University Erlangen-Nuremberg, Martensstraße 9, 91058 Erlangen, Germanyhetzner@mfk.uni-erlangen.de

J. Koch1

 Chair of Manufacturing Technology, Friedrich-Alexander-University Erlangen-Nuremberg, Egerlandstraße 13, 91058 Erlangen, Germanyj.koch@lft.uni-erlangen.de

S. Tremmel

S. Wartzack

 Chair of Engineering Design, Friedrich-Alexander-University Erlangen-Nuremberg, Martensstraße 9, 91058 Erlangen, Germanywartzack@mfk.uni-erlangen.de

M. Merklein

 Chair of Manufacturing Technology, Friedrich-Alexander-University Erlangen-Nuremberg, Egerlandstraße 13, 91058 Erlangen, Germanym.merklein@lft.uni-erlangen.de


Corresponding author.

J. Manuf. Sci. Eng 133(6), 061011 (Dec 09, 2011) (11 pages) doi:10.1115/1.4005313 History: Received July 15, 2011; Revised September 11, 2011; Published December 09, 2011; Online December 09, 2011

This paper is focused on a combined deep drawing and extrusion process dedicated to the new process class of sheet bulk metal forming (SBMF). Exemplified by the forming of gearings, combined sheet and bulk forming operations are applied to sheet metal in order to form local functional features through an intended and controlled change of the sheet thickness. For investigations on the form filling and the identification of significant influencing factors on the material flow, a FE simulation model has been built. The FE model is validated by the results of manufacturing experiments using DC04 with a thickness of 2.0 mm as blank material. Due to the fact that the workpiece is in extensive contact to the tool surface and that the pressure reaches locally up to 2500 MPa, the tribological conditions are a determining factor of the process. Thus, their influence is discussed in detail in this paper. In the first instance, different frictional zones having a distinct effect on the resulting material flow are identified and their effect on improved form filling is demonstrated. Subsequently, a more comprehensive methodology is developed to define tribological zones of forming tools. For this, a system analysis of the digital mock-up of the forming process is performed. Besides friction, other relevant aspects of forming tool tribology like contact pressure, sliding velocity, and surface magnification are considered. The gathered information is employed to partition the tools into tribological zones. This is done by systematically intersecting and re-merging zones identified for each of the criterion. The so-called load-scanning test allows the investigation of the friction coefficient in dependence of the contact pressure and possible loading limits of tribological pairings. It provides an appropriate tribological model test to evaluate tribological measures like coatings, surface textures and lubricants with respect to their targeted application in particular zones. The obtained results can be employed in the layout of further forming processes to reach the desired process behavior. This can be, for example, an improved form filling, less abrasive wear and adhesive damage or lower forming forces, respectively tool load for an improved durability of the die.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Set of synchronizer rings made of steel (a), (Diehl Stiftung & Co. KG, Nuremberg) and FE simulation of the outer synchronizer ring manufactured by a combined deep drawing and extrusion process (b)

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Figure 2

Procedure for definition of tribological zones of forming tools based on a system analysis

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Figure 3

Geared sheet metal component for the investigations on SBMF extrusion

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Figure 4

Geometrical deviation of the FE simulation from the produced part

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Figure 5

Progression of the forming force of the SBMF extrusion process

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Figure 6

Material flow at the beginning of the cavity filling (a) and at the half-finished forming process (b)

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Figure 7

FE model and frictional zones of the SBMF extrusion tool with integrated deep drawing unit

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Figure 8

Comparison of the forming force of a combined deep drawing and extrusion process with adapted tribological zones and the same process with average friction factor

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Figure 9

Comparison of the form filling at F = 2100 kN with a homogeneous m = 0.12 (a) and a locally increased/decreased friction factor of m = 0.3 and m = 0.05, respectively (b)

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Figure 10

Partitioning of the SBMF extrusion die into tribological zones: (1) deep drawing zone, (2) gearing teeth feed zone, (3) gearing infeed and cavity, (4) teeth clearance, and (5) flash area

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Figure 11

SEM micrographs of laser-textured steel surfaces: (a) isolated micro-pits and (b) crossed channels

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Figure 12

Silk-screen printing of paste-like lubricants

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Figure 13

Load-scanning test: (a) test rig, (b) schematic of the specimen configuration, and (c) schematic of the test kinematics

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Figure 14

Coefficient of friction versus normal load and corresponding computed contact pressure for a-C:H:W-coated and uncoated cold work tool steel 1.2379 sliding against stainless steel 1.4301 under dry and oil-lubricated conditions




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