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Dimensional and geometrical precision of powder metallurgy parts sintered and sinterhardened at high temperature

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Abstract

The effect of the sintering and sinter-hardening temperature on the dimensional and geometrical precision of ring-shaped parts was investigated. The parts were produced with a 3%Cr-0.5%Mo-0.5%C steel, compacted to 6.8 g/cm3 and sinter/sinter-hardened at 1250°C, 1300°C and 1350°C. The increase in the sintering temperature enhances the fraction of load bearing section and leads to an expected significant improvement of mechanical properties. Dimensional shrinkage increases with the sintering temperature, however, the dimensional and geometrical precision obtained in all the cases is very good even at very high sintering temperature. Dimensional variations are anisotropic, and the effect of anisotropy was estimated by evaluating the lack of precision attained when green parts are designed assuming an isotropic behavior.

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Abbreviations

A:

area of the cross section of the pore [μm2]

cext :

circumference related to the external diameter in the sintered/ sinter-hardened part [mm]

cext 0 :

circumference related to the external diameter in the green part [mm]

cint :

circumference related to the internal diameter in the sintered/ sinter-hardened part [mm]

cint 0 :

circumference related to the internal diameter in the green part [mm]

De :

external diameter of the sintered/sinter-hardened part [mm]

De0 :

external diameter of the green part [mm]

Deq :

equivalent diameter of pore [μm]

Dext :

required value for the external diameter of the final part [mm]

Di :

internal diameter of the sintered/sinter-hardened part [mm]

Di0 :

internal diameter of the green part [mm]

Dint :

required value for the internal diameter of the final part [mm]

fcircle :

shape factor

h :

height of the sintered/sinter-hardened part [mm]

H:

required value for the height of the final part [mm]

h0 :

height of the green part [mm]

P:

perimeter of the cross section of the pore [μm]

t:

wall thickness in the sintered/sinter-hardened part [mm]

t0 :

wall thickness in the green part [mm]

w:

maximum deviation of measured θ from the nominal value in the sintered/sinter-hardened part

w0 :

maximum deviation of measured θ from the nominal value in the green part

ΔV/V0 :

volume change

Δθ:

maximum difference between θ in the sintered/sinter-hardened part and θ in the green part

Φ:

fraction of load bearing section

ɛ:

fractional porosity

ɛi :

isotropic dimensional change

ɛr :

dimensional change in the radial direction

ɛz :

dimensional change in the axial direction

ɛθ ext :

dimensional change in the tangential direction in the external circumference

ɛθ int :

dimensional change in the tangential direction in the internal circumference

θ:

angle formed by the median planes of the grooves in the sintered/ sinter-hardened part [°]

θ0 :

angle formed by the median planes of the grooves in the green part [○]

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Authors and Affiliations

  1. Department of Industrial Engineering, University of Trento, Via Mesiano, 77, 38123, Trento, Italy

    Ilaria Cristofolini, Melania Pilla & Alberto Molinari

  2. R & D Key — RK S.r.l., Viale Caproni 7, 38068, Rovereto (Trento), Italy

    Andrea Rao

  3. TFM Group, Via del Lavoro 32, Grisignano (Padova), Italy

    Stefano Libardi

Authors
  1. Ilaria Cristofolini
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  2. Melania Pilla
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  3. Andrea Rao
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  4. Stefano Libardi
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  5. Alberto Molinari
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Correspondence to Ilaria Cristofolini.

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Cristofolini, I., Pilla, M., Rao, A. et al. Dimensional and geometrical precision of powder metallurgy parts sintered and sinterhardened at high temperature. Int. J. Precis. Eng. Manuf. 14, 1735–1742 (2013). https://doi.org/10.1007/s12541-013-0233-5

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