Research Papers

Direct Sinter Bonding of Metal Injection-Molded Parts to Solid Substrate Through Use of Deformable Surface Microfeatures

[+] Author and Article Information
Thomas Martens

JTEKT Corporation,
Greenville, SC 29607
e-mail: thomas.martens@jtekt.com

M. Laine Mears

Clemson University—International Center
for Automotive Research (CU-ICAR),
Greenville, SC 29607
e-mail: mears@clemson.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF Micro AND Nano-Manufacturing. Manuscript received June 20, 2012; final manuscript received January 23, 2013; published online March 22, 2013. Assoc. Editor: Jian Cao.

J. Micro Nano-Manuf 1(1), 011008 (Mar 22, 2013) (9 pages) Paper No: JMNM-12-1034; doi: 10.1115/1.4023532 History: Received June 20, 2012; Revised January 23, 2013

In the metal injection molding (MIM) process, fine metal powders are mixed with a binder and injected into molds, similar to plastic injection molding. After molding, the binder is removed from the part, and the compact is sintered to almost full density. Though able to create high-density parts of excellent dimensional control and surface finish, the MIM process is restricted in the size of part that can be produced, due to gravitational deformation during high-temperature sintering and maximum thickness requirements to remove the binding agents in the green state. Larger parts could be made by bonding the green parts to a substrate during sintering; however, a primary obstacle to this approach lies in the sinter shrinkage of the MIM part, which can be up to 20%, meaning that the MIM part shrinks during sintering, while the conventional substrate maintains its dimensions. This behavior would typically inhibit bonding and/or cause cracking and deformation of the MIM part. In this work, we present a structure of micro features molded onto the surface of the MIM part, which bonds, deforms, and allows for shrinkage while bonding to the substrate. The micro features tolerate plastic deformation to permit the shrinkage without causing cracks after the initial bonds are established. In a first series of tests, bond strengths of up to 80% of that of resistance welds have been achieved. This paper describes how the authors developed their proposed method of sinter bonding and how they accomplished effective sinter bonds between MIM parts and solid substrates.

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Fig. 1

Schematic of some limitations in MIM

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Fig. 2

Effect of gravity during sintering

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Fig. 3

Ideal sinter shrinkage [6]

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Fig. 5

Green MIM part on solid part (left) and sinter bonded composite part (right), substrate size: 25 mm × 25 mm

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Fig. 6

Cross cut of a flat MIM compact bonded to a flat, 2 mm thick solid substrate

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Fig. 7

Sinter bond between powder compact (top) and solid metal part (below)

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Fig. 8

Etched micrograph detail of bonded area

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Fig. 9

Hypothesized cause of deformation

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Fig. 11

Point contact on V-slot composite part

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Fig. 12

Point contact on V-slot composite part (detail right side of separation)

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Fig. 13

MIM compact on substrate with high surface roughness

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Fig. 14

Sintering on a substrate with friction

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Fig. 15

Sinter bonding using micro surface features

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Fig. 16

MIM compacts with surface features

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Fig. 17

MIM compact (top) bonded to solid metal (below)

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Fig. 18

Micro features bonding powder compact and solid substrate

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Fig. 19

Part of the evaluated area of sinter bonded parts showing grain structure in micro features

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Fig. 20

Determining the point of bonding

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Fig. 21

Substrate expansion/powder shrinkage versus time and temperature

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Fig. 22

Cross section of shear test fixture

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Fig. 23

Shear test fixture installed on INSTRON testing system

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Fig. 24

Shear diagram of sample with 100 μm feature size

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Fig. 25

Bonding surface after shear test

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Fig. 26

Shear strength of different joining processes




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