Feature article: PIM International, Vol.4 No. 1 March 2010, pages 43-46, 1789 words

Authors: Dr Thomas Hartwig, IFAM, Germany [1] and Renan Schroeder, Federal University of Santa Catarina, Brazil

[1] IFAM, Fraunhofer-Institute for Manfacturing and Advanced Materials, Powder Technology Lab, Bremen, Germany
[2] Materials Laboratory, Federal University of Santa Catarina, Florianópolis, Santa Catarina, Brazil

By coupling a mass spectrometer to the exhaust system of an industrial scale furnace, researchers have gained a detailed insight into the changes and reactions that take place during the critical debinding and sintering stages of the MIM process. Thomas Hartwig and Renan Schroeder report their initial findings.

Quality assurance for the debinding and sintering stage of the powder injection moulding (PIM) process is difficult and not very elaborate. The problem is that one cannot really look into furnaces and see what is going on. This situation has been improved by connecting a mass spectrometer to the exhaust system of a MIM batch furnace. The spectra show clearly at what temperatures changes take place and allow a valuable insight into the processes.

Introduction

A critical step in furnace monitoring is the composition of the gas atmosphere during debinding and sintering of powdered precision parts. The concentration of reactive compounds carried into, or produced, in the furnace may be considered a main concern for all available gas conditions. The evolution of these products can greatly alter process effectiveness and material chemistry.

A straightforward control of the atmosphere may reduce cycle times and prevent and help to understand undesirable aspects occurring during MIM processing like varying carbon level. Unfortunately, as of today, there is hardly any opportunity of looking into a MIM furnace and identifying the gas atmosphere variation online. Dew point sensors are often used, sometimes sensors for the detection of hydrocarbons are introduced. In some studies [1, 2], mass spectrometry has been applied in a laboratory scale aiming at understanding sintering of PM parts. ........

Further sections of this article include:

Introduction
Experimental Procedure
Mass spectrometry
Experimental debinding and sintering
Results and discussions
Conclusions
References

Figures and Tables:

Fig. 1 The Elnik debinding and sintering furnace (left), located at IFAM's MIM laboratory in Bremen

Fig. 2 Schematic drawing of the furnace and mass spectrometer connection

Fig. 3 Typical mass spectrum obtained via analog scan: The largest peak stands for hydrogen (2 amu). The other signals are dominated by hydrocarbons produced during binder decomposision. One can see various fragments from C1 to C7 hydrocarbons as well as some water (18 amu) 

Fig. 4 Typical mass spectrum obtained via MID mode

Fig. 5 Mass spectrum for atomic mass 27 (C₂H₃⁺) as well as the process temperature as a function of process time for the different gas atmospheres 

Fig. 6 Mass spectrum for atomic mass 16 as well as the process temperature as a function of process time for the different gas atmospheres. The arrows represent the assumed molecules causing the signal 

Table 1 Expected gas specimens and their fragments, the unit being atomic mass units

Table 2 Summary of obtained gas products from grade CC sintered under H₂

Table 3 Carbon content in the sintered parts processed under different gas atmospheres