Technical Paper: PIM International, Vol.4 No. 1 March 2010, pages 50-54, 2265 words

Authors: Hao He, Yimin Li, Pan Liu and Jianguang Zhang

State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China

Abstract

Gears with a skin-core structure have been designed and produced using a novel metal co-injection moulding technique. The effect of skin temperature and injection velocity on the material distribution of the co-injection moulded specimens has been studied.

It was demonstrated that the temperature exerts a more important influence on the phase distribution than injection velocity. The adequate selection of the processing conditions enabled an accurate control of the relative thickness of the layers of the parts.

Introduction

Gears are now used for a wide range of industrial applications for transmitting power or rotational force from one component to another. Modern gears are made from a wide variety of materials. Of all these, alloy steels are widely used due to their outstanding characteristics of high strength per unit volume and low cost per pound [1].

Heat treatment is often conducted after gears have been shaped in order to combine properly the toughness and tooth hardness. However, the surface treatment represents an additional step in the manufacturing cycle with the associated increase in manufacturing costs. Recently, metal co-injection moulding (co-MIM) has been described as an alternative manufacturing method for the production of this type of gear [2].

Co-MIM uses two different powder/binder mixtures which are injected into a mould sequentially, so that one mixture forms the surface layer of the component and the other forms the core. It offers the ability to accomplish the “surface treatment” in a single process rather than post-processing procedures. In this way, the number of processing steps can be reduced, making cost-effective products feasible. This is why co-MIM has attracted growing attention in recent years......

Further sections of this paper include:

Experimental
Results
Core penetration
Skin uniformity
Discussion
Manufacturing of prototype gears
Conclusions

Figures and Tables:

Fig. 1 Viscosity-shear rate data for core (a) and skin melts (b) at different temperatures

Fig. 2 Schematic picture of the measurement of core penetration

Fig. 3 Co-injected plates at various skin temperatures (a-152°C, b-158°C, c-164°C, d-170°C, e-176°C) and a constant core temperature of 158°C

Fig. 4 Influence of skin temperature (a) and injection velocity (b) on the core penetration depth

Fig. 5 Influence of skin temperature (a) and injection velocity (b) on skin thickness uniformity

Fig. 6 Ln viscosity vs. ln shear rate of core (a) and skin (b) melts at different temperatures

Fig. 7 Photographs of the as-moulded and sintered gear prototypes (a) and a morphology of the interface after sintering (b)

Table 1 Moulding conditions used

Table 2 The calculated viscosity of the core and skin melts at different temperatures