1. Field of the Invention
The invention relates to a method for manufacturing a camshaft for use in a valve mechanism of an internal combustion engine, and more particularly to a process for providing a camshaft in which each fitting member, such as a cam lobe and a journal, is easily bonded to a stem and machine-workable after bonded.
2. Description of the Prior Art
The composite camshaft has a tubular stem of steel and a plurality of fitting members, such as cam lobes and journals, fitted on the tubular stem. The camshaft is light and efficient as compared with the conventional camshaft as casted as one body. Conventionally, the fitting member has been bonded to the stem by either of welding and brazing means, which disadvantageously need many manpowers for handling welding machines or arranging brazing materials. Besides, welding is likely to cause strain in the product due to thermal stress, while brazing fails to provide a sufficient contact between the fitting member and the stem.
There has been proposed another method by which the fitting member is made from a liquid phase sintering material and sintered to join the steel stem. The obtained camshaft is superior in wear resistance but disadvantageously poor in machinability, because the material sintered in the presence of liquid phase is too hard to be machined with ease.
It is known to provide the camshaft with an oil passage extending radially from the outer periphery of each fitting member to the hollow inside of the tubular stem. However, it is costly to form such an oil passage by the known method as disclosed under JP No. 57-154556 in which the oil passage is machined in the fitting member hardened by sintering.