Abstract
There are two cases in drilling. One is a semi-automatic operation with the boring machine bitted with an auto-feeder, and the other, a hand operation by skill feeding. The former belongs to a drilling machine operative with constant feeding speed as shown in the previous report, while in the latter the work is only pressed down by a force well in keeping with the thrust of material. In this paper, the boring machine is set with a feeding a pparatus so as to operate in constant drilling force, and the drilling machinability of the rought aluminium, such as, 17ST4, 27ST4, 52SF and 56SF are experimented.
The drilling resistance is measured by using the trial powermeter for two compornent of resistance, and it is found that the thrust is constantly balance with the drilling force no matter what the drill diameter is in every work and that drilling characteristics of work make appearance as a difference of the torque. Consequently, when the drilling time under constant drilling force, i. e., the time required in drilling the unit depth, S (sec/mm), is measured on the oscillo-paper of drilling resistance which is picked up from the powermeter, the torque Tq experimentaly formulates S=k•Tqβ where, even though the torque is the same in quality, the larger the material constant k and β grow, the longer time does the drilling take and the machinability gets the worse. This experiment shows that the drilling machinability can be made better in order of 17ST4, 24ST4, 56SF and 52SF, and that in a certain drilling, say, of 10mmφ under the same drilling force, the torque in the case of predrilled drilling becomes several times larger than usual cases of drilling, with the consequence that the drilling time becomes far shorter. So it is advisable to adopt the pre-drilling method particularly in drilling materials of inferior machinability.
This study was conducted with funds furnished by Scholarship Committee of the Institute of Light Metal Foundation, for which we feel deeply grateful.
