Micro-drilling Using Step-forward Method

1. Micro-drilling Using Step-forward Method 2004. 9. 9. Jae-hoon, KANG * Jong-kweon, PARK Jun-yeop, SONG Intelligent Precision Machine Dept. Korea Institute of Machinery & Materials

2. Human hair (D)80 mm Micro-drill (D) 30 mm Introduction Micro-drilling is regarded as useful process technology to make tiny holes and widely used at electronic, semiconductor, medical, fuel injection, watch, spinneret, dies related industry fields Medical devices Micro-drill Watch component Spinneret & dies Military & aerospace components Electronics & semiconductor Fuel injection nozzle

3. Motivation It became a common understanding that it is necessary for machining tiny holes smaller than 100 mm in diameter to apply the laser systems However, it is also true that laser systems have several disadvantages compared to conventional mechanical drilling And the mechanical system could be competitive against the laser system, if they can have micro drilling capabilities Thus, many manufacturers have been making efforts to retry the traditional mechanical precision drilling machine for machining tiny holes with high productivity Recently, creative precision has complete micro hole drilling capabilities for holes down to 30 mm in diameter But conventional micro-drilling has also several problems such as excessive forces, tool breakage, chatter, burr formation in metals

4. Objectives Accomplishment of direct practice to obtain preliminary knowledge for ascertain mechanical micro-drilling behavior through the experimental study Examination to application capability of presented proper method to control tool damage * Trouble-shooting to occurred tool breakage mode frequently during previous precedent conventional micro-drilling experiment * Presumption as the trouble is resulted in the poor chip cutting & evacuation * Application of step-forward feeding method during micro-drilling process

5. Experimental System for Micro-drilling Specifications of the micro drilling apparatus Stepping motor Pressure gauge box Air bearing spindle Micro-drill Work-piece Tool dynamometer Controller Experimental apparatus for micro drilling experiment

6. Measuring Instrument A/D converter DAQ Amplifier Microscope with built-in monitoring system Data acquisition system Measuring instruments for cutting force Micro drill Work-piece Vision system

7. Micro-drill Tool Geometric feature of micro-drill Straight-fluted Micro-drill Dimensions of micro-drill 0.2(d)mm 0.3(d)mm 0.5(d)mm

8. Data acquisition system Work-piece Mounting Device Micro drill U. F Work-piece Work-piece Work-piece (dummy style) Mounting device Tool dynamometer B. F Computer Tool Dynamometer Y Z A/D Board Amplifier Experimental setup components for secure clamping of work-piece

9. Experimental Conditions Machining Conditions of Micro-drilling Diagram of Step-forward Feeding Type Non Step Micro-drilling • Trouble-shooting to Bird Nesting Problem • proper chip cutting • efficient chip evacuation

10. Comparison of Cutting Force Micro-drill diameter : 0.2mm, Step number of times : 4 Cutting oil supplied drilling Dry drilling Micro-drill diameter : 0.3mm, Step number of times : 5 Cutting oil supplied drilling Dry drilling

11. Comparison of Cutting Force Micro-drill diameter : 0.4mm, Step number of times : 5 Cutting oil supplied drilling Dry drilling Micro-drill diameter : 0.5mm, Step number of times : 5 Cutting oil supplied drilling Dry drilling

12. Comparison of Cutting Force For cutting oil supplied drilling, the cutting force is lower than dry drilling distinctly But, there is a little difference in cutting force between cutting oil supplied drilling and dry drilling as the hole diameter is smaller --- Caused by insufficient supply condition of cutting oil Variation of cutting force according to tool diameter

13. Comparison of Burr Formed For cutting oil supplied drilling, the burr formed extent is diminished than dry drilling in a greater or less degree Cutting oil supplied drilling Cutting oil supplied drilling Dry drilling Dry drilling drill diameter 0.2mm drill diameter 0.3mm Burr Cutting oil supplied drilling Cutting oil supplied drilling Dry drilling Dry drilling drill diameter 0.4mm drill diameter 0.5mm

14. Morphology Comparison of Chip Formed For cutting oil supplied drilling, the continuous flow type chip can be obtained distinctly relatively to dry drilling Cutting oil supplied drilling Cutting oil supplied drilling Dry drilling Dry drilling drill diameter 0.2mm drill diameter 0.3mm Cutting oil supplied drilling Cutting oil supplied drilling Dry drilling Dry drilling drill diameter 0.4mm drill diameter 0.5mm

15. Comparison of Tool Morphology For step-forward drilling, the tool damage can be restrained efficiently relatively to conventional drilling Initial tool morphology Tool breakage mode Closed-up broken region Conventional micro-drilling ( Example 1 : Trouble mode occurred at 5th hole machining process ) ( Example 2 : Trouble mode occurred at a moment tool contacted to work-piece ) The other tool breakage mode Step-forward type micro-drilling ( Example 1 : Normal mode maintained after 3rd hole machining completed )

16. Summary & Conclusion Preliminary experiment were performed to obtain basic knowledge for ascertain process behavior of micro-drilling Step-forward type feeding method was applied for micro-drilling process to cope with troubles occurred precedent case study Cutting force was decreased in micro-drilling using tool diameter of 0.3mm or under For cutting oil supplied drilling, the cutting force is lower degree of 5~15% than dry drilling distinctly There is a little difference in cutting force between cutting oil supplied drilling and dry drilling as the hole diameter is smaller For cutting oil supplied drilling, the burr formed extent is diminished than dry drilling in a greater or less degree For cutting oil supplied drilling, the continuous flow type chip can be obtained distinctly relatively to dry drilling For step-forward drilling, the tool damage can be restrained efficiently relatively to conventional drilling

17. Thanks … for your attention