Process Improvements via Manufacturing System

There are three types of interaction between laser and target material: the light can be reflected, transmitted or absorbed. In reality, all three occur to some degree. In order for laser milling to be possible, the material must absorb the laser light. Reflected and transmitted light represents energy that is lost to the manufacturing process. Only absorbed light is used to perform material removal.

The wavelength of the light used is the basic characteristic that affects good material processing. Different materials absorb light at different parts of the electromagnetic spectrum. It is necessary to choose the correct laser wavelength so absorption of the photons can occur.

Micro milling fundamentals

One of the main differences between micromilling and macromilling is due to the reduction of chip thickness which becomes dimensionally of the same order as the cutting edge radius of the tools and the material crystalline size. This is usually referred to as the minimum chip thickness effect on the process conditions. In particular, the minimum chip thickness can be defined as the minimum undeformed thickness of a chip removed from the workpiece surface and under which no chips removed under ideal conditions as shown in the Figure. In macromilling, the chip thickness is sufficiently large and it is not necessary to consider the effects of edge radius and hence the uncut chip thickness.

Thus, any small change in the chipload can have a significant influence on the material removal mechanism by altering machining conditions from proper cutting to ploughing or shining and slipping. The effect of the minimum chip thickness was investigated by a no of researchers employing analytical and experimental methods.

And it can be concluded that if the undeformed chip thickness is smaller than the minimum chip thickness no chip will form and the ploughing mechanisms is dominant

And if the undeformed chip thickness is in the same range of the minimum chip thickness the mechanism is a mixing between cutting and ploughing and finally if the undeformed chip thickness is bigger than the minimum chip thickness the cutting becomes more dominant. So, the surface generation process is affected by cutting mechanism cutting and ploughing.

One of the main factors that affects the cutting mechanism in the micro scale cutting is the material microstructure effects, as the length scale of the crystalline grains of most commonly used materials is similar to that of chiploads in the micromilling process and the features to be produced, cutting sometimes occurs inside the individual grains themselves. So, the workpiece material cannot be considered isotropic or fully homogeneous. This scale issue can be regarded as one of the main distinguishing characteristics of microcutting in comparison to macrocutting.

Micro milling tool failure detection techniques

· RSBLS:

· Laser beam focused on the cutter and the beam reflection is directed towards a receiver

· Detect tool breakages instantly.

· Difficult to apply when machining deep features.

· TWVMS:

· Detection of abrupt voltage variations during milling

· Closed electrical circuit between the spindle and the workpiece.

· Strong potential of this approach.

· Applicable only with conductive materials.

· “off-line laser system”

· Tool measurement routines to be carried out “off-line”

· Employs standard laser systems commonly used on micro machining centres for automating tool setting up procedures.

· No investment in additional hardware

· Increases the machining time

· Tool failures cannot be detected between the measuring cycles.