Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)59

Introduction of Measuring Method Applied to
3D Laser Machining

S a l e s D e pa r t m e n t , M a c h i n e To o l D i v i s i o n ,M a c h i n e r y, E q u i p m e n t & I n f r a s t r u c t u r e

In high-accuracy, high-quality machining with a three-dimensional laser processing machine,
focal position adjustment at the machining laser head is a particularly important element.
Conventionally, a measurement head separate from a machining laser head has been used tomeasure the machining surface position, and based on measurement results, focal position
adjustment has been made at the machining laser head. This has been a factor requiring more time
for measurement, namely, non-machining, than machining, thereby spoiling productivity. For
higher productivity, it is necessary to accurately measure the machining surface position needed in
focal position adjustment and shorten the focal point positioning time.
By taking advantage of the expertise we have cultivated for machine tools, Mitsubishi Heavy
Industries, Ltd.’s (MHI) laser processing machines have made it possible to specify the machining
surface position at a high speed with high accuracy for positioning the focal point. This paper
introduces a measurement head arranged on the same axis as that of the machining laser as adevelopment by MHI for higher productivity, together with technology to shorten the time for themeasurement of machining surface position.

|1. Measurement head arranged on the same axis as that of themachining laser
Figure 1 shows the configuration of MHI’s laser processing machine’s machining laser
head. MHI’s machining laser head has a laser interference-type length measuring sensor integrated
into the same optical system as that of the machining laser head as a solution for the accurate andfast measurement of the focal position. The integration of measuring equipment into the same
optical system makes both machining and measuring positions identical, thereby enabling highly
accurate measurement. Furthermore, when moving to the next machining position at the end ofmeasurement, the wasteful motion for measuring the machining surface position can be omitted
and thus non-machining time can also be saved.

Figure 1 Machining laser head configuration

Figure 2 Outside measuring (equipment example)

Mitsubishi Heavy Industries Technical Review Vol. 52 No. 3 (September 2015)60|2. Technology to save measurement time(1)

Outside measuring equipment
The adoption of an APC (automatic pallet changer) and equipment of an outside
measuring device on the set-up station as shown in Figure 2 have enabled machining surface
positions to be measured outside the machine.
In the measuring equipment, a highly reliable triangulation sensor is employed tomeasure the workpiece shape outside the machine during a machining cycle. The correction is
automatically calculated at the time of machining laser head movement based on machining
surface position information obtained from measurements, and laser head positioning time has
been reduced substantially.
(2) Highly accurate measurement against a glossy surface
If the machining surface is glossy, laser measurement is regarded as difficult. Optimum
tuning in accordance with the material and glossiness of a target workpiece has realized highly
accurate measurement with a tolerance of ±0.05 mm or less.
(3) Shape scanning function
When a workpiece has many holes machined on it, it takes considerable time to measure
the workpiece’s hole positions. A shape scanning function is applied to workpieces with planeor axisymmetric machining surfaces, thereby substantially contracting measurement time
(Figure 3).
The shape scanning function is a function for estimating the surface position from nearby
measuring points instead of directly measuring the surface position at the machining point tocalculate the surface position at the machining point by interpolation. This function enables allof the machining surface positions of a workpiece with many machining points to be calculated
from a small number of measuring points.

Figure 3

Shape scanning mode

|3. Future outlook
At present, workpiece shapes for which the shape can be scanned are limited to planesurfaces or axisymmetric parts. We will develop a shape recognition system using athree-dimensional scanner so that shape scanning can become compatible with any desired
three-dimensional surface, and thereby seek to expand the applicable shapes and further reduce
measuring time.