Precise direction of impact for milling applications

Automotive engineering Underbody protection

Parts are produced with a milling robot in a rapid prototyping procedure.

Precise direction of impact for milling applications

Cell description

The customer operates an ABB IRB 6400RF robot to mill parts produced using a rapid prototyping process. The workpieces are clamped onto worktables and processed by the robot. The robot has as its tool a milling spindle with cutter in an HSK chuck. The milling cutter is replaced at a tool changing station.

Task definition

One of the customer's requirements was to be able to machine-finish predrilled holes with a milling cutter. The cutter often got stuck in the hole because the cutter's direction of impact deviated slightly from the theoretical values as a result of production tolerances. In the past the customer had always remedied the situation by manually modifying the quaternions of the tool definition at the third decimal place until it more or less fitted.

With milling robots it is always difficult to measure a direction of impact very precisely. The standard procedure is to have the robot move a milling head dummy into a drilled hole on the workpiece holder. The direction of impact is determined from this, based on the Z-component of the work object. The level of accuracy achieved with this procedure was too low for the customer.

Implementation

To achieve the level of accuracy required by the customer for measuring the direction of impact, two measuring rods for HSK chucks were manufactured with high precision. These were inserted in the chuck and measured in turn.

At the first attempt the measurement was considerably more accurate than anything the customer had achieved before. It turned out that the error in the direction of impact was only 22 hundredths of a degree. This deviation was the reason for the cutter becoming stuck in the hole. As a test measure, the cutter was moved into a test hole and for the first time the customer was able to rotate the tool freely by hand without it getting jammed.

Measurement of work objects was implemented on the jig with base:in and four measuring rods.

Customer benefit

By using a LaserLAB and tool:in the cutting tool's direction of impact was determined highly accurately in just a few minutes. Manual adjustment of the quaternions is now a thing of the past.

With a precise knowledge of the tool and work object the customer is now able to implement rapid prototyping with the milling robot.