Robot cell boosts efficiency of complex grinding operation

Alfa Laval is a leading global provider of specialised products and engineered systems, and the company's Eastbourne plant has established itself as a centre of excellence for the design and manufacture of positive rotary lobe displacement pumps.

The plant and, indeed, the whole Alfa Laval Group, is working towards World Class Performance in line with Six Sigma and 5Ss philosophies, and intends to have this completely rolled out by 2008. In line with this initiative, Alfa Laval has made a significant investment in the Eastbourne plant in recent years. A key investment has been the introduction of a two-tier, flexible manufacturing system that incorporates a rail-guided vehicle and a series of Mandelli 5 and Mandelli 7 horizontal machining centres for the production of rotors, rotor cases and pump end covers.

A further investment has been made in the development of a robot-based, flexible automation cell to replace labour-intensive fettling and blending operations on rotor case inlet and outlet ports.

The ports are attached to the rotor case by means of orbital TIG welds - the exact port size, configuration and location being dependent on the requirements of individual end-users.

Weld penetration

The semi-automatic TIG welding process results in significant weld penetration into the port internal diameter, which, particularly on aseptic applications, must be removed, as imperfections in surface finish can become a breeding ground for bacteria.

Previous manually-intensive methods for removing weld build-up were dirty, exhausting and painstaking tasks, which carried with them possible risks of repetitive strain and white finger complaints, plus the unpleasantness of working in cumbersome protective clothing and face mask to protect against the dust-laden environment.

The new robot cell, designed and supplied as a turnkey project by ABB Robotics of Milton Keynes, was installed in 2005 and its introduction has been significant step forward in enhancing the workplace ergonomics within the port welding and finishing facility. The introduction of the robot cell has also saved on labour; it is staffed by a single operator who can conduct welding operations while the robot cell carries out its cycle. The only manual input is the loading and unloading of rotor cases onto a two-way rotary table that feeds the cell.

Best overall package

Discussing the rationale for opting for an ABB-supplied cell, Alfa Laval production engineer, Bill Boniface, comments: "The final choice of supplier came down to ABB and one of its leading competitors. ABB was chosen because we thought they offered a better overall package and they assured us they could carry out the complete installation themselves. Added to this, we were reassured by the fact that our parent company in Sweden has operated ABB robots for a number of years."

The cell incorporates: an ABB IRB 6600 FoundryPlus six-axis robot and control system; pneumatically-operated grippers; a rotary table with adjustable fixtures for five rotor cases per side; a pneumatically operated touch probe; a bar code scanner; a Renishaw probe; eight internal and two external, electrically-powered abrasive wheels; plus a dust extraction system with inlet ports stationed at each set of wheels.

The cycle, which on average takes 20 minutes to complete, starts with the robot gripper using a pneumatically operated touch probe to search each fixture nest for a rotor case. Once found, the robot gripper picks up the rotor case and then transfers the workpiece to a bar code scanner station. The bar code scanner reads a standard product label affixed to the rotor case, so that the specific pump type can be identified, and hence the port configuration and dimensions ascertained and the relevant robot program and abrasive wheel set-up correctly assigned.

At the next station, the robot manipulates the workpiece so that both rotor case ports, in turn, are inspected by the Renishaw probe for correct alignment with the rotor case. The 'standard' product dimensions derived from the bar code are then cross-checked against the 'actual' dimensions measured by the probe. Should the dimensions differ minutely, the robot program can be amended accordingly and the robot's positioning at the relevant abrasive wheel dimensionally offset in order to take the difference into account.

Grinding and finishing

The robot then transfers the rotor case body to the weld finishing area for grinding and finishing of each port in turn. Internal weld grinding is carried out using cotton bonded abrasive wheels before the workpiece is transferred - first to a semi-finishing abrasive flap wheel and finally to a finishing abrasive flap wheel to achieve surface finish levels of Ra 0.6um or better.

A further station, incorporating a pair of bristle brush wheels, removes heat discolouration around the external weld circumference of the port.

When dressing is complete, the robot returns the rotor case to its original fixture on the rotary table and then probes the next fixture nest to start a new cycle. When all five rotor cases have been processed, the two-way table is rotated through 180 degrees by an operator command to present the next batch of units.

Having worked-up the cell and refined the process through the latter part of 2005, satisfactory operating levels were achieved around Christmas of 2005, and payback is expected in four years.

Summing up, Bill Boniface comments: "Achieving the desired level of efficiency we required has been challenging for both ABB and ourselves. Having collectively 'rolled up our sleeves' and painstakingly reviewed and refined the process, that standard has now been achieved. We now have in place a highly efficient production cell with an extremely clean working environment, which complements and aligns with our plans for World Class Performance at the site by 2008."