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Redefining Robotic Laser Cutting

January 15, 2020

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Material processing in automotive, specifically laser cutting has come a long way in the last 30 years.  The market requirements for improved strength, weight savings, and lower costs drive the need for manufacturers to use materials such as high strength steel and aluminum.  Hot press hardened steels (PHS), generalized as high strength, include many different trade names.  The key aspect to gaining toughness is through heating of the material in the stamping press, forming the part and then quenching to achieve hardening of the steel while forming the stamped shape. In a traditional automotive stamping, a part goes through various stages of die forming with a final trimming die to form the metal to the net shape.  PHS parts are hard and nearly impossible to trim in a die, and require a machining process to create the correct net shape.  The most effective and popular choice for trimming PHS is through laser cutting.   There are two primary means of laser cutting including robotic and CNC laser cutting. 

Robotic cutting has evolved with improved robotic motion performance by accurate mathematical models of the robot mechanism and the improvements in the controller’s servo performance and path planning.  This has allowed robotic laser work cells to offer a competitive cost-per-interchange part when compared to a CNC cutting operation.  This is especially true when processing automotive components that have a varied shape and require 5+ axes of motion to process the 3D parts as compared to traditional CNCs used for sheet or plate processing.   Today’s six-axis robots such as the FANUC M-20iB/25 offer the best robotic accuracy and speeds but do not equal the accuracy of a purpose-built CNC.   Manufacturers need to consider the tradeoffs of slightly less accuracy of a robot but with much greater throughput than a CNC. Robotic laser cutting capabilities offer improved density of the laser processing and how many ‘laser heads’ can be put on the part at the same time.  There is more… New developments in robotic cutting continue to close the gap on path accuracy with speed, taking the robotic to CNC performance levels and with higher throughput.

The latest improvement in robotic laser cutting performance comes from a company called Shape Process Automation (formerly DRS Robotics).   Shape collaborated with Laser Mechanism and FANUC America to develop the NEWTON – Robotic Cutting Head.  NEWTON is a robot-mounted 2-axis shape-cutting device that offers path accuracy up to +/- 0.05mm within a 30mm operating range.  The device is also capable of the fastest laser hole cutting speeds at 0.3 seconds for common size features.  The FANUC M-20iB/25 robot already has impressive path performance and the NEWTON takes it into new territory. This capability nearly eliminates the gap between robotic and CNC laser cutting for 3D automotive type components. 

The NEWTON design is a patent-pending device that is inertial balanced, and controlled directly from the robot teach pendant. The operation is simple with pre-canned motion planning for common shapes including circles, slots, squares, hexagons, and many others in the robot’s library.  For users it is as simple as moving the robot head to the feature and then selecting the cutting shape from the library.  The shape attributes are easy to modify to make quick programming.   Robot users will easily transition to the NEWTON because the programming is familiar and easy to use. NEWTON can reduce the cycle time over a typical six-axis cutting robot by as much as 70%.

Operational efficiency is the name of the game and Newton is a radical change.  Now robotic laser cutting systems perform well in a work cell or a linear arrangement.    When reviewing the processing layout for cutting PHS components it is the manufacturer’s choice to develop the best layout based on material flow.  For example, a station type robotic work cell may mimic the CNC cellular approach while a series of robots in a line offers higher throughput capacities.  The layout depends on the part mix or variety, and the required production volume.  Work cells may offer improved capabilities for change-out of the tooling and part mix, while a series production line offers higher throughput due to the dedicated tooling, high laser density, more on time, and overall increased productivity.  The NEWTON cutting head is an enabler for both work cells and line processing and has many advantages for 3D laser processing.   A robot can process a variety of parts and part shapes because the serial link arm construction enables more robot arms on a part fixture. More arms means more laser processing heads and increased productivity.   The CNC design is rectilinear, where the motion device consists of a horizontal bridge structure with a single laser head within the working area of the enclosure. 

Part processing cycle time needs consideration when reviewing the laser cutting application.   The CNC may have only one laser cutting head on the part at a time and if the total cut time is <30 seconds then it causes an operator imbalance.  In other words they cannot load or unload the material fast enough for a single part cycle of <30 sec.  If you take the same cycle time and double the part then the cost for tooling doubles and the area of the laser cell doubles too, while the part processing time per head is still the same.  Some of these issues may be resolved with robotic load and unload of the CNC but the number of processing heads per part is still 1:1 and the floor space becomes larger.  All of this adds up to more laser heads per part and allows you to achieve better on-time production.   A side benefit to fewer fixtures or tools per part type is the improvement in process capability (Cpk).  The proportion of cycle time and the number of heads per part need to have balance and match the material flow requirements.  

The capital costs and space savings become more apparent when a flexible work cell manages material flow through a turntable axes, often referred to as an interchange.  These types of robotic cells provide the user with a balanced load and unload time within the laser processing cycle.  Work cells with a single turntable offers increased flexibility allowing dynamic part fixture or tooling swaps for other model parts.   Two-sided turntable cells allow continuous operation, realizing simultaneous planned tool change-out for one side while the other is in production.  Sometimes referred to as a dual-wall cell with turntable axes, with walls on each side of the cell to provide a safe light-tight operation.  An additional concept uses the same method but with a three-station wall axes or tri-wing turntable, that rotates the part and tooling into the laser cell with three positions at 120⁰ each on one table.  The tri-wing design of the triple station can achieve higher production rates while offering the capability to do part changeover during production.  The high speed and accuracy of the NEWTON cutting head complements the productivity increase of the dual-wall and tri-wing designs.

The capability of the NEWTON head enables robots to overcome the cycle time and accuracy penalties from their predecessors.  This new technology has capabilities that allow for series or cellular production without penalty. The flexibility of adding more laser heads per part saves on tooling costs and helps balance the operation cycle time while improving Cpk.  NEWTON is a key enabler to keeping robotic laser cutting at the forefront of manufacturing.  This unique inertia-balanced design and control through the FANUC iPendant will usher in a new era, redefining robotic laser cutting.

Redefining Robots appears in the Nov/Dec 2019 issue of Shop Floor Lasers

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