The 'six-axis' success story
Competitive pressures are urging plastics injection moulders to seek
faster, more agile methods of parts manipulation in increasingly complex
downstream, post-moulding operations. Robert Hopper describes how six
axis robots can help, without being a drain on your capital investment
budgets
Companies engaged in plastics injection moulding have, for years, sought
not merely to supply end products in pristine condition, but to add value
in the form of printing, decoration or even partial assembly. Robots of
the beam or cartesian type are still extensively employed for such
purposes, transferring moulded parts from the moulding machine to various
downstream processes, with a degree of success. However, two factors have
recently arisen, which widen the potential for using six-axis robots in
these increasingly complex post-moulding applications.
Firstly, modern injection moulding machines offer much faster cycle
times, so faster and more flexible robots are required for the downstream
processes, simply to keep up. Secondly, there is pressure on the UK
moulding industry to automate its methods in order to remain competitive
in a global market. The industry now regards investment in such areas as
six axis robots as essential if it is to compete against foreign moulders
with the advantage of a lower cost base.
A supplier of both cartesian and six-axis robot systems, ATM Automation,
reports that one in every four robots that it has delivered over the past
year was of the six-axis type. While this suggests that six-axis systems
have gained a significant share of the overall robot market in the
plastics industry, ATM believes that this has not been at the expense of
the cartesian type, for which a substantial market share remains. The six
axis robot has an additional role to play, which supplements that of the
beam design. Thanks to the lower costs of servo components, moreover,
six-axis robots are not the major investment they used to be. And while
cartesian robots are generally still lower in cost, the special
advantages of six-axis models often justify the extra outlay.
ATM first became involved in the supply of six-axis robots to the
plastics moulding industry as a response to the requirements of mobile
phone component manufacturers. Their considerably greater flexibility
means that they can be quickly adapted to new product designs, so for an
industry in which model changes take place frequently, easily adapted
robotic equipment can make all the difference.
A typical installation might involve an injection moulding machine
producing two mobile phone components simultaneously on a 12 to 14 second
cycle. Decorative foils are now widely used for mobile phone lens and
bezel components, and six-axis robots are used to collect, clean and load
pre-cut printed foils into the injection mould tools. Plastics material
is then moulded over the foils, an in-mould decoration process that
eliminates the need for post-mould painting or printing. The robot
extracts the finished parts and places them in a tray located on a
transfer conveyor, or places them to a tape-and-reel system, usually
following a vision inspection stage. The high speeds of six-axis robots
during the de-moulding cycle are ideally suited to this type of
application, where the non-productive time of the moulding machine during
the unload sequence can be reduced to a minimum.
Six-axis robots have undergone a number of developments over the years,
which have vastly improved their applicability to plastics injection
moulding. One of these is a function called 'soft float', which is
enabled within the robot program when mouldings are extracted from the
mould. The end-of-arm tooling of the robot first places vacuum pads on
the parts to secure them, and they are then pushed out of the mould
cavities by the ejector pins. The soft float function effectively
accommodates the ejection stroke of the pins, minimising the 'handover'
time between mould tool and gripper, and allowing the robot to move
smartly away from the tool with the parts securely held in the grippers.
Soft float pressure and sensitivity can be adjusted to match the pressure
of the ejector pins, a useful function for insert loading into a mould
tool, or for applications where the robot gripper may be required to dock
with the tool on tapered pins. The function enables the robot program
positions to be set in roughly the right position, and the soft float
function is then used to ensure complete alignment on to the taper pins.
Another useful function is collision detection, which is enabled during
that part of the cycle, when the robot enters the mould tool. More
importantly, the collision detection function can be set for sensitivity,
particularly if collision detection is vital to preserving the integrity
of a very expensive mould tool. The robot is halted if a collision or
overload condition on any of the robot motors is detected. These
functions, when employed with a standard Euromap 12 Interface, plus cam
switches on the first and second axes of the robot, provide a robust and
safe interface between the robot and moulding machine.
Another application of six-axis robots, involving extreme complexity of
movement, is the manufacture of cloth-covered interior trim panels for
the automotive industry. The current method places fabric or cloth inside
the mould tool, the plastics material being injected behind it. Following
the moulding process, excess cloth or material has to be removed from the
perimeter of the moulding, and additional apertures may need to be cut
into it. The robot retrieves the moulded component and passes it beneath
a static laser cutting system, manipulating the component through a
series of complex three-dimensional cutting paths, trimming away excess
material and providing a consistent and repeatable finish. And, as with
the mobile phone example, the system is easily reprogrammed for new
models and shapes.
Vehicle dashboard components are now also being manufactured in a similar
way. The inside surface of the dashboard, housing the passenger airbag,
is covered with a piece of flexible cloth, which is fed from a reel,
laser cut to shape and size, and then loaded to the mould tool using a
six-axis robot. The material is then moulded integrally with the
component. The robot removes the moulding and presents the component to a
vision inspection station, where the insert moulded material is checked
automatically. The robot then presents the moulding to a bar code label
printer, before placing the finished and inspected parts on a transfer
conveyor.
In addition to these applications, ATM Automation has also found uses for
its six-axis robots in the food and packaging sectors, having completed a
number of installations over the past twelve months. You can find out
more about these and other potential applications by visiting
www.dpaonthenet.net and clicking on the relevant links to ATM's web site.
Robert Hopper is with ATM Automation
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