Carrier finishing machine uses servo-pneumatics for precision control of
welding forces.

Carrier finishing machine uses servo-pneumatics for precision
control of welding forces of its two welding units, to accommodate different
carrier variants.

The specialist automation company Lambert Engineering
has developed a unique plastic component assembly machine, using Festo servo-pneumatic
drives to provide ultra-precise control of welding force.

By combining low cost linear positioning technology with
innovative feedback techniques, the company has significantly lowered the
system’s build costs and produced a highly reliable manufacturing tool.

TI Automotive, one of Lambert Engineering’s key customers
in the automotive sector, recently contracted the company to develop a turnkey
manufacturing solution for assembling fuel-carrying plastics components used
on a leading 4-wheel drive vehicle.

Aside from meeting the tight cost constraints that are
standard in the automotive supply industry, the machine needed to be capable
of handling complex component shapes, and perform very carefully controlled
hotplate welding operations to ensure product quality and consistency.

In addition to this it effectively had to accommodate
four different types of component assembly operation, meet stringent operator
safety standards, and provide fast and reliable operation to maximise product
throughput.

In this instance, TI Automotive required a machine to
fully automate the welding of hose assemblies to a large moulded plastics
component known as a ‘carrier’, which is subsequently fitted inside the special
fuel tank used for a new 4WD model.

The carrier is a multi-function component, designed to
provide level sensing and other functions, as well as fuel take-off.

Since it forms an integral part of the fuel tank, which
is effectively built around it, all the carrier’s hose connections need to
be of the highest integrity to ensure long-term reliability – it would not
be possible to inspect or repair them after manufacture.

Furthermore, TI Automotive’s contract with the vehicle
manufacturer involved the provision of two physically different variants
of carrier, each of which needed to be produced in two versions – one for
petrol tanks, the other for diesel.

Both carrier variants require the welding of breather
pipe and roll-over valve (ROV) clusters; diesel carriers are fitted with
a single ROV cluster, while petrol carriers are fitted with two separate
assemblies.

Lambert Engineering has considerable expertise in developing
machines that use pneumatic rather than electrical drive technology to provide
robust and reliable operation, combined with relatively low build costs.

In this case, the precision positioning and force control
capabilities needed to ensure high quality welds made closed-loop control
essential, and the company chose to use Festo servo-pneumatic drives and
proportional valves for all of the machine’s critical functions.

As Matthew Cox, Lambert Engineering’s sales engineer responsible
for this industry sector, points out, ‘We use Festo pneumatic components,
including servo technology, for many of our automation designs, and consider
them to be the most reliable and cost-effective products on the market’.

‘This particular machine also employs Festo pneumatic
cylinders
and Profibus-controlled CPV compact valve
terminals
on many of its other motion axes.’ The carrier finishing machine
comprises two functionally independent assembly
stations
– one for each carrier variant – housed in the same cabinet and
sharing the same control system.

Each assembly station is equipped with two hotplate welding
units, one for attaching breather pipes, the other for ROV clusters.

The entire machine is controlled by a PLC, using a profibus
network
for communication with many of the system’s I/O functions, including
hotplate temperature control and most of the pneumatic
control
valves.

An HMI running Windows CE is employed for all operator
control and process monitoring functions, and makes extensive use of graphical
mimic diagrams to present information very clearly and help prevent operator
error.

Each welding operation is critical, involving precision
control of temperature, force, travel distance and time, and is completely
automated.

After loading the hose assemblies and carrier body into
pneumatically actuated gripper units
on the appropriate assembly station, the operator simply activates the process
from the front control panel.

Built-in light guards
ensure safety compliance, immediately shutting the machine down if anyone
crosses the threshold.

The machine checks that the correct components have been
loaded for the requested assembly operation and then begins the welding process.

Although each assembly station has separate welding units
for the breather pipe and the ROV cluster(s), they operate simultaneously
to maximise machine throughput.

The sequence is similar in each case.

Taking the ROV cluster welding unit as an example, the
hotplate is driven into position by three pneumatic cylinders, trapping the
plate between the carrier body and plastic nipples on the cluster to preheat
the surfaces.

The main drive cylinder in the welding unit – a Festo
ADVU unit – initially exerts a high force to square up the surfaces, then
reduces the force while heat penetrates the components.

The hotplate is then withdrawn and the main drive cylinder
again exerts a high force – this time to join the components and compress
the weld and then reduces the force to hold the components together while
the weld sets.

Each stage of this operation demands ultra-precise control.

The hotplate is held at exactly the right temperature
– normally around 250 deg C – by a Profibus-based multi-loop temperature
controller, which also monitors the hotplate in the breather pipe welding
unit, and in the two welding units in the second assembly station.

The main drive cylinder is fitted with an LVDT (linear
variable displacement transducer) to provide analogue feedback of position
data to the PLC, while the force that it applies is measured by a load cell
located between its output rod and the component gripper unit; after amplification,
this force signal is also fed back to the PLC.

The forward pressure in the cylinder determines the maximum
force that can be generated, and is set by an MPPE precision regulator, with
a pneumatic valve dictating whether the cylinder is extended or retracted.

The actual force that is applied by the welding
head
is determined by the cylinder’s pressure balance – the back pressure
is controlled by a Festo proportional control valve that receives analogue
signals from the PLC.

Providing that all processes are accomplished successfully,
the machine opens the gripper clamps and deactivates the light guard, allowing
the operator to remove the completed assembly and reload the machine.

Any process errors are immediately flagged to the operator,
and used to build audit trails for the manufacturing operation.

They are also used to build an empirical history file,
enabling the next welding cycle to ‘learn’ from its predecessor and automatically
make running adjustments to ensure process consistency.

These extensive real-time monitoring functions are backed
by powerful diagnostic facilities help minimise system downtime.

The carrier finishing machine was installed at TI Automotive’s
Deeside, UK, facility at the beginning of this year, and its performance
is proving highly satisfactory.

Matthew Cox adds, ‘There are no comparable manual or automated
assembly
times for this complex component assembly task, simply because
none exists – this machine provides a unique solution’.

‘It is consistently achieving an overall cycle time of
55 seconds – the weld processes take up some 70% of this figure – enabling
TI Automotive to meet its customer’s demands for volume delivery of high
quality components.’ * About Lambert Engineering – Lambert Engineering is
a world class manufacturer of special
purpose machinery
and automation, serving a wide customer base across
multiple industries.

It is especially well known for consumable product manufacturing
equipment, numbering many of the world’s leading personal hygiene, healthcare
and baby care product companies amongst its customers.

Founded in 1973, the company is based in Tadcaster, North
Yorkshire, where it has a large 70,000ft2 purpose-built facility which includes
a secure assembly area for sensitive projects.

Although the automotive sector accounts for a relatively
small share of its overall business, Lambert Engineering has acquired considerable
expertise in this area over the past 15 years and counts TI Automotive as
one of its key customers.

Source : www.manufacturingtalk.com