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.