An automated injection moulding cell has been designed and built by Kettering integrator, Hi-Tech Automation, to produce electrofusion couplers for joining plastic utility pipes at a significantly lower cost than previously. It is the first of its kind to be built in the UK and the high productivity will allow manufacturers in the West to compete with low-wage countries, notably China.
A majority of the key elements that have gone into the dual production line cell, including robots, controls, drives and injection moulding machines, were supplied by FANUC from its new Coventry headquarters, where its previously separate divisions are now merged. Hi Tech, due to its expertise in injection moulding, became a preferred partner to FANUC in 2007 and has also installed over 100 automated systems incorporating the Japanese firm’s robots.
In this project, the Hi-Tech customer was GPS PE Pipe Systems, Huntingdon, which develops pressurised polyethylene pipe systems for the utility markets. The turnkey cell will be installed at Akatherm in the Netherlands and will produce 110mm diameter electrofusion couplers, 24 hours a day, seven days a week. Each coupler has an electrical heating coil embedded around the inside diameter. By applying a voltage across two external connector pins, the coil melts the inside of the fitting and the outside walls of the two pipe ends to produce a strong, homogeneous joint that will not leak water or gas.
A feature of the production cell is that a hot-runner tool in an all-electric injection moulding machine has replaced formerly-used hydraulic machines with cold-runner tools, reducing component weight and saving up to 20 per cent of raw polyethylene. A further saving was achieved in the capital cost of the two moulding machines, as the FANUC Roboshot α-S150iA150-tonne models were upgraded by the manufacturer to 180 tonnes capacity to allow the locking force and shot weight to be increased.
A technical first
In what is claimed to be a technical first, FANUC engineers have developed an ingenious system for winding the internal coils, which are formed from 0.7mm diameter stainless steel wire. As a result, the number of coil windings needed has been reduced from 17 to 16, cutting the consumption of this expensive metal by nearly six per cent.
A FANUC Power Motion iA CNC motion controller, using multi-group control, oversees operation of the winding machines in each of the two lines. The wire feed control tracks the speed of the robot to ensure that delivery of the wire onto the core is accurate and under tension. A synchronous function continuously controls the delivery of wire from the feed roller axis to the rotary axis that turns the core. A contra-rotating motor and FANUC’s digital servo torque control constantly adjusts the tension to within preset limits, without the need for additional rollers. Wire breakage detection has also been incorporated. In a further operation, the robot snips the wire at the end of the coil.
It is the high accuracy of control over the winding process that reduces wire usage by allowing the coils to comprise one fewer turn, without compromising the resistance and therefore the heating of the coil when the coupling joins two pipe ends. The tension control also ensures that the coils stay in place during over-moulding in the Roboshots.
As well as orchestrating the various motions within the coil winding stations, the Power Motion iA controls the de-coring process and the inspection station. Using FL-NET Safe protocol, communication over simple Ethernet cabling between the two Roboshot injection moulding machines, three 6-axis robots, the CNC coil winding stations and the Power Motion iA provides a secure interface between the various FANUC elements of the cell and vastly reduces wiring and cabling. These safe networks allow total visibility of all communication signals from any device.
It is noteworthy that all FANUC robots and CNC systems are preconfigured to interact seamlessly with each other and can easily be coupled with the manufacturer’s machines. Robot status and programme selection can be displayed and adjusted at the machine control, while the robot screen displays CNC-specific information that the user can access for maximum productivity. Programs can be called up and a robot activated without recourse to a separate robot controller, saving time and enhancing system safety. It underlines the benefits of sourcing all main elements of a production cell from a single supplier.
The production process
Two separate FANUC M20iA robots place steel cores onto the rotary table of each coil winding station and retrieve them afterwards, placing them onto buffer stations. A single FANUC R2000iB robot picks up two wire-wound cores from one station and inserts them into a plastic injection mould in one Roboshot, repeating the process with the other buffer station and the second Roboshot. In the same operation, a pair of over-moulded polyethylene couplings with coils embedded are retrieved by the robot gripper in a total cycle time of just under 10 seconds.
The design of the four-impression injection moulds was optimised by Hi-Tech so that the moulded couplings become perfectly round when they have cooled. After they have done so, the cores are extracted. Two die-cast termination pins are fed by a vibratory bowl via an orientation device, picked up and inserted, again by a robot, into connector shrouds moulded into each coupling.
The two production lines are identical up to this point and operate simultaneously on a 120s cycle time. Zoned safety measures, including full guarding and FANUC Dual Check Safety, allow production to be maintained on one side of the cell while the other side is being changed over or undergoing maintenance.
Couplings from both sides are placed sequentially at a designated orientation in an inspection station equipped with a vision system and a resistance test station. The component is subjected to a series of more than 130 checks, including for the presence of flash, shorts and date stamp, while wire spacing and connectivity as well as pin placement are all verified.
The products then go to an automated packing station, which again uses a FANUC 6-axis articulated robot to fill boxes automatically on a conveyor, ready for delivery. An HMI screen provides the user interface, giving a comprehensive status overview of the entire cell and alarm feedback for troubleshooting.
To learn more about robots, controls, drives and injection moulding machines from FANUC, please visit www.fanuc.eu.