Flexible Automation Buffers In-line Assembly

More and more, OEM moulded parts customers are looking to moulders toperform more than just moulding. It isn't always enough to simply use arobot to remove parts from the mould and place them in a carton to be shippedelsewhere for postmoulding operations. If moulded parts can be removedand deposited at an exact location, in the proper orientation, subassemblycan be automated downstream of the moulding machine, without the need foran operator to reorient the parts.

The Ego Kunststoffwerk AG in Altstätten, Switzerland, a subsidiaryof the Swiss-based SFS Group with its worldwide activities, develops, produces,and distributes plastic parts as well as subassemblies and complete assembliesof plastic components. Ego possesses special know-how regarding metal-plasticcombinations and the overmoulding of plastic components onto electric cords,cable, and wire. This also includes automated processing of wire mesh,e.g., fabricating and insert moulding of protective covers, filter components,and the like.

Altogether, 40 injection moulding machines are in continuous operation,some with CNC part handling robots and integrated with assembly equipment.Peter Savoie, Technical Director and member of the company's management,explained to IMI how production of a subassembly (Figure 1) used in a firealarm system for Cerberus AG, MSnnedorf, Switzerland, was automated.

During a test phase, the subassembly was produced in small quantities,packed, sent for completion to the company's in-house assembly department,repacked, and shipped to the customer for final assembly. With the actualstart of mass production, Ego wanted to automate to the highest reasonablelevel for quality and economic reasons. Integrated production of the injectionmoulded parts with subsequent completion into subassemblies was providedby Afag AG in Huttwil and Aarberg, Switzerland.

The task included more than just coupling two injection moulding machinesand conveyors for the injection moulded parts. On the one hand, the stagingcycles for various components had to be taken into account, while on theother, the output from the type-specific, multifunctional injection mouldshad to be considered. Making matters even more difficult was the requirementthat, in the event of a malfunction or under special conditions, each productionunit had to be capable of producing the individual components independentlyand permit manual completion of the subassemblies. Integration of the existinginjection moulding machines and their part handling robots also posed problemsfrom the controls standpoint.

Modular Automation

The handling, feeding, and transport systems were selected from a modularsystem for production and assembly automation (Figure 2). System layoutand the process sequence are as follows. The various injection mouldedparts, such as protective covers and grilles, are produced independentlyin two moulding machines, removed by the associated part handling systems,and placed in the proper orientation in sets of two onto waiting carriers.The third injection moulded part is a ring that, because of different mouldingcycles and cavitation, is produced on a moulding machine that is not coupledto the automation. These parts are stored in bulk in a bin. With the aidof a vibratory feeder, the rings are brought to the loading position inthe proper orientation. A part handling system takes them from there andclips them onto the waiting protective covers on the carriers.

After a short distance, which also serves as a buffer zone, a bridge-typeloading station removes the completed subassemblies from the two carriersand places them directly into trays holding 12 carriers each (Figure 3).Theempty stacking station holds 30 trays; the palletizing system itself hasspace for three full stacks of 10 trays each. With this design, the systemcan operate independently for 1 hour.

Loading of the station with empty trays and removal of the full traysis performed manually without stopping the system. At the production end,the trays serve as protection and packaging, while at the customer, Cerberus,they function as transport and staging element in its assembly line. Thetrays and associated containers circulate permanently between Ego and Cerberus.

Buffer Zones

Various buffer zones have been incorporated to assure a continuoussupply of components under all conditions, as well as uninterrupted productionof special orders even in the event of malfunctions involving the couplingelements to the assembly units (moulding machines, handling systems, etc.).This system allows, for instance, protective covers to be directed firstinto a buffer and then onto a conveyor in case of a malfunction or duringa production changeover. The buffer can accommodate approximately two hoursof production. With this higher level of integration and automation, operatorinvolvement was reduced by 70 percent.

At present, production operates three shifts per day for five days,corresponding to an annual production of about 2 million subassemblies.The customer orders subassemblies in lot sizes of up to 20,000 pieces perweek and expects the highest product quality and perfect optics.

Process monitoring, already incorporated into the moulding machinecontrol system, is employed to assure quality. A tolerance range is specifiedfor every parameter relevant to quality. If the upper or lower tolerancelimits are exceeded, the resulting moulded parts are removed by the handlingsystem. The component is not placed on a carrier, however, but rather ona conveyor belt from which it is removed for inspection. After being mouldedand before being placed on the carrier, the grille is directed to an inspectionstation where an optical testing system is installed. The handling systemcarries the part past this system, which automatically checks for a completeand defect-free wire mesh. In addition, a special sequence that initiatesdirect removal of one or more moulded parts can be triggered by an inspectorfor control shots.

Contact Information: Afag AG Mr. Thomas Ammann Fiechtenstraße32 CH-4950 Huttwil Switzerland Phone: (41) 62 959 8686 Fax: (41) 62 9598787