MACHINERY AND EQUIPMENT: Possibilities abound for automated finishing equipment
As the accuracy and precision of assembly and decorating equipment continues to improve, the possible combinations for in-line, automated post-molding operations multiply.
February 1, 2002 by Cindy Macdonald, associate editor
Seldom is part ejection the final step before shipping at injection molding or blow molding plants these days. More likely some assembly or decorating function will occur at the processor’s plant. Canadian Plastics’ 2002 Injection Molders Survey reported that almost 50% of respondents perform printing and decorating, while 35% are equipped for welding and bonding.
Post-molding operations such as assembly, printing and testing are frequently being combined in multi-purpose automated units as processors adapt to the market-driven ethos “do more for less.”
Cassco Machines president Ken Thuro notes that “We have seen our customers turning more and more to in-line automation in an effort to remain competitive and keep a step ahead of their competitors. Press side automation can often be as simple as the addition of a basic machine beside the molding machine, and can have surprisingly short payback times.”
There are a wide range of processes for assembly, testing and decorating that can be integrated and automated at press-side. Cassco, for example, has installed in-line with the molding press one system that combines multi-color hot stamping with hot-melt glue application and assembly. Another installation, which prints engine covers at press-side, incorporates a sliding table so that the parts can be loaded by the molding machine’s robot.
Thuro notes that hot stamp and heat transfer processes lend themselves well to automated processes, because they can require little attention and can run 24 hours/day without needing skilled personnel to monitor ink viscosity and density, as may be the case for pad printing.
Other processes that were formerly performed by hand — laser marking, laser trimming, heat staking, and others — can also now be automated, he adds.
For pad printing, the development of sealed ink cups and viscosity monitoring has greatly facilitated the incorporation of this printing process into automated lines. A European machinery manufacturer, Madag, has patented the Viscomat 100, which allows for automatic correction of ink viscosity and automatic mixing of ink. Viscomat was specifically developed for use in plants where factors influencing ink viscosity change continuously, but where uninterrupted production runs are required. If viscosity varies outside a preset range, solvent is automatically added to bring the ink back to proper viscosity. The Viscomat is mounted directly in the cup to allow for easy clean-up and color changeover. For multicolor operations, each cup has its own Viscomat.
Madag also offers single and multi-head pad printing machines. The Sigma model offers up to five color printing and cycles at up to 1600 parts/hr.
Even off-the-shelf systems do it all
MOSS produces an in-line silk-screen printing system for blow molders that can automatically sort and unscramble bottles, load them, flame treat and de-ionize prior to printing. The Model MS 1050 then prints the bottles, dries the ink using UV curing, unloads and stands up the bottles. It prints in up to eight colors. It is suitable for oval or cylindrical plastic bottles, and has a maximum output of 6000 pieces/hr when printing four colors.
For the expanding optical media category (CD and DVD production), Graphics International Group has develped the Canadisc 5055 five color screen printer. It incorporates a high-precision index table with 25 stations and programmed vacuum hold-down. Print accuracy is said to be less than +/- 0.05 mm. UV lamps are positioned after every print head. Servo driven squeegee drives and adjustable squeegee angle provide superior print quality.
Assembly systems more accurate, flexible
A high-powered 30 kHz welding system from Dukane is paired with the company’s Dynamic Process Controller (DPC) to offer digital amplitude control and a multi-tasking operating system. In its Level IV DPC model, the controller provides digital amplitude control in 1% increments. The operating system allows simultaneous control of process parameters, and primary and secondary control functions to reduce rejects and increase part consistency. The 30 kHz system is suitable for applications that require higher amplitude and power than 40 kHz systems, but are too delicate for larger 20 kHz systems.
Branson Ultrasonics’ SWServo2 spin welder is suitable for either manual or automated assembly. The unit has Angular Spin capability — a reciprocating angular motion — which allows parts to be welded that may have wires or other attachments that cannot be freely rotated. On the SWServo 2 model, servos control both the spin and actuator downstroke, creating a high-precision system. A free-standing operator interface allows the following adjustments: revolutions per minute, revolutions per cycle, hold time. The controller monitors RPM, revolutions per cycle and motor torque for quality control reporting.
Using a rotary indexing table, Plastic Assembly Systems’ Solutions Series .50IASR thermal assembly system provides increased productivity compared with traditional single-load heat staking equipment. The indexing table allows for part inspection, additional part loading and auto eject stations.
The .50IASR has a modular power supply and an operator interface panel that permits easy modification of machine programming. The system has true closed-loop control with process alarms for final assembly distance, overall process time, and machine tooling temperature. It also has multiple program memory storage.