Displays & Interfaces
New Appliance Panel Decorating Solutions
January 3, 2013
The technical evolution of pad printing, thanks to advances in many areas, has gained by stepper motors that add even more capability.
Appliance manufacturers are constantly looking for ways to design and manufacture their products so as to differentiate them from the competition. One of the most influential trends has been the dramatic change in the design of control panels used on newer appliances such as washing machines, dryers and dishwashers.
In the past, appliance panels were typically flat.
But in recent years, designers have gone to great lengths to incorporate more attractive curved surfaces into their panels with the aim of differentiating their products from those of competitors. To make matters more interesting, new panels often feature an assortment of multicolor graphics across their surfaces, and the panels may be as wide as the appliances on which they are mounted.
When curved and contoured panels emerged in Europe, the only available options for decorating them were to use in-mold decorating technology or turn to conventional pad-printing equipment. Neither option is ideal, especially considering that the same panel might be used on products sold in a dozen different countries with a dozen different language requirements, or under several different brand names, with and without specific options. For the decorator, this means the order isn’t really a single project, but a collection of short-run jobs.
Adding to the difficulty is the fact that many appliance OEMs demand just-in-time manufacturing on their orders. Under these circumstances, the make-ready required for in-mold decorating and the frequent press changeovers necessary with conventional pad-printing equipment simply aren’t practical.
But with the latest generation of pad-printing machinery, it is no longer necessary to perform multiple setups, use multiple machines or rely on inaccurate conveyors to move large-format parts through a multicolor pad-printing line. Today, pad presses are available that can print the entire length of large panels with as many as ten printing operations per cycle, with production rates of several hundred parts per hour. The secret behind this new level of performance is found in the stepper motor and the digital systems that drive it.
Since their inception in the mid-1980s, stepper motors have revolutionized the pad-printing industry in Europe. In basic terms, a stepper motor is a digitally controlled electric motor that doesn’t rotate continuously (like a servo motor), but moves in small increments or steps of a predetermined distance (measured in degrees).
A stepper motor can be programmed to travel specific distances at specific speeds. When applied to pad printing, stepper-motor technology allows the machines to precisely control the position (linear or rotational) and motion (speed, direction, delays, etc.) of parts along multiple independent axes.
In one example, the operator loads from the far left side of the linear indexer, so the part travels right/left along the Y axis via a linear indexer and in the R axis (rotation) via a rotary table, while the pads travel in/out along the X axis, and up/down along the Z axis. On such machines, the accuracy of the image placement in each axis can be +-0.05mm.
Before stepper motors, pad printing presses were either driven with simple pneumatic cylinders or electro-mechanical methods. Older presses might employ a mechanical stop or a limit switch, but they couldn’t move that stop or switch during a print run to vary the distance the machine moved in any particular direction. With a stepper motor, however, the operator can select the exact distances he or she needs the print head and part to travel in each axis and vary these distances over the course of the print run if necessary.
Additionally, with stepper motors, you can program in delays in each axis of motion, a necessity for obtaining maximum print quality in pad printing.
Another, much slower solution for pad printing appliance panels is to pick up and then print one image at a time, using a multiple-axis robot. In this scenario the transfer pad essentially acts like “end of arm” tooling, with the cycle time being anywhere from two to three times as long.
Benefits of Stepper Motor Technology
The programmability of stepper motor driven machines means better process control, and, in many multicolor industrial applications, a faster and less expensive alternative to in-mold decorating.
Earlier this year the author was involved in a Whirlpool project that required six different versions each of washer and dryer control panels to be pad printed with six or seven operations each. Two different molding companies were tasked with molding, pad printing and assembling over 1.4 million units annually. Instead of decorating with in-mold labels, Whirlpool elected to pad print directly, saving an average of about 60 percent on decorating costs, which was equivalent to about 26 percent of the total part cost including material, molding, decorating and assembly.
The switch to pad printing also enabled the molders to “print to order” all of the various versions of panels and graphics using only two large, stepper motor driven, pad printing systems from TOSH.
Other Benefits of Stepper-motor Driven Pad Printing Systems
Besides supporting a broad range of part-conveyance accessories and motion sequences, pad presses driven with stepper motors also allow users to employ combinations of varying ink cup diameters, and the corresponding cliché dimensions, in a single setup. The first image might be very small, requiring only a 90mm (diameter) ink cup, whereas another image in the sequence may be 115, 130, 160mm (or even larger) ink cup. This feature minimizes costs for ink and additives, and in some cases, reduces cycle times by shortening doctoring stroke distances.
What about registration?
Most stepper-motor pad-printing machines come with prepress equipment specifically designed to “preregister” films to clichés before they are exposed with the image. Typically, polymer clichés are used that are pre-punched with holes that correspond to pin-registration systems. The films are then aligned and punched with registration holes so that they align precisely where they’re needed on the clichés. The machine components driven by stepper motors generally maintain tolerances of ± 0.01 mm.
To reduce changeover times, presses like the one pictured have one large cliché platform that can accommodate all of the clichés and ink cups on a pin registered system. The beauty of this is that all of the clichés and ink cups can be removed at once, as a set. By having spare cliché platforms and accessories available, changeover times of 10-15 minutes can be obtained, even for applications that involve as many as ten printing operations.
Labor reduction is a key justification for adopting stepper-driven pad presses. These labor savings are realized primarily by interfacing the machines with other elements of an automated production line. Because they are stepper-motor driven, the pad presses can be easily connected with the programmable logic controllers and computers that drive other systems, creating an integrated manufacturing system that be controlled through one operator interface.
Stepper-motor technology also allows machines and part-conveying accessories to be easily integrated with non-print-related automation. Picture a part-handling robot and a stepper pad-printing system configured with a plastic-molding machine. When the mold opens, the robot rapidly removes two bezels that were just formed, placing the parts, one at a time, on a rotary table. The table indexes to print the first bezel, then again to print the second. While the second is being printed, the first is being dried with a hot-air dryer that is also integrated with the system. As the parts leave the dryer, the robot picks them up and deposits them in a package, which is sealed and whisked off by a conveyor to the shipping department. By eliminating several material handling steps, several machines working together can mold, convey, print, dry, assemble and pack more bezels than a team of human workers using conventional production methods.
The Future is Now
Orchestrated by the programmable logic system, the motions of a stepper-motor press are fantastic to see, and the speed at which complex printing jobs can be processed becomes instantly apparent. This author’s first exposure to this technology occurred at a trade show in Milan, Italy, a dozen years ago, watching in fascination as a stepper-driven pad press printed toy train cars on five sides using a combination of different part conveying accessories. While clearly built for industrial applications, the solution was so elegant that it was like watching a pad printing ballet.
The technical evolution of pad printing from a labor-intensive specialty printing process to an automated industrial decoration method has been made possible by advances in many areas, from computer-based filmmaking and photopolymer clichés to self-regulating inking systems and digital controls. The introduction of pad presses driven by stepper motors adds even more capability to a process already sought out for its versatility. With this technology, industrial printers can provide an efficient and accurate decorating method that supports both high-volume, high-speed production and short-run, just-in-time applications.