You have no idea how much robots can do
By Cindy Macdonald
Despite a drastic drop in injection molding machine sales during the last 3 years, and a corresponding dip in the overall auxiliary equipment market, automation sales actually have shown an increase d...
Despite a drastic drop in injection molding machine sales during the last 3 years, and a corresponding dip in the overall auxiliary equipment market, automation sales actually have shown an increase during the same period, according to auxiliary equipment manufacturer Conair. Jim Healy, Conair’s vice-president automation sales, says he expects robots will continue to lead other equipment sectors. That’s largely due to the fact that an investment in automation usually has a significant impact on overall competitiveness.
“Over the last few years, North American molders have struggled mightily to cut costs in almost every area of their operation,” Healy notes, “and there is precious little left to cut in areas other than labor costs. Even when robots take care of part picking and machines run automatically, there are usually labor-intensive downstream functions like cavity separation, assembly, finishing, inspection, palletizing, packing, etc., that can still be automated. I think that’s at least part of the reason for the increased interest in automation in recent years.”
Troy Smale, robotics sales engineer with machinery supplier En-plas Inc., agrees. “Automation is one of the only key strategic options left available for Canadian molders. In addition to part extraction operations, molders must also start considering post-molding handling, such as packaging.” En-plas represents Yushin linear robots and Motoman articulated units.
In broad terms, the possible functions for robots in the plastics industry include: machine tending (loading inserts, part removal, sprue cutting, part placement); finishing operations (cutting, trimming, routing); painting and surface treatment; assembly (gluing, dispensing, welding); packaging (individually or controlled placement in a container).
Yvon Millard of automation integrator Axium feels robots are not deployed frequently enough in the plastics industry. “People just don’t realize what robots could do for their plants.”
The basic goal of robotics is to boost productivity and reduce variable overhead, explains En-plas’ Smale. “Robotics allow this to occur by increasing the speed of product removal and reducing labor that is associated with value-added operations, as well as reducing scrap and improving part quality by imposing consistency on the process.”
THREE AXES VS. SIX
Suppliers of articulated robots say their product is making inroads in the mid-tonnage range of injection molding machines. It is generally accepted that linear robots are more cost-effective for smaller machines and small parts. At the other extreme, large parts with long molding cycles and post-molding operations are often better suited to articulated robots. In the middle, linear robots are the traditional option for machine tending functions. However, as molders seek more functionality and the price differential between a linear robot with complex EOAT and an articulated robot decreases, “six-axis units are moving down to where linear used to play,” says Doug Niebruegge of ABB, a supplier or articulated robots.
“When you live in the world of linear robots, you have no idea what six-axis can do. It’s a different paradigm,” he adds.
Joe Campbell, director of strategic alliances with six-axis robot supplier KUKA Robotics, estimates the price of an articulated robot for a mid-tonnage IMM would be about US$50,000 to US$60,000, while one linear robot manufacturer estimates that a servo-driven linear robot would typically start at about US$40,000.
Although they may compete for work in some scenarios, often linear and articulated robots are viewed as complementary partners.
“Articulated robots can complement linear robots,” says Joe Calomino, product manager for Tracer robots with Husky Injection Molding Systems Ltd., which produces linear robots for use with its own injection molding machines, and for individual sale. “A linear robot mounted in-line to hand off parts to an articulated robot behind the clamp can optimize cycle time, flexibility and floor space.”
At Nucon Wittmann Inc., a supplier of linear robots and auxiliary equipment, Wittmann product manager Christian Weiss says linear units can go beyond mere part removal functions. “We are seeing robots used for much more than machine tending. Adding AC servo motion of the “wrist” (at the end of the vertical arm) is like adding a hand,” says Weiss. “It allows us to position parts for different actions, perform side sweeps, and even do complex motions for degating. It can perform multiple actions at once, and the flexibility is tremendous.”
He asserts that six-axis robots require more floor space, and that safety considerations often require them to enter the mold from the non-operator side of the machine.
In addition to a higher price tag, Joe Campbell at KUKA believes the perception that six-axis robots were too complicated to program used to scare people off. Manufacturers have addressed that by incorporating icon-based programming, pendant-style controls and off-line PC-based simulation. “Now we’re getting good feedback from our customers that a six-axis robot is different from a three-axis, but no more complicated,” says Campbell.
CUSTOM MOLDERS RECOGNIZING THE VALUE
While some may argue that short runs and frequent product changes make custom molding unsuitable to automation, Campbell says these realities actually make a strong case in favor of flexible automation, such as an articulated robots. “In custom molding, they want rapid changeover. That class of molders needs as much flexibility as they can get.”
As well, custom molders are realizing that the payback for a robot might not be associated with just one part, says Nucon Wittmann’s Weiss.
Falling prices are also contributing to increased robot sales. For example, Wittmann’s latest robots are priced about 20% less than their predecessor.
Campbell says most manufacturers are moving toward more sophisticated financial analyses to assess automation projects, such as utilization of assets benchmarks and return-on-investment.
“Payback period may be the first test, but generally a project has gone through a more thorough analysis by the financial department before it gets approved.”
POSSIBILITIES ARE ENDLESS
As the plastics industry adopts automation, innovations in robotics continue to broaden the range of possibilities. For example, both KUKA and ABB have simplified the process whereby multiple robots can work cooperatively as a team. This means several robots could hold and manipulate a large panel-shaped product while another robot performs functions on it, such as applying adhesive or trimming. In ABB’s cooperative scenario, a single controller can control up to four robots, which minimizes the investment for this type of installation. In KUKA’s RoboTeam, all events that influence the motion characteristics immediately affect the entire group, which results in precise geometric coordination and synchronization of sequences within the group.
Another interesting development from ABB is called CaviGrip. The concept uses an EOAT shaped like the mold cavity, so that the part can be removed from the mold before it is completely cooled. The part is affixed to the EOAT with high vacuum. Additional cooling occurs outside of the mold, assisted by cooling lines in the EOAT. This technique has shortened cycle time by as much as 25% in some cases.
To paraphrase Niebruegge, you have no idea what automation can do.
Automated part removal almost eliminates scrap
Quality Safety Systems (Tecumseh, ON) has automated six of its fifty injection molding machines in an effort to improve efficiency, quality and competitiveness. According to Ashish Brahmbhatt, chief engineer, the company had five operators servicing those machines and, since automating them four years ago, has been able to run with three operators.
At the same time, QSS wanted to reduce the amount of sc
rap resulting from the scratches and dents that occurred when parts were allowed to drop from the mold onto a conveyor. By automating part removal using Conair Sepro beam robots and a QSS-made robot, the scrap rate has been cut from about 10% to just 0.2%, Brahmbhatt says.
Sometimes, Brahmbhatt concedes, cycle times are a second or two longer than before the machines were automated, but the more consistent cycle time results in benefits such as improved part quality and smoother production. By eliminating human error, automation also helps ensure the QSS assembly department receives only good parts. Since the products QSS makes are safety-related, it is imperative that only good parts get shipped to customers.
In one molding cell, QSS and Conair created a system that handles multiple operations in the production of automotive seat-belt slip-tongues. These are over-molded metal stampings that slip into the seat-belt clasp to secure the belt around the driver or passenger. Conair supplied a Fanuc M-16iB six-axis robot, two rotary tables, cell guarding and conveyors, while QSS toolmakers developed the end-of-arm tooling (EOAT) and insert nesting devices.
In this molding cell, the high-volume slip tongues are molded eight-up in a 300-ton horizontal-clamp injection molding machine. An operator outside the safety guarding loads inserts onto the two rotary tables, which transfer them to the robot. The production cycle begins as the EOAT on the end of the articulated Fanuc arm picks up four inserts from each of the two rotary tables and places them in a nesting fixture. The same tooling then rotates and picks up all eight inserts and transfers them into the mold, where they are held in place by magnets. The robot arm exits the clamp area and the parts are molded. In this cell, the parts are durable enough that they can be allowed to drop onto a soft conveyor belt before the next cycle begins. With lower labor costs, reduced scrap rates, and higher quality and productivity, Quality Safety Systems has found that automation can be a significant competitive advantage.
QSS is a Canadian subsidiary of Tokai Rika of Japan. The company employs 900 people in two plants in Ontario and is a major supplier of seatbelts in North America.
Flexible automation suits complicated assembly
An automotive manufacturer who needed a machine to weld plastic lens/reflector assemblies brought the challenge to Dukane after realizing the traditional approach wouldn’t work. The automaker’s initial idea would have resulted in a nine-headed welding unit that was difficult to align and limited to welding similar assemblies. In addition, it couldn’t be built due to size constraints and interference problems.
Dukane is a global supplier of ultrasonic, spin, laser, vibration and hot-plate welders. By incorporating a six-axis robotic arm in place of nine pneumatic thrusters, Dukane built the manufacturing cells in less time for slightly more money than conventional multi-head systems.
The welding arm is extremely agile yet accurate, and requires no modification for different subassemblies. The smart part-fixture determines whether the subassembly is a left or right hand unit, then selects the correct welding path and adjusts the welding pressure at each weld tab. The ultrasonic generator monitors the weld energy to ensure each value is within specifications.
The robotic welders provide much greater versatility since the only changes required for producing different assemblies are a new part fixture and a new weld-path parameters program.