Many fabricators are discovering the benefits of robotic welding in areas they never before suspected. In fact, more and more job shops, small businesses and large manufacturers are finding enormous productivity gains moving to welding automation in previously ignored applications.
While robotics was once considered a means exclusively for mass production, companies such as Crown Equipment Corp. have dispelled that myth and continue to find substantial gains welding as few as one unit for a variety of separate parts using automation.
Crown manufactures electric lift trucks worldwide as high as 45 feet to assist in a variety of material handling and manufacturing applications. The company’s trucks are used to transport materials and goods in warehouses, distribution centers and manufacturing facilities.
In a unique production model, the company produces nearly 85% of all its truck parts within the company. Each part is often made in small quantities — as few as one to twenty at a time, to meet real-time demand on the assembly line.
For years, however, the Greencastle, Ind. location had manually welded more than 1,500 miscellaneous parts in nine welding stations using MIG processes, along with the welding of the frame of four different models of lift trucks. Five years ago the company began reevaluating that strategy.
Crown chooses Lincoln Electric
A Crown manufacturing engineering team began looking into automation. The first step was to ask for an automation survey of Crown, its parts and its processes by a team composed of Crown personnel and experts from the welding and robotic industry. As a result, Crown invited Fanuc Robotics, The Lincoln Electric Company and several other automation and welding companies to review their operations.
The invited companies performed a two-day review of Crown’s complete welding operations and procedures, both manual and robotic. They discovered hundreds of parts could in fact be welded better, faster and more consistently with robots, despite the small unit quantities. Moreover, the data showed Crown that the investment would pay for itself in a matter of months.
Lincoln Electric tested its assessment in its Cleveland headquarter laboratories and presented Crown with the final results. Crown engineers took those findings to its senior management team and purchased the first of three Fanuc Robotics robots and Lincoln Electric welding cells, all powered by Lincoln Electric Power Wave 455M power sources with Super Arc L-56 MIG wire.
The welding and material handling process
But the changes didn’t stop there. Crown engineers, using a universal mounting and fixture plate system, started building dozens of robotic welding fixtures for the new welding cells. They were all built on common fixture plates that matched up with the locating pins on the frames and tables in the robotic weld cells for easy installation and removal. This allowed every welding fixture the ability to be quickly changed in and out as needed or moved from one robotic weld cell to the other.[pullquote]
They found that the average fixture change-out time was about five minutes, using the new universal plates and pinpoints. Crown put the new system to work on parts identified by the survey for immediate cost savings, such as motor mounts, cross braces, brake pedals, carriages, latch plates, light brackets and battery retainers.
Overcoming the material handling issues involving all of the parts and fixtures entering and leaving the cells was a key to success of this automation project. Crown utilized its own material handling expertise to tackle this problem. The solution was the design and installation of a system of 20-foot-high industrial racking and fixture storage shelving. Fixtures and parts to be welded on the robotic weld cells are stored on the new racks, often weighing several hundred pounds each.
As needed, the fixtures and parts are retrieved from the shelves with a Crown TSP lift truck and placed in a short-term staging area for installation and use as soon as a robotic cell becomes available. Crown designed the TSP 6000 Series Turret Stockpicker to maximize cube utilization navigating very-narrow aisles. The TSP 6000 is equipped with features setting new standards in operator comfort and confidence. Productivity is enhanced through blending. Crown’s exclusive multi-task controls allow the TSP 6000 operator to blend multiple load handling tasks simultaneously. In addition, Crown incorporated ergonomic features such as its MoveControlTM seat that swivels to four different positions, a revolutionary platform design, multi-task controls and adjustable, cushioned armrests.
The TSP 6000 Series is a man up lift truck. The features allow operators to pick, transport and move items as necessary. Its three-point design offers tight turning radiuses and powerful AC lift and traction motors provides industry-leading travel speeds — 25% faster than typical trucks — with smooth and precise acceleration. The main lift speeds are more than 40% faster than industry standards.
The TSP works well in applications utilizing very-narrow aisles. The method Crown put in place in Greencastle reduces downtime and minimizes the amount of time for an operator to locate a fixture and parts. Once a fixture is changed, the same people who arrange and coordinate the fixtures in and out of the welding area return the previously used ones to their assigned storage area on the shelves using the TSP lift truck. Another benefit of this material handling solution was the physical floor space savings realized by utilizing the high density storage racking.
As soon as a new fixture is installed into the welding cell, an operator calls up the stored programming code for the part to be welded by entering a three digit code using a thumbwheel switch on the operator panel of the robotic weld cell. This automatically loads the stored program into the robot’s teach pendent that corresponds to that specific fixture. From there, the operator loads and unloads component parts for as many times as welded parts are needed.
Fanuc Robotics robots and Lincoln Electric power sources interface with each other so that operators need only enter one code into the robot. This stored code retrieves all the previously programmed instructions for both the robot and power source for that part, including travel path, travel speed and arc characteristics, such as constant voltage or pulse-on-pulse.
The programs can even be designed to change arc characteristics within a single program. For instance, the robot and power source can instantly switch to pulse-on-pulse process when the arm shifts to a vertical weld. When the arm swings back to a horizontal weld, the power source can instantly change back to constant voltage.
This is one reason that despite the small unit production, robotic welding has helped Crown’s overall process.
Crown reports dramatic improvement in productivity — by a factor of at least three or four. Welds are more consistent and are overall better in quality. Crown performs destructive testing on the first run of each part and periodically there after, and the improved quality is clear.
According to Crown, the robot’s speed outperforms manual welding so well that it overcomes downtime associated with automation, even when producing a single unit. The new fixtures have been designed to eliminate the need for tack welding previously used in their manual operations, providing additional timesavings.
Companies such as Lincoln Electric and Fanuc Robotics routinely perform free welding evaluations for companies to determine a variety of needs. The process can increase productivity and in some cases, even improve the quality of the finished product without spending a dime.
The survey begins when robotic welding specialists audit operations and first identify immediate opportunities for cost savings and productivity gains. If automation is seen as a viable option, Lincoln Electric can actually simulate a specific automated welding process in its Cleveland laboratories and determine realistic costs savings in each case.
“Customers really appreciate seeing their parts welded first-hand. It allows production personnel to see how a proposed welding process performs with actual travel speeds and cycle times — and how forgiving a process might be for expected gaps, fixture tolerance, or if improvement in component part fit-up is needed to make the application a successful one,” said Geoff Lipnevicius, Automation Manager for Lincoln Electric. “This gives companies a sense of expected productivity gains in an effort to avoid any surprises after the purchase. It also allows the finance committee, prior to the commitment of an investment, to make an informed decision with real data to insert into payback or return on investment (ROI) calculations.”
For Crown, the first robot, a Lincoln Electric System 30, paid for itself in just four months. The second cell, a Lincoln Electric System 30HS, paid for itself in nine months. Both of these successes resulted in the company looking to add more automation, and a Lincoln Electric System 50HP has recently been purchase and installed. The automation survey provided Crown with a sense of due diligence and an independent assessment, which its engineers could provide to senior management to support their own estimates.
Throughout Crown’s survey, Lincoln Electric, Fanuc Robotics and Crown identified other production issues, such as bottlenecks and weld quality. Fixtures previously used in manual welding were not centralized, and in some cases, were located off site.
Today, the robotic fixtures are mostly built on standardized 24- by 36-inch plates or 30- by 54-inch plates, which are stored in assigned locations and listed in the work order packets used for production. The programs are catalogued and maintained in a spreadsheet and posted at each cell. This allows very quick changes of fixtures and programs.
Robotic welds tackle a variety of Crown’s work on carbon steel in thicknesses ranging from 16 gauge to ¾ inch. Crown uses Lincoln Electric Super Arc L-56 wire in .035 and .045 diameters. Raw plate steel first enters the plant, where it is laser cut, formed, machined and, in many cases, welded into the final part. From there, it is painted and sent to assembly for final installment.
Parts production had been slower before automation, but organizing the entire process accomplished several improvements. Crown first organized the production process overall, as well as precise procedures for each part. It reduced the space of the welding area, organized the fixtures for easy retrieval and dramatically increased product flow to assembly.
Return on investment
The average welding time of each part dropped from five to ten minutes down to two to three minutes. The Lincoln Electric robotic cells are a System 30, a System 30HS and a System 50HP. All are dual station cells, which allow the robotic arms to alternate between two work areas.
As work is replaced on one side, the robot welds on the other and vice-versa. The operator simply replaces finished product with the component parts to be welded next. In doing so, the robot is always kept in motion resulting in total time savings of nearly 80%.
This newfound productivity has allowed Crown to begin new production in the Indiana facility without a significant impact on employment.
“Lincoln Electric and Fanuc Robotics really helped us realize this change, and it was their experience finding these kinds of opportunities and making them work, along with the equipment design and integration, that ultimately resulted in Crown choosing Lincoln Electric and Fanuc,” said David Besser, Crown Senior Vice President of Manufacturing. “And quite frankly we have not had a single equipment failure with any of these products. We are very pleased with all the results.”