Emerald Group Publishing Limited
Copyright © 2008, Emerald Group Publishing Limited
Jaguar installs servo guns for XF saloon
Jaguar installs servo guns for XF saloon
For the first time manufacturing engineers are using servo-controlled spot welding guns in a production Jaguar vehicle.
The servo-controlled guns, from Obara Corporation in Japan, were selected because it was impossible to access parts of the body-in-white (BIW) shell structure of the new XF luxury sports saloon using conventional bulky pneumatic spot welding guns.
Jaguar process engineers have installed the four servo guns across two Kawasaki robots to undertake some intricate welding. The welding was required due to the unusual styling features of the car.
At present, only four servo-controlled guns are in use in the XF BIW production line at Castle Bromwich. But, it is expected that both Jaguar and Land Rover could make greater use of these guns as new models are developed.
Job 1 (start of production or SOP) for the new Jaguar XF luxury sports saloon was set for November 26, 2007 with the aim of ramping up production of the new model to achieve a target output of 3,000 cars by the time deliveries began to customers in March 2008.
The XF, with its steel body shell, is assembled at the Castle Bromwich plant of Jaguar Cars in the West Midlands, UK. The XF is a replacement for the S type and, with executives bearing down on plant costs, both new and retained robots are used on the BIW lines.
Executives opted for the tried and tested Kawasaki robots that have performed well in S-type BIW manufacture. The principal line builder for the BIW facility was again Comau, the factory automation division of Fiat. However, ThyssenKrupp Drauz Nuthelfer built a new facility for producing closures.
Previously, to manufacture S-type body shells required some 120 robots. However, for the XF about 95 of these have been retained, boosted with a further 55 new robots, including 28 machines used in the manufacture of closures.
According to sources, servo- controlled guns offer other advantages besides accessibility. For example, although initially more expensive by some 25 percent than pneumatic guns, they can be paid for in six months' of operation thanks to energy savings alone – there is only one power supply, namely electricity.
Figures from Japan suggest that the cost of supplying air to a pneumatic servo gun is 0.001yen/spot weld. The cost of operating an electric servo gun is 0.0003yen/spot weld – a cost saving of two-thirds.
In a nutshell, the main gains are: reduced cycle time, thanks to minimum gun stroke for each step; reduced running costs because of reduced tip wear; improved factory environment due to reduced noise; and reduced fixture costs because of the “soft landing.” It is also claimed there is improved weld quality due to reduced spatter.
Over 1,000 servo-controlled spot welding guns are in use in the UK motor industry; 400 are in the plant of Toyota Motor Manufacturing at Burneston, Derbyshire, UK and a similar number are at Nissan Motor UK in Washington, on Tyneside. Honda at Swindon, also in the UK, is beginning to use servo-controlled spot welding guns. General Motors is also studying their use.
Toyota has used servo weld guns for over ten years and is working closely with Obara in the development of next-generation machines due in two or three years.
A typical transformer on a servo guns weighs in the region of 35kg; the aim is to reduce this to around 10kg. These lighter guns will enable process engineers to install lighter weight robots, typically moving down from a 180kg machine to a 160kg robot. These lighter weight robots are also cheaper. Kawasaki Robots and Nachi supply most of Toyota's robots in the UK.
In future, more widely available Obara guns will weigh 15kg.
Conventional pneumatic guns have an operating cylinder to provide the one-stop motion for spot welding. In the servo design, a servomotor connected directly to a driver unit replaces the cylinder, controlling speed, point pressure and stroke. The servo offers a more flexible approach to spot welding.
In addition to their energy-saving attributes, servo-controlled guns are much more precise in their operation. The servo does not punch the joint, but offers a soft touch for the last few millimetres of stroke before squeezing at the point of contact. This action brings a 50 percent saving in consumables.
Interestingly, Kawasaki holds a fundamental patent in controlling an integrated servo weld gun in one axis of the robot in synchronisation with other axes of the robot.
Meanwhile, Ford in the USA has used servo weld guns for the last two years but this is the first time they have been used by the company in the UK at Jaguar.
Jaguar engineers could extend their use of servo-controlled spot welding guns when they implement new cells for the upgrade of the XJ aluminium- intensive saloon, dubbed X351. Due in 2009, this will extend aluminium spot welding in place of self-piercing rivets.
Later, in 2010, when the new Mini Freelander appears at Halewood, Merseyside, UK there will be another opportunity to use servo guns.
However, the future of vehicle body process technology at Jaguar and Land Rover depends on the direction and requirements of their new owner – or owners.
Latest Mitsubishi robot installed in “High Tech Garden Shed”
Robotics and industrial automation are commonly associated with capital intensive, large volume manufacturing, high-speed repetitive processes and advanced products. Yet, Brass Products, a name redolent of traditional engineering and craftsmanship, employs a comprehensive level of automation at its three-man operation near Ashford, Kent. Furthermore, in what owner Duncan Rye describes as “the most high tech garden shed you'll find,” robotics specialist Barr & Paatz has just installed and commissioned one of the latest generation of Mitsubishi six-axis articulated robots for feeding a CNC milling machine, a previously tedious and potentially hazardous manual operation.
Developed specifically for handling low payloads up to 6kg and aimed particularly at small and medium scale enterprises, the Mitsubishi RV-6S has a precision repeatability of ^0.02mm and working speeds of up to 9,500mm/sec, enabling it to complete “the 12-in. test” in less than a second. Its slim, compact construction, space- saving robot controller and working radius of 695mm make this machine ideal for applications where there is restricted floorspace, such as Brass Products 193ft2 “shed.” Installed by Barr & Paatz around the turn of the year, it is has impressed Duncan Rye with its 100 percent reliability and ability to perform pick and place tasks perfectly, time and time again; so much so that, with a move to rather more spacious premises scheduled shortly, he is considering another longer-arm RV- 6SL (Figure 2), for operating in conjunction with a high-performance CNC drilling centre.
Figure 2 The Mitsubishi RV-6SL, one of their latest generation six-axis articulated robots
Brass nuts, machined and threaded from hexagonal bar stock, are loaded into a CNC milling machine by the Mitsubishi robot, which picks unfinished nuts individually from a tray, feeds them into the machine, then rotates them 608 at a time until every face has been skimmed to produce a high-surface finish, before being returned to the tray.
Barr & Paatz despatched its Senior Robot Engineer, Steve Gould, to Brass Products' premises in Kent, in order to study the application and make recommendations based on the required throughput and geometry of the available workspace. The extremely limited operating envelope and the need to replicate the motion of a human hand, dictated a six-axis robot configuration, with its rotating wrist joint and capacity to twist and tilt workpieces; taking into account the high-speed process, small installation footprint and modest payload, Barr & Paatz specified one of the newly available Mitsubishi RV Series robots, which has six degrees of freedom. Exploiting its engineering heritage, Brass Products itself sourced appropriate end of arm tooling and manufactured the gripper fingers that hold the brass nuts, while Barr & Paatz provided specialist on-site training.
Since, space is indeed at a premium, the parts tray currently holds only sufficient stock for a 30min work cycle, although the robot/machine combination still manages to produce a month's supply in just three days, adapting easily to different sized nuts (Figure 3). The lightweight robot is mounted on an overhead gantry and, between batches, is simply swung aside to allow routine machining work.
Figure 3 Modern robotics technology, in the shape of a Mitsubishi machine installed by Barr & Paatz, plays a role in the manufacture of Brass Products' traditional radiator valves
With spacious new 2,000ft2 premises already earmarked nearby, Duncan will soon have room to handle larger batches, with a consequent increase in throughput. An additional RV-6SL robot, with a working radius of 900mm, will then be teamed with the latest Robodrill, to facilitate a second fully unmanned machining system.