Automotive industry – standing on a new threshold of robot use?

Automotive industry – standing on a new threshold of robot use?

Automotive industry – standing on a new threshold of robot use?

John Mortimer is an engineering journalist, based in Milton Keynes, UK. He specializes in component design and automation in the automotive industry.

Keywords: Automotive industry, Robots, Automation, Welding, Aluminium

Nearly 50 years ago, in 1954, inventor George Devol took out a patent in the US for a programmed transfer device; Three years later, British inventor Cyril Kenward received a British patent for a programmable manipulator arm. Later, in 1961, Devol’s idea was issued in 1961 as US patent 2,988,237. This patent was to form the basis of the Unimate, the world’s first industrial robot. Since that fragile start, and the sale in 1960 of the first robot to Ford Motor Company for tending a die-casting machine, the industrial robot has blossomed, mainly in the US, Japan and Europe. In the US alone, half of the nation’s 118,000 robots are at work in the automotive industry – the single biggest robot user.

Indeed, the automotive industry has played a significant part in increasing the capabilities of the robot. Indeed, both have “grown up” together, the one helping the other. And if the robot has come of age, then so too has the automotive industry – which includes both cars and trucks. For hand-in-hand with the robot’s increasing maturity, the automotive industry has been transformed as design and manufacturing engineers work simultaneously towards lower costs and “design for manufacture”. Design now forms a part of manufacturing processes. New, higher standards of quality, reliability and durability have been achieved with advancing automation, while costs of manufacture has been reduced. Electronics and software have helped in the transition.

At the same time, the industrial robot has achieved new levels of accuracy, repeatability and dexterity, driven by increasing pressure from the automotive industry. In addition, the mean-time-between-failure (MTBF) of robots has fallen encouragingly. All of this would not have been possible without an exponential increase in computing power and software expertise. The robot is now just a common, but sophisticated tool.

Could Devol and Kenward have ever envisaged a scenario in which there is hardly a place on the automotive shop floor where robots are not used – from inspection, handling and assembly, through spot, arc and laser welding, to sealing, painting and glazing?

New phase

But the robotics industry and the motor industry are about to move into a new phase. In the search for lighter-weight vehicles on the back of agreements to cut greenhouse gases like carbon dioxide (CO₂), there are signs that steel will increasingly give way to aluminium, magnesium and composite materials in vehicle body construction. This is already having implications for industrial robots because these materials require “new” joining techniques. Laser welding is already coming into view.

This new experience in manufacture will soon be put to the test in a unique British automotive development in which robot automation, “new” materials and “new” joining techniques are brought face-to-face with one another. Jaguar Car’s new XJ saloon car (the X350) and its long-wheelbase counterpart (X350L), are the first medium- volume passenger cars with a unitary aluminium unibody. Because aluminium is difficult to spot weld, the new XJ uses over 3,300 self-piercing rivets (SPRs) per vehicle. The SPR does not require a pre-drilled hole – it merely pierces the sheets of material under high loading and locks firmly in place.

Audi, part of Volkswagen, broke the mould in 1994 with its A8, the world’s first aluminium spaceframe passenger car. Over 105,000 A8s have so far been produced. The A8 uses SPRs – but nothing like on the scale of the XJ.

Jaguar’s engineers did not want to take the same adventurous step as Audi, preferring instead to adopt the traditional unitary method of body construction with which there is so much experience with steel-bodied cars. The result is not such a “lean” design as might at first be expected. The ultimate lean design was to be Jaguar’s F-Type (X600) aluminium spaceframe sports car – but this has now been delayed. Nevertheless, the XJ is a step on the road to lighter weight vehicles – a step that many people round the world will be watching with interest.

To rivet this car requires nearly 150 electric servo guns with the rivets being fed to the guns on a tape. This technology has created new challenges for manufacturing engineers in terms of non-destructive joint monitoring, process control, software, robot programming and systems to share tool changing. Because an electric servo gun with tape feed typically can weigh anything between 40 kg and 200 kg at the robot wrist is clearly an important consideration. The maximum payload is clearly at the upper limit of a 200 kg payload robot – higher payloads and the riveter must be pedestal-mounted and the robot used to feed the panels in for riveting.

Servo gun design for robot use has yielded special C-frames to meet a number of difficult access points, whilst staying within the payload capacity constraints of the special Kawasaki robots. With throat sizes up to 850 mm, some of these C-frames can be large, demanding special lightweight construction. These lightweight frames have, in themselves, posed new challenges in terms of design, development and material selection to achieve the high stiffness/weight ratios required for alignment and positional accuracy. In addition to the electric servo guns attached to the Kawasaki robots, there are over 50 manual guns for operators to handle. Unlike the sparks from spot welding, riveting is more environmentally friendly.

Also representing part of the overall challenge is the mix of materials in the XJ body – aluminium sheet, aluminium castings, mild steel and stainless steel. To add to the process complexity, these materials are joined with and without adhesives – as required by design and operational considerations.

Adding to the complexity of the overall operation is the fact that at least 15 different types of rivet are required to meet strength and manufacturing considerations. For what makes joining by self-piercing riveting so special as a process is the fact that rivets can pierce multi-material joint stacks from as thin as 2 mm right up to 9 mm in thickness.

Overall, in a seemingly simple switch from steel to aluminium, many aspects of design and manufacturing engineering are affected. Significantly, on the wider scene, what is happening today at Jaguar in the UK has profound implications for other industries where robots and self-piercing rivets will be working more closely, hand-in-hand. Devol and Kenward would be proud to see the results.