A tale of two paintshops05 May 2017 | Mike Farish
A major new double paintshop project is under way at Bowling Green which GM say will achieve unprecedented levels of first time quality and throughput
By any standards $439m represents a significant investment. Even more so when the money goes towards the construction of an automotive painting installation covering a little over 500,000 sq.ft (46,451 sq.m) that will, initially at least, process only 40,000 vehicles a year. Nevertheless, that is the amount of money involved and the projected output for the new paintshop that GM is currently running up towards the start of operations at its Bowling Green plant in Kentucky, US, where it produces its high-end Chevrolet Corvette sports cars and ‘super cars’.
The observation above is made Kai Spande, plant manager at Bowling Green and the individual with the responsibility for ensuring the investment pays off. Spande also confirms that the last week of March saw a significant milestone in the commissioning process with the first trial spraying of “two panel sets” in the facility. He explains that a distinctive feature of Corvette painting is that it is a “panel off” process in which the carbon fibre and sheet moulding compound (SMC) panels for the vehicle are painted separately before being mated with the aluminium body structure. The bonnet and roof, he adds, are made from carbon fibre with all of the other panels in SMC, apart from the front and rear fascias which are injection moulded.
New generation of paintshops
Despite that achievement the company is still left with a lot of further process development before it can transfer over to the new facility all ten colours currently applied in the existing old paintshop that has been operational on the site for over three decades. Indeed, says Spande, that facility is at the moment “the oldest operational GM paintshop in North America”. But, he adds, during its lifetime the vehicle has gone through “four generations” of its own, and given that GM cannot countenance any interruption to vehicle production, retrofitting the old paintshop to meet today’s requirements was not feasible.
In technical terms, a major feature of the new paintshop will be how it extends the low-temperature curing of painted panels that is already a hallmark of the process. Indeed, states Spande, it “will break new ground” in that respect. Specifically, whereas the old facility carried out curing at 265°F the goal for the new one will be to carry out the same procedure “at 225°F or maybe less”. But, Spande stresses, the same panels will be involved and there will be no detriment to the paint finish quality perceived by customers. Indeed, he says, lowering the temperature at which curing takes place is “inherently good” for both the substrates and the paint materials themselves.
However, there will be some difference in the actual “paint formulation”, which will be altered slightly to suit it to the lower temperature process. In addition, both the physical length of the ovens in which the curing is carried out and the time the panels spend in them will be noticeably extended. On the latter count Spande says that the curing time in the old facility is currently around 90 minutes and that in the new facility this might well be extended by “around 25%” though until intensive validation has been carried out that remains an estimate.
The actual painting process for the panels remains one that utilises GM’s ‘three-wet’ process in which primer, basecoat and clearcoat are applied wet-on-wet without full-scale oven drying in between coats. It will also continue to use water-based materials. But, Spande says, there have been some significant enhancements in other respects. The new paintshop will now use “state-of-the-art” bell applicator technology, robotic controls and paint colour changeover techniques. He also points out that, as non-metallic materials are being painted, there is no opportunity to use electrostatic charging technology to help enhance adhesion and so mitigate wastage.
The fact that the facility handles both metallic and non-metallic parts – in the first case the vehicle body structures and in the second the panels – means that it has “two distinct material flows”. But though the technologies supporting the second of those have been enhanced, the first of them is, Spande confirms, a precise replication of the existing e-coating process – the most distinctive feature of which is that it gives the aluminium a black rather than traditional light metallic appearance. But one thing both flows will share in the new paintshop is the enhanced standard of environmental control, which means that the whole facility, rather than just segregated paintbooths, will meet the same standards of air purity, humidity and temperature.
Spande is emphatic on the matter. “The whole paintshop is cleanroom,” he states. This means that there will be just one combined entrance and exit to the facility for personnel who work there. Moreover, as Spande observes, once they are in the facility and “have gone through the airwash, walked across tacky paper and donned their lint-free suits” that it will then “be their environment and is where they will stay for the day.” Once it is up and running, the facility will employ 125 “hourly paid” shopfloor personnel per shift with a few extra “salaried” technical staff as well.
It also means that the secondary structures that enclose the actual painting booths play no role in ensuring air quality at the point of application. Instead, says Spande, their role is to control overspray in the first step in an aspect of the facility’s operations in which it genuinely does set a new benchmark for the company in its home continent. This is that the paint booths use a ‘dry scrubbing’ process to capture and remove paint overspray from air that has passed through them. In fact, Spande confirms, the new Corvette painting line at Bowling Green “will be the first General Motors’ facility in North America to use dry scrubbing,” though he does say that the company already uses the technique at a couple of its plants in China.
“We owe it to our customers when they buy a $140,000 sports car that they should get a quality paint finish” – Kai Spande, GM Bowling Green
Spande is absolutely explicit, though, that all this will have to help GM Bowling Green achieve “unprecedented levels of first time quality and throughput”. The reason for that is a dramatic reconfiguration in the way the paintshop will interact with the downstream assembly process – specifically in a drastic reduction in the buffer store between the two sets of operations.
Standard GM practice, Spande says, is to have “giant storage facilities for fully painted body systems”. But what works in a volume car environment is not suitable for Corvette production, in which the plant works to a “three-week window of sequenced body structures” and also only makes “12 vehicles per hour”. As such, the plant previously worked with what in GM terms was, therefore, still a fairly stringent buffer of 12 hours worth of parts between painting and assembly. But in the new set-up the safety margin will be barely one sixth of that – “less than two hours of painted parts”. That is, he observes, “a very lean operation” which, in turn, means quite simply that in the new regime “we will not be able to withstand downtime of more than a couple of hours.”
Right now, though, the emphasis is on completing the commissioning process and transferring operations over from the old facility. On those counts Spande says that the immediate aim is to have the new paintshop applying “four or five colours by the Fall of this year”. The remaining colours should follow within another six months, enabling the old facility to be shut down completely. Interestingly, Spande adds that for the new facility “we are also working on some things that are not mainstream,” though for the moment he will say no more.
Nevertheless, it is clear that GM’s ambitions for the new facility are considerable. As Spande confirms the objectives include “a significant improvement in the exterior paint quality of the cars and a much higher level of uptime to cope with the inventory reductions”. Moreover, the whole project is “predicated on an idea of asset sustainability and a total enterprise cost solution”. The bottom line though is that “we owe it to our customers when they buy a $140,000 sports car that they should get a quality paint finish.”
A new paintshop for Flint
At the GM Flint Assembly truck plant in Flint, Michigan, a new paintshop has been operational for a year, confirms paintshop area manager Craig Jones. As at Bowling Green, the new Flint facility has been constructed to replace a previous installation that was finally shut down in October last year after a six-month transition period. In fact, says Jones, that former facility dated back to the 1940s and was far from even approximating to the cleanroom standards GM now sets for its paint installations. “More than half of it was open to the air,” he reports. In contrast, the new paintshop, which represents an investment of some $600m, is “a completely enclosed cleanroom from end to end with all the latest technology.”
Jones says that the facility was actually designed with the next generation of GM trucks in mind, but that though they are not due to start production until a modernisation of the assembly areas is completed in 2019, the decision was taken to get the new installation into operation in any case. At the moment, therefore, the facility is processing GM’s established K2xx heavy-duty truck range at a rate of 32 vehicles per hour, though, Jones adds, its maximum projected throughput can be as high as 47 vehicles per hour.
As Jones also confirms, in the old set-up the process used a solvent-borne primer and basecoat that were finished off with a solvent-borne 1k clearcoat. But in the new set-up GM has replaced the previous primer and basecoats with water-borne counterparts, while the clearcoat remains solvent-borne in this case of a 2k formulation. That latter, says Jones, is harder than before and provides for enhanced visual quality.
Moreover there has also been a significant procedural change. As Jones explains, in the old facility there was an inspection and possible manual remediation stage as well as an oven-bake in between the application of the primer and basecoat. This has now been completely obviated and the process is now a continuous three-wet operation. Immediate consequential benefits, he reports, include reductions in both energy consumption and sludge generation, though overspray control remains a water-based not a ‘dry’ process.
Jones notes that the configuration of the paint booths is now “longer and narrower” than previously, to provide for better “balance and transfer efficiency” within them. The facility also contains two parallel booths in contrast to the single booth used previously – a change that both facilitates the increased throughput potential and enables work to continue should either booth become inoperable. But outside the booths, in the areas where people actually work, the opportunity has been taken to implement best practice in the techniques of ‘visual management’ that GM is now seeking to make routine in all its plants.
One visual aspect of the facility that no-one can miss is a sheet metal partition wall that demarcates the operational area where people work and painting processes take place, from one that contains most of the storage tanks and process equipment such as that for phosphating. The reason, though, is not to stop people wandering into unauthorised spaces but to increase the effectiveness of internal air recirculation. As Jones explains, the air within the paintshop is recirculated from two to four times, but when it first enters the facility it does so in the operational area “where the people are” after which it is “cascaded back” into the areas that are normally people-free. That means that the comfort of those working in the first area is unaffected either by the temperature increase of the air generated by its contact with equipment or by any fumes it may pick up. On the first of those counts Jones estimates, for instance, that the air temperature on the far side of the partition from the personnel in the facility is “five to ten degrees higher” than when it first enters. The paint booths themselves, of course, are on the people side but are enclosed in the normal fashion in order to minimise their effect on the surrounding environment.
Lower energy use – higher morale
After a year of operation Jones says that GM now has several sets of benchmark figures to demonstrate the efficiency of the new facility. Perhaps the most basic is an improvement in energy consumption per vehicle that passes through it of 0.6MW. Throughput potential, though currently not being exploited to its limit, is also over 50% greater than previously since the maximum number of vehicles per hour the old facility could manage was just 30.
Getting to that position is not necessarily quick. Jones estimates that it takes at least six months for people to get used to a new working environment and adds that the changeover is particularly challenging for the technical and maintenance staff dealing with the greatly enhanced level of technological sophistication – not least the more than 100 state-of-the-art robots. But a difference that is evident everyday to Jones, who held the same position in the old facility as he does in the new one, and can therefore make the comparison, is just in the way the people now set about their work. “They are tremendously more involved and happier,” he states. “Morale has improved, output has improved. We had good quality in the old shop but the new one just blows away the old one.”