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Industrial : Automotive drives screen to the limit
Automotive components call for a quality audit to end all quality audits
So what has The New Angel Restaurant in Dartmouth got to do with screen printing? I have to say it is becoming one of my haunts, fabulous food, excellent service, superb wine and situated in one of the most beautiful parts of this sceptered isle. No, I am not getting a free meal!
What you learn when eating at this establishment is the supreme process control required to achieve this gastronomic distinction. Twelve staff in the kitchen and a similar number out front. The works order arrives from the front of house and ‘The Gaffer’ John Burton Race speaks a few words of instructions to his team of chefs and within a few minutes plates appear on the serving shelf and the various chefs proceed to place the individual elements of the dishes on the plates with watch like precision.
Whilst this is happening the Gaffer is overseeing every spoonful and putting final garnishes onto the dish. The efficient front of house staff whisk away the dishes, also checking that there are no fugitive splashes on the edge of the plate, then to the table. As the customer, all our senses have to be pleased. The combination of food, wine and ambience have all been carefully considered nothing is left to chance. Before service commences all staff are briefed on dishes, tactics and the number of covers that is inevitably near 100 per cent.
Screen printing, gastronomy? Everybody knows what their responsibilities are. They are highly skilled. They work as a team. They use the best consumables. They respect each others capabilities and most important of all the boss leads from the front and aims to continuously improve his product offering.
Bill Jordan of Tamworth-based Jordan Print Solutions doesn’t cook like John Burton Race but he has many of his qualities. Leading a team of highly skilled staff in a very challenging sector of industrial printing. Automotive fascias (speedometer dials to the rest of us.) As with gastronomy there is no compromise in screen printing terms, the client is looking for perfection and unlike restaurateurs the customer demands and gets a three per cent year-on-year price reduction. Bill must be mad! No, he is a business man in manufacturing, which probably is an indication of madness.
Excellence is key
To be successful in this market the application of best practice in every aspect of production and managing the business is essential. Not only for the sake of the company but the client insists on an ‘open book’ policy which means the client requires access to all costings, production records, production methods, staffing and production capacity. They will carry out ‘value analysis/value engineering (cost reduction but maintain quality) on your quotation using ‘quotation analysis forms’. They can make pebbles bleed! This is a quality audit to end all quality audits and the department that deals with it is a separate entity to your customers’ procurement department.
Having gone through all of this they will then want to be assured that you have sufficient capacity to manage peaks in demand and cope with breakdowns in parts of your production. Then of course is the famous Poke Yoke. No people, that is not what it means, sit comfortably! Poke Yoke is a simple but excellent concept where elements of production require precision and certainty can only be carried out in one way. They have to be foolproof.
A 13 amp plug is a perfect example. It will only fit one way into a socket. Jigging, register marks and the like, all should work on the same principle.
Fourteen ink layers
Accepting all the procedural strictures and cost pressures, automotive fascias provide a whole range of challenges for the printer. Fourteen ink layers is the norm. Using both UV curing inks and solvent based systems is necessary in most designs. Add to this the need to achieve a specific light output and colour and you are dealing with a complex printing problem.
As with all screen printing the achievement of quality starts with the stencil, no pinholes fine edge definition, controlled Rz and standardised tension are all essential. Faults in a back lit image will show up instantly and miss-registration in a fourteen-layer print can be a nightmare.
Another key issue is how well one layer of ink sticks to another. When printing solvent inks on top of each other, there is normally not a problem but as soon as you introduce UV curing ink in several layers the issue of wettability of previous layers becomes an issue. In theory UV curing inks cure instantly, the reality is that the cure happens over several hours and if it is left too long before overprinting then problems with intercoat adhesion can occur. Additionally several passes through a UV dryer will potentially over-cure UV curing ink films and they can become brittle.
An important subject is the retention of solvents in the multiple ink layers. The solvents have to be removed with careful drying as the slow release of solvents whilst the fascia is mounted in the instrument cluster can cause solvent cracking of the acrylic lens covering the instruments.
Inevitably the stencil is key to successfully printing these fascias. Working with variable quality stencils makes this application a profit killer. Correct tension, fine edge definition and a total lack of pinholes is a prerequisite. If there is a fault in one of fourteen or more layers the whole batch is ruined.
You may say that clean room conditions are required for such high quality stencils. The reality is that a room that is clean is what is necessary. This includes the stencil dryers that must be thoroughly cleaned inside and out every week. Vacuum blankets and glass on the exposure frames need to be in pristine condition and the simple use of a wet and dry vacuum in cleaning the mesh prior to coating will go a long way to reducing dirt contamination. Of course drying the emulsion adequately is key to the elimination of pinholes due to moisture entrapment in the emulsion coating.
For those who want to consider clean rooms as an ideal in a printing environment a Class 10,000 room is the norm. This means that there are not more than 10,000 particles of greater than 0.5µm within 1ft3 of air. To achieve this the air has to be changed between 45 and 60 times a minute and filtered through HEPA (High Efficiency Particle Arrestance) filters. A Class 1,000 room has 1,000 particles per ft3. So, the lower the number the cleaner the room.
Billions of particles
A person sitting generates about 100,000 particles per ft3 sitting down or about 2,500,000 particles per ft3 standing up. Walking generates about 10,000,000 particles per ft3. Grinding, sweeping, welding (including soldering) adds billions of particles per ft3.
This means that for a clean room to be effective the occupants must at least wear lint free coverall clothing to arrest the contamination that is created by their skin and hair. How far do you go? That depends on the price you pay for contamination and whether the ‘clean room’ is just window dressing.
Back to Bill and his automotive fascias. As well as dealing with the challenges of printing multi-layer the final effect has to be carefully checked and measured. One of the main issues is light output of the illuminated fascias. Nowadays these are backlit by LEDs and the output from these point light sources has to be diffused and measured. The diffusion is accomplished by printing a tone on the back of the facia.
To check the colours and levels are to specification, output from the illuminated fascia is measured with a spectrophotometer. During production densities of filters have been checked with a densitometer.
Once printed the fascias have to be punched or cut out of the sheets. At this point if the adhesion and cure levels of the ink layers are not satisfactory de-lamination can occur. Final inspection looks for the slightest flaw as these clients insist zero defects.
Exceptional screen printer
So if you want to work in a market that insists on price reduction year-on-year, on a product that tests the screen printing process to near its limits, and you can accept quality auditors crawling all over your company working on an open book policy, go for it. If you did and you succeeded you would be an exceptional screen printer who is just a little crazy.
