Did you always think that bike helmets would fall off the conveyor belt like ready-made pizzas? You thought wrong. At the helmet manufacturer Alpina in Obernzell, Bavaria, we were able to experience just how complex the production of a helmet really is. Just a few kilometres from Passau, Alpina still manufactures around 70 percent of its entire production in the factory of its parent company B-S-A - around 800,000 mountain bike and ski helmets are produced every year. Manual labour still plays a major role. A modern cycling helmet from Alpina consists of around 30 parts and is manufactured using the in-mould process. At the very beginning, there is a 350 x 415 millimetre polycarbonate plate about one millimetre thick - the future upper shell. The sheets are supplied unfinished by the Bayer chemicals group and their final design is screen-printed in the region. Here you can already get an idea of what the finished helmet will look like in the end.
The polycarbonate sheets are heated in a drying oven at 80 degrees Celsius for one hour so that they can be moulded into the desired shape. This vaporises any residual moisture from the screen printing.
One corner further on, an employee is already waiting at the thermoforming machine for the hot plate. The upper shell blank is clamped here and heated for 37 seconds at 450 degrees Celsius. As if inflating a balloon, an aluminium mould is now raised and the outer shell is pulled into its final shape. In the process, the shell thickness shrinks by up to 30 per cent in some places. The final design is now revealed.
Incidentally, the appropriate distortion of the graphics was not previously worked out using powerful computer programmes. A simple polycarbonate sheet covered with a special chequered pattern is used to calculate how far the graphic deforms during thermoforming.
A quick turn and the chips are flying around our ears. A milling machine cuts the ventilation openings and the final shape into the upper shell that has just been drawn fully automatically. The milling head covers a milling path of up to 15 metres with millimetre precision. Snippet after snippet flutters to the ground. However, the surplus material does not end up in the rubbish bin, but is processed into new raw material by external recyclers.
The next machine requires no human assistance at all. A CNC-controlled cutting and sewing machine cuts endless belts to the right length, depending on the model and size. The ends are ultrasonically welded and the loops are sewn to the ends of the straps. Less than five seconds later, a finished strap flutters into the collection container under the machine.
In the next step, manual labour is required again. All the headbands and chin straps are prefabricated at home. Alpina sends the individual parts, together with the appropriate template, to its 45 helpers in the region. The headbands and straps are fitted with loops, padding and chin buckles virtually at the kitchen table at home. Back on the production line, all that remains to be done is to fit the size adjustment systems, including the swivel ring. One worker assembles around 2000 systems per shift. With such nimble hands, it would be nice to watch the process in slow motion.
In the next hall, we finally approach the actual helmet production area. Here, the polystyrene raw material is stored in large silos. Initially, the granulate is still in the form of tiny sticks. These are foamed with the help of 90-degree water vapour. The sticks pop like popcorn in a pan. Small balls now trickle out of the machine, which are known as expanded polystyrene, or "EPS" for short. In a maturing process lasting around ten days, the volume of the EPS beads increases to 70, 80 or 100 grams per litre. The denser the foam, the stiffer the final product - but also the heavier.
To turn the raw mass into a helmet, the EPS is fed via a pipe system to the 16 injection moulds, which fill almost the entire hall in rows. Two helmets are baked per cycle in the huge pneumatic machines. Before the EPS is injected, a worker inserts all the individual parts into the injection mould by hand. Outer shell, inserts, fly screens, belt holders - up to ten parts have to be placed in the mould with millimetre precision in the shortest possible time. The two halves then move together pneumatically. At this stage, it is better to be behind the barrier and outside the machine. While the injection mould is preheating, residual water and air are evacuated by vacuum. The mould then fills with the EPS beads. Depending on the model, around 120 grams of the material is required. While steam heated to 120 degrees flows into the mould, the polystyrene beads slowly begin to fuse at their edges. The helmet now bakes in its mould for around four minutes. Finally, the mould is cooled to around 60 degrees and the worker can remove the helmets while they are still "warm from the oven". Voilà: The helmet core and the outer shell are now firmly bonded together.
What is still missing is attached to the helmet by the ladies while it is still warm. Velcro pads are glued in, straps and adjustment system are clicked in, safety instructions are stuck on. Of course, one thing is a must: the Made in Germany sticker. Alpina is particularly proud of this. When the helmets now disappear into the packaging after a final visual inspection, a whole 30 minutes of net working time have passed from the thermoforming of the PC plates to the bonding in the injection mould. An effort that we would not have expected.
Stefan Frey
Editor
