Precision on a grand scale

Large-scale machining centres from Chemnitz in mould making

Stefan Zatti, member of the board of management: “We average around 21 hours of running time 7 days a week”

Entrepreneurs sometimes have to make extremely brave decisions in order to achieve success – as demonstrated by the history of Otto Hofstetter AG. Thanks to these brave decisions, the medium-sized Swiss company has achieved such feats as becoming number two in the global market for mould manufacturing in the area of preforms for PET bottles. The decision to bring plate production in-house and to purchase three Heckert HEC 1250 large-scale machining centres for this purpose was also a significant factor in achieving the company's current success.

Otto Hofstetter Senior founded the company in 1955 as a sub-contractor for local companies but, just two years later, he began to produce injection moulds. He had recognised the potential of the emerging plastics and of the injection moulding procedure and quickly built up a good reputation as a manufacturer of high-precision moulds. The company specialised in moulds for thin-walled products involving highly-complex injection moulding, particularly in food packaging. 1977 saw a decisive turning point for the company from Uznach, Switzerland, when Coca-Cola began the search for new packaging, looking for a lighter alternative to the glass bottles used up until that point. A partner of the drinks giant developed a plastic bottle, but was unable to find a mould manufacturer to produce them. Although plastic bottles are blown into shape, the material is placed into the blow-moulding machine as a preform. This injection-moulded preform consists of the threaded neck and a contour similar to a test tube; this is the material that is used to blow- mould the bottle into its final shape. Otto Hofstetter made an excellent im- pression in the subsequent selection phase and won the drinks giant’s custom. As a result, the company spent ten years as the exclusive manufacturer of the injection moulds for the Coca-Cola bottle preforms in the USA.

Range of cartridges: Silicon and coloured cartridges in various sizes. The distribution sector is the main customer group.

In the mid-1990s, the boom in plastic bottles reached Europe and the business exploded with the corresponding moulds. The son of the company founder Otto Hofstetter, who had taken over the management in 1997, decided on a largescale expansion of production capacities: he intended to develop in-house production capacities for the preform plates, which had previously been manufactured externally. Of course, this meant that new machines had to be purchased, as the maximum workpiece size of the existing milling centres meant that they were far too small. Depending on the mould, the plates are up to 1.5 × 1 metres in size, 20 centimetres thick and 2,500 kilograms in weight, with a high level of precision required. A mould can have up to 144 cavities and the tolerance across the five base plates – which together form one mould – is less than one hundredth of a millimetre. After all, the base plates not only have to be exact in themselves, but they also have to be a perfect fit with each other.

Silicon and coloured cartridges

“The product is right, the price is right, the service is right – this has been confirmed time and again with seven machines from the Starrag Group over the course of many years.”

As Hofstetter was already successfully using two Heckert CWK 800 machining centres with horizontal spindles, the decision was taken to approach the Starrag Group once again in the interest of increasing capacity. Stefan Zatti, member of the company board of management and Head of Sales and Marketing, recalls: “Both existing CWK 800 systems have proven to be reliable machines with a high level of availability so, when we were looking for larger machines for base plate production, we decided to approach the Starrag Group again. Another important consideration for us was that Starrag had already proved to be a reliable, stable partner.” After visiting the Chemnitz site, the Hofstetter decision-makers were so impressed that they bought two CWK 1250 machines, instead of the one they had planned. In addition to the high level of quality of the machines, another characteristic that swung the decision was the pallet changer, which allows the automatic removal and replacement of work- pieces. The CWK 1250 has two pallet clamping areas, where two workpieces can be clamped on each pallet. This means that up to four workpieces can be processed in succession in an unmanned operation. As Zatti says, the CWK 1250 enabled “an internal production rate of 100 % in plate production within a year of fully purchasing the equipment”. After eight years, the production capacity of these machines had been exhausted due to the high number of operating hours and the time had come to consider investing in replacements.

seven machines from the Starrag Group

Hot runner plate: Section of a PET hot runner plate. More than 70 % of the original plate is machined.

So Hofstetter ordered the first of a total of three HEC 1250 machines, each with three pallet areas. The two additional machines followed. The third machine even enabled enough capacity to produce additional components in-house again, which were previously assigned to suppliers. The three machines stand next to each other in the purpose-built hall. Albert Kuster, Department Manager for mould base plates, is particularly impressed by the tool magazines of the HEC 1250: “Other machines feature chain magazines, which make the moulds difficult to access as you can only unload them from an unloading station. The Starrag Group systems use magazines with four towers each, where each mould is stored in four profiles, one on top of the other on the side. You simply look for the corresponding mould at an operator station, rotate the relevant tower, then open a door and remove the mould.”

The three systems have wear monitoring systems, which measure the required torque of the spindle during cutting and use this to calculate the status of the processing tool. In addition, breakage monitoring is carried out using laser measurement systems for workpiece measurement, so that long unmanned machining operations are also possible. If a mould ruptures, the machine auto- matically continues to function with a replacement mould – if possible – or notifies the on-call employee via mobile phone. This means the machining oper- ations, which can last up to 12 hours per workpiece, can be performed very efficiently overnight or at the weekend, without requiring shift work. This is an important factor in a country with high wages such as Switzerland. “We average around 21 hours of running time seven days a week,” Zatti adds. “The remaining three hours are spent on retrofitting and maintenance work. We are extremely happy with this high level of availability offered by the machines.”

Hot runner plate

Impressive machines: The hall built by Hofstetter AG with the three Heckert HEC 1250 machining centres.

“We were extremely satisfied with the assembly performed by the employees of the Starrag Group. We were even able to pick the service team and were therefore able to choose the employees we had already been working with for some time. Commissioning took six weeks per machine – an impressive number for such large machining centres. I found it extremely positive that our sugges- tions and proposed improvements were taken into consideration. So, the second machine incorporated improvements that we suggested based on our experiences with the first one – and the first machine was also brought up-to-date when the second system was commissioned!”

three Heckert HEC 1250 machining centres

16× cartridge mould: A 16× mould for the manufacture of silicon cartridges.

“Our wishes are heard,” Zatti continues, “and that is a good feeling. The three machines – and the new hall for them – were a major investment for our company. Thanks to the speed with which the machines were commissioned, we were able to start recouping the capital spent on the machines straight away. That is crucial in terms of the return on investment. Our injection moulding tools are used to produce up to one million preforms a day; this is only possible with the most stringent requirements for the mould and its manufacture. It’s not without good reason that we are number two globally when it comes to PET moulds. We have achieved this position with maximum quality and short delivery times, and the HEC 1250s are a key factor in our success on both counts.”

When it comes to the collaboration with the manufacturer, Zatti’s response is purely positive: “The product is right, the price is right, the service is right – this has been confirmed time and again with seven machines from the Starrag Group over the course of many years. Our relationship with our suppliers is a partnership, not a typical supplier rela- tionship, and that has always worked perfectly with the Starrag Group – especially in times when we have disagreed on things. If you want to move mountains, you need a reliable partner – and we have found this in the Starrag Group!”

mould for the manufacture of silicon cartridges