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Productive single-item production

Extrusion dies for plastic pipes are among the key products of the Dutch supplier company Romit. By optimising production with a Heckert HEC 800 Athletic HV MT milling/turning centre, they were able to reduce the total processing time of such tools by up to 65%.

Heckert horizontal machining centre HEC 800 HV MT, Romit, Netherlands

+ Profitability + Process reliability + Product quality


For Auke Sjoerd Tolsma, CEO of Romit BV in Dedemsvaart, the situation is clear: “We need to optimise our production continuously in order to survive in an increasingly competitive global environment.” His company was formed in 2001 from the machining department of Rollepaal BV, one of the leading global manufacturers of extrusion lines for PVC and PO pipes. In the same year it was founded, Romit already acquired the neighboring tool- and mold-manufacturing company Ramix, thus extending its range. As a result, the company, which employs approximately 70 staff, quickly became an established service provider for machining and assembly tasks serving the plastics industry, oil and gas drive engineering, and the maritime sector. The manufacture of extrusion dies has remained one of Romit’s core tasks. Auke Sjoerd Tolsma applied his optimisation initiative to the demanding precision machining of these components: “Extrusion dies are manufactured mostly as single parts or mini-series of up to three pieces. Because of their rotational symmetry, they mainly require turning, but also drilling and milling. Until recently we used vertical lathes and bed-type milling machines for the purpose. But the time spent on machine changes and weaknesses in process reliability gave us the idea of switching to complete processing and automation.”

65% reduce of total processing time

In early 2013, CEO Tolsma and his machining specialists began their search for a turning/milling centre that is able to machine the components, which measure up to 850 mm in diameter and weigh up to two tons, in a maximum of two setups. In addition, the sought after machine should reliably meet the required tolerances in order to also permit unmanned operation and handle maximum spindle hours.

Of five multi-functional machines tested with a reference component, two provided the level of performance required. In the end, a number of essential details, such as the load capacity of the table and the simple use of strongly cantilevered tools, determined the final decision: In mid-2014, Romit invested in an HEC 800 Athletic HV MT milling/ turning centre made by the Chemnitz Heckert GmbH, which is part of the Starrag Group, a global technology leader in precision machine tools. Auke Sjoerd Tolsma explains: “I’ve long been aware of Heckert as a renowned supplier of machining centres for serial production. The test operations finally convinced me that Heckert can also provide highperformance solutions for the complete machining of individual parts.” And adds, satisfied: “In our case, the best solution even.”

Precision and dynamics

Romit’s demands on the machine are high: For five-sided machining they require a minimum of three linear and two rotatory axes - one for turning and one for the swivel movement of the tool or workpiece. It needs to be mounted extremely stably in order to ensure high precision milling, turning and drilling. At the same time, a high dynamic range is required in order to keep processing times short. Because of the size and high weight of the components, the load capacity of the table and the working space available play an important role. Benny Van Haver, responsible as Sales Manager Benelux in the Starrag Group for the Dutch company Romit, helped with the selection: “Heckert’s HEC series horizontal machining centres have a completely modular design and are therefore highly configurable. For Romit, the HEC 800 HV MT was ideal, on account of the requirement for milling/turning operations and an 800 pallet size.”

The selected high-precision NC rotary table is loadable with two tons and provides 57 kW power (at 100 % duty), up to 500 rpm, and a maximum torque of 2,520 Nm. The swivel horizontal / vertical milling head also provides decisive advantages: It saves on a pivot function for the table that would take up valuable working space. Auke Sjoerd Tolsma argues: “This means we can easily use strongly cantilevered tools such as a 450 mm long core drill.” This tool, with a diameter of 120 mm, is used for the required pilot drilling before the inner contour of an extrusion die can be milled out. Thanks to the high torque of 1,088 Nm (at 60 % duty) of the two-stage gear spindle (6,000 rpm, 30 kW), it is possible to drill into solid material even with highly tempered steels. Here, the internal coolant supply with 80 bar flushing pressure comes into effect, ensuring the reliable removal of swarf.

The HV-head has two working positions, horizontal and vertical, in which it can pivot even when the spindle is running. If the respective final position is reached, the head is locked in a Hirth coupling. The positive fit this creates contributes to a high stability, which is especially important in turning. The turning tools, for which HSK-100T holders are used, are disengaged when the spindle is inserted and fixed with a second Hirth coupling, secured against turning with the positive connection. Thanks to the overall stability, it is even possible to use 450 mm long standard turning tools, which would require damped boring bars in other machines.

Other important criteria in the decisionmaking process were the inclusive pallet changer and the option to integrate the machine into an automation solution with pallet storage. Auke Sjoerd Tolsma explains: “At the time, a dual changer system was important for us so we could already reclamp parallel to machining.” In addition to the standard 800 × 1,000 mm pallet with T-slots, he ordered two round pallets 1,000 mm in diameter, also equipped with T-slots and a claw system. In order to be able to precisely align rotationally symmetrical workpieces on the setup station already, he had it equipped as a highly precise swivel load/unload station with a bearing that has a rotational accuracy of under 1/100 mm.

Equipped for safe processes

In the near future, the installation of a fully automated high-bay warehouse is planned with a pallet system to which the Heckert HEC 800 HV MT and other equipment will be connected. The most important requirement for automatic operation is safe processes. The machine concept of the Heckert milling / turning centre HEC 800, with its rigid, thermosymmetrically designed main assemblies, the digital AC feed drives, and elaborate profile rail guides and ballscrews in all linear axes provides a solid basis for the job.

As an extra safeguard, Romit opted for additional sensors. Auke Sjoerd Tolsma explains: “Since we often process highalloy steels and other difficult materials, we wanted to exclude the possibility of a crash during unattended machining. For this reason, we decided on the supplementary Brankamp collision monitoring system.” Even greatersecurity is provided by utilisation monitoring, which actively checks during processing whether the machining is proceeding according to plan. If there are any deviations, processing stops automatically. A vibration sensor on the spindle also shuts down the machine in case of tool damage.

Benny Van Haver also mentions the automatic imbalance detection, which comes as standard in the HEC 800 Athletic. If any imbalance occurs, the machine is able to measure it as well as indicate the position and size of the necessary counterweights.

Hoped for savings realised

The Heckert HEC 800 HV MT has been running in production mode since mid-March 2015. For Auke Sjoerd Tolsma the investment has paid off completely: “With this solution, we are able to implement processing that previously took place on two different machines in two set-ups, on one machine with complete production. Depending on the size of the component, we save between 30–65% of the total processing time.” The CEO sees the HEC 800 HV MT’s performance data, which exceed the previous possibilities even in turning, as a crucial factor: “For example, we can machine an extrusion die from a 1,500 kg ingot to completion in about six hours, finish machined with a surface quality of Ra = 0,4μm.” The resulting swarf - up to 50% of the weight of the unmachined part - is disposed of at an ejection height of 1,500 mm via a link belt chip conveyor into a spacious container.

The dimensional accuracy is also correct. “On average, we need an accuracy of 5/100 mm. For sensitive parts, we need to be accurate to 15 microns”, Auke Sjoerd Tolsma explains. “With our Heckert machining centre, we can reliably adhere to such diameter tolerances over a turning length of 600 to 800 mm. We check this with a measuring cycle, which we developed jointly with Heckert, to correct any tool wear occurring. The machine meets the required dimensions even in our non-air-conditioned hall, where temperature fluctuations are quite possible.”

Promising prospects

After its successes with the complete machining of extrusion dies, Romit is extending the scope of application of the milling/turning centre. In the meantime, contour parts for mold making have been milled, and the HEC 800 HV MT is also earmarked for single parts from the area of compressors. After all, those in charge have set the initial target of 100 hours’ operation per week.

To make production even more cost-effective, Romit invested in a new CAM system, which masters milling and turning equally and is able to map and optimize complete processes. Next in line is the planned automation system and other machines, probably beginning with a slightly smaller fiveaxis centre. The plans have already been drawn up.

Conclusion

With the new HEC 800 HV MT milling/ turning centre, the Romit company succeeded in sustainably increasing its profitability. Processing times decreased by 65%, the time previously spent on changing machines was eliminated completely. The staff’s workload decreased due to the quality and reliability of the machine. The integration into a comprehensive automation system is already prepared.

Auke Sjoerd Tolsma

“With this solution, we are able to implement processing that previously took place on two different machines in two set-ups, on one machine with com- plete production. Depending on the size of the component, we save between 30–65% of the total processing time.”

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