VERICUT proves the safest road to tyre mould production for Continental Barum

VERICUT ensures master mould’s safety

As one of the leading global manufacturers of automotive tyres, Continental Barum has a long and rich history. From supporting race winning motorsports teams to providing safe and secure road holding for everyday passenger vehicles, the company’s products are trusted to perform. This reputation is important to the company, and in turn the company trusts CGTech’s CNC simulation software VERICUT to protect its mould tool facility.

Located in Otrokovice, in the Central Moravia region of the Czech Republic, Continental Barum employs around 4,500 people with an active policy to bring new students into the company; a graduate scheme run with the local university attracts the brightest young people to the business.

The plant in Otrokovice is the largest of its kind in Europe, producing around 20 million passenger car tyres per year. Commercial HGV tyres are also produced at a rate of 180,000 per year. The facility has specialised in mould tool manufacture since 1997, and supporting these production volumes requires 1,200 complete mould tools per year, made up of the circumference tread pattern moulding segments and side walls.

Continental Barum in Otrokovice

Over a third of the mould tools will be for new products, which are developed with the combined skills and knowledge of the R&D engineers and the material technologies teams within the company. The rest are to replace worn moulds or to support increased volume of tyre production.

Tread pattern designs are a closely guarded secret and they are optimised for seasons, with specific treads for summer and winter and an internal ‘carcass’ structure that can feature more than 20 layers of different material to meet the performance criteria specified by the customer. The designs are provided in 2D and 3D CAD formats to the mould tool production facility.

While the steel side walls of the mould tool are relatively straightforward, the segmented method of producing the tread pattern is the complete opposite. As Roman Miko, IT specialist – Mould Production Division, explains: “The mould side walls are directly machined with the company’s logo and the tyre product name, along with details of the tyre size and width as well as road speed rating. A segmented tool design is used to allow the tyre to be removed from the mould after it has been cured. However, the nine segments that form the circumference of the tyre mould, producing the tread pattern, are far more complex and require 5-axis machining.”

Verified NC files sent to 5-axis machine tool

Prior to 5-axis machining the company’s team of CAD/CAM engineers prepare the data using 15 seats of Siemens NX 5-axis CAD/CAM software. The engineers produce the CAM files from the CAD models and post process these files to produce the NC code to produce the mould tools. The NC code is then verified using one of the five VERICUT seats to independently check each program for machine axis over-travel, collision errors or gouge cuts into the mould segment.

For less complex tyres the mould tool shop will machine the tread pattern directly into the aluminium segment, using one of a bank of Fidia Digit 218 5-axis machining centres or the recently installed DMG MonoBlock 5-axis machining centre. For more complicated tyre designs the segments are cast in aluminium.

The first step of this process involves a 5-axis machined resin master mould model segment. As the accuracy of the finished mould tool is transferred directly from the master model its correct preparation is vital to the finished tyre, and the thermal expansion knowledge of the materials used has been encapsulated within the software. Roman Miko says: “Machining cycle times depend on the complexity and size of tyre, ranging from 3 hours to more than 24 hours in resin. For aluminium machining the cycle time can be even longer, the largest single segment we made took 42 hours. With the volume of tools we have to produce and the demand from production for our support we cannot afford to damage one of the machine tools or scrap the mould segments.”

Resin master mould

As cast aluminium tread mould

File preparation is everything, with at least as long as the machining cycle time required for programming and verification. “We can spend up to 40 hours creating the correct NC code from the time the design file is received until it has been approved by VERICUT and is released to the shopfloor,” Roman Miko states.

The NC programs are made longer by the necessity to use very small diameter cutting tools because of the complex details of the mould. The smallest tool used is 0.4mm diameter to cut the sipes required to disburse water; essential for winter tyres.

Fully machined and ready to go to production

Says Roman Miko: “Using VERICUT we check the CNC code for one of the master model segments, one that features each type of pitch used on the tyre. The pattern pitch is used to disrupt road noise harmonics, to improve driver comfort. If the program for that segment proves clear the rest of the segments are batch tested. They are verified automatically overnight in VERICUT and an error log file will highlight any issues. If any of the segments throw up a problem the CAM programmer will modify the NC code and recheck again using VERICUT.”

CGTech’s agent for the Czech Republic, Axiom Tech, prepared the automated batch checking code for Continental Barum, as well as the models and dynamics for each of machine tools used by the company.

The mould tools produced at the facility support the Continental Group’s tyre production facilities across the globe. As well as protecting the advanced machine tools used VERICUT is also supporting the drive for efficiency. While Zero Point clamping is used on each segment so the datum point remains consistent, with machine-to-machine tolerances tightly held.

“We have to compete with outside mould tool suppliers, on quality, cost and delivery lead times,” concludes Roman Miko. “VERICUT ensures our machine tools are safe and always available to us, and protects the machined mould tool components from any programming errors. Both of these have a direct influence on our ability to meet our promises to deliver.”

Article published in ETMM – December 2014 [PDF]