High accuracy mill-turning of forging dies

The investment represents a major advance for the company and has made it more flexible in responding to orders and more reliable in delivering them. The company has been producing drop forgings for the last 300 years, currently in medium to large batches from 2,000 to 500,000. The automotive industry is the main recipient, while the motorsport, off-road vehicle, passenger lift and railway sectors are also supplied.

Franz Krammer, toolmaking manager at Krenhof said: “Customers in the automotive industry want the 10,000th forging to look exactly like the first, so quality as well as price is increasingly important.

“One factor helping us to maintain high standards is our use of modular carriers with replaceable die inserts, enabling optimum tools always to be used in our forging process to guarantee precision.

“The universality of the HEIDENHAIN TNC 640 CNC system is also important to us in achieving top quality standards, as it controls both milling and turning operations on the machining centres well.”

Behind Krenhof’s progression to 5-axis prismatic machining with integrated turning was a desire to achieve one-hit die manufacture to enhance accuracy. The pair of Alzmetall GS 1200/5-FDT machining centres with the TNC 640 control option were ordered after research into the best machining solution for the Köflach operation. Krammer was impressed with the way his team familiarised themselves with the new process after just one week’s training.

He explained: “Small inaccuracies in toolmaking lead to large inaccuracies on the finished forged part, so we chose the 20-tonne Alzmetall machine with its quadruple guideways in the linear axes for maximum stability.

“Dynamic, precise motion control provided by the TNC 640 CNC exploits the potential of the machine to the full.

“The control is also convenient to use. Downloading the NC program from the CAM system, for example, is quick and easy via HEIDENHAIN’s TNCremo Windows-based communication software.”

The TNC 640 simplifies the structuring of subroutines, allowing complex programs to be assembled and run. The young Krenhof team found no difficulty programming on the shop floor in HEIDENHAIN's Klartext conversational language. The operators are particularly keen on the availability of numerous canned cycles, such as those for drilling, which are simply and quickly parameterised.

Krammer confirmed that operation is clear and logical despite the wide functional range of the control. It is particularly easy to combine both turning and milling in a single programme, with changeover achieved simply by calling up a short subroutine.

For components requiring multi-sided machining, operators use the PLANE function to define an inclined surface above the tilting rotary table. Programming and machining is then performed in the normal X/Y plane. Probing a reference point on a tilted plane is also simple and frequently used.

Krammer concluded: “Entering the realm of 5-axis prismatic machining with the added complexity of in-cycle turning was possible for us thanks to the reliability of the available technology. It is also helpful that the HEIDENHAIN control has all the necessary functions as standard – and it's easy to learn.

“The change in toolmaking strategy here has brought with it long-term dimensional accuracy and above all reliability in the forging process.”