A matter of quality and reliability

Toolmaker Paul Horn in Tübingen, Germany has developed its own grinding machines for manufacturing carbide tools and for its in process measurement requirements, the company uses m&h production touch probes extensively.

Production managers Walter Wiedenhöfer and Jürgen Bahlinger are operationally responsible for the machines and CNC programming and explain their approach to automated measurement.

Horn is renowned as a premier manufacturer of carbide cutting tools but not as a manufacturer of grinding machines?

Mr Wiedenhöfer: That's correct. We need grinding machines for our own manufacturing of carbide tools. Since we have very specific manufacturing requirements, we decided many years ago to go our own way with grinding machines. Past experience resulted in homemade developments based on cast bodies from one machine tool manufacturer and these are only available to Horn. Using these special machines we are able to produce complex moulds and geometries to very high precision and this makes our tools both efficient and process reliable.

You use touch probes on these machines?

Mr Wiedenhöfer: The only way to achieve the required accuracy for carbide cutting inserts is to permanently monitor the process. Influences such as grinding wheel wear, coolant, temperature plus other factors affect the ground moulds and geometries of our tools. Since tools of a certain type must be identical, we still always measure on the machine during the process.

m&h touch probes are mostly used on machining centres whereas you use the production touch probe 41.00-PP on grinding machines?

Mr Wiedenhöfer: A few years ago we came across these probes and following a recommendation we decided to give them a try. With their stainless steel body, double membranes for excellent sealing and absolute insensitivity to aggressive coolant and carbide abrasion, these probes sit well with our machine construction philosophy and won us over from the very first day with their trouble free operation. Some of them have been in use on machines for some years without ever being cleaned. Even carbide abrasive slurry that solidifies over the weekend doesn't have an effect on these probes.

What precisely do you measure on your grinding machines?

Mr Wiedenhöfer: Our range and diversity of carbide tools has continuously grown. Initially we focused on grooving and parting off tools but today we also have tools for turning, drilling and milling. Increasingly, our customers are buying our special tools which we grind from standard blanks.

Manufacturing processes have become more complex resulting in more measuring tasks. Despite the comprehensive final inspection of our inserts we do a lot of in process measurement on the grinding machines. This ranges from dimensional inspection of the workpiece to positional monitoring, verification of orientation and clamping concentricity to checking for thermal growth and measuring grinding wheel wear.
 
Mr Bahlinger, the tools being ground are not large. What accuracies and tolerances do you work to?

Mr Bahlinger: Generally we work in the range of a few microns, however on some specific grinding operations it really is the micron that matters. For example, we have a measuring procedure to monitor thermal changes on the machine, where compensation starts with a deviation of more than 1.5µm. This accuracy is important for the functionality of our tools. As we also manufacture small batch sizes in automated operations, precision and close tolerances can only be achieved with frequent in process measuring.

What does that mean for the touch probes?

Mr Bahlinger: Obviously the touch probes must very precise but also they have to be absolutely reliable and repeatable. Because of the aggressive coolant our machines are usually lined with stainless steel. The bodies of the m&h probes are also stainless steel. They must not be affected by the adverse environmental conditions inside the grinding machine as they are permanently subjected to coolant and abrasive particles.

And that's where the m&h probes have proved their worth?

Mr Wiedenhöfer: I can justifiably say yes. The sealing mechanism of the probes is outstandingly designed and the stainless steel body ensures a long lifetime even in the rough environmental conditions of grinding machines. Some probes are in multi-shift operation and often trigger more than 20 times per hour.

The last thing a production manager needs during a process are problems and with the m&h touch probes we get reliable performance day in, day out. Even when we start on Monday and the film of abrasive slurry has dried and hardened over the weekend, there are still no problems.

What is the reason for the particularly high use of touch probes in your manufacturing?

Mr Wiedenhöfer: Our carbide grinding workshop is almost completely automated and we also produce small batch sizes and special indexable inserts this way. They must be identical and capable of being reliably reproduced at any time – which is why we carry out in process measurement to determine the state of the machine and any changes to the workpiece. In process measuring is the key to reliable manufacturing.

Do you use a high number of m&h touch probes? Mr Wiedenhöfer: I don't know exactly how many we have but I'm certain we have more than one hundred m&h probes. Only integrated measuring can ensure quality and process reliability on a grinding centre – so our customer is always sure of receiving consistently high quality cutting tools.

m&h
www.mh-inprocess.com Horn
www.phorn.co.uk