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A Focus On Precision For Turning Operations

High-precision turning operations using high-positive indexable inserts are able to deliver the required accuracy for machine shops. Contributed by Arno

Heidelberger Druckmaschinen AG (Heidelberg) manufactures high-precision and reliable digital and offset printing machines. The manufacturer has set itself the goal of integrating and automating its entire value-added chain for its customers—the print shops—thereby increasing their competitiveness. The manufacturer has around 11,500 employees worldwide and its highly automated and versatile machines in all format classes are manufactured in accordance with customer requirements.

Keeping Costs Low

Heidelberger set the goal to keep workpiece costs as low as possible without affecting quality. In this context, the company only works with partners who are also constantly pushing forward further developments in this direction such as Arno, a manufacturer of cutting tools in the field of turning, engraving, drilling and milling.

Harald Johann, head of work planning for cams, gears and model parts, and Andreas Knopf, technical expert for turning and tools at Heidelberg, are responsible for the production of gear wheels for offset printing presses. As part of an integral review of the existing production process for gear wheels, the company examined the indexable inserts being used in the turning process in detail.

These inserts can be an important cost-reducing factor when tool lifetimes are increased. Significantly increased tool life and the resulting reduction in tool change and calibration times will have a positive impact on unit costs in the longer term. As a result of this investigation, Mr Knopf was looking for an economically attractive alternative to the previously used indexable insert.

Supported by an application technician at Arno, Mr Knopf attempted to use the indexable insert TCGT16T308FN-ALU AL10 to carry out inside turning and finishing of gear wheels made from cast steel. The indexable inserts have a rake angle of 27 deg, which are periphery ground with polished chip breakers and thus have a sharp cutting edge, which means they only require minimal cutting forces.

The challenge lies in maintaining the required accuracy for each and every gear wheel.

Increasing Tool Lifetime

High-quality print products can only be produced with a high-precision printing machine. This begins with the internal fit of the gear wheels. Each printing unit is connected to the next printing unit via the gear wheel, which is optimally adjusted via the gear train. Unless the internal fit is exact to within one-thousandth of a millimetre, the toothing will not mesh correctly with the next gear wheel. Machines containing a larger number of printing units require a correspondingly larger number of gears, making the degree of precision even more important.

“The results we achieved in the field matched those that had been previously promised. In production, you quickly realise whether someone can actually put theory into practice,” explained Mr Knopf.

This laid the foundation for further collaboration between the two companies and a wide range of parts were inspected and new indexable inserts tested. At the same time, challenging fitting tolerances was required. The quality achieved was not only very good, but the new indexable inserts also increased tool lifetimes by up to 100 percent, even with difficult-to-produce workpieces.

Achieving Consistent Quality

The tool manufacturer implemented a number of specific measures, which led to very high-quality results when the indexable inserts were used in the grinding process. For example, Arno only produces indexable inserts on Swiss grinding machines using the EcoDress process. During this process, the grinding wheel is cleaned and stripped after each grinding operation to ensure that the quality of each grinding operation remains consistent, the grinding wheel does not become clogged and no cutting pressure is generated. This allows very close machining tolerances to be maintained.

Compared to the conventional grinding process, the process reliability and removal efficiency are both increased, which in turn improves the finish quality and edge roughness of the indexable inserts. Depending on the insert type, a distinction is made between a sharp cutting edge or a rounded version.

The standard rounded cutting edge contributes to a considerable increase in tool life and smooth running of the indexable inserts. Each insert’s cutting edge is created by wet blasting or slide grinding, after which an automated or optical 100 percent inspection of all finished indexable inserts is carried out, underlining its commitment to quality assurance.

Quality and reliability are also important criteria at Heidelberger. With a weight of around 600 kg, the cast iron gear wheels have a material value of several hundred euros. For this reason alone, special attention was paid to process reliability during the test phase. The new indexable insert runs without problems.

Customised Tool Order

From Mr Knopf’s extensive experience with indexable inserts, he knows that they are prone to damage from cavities. That costs time and money—a key factor given the lot sizes at Heidelberger, which range from 50 to 500 pieces. One major advantage of this particular indexable insert is that, as a standard item, it is always in stock with only a small minimum order quantity.

By contrast, the inserts that were used previously were subject to relatively large minimum purchase quantities. Punctual delivery, the stocking of enough indexable inserts to be able to react quickly to specific requirements, as well as generally shorter delivery times were all important additional factors. One month’s supply of the indexable inserts can usually be delivered within three days, due to precise coordination between the business partners.

Reducing Downtimes

A broad usage range is very important for Mr Johann when it comes to developing the machines. A reduction in complexity is also a major focus. This means using fewer indexable inserts for a wider range of applications. Understandably, he also wants to minimise both the degree of utilisation and downtimes. The technical expertise of its internal and field sales staff and application engineers allows Arno to meet these requirements and, in collaboration with Heidelberger, to lay the optimal foundations for the future. Finding solutions remains everyone’s focus, which is why the partnership is successful.

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