From the initial powder through to the finished insert – Achieving success from inner strength

12Nov. 2020
Jessica Nossek
Jessica NossekKommunikationsreferentinPaul Horn GmbH

The philosophy of Paul Horn, founder of Paul Horn GmbH, was this: “The only way to achieve the best possible results is to control the entire process chain for my tools!” This idea is now being consistently pursued by his son, Lothar Horn, and his grandson, Markus Horn, as the basis for the company’s success.

Given the short lead times for which HORN is renowned, the only way to manage the production volume it has built up over more than 50 years is to use highly automated – the degree of automation is currently 97 per cent – and very flexible processes. Among other things, this means having to continuously adapt increasingly complex manufacturing processes to the latest technical, logistical and organisational advances and, in turn, involves mastering different process chains and technologies from development all the way through to delivery.

Horn Hartstoffe GmbH

The Horn Hartstoffe GmbH plant currently covers an area of 5,000 m² (53,820 square feet), of which 4,500 m² (48,438 square feet) is production space. With its various shaping processes, sintering equipment and powder preparation techniques, the company’s carbide production represents the state of the art. Carbide production is structured according to material flow principles, with downstream processes organised in series.

Quality starts with toolmaking

Cost-efficient shaping processes require high-precision injection moulding or pressing tools – quality products that are made by the in-house tool shop. In response to the increasing demands on carbide production, capacity in this department has been updated accordingly, not only with regard to milling, eroding, surface and jig grinding but also in terms of other operating equipment. In the tool shop, the insert tool design and chipbreaker geometry development processes run almost concurrently. Whenever a new idea is presented by the development department, the tool shop checks its feasibility.

From powder to green compact

The manufacturing process for an insert starts with mixing and preparing various substances – carbide alloys in powder form, pressing aids and additives – to create mixtures that are ready for pressing. The carbide alloys are supplied in grain sizes of 0.6 (0.00002") to 6 µm (0.00024") and in batches with a weight of approx. 1,000 kg (2,205 lbs) for uniformity in the powder composition. Maximum precision is required during the weighing and dosing of important pressing aids and additives for subsequent shaping, as even slight differences (the pressing aids are weighed out with a tolerance of 0.01 g (0.00002 lbs)) can significantly change the final product. The mixtures for pressing are then prepared for the various shaping processes in vertical carousel storage areas in accordance with the first-in/first-out principle.

Direct and indirect shaping processes

A mixture for pressing is turned into inserts or tool shanks using direct and indirect shaping methods. Extrusion and isostatic presses are used for indirect shaping. The green compacts produced in this way are pre-sintered, then machined and final-sintered. In the case of direct shaping (axial pressing or injection moulding), the only downstream processes are pre-sintering and then HIP (hot isostatic pressing) sintering. 

Two ram extruders press the mixture to create extrusions whose cross-sections match those of Supermini tools or various rotating shanks. The extrusion, which is formed continuously, is automatically cut to a length corresponding to the support plate, transported for pre-sintering and then cut into sections appropriate for the tools before being profile-machined, cleaned and final-sintered.

In the case of isostatic pressing, the mixture is poured into a flexible bag, radially compacted at a pressure of around 2,000 bar with the help of a liquid and then shaped into a tool. A built-in set of scales enables the cylindrical pressure container to be filled automatically. This process produces round and oval cross-sections, with or without a bore, as well as rotating shanks. At a pressure of around 2,000 bar, the pressing process for a rod measuring 500 mm (19.685") in length and 70 mm (2.756") in diameter takes around 90 seconds.

Since 2012, axial press systems (multi-level powder presses) have also been in use. The outstanding design features of these systems are the servo-electric drives for the upper and lower dies, as well as the hydraulic transverse press elements that act horizontally. They make it possible to manufacture complex inserts extremely cost-effectively. The automatic work process (which includes monitoring the weight of the fill quantity) is subject to process control to ensure that all parameters are monitored continuously.

Injection moulding of complex shapes

Injection moulding supports a large number of degrees of freedom – such as required for undercuts, free-form surfaces and a diverse range of chipbreaking geometries. Complex inserts of this kind are manufactured using injection moulding machines that feature automatic workpiece handling. The automation equipment, developed in cooperation with the HORN operating equipment manufacturing department, removes the injection-moulded part from the machine and sets it down so that a laser can separate the sprue. HORN became the first tool manufacturer in the world to mass-produce indexable inserts using an injection moulding process with high process reliability way back in 1992.

Pre-sintering and final sintering

After pressing or injection moulding, the green compacts are still unstable and brittle. However, their consistency changes during the pre-sintering process thanks to the release of the pressing aids. This occurs at around 820°C (1,508°F) in a hydrogen atmosphere. The parts, which have changed from green compacts to brown parts, can then be machined by grinding them with diamond tools. The pre-sintering and machining processes turn the green compact into a fully shaped brown part. This obtains its final strength by means of HIP sintering, a time-controlled and temperature-controlled heat treatment method. Sintering takes place at a temperature of between 1,300°C (2,372°F) and 1,500°C (2,732°F), depending on the carbide composition. Final sintering – the actual compacting process – is performed in a vacuum in a protective gas atmosphere in the sintering HIP furnace when the binding agent is in the liquid phase. This improves the microstructure of the carbide and the porous brown parts turn into extremely strong and tough carbide inserts, whilst their volume is reduced by around 20 per cent.

Ongoing checks and in-process controls

Even though HORN utilises modern process technology and reliable working methods, every manufacturing step is still monitored, tested and checked. By employing comprehensive checks and the latest measuring and testing systems, our quality control measures ensure that the carbide blanks live up to the stringent requirements placed on them. All sintered inserts are subject to 100 percent dimensional checks in fully automated measuring machines. They are then visually inspected for damage and deformations by specially trained employees. In our carbide laboratory, our employees test and monitor the physical and metallurgical properties of the carbides, from the starting material in powder form right through to the final-sintered carbide tool. Alongside materials analysis and testing and optimisation of the sintering process, batch-specific physical measurements are taken from samples and microscopic porosity and structure examinations are carried out.     

Grinding machines with micrometre tolerances

HORN uses five-axis CNC machines of a bespoke configuration. These are converted and upgraded at our internal mechanical engineering department to suit our requirements. Upgrading a base machine to a high-tech machine essentially involves integrating additional functions for specific products – e.g. functions for measuring, dressing, clamping, positioning, turning and transporting – in a manner compatible with our automated grinding technology. Examples include standardised interfaces for mounting modular assemblies and clamping equipment, a grinding wheel changer and an NC dividing head with a concentricity of 1 µm (0.00004"). The ratio of standard inserts to special inserts is roughly 50:50. More than 95 percent of inserts undergo grinding during production. Depending on the nature of the product and the requirements, accuracies of ± 1 µm (0.00004") have to be achieved in the course of this and/or the cutting edges have to be verified as fracture-free when magnified 200 times, such as in the case of the µ-Finish system. The grinding production area takes up the biggest amount of space and has the most machines of all the production facilities at HORN.

Self-regulating, cross-departmental order processing according to priorities 

The available production capacity levels are such that they demand an appropriately tailored environment and very fast order processing. To enable this to happen as effectively as possible with the small order quantities applicable to special inserts and tool holders, HORN developed something called the Greenline process. This is a company-wide, rapid order processing system that is self-regulating and requires minimal planning and administration. It means that production orders for insert batches of up to 50 never take more than three days to produce, and that – following other processes, including coating – the products are delivered within one week of the drawing having been approved by the customer. For tool holder production order sizes of up to five parts, the lead time is two weeks.  

Coating department adds the final finishing touches

A coating of only a few thousandths of a millimetre in thickness can decisively influence tool wear along with all its associated effects on the machine, energy requirements, equipment and supplies. This is why HORN has been applying coatings for more than 30 years. For this, the company uses PVD sputter coating systems that have been specially tailored to HORN requirements. The process of cathode sputtering generates topographically even surfaces in the micron range and enables the application of different coating materials. Between them, the nine systems (with coating capacities ranging from 1,400 to 6,000 inserts) are capable of applying all standard coatings – such as TiAIN, TiN and TiAlCN – as well as coatings that have been developed in-house at HORN. Coatings are applied in the working chamber under vacuum. After plasma cleaning, the inserts are coated at around 480°C (896°F) with a carbide coat 1.5 µm (0.00004") to 10 µm (0.00039") thick, depending on the tool. This process lasts 7 to 14 hours, depending on the coating thickness. Once the process is complete, the thickness, adhesion, design, structure and composition of the coating are tested and quantified using the latest procedures.

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