All tool manufacturers are hard-pressed to meet the increasing market demand for higher accuracy, better efficiency and shorter lead times combined with price pressure. Manufacturers of precision tools are faced with these issues on a daily basis. As a manufacturer of gear cutting tools, Samputensili has been dealing with this challenge in the manufacturing of gear hobs for 70 years and knows that, in this respect, the choice of raw materials suppliers is fundamental. In order to combine the right materials to build a product that best meets customer requirements, a tool manufacturer needs to have in-depth knowledge of its manufacturing processes and combine them in the right way. The process chain to manufacture hobs includes soft machining, heat treating, hard machining and the preparation of cutting edge and surface.

Sawing, turning and milling are defined as soft machining processes, in which the tool is brought as close as possible to the desired finished contour. In this context, the part is heat treated to suit its geometry and the selected base material. After this step, the part undergoes hard machining. This process is subdivided into the machining of contact surfaces, machining of bore or shank and hard machining of the hob teeth, also known as relief grinding.

Relief grinding must generate the desired profile on hob teeth. This profile is designed specifically for the gearing to be obtained later on. Thereby, the dimensional accuracy of the tooth profile must be maintained along tooth length to achieve optimum results even with a reground hob. In addition, relief grinding is faced with the challenge of limited wheel dresser runout. While the teeth in a row are being profiled, the teeth in the next row form an interference contour which limits grinding wheel runout. Therefore, grinding wheels with very small diameters are used to relief grind hobs.

This is exactly what makes the new Samputensili INNOHob different from any other hob on the market. A newly developed grinding wheel with optimized process control is used during hob tooth profile cutting.

The INNOHob tools are manufactured using specially developed latest-generation hob grinding machines. When combined with one of the special-specs grinding wheels mentioned above and optimized process parameters, they achieve significantly lower surface roughness of the hob. While flank roughness on a standard hob is about Ra = 0.3 to 0.4 µm, optimized relief grinding can achieve a surface roughness of Ra = 0.1 to 0.15 µm. The aim is to reduce the witness marks that occur during grinding. A ground surface is characterized by peaks and valleys whose size can be expressed in terms of surface roughness. In particular, the protruding peaks are the most delicate zones on the flank, where the first signs of wear occur. Initial damage of the coating appears at these locations before a wide wear area develops. This means that significantly lower roughness involves fewer peaks in the machining marks.

The surface of the INNOHob hardly shows any appreciable machining marks due to relief grinding. There are hardly any peaks along the machining marks, which dramatically reduces the number of weak points at which flank wear initially occurs.