MMC Hitachi Tools has increased the efficiency of the milling processes at Harting. Both cost and time were saved by employing the right strategies at the company for the grinding of valves.
The grinding of valves has been replaced by automated hard milling in the toolmaking sector of Harting Applied Technologies. To increase efficiency and process reliability, the milling processes were jointly analysed and optimised together with MMC Hitachi Tool in Espelkamp, Germany. The result: Longer milling cutter service life, improved surfaces, shorter processing times and manufacturing costs that are 60 % lower in comparison to grinding.
“We are specialised in the design, development and production of sophisticated injection moulding moulds, punching and bending tools and special machinery as well as micro-technology manufacturing processes,” explains Managing Director Dr Volker Franke, who is responsible for toolmaking at Harting. “High-tech” does not only apply to the products made in Espelkamp, but also to the toolmaking.
Harting had already established itself at a relatively high level in the area of milling, but there was still room for improvement, particularly in the area of hard machining. The Westphalian company’s own attempts in this area had been fruitless. Thus, they contacted MMC Hitachi Tool. The process optimisers of the Japanese tool manufacturer are known for collaborating with customers in developing more efficient processing strategies.
After the analysis of the current situation, which is obligatory at MMC Hitachi Tool, the initial general tests were soon carried out. These were so promising that the company wanted to transfer the knowledge into everyday business. A valve with similar geometry but different dimensions, which constitutes the volume business at Harting during hard processing, was selected for this purpose. These valves had been ground in the past. Well over 20 identical valves of this kind are used in multi-cavity moulds. They are used to inject the plastic levers that act as a locking mechanism for the well-known, modular Han connector. This valve is made from thermal, wear-resistant X38CrMoV5-1 (1.2343) plastic mould steel. After roughing, it is pre-hardened from 52 to 54 HRC and the surfaces semi-finished from 0.2 to 0.02 mm and then finished to the final dimensions. The tolerance specification for these surfaces is between 0 mm and - 0.01 mm in the overall dimensions.
Firstly, the feasibility was analysed. Different tools and cutting values were tried out together, machining times, wear behaviour and surfaces were compared, and it was checked time and time again whether improvements were possible. Starting with different ball cutters and other types of milling cutters, they finally arrived at the EHHR milling cutter, which was also tried out in different diameters. A test workpiece with a diameter of 8 mm quickly proved to be ideal.
The result surpassed all of the previous tests. The EHHR (Epoch High Hard Radius) is a six-bladed VHM cutter that is designed exclusively for hard machining. It features a slightly polygonal design and is manufactured by MMC Hitachi Tool, which has an in-house ATH coating system. The diameter of the side cutters, which are offset by 120 degrees, is slightly tapered compared to the end cutters, resulting in a high material removal rate and, simultaneously, a long tool life. In conjunction with the six blades of the tool, this results in high feed rates and, therefore, very short machining times. The fast cutting speeds achieved in Espelkamp with the EHHR are impressive: With bigger parts, where a diameter of 12 mm was used, speeds of up to 350 m/min were achieved for pre-finishing, even in excess of 500 m/min for final finishing.
Only two EHHR cutters with diameters of 8 mm — one for semi-finishing, the other for finishing — had in the end been sufficient for machining a complete set of valves to the final dimensions. And this was carried out extremely quickly and with top-quality surfaces. Even after the last valve was completed, the tool featured so little wear that it was still well within tolerance. It would have been possible to mill even more valves before the EHHR had gone out of tolerance. But that was not tested. The EHHR is currently being used with diameters of 6 mm, 8 mm and 12 mm in the toolmaking shop at Harting because of the many different components. This way, all of the current valve types are automatically manufactured in accordance with the sample that has been jointly developed by Harting and MMC Hitachi Tool. The proven production strategy will also be used for forthcoming projects in Espelkamp and declared the manufacturing standard. Harting Applied Technologies now obtains more than 80 % of its milling tool requirements in the hard milling sector from the Japanese toolmaker. Along with the quality of the tools, the process development expertise of MMC Hitachi Tool is becoming increasingly important to the company from Westphalia.
As part of the ‘Production 50’ manufacturing concept developed for tool and mould construction by MMC Hitachi Tool, a cost-effectiveness calculation was carried out for the test valve at the conclusion of the project, which is based on values for previous surface grinding and documents and compares the costs on the basis of the new milling processes. The result: Cost savings of 60 % have been achieved by using milling rather than surface grinding. “There are also the significantly reduced throughput times, the elimination of manufacturing bottlenecks when grinding and the additional flexibility achieved by the changeover to milling. We have now made the breakthrough in automated hard milling,” says Dr Volker Franke. “We have achieved exactly what we wanted with regard to parallelism, angularity, wear and process reliability. In terms of the surfaces and tolerances, we have even surpassed the specifications, also in comparison to grinding.”