Case Study: Cutting Tools Support pays off: Milling processes save time and costs
Milling up to 70 % faster. A result of optimisation solutions that Zimmermann Formen- und Werkzeugbau developed with MMC Hitachi Tool.
Milling is certainly one of the key technologies for Germany-based Zimmermann. The injection moulding tool specialist says that whatever challenges in milling technology can be achieved and the possibilities should certainly be exploited. As a prerequisite, considering the economic view is a must as milling is a huge cost factor. At the company's CAM department at the Gladenbach headquarters, tools are programmed with WorkNC at 11 workstations, which are close to the machine as well as at other three stations in the CAM department office. Here, tools take top priority. After all, the tool also has a positive commercial influence on the process, which is the reason MMC Hitachi Tool was known to Zimmermann, because the tool manufacturer offers the optimisation of the milling processes on-site through assigned projects.
“Our joint-optimisation project was about a highly topical issue, where CAM strategy and tooling are at the centre of attention: Trimming large sloping surfaces with barrel cutters,” Michael Neumann, manager at Zimmermann notes. He added that two mould cores of approximately the same size, measuring just about 2000 mm x 600 mm x 500 mm, were selected for a door sill mould in an optimisation project. However, both mould cores had different slopes: 11° and 17° respectively. Moreover, the cores were made of different, non-prehardened (32 to 34 HRC) sectional steel grades, namely 40CrMnMoS8-6 and 40CrMnNiMo8-6-4. Both cores were milled on two different machines. On each of them, the slopes were previously trimmed with Z-constant, that is, each z-plane was processed individually with the milling cutter. Furthermore, the roughness and dimension were bound to the corner radius of the tool when finishing the inclines, the company explained.
For the inclined areas, the company previously used a screw-in, double-edged, solid carbide torus milling cutter with a 16-mm diameter and R1 radius for finishing on the Fidia Digit. The tool worked well, but the relatively small depth of cut resulted in long machining times of up to 14.5 hours, according to Zimmermann. With the tools from MMC that were deployed on the Mecof for finishing the 17° bevels, the ASPVM mini, indexable insert milling cutter with a 16-mm diameter for trimming with a Z-constant was used successfully. Currently, these MMC tools are also used in other sizes at Zimmermann for various other applications.
Both tools were replaced with MMC’s GF1 series insert-barrel cutters as part of the optimisation project. On the Fidia Digit, it was the GF1T with a 16-mm diameter and a 30-mm plate radius, while the GF1G with a 25-mm diameter and a 20-mm plate radius was used on the Mecof. Both replacements are barrel tools with different plate bodies and inclination angles to cover as many geometries as possible, the company explained. Viewed from the Z-plane, the inclination angle of the G-shape that was raised up to 11° on the Fidia Digit, would no longer be ideally suited to the 17° on the Mecof, nor would the required surface quality be achieved with the set cutting depth/width used. This is because both surface quality and dimensional accuracy are criteria for the inclines.
According to Zimmermann, the GF1 delivered excellent results with impressive cutting values on both machines right from the start. With the barrel milling cutter, the speed of rotation remained more or less the same during finishing, but the axial feed was set to 0.7 mm in all inclined areas. Compared to the previous 0.3 mm, this was of course a huge success, allowing for a large time saving potential to be achieved. In addition, the inserts of the barrel milling cutter showed no wear.
Another highlight was that the strategy developed by MMC enabled the GF1 to mill on three axes on both machines and not on five axes, simultaneously or in an inclined position, as is often recommended. Despite jumps in the contour, everything was milled absolutely true to size with three axes.
Overall, the running time for the entire finishing process on the Fidia Digit was reduced from 14.5 hours (in the past) to four hours and 20 minutes, which represents a time saving of around 70 %.
The result on the Mecof is also interesting. Here the GF1 had to compete with the ASPVM mini, indexable insert milling cutter from MMC — both with 25-mm diameters. Despite the very high feed rates using the ASPVM, the barrel milling cutter delivered significantly better results. In comparison to the already very good ASPVM, another 18 hours of machining time could be saved in the finishing process, which now actually took only 7 hours using the GF1. “Of course, the enormous time advantage achieved also has a very positive effect on production costs,” emphasises Neumann, while praising MMC’s energetic commitment: “Without this on-site support, we would not have been able to achieve this great result so quickly with the barrel milling cutters.”
Started as a foundry and model making company
Founded in 1886 as a foundry and model maker, Zimmermann has 95 employees today and is an experienced specialist in technically, sophisticated injection moulding tools of usually larger designs, weighing up to 50 t and more, which include injection, back injection or two-component moulds. Included too are those with insert technology, some with very different designs. Examples are stacks, rotary tables and transfer moulds. In the automotive sector, these are used to produce large to very large parts like instrument panels, bumpers and spoilers of many well-known European car brands. In non-automotive applications, the spectrum ranges from garden chairs to waste bins. The toolmaker sees itself as a full-service provider — covering the entire value chain from delivering the CAD model of the plastic part to serial production.
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