Solid carbide cutters Sharp-edged machining of filigree parts

From OSG Reading Time: 7 min

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When it comes to solutions for plastic parts, Rodinger Kunststoff-Technik is a first address. From the idea to the construction of the injection moulding tool to the production of the individual part or the assembly, RKT offers complete solutions from one source. In toolmaking, Rodinger relies on tools from OSG.

Sharp edges and clean transitions were decisive criteria for the hard machining of the tool insert.
Sharp edges and clean transitions were decisive criteria for the hard machining of the tool insert.
(Source: OSG)

With its main focus on medicine, pharmaceuticals and life science, RKT has decades of experience in the field of plastics processing. The company has established itself in particular as a specialist for microfluidics. In this field, the Roding-based company not only acts as a production partner, but has also developed a strategy for start-ups to enable them to industrialise microfluidic applications. The company offers technologies for the production of products that can be used to improve disease prevention, the effectiveness of medical treatments and diagnostics.

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Support for the entire production chain

RKT supports companies right from the concept phase. The goal is the mature component that — closely adapted to the application — can be reliably produced in series. To achieve this, the production process is already laid out in the design phase according to the principles of Design for Manufacturing, whereby this design includes the injection moulding process itself, but also downstream processes such as filling, assembly and packaging. At the same time, application requirements such as temperature resistance are included in the concept, and the flow of goods in production and logistics is taken into account. In addition, RKT supports customers in advance quality planning, the development of measurement strategies for series production and with solutions for operational risk management. Finally, on injection moulding machines with clamping forces of 40 to 250 t, all thermoplastics including the common functional additives are processed in the 1K, 2K and 3K process in grey as well as in ISO 8 and ISO 7 clean rooms, if required also analyte-free.

Stable processes, long durability

RKT already sets the course for series production with the design of the injection moulding tools. Starting with the general design of these tools, this extends to support through filling simulations. “During construction, we rely on classic machining processes as well as lasers or lithography, electroplating and moulding,” reports Reinhard Schneider, Team Leader NC Process Engineering. “Our goal is an injection moulding tool that — designed for stable production processes — has a long durability.” To achieve this, RKT not only validates the injection mould according to user specifications, but also maintains self-operated systems with preventive concepts. “The injection moulds we produce under these premises have a size of up to 900 x 600 x 500 mm and weigh up to approximately 3 t. Because the plastics are often very abrasive during subsequent injection moulding, wear-resistant steels are used for their production, which usually have hardnesses of around 53 HRC.” It is also important that the steels are resistant to plastic outgassing.

Hard milling from the block

Today, a whole range of OSG tools are used in RKT's toolmaking department. The beginning of the cooperation goes back a long time. Last year saw a significant intensification. “We want to further develop the tool and mould making sector,” Magnus Hoyer, Head of Academy at OSG, elaborates on the background. “We are implementing this with a growing sales force that operates close to the user.” The growing relationship between the two companies can therefore also be traced back to a concrete project that the field service in the person of Stefan Reitmeier has developed and implemented. The corpus delicti that initiated the ramp-up curve is a tool insert made of hardened steel 1.2343, which is particularly filigree. Usually, RKT pre-machines inserts softly before they go to hardening and are finally finished. In this case, however, the contours were so fine that it was decided to mill everything hard from the block. If the filigree geometries had first been soft-roughed and then finished with small milling tools, the probability of tool breakage would have been very high due to the rapidly changing allowances. At the same time, precise tool work would have been difficult because their exact position is hard to determine.

The right gauge is always applied

The insert was therefore first milled softly from the blank on all sides with two tenths of an allowance on the outside. Then a 9 mm flat hole was drilled for the insert cooling with a solid carbide flat drill ADF from OSG, followed by an 8 mm pilot hole with a solid carbide drill ADO-SUS 3 x D and the creation of classic cooling channels with an 8 mm deep hole drill ADO 30 x D from OSG. After hardening to 52 HRC, the insert was ground to an accuracy of ± 5 µ before being HSC-milled on an Exeron HSC 600. In order to create as even an allowance as possible and thus create the prerequisite for the finishing tool, RKT used the solid carbide milling cutter WXS-CRE in diameters of 6, 4 and 3 mm. After roughing, torus cutters AE-CPR4-H of diameter 1 and 0.7 mm were used for finishing. Finally, the entire component was also finished with a 0.7 milling tool. “The AE-CPR4-H are particularly suitable for filigree contours because they produce corners with sharp edges and high precision,” Reitmeier points out. “No matter where the milling tool is used, the correct measurement is applied to the component.”

Guaranteeing uniform dimensions

OSG has had the WXS-CRE series of roughing tools in its range for over ten years. “These are toroidal milling cutters with a unique geometry that resembles an end mill with a large corner radius,” explains Hoyer. “Characteristic of the milling tool is the corner radius, which has a tolerance of ± 5 µ. Because the manufacturing tolerance is half that, a particularly uniform allowance can be produced during roughing.” This means that the finishing tool can be used directly and, like semi-machining, time and effort can be saved. “In addition, the cutter achieves a large high-feed effect due to its large corner radius,” Hoyer continues. “With its crowned cutting edge, it dips gently into the material, which contributes to its robustness. The strongly negative rake angle of 10° provides additional stability and tool life, so that the WXS CRE can already precisely work the contours during pre-machining.” After the corner radius, the milling tool cuts flat, making the rake angle positive and allowing the cutter to plunge. Finally, high feed rates can be run with the WXS CRE, producing exact contours, tolerances and radii. The main focus, however, is on uniform stock allowance. Hoyer: “The user knows exactly: if I have allowance X at this point, I also have it in the opposite corner.”

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In addition, the cutter achieves a large high-feed effect due to its large corner radius. With its crowned cutting edge, it dips gently into the material, which contributes to its robustness. The strongly negative rake angle of 10° provides additional stability and tool life, so that the WXS CRE can already precisely machine the contours during pre-machining.

Magnus Hoyer, Academy Manager at OSG

“The radii must look good”

The AE-CPR4-H is the latest generation of solid carbide cutters from OSG. “Even with small diameters such as 0.7 mm, the torus cutter has four cutting edges so that sharp-edged corners with good transitions can be produced,” Reitmeier describes. “To provide wear protection at the same time, the AE-CPR4-H works with a corner radius of two hundredths. In this way, not only can the tolerance be maintained, but the uniform radius can also be ensured — even if the contact points are located differently.” When finishing the insert with the four-flute AE-CPR4-H, RKT could theoretically have run twice the feed rate compared to a ball cutter. “But we have to machine the entire component with the zero cutter,” Schneider emphasises. “So we decided to run slower with less wear. If at all, we are not much slower than with a ball cutter.” According to the team leader, the decisive factor is something else anyway: “We have to make sure that the radii - with a view to the plastic part — look good, i.e. that they don't have any offsets, markings, and so on. With the ball cutter, the line offsets would be larger, and I would have extra work when I go from the radius to the bevel. The fact that I can save this effort is worth investing in runtime for me.” Relevant for the quality is not least that the AE-CPR4-H with its unequal pitch suppresses vibrations. For larger diameters, a radius is also ground opposite the cutting edge so that the chip comes out of the groove easily.

Better and longer with less effort

So for all the machining on the Exeron HSC 600 HSC milling machine, RKT and OSG decided to go for tool life rather than speed. “For this application, machine running time is secondary,” Schneider emphasises again. “What is important is the high dimensional accuracy of the milling tool at a long running time. Moreover, we used to run comparable machining operations with twelve milling tools. Today there are six, and we save about 60 percent of the programming effort. This simplifies the associated tool tuning considerably and lowers the milling tool costs. Ultimately, we produce better contours with longer tool life today with fewer milling tools.”

Cooperating across the board

In addition to the milling cutters, drills and flat drills that RKT uses in this application, the Roding-based company also works with standard, fine and hard taps. “In the future, we also want to improve deep-hole drilling to a greater extent,” Schneider elaborates on upcoming developments. “The first tests were already running, in which we drilled with 1.2-mm twist drills in extremely tough steel with a chromium content of over 17 percent. The fact that this is possible at all and then, with such speed, impressed us greatly. A promising start, if not a quantum leap. So the cooperation with OSG is promising for us and has a promising future. Milling has already shown that.”