Moulds for medical products Can high-speed machining achieve the quality demanded for medical products?

Updated on 28.06.2022 From Mag. Victoria Sonnenberg

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In a joint project, GF Machining Solutions and Zecha compare four different automated manufacturing processes for injection moulding — with a focus on their qualities and runtimes.

Using cooling lubrication, even high-alloy, soft materials can be dry-finished, semi-finished and fine-finished with maximum precision and component shape accuracy just as well as high-strength, hard materials.
Using cooling lubrication, even high-alloy, soft materials can be dry-finished, semi-finished and fine-finished with maximum precision and component shape accuracy just as well as high-strength, hard materials.
(Source: GF Machining Solutions)

Production equipment from GF Machining Solutions and Zecha milling cutters open up four economical options with different surface finishes for the implementation of cavities in a mould insert made of 1.2343 with a hardness of 52 HRC. The first manufacturing process for producing a cavity is EDM using a graphite or copper electrode.

Production of injection moulds by means of graphite electrode

The complex production process consists of hard milling of the mould insert, electrode milling and subsequent die-sinking EDM. The process for producing an injection mould using a graphite electrode takes just under 57 minutes in total, but requires many work steps. With Zecha tools from the Seagull family on the GF machines, the Mikron Mill S 600 U and the Form X 600, users benefit from tolerances of ± 0.005 millimetres as well as surface qualities Ra 1.6 micrometres and VDI 24. The machine bed made of polymer concrete with high thermal inertia and good damping properties makes the Mikron Mill S series special. All five axis are equipped with direct drives (X, Y, Z, B, C drives) and thus enable rapid traverses of up to 100 metres per minute and µ-accurate positioning.

Thanks to a spindle with Opti Cool or Cool Core technology, the temperature management system consisting of independent cooling circuits ensures optimum cooling of all heat sources and the machine bed. Process reliability, productivity and part precision are achieved through the stable thermal system, integrated automation and high performance.

Special geometry minimises cutting pressure

The Seagull tools are stable ball and torus cutters with an extremely short cutting edge and special geometry for minimising the cutting pressure in graphite electrode production. The patented (EP 2 540 427 B1/DE 10 2019 122 039 B3 ), very short cutting edge of the Seagull cutters enables easy-cutting milling of graphite and other hard-brittle non-ferrous materials in dry and wet machining in the specially developed interaction of carbide, diamond coating and geometry.

Seagull high-end 567 and 577 series cutters offer very tight tolerances. Each tool is measured and the packaging label is provided with the actual values. Seagull quality cutters in the 568 and 578 series are for price-conscious users. New to the Seagull family is the 576.T3 torus cutter. With its combined geometry characteristics and cutting edge dimensions, the milling cutter creates a lot of chip space for cutting volume and a high stock removal rate for roughing as well as finest engagement ratios for finishing.

The production time for the procedure with a copper and graphite electrode is extended by 180 minutes to a total of 3 hours and 57 minutes. Here, too, the machining centres from GF Machining Solutions equipped with solid carbide torus and ball end mills from the 556 series enable Zecha tolerances of ± 0.005 millimetres and surface finishes of Ra 0.22 µm and VDI 7. The solid carbide torus end mills for HSC machining of non-ferrous metals are available as short versions with free length and precision-ground, polished cutting edges and chip chambers. For precision in the μ-range, Zecha manufactures this tool series uncoated as standard or, on request, with a coating optimally matched to the machining.

High-speed milling

High-speed milling is another manufacturing process for injection moulds. In the first two work steps, roughing is carried out with a ball cutter with a diameter of 3 millimetres and feed rates of 4 metres per minute. In contrast to machining with a larger tool, the reduced machining times mean that set-up times and costs are reduced, as are the number of tool stations. Almost 90 % of the total machining time is spent on finishing, which places the highest demands on the tool in terms of maximum surface quality, accuracy and tool life.

Tolerances of ± 0.005 and surface finishes of Ra 0.1 microns and VDI 0 were achieved in the three machining steps in 60 minutes. The high-performance end mills and ball mills of the Peacock tool series used on the Mikron Mill S 600 U develop their potential in the machining of soft, hard and powder metallurgical steels up to 70 HRC.

The Peacock family is the innovation in Zecha's hard milling cutter range for high-speed machining in tool and mould making. The multi-flute Peacock ball nose and torus end mills are available in various dimensions: 581P series ball end mills from diameter 0.2 to 12.0 mm and 583P and 597P series torus end mills from diameter 0.2 to 6.0 millimetres and 0.8 to 6.0 millimetres respectively. The additional 599 series complements the Peacock line with immediate effect with new ball and torus cutters from diameters 0.1 to 12.0 millimetres. Furthermore with the new lines 599.F4 and 599.F6 - special high-performance end mills: 599.F4 with a finely ground protective radius of max. 0.05 millimetres and 599.F6 with a defined grinding radius, providing additional edge protection. The new cutter design guarantees high machining efficiency through great performance and wear resistance for a wide range of materials, alloy components and material hardnesses also up to 70 HRC.

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A new coating technology in combination with the right solid carbide substrate, a stabilised geometry, finest micro-geometry as well as rounded shank transitions cover additional applications in all shapes and component hardnesses. Even high-alloy, soft materials can be dry-finished with cooling lubrication just as well as high-strength, hard materials, not only roughing but also semi-finishing as well as fine-finishing with the highest precision and component shape accuracy. Minimised friction thanks to optimised and homogeneous coating surfaces as well as coating adhesion additionally achieve better repeatability and safety in the application. The resulting potential for tool life and surface finishes offers significant added value for the customer.

The new CBN line 950 is offered as ball nose and torus end mills in the range of 0.2 to 2.0 millimetres. The high hardness of the substrate contributes to an increased lifetime of form and dimensional accuracy. The specifically applied geometry achieves an optimum surface finish on the component. Likewise, this shape contributes to the stabilisation of the cutting edges, which is reflected in a long service life.

Combining milling and laser texturing

Complemented with digital laser technologies, aesthetic and functional texturing can be implemented and reproduced easily. Even complex 3D geometries, including precision parts, are precisely textured, engraved, structured, marked and labelled. Using the Laser P 400 U from Schorndorf, the last step, namely finishing, can be replaced by lasering in the aforementioned process. Compared to the milling process with integrated finishing, the production time is reduced by 22 minutes to 37 minutes for the production of the injection mould. With the intelligent combination of milling and laser texturing, the two experts create an economical alternative for surface finishes of Ra 0.6 MIkrometer and VDI 16 as well as the lowest tolerances of ± 0.005 mm.

Together, GF Machining Solutions and Zecha cover all manufacturing processes with their product portfolios. For the customers of the two precision experts, this cooperation results in a wide range of possibilities, including the production of injection moulds for medical technology. The GF machines paired with the Zecha moulds make manufacturing with a wide range of technologies from a single source a reality. The resulting supplier savings allow the customers of the two experts to benefit from a reduction in costs. GF Machining Solutions and Zecha are continuously working on optimising EDM technologies to increase machining speed and reduce electrode wear with highly polished surfaces of Ra 0.1 microns. In this way, GF Machining Solutions and Zecha have the most economical and highest-quality solution ready for every application with specified tolerances, surface qualities and production times. In the future, the partners will continue to optimise their machines and tools together to ensure the best possible added value and support for customers.