Machining tools High-precision tooling for accurate superalloy machining

Editor: Alexander Stark

Italy — When highly demanding projects must comply with very tight tolerances on unique components manufactured from hard-to-machine materials such as Inconel, a tool needs more than just industry-leading reliability. An example of this is the long-term technological partnership between Big Kaiser and Covis, where high-precision tooling products have enabled Covis to meet the tough requirements of its customers.

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Covis relies on Big Kaiser for its precision machining: boring heads, roughing heads and the modular Smart Damper vibration damping system from the Swiss tooling supplier help Covis to adhere to very tight tolerances even on exotic materials and superalloys.
Covis relies on Big Kaiser for its precision machining: boring heads, roughing heads and the modular Smart Damper vibration damping system from the Swiss tooling supplier help Covis to adhere to very tight tolerances even on exotic materials and superalloys.
(Source: Big Kaiser)

Founded in 1994, Covis designs and produces tailor-made solutions to strict deadlines and quality standards, managing and certifying the entire production cycle at its three operating sites in Italy. The company specializes in precision mechanical machining and welding, including machining of exotic and treated materials such as steel, Inconel, Duplex and Super Duplex and other special alloys. The components it manufactures include highly-specific precision parts for the energy sector, such as for offshore and onshore oil drill rigs and platforms. Fabio Soprana, Technical Manager at Covis, explains that the company works closely with multinational companies, guaranteeing the stringent standards and requirements throughout the production chain — from the purchase materials from certified suppliers to the certification and tracking of all subsequent processes.

Flawless quality assurance is a basic prerequisite in the energy and petrochemical sector. To meet the high standards demanded by its customers, the company has to overcome multiple challenges in its day to day machining operations, requiring specialized techniques, tools and procedures. The manufacturer is quite specialized and produces unique parts and components as one-off's, or in small series runs.

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The production process consists essentially of three phases: first phase preparing the piece, followed by the material coating process, after which the piece is precision machined to the final finish. Sometimes the material that is machined is exclusively Inconel or Super Duplex. Inconel is a nickel and chromium based super alloy that is exceptionally resistant to oxidation, high temperatures and corrosion, but its hardness makes it extremely challenging to machine. The heat generated during the machining process flows into the tool, subjecting it to a sustained barrage of stresses and strains. “Cutting speeds are low, contact times are long and machining sessions are protracted,” says Soprana.

Medium to large parts for the energy sector are machined in the main production site, with diameters ranging from 500 to 2500 mm. To achieve the best possible finishing result on such difficult materials, the machining process requires the additional use of vibration dampening systems. Further exacerbating the issue, the depth of the holes to be finished is substantial (8-9xD, f. e. 45x420 to 53x480) and tolerances are very tight, with finishing grades pushed down to a roughness of 0.4~0.2.

Such conditions require the participation of a tooling partner such as Big Kaiser, capable of ensuring maximum precision and repeatability at all times, and eliminating vibration levels that could impact the company's high-quality standards.

Solving the problem of vibration

Covis uses a variety of tools from Big Kaiser, including boring heads, roughing heads and the modular vibration dampening system Smart Damper. The Smart Damper bars have enabled deep boring with high precision finishes on valves with Inconel, with substantially better results than were possible using solutions from other suppliers.

All the machining centers in the workshop are also equipped with the Big-Plus spindle system, the only system in the world to guarantee double simultaneous cone-flange contact between the spindle and the machine. This is another important step that gives more rigidity to the machine and keeps vibrations under control. Soprana explains: “When working with deep bores and anti-vibration bars, it's important to add additional rigidity to the machine. After several years of having used Big-Plus and the comapny's vibration-dampening solutions, I can honestly say that they have never let us down.

The weld seams have a strongly interrupted cut, which allows inserts with large radii to be used. Big Kaiser's tools ensure continuous machining, meaning that Covis does not have to perform adjustments or breakage checks at every hole, which saves time and resources.

In the hole-finishing and re-centering phases, there are several aspects that need to be taken into consideration. Firstly, the tool must reach the bottom of the hole within a certain cutting time; secondly, it must remain within tolerance and roughness specifications and thirdly, it must guarantee the concentricity of the hole. Soprana explains that it is not possible to obtain precise results on such demanding machining operations using reaming processes. That's why the company relies on boring heads.

Roughing must also be done with attention to detail since a rough-cut piece with high roughness invariably impacts the quality of the finish. Covis has, therefore, invested into improving the roughing process by utilizing Big Kaiser roughing heads that have enabled high-precision finishes on pieces that have already been surface treated.

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