Round off, deburr or calibrate? Hydroerosive processing of aerospace components

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Sonplas GmbH

Fastems Systems GmbH

Aerospace components are exposed to extreme environments. Uncontrolled surface finishes and bores with burrs and sharp edges are unsuitable for use under such conditions. Sonplas offers an efficient solution with its 'HydroEROsive' (HERO) process, in which an abrasive‑laden fluid is pumped at high pressure through the internal geometry of a workpiece.

Deburring or calibrating bores in aerospace components can be extremely challenging. Parts are often made from specialised materials such as high‑performance composites, and they must meet demanding operational and technical requirements. “To achieve extremely smooth surface topographies, we offer our HERO process,” says Werner Riederer, sales engineer at Sonplas GmbH in Straubing, Bavaria. With this flow‑abrasive process, internal bore transitions can be deburred or edge‑rounded efficiently and — crucially — in a controlled manner. This both improves high‑pressure resilience (reducing wear at high pressures or slowing it substantially) and effectively performs an artificial pre‑ageing of the component. The user benefits from consistent performance over the part’s entire service life.

An abrasive‑laden fluid flows through the component like liquid sandpaper, following the internal bore transitions or geometry. Werner Riederer explains: “If a bore feeds into a bore of smaller diameter, a sharp edge forms at the diameter reduction where abrasive particles accumulate under high pressure. This leads to material removal. The effect depends on the fluid pressure and on the abrasive particles used.”

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Flexible with regard to component types

A broad range of workpieces can be processed. “The decisive factor is always the bore size to be treated. Our systems can grind bores with diameters from 0.1 mm up to 5 mm,” says Riederer. Workpieces may be made of steel or stainless steel, but aluminium, magnesium and precious metals such as gold, silver or platinum are also possible. Carbides, glass, ceramics, plastics and fibre‑reinforced composites can likewise be treated.

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Process medium optimised to the task

First, the properties of the process medium are tailored to the requirements of the part to be processed: the optimal rheological specification is defined to achieve the desired flow rates, geometries and rounding radii. Depending on the application, the media are formulated as mineral‑oil‑based or water‑based and adjusted to viscosities from 0.5 up to several 10,000 mPa·s. The type, concentration and particle‑size distribution of the abrasives in the medium largely determine the achievable removal rate and the surface quality of the parts. Highly abrasive ceramics such as boron carbide or aluminium oxide — and even synthetic diamond — can be used as the abrasive grain.

“This versatility allows us to process parts with cycle times optimised for production,” Riederer says. Through targeted additives, the grinding fluids also act as effective corrosion protection for the customer parts. Good wetting properties and compatibility with rinsing and inspection fluids also allow particles that cannot otherwise be removed to be washed out with ease. Intelligent process engineering makes it possible to meet required cleanliness classes according to VDA 19 / ISO 16232. Users thus profit from a holistic process that can eliminate further costly processing steps.

Sonplas also offers a water‑based version of the conventional process medium. This has several advantages: it is environmentally friendly and hygienic, has a lower CO2 footprint, and — because it does not endanger groundwater — disposal costs are lower.

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Calibrating flow with confidence

In addition to edge‑rounding and deburring, the HERO process can also be used to calibrate the flow rate of bores. For this purpose the operator selects a low‑viscosity fluid. “We place the component in our system, round off the entry edges of the injection holes and increase the flow by 10 to 40 per cent,” explains Werner Riederer. This offers a decisive advantage: after mechanical erosion the bore accuracy is around ±3 per cent, whereas following the HERO process it is a process‑secure ±1 per cent. Hydroerosive machining therefore allows the user to calibrate flow rates on their components to a very high degree of precision. The operator can monitor the rising flow online throughout the process, set the required value exactly and establish flow tolerances in a process‑reliable manner.

Whether deburring, edge‑rounding or calibrating, the hydroerosive process provides three distinct application options. By adjusting the respective process parameters, the operator can meet the differing machining requirements reliably and reproducibly. “The process thus fulfils all drawing‑ and component‑specific requirements,” says Sonplas expert Riederer.

Tailor‑made systems

Sonplas also equips its systems with rotary tables so that processes such as grinding, rinsing and/or flow measurement run in parallel. Depending on the requirement, each component can pass through up to eight stations. The slowest operation dictates the cycle time. The customer can configure their bespoke machine modularly to meet specific needs and can subsequently add process stations such as rinsing or measurement units. Databases and MES systems can be integrated. Appropriate component markings (DMC/data‑matrix codes) enable full traceability of machining and process data. “Flow control and master parts, which the integrated software feeds into the process at defined intervals and checks regularly, are also available,” says Werner Riederer.

Because the systems operate as closed processes, user errors are effectively eliminated. The human operator only needs to load parts manually or change pallets when required — the process then runs automatically. For higher volumes automatic loading is also possible, for example by means of a robotic loading module. “This allows us to link processes together,” Riederer explains. For instance, the loading module can be positioned after erosion or laser drilling and before HERO processing. The customer then simply places the blank in the system and collects the drilled, deburred or calibrated component from the other end, neatly stacked on a pallet. “We deliver everything from simple development machines to production‑ready, high‑volume systems, depending on customer requirements,” emphasises Werner Riederer.