Chemical & ElectroChemical Treatment
Electropolishing rounds edges, polishes and smoothes metal surfaces, and improves the corrosion resistance of sophisticated medical devices. ANV Lasers provides the following electropolishing and electrochemical services:
- Electrolyte formulations and technological processes for electropolishing NiTi, CoCr, Ti, and stainless steel stents and frames (surgical implants).
- Part cleaning (degreasing), deburring, descaling, deoxidizing, and passivation.
- Electrolyte analyses for metal content, free acid, and water content by volumetric titration, spectrophotometry, and polarography (cyclic voltammetry).
- Electrolyte conductivity measurements.
- Corrosion testing, with extensive expertise regarding every aspect of this highly complex test protocol.
- Electrochemical thinning, to achieve the part’s defined electrical resistance specification.
- Technological equipment design, including part holders, part reversed rotation devices.
- Pulse current supply, electrolyte chilling systems, bath and cathode geometry fittings.
Electropolishing and other finishing treatments, such as passivation, are a critical last step in the production of complex micro-components. Electropolishing, for example, serves several important purposes:
- It achieves a very high level of surface smoothness.
- It rounds any rough edges that may have formed during laser cutting.
- It reduces any dimension gain that may have been introduced by laser cutting.
- It ensures chemical homogeneity of the device material.
- It provides primary passivation against corrosion.
The head of ANV Laser’s electrochemical treatment department is a PhD with 40+ years of experience in the field and our electrochemical treatments are designed and executed by in-house chemical engineers.
ANV Lasers’ Electropolishing Innovations
At ANV Lasers, we formulate our own electrolyte solutions, including a novel formulation that can be used at near-room temperature (15-20° C), NRT, as opposed to traditional electrolytes that require a very low working temperature (-10°C). These innovative electrolytes can be used without the deep chilling required by traditional electrolytes, which eliminates the atmospheric moisture condensation onto the electrolyte surface – the factor that basically limits the essentially nonaqueous electropolishing electrolyte capacity in respect to maximum amount of the parts that can be treated in a given volume of electrolyte before its complete replacement. Moderate chilling in this process is solely needed in order to only compensate a heat generation during processing and not for the low temperature keeping. The electropolishing process becomes far more efficient, with the ability to process up to 3 times more devices before having to change the electrolyte solution.
Another advantage of our NRT process introduced is related to current density (i), which is a critical parameter in the electropolishing process. In a typical electropolishing procedure, one needs to apply a current density of 0.5A/cm2, i.e., ~10A for a 20 cm2 device. That level of amperage can cause “contact marks” (one of not tolerable defects of electropolishing) on the device. ANV Lasers’ NRT works with 5x less current density, i.e., 0.1A/cm2, making possible a large part treatment at low currents, avoiding thereby contact marks.
With our extensive experience and expertise in all aspects of electrochemical treatments and quality assurance, it is not surprising that many customers entrust us with the finishing and testing of their devices even if they have been manufactured elsewhere.
Deoxidation: In contrast to widely practiced and heavily controllable chemical etching, we have developed electrochemical deoxidation process (necessary prior to electropolishing), benefiting from an easy control of the process’s current, potential, and duration. Another advantage of electrochemical deoxidation is much lower the weight (thickness) loss required in this process and its proven effectiveness also in treatment of not sand-blasted parts.
Passivation against corrosion: We have found in our precise measurements that electropolishing itself or recommended in literature treatment in 35% nitric acid hardly (if at all) improves the corrosion resistance of NiTi (compared to not finished material). Our designed anodizing treatment, in contrast, provides at least 25-x protection effect, measured in terms of corrosion test.
NiTi wire thinning: What is required in many implantable devices made of NiTi wire is simply to reduce the wire diameter on the part of its length. It may become difficult to resolve task in case the required relative diameter reduction reaches 30 or more percent. We use unique electrochemical technique allowing up to 50% the wire even diameter reduction.
Mathematical model of the electropolishing process: We have elaborated a math model allowing calculation of required current and the process duration for galvanostatic conditions, provided that such target parameters as the device’s relative weight loss (relative size reduction) and/or final the device surface area are specified.