Medical Instruments, Part 2 – Mass Finishing or Shot Blasting, Which Technique is Best?

The medical industry is constantly looking for better, more suitable materials that will offer greater performance and longevity for medical devices, implants, and instruments while simultaneously searching for more efficient manufacturing technologies.

When it comes to surface finishing, such newly developed materials and manufacturing processes can pose considerable technical challenges. That’s why close cooperation between the medical device manufacturers and qualified surface treatment experts is essential during the development and prototyping phase.

In our last medical instrument blog, Rosler Metal Finishing discussed the surface finishing requirements for medical instruments. This blog will dive deeper into the techniques used in surface finishing and answer the question: What is the best type of surface finishing for medical instruments?

The short answer is a combination of mass finishing and shot blasting. Guidance for a surface finishing expert can help determine the best process – typically a series of processes – for a specific medical instrument.

Grinding Solutions Offered by Mass Finishing

Pressure between the media and work pieces creates a constant rubbing and helps polish and smooth a workpiece through mass finishing.

Specific finishing tasks for mass finishing include:

  • Deburring and Edge Radiusing – Sharp burs are ground off and edges are rounded.
  • Surface Cleaning – Scale from forging, heat treatment, or castings as well as oil, coolant, shavings, and other surface impurities are removed.
  • Surface Smoothing – In preparation for polishing, plating, and electro-polishing, a smooth surface is created. This is often referred to as “cut-down”.
  • Polishing – For appearance and stain resistance, high-gloss polishing can be achieved down to Ra = 0.8 micro inches.

Impact Systems Created by Shot Blasting

In shot blasting, small metal or mineral pellets are thrown onto the surface of a work piece at speeds of 200-800 feet/second. The impact on the work piece surface produces the desired cleaning, peening or texturing effect.

For medical applications, mainly air blast systems are used. Generally, shot blasting makes a surface rougher. The smoothest finishes achieved with shot blasting are about Ra = 32-16 micro inches.

Specific finishing tasks for mass finishing include:

  • Surface Cleaning – In addition to cleaning, descaling after forging, casting, or heat treatment often produces a rougher surface.
  • Peening – Surfaces treated with compressive stress create more resistance against general wear and corrosion stress cracking.
  • Cosmetic Blasting/Texturing – Producing a very fine, matte, anti-glare finish improves an instrument’s aesthetics.
  • Surface Preparation for Coating – Surface texturing creates better adhesion of the coating material.

Common Characteristics

Even though their technical characteristics are quite different, mass finishing and shot blasting share many common features.

Both methods:

  • Create homogeneous, all-around “isotropic” finishes as opposed to “anisotropic” surface appearances produced by machining, belt and wheel grinding, rolling, drawing, or extrusion.
  • Can handle practically any type of material, from very tough metals like titanium, cobalt-chrome, and even tungsten carbide to softer metals like aluminum and magnesium, but also plastic and even ceramic.
  • Produce a wide spectrum of consistent, absolutely repeatable finishing results with easy-to-control mechanical processes. They completely eliminate quality fluctuations inherent in manual finishing operations!
  • Enable users to select from a wide spectrum of equipment, from simple, low-cost, stand-alone machines to fully automated finishing systems.
  • Are eco-friendly. Their operation does not pose any health hazards, and the sludge from mass finishing or metal dust from shot blasting can typically be disposed of in landfills or recycled (please check with your local laws and regulations).
  • Are used at various manufacturing stages. For example, for general cleaning, deburring/edge radiusing immediately after casting, forging, machining, welding, 3D printing, and intermediate finishing as preparation for coating, plating, or electro-polishing all the way to placing the final, finishing touch in the form of high-gloss polishing, or very smooth, non-glare finishes.

Combined Efforts

Mass finishing and shot blasting go hand-in-hand. For example, shot blasting is used as a preparatory cleaning or peening step followed by a mass finishing process for surface smoothing and polishing or the other way around.

Certain medical instruments like tweezers, scissors, and scalpels must be polished by mass finishing and then blasted to place a matte, non-glare surface finish on the work pieces.

Consider the finishing process medical pliers:

Economic Advantages

Both technologies are highly adaptive to customer needs and offer flexible, modular solutions. The equipment spectrum ranges from small manual or semi-automatic machines for low production volumes to fully automatic systems for high volume.

The customer decides how much they want to spend and what degree of automation they desire. The costs for work piece fixtures – if required – are manageable, and due to the high degree of mechanization, the personnel costs are only a small percentage of the total costs.

For relatively simple processes, the costs per piece can be as low as a few cents. With more complex, multi-step finishing operations for high-value work pieces like orthopedic implants the costs for cut-down after casting/forging, followed by surface smoothing and polishing may amount to several dollars, a small fraction of the total component costs!

The big savings are, however, achieved by the stability of the finishing processes, ensuring absolutely repeatable, high-quality finishing results with zero scrap rates!

The Rosler Way

We understand the importance of precise finishing on medical instruments. Whichever step and finishes your workpiece requires, Rosler Metal Finishing to help you find a better way and achieve exact results. Contact us today to discuss your unique challenges.

Check back for additional blog posts about medical instruments in the future and be sure to catch up on our previous post in the series, “Part 1 – Surface Finishing Requirements for Medical Instruments.

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