Along with the material choice discussed in Part 1 of our Spinal Implants series, surface treatment is the most important factor affecting the functionality, performance, and longevity of spinal implants and instruments.
During the manufacturing process they may have to undergo multiple
finishing operations including burr removal from previous manufacturing
operations, rounding of sharp edges, general surface cleaning, surface
smoothing, and, frequently, high gloss polishing.
Treatment steps can also include surface texturing/profiling and shot peening, areas Rosler Metal Finishing has extensive experience in.
This blog post will focus on the finishing requirements and challenges
of spinal implants as well as the solutions provided by mass finishing and shot
blasting processes and the associated costs.
For the comfort of patients and effectiveness of the components, spinal
implants must be finished to precise specifications, including:
- The removal of sharp edges and burs to prevent rupturing blood vessels during implantation.
- A smooth, sometimes polished surfaces to prevent osseointegration in some types of implants.
- Textured (somewhat rougher) surfaces to promote osseointegration in some implants or as preparation for coatings.
- Absolutely clean surfaces to prevent infections.
- Improved resistance against tensile and bending loads for longevity. This is achieved with shot peening mainly spinal rods, screws and cervical plates.
Additive manufacturing is rapidly evolving from a purely prototyping
method into a full-fledged manufacturing system, bringing challenges and
opportunities with it.
Titanium interbody fusion cages are already made using additive
manufacturing with great success.
While we expect the trend towards 3D printed orthopedic implants to
accelerate over the coming years, additive manufactured components pose
enormous finishing challenges.
In addition to successfully removing support structures and sintered
metal particles, these implants have significantly higher surface roughness to
overcome. The initial surface roughness of a 3D printed component can be as
high as Ra = 800 micro inches, while the initial surface roughness of a cast or
forged part amounts to Ra = 120-320 micro inches.
Additional processing and time are required to achieve similar finishes
between additive manufacturing and forged work pieces.
Many surface treatment technologies are utilized for finishing spinal
implants, yet the numerous cost benefits and technical flexibility shot
blasting and mass finishing are probably the most widely used treatment systems
for surface preparation and finishing of medical components.
Mass finishing works as a grinding system to create pressure and rubbing
between work pieces and media. This smoothing, polishing effect can achieve
surface finishes as low as Ra = 0.8 micro inches.
Uses include deburring/edge radiusing, surface cleaning (descaling,
de-oiling) after casting, forging, blanking, machining, heat treatment, thread
rolling for screws, and additive manufacturing.
Shot blasting utilizes the impact of small metal or mineral pellets to
produces cleaning, peening, or texturing effects on a work piece. With throwing
speeds of 200-800 feet per second, this method can achieve surface finishes of
16-32 micro inches.
Shot blasting is an exceptionally versatile surface treatment technology
that is used for deburring/de-flashing, surface cleaning (de-scaling,
de-rusting, stripping of coatings), surface preparation for coating, for
cosmetic purposes, and surface improvement. Most medical applications utilize
air and wet blast systems.
Individually and when combined as a multi-stage process, mass finishing
and shot blasting offer a number of benefits.
- They create homogeneous, all-around “isotropic” (multi directional) finishes as opposed to “anisotropic” (mono directional) surface structures produced by machining, belt and wheel grinding, drawing, and extrusion.
- Both can handle all materials, from the toughest metals like titanium and platinum to all kinds of polymers and, even ceramics.
- Whatever the task, mass finishing and shot blasting produce consistent, absolutely repeatable finishing results. They completely eliminate quality fluctuations inherent in manual or other mechanical finishing methods.
- Users can choose from a broad equipment spectrum, from simple, low-cost stand-alone machines to fully automated finishing systems.
- In combination with other methods, both technologies create perfect surface finishes on additive manufactured parts.
In addition to being very cost-effective, both mass finishing and shot
blasting are highly adaptable to customer needs. The equipment spectrum ranges
from small manual or semi-automatic machines for low production volumes to
fully automatic systems for high volume production.
The customer decides, how much they want to spend and what degree of
automation is desired. The costs for work piece fixtures – if required – are
manageable, and due to the high degree of mechanization and automation 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
components like surgical instruments the entire finishing costs will amount to
no more than just a few dollars.
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
No matter what condition your spinal implants start in, Rosler Metal Finishing to help you find a better way and achieve precise finishing. https://us.rosler.com/us-en/contact/)Contact us today to discuss your unique challenges.
The complete Spinal Implants Series includes:
- Part 1 – Surgical Specifications.
- Part 2 – Processed to Perfection.
- Part 3 – Mass Finishing Versus Shot Blasting Methods.
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