Fabricating orthopedic implants, such as artificial knees and hips, requires abrasives to bring the cast implant to its precise geometry and required finish. Selecting the right abrasive product and using it at the proper pressure and recommended cutting speed can result in fewer abrasive steps, less re-work, faster turnaround, and reduced costs.
Orthopedic implants are initially formed using investment casting. The first step is to remove the gate with an abrasive belt. As the implant goes through a series of machining steps to gain its net shape, the use of proper abrasives is important to remove the machining lines. Further abrasive processing with a sequence of grades is required to prepare the part for the final finish. Lastly, the part is buffed to achieve its desired mirror polish.
To successfully manufacture orthopedic implants, three factors determine the outcome: pressure, speed, and finish.
Pressure – Select the correct abrasive, run it at the right pressure
Abrasive minerals must break down to reveal new cutting edges. If this point is not reached, the maximum output potential is reduced. Signs that belt selection and/or application pressure should be adjusted include the appearance of shelling or glazing (pictured below).
Typically, when the application pressure is too low for the product selected, glazing is the outcome. When the abrasive rubs rather than cuts the substrate, friction increases heat between the belt and the workpiece, and the debris from the workpiece welds to the abrasive. In these situations, try switching to a belt designed for lower pressures.
When excess pressure is applied to an abrasive, abrasive grain can flake off, causing shelling. If this happens, lower the pressure or switch to a belt designed for higher-pressure applications.
Identifying the optimal breakdown point helps to extract the full potential of the abrasives and lowers operating costs. If unsure of application pressure, start with a medium-pressure belt and observe belt feedback for signs of too much or too little pressure. Adjustments can then be made to extract the most value from the abrasive.
Speed – Balancing throughput with temperature
Typically, increased speed means increased throughput. However, temperature also increases, which can put the finished product surface at risk.
While grinding a gate to the desired shape with a coarser grade belt, higher speeds and pressure are necessary. In finishing, finer grades tend to impart more heat to the workpiece than coarser grades. Therefore, when switching to finer abrasives for finishing steps, decrease speed by approximately 30% to 50% to prevent heat damage to the implant’s surface.
Orthopedic implants are made of exotic alloys such as cobalt chrome and titanium, which tend to conduct heat poorly, making them more susceptible to heat damage. 3M Cubitron Abrasives with heat-resistant grinding aids can keep parts cool and prevent over-heating.
Finish – Match abrasive to coating
After an implant has been shaped, the surface will still have machining lines (steps) that need to be blended and finished.
Orthopedic implants require a consistent, clean metal surface free from burns or damage.
Uniform abrasive mineral configuration in 3M Trizact abrasives refine finish without changing part geometry. Trizact abrasives produce more consistent finishes with higher cut rates and cooler grinding and finishing temperatures.
The right sequence of abrasive grades can reduce the number of steps necessary to get the required finish and save subsequent polishing time.
Choosing the right abrasives
Being mindful of abrasive product choice, cutting speed, and appropriate application pressure will extract the full potential of the abrasives, which can help increase throughput, improve productivity and profitability, and lower operation costs.