Question

heat is a big concern when machining metal. Heat build-up can destroy the work material, create dimensional problems, and shorten the life of the cutting tool, which why machining operations generally use some type of cutting fluid in machining. However, coolants present problems in machining due to cutting fluid can stain the work material or contaminate it. Consider a medical implant, such as a ball joint for a hip. Cutting fluids are undesirable where there is the fear of contamination. Through your analysis, suggest the solution to solve the problem of machining ball joint for a hip. Additionally, the process ability, accuracy, tolerance, and defects should also be considered based on your analysis.

Answer 1

Considering Medical implant such as a ball joint for a hip, below are some solution that will solve the problem of machining ball joint for a hip.

Description of Hip Implant :-
Hip implant is an orthopedic procedure where hip joint is replaced by artificial implant in order to replace arthritic or dys-functional joint surface.
However,the metal-on-metal hips articulation suffers from friction due to the moving metal surface thus, shortening the surviving of the joint. A micro pits formation is therefore used for lubrication purpose, which eventually prolong the life span of the hips.

Significance of Hip Replacement
Hip replacement procedure becomes more significant and most preferred option to replace disease joint which improvesthe quality of life for patients who suffer from joint disease.

Earlier Technique Used :-
Material combination that early used in the hip implantconsists of metal femoral head and an ultra high molecular weight polyethylene (UHMWPE) acetabular cup. However,these combinations of materials results in failure of theimplant because it has been found that it produces more wear and aseptic loosening.

Challenges Faced :-
Wear and friction problem

Solution 1 ( EDM )
In order to reduce wear and friction that occur in hip implant contact surface, lubrication activities must be presented to prolong the lifespan of the hip implant.

Lubricant to be sustained into the space between the cup and the head thus causing a constant pain faced by patient whenthe two parts ground together. Therefore, surface texturing or micro pits (which also known as oil pockets, holes, dimples, or cavities) formation on the material surface need to be formed on the hip implant surface. The pits will allow a quick influxand give an optimal distribution of fluid articulation surfacesto the implant. Numerical and simulation studies shown that the surface texturing would give beneficial effect in reducing wear and friction between contact surface of hip implant and it also improve the lubrication performance of the implant

In order to produce micro pits or doing surface texturing,the existing traditional methods of machining micro pits on the metal surface such as drilling, milling and grinding seems to be not yet practical for this application since the result of drilling and stamping could deteriorate the work piece structure of hardening material. In addition, machining hard metals and alloys demand more time and energy. The cost also is increasing as result of tool wear and the induced stresses during machining. Therefore, for machining micro pits on hip implant material application, electrical discharge machining, EDM is chosen as manufacturing method instead of using conventional machine.The development also could machine the hardened material with less crack effect

Electrical discharge machining (EDM) technology is now become more significant and having a high demand in most of manufacturing process. It is a non-traditional precisionmachining process which removes electrically conductivematerial into the desired shape in form of spark based onthermoelectric energy between work piece and electrode. Thismethod involving non-contact process, which it couldeliminate mechanical stresses, chatter and minimally vibrationduring the machining process thus resulting in better surfacefinish other than provide greater dimensional accuracy

Solution 2 (Round Inserts)
Round inserts offer you all the best advantages for the machining of cobalt chromium and titanium implants.
These inserts, when used for internal turning of the spherical cup in a ball and socket hip joint, optimise the roughing process. An excellent balance of security and productivity, in short, they do nothing less than double your productivity and reduce your tooling costs.

Key Benefits
In roughing applications the round shape imparts a strong cutting edge and excellent resistance to excessive notch wear. Choosing round inserts has two clear advantages:

1-Secure, quality, reliable machining
Applying a round insert with an approach angle of less than κr 45º significantly reduces notch wear, a common problem which leads to an inferior quality component and a reduction in productivity.
Apply for reliability and durability, fewer tool changes and trouble free machining.

2- Increase feed and speed for maximum productivity
By using a round insert with the depth of cut well below the radius, the chip thickness
hex is reduced relative to feed and the cutting edge length increased. This results in lower temperatures being generated and the opportunity to increase both feed and speed for maximum production.