Tumbling/Polishing/Vibratory Finishing vs. Electropolishing of Titanium

ASM Metals Handbook Vol. 5: "Surface Engineering"

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A. Kurt:

A nice mass finishing process for Titanium is available from REM Chemicals, Inc. in Southington, CT. It is a vibratory process (TIMIL) that utilizes a proprietary chemical compound to rapidly refine surfaces ending with very low Ra surface values. It is successfully in use to refine Titanium turbine blades and other engine components, surgical implants and golf clubs to name just a few. Most installation use standard vibratory equipment, high density non-abrasive media and of course, the magical chemical compound.

I hope this is useful and best of luck in your search for information.

Bill

A. Hi Kurt. If you can give us an idea of the size of the parts, production rates, and degree of polish necessary -- so that we can dismiss some swaths of alternatives like automatic buffing machines, electropolishing, manual deburring with a Dremel tool, and stuff like that -- I think we can present some alternatives for your consideration. In the meanwhile ASM Metals Handbook Vol. 5 has some concise info on different approaches for different situations but emphasizes that, regardless of method, you'll probably need multiple stages (you need fine abrasive as the last step, but getting from rough to fine with a fine abrasive would take forever). Good luck.

Regards,

A. A couple of thoughts. You never did mention a specific surface finish except nice. If you were getting your parts with a blast finish the RMS was probably around 25 or higher. If you are looking to mechanically surface harden parts shot peening is probably about the best, which is blasting with steel shot.

From your description of your part, peening might be possible and would give you a brighter appearance than glass bead. Then again, another good surface hardening system is a mass finishing system using steel ball media. The latter will not improve your RMS much without a cut down or deburring step first; however, a 2 step process would probably be the best hardened surface finish and could achieve maybe a 12-14 RMS.

The amount of parts you mention probably would not justify a large deburring or blasting system alone. However, a 1 cu.ft. vibratory mill plus ceramic and steel media can do the job for under $2500.

A. Ryan,

I just ran into problem with another customer concerning titanium. The biggest problem we had to over come was the roughness of the existing surface finish or profile. The raw material looked like a sand blasted finish. That means that the RMS was well over 75 or 95. That's rough. I tried an aggressive vibratory mill for over 96 hours and still couldn't get the surface finish within the polishing tolerances of 16 to 18 RMS. The only way we succeeded in getting a mirror finish was to go to a high energy centrifugal system. Even was a 3 step process and took over an hour for each process. Parts looked beautiful but this took a lot of time. If you can improve the surface finish by wheel or belt systems down to at least 35 RMS, you can significantly reduce over all finishing time.

A. I have run across companies that are achieving mirror finishes on titanium from rough castings and they are using a chemical accelerator in a two step process. The first step is to cut down the rough surface with the acid accelerator and then a chemical burnishing compound is used to achieve the mirror finish. This process still takes several hours to do in a vibratory machine and the chemicals must be flushed between the two steps. The described process uses a non-abrasive, high density ceramic media to scrub away at the surface of the metal that has been softened by the chemicals.

A. Not sure if it would work for your type of designs but I use a vibratory tumbler on our jewelry (titanium, stainless steel, brass, aluminum etc etc) and it works very well. Mirror polishes are easy and much less time consuming. You will need a "jewelry" type setup not a machine shop setup. Most machine shops just tumble to deburr. Jewelry setups work down to a rouge. The abrasive media lasts years..our setup cost about $500 altogether and other then buying fresh rouge its all lasted for 7+ years, and we tumble on average 2,000 earrings at a time.

A. If you wish to try polishing - ref a book. Please read MSDS first 6% HF BY WEIGHT + 6% water + 88% ethylene glycol. Room temperature or around 40 °C 8-11 A/sq dm but not less than 5.4 A/sq dm. Good luck and TAKE CARE WITH HYDROFLUORIC ACID .

A. Looking at the visuals posted you have a couple of problems. You can achieve a shiny part and still be rough per 2nd visual. The roughness of the parts must be refined and will probably require multiple steps. Unless you have plenty of time on your hands, your barrel system won't get you the 6RMS results you are looking for and vibratory is marginal for 40 hrs or more. Most good companies who sell or process parts will run sample parts and recommend media, time and equipment, including us. Cost is another factor.

A. Sir,

You can try a centrifugal finishing machine for your components. Time required in the same is very less and for your components and the finish you want can be easily achieved. The process would be 2-3 step process.

Regards,

A. Titanium is a difficult metal to polish. It can be done in many ways; however, you are normally talking about long time cycles. Most of the samples we have run have been in high energy centrifugal systems. The cost of this equipment is relatively expensive. It can be done in vibratory systems but you a talking 24 hour cycles or more. The condition of the raw material is also very important. In most cases you need at least a 2 or 3 step process. If you need more specific info get in touch.

A. Dave, please tell us what you are doing, as it's hard to propose much useful with little to go on. We could say "try increasing the process time by 50 percent" as that is sometimes the answer -- but we don't have any info to tell us if such advise is actually helpful. Thanks.

adv.
Titanium implants can be easily electropolished by safe simple to handle method in environmentally safe solution. There are no problems in receiving the same rate of removal during continuous polishing one load after another. No burrs, no uneven material removal, no additional passivation afterwards, no surface contamination with abrasive materials. Contact us for more information.




Anna Berkovich
Russamer Lab

Pittsburgh, Pennsylvania

A. Titanium is an SOB to finish. #1 The machine you are using is a low energy system and does not transmit a lot of energy to the mass, so you have to make up for that with time. Maybe 24-48 hours or more for first step. If you are starting out with flat parts, I suggest you use a 3/8" triangle of either a medium of coarse composition with a slightly acidic deburring compound. You need a flow though liquid system to eliminate film. If you can still see lines after the first cycle, you may want to follow up with a fine comp of the same size. A 2-step process might get you down to about 12-14 RMS. You may require a 3rd step fine abrasive to get down to an 8 RMS. Not sure if this is fine enough, but last step should be dry organic polishing media. This can be a 2-step process as well.

A. Benjamin,

Titanium is hard to simply polish mechanically - the surface is soft and during vibratory finish the polishing media is incorporating into the titanium surface. Experienced polishers use chemical-mechanical polishing, with final etching-cleaning of the surface from polished particles. This process require use of hazardous chemicals.

Another option is to electropolish your samples.

adv.
You can send them to me for electropolishing job. Please contact me directly.

A. In my 25 years of finishing metal for the implant industry, no tumbling process can produce a mirror finish on titanium. Is has to be a hand buffed final. Tumbling can get it very close, but I need an RMS 4 finish and tumbling can't do that to titanium, from what I've seen with many other manufacturers. It works on SST quite well though. I'd like to see a process that CAN produce RMS 4-10 on titanium of anyone has any proof that it exists.

A. Hi Tom,

It all depends on complexity of the titanium parts. Mass tumble does not work when titanium parts are of complex forms.
We used to buy Grainger glass beans buckets. Under microscope the beans are of equal rounded shape. They provide good matte finish. It takes about 30 seconds on each part to process at a distance of about 3 inches. The cheaper beans from some vendors can cause sparks and can damage the titanium surface. If you look under microscope, you will see that such cheap beans can have broken glass pieces with sharp edges. This is NO-NO for soft titanium surface.

Later we developed special regimes for titanium electropolishing that create dull surface and at the same time increase surface smoothness. The surface is surgically clean afterwards.

By using electropolishing there is no need for final etching (which is especially important for medical implants). If not properly rinsed and dried, etched acids can cause local corrosion and further troubles for implants.

A. I have had some good looking titanium finishes using a dry burnishing process with porcelain. For a satin finish (shorter time cycle) I use a pumice organic mix

A. Hi Eli,

If the parts are grade 5 (6Al-4Va) alloy, we can electropolish them for 30 seconds in low voltage plasma. The dimensions are not changed, because plasma impacts only burrs on the surface if electropolishing duration is short.

A. Hello Eli, I have found that magnetic deburring machines work very well for burrs on threads.