Finishing Aluminum Castings: burrs / flash / lamination issues

A. There are too many unknowns here to answer your question properly. Because you mentioned the use of a hand file, the alternatives you suggested did not sound aggressive enough. Part size, volume of pats, configuration or accessibility as well as what is the final surface finish are all important to answer this question.

A. Sounds as though it's past time for new dies, so the flash doesn't occur in the first place. You can't make good quality product from worn or badly made tooling.

A. It sounds like the part itself eliminates several of your options. The part is probably to large for thermal deburring, and because of the passages you definitely would not want to attempt vibratory deburring. It is hard to say without seeing the part but, have you thought of brush deburring. It may require Robotics and or fixturing, but if the volumes are high enough it could be justified.

A. Typically the options you outlined are options as follows:

1.Thermal de-burr is for small sized castings because of the chamber size and competitive pricing means filling it up to the top; Also, a thermal de-burr is good for this type of flash as you have described but the casting sounds too big.

2.Chemical mill is much more effective on zinc and for much thinner flash ( approx. 0002"-.008").

3.Vibratory de-burr could work, but needs the internal core (where the flash is)to be of a size so the media doesn't get stuck in the casting interior; Additionally, if the flash is too heavy, it just rolls it over,causing more of a problem. Also, the castings may be too large for the mills; Common mill size is from 6-10 cubic feet.

4.A small de-burring tool is probably the most plausible solution if the castings are too large for the above options; A good solution is a miniature air driven belt sander that allows the operator to go into the casting and eliminate the flash from the intersecting cores,but if the flash is too thick, it will tear up the belts, and be quite expensive and time consuming......so, files may be your only option besides fixing the tooling.

A. Sorry it took so long to get back to you, but you got some good responses. My best suggestion is to look into abrasive honing or extrude hone technology. This is an expensive system, but it is probably the best suggestion I can come up with.

A. There are rotary disc type brushes that can be custom designed for de-burring, they are an abrasive nylon filament impregnated silicon carbide. These are typically used in a variety of applications for de-burring.

A. For Americans, LM6 is ~equivalent to A413, with ~12 wt% Si as the predominant alloying element.

LM25, with 6.5-7.5 wt% Si, is similar to 356 & A356. LM25 has slightly lower limits on other alloying elements than 356, and slightly higher limits than A356.

According to Casting Kaiser Aluminum, 3rd edn. (1974), 356 & A356 "have good polishing characteristics....Anodizing appearance is fair to very good; color is gray." LM25 should be similar, with the gray due to the Si.

A413 & LM6, with about 12 wt% Si, polish poorly. Anodizing appearance is also poor. Plating gives a better appearance.

Do you solutionize the LM25 at 1000 °F (538 °C)? What is the furnace atmosphere used?
How are you currently finishing parts: mass finishing (tumbling or vibratory barrel), bead blasting, polishing..?

A. Joe,
Cream of tartar works well for removing natural occurring oxide from aluminum. Make a workable paste with cream of tartar & warm water. Apply with a soft brush, and let sit for a few minutes. Wipe clean with warm water and rag. When all the oxide is removed apply a good aluminum polish available at your local auto parts store. This should give you better results.

A. Polishing out parts that have been polished in the past, such as your valve covers, will usually brighten up using some polishing compound and elbow grease. However a raw sand casting such as an intake manifold will require courser more aggressive materials such as rough grit sandpapers starting with about 150 grit and working down to finer grits (220 then 320,then 600) making sure you get every grit line out from each previous sandpaper. Then try to use a buff with brown tripoli buffing compound ⇦this on eBay or Amazon [affil links] .
When you use tripoli on a buff before smoothing out a rough casting will result in getting the tripoli pushed into the rough texture of the casting leaving a hard black gunk in the rough texture. It would also help to soak and scrub the casting completely clean with very hot soapy water and a good tampico scrub brush ⇦this on eBay or Amazon [affil links] to get any oil and grease out of it. Otherwise you will just clog up your sandpapers and buffs making the job almost impossible.