For a plain-speaking answer to this question, standard Powder Metallurgy production sequences do indeed create dimensionally accurate items. An end-process part is so precisely manufactured, so close to being surface-finished, that it simply doesn’t require much additional machining. Of course, a straight-to-the-point answer might create more questions than it resolves. Ever mindful of this prospect, let’s delve deeper into the mechanisms and processes that reduce the need for PM produced parts machining.
Winning the Productivity Competition
Entire books are written about ways to enhance factory productivity margins. They’re piled up on bookshelves next to a number of thick textbooks, which probably mention quality assurance measures a lot. Well, fabrication methods tend to split themselves into two or three discrete manufacturing stages, so it’s not easy to run a quality assurance program that can boast an accelerated output rate. There’s machining work to be done. Alternatively, a casting is made. Perhaps there are elements of both of those methods present in a high-end manufacturing process. Not even close to being finished yet, then the partially fabricated part requires a special polishing operation. Meanwhile, having switched to a Powder Metallurgy system months ago, a wiser manufacturing business has gotten ahead of the game. With complex geometrical profiles directly laid down during the initial product creation phase, there’s very extra subtractive machining work to be done after a PM produced component has been formed.
Dimensional Control: Green Part Sintering
With powdered metal compressed into a complex shape, complete with all opening and component details, it’s shunted forward to a sintering chamber. The process settings leverage control over a part’s density, so it’s either almost entirely solid or infused with a percentage-rated porosity quotient. Counterbalancing a part’s density against its dimensional constraints, the thermal energy triggers the necking and sintering phase. Never melting or collapsing structurally, the still solid metal powder coalesces while maintaining its rigidly set outlines. There are no drill holes to apply afterwards, so there’s no deburring work to implement. Likewise, there are no heat-introduced deformations to correct.
Exiting a Powder Metallurgy output station as a net-shape end product, there’s not much left to the process. A special coating could be in the cards, but such options aren’t common, not when they could compromise the part’s porous structure. Advanced polishing procedures are desirable, especially when the PM work imparts a heat treatment feature. Incidentally, secondary machining options, ones that perhaps add a series of narrow-thread screw openings, can be done during the sintering phase if the Green compact fills every iota of a geometrically dense die. Even so, it takes a great deal of foresight to add the necessary inserts. At this point, a simple threading machine simply makes more sense as a secondary processing tool.