Lack of English language sources for the topic at hand is a serious issue. Nevertheless, let me try make up a history of Xian aircraft industrial corporation production history. Please do bring out new sources if you have them, ones that'd correct the timeline I am about to present here:
In 1958, XAC is formed.
Its first job is to assemble Tu-16 bombers as H-6. That is done in 1959.
H-5 bomber, made in china (based on IL-28) flies in 1962. Several hundred are made over the next few decades but there is no info on them whatsover. It'd be really nice if end of production date, for example, was available. That being said, stemming from the produced volumes, it's likely serial production lasted from mid 1960s to at least sometime in 1980s. Possibly 1990s.
During that time, other production facilities made H-6. Reverse engineered one first flew in 1966, allegedly. One might assume serial production lasted from, roughly, 1970 throughout 1980s and possibly even later. So H-6 and H-5 were produced at the same time.
In 1970, first flight of reverse engineered An-24, named Y-7 happened. But development and production lagged. Allegedly in 1982 preproduction was ready and first serial production standard airframe flew in 1984. Since then some 100 airframes were made of the basic model. Allegedly until 1992.
Further models were made during 1990s, but in small quantities?? From 2000 onward civilian model production seems to have overtaken the military models, with MA60 flying in 2000. Apparently the differences from military models were minimal as first customer also got their plane in 2000. Some 110 were made until today. This may not include the newer model, MA600, for which prototype flew in 2008 and first customer got it in 2010. MA600 seems to be produced at a steady pace, with 200-300 more orders to be fulfilled.
So... either during 1980s and to beginning of 1990s three models were built at XAC. H-5, H-6 and Y-7.
Or one of those had its production seriously curtailed. Both H-6 and H-5 are candidates for that, actually.
H-5 was visibly obsolete even in 1980s. While there's no proof of it, it does seem sensible that H-5 production was curtailed during 1980s.
H-6 was a more demanding plane. Basically, not more than 140-ish ever served at one time with Chinese forces. Some (several? One dozen?) H-6 were also exported to Iraq. With some minor attrition taken into account, it would seem 150 to 160 H-6 were ever produced, not counting the H-6K airframes.
Now there's the issue of H-6 modernizations. Some sources like to claim that various H6, such as H6M or H6G are newlybuilt. But it's equally possible, perhaps even more likely, that they were in fact conversions of existing planes. Airframe such as Tu-16 is not subject to much stress and can be flown for decades on end. A 2003 hypothetical conversion of H6D into H6G would have happened in 22nd year of airframe's life, for a D model flying in 1981. Certainly, H6 were produced in 1980s as well, as D was the first model specifically made for maritime strikes. But H6F might have very well been a conversion job, flying in 1994. Same for G, H and M models.
Then we have the JH-7. Prototype flew in 1988. Production of basic variant started sometime in 1990s but I can't find when exactly. There may have been a hiatus of a few years between the basic and A variant, starting deliveries in 2004, but there may also not have been, with possible low rate preproduction of JH7A with no deliveries in years in between.
To sum it up, here's one hypothetical timeline: (give or take a few years)
1965-1984 serial production of H-5
1970-1990s serial production of H-6
1984 to 2000, serial production of Y-7, taking over the H-5 production line assets/team
1990s to 2011, serial production of JH-7/a, taking over the H-6 production line assets/team
Then we have the new developments. H-6K appeared in PLAAF front line regiments in 2012, suggesting serial production final assembly since 2011 (or possibly 2010). Last unit to get new JH7A was also in 2011.
Thus the suggested further timeline goes that from 2011 onward, H-6K took over the JH-7 production line/assets team.
Since 2010 production of ARJ21 parts has been kicking in the higher gear, with actual deliveries starting in 2015. So far the volume is small, but it's being expanded to several per year. Xian allegedly does major parts of that plane, the fuselage (sans nose and tail?) and the wings. Most likely, a whole new production facility with a whole new team stood up for that purpose. Though planes aren't assembled in Xian to my knowledge. Rather, parts get shipped to other planes. If someone has different info, please share!
Finally, there's the Y-20. Preproduction was done in some of the existing halls, but when requirement for greater volume was to be fulfilled, the new final assembly facility, seen on GE images as complete from 2015 most probably took over. Basically, a new team and new facilities were made for Y-20 programme.
If one checks out the newly added production halls near XAC, one can see the following:
From 2010 onward two new halls, each at least 220*100 meters seemed finished.
While they may have something to do with H-6K, personally I think it's more likely they are mostly there due to plentiful MA600 orders that have happened in that period. Possibly even preparation for ARJ21 production, which may have proven to be a bit too premature at the time.
By 2012, another such hall and another 220*200 meters seemed finished. Now these are possibly due to Y-20 production, not final assembly but parts production. But that may be a bit too premature, having in mind Y20 prototype first flew in 2013. Also likely reasons is demand for ever increasing MA600/ARJ21 production.
By 2015, besides the already mentioned likely Y-20 hall there was an expansion of one of the 2010 halls, turning it into a 230*220 m hall. Parts production for Y-20 on a more mass scale is likely.
No one knows when H-20 will come but at the current pace of H-6 production, it does seem likely all of the older H-6 airframes will be replaced by H-6K during next several years. Meaning it's just as plausible H-6K facilities may become J-20 production facilities. There's the possible issue of size, but until we actually learn of H-20's dimensions that's hard to assess. Certainly, it would be illogical to have those H6K halls empty, so either some of exisiting products will get their assets relocated to H6K halls or their order books will increase so much they will need more (MA600/ARJ21 perhaps?) and H-20 will get brand new halls, or H-20 will be made where H-6K is made today.
There's also the issue of C919. Xian is producing wings for that plane (don't know if other parts as well) so at least some of thew new facilities at Xian is there to "hand-make" those few prototype wings. In the coming year or two we might very well see a whole new facility be built for mass production of C919 wings. Certainly, the timeline of mass production of C919 shouldn't allow for waiting for H6K facilities to be vacated. (I'd say at least 3-4 more years of H6K. Not counting possible Tanker variants)
In 1958, XAC is formed.
Its first job is to assemble Tu-16 bombers as H-6. That is done in 1959.
H-5 bomber, made in china (based on IL-28) flies in 1962. Several hundred are made over the next few decades but there is no info on them whatsover. It'd be really nice if end of production date, for example, was available. That being said, stemming from the produced volumes, it's likely serial production lasted from mid 1960s to at least sometime in 1980s. Possibly 1990s.
During that time, other production facilities made H-6. Reverse engineered one first flew in 1966, allegedly. One might assume serial production lasted from, roughly, 1970 throughout 1980s and possibly even later. So H-6 and H-5 were produced at the same time.
In 1970, first flight of reverse engineered An-24, named Y-7 happened. But development and production lagged. Allegedly in 1982 preproduction was ready and first serial production standard airframe flew in 1984. Since then some 100 airframes were made of the basic model. Allegedly until 1992.
Further models were made during 1990s, but in small quantities?? From 2000 onward civilian model production seems to have overtaken the military models, with MA60 flying in 2000. Apparently the differences from military models were minimal as first customer also got their plane in 2000. Some 110 were made until today. This may not include the newer model, MA600, for which prototype flew in 2008 and first customer got it in 2010. MA600 seems to be produced at a steady pace, with 200-300 more orders to be fulfilled.
So... either during 1980s and to beginning of 1990s three models were built at XAC. H-5, H-6 and Y-7.
Or one of those had its production seriously curtailed. Both H-6 and H-5 are candidates for that, actually.
H-5 was visibly obsolete even in 1980s. While there's no proof of it, it does seem sensible that H-5 production was curtailed during 1980s.
H-6 was a more demanding plane. Basically, not more than 140-ish ever served at one time with Chinese forces. Some (several? One dozen?) H-6 were also exported to Iraq. With some minor attrition taken into account, it would seem 150 to 160 H-6 were ever produced, not counting the H-6K airframes.
Now there's the issue of H-6 modernizations. Some sources like to claim that various H6, such as H6M or H6G are newlybuilt. But it's equally possible, perhaps even more likely, that they were in fact conversions of existing planes. Airframe such as Tu-16 is not subject to much stress and can be flown for decades on end. A 2003 hypothetical conversion of H6D into H6G would have happened in 22nd year of airframe's life, for a D model flying in 1981. Certainly, H6 were produced in 1980s as well, as D was the first model specifically made for maritime strikes. But H6F might have very well been a conversion job, flying in 1994. Same for G, H and M models.
Then we have the JH-7. Prototype flew in 1988. Production of basic variant started sometime in 1990s but I can't find when exactly. There may have been a hiatus of a few years between the basic and A variant, starting deliveries in 2004, but there may also not have been, with possible low rate preproduction of JH7A with no deliveries in years in between.
To sum it up, here's one hypothetical timeline: (give or take a few years)
1965-1984 serial production of H-5
1970-1990s serial production of H-6
1984 to 2000, serial production of Y-7, taking over the H-5 production line assets/team
1990s to 2011, serial production of JH-7/a, taking over the H-6 production line assets/team
Then we have the new developments. H-6K appeared in PLAAF front line regiments in 2012, suggesting serial production final assembly since 2011 (or possibly 2010). Last unit to get new JH7A was also in 2011.
Thus the suggested further timeline goes that from 2011 onward, H-6K took over the JH-7 production line/assets team.
Since 2010 production of ARJ21 parts has been kicking in the higher gear, with actual deliveries starting in 2015. So far the volume is small, but it's being expanded to several per year. Xian allegedly does major parts of that plane, the fuselage (sans nose and tail?) and the wings. Most likely, a whole new production facility with a whole new team stood up for that purpose. Though planes aren't assembled in Xian to my knowledge. Rather, parts get shipped to other planes. If someone has different info, please share!
Finally, there's the Y-20. Preproduction was done in some of the existing halls, but when requirement for greater volume was to be fulfilled, the new final assembly facility, seen on GE images as complete from 2015 most probably took over. Basically, a new team and new facilities were made for Y-20 programme.
If one checks out the newly added production halls near XAC, one can see the following:
From 2010 onward two new halls, each at least 220*100 meters seemed finished.
While they may have something to do with H-6K, personally I think it's more likely they are mostly there due to plentiful MA600 orders that have happened in that period. Possibly even preparation for ARJ21 production, which may have proven to be a bit too premature at the time.
By 2012, another such hall and another 220*200 meters seemed finished. Now these are possibly due to Y-20 production, not final assembly but parts production. But that may be a bit too premature, having in mind Y20 prototype first flew in 2013. Also likely reasons is demand for ever increasing MA600/ARJ21 production.
By 2015, besides the already mentioned likely Y-20 hall there was an expansion of one of the 2010 halls, turning it into a 230*220 m hall. Parts production for Y-20 on a more mass scale is likely.
No one knows when H-20 will come but at the current pace of H-6 production, it does seem likely all of the older H-6 airframes will be replaced by H-6K during next several years. Meaning it's just as plausible H-6K facilities may become J-20 production facilities. There's the possible issue of size, but until we actually learn of H-20's dimensions that's hard to assess. Certainly, it would be illogical to have those H6K halls empty, so either some of exisiting products will get their assets relocated to H6K halls or their order books will increase so much they will need more (MA600/ARJ21 perhaps?) and H-20 will get brand new halls, or H-20 will be made where H-6K is made today.
There's also the issue of C919. Xian is producing wings for that plane (don't know if other parts as well) so at least some of thew new facilities at Xian is there to "hand-make" those few prototype wings. In the coming year or two we might very well see a whole new facility be built for mass production of C919 wings. Certainly, the timeline of mass production of C919 shouldn't allow for waiting for H6K facilities to be vacated. (I'd say at least 3-4 more years of H6K. Not counting possible Tanker variants)
