Niigata HMC's

[mrainey]

The company I work for is considering a Niigata 1000mm horizontal machining center. It would be used primarily for machining large iron castings and steel weldments, in an environment where preventive maintenance and operator training are somewhat below par.

I’d like to get feedback from anyone who has experience with Niigata, particularly in the areas of reliability and support. Thanks.


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[EdDanzer]

Although we have never owned a Niigata, we did try to by a used 800mm machine. The people who had them spoke highly of them and priced the machines accordingly. The one thing that I had concern with is that they use Turcite on the ways. We have only had two machines with Turcite and did not think the Turcite was as rigid as true box way machine.

 

[mrainey]

Thanks for your info. I'll pass it along to our project person.

We don't have a lot to choose from in terms of available machines that have the required combination of swing, adequate Y-axis travel, and minimal Z-axis "dead zone". We have some workpieces that are 62" high (Y). Others are shorter but require the swing of a 1000mm machine. The last group is composed of relatively small items that are difficult to reach with a rigid tool (Z).

We've pretty much narrowed it down to the Niigata, which is a conventional HMC, or a Makino with ram-style spindle (an auxiliary quill) which adds about 11" to the total Z-axis travel (required to compensate for the 17" Z-axis dead zone). There's a significant price advantage for the Niigata.

We've been machining most of these things on a G & L Orion with special, extended Y axis. The machine is nearing the end of its life, and we can't take the time for a rebuild because we don't have a backup. Plus, parts aren't as readily available as we'd like.



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[EdDanzer]

We have an older K&T Orion 2300 that has roller packs. The machine has some poorly designed area, but works ok. I would guess the Niigata would work just as well with Turcite as the G&L with roller packs.
We had a Kuraki MH400, this was a ram type 40 taper machine with Turcite on the ram slide way. This was not a good design, and we had to replace the Turcite twice and adjust the gib frequently.
We almost bought a G&L Ram 630. When we were at the G&L factory, I ask if they compared FEA calculated deflection to actual deflection, no one knew, so I do not think they did. My position on a ram type machine is the ram is a boring bar with an interchangeable head. Length to diameter ratio will affect accuracy and ability to do roughing.
If you could post the results of changing from the G&L to another make of machine, it will be a great reference.

 

[mrainey]

Ed,

We also had a Ram 630 and it was a reliability nightmare. Finally replaced it with an Okuma & Howa HMC, which has had virtually no downtime attributable to machine problems over the past two years, and is quite rigid for a machine of its size.

I'm not crazy about the ram approach of the Makino either. We machine large, rough castings and weldments with widely-varying amounts of stock, hard spots, etc. What the Makino guy shows us are videos about high-speed machining of molds with the ram stuck out (.040 consistent depth of cut with the tool moving REAL FAST). This has very little to do with our requirements.

I'll be sure to post any useful information that comes out of this. Thanks again.

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[EnglishMuffin]

EdDanzer: There is nothing wrong with a machine having box ways lined with Turcite, or even better, Rulon, provided it is correctly designed and lubricated etc, and such a machine will often be found to have a dynamic stiffness which is far superior to a roller way machine since the damping is usually so much better. The use of Turcite or Rulon is almost mandatory for non roller bearing NC machines with heavily loaded box ways because of the stick-slip issue, unless they use hydrostatics. I'm not sure why you would not call such a design a "true box way" just because it has low friction linings - I always have, and I think most people in the machine tool industry would too.

 

[EdDanzer]

We have had several different CNC turning centers. The Hitachi Seiki’s we had would be considered a true box way. The oiling system would not qualify as a hydrostatic way. These machines were able to machine parts other machines have difficulties doing.
All polymers have a level of compressibility, and must have some running clearance just like cast iron against steel. From an assembly stand point Turcite or any polymer is more forgiving of high spots than cast iron. I think roller packs, if properly designed will be similar in stiffness to spindle bearings. A proper preload and adequate size will provide excellent stiffness.
I am not convinced the K&T we have is well designed, but it does bore the best holes we have seen. We do not have a lot of experience with larger horizontals. I do not think we would buy another like it.

 

[EnglishMuffin]

EdDanzer: Well, the thing is that if you use a thin enough layer of Teflon with enough area, the compressibility is negligable in comparison with the rest of the structure. With Rulon (glass filled teflon) good results are obtained by machining it down to .03" after bonding, provided you use a large enough area. I must confess that I have not seen anyone go quite that thin with Turcite (Bronze filled teflon) and most grades do seem to be a bit squashier than Rulon, which also tends to have better wear resistance. You should also bear in mind that the stiffness is about double what you would expect based on a simple "E" value, because the Poisson ratio effect is supressed.