Hartturning vs. Grinding [Flexibility] 3

[sergo92]

I am currently working on a presentation on hard turning. My part is to compare hard turning with grinding in various aspects. One of them is "flexibility". I have found a lot of articles and literature saying that hard turning is more flexible than grinding. The only problem is, after a lot of research on grinding, I found universal machines that disprove the flexibility of hard turning. With modern universal grinding machines, it is also possible to machine complex geometries in a single clamping operation and with just one tool. With modern CNC-controlled grinding machines, it is theoretically possible to machine several surfaces in one clamping and with one tool, just as with hard turning.
How do I best explain the flexibility in the presentation so that in the end it is clear that hard turning is more flexible? Please help me, I have already read over the topic.
Thank you very much!

 

[Heaviside1925]

OP,
You're being asked to make an argument and if you truly believe that With modern CNC-controlled grinding machines, it is theoretically possible to machine several surfaces in one clamping and with one tool, just as with hard turning. then you are going to have a difficult time making your case. I'd start by removing that thought and think about a turning tool, it's application to machining and all the different purposes a turning tool can be used for. I think you will discover that there are many cases where a turning tool can serve functions that a grinding tool cannot. Instead of a book or a web link, find a local machine shop and pay them a visit. I can almost guarantee they will be happy to show you many different applications and techniques they use, and you may very well answer your own question. It would make your presentation much more meaningful as well.

If you want to go into a more theoretical space, instead of looking at flexibility, you could go into contact mechanics and tribology (google these is you don't know what they are). Consider what is happing at the surface of the material being machined and the differences in how that material is being removed, how the forces and stresses are being applied and distributed, the results of surface defamation and material property changes due to the deformation, temperature and stresses. These are highly specialized developed fields that I think would give you a lot of insight into the science behind different machining techniques.

 

[BrianE22]

With turning you can usually use the same tool for OD turning and facing. Also, if you have a tool changer on your lathe you can bring in different tools (like a grooving tool for narrow grooves). You don't have to true or dress a turning tool (though you might have to replace it when worn).

Did you check out

https://hardinge.com/blog/hard-turning-vs-grinding/

?

 

[GregLocock]

On a conventional lathe I can machine an entire steam engine. Let me know when you've done that on a grinding machine.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[sergo92]

@BrianE22 look at the photo I uploaded. It shows that you can also use a grinder for surface turning. So this example raises the question of what the difference in flexibility is?



I also have another example:

https://www.youtube.com/watch?v=YAyd7vkHRXs&ab_channel=EMAG

Although 2 tools are used in the video, it would have been possible to grind both surfaces with one tool and, of course, one clamping, wouldn't it?

Translated with DeepL.com (free version)

 

[3DDave]

Hard turning will always have an advantage in material removal rates as it only needs to shear the material, not tear off billions of little chunks. In addition, the material removed by hard turning can be collected and recycled, unlike the usually oxidized powder that is left from grinding.

In the example video the grinding starts on a part that was turned with a hard tool to get it to near finished shape.

If only one can be chosen it will be hard turning. Cutting tools are far easier to make for it and will be cheaper.

 

[Heaviside1925]

OP,
I've gotten to the point where I was asking myself "Do I need to draw this person a picture?" so here it is.
What is going to happen to the areas I circled compared to the areas in contact with the piece over the course of repeated passes?

Additionally, the other posters have given you some very good points and I hope you are understanding them.

 

[sergo92]

@Heaviside1925 There will be unevenness in the grinding wheel because the marked areas are not in contact in the one process. However, this can be restored by a dressing process and the workpiece can still be machined in one clamping and one tool or not?

 

[Heaviside1925]

OP,
The number of tooling changes was never my point. Dressing and trueing would need to be applied at each step in diameter and axis. Each of those processes would require a machinist to re-true before proceeding to the next face. What can be performed in a single process with hard turning requires no less than 18 separate processes for using grinding, given your example. 6 faces, 6 dressings, 6 trueings. Flexibility can be in terms of efficiency as well.

 

[sergo92]

@Heaviside1925 thank you very much for your answer. The repeated dressing required is a very good way of describing the flexibility in this example. But do you actually have to align the disc again and again after each step/face? I would have thought that you only do this when you replace a disc or reassemble it?

 

[sergo92]

In this video it looks like it is not necessary to dress. Check last step.

https://www.youtube.com/watch?v=HNlGvJ4Gm7Q&ab_channel=WEMAGlauchau-BRANDOFTHENSHGROUP

 

[3DDave]

It's a computer generated animation, and it is removing a very small amount of material from a pre-turned part. The animator didn't show any process other than what was in the script.

I think the greater flexibility of turning over grinding is already demonstrated.

However, if one is to argue they have read something, then link to that material.

How would any article disprove that the most flexible machining systems weren't flexible?

 

[sergo92]

i'm not interested in proving the opposite. i'm interested in a clear, simple machining example that makes it clear that hard turning is more flexible. Let's forget the example picture for the moment. in the video (

https://www.youtube.com/watch?v=HNlGvJ4Gm7Q&ab_channel=WEMAGlauchau-BRANDOFTHENSHGROUP

) that I posted earlier, a peripheral surface and a flat surface are carried out in one step at the end in the last step of the video, without dressing in between. if you apparently use a thin disc at a certain angle, the flat surface can be ground first, then you change the angle parallel to the machining surface, move it off without creating an unevenness due to "no contact surface" (see explanation of the picture example above), because we choose a thin disc thats moves from the beginning of the face till the end with even pressure and wear . The next surfaces can then be machined without the need for dressing and we are back to one machining step(no reclamping, no dressing, just one tool ) as with hard turning. Simply incomprehensible to me. Please help me to undestand.

 

[3DDave]

Grinding only removes tiny amounts of material. That may be what you don't understand. The example of two surfaces is after the turning operation with regular cutters has removed 99.9% of the material already. Without that those surfaces would never be touched by grinding.

 

[Heaviside1925]

OP,
In all the examples you have shared the grinding is being applied to a part that has already been machined. You are making the assumption that the grinding previously performed all of the material removal. Many posters have tried to communicate to you, that grinding does not remove very much material. Hard turning is used for bulk material removal. Hard turning can also be used for finishing / surfacing. My original recommendation remains the same, step away from the computer and YouTube videos and find a local machine shop. This could be an independent machine shop, most factories have in house machine shops, technical colleges have machine shops. Go find a machine shop and ask, watch and listen. Hands-on knowledge is invaluable in a field like machining.

 

[Gr8blu]

OP - or look at it another way. Would you consider shaping an entire table leg from a large chunk of tree using a machine tool (i.e. cutter on a lathe), or with sandpaper? Hard turning would use the tool; grinding would use the sandpaper.

Converting energy to motion for more than half a century

 

[mfgenggear]

Sergo92
Each machining center is specialized. Milling and turning are specialized to remove large amount of material. To under stand feeds and speeds have to be studied. Roughing operations deep depth of cut with slow feedz unless ceramics are used. Then high amount of material is removed.
Some can argue that hard turning is roughing but it is not it isca semi finishing operation.
When heat treat distortion is causing to much distortion it is hard turned.

Grinding in general is a finishing operation and ultra high precision operation and it has its nitch.. machines have standard precision, precision, and ultra precision.
It really depends on the product and how it is made. Example is centerless bar grinding, is a very efficient method to remove zat lot of material.crush grinding on shafts is an other methodi for removing material. So basically each machine process has its use. Excuse the typing small cell phone.