Comparative test with an unbalanced and a balanced boring tool
Within only a few minutes the following case study about a boring operation with an unbalanced and a balanced boring tool illustrates that a tool that was balanced with the HAIMER Tool Dynamic balancing machine is the decisive factor when it comes to process reliability, tolerance and workpiece precision.
The trial also shows that the vibrations of the unbalanced boring tool not only have a negative effect on the workpiece, but also the lifetime of the spindle and machine tool.
| Application: | Boring out D=18,0 H7 |
|---|---|
| Tool: | F101 02GN735 PKDD30 |
| Material: | Aluminum |
| Overall length [mm]: | 200,104 |
| ae [mm]: | 0,25 |
| Number of teeth: | 1 |
| vc [m/min]: | 565 |
| fz [mm/tooth]: | 0,1 |
| n [Rpm/min]: | 10.000 |
| vf [mm/min]: | 700 |
SEQUENCE OF THE COMPARATIVE TEST
1. BORING OUT WITH UNBALANCED BORING TOOLS
Loud vibration noises during the bore out operation!
The resulting vibrations put a heavy strain on the spindle which, based on general experience, reduce its lifetime by up to 50%. Machine tool and spindle manufacturers have therefore come up with very detailed regulations which address the balancing requirements of rotating tooling systems (DIN Norm 69888). When these balancing requirements are not met the warranty for the spindle becomes completely or partially invalid.
The bad runout also reduces the tool-life and additionally has a negative effect on the tool tolerance and precision (see point 4 and 5).
2. BALANCING THE BORING TOOL
With the user-friendly HAIMER balancing technology balancing the entire tool only takes a couple of minutes. The machine measures the centrifugal forces which occur during the rotation of tool and tool holder and illustrates how these forces can be compensated.
The index measuring with two measuring runs shows that the unbalance of the unbalanced boring tool is outside of the acceptable tolerance range (here: 10.000 r/min; G = 2,5). The balancing grade is G = 97,3. Instead of the previously used rotational speed of 10.000 r/min the tool was actually only allowed to be used at 256 Rpm/min in order to meet the requirements for the tool spindle.
In a second step the unbalance of the boring tool is compensated with balancing screws. The software of the balancing machine illustrates how much balancing weight needs to be applied to the highlighted area in order to make the necessary correction.
With a final control measurement with two measuring runs the balancing grade gets checked. The measuring result shows that the unbalance is within the acceptable tolerance range (here: 10.000 r/min; G = 2,5). The balancing grade of the fine-balanced boring tool is G = 1,9 and the tool can be used at 10.000 Rpm/min without any hesitation.
3. BORING OUT WITH A BALANCED BORE TOOL
During the boring operation with a fine-balanced tool you won't hear any vibration noises. The machine tool runs "quietly and smoothly".
4. MEASURING THE FIT WITH A LIMIT PLUG GAUGE
When checking the fit of the borehole with a limit plug gauge you will notice that the plug gauge won't fit into the borehole because of the tolerance deviation that was created with the unbalanced boring tool.
The bore is scrap!
5. EXAMINING THE FIT WITH A CENTRO
An additional control of the borehole with the HAIMER Centro measuring device visually illustrates the tolerance deviation of the bore.
6. Form accuracy of the bore
A final, highly-precise measurement of the bore on a portal measuring machine provides a detailed explanation on why the plug gauge doesn't fit into the bore.
The bore of the unbalanced boring tool is oval!
The bore of the balanced boring tool however is highly form-accurate!
In conclusion, it can be said that fine-balanced tools offer numerous advantages. Next to a long tool and spindle life the possibility to increase productivity, process reliability and workpiece-accuracy are surely some of the strongest arguments in favor of balancing. Ideal processing parameters on the machine tool can only be selected if both tool and tool holder have a high runout accuracy and balancing grade.
Therefore it is essential to balance the entire tool after each tool change!