2. Infeed and Internal Instruction
▪Grind one component at an infeed rate with high enough power consumption (60% or more of available power); keep spark out time to zero. Measure the diameter of the component and record the net actual power consumption.
▪Grind a second component in the same setup with spark out set to 10 seconds or more. Measure the diameter of component.
There is more to grinding than only the basic principles covered, but this will serve as an introduction to the capabilities of the software.
GRINDING SIMULATOR SOFTWARE
There are eight different types of grinding operations built into the Grinding Simulator, Fig. 2-3-3A to D:
1.Thrufeed grinding with one machine (A)
2.Thrufeed grinding with multiple machines in line
3.Centerless Infeed (B)
4.Centertype Infeed
5.Microcentric
6.Angular (C)
7.Multiple-Diameter Centerless Infeed (D)
8.Multiple-Diameter Centertype.
It would be difficult to discuss all these grinding operations in detail since the same basic principles apply to all. Therefore for this example, the focus will be on Thrufeed Grinding for one machine with multiple passes.
Part Information
Figure 2-3-4 shows the Part Information page, which lists various material groups, each containing several specific materials. There are a total of eighty different types of materials and other materials can be added, provided that its thermal conductivity at 300°C is known.
There are different types of tolerances that play a role in the grinding process and are related to each other. In the Part Information Page, the print final size tolerance is an input, and automatically the expected roundness tolerance and cylindricity tolerances are calculated. The software allows users to type in their own roundness or cylindricity tolerance. This would then initiate a reverse calculation for the final size tolerance. Another important input is the CPK (Capability Index). The print tolerance and the shop tolerance are not the same when the CPK is larger than one. The relationship between shop tolerance and print final size tolerance is
| (8) |
For each input where there are metric and inch units, each unit system can be used. The green label shows the converted value from one unit to the other.
The part’s information can be saved in a database and be reloaded or modified at any time.
Machine Information
Figure 2-3-5 shows the Machine Information page. The speed ratio is defined as
| (9) |
The user can enter the Speed Ratio, or it can be selected from the general ranges. A high-speed ratio means a low workpiece speed that makes the chip length larger. This would then make the grinding process more sensitive for surface damage due to heat. A speed ratio higher than the High Speed Ratio selection will result in burning of the workpiece. The selection of High Speed Ratio should be used in cases where workpiece out-of-balance takes place or where the machine dynamic stiffness does not allow higher work speed.
A selection of Typical means an average moderate work speed that is used on most grinding operations. The selection of Low speed ratio means a high workpiece speed and can be selected when the machine has a high static stiffness. With weaker machines, a low speed ratio may cause chatter on the workpiece. The practical speed ratio has a correlation between the wheel speed, workpiece speed, and with the part diameter.
When the user enters in a wheel speed, the wheel r/min is automatically calculated. It is possible to enter the wheel r/min that would result in a wheel speed calculation. The workpiece r/min is automatically calculated when the speed ratio is selected. The user can enter the workpiece r/min at which time the speed ratio selection will go to None. There is an important correlation between workpiece r/min and wheel r/min. The ratio between wheel r/min and work r/min is called the Beta ratio. It is defined as
Fig. 2-3-3 Types of centerless grinding: A. Throughfeed (Cincinnati Machine, A UNOVA Co.) B. Centerless infeed (Carborundum Abrasives, Div. Saint-Gobain Abrasives.) C. Angular (Cincinnati Machine, A UNOVA Co.) D. Multi-Diameter Infeed (Carborundum Abrasives, Div. Saint Gobain Abrasives)
This relationship is important when the grinding process results in triangle or other non-round parts. When the Beta Ratio is exactly 3 or close to 3, then it could indicate a triangle part problem. Another important calculation that depends on the workpiece r/min and the speed ratio is the regulating wheel r/min. Whenever the workpiece r/min is changed, the regulating wheel r/min is changed accordingly.
Quick Results
Figure 2-3-6 shows the most important calculated parameters. The first item shown in the calculations is the surface finish. If no static stiffness constraints or available machine power constraint occurs, then the surface finish in the finishing operation should be the same as the requested surface finish. The next item is the Specific Metal Removal Rate Q’. For certain fluids, the Q’ cannot exceed a certain value. In case this occurs, it will appear in the messaging box. The other calculated values are important but need no detailed discussion.
The messaging box shows the factors that can occur that could limit the production rate. Whenever there is enough system static stiffness available, the software calculates at what CPK value the job should be able to run. The message box suggests changes to increase productivity whenever possible.
Machine Setup
The Machine Setup page is shown in Fig. 2-3-7. There are four items that are shown in this page.
1.If a machine picture is available, it would be shown in the upper left corner.
2.The upper right corner lists the machine manufacturer, the machine model, the static stiffness of the machine when built, and the date of the last static stiffness test.
Fig. 2-3-4 The Part Information page of the Thrufeed One machine with multiple passes.
Fig. 2-3-5 The Machine Information page of the Throughfeed One machine with multiple passes. (Bethel Technologies, Inc.)
3.The lower left corner shows a graph of the static stiffness of the machine as a function of time. In this example, the static stiffness of the machine is slowly deteriorating.
4.The lower right hand corner shows the machine setup.
▪The center height is the height above the centerline of the grinding wheel spindle and regulating wheel. The calculated center height is close to the actual center height that should be used in the actual machine setup.
▪The throughfeed angle