There are two types of machine static stiffness tests: thrufeed, and infeed.

1. Thrufeed Instruction

Grind enough components with total stack length larger than twice the wheel width. Operate the grinder at a power consumption that is larger than 60% of the available power. Take one component in the middle of the stack out of the flow. Measure its diameter accurately and record this number for the first measurement input of the program.

After taking the part out of the flow, the flow can be stopped, however leave the machine running but do not change any settings. Use the measured component and feed it through the grinder again. Measure its diameter and record it for the second measured input of this program.

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.

A

B

C

D

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)

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.

Fig. 2-3-4 The Part Information page of the Thrufeed One machine with multiple passes.

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)

Fig. 2-3-5 The Machine Information page of the Throughfeed One machine with multiple passes. (Bethel Technologies, Inc.)

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

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.