CADFamily.com: KISSsoft Tutorial-Tooth Form Optimizations Part A

KISSsoft Tutorial-Tooth Form Optimizations, Tooth Form Modifications specifically for Plastic, Sintered, Wire-eroded and Form-forged Gears

1 Introduction

1.1 Summary of the design strategy

These instructions describe a strategy for optimizing the design of gears that are manufactured

using moulding methods (injection moulding, sintering, forging etc.). These special methods for

sizing and optimizing gears manufactured using these methods are integrated in the KISSsoft calculation software.

The sizing process involves these steps:

- Define the approximate sizes (module, face width, etc.) using the strength calculation

- Define allowances

- Optimize tooth height (aim: achieve effective transverse contact ratio 2.0 whist taking

into account tip rounding, running-in curve for noise reduction)

- Tip-rounding

- Optimize running-in curves/profile correction (aim: improving the wear safety factor)

- Optimize root fillet (increased the root safety factor)

- Determine a mould for the manufacturing process

1.1 Introduction

Nowadays,gears are increasingly manufactured from plastics because the development of new materials has made them able to achieve increasingly higher load capacities. The special

properties of plastics allow them to be used in many more areas than steel. A designer can therefore select the best possible material for their particular application. In doing so, they define the most important properties of a gear pair, such as load capability, resistance to wear, compression ratio, stiffness and noise emissions.

Metallic gears are usually manufactured in a milling process. In contrast, plastic gears are

usually injection moulded. If the mould is produced by a wire erosion process, the tooth form can be optimized at no additional cost. In a milling process, this is only possible with expensive, specialist tools.However, the injection moulding process does not achieve a particularly good toothing quality and, once again, this is a problem that can only be solved by implementing specific measures. Gears that have been modified in this way are referred to as hybrid tooth forms in the technical literature.

The KISSsoft calculation software includes a large number of special methods for sizing and

optimizing plastic gears. These procedures are fully integrated into a comprehensive, modern

software system that enables you to develop and monitor both standard and hybrid tooth forms.

2 Defining tooth geometry

2.1 Introduction

You can change tooth geometry in many different ways to achieve the optimum ratio of tooth contact. Depending on the importance of the targets to be achieved, such as low noise emission, low vibration, strength, sliding, balance, you must prioritize the measures to be taken. When you start this optimization process, we recommend you set the following defaults:

2.2 Tip-rounding

For tooth forms produced using a moulding process, the tooth tip edges must be rounded,because corners can never be created accurately in injection moulding. It is a good idea to input this data in the main screen for gear 1 and gear 2. As a result, all the most important data (such as contact ratio, etc.) will then be calculated to include tip-rounding.

This is now illustrated in an example: The KISSsoft system has a tutorial file for this calculation.

This is "Tutorial - 011". Open this file in the cylindrical gear calculation module:

Figure 2.1 Opening cylindrical gear calculation and the tutorial file

Figure 2.2 Example file for plastic gears, after calculation ("")

Click in the tool bar or press "F5" to calculate the tooth form data. Without tip-rounding the

contact ratio would be 1.6680. You can see the tooth form as a graphic in the lower part of the

window. You can also view the tooth form here and move it to the required position (see the marking on the lower right of Figure 2.2).

Figure 2.3 Tooth form display

You should now save the tooth form locally. To do this, open the "Property browser" (1). Activate the tooth form of Gear 1 (2) and click the "Save" button (3). This opens an information window. Here you can make any necessary changes (for example, color) and additional entries (4). Then click "OK" (5) to save Gear 1's tooth form. Follow this procedure again to save Gear 2's tooth form. You can now view the changes you have made to the tooth form. Then, close the "Property browser".

Figure 2.4 Saving the tooth form

To define the tip-rounding, go to the "Modifications" tab (see the uppermost marking in Figure

2.5) and input the relevant values for Gear 2 and Gear 5:

Figure 2.5 Defining tip rounding, here 2 mm radius

Then click onto apply the changes. If you look carefully at the graphic, you will see the rounding on the teeth. The original tooth form is also displayed (in black/green or blue).