Kisssoft Tut 011 E Toothform

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KISSsoft Tutorial:Tooth-Form Optimisation and Tooth-FormModifications Specifically for Plastic, Sintered, Wire-Eroded and

form-forged Gears_____________________________________________________________________________________________

For Release: 10/2008

kisssoft-tut-011-E-toothform.docLast modification: 05/11/2008 12:17:00

_____________________________________________________________________________________________

1 Introduction1.1 Summary of the Design Strategy

In these instructions, the strategy for the optimisation of gear design parameters will be described

for gears manufactured by forming methods (injection-moulding, sintering, forging, etc.). Thesespecial design and optimisation methods for gears have been integrated into the KISSsoft

calculation software.

The course of the design procedure comprises of the following steps:

- Define the approximate sizes (Module, tooth width, ...) for a strength calculation

- Define allowances

- Optimise tooth height (Aim: Achieve a contact ratio of 2.0 taking into account tip-rounding,

and running-in curves for the reduction of noise)

- Tip-rounding

- Optimise running-in curves/profile correction (Aim: Noise reduction, improvement of wear

safety factor)- Optimise root fillet (raise the root safety factor)

- Establish mould for manufacturing

1.2 Introduction

Gears are increasingly made from plastics, which through the development of new materials are

capable of ever higher load bearing capability. The properties of plastics allow its implementation

in a far higher number of areas than steel. This permits a designer to choose more specify an

optimum material for the required application. In doing so, the most important properties of a gear

pair such as load capability, wear, compression ratio, stiffness, and noise development will be

defined

KISSsoft

Tutorial011:ModificationsSpecificallyfo

rPlastic,S

intered,W

ire-Erodedandform

-forgedGears


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Normally, metallic gears are manufactured using a generating process, whereas in contrast those

produced in plastic are injection-moulded. If the mould is produced by a wire erosion method, the

tooth form can be optimised without additional costs. In a generating process this is only possible

with expensive special tooling. Having said this, the injection process of the plastic does not permit

a very high quality to be achieved, a problem which again can only be addressed through special

methods. So modified gears are referred to as hybrid tooth-forms in technical literature.

In the KISSsoft calculation program, many special methods for defining and optimising plastic

gears have been integrated. The procedures offered are part of a complete and comprehensive

modern software concept, such that allows the development and control of standard and hybrid

tooth forms.

2 Definition of Tooth Geometry2.1

Introduction

The tooth geometry can be changed by various different measures in order to achieve an optimum

ratio of tooth contact. Depending upon the emphasis of the targets to be reached such as noise, low

vibration, strength, sliding, stiffness, balance, etc. then will one or another measure chosen to be

prioritised.

Before beginning the following optimisation, it is recommended to set the following defaults:

2.2 Tip-Rounding

For tooth-forms produced by a forming process, the tooth tip edges have to be rounded so that the

injection moulded part can also be removed from the mould. This input setting is advantageouslyencountered already in the main interface, and beside Gear 1 and Gear 2 in the Tab

Modifications. As a result, all known data (such as contact ratio, etc) will be calculated with

consideration of tip-rounding.

This will now be demonstrated through an example: There exists in KISSsoft a file containing

example data for plastic gear calculations Tutorial 011. This file should be opened from the

cylindrical gear pair calculation:

Figure 2.2-1: Open the Cylindrical gear pair calculation or the Tutorial file.


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Figure 2.2-2: Example file for plastic gears after carrying out the calculation orF5.

When in the Tool bar the icon (or the button F5) is pressed, the tooth form data is calculated

showing contact ratio without tip-rounding of 1.6680. By pressing the button (that marked bottom

right in Figure 2.2-2) the tooth form can be viewed:

Figure 2.2-3: Tooth-Form Illustration.


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Here the tooth form should now be saved locally (i.e. in the working directory of the program), for

this open the Property browser (1). The tooth form for Gear 1 is to be activated (2). By pressing

the Save-Button(3) a new window is displayed (4). Here are some changes possible (e.g. color)

entries (Label) can also input. After pressing [OK] the tooth form is saved. For Gear 2 the same

procedure is required. After then the Proberty prowser is to be closed. In doing so, any relative

changes in the tooth form become easily visible.

Figure 2.2-4: Saving the thooth form.

The tip-rounding is defined in the tab Modifications for Gear 1 and Gear 2 as follows:

Figure 2.2-5: Definition of the tip-rounding in the S-interface, here it is 2mm radius.

The changes will apply after pressing in the Tool bar the icon . Looking at the geometry the

changed tooth form, the rounding can be seen. Likewise the original tooth form can be seen.


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Figure 2.2-6: Rounded tooth tip with simultaneous representation of the original tooth form.

Important hint:

Through the storage of the tooth form all previous calculation operations are active.

Maybe it is better to activate or deactivate one of single calculation step to trace the made

modification.

The graphics properties can put back. This is going by an automatic function if in the geometry

window the representation is changed. The different alternative is by reset ofGraphics properties

via pressing Extras->Configuration tool activate the check mark in Graphics properties and

press [Reset].

Figure 2.2-7: Reset ofGraphics properties.


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Figure 2.2-8: Reset ofGraphics properties.

In the main interface the calculated value fort he contact ration has reduced to 1.3639:

Figure 2.2-9: Reduction of the contact ratio following tip-rounding.


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2.3 Minimum tooth thickness at the tip

The necessary minimum tooth thickness at the tip is set by default to 0.2*Module. For plastic gears

(with tip-rounding) this value is extremely low. A more reasonable value is 0.4*module. This

default can be set under Calculation->Settings on the tab General:

Figure 2.3-1: Default values for the required minimum tooth thickness at the tip found under module specific settings.

Significant and effective measures for the optimisation of geometry are:

2.4 Geometry changes for defined reference profile:

The geometry of the tooth contact can significantly altered by variation of module, pressure angle,

and addendum modification of a reference profile. In particular with helical gears, with these an

optimum solution can be found in most cases. Here the KISSsoft software programs serve as a

particularly effective tool for optimising the design. This facility compiles for a given set of

conditions all possible solutions which achieve the targets, and classifies the results according to

operating criteria.

The precision design procedure is called using under Calculation->Fine Sizing in the main

interface. A more comprehensive description can be found in the KISSsoft Tutorial kisssoft-tut-

009-E-gearsizing.doc.

The interface for precision definition of parameters:


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Figure 2.4-1: Cylindrical gear pair fine Sizing.

2.5 Changing Geometry through variation of the reference profile:

A reference profile change (normally an enlargement of the tooth height) gives a change in the

profile contact ratio. For low noise and smooth running tooth forms, a ratio of 2.0 (or even higher)

is sought. In doing so the stiffness jump brought on by changing from single to double contact can

be minimised. The required contact ratio can also be reached through a corresponding change in the

reference profile, though admittedly in most cases interference will appear during the generation of

the gears. The possible solutions are therefore limited. In order to efficiently work on this problem,

the previously mentioned KISSsoft-Fine sizing design functions offer the possibility (as an add-onfeature) to pick-out and show all possible solutions for a given theoretical profile contact ratio.

This method can be activated in the Fine Sizing interface by choosing the tab Conditions II

access the appropriate sub-interface:

Figure 2.5-1: Activation deep tooth form.


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Here, the Flag Sizing of deep tooth form () must be activated.

The required contact ratio will be inserted in the main menu under Calculation/Settings on the tab

Sizing.

2.6 Elimination of the Contact Shock through corrections to the Tooth Form:

During the meshing of a gear pair, there appears as so-called Contact Shock due to the contact oftwo new teeth. This impact produces noise and is all the larger for further inaccuracy in the pitch

and for deformation of the teeth under load. For plastic gears therefore, the involute in the tip region

is modified through a relief curve. For metallic gears this process is called profile correction at the

tip, though in this case the amount of correction is a great deal smaller because of the much higher

stiffness. Normally the curve will be applied to the tip of both gears; for variants (e.g. rack drives)

the correction is applied only on one gear and in the root. The curve advantageously consists of

three smaller circular arcs, which when selected are independently calculated and then integrated in

KISSsoft.

We have 2 options in KISSsoft for input a tip-relief and the modification curves:

A) With the tab ModificationsThis is a new option with Release 03-2008.

In tab Modification can be defining a linear and curved profile correction at the tip and/or the

root.

The advantage is, that the inputted corrections in the main protocol are documented. The

overview is now better and clearly arranged. The input process can be faster executed.

We recommend with Release 03-2008 this variant. The course of action will be described in

another Tutorial. Now we will describe the variant B).

B) In tab Tooth form (until now)The input and calculation of tip-relief and the modification curves is carried out within the tooth

form calculation. For this call up the tab Tooth form:

Figure 2.6-1: Tooth Form Calculations.

With the predefined step automatic all the settings from the main dialog are used, mainly

reference profile and tip rounding or chamfer.
http://dict.leo.org/ende?lp=ende&p=eL4jU.&search=executed


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To add modifications, click with the right mouse button on automatic and select Add operation

and then choose from the list an option with left mouse button.

Figure 2.6-2: Possible operation for the tooth form on gear 1

The tip rounding should be the last operation; otherwise it will collide with the tip relief. Therefore

the check button for Consider Tip chamfer/Rounding in the automatic step is deleted:

Figure 2.6-3: Deactivate Consider Tip chamfer/Rounding on gear 1

After the definition of the basic gear geometry, the modification of the involute is carried out.

Various methods for doing this have been integrated into the software. The options consist of:

Linear or progressive profile correction, or Running-in curve from three circular arcs according to

H. Hirn [1]; each modification can be combined with tip chamfer or tip rounding. The inputs to by

specified are the correction height (diameter at which the correction begins) and the tip relief value.

For both values there exists a function to suggest the optimum design parameters based on contact

ratio, quality, type of material (plastic or metal), the stiffness, and the load. For the progressive tip

relief (option Progressive profile correction) by changing a Factor the form of the curve can

even be given in directly by the user!

With progressive profile correction the length of the contact ratio and the local lubrication

properties can be improved compared to those achieved through linear profile correction. The

formulae for the profile corrections are defined as follows:

Linear correction: s(r) = Ca * r /rK

Progressive correction: s(r) = Ca * (r /rK)Exp

Where:s Profile relief (Change in tooth thickness)

r Radius of an arbitrary point on the tooth form.


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Ca Profile relief at Tipp.

r ra r

rK ra raK

ra Tip radius

raK Radius at the beginning of correction

Exp = Factor/5

Factor: Range 1-20, normally in the range 5..10(Factor: Can be introduced)

Figure 2.6-4: Kinds of profile corrections.

The button to the right of the input field Modification starting at diameter tells the program to

determine an appropriate suggestion for the beginning and size of the relief.

Figure 2.6-5: Proposal tip modification.

For the manufacture of gear by moulding (injection or sinter) it is important to round the corners in

all cases. The rounding radius (filet) at the tip can be given independently of the chosen profile

correction.

Figure 2.6-6: Add tip rounding.

The different forms of running-in curve/profile correction are described in the programs help

directory (and in the manual). The course of the curves can be influenced by the Factor (factor for

the tip rounding).

To determine the best Factor the choices must be tried out. The tooth form can be viewed in the

interface for the illustration of the gears. In addition, by pressing the described button see Figure

2.2-4 to Save Gear 1. Go back to the main window in Tab Tooth form and there change the

Factor for tip rounding. Carry out the calculation again, and then view the image once again. Theearlier form and the new form are shown:


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Figure 2.6-7: comparison of tip modification

In the previous tooth form calculation the settings for operation Add tip rounding theTip

rounding was r=1mm whereas for the operation Progressive profile correction the Factor for tip

rounding was 18. The calculation is run again with a progressive profile correction with factor 10

and tip rounding (r=2mm).

2.7 Optimisation of the Tooth Root

The fatigue safety factor can be significantly improved by a large radius in the transition from the

involute in the root filet. In the manufacture of gears by a generation process it is sometimes

difficult to achieve an optimum rounding even when using tools with well rounded tips. Through acorresponding modification, which naturally is only permitted below the usable root diameter, the

safety factor can be noticeably improved.

This modification can also be VERY useful, if a tooth form has an undercut. The undercut can be

completely eliminated.

This modification can also be carried out automatically by KISSsoft.

The input and calculation on optimum tooth form rounding is carried out within the tooth form

calculation, using Elliptic root optimisation, analogous to the tip relief as described in Section 2.6.

Figure 2.7-1: Root form without (black, with undercut) and with (blue) optimisation.

Important: In combination with a running-in curve or tip rounding on the mating gear, the beginning

of the filet can encroach above the root circle. In this case it is essential to check the meshing (see

next section).


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2.8 Control of the Meshing

After carrying out the tooth form optimisation, it is recommended to check precisely the meshing of

the gears. The contact between the gears should always be in the region of the actual involute. A

crash between the teeth, especially from the tip of the driving to the foot of the driven gear, can be

very damaging. The check should be carried out using the minimum centre distance value (and

safety reasons also with maximum centre distance). The centre distance can be defined using the

button in the geometry window.

A good help for this check of generation is the function Collision check, which can be activated in

the window Property browserunder Display Tooth Shape.

Figure 2.8-1: Push the symbol for Property browser and the property windows is show you can activate the

Collision check.

In the following example, the collision indicator highlights contact in the root region of the pinion:

For a correct meshing of the flank in the involute region (contact shown towards the top of the

diagram as black boxes on tooth form) there is interference in the root region (contact shown

towards the bottom as red boxes). The optimisation of the pinion therefore begins too early.

Figure 2.8-2: Collision check.

Crash correct contact


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2.9 Control of the Seizure in the Gears

A seizure of the gears can be avoided by a corresponding tooth thickness deviation (as described in

Chapter 4). If the change can not be made as large as theoretically needed (e.g. the remaining tooth

thickness would be too small), or if a seizure could occur on some other ground, then it is important

to check this:

In running the gears together in mesh, the teeth should seize before the tip encroaches encounters

the root circle (i.e. for backlash 0.0 there must still be some tip clearance). This is an important

point direct from working practice in that an encroachment upon the root is more serious than a

seizing of the flanks.

In KISSsoft this check is carried out directly in the window Tooth Contact Gear1-Gear2, in which

the centre distance is reduced until the backlash is removed. In this position there must still be

clearance between the tip of one gear and the foot of the other!

Figure 2.9-1: Here is a bad example: After removing the backlash the tip of gear 2 is already within the root region of

the foot of gear 1!

3 Strength Calculation3.1 Introduction

For the drafting and optimisation of gears the calculation of the tooth root, flank, and wear safety

factors at the projected life is important.

As with steel, the material property values for plastics (root resistanceand flank strength) are

dependent upon the number of load cycles. In addition there is for each a strong dependency on

temperature and type of lubrication (oil, grease or dry).

While with steel the root strength calculation depends on one single value (e.g. for root resistance

the admitted fatigue strength tooth root tension Flim of 17CrNiMo6: 525 N/mm2) is sufficient, farmore graphs are needed for plastic gears. In KISSsoft this data is tabulated for each of oiled,


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greased, or dry running, which is automatically utilised during the calculation. Because of this, the

material properties data can be very easily modified by the user.

3.2 Input of New Property Data for Plastic

There are already a few plastics available in the KISSsoft materials database. If some others have

known properties, then they can also be entered in the database as the following example using

POM demonstrates:Start the Database using Extras->Data base Tool. Open the material database and activate the

data for gear calculations:

Figure 3.2-1: Opening the gear material database.

If a new material is to be defined then press +:

Figure 3.2-2: Generate a new data set.

The following is an example (that already exists in KISSsoft) showing the required entries for the

specification of material POM. These are the General Data and Module-Specific Data Z000:


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Figure 3.2-3: General Data for plastic.

The most important information is the entry under Polymer Data, as marked in Figure 3.2-4. Here

the name of the file is entered in which the temperature and lubricant dependent data will be stored.

The file is stored in the installation directory (typically C:\Programme\KISSsoft-10-2008):

Figure 3.2-4: Saving the Plastic Data.

The newly entered material data now has its own file (name can be freely chosen). Next, the best

method to enter new data is to copy a full data set directly from an existing equivalent file into this

new file (e.g. the file Z014-100.DAT for POM), rename and then edit.

Extract from Z014-100.DAT (for POM): Modulus of Elasticity (Elastizittsmodul)

(One-dimensional table relating E-Modulus dependency to temperature)

:TABLE FUNCTION ElastizitatsModulINPUT X ZahnTempFuss TREAT LINEAR

DATA

-20 0 20 40 60 80 100 1204400 3950 3500 2950 2400 1800 1400 950END


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Extract from Z014-100.DAT (for POM): Flank strength with oil lubrication (Two-dimensional

table with sig.Hlim dependency to temperature (Columns) against load cycles (Lines))

-- Daten fr Flankenfestigkeit bei lschmierung-- Aus Niemann, Bild 22.4/4, fr PA66, lgeschmiert:TABLE FUNCTION FlankenSigHNOel

INPUT X ZahnTempFlanke TREAT LINEARINPUT Y Lastwechsel TREAT LOG

DATA20 40 60 80 100 120

0 120 115 108 99 91 761E5 120 115 108 99 91 761E6 95 90 85 78 68 571E7 70 67 63 58 50 401E8 52 50 47 44 37 281E9 45 42 40 38 32 251E10 43 41 38 36 30 241E11 43 41 38 36 30 231E99 43 41 38 36 30 23

END

3.3 Strength Calculation with Consideration of Effective Tooth Form

The calculation of the root strength according to the methods in the standards VDI2545, DIN3990,

ISO6336 or AGMA2001 use a simplified model for calculating the root stress, in which the stress is

calculated for a nominally defined cross section (at a point of the 30 degree tangent on the root filet

in DIN or ISO). This cross section can however significantly differ form that specified in gears with

pressure angles which deviate from 20 deg, or through post-optimisation of the root filet (see

below).The Graphic Method in KISSsoft performs the calculation exactly according to the

corresponding formulae of the chosen calculation methods (YF and YS in DIN, ISO, AGMA) in

approximately 50 cross sections in the root region from the mid-tooth height to the root, and

determines the cross section with the highest bending stress. This data is carried over to the

calculation. In doing so, this gives a significantly more accurate calculation procedure with which

even non-involute tooth forms can be calculated. See also Chapter 6.

The Graphical Method is activated in KISSsoft as follows:


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Figure 3.3-1: Activation of the strength calculation according to Graphical method.

Now each calculation will automatically calculate the tooth form first, and then derive the YS and

YF values from it.

KISSsoft also permits the graphical representation of the tooth root stress in the root.

Choose the tab Path of contact and set the necessary settings.

Figure 3.3-2: Calculation Path of Contact.

The Stress curve(dark blue and green) shows the effective root stress F on gear 1 and gear 2

over the roll angle. The light blue curve shows Hertzian Surface Pressure. Also is shown the

situation for the maximum of the stress with the respective tooth forms of the respective gear.


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Figure 3.3-3: Root Stresses and Hertzian Surface Pressure Characteristics over one mashing cycle displayed fromfile

Tutorial 011.Z12 with modification (Progressive profile correction with factor 10 and tip rounding (r=2mm).

Figure 3.3-4: Tooth root Stresses Characteristics

4 Determine the Tooth Thickness Deviation (backlash)4.1 Introduction

In the field of high precision technology the tooth thickness deviation (backlash) are usually much

higher than for gears with module 1.0 or greater. When the relative centre distance tolerance is

large and the tooth quality is low, the deviations have to be chosen large enough to avoid seizing

during operation.

Additionally there is a tendency in many plastics to absorb water over time and swell.


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Therefore, subject to experience, it makes good sense as a first step in the determination of the

parameters to define the required deviation. It would be of no use to optimise a tooth form (as is

described here), and then afterward find that through and the deviation this carefully optimised tip is

chewed at the tip!

The definition of the deviations is given according to the methodology in DIN3967. Additionally

the operating temperature and the thermal expansion coefficient of the gears and the housing haveto be known. Further, the swelling should be taken into consideration. Here Polyamide (PA) is most

critical of all (up to 2% due to water in-take).

4.2 Calculation of the Operating Backlash

In KISSsoft there is an example file available to demonstrate plastic gear tooth calculation called

CylGearPair 2 (Plastic-Deep Tooth Profile). This should be opened from the Cylindrical Gear

Pair module:

Note the selected tolerances for Gear 1 and Gear 2 and the centre distance:

Figure 4.2-1: Pre-selected tolerances for Gear 1 and Gear 2 and centre distance.

Before the operating backlash calculation can be performed, the tooth form must be calculated

using Calculation . Afterward the calculation of the backlash can be called using the tabOperating Backlash:


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Influence of the

manufacturing

precision (axis

position)

Influence of thetemperature on

expansion of the

housing and the

gear bodies

Choose material

for housing

Figure 4.2-2: Set-up for the operating backlash calculation.

This example has been defined such that seizing can occur during operation. During the calculation

the following warning will appear:

Figure 4.2-3: Warning that seizure could occur during operation.

On selecting Results the following documentation is shown:...

Results :Change of center distance by:Warming (mm) [DaC] 0.037 Casing

(mm) [DaW] -0.352 Gears

Backlash change due to:center distance tolerances (maximal) (mm) [Dja.e] 0.006(minimal) (mm) [Dja.i] -0.006

Swelling due to absorption of water (mm) [DjQ] -0.068Warming (mm) [Djtheta] -0.207Misalignment of axles (mm) [DjSigmabeta] -0.006Mesh single deviation (mm) [DjF] -0.014 -0.014

Theoretical backlash- Circumferential backlash

(min.) (mm) [jt.i] 0.118(max.) (mm) [jt.e] 0.201

Acceptance-backlash- Circumferential backlash

(min.) (mm) [jta.i] 0.102(max.) (mm) [jta.e] 0.186

Operating backlash- Circumferential backlash

(min.) (mm) [jtw.i] -0.174(max.) (mm) [jtw.e] -0.090

- Normal backlash(min.) (mm) [jnw.i] -0.165(max.) (mm) [jnw.e] -0.085

- Torsional angle with fixed gear 1(min.) () [Dphit.i] 0.0000(max.) () [Dphit.e] 0.0000

...

Figure 4.2-4: Sample of a documented report from the calculation of operating backlash


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The negative values for the circumferential backlash shows that the gear will seize.

4.3 Enlarge the Operating Backlash

The circumferential backlash is in the most serious case -0.173mm (see yellow text marked above).

So that no seizing occurs, this value has to be greater than zero. For this the tooth thickness

deviations should be changed (teeth made thinner). Both teeth should become 0.1mm thinner (so

that the circumferential backlash is raised by 0.2mm in total and thus remain positive in all cases).To do this the tooth thickness tolerances in the main mask under tolerances should be set to Own

Input, and the circumferential backlash for each gear increased by 0.1mm (for the lower and upper

deviation):

Figure 4.3-1 Before original tolerances cd25 according to DIN3967) and after (Own Input)

Figure 4.3-2; Raising fort he circumferential backlash for both gears to 0.2mm in each case

After this input has been given, the tooth form must again be calculated using Calculate, and then

the re-defined operating backlash values can be viewed as described above. This time no warning

appears that the gears should seize, and a positive operating backlash is displayed:

...Operating backlash

- Circumferential backlash(min.) (mm) [jtw.i] 0.026(max.) (mm) [jtw.e] 0.110

- Normal backlash(min.) (mm) [jnw.i] 0.025(max.) (mm) [jnw.e] 0.106

- Torsional angle with fixed gear 1(min.) () [Dphit.i] 0.0318(max.) () [Dphit.e] 0.1318

...

Figure 4.3-3: Sample of a documented report from the calculation of operating backlash showing that the backlash is

now positive


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5 Calculation of the Injection Mould5.1 Introduction

The theoretical tooth form which has been optimised as described above is calculated by KISSsoft

using the mid-value of the tooth thickness deviations. This gives the complete tooth form, which

can be transferred to a CAD system using integrated DXF or IGES transfer interface. This contour

can, for example, be used to machine gears in which a projection procedure is used.

In addition, the injection mould form can be defined by calculation. During the injection process of

plastic gears, there emerges shrinkage during the solidification of the plastic. In order to compensate

for this shrinkage, the mould is manufactured slightly larger. This is related by radial and tangential

expansion. Radial expansion gives an aspect ratio change in the radial direction (i.e. a shift of each

point on the tooth outer contour in a straight line from the centre point). Tangential expansion gives

a thickening of the tooth and a corresponding reduction in the tooth space. For the calculation of the

mould in KISSsoft, the required radial expansion at the tooth tip and root as well as the tangential

expansion as a percentage should be given.

5.2 Modification of the Mould for Shrinkage

These modifications are activated under the tab Tooth Form. There you must add to the already

existing operation Automatic additional operations:

Figure 5.2-1: Tooth Form Calculation with modification for mould building.

The radial and tangential expansion can now be entered. The resulting tooth form will now be

generated by pressing Graphics/Geometry, and can be viewed using Meshing:

Figure 5.2-2: Modifications for mould construction.


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Important:The modified form for the mould will not be displayed automatically. The display

has to be activated by setting as Choose as result:

Symbol with blue/blue indicates, that this operation is used for the display!

Figure 5.2-3: Display the gears enlarged with the given shrinkage.

In order to utilise the tooth form to manufacture the mould, it makes sense to export the gears

individually. Under Admissible deviation a value in m can be introduce, which defines themaximum admissible deviation of the tooth from (when using splines or circular approximation).

The display of gear 1 and gear 2 can now be seen by choosing in the list Tooth form of gear 1 or

Tooth form of gear 2:

Figure 5.2-4: Admissible deviation, unhinge graphic window.


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Figure 5.2-5: Call the tooth form display for an individual gear, and export forms via DXF or IGES.

It is very important to check the title of the graphic: The left picture shows the modified tooth form

for the moulding form. The right picture shows the unmodified black curve!

This procedure can be used to generate tooth forms which compensate for shrinkage as indicated in

Figure 5.2-5.

5.3 Display of the Eroding Wire / Spark gap

An additional feature of the software is that for a calculation of the mould form, the Spark gap can

also be considered if the electrode should be defined. The Spark gap is that which forms the space

between electrode and tool during erosion. The electrode has also to be thinner than the Spark gap,

in the case of tooth forming electrodes the tooth will be correspondingly thinner. In the case where

the mould is formed by wire erosion, the feed path of the wire can be defined with the sameprocedure (Spark gap and wire radius).

To consider the Spark Gap, the operation Modification for wire cutting has to be added.

Important: The wire form will not be displayed automatically. The display has to be activated by

setting as Choose as result:


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Figure 5.3-1: Tooth form without modification.

Figure 5.3-2: 1 mm given for the Spark gap.

Figure 5.3-3: tooth form increased by a positive value 1 mm given for the Spark gap

Note: If there is a negative value given for the Spark gap, the tooth form will be decreased.

Figure 5.3-4: -1 mm given for the Spark gap


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Figure 5.3-5: Tooth form reduced by a negative value -1 mm given for the Spark gap.

5.4

Control of the Diameter by ErosionLoad the example file Tutorial-011.Z12 again. The intended diameter of the erosion wire should

be checked. This is possible in the tab Tooth form. Following steps must be done:

At First add the option Modification for wire cutting the spark gap must be negative and the value

for s is the half wire diameter. After then add again Modification for wire cutting and activated

by setting as Choose as result. The half wire diameter is now positive. Switch all settings for all

calculation steps in the Property browser ofTrue.

Figure 5.4-1: Input the half wire diameter as spark gap.

All calculation steps will be shown in the tooth form geometry. The dark green curve is the position

of the centre of the wire when moving. The curve shows the produced tooth form, the dark blue the

required form.


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Figure 5.4-2: Checking.

5.5

Calculate the 3D mould3D-data can be generated in standard format (IGES, STEP or SAT) in this case choose PartGear

- or be generated directly in a CAD system in this case choose UG, ProE, CATIA, SolidWorks,

SolidEdge, SolidDesigner or Inventor.

Figure 5.5-1: Selection of interface.

Figure 5.5-2: Export the 3D mould according to various geometry formats.


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6 ANNEXE6.1 Foot Strength Calculation (Graphical Method)

The fatigue safety factor can be significantly increased by an optimal transition of the involute part

of the tooth form in the root. In the manufacture of gears by generation methods, even tools with

well defined tip rounding do not always produce optimum rounding. Through a specific

modification, that naturally must be adapted to the meshing criteria, the strength can be significantly

raised. This modification has also been integrated in the software.

Figure 6.1-1: Derivation of the Tooth Form Stress at an arbitrary point of the foot from YF(r) and YS(r).

There exists a choice: progressive rounding from ellipses, which can be defined by the users

through changes in aspect ratio. The default values are the required free arc length in the root aswell the diameter at which the optimisation should start. A very trustworthy algorithm has been

developed based on notes in standards, technical literature, and comparisons of calculations from

FEM-programs. Subsequently, the costly FEM-Modelling process can be dispensed with! All

normal calculation methods define the tooth root stress by a simplified model of the actual

conditions. In DIN and ISO the critical cross section is found by sitting 30 tangents on the root

contour. Depending upon the actual form of the root rounding there will be a larger or smaller

resulting error. In a publication from B. Obsieger [5] years ago, an approach for the distinct

improvement of the calculation procedure has been suggested. Based on the actual tooth form, the

Tooth Form Factor- (YF) and the Stress Factor (YS) is calculated for every point in the root region,

and the critical position defined in which the product YF*YS is a maximum (Figure 6.1-1).

This calculation procedure is integrated into the KISSsoft software. The critical tooth root cross

section can be determined based either on the force application on the tip (AGMA: Loaded at tip),


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or the force application at the single point of action (AGMA: Loaded at PSTC). The strength

calculation according to ISO, AGMA or DIN is then completely performed using these specific

data. The course of the stresses can also be graphically shown, see Figure 6.1-2.

The computation of the Hertzian-pressure along the tooth flank is also calculated based on the

actual tooth form. For each point of action the corresponding radii of curvature are determined for

both gears and starting from this the pressure is computed.

Figure 6.1-2: Course of the tooth stress, calculated based on the actual tooth form and conditions.

Documents

Kisssoft Tut 011 E Toothform