CAM-Lavorazioni Del Pattern Drilling

Introduzione

Il meccanismo di funzionamento del GESTORE CICLI FISSI lo si è visto nel capitoli precedenti.

Ora si vedranno nel dettaglio le lavorazioni possibili e quale utilità possono avere.

Le possibili lavorazioni che ci sono nel Pattern Drilling sono 15 e sono le seguenti:

1. CENTRATURA

2. FORATURA

3. ROMPITRUCIOLO

4. A TUFFO

5. PUNTA CANNONE

6. FORATURA INCROCIATA

7. LAMATURA

8. ELICOIDALE

9. CURVA 2D

10. SMUSSO 2D

11. SVASATURA

12. BARENATURA

13. ALESATURA

14. MASCHIATURA

15. FILETTATURA

Scopo di questo capitolo è di vedere nel dettaglio i parametri relativi a tutte le lavorazioni.

Per far ciò, siccome alcuni parametri sono gli stessi per gran parte delle lavorazioni,si è diviso questo

capitolo in due parti: la prima in cui vengono elencati e spiegati i parametri uguali per tutti, la seconda in

cui verranno trattati e spiegate le lavorazioni elencate sopra e i parametri che le caratterizzano senza più

trattare quelli visti nella prima parte.

Parametri Comuni Alla Maggior Parte delle Lavorazioni

- Libreria Utensile:

Se si sceglie Sfoglia si puo’ scegliere l’utensile che si vuole

prendendolo dal database utensile

- Numero:

Numero associato all’utensile

- Correttore:

Correttore dell’utensile

- Diametro:

Diametro della punta o fresa o maschio

- Numero Giri:

Velocità di rotazione del mandrino (SPEED)

- Avanzamento Z

Avanzamenti in Z (Z FEED)

- Avanzamento Z Di Rientro

Questa funzione è stata progettata per consentire all’utente

di immettere un avanzamento per forare una determinata

parte di un foro senza rapidi.

Per esempio, se si sta forando un foro profondo 200mm e

la prima foratura che si deve fare è profonda soltanto 150

mm, eseguire questo ciclo di foratura come al solito.

Qualche volta, quando si deve effettuare la seconda foratura,

che è abbastanza lunga per completare il foro a 200 mm,

l’utente vuole che mentre si fora questa parte, il percorso non

abbia alcun rapido. Così, in questo caso, si immette un

avanzamento in questo campo e il foro (in questo caso al di

sotto dei 150 mm) sarà forato con questo avanzamento.

Se sarà immesso in questo campo un qualsiasi valore

differente da zero, il ciclo di foratura deve essere punto a

punto (nel Gen. Post deve avere il segno di spunta

l’opzione Esplodi Foratura ) perché molti controlli a CNC

non hanno un ciclo che supporta la funzione di leggere solo

il punto iniziale e finale della foratura.

- Lunghezza Utensile

Andare su Applica e scegliere la Profondità Max di

Foratura

http://www.cadfamily.com/html/Article/CAM-Lavorazioni%20Del%20Pattern%20Drilling_873_1.htm

http://www.cadfamily.com/html/Article/CAM-Lavorazioni%20Del%20Pattern%20Drilling_873_2.htm

http://www.cadfamily.com/html/Article/CAM-Lavorazioni%20Del%20Pattern%20Drilling_873_3.htm

http://www.cadfamily.com/html/Article/CAM-Lavorazioni%20Del%20Pattern%20Drilling_873_4.htm

Walking Through Layers with LAYWALK

Have you ever needed to check whether objects are on the correct layers of your drawings? Is everything on the right layer? Have you repeatedly toggled layers on and off to show and hide them for temporary viewing? All of these actions (and others) can be accomplished with a simple but useful command in ZWCAD 2011, LAYWALK – short for “layer walk”. Lets take a look at how it helps you manage layers in your drawings. Tutorial 1: Showing and Hiding Layers When you first open the Layer Walk dialog box with theLayWalkcommand, all of the drawing’s layer names are listed. All those not turned off are down selected (are highlighted) automatically, so you can see the layer visibility settings as they were in the drawing before you started this command.

Now, whenever you select a layer name from the list, the corresponding layer is displayed in drawing area, and other layers are turned off instantly. (You don’t need to exit the dialog box to see the changes.) This allows you to view dynamically only the objects assigned to this layer. You can hold down theCtrlkey to select more than one layer for viewing at a time; also, you can hold down theShiftkey to select a contiguous group of layer names. A simpler way to select multiple, contiguous layer names is to click on one layer, and then drag down the list with your mouse. The dialog box works in reverse, too: when you choose one or more entities in drawing by Pick button, the dialog box highlights the layer names of those entities. In this way, it functions like the Layer Isolate command.  

Tutorial #2: Filtering Layer Names At the top of the Layer Walk dialog box, there is a text entry box, in which you can input expressions to filter the names of layers. This shortens the list of layer names displayed, and is very useful in complex drawings with many layers. The filter function supports wildcard characters, such as * (all characters) and ? (any single character). For example, if you want to list and view all layer names starting with the letters “gr”, then follow these steps: (1) enter gr*” in the text entry box, and then (2) tick the “Filter” option. Notice that the dialog box lists only those layer names that begin with “gr.”  

Tutorial #3: Using the Right-click Menu You can right-click on the list of layer names at any time to display context menu with additional functions for selecting, viewing, and summarizing the layers.  

For example, theHold Selectionoption keeps your current selection always turned on as a reference; based on it, you can select other layers. The on-hold layer is prefixed with the “*” character; you can select it, release it, or release all. Another useful option isInspect, which provides a detailed summary of the currently selected layers; see the figure below.  

Tutorial #4: Using Other Controls in LayerWalk You may notice thePurgebutton at the bottom of the dialog box. It allows you topurgeempty layers from drawings, those layers that have no entities. This button is disabled until you select one or more empty layers. TheRestore on Exitoption means that the layer state will be restored after you end this command -- regardless of what you’ve done while in the dialog box. When this option is turned off, keeps the layer state when you exit the dialog box, which can be very useful. By the way, this command works both in model space and in layout tabs.

http://www.cadfamily.com/HTML/Article/Walking%20Through%20Layers%20with%20LAYWALK_875.htm

Creating Curves in ZWCAD Quickly with Excel

In surveying and mapping, we get coordinates by taking measurements in the field, and then we make curves from these coordinates. To draw the curves in ZWCAD, we have to input the coordinates one by one at the command line, unfortunately. When there are many coordinates, then it becomes inefficient to draw curves in this way; in any case, this form of manual input is prone to making mistakes.Now there is an easier way to draw these kinds of curves by using ZWCAD and Excel together. This makes the task efficient and more precise. Here are the steps to carrying this out. 1. First, enter the coordinates into a spreadsheet, such as Excel or LibreOffice. In the figure below, column B contains the x coordinates and column C contains the y coordinates. 2. Next, define column D as “Point (X , Y).” 3. Input the following formula in cell D2:=B2&","&C2 4. Copy the formula to all rows by dragging the cell down the column, as shown by the following picture. When you are done, the x,y coordinates are generated automatically in column D. (Sample) 

5. Now switch over to ZWCAD, and then start Spline command to begin drawing the curve.
6. When the Spline command prompts you, “First point for spline,” copy the x,y coordinate from cell D2 to the last one in the Excel document, and then paste them in the command line in ZWCAD.
Command: spline
First point for spline: 2345,234
Second point: 2789,289
Close/Undo/Fit tolerance/<Next point>: 2900,320
Close/Undo/Fit tolerance/<Next point>: 3320,409
Close/Undo/Fit tolerance/<Next point>: 4637,500
Close/Undo/Fit tolerance/<Next point>: 4873,579
Close/Undo/Fit tolerance/<Next point>: 5032,620
Close/Undo/Fit tolerance/<Next point>: 5107,707
Close/Undo/Fit tolerance/<Next point>: 5453,813
Close/Undo/Fit tolerance/<Next point>: 5500,974
Close/Undo/Fit tolerance/<Next point>:
Select starting tangent point:
Enter tangent for ending point:
7. As you do, the spline will be created automatically, as shown by the figure below.

This method using ZWCAD with Excel makes it easy to quickly create the measured curves with x,y coordinates, but without making mistakes -- no matter how many points you have to input.

http://www.cadfamily.com/HTML/Article/Creating%20Curves%20in%20ZWCAD%20Quickly%20with%20Excel_876.htm

Introductory FLUENT Training-Turbulence Modeling Part B

The k Equation

Turbulence kinetic energy k equation is used to determine the turbulence velocity scale:

where Pk is the rate of production and ε is the dissipation rate.

Production actually refers to the rate at which kinetic energy is transferred from the mean flow to the turbulent fluctuations (remember the energy cascade). Pk is the turbulent stress times mean strain rate, so physically it is the rate of work sustained by the mean flow on turbulent eddies

Obviously Pk needs to be modeled due to the presence of Rij in the term

Direct Numerical Simulation (DNS)

In DNS, the 3D unsteady Navier-Stokes equations are solved numerically by resolving all scales (both in space and in time)

For simple geometries and at modest Reynolds numbers, DNS has been done successfully. For example, for a simple turbulent channel flow between two plates:
Reτ = 800, N = (Reτ)9/4 = 10,000,000 (cells), Δt = 10-5 sec.

DNS is equivalent to a “numerical wind tunnel” for conducting more fundamental turbulence research

For practical engineering purposes, DNS is not only too costly, but also the details of the simulation are usually not required.

Two general engineering approaches to modeling turbulence: Large-Eddy Simulation (LES) and Reynolds Averaging Navier-Stokes (RANS) models

Turbulent Heat Transfer

The Reynolds averaging of the energy equation produces a closure term and we call it the turbulent (or eddy) heat flux:

– Analogous to the closure of Reynolds stress, a turbulent thermal diffusivity is assumed:

– Turbulent diffusivity is obtained from eddy viscosity via a turbulent Prandtl number (modifiable by the users) based on the Reynolds analogy:

Similar treatment is applicable to other turbulent scalar transport equations

The Spalart-Allmaras Turbulence Model

A low-cost RANS model solving an equation for the modified eddy viscosity,

Eddy viscosity is obtained from

The variation ofvery near the wall is easier to resolve than k and ε.

Mainly intended for aerodynamic/turbomachinery applications with mild separation, such as supersonic/transonic flows over airfoils, boundary-layer flows, etc.

RANS Models – Standard k–ε (SKE) Model

Transport equations for k and ε

SKE is the most widely-used engineering turbulence model for industrial applications.

Robust and reasonably accurate; it has many submodels for compressibility, buoyancy, and combustion, etc.

Performs poorly for flows with strong separation, large streamline curvature, and high pressure gradient

RANS Models – k–ω Models

Belongs to the general 2-equation EVM family. Fluent 12 supports the standard k–ω model by Wilcox (1998) and Menter’s SST k–ω model (1994).

k–ω models have gained popularity mainly because:

– Can be integrated to the wall without using any damping functions

– Accurate and robust for a wide range of boundary layer flows with pressure gradient

Most widely adopted in the aerospace and turbo-machinery communities.

Several sub-models/options of k–ω: compressibility effects, transitional flows and shear-flow corrections.

Menter’s SST k–ω Model Background

Many people, including Menter (1994), have noted that:

– The k–ω model has many good attributes and performs much better than k–ε models for boundary layer flows

– Wilcox’ original k–ω model is overly sensitive to the free stream value of ω, while the k–ε model is not prone to such problem

– Most two-equation models, including k–ε models, over-predict turbulent stresses in the wake (velocity-defect) regions, which leads to poor performance in predicting boundary layers under adverse pressure gradient and separated flows

– The basic idea of SST k–ω is to combine SKW in the near-wall region with SKE in the outer region

Menter’s SST k–ω Model Main Components

The SST k–ω model consists of

– Zonal (blended) k–ω / k–ε equations (to address item 1 and 2 in the previous slide)

– Clipping of turbulent viscosity so that turbulent stress stay within what is dictated by the structural similarity constant (Bradshaw, 1967) - addresses the overprediction problem

The resulting blended equations are:

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Turbulence%20Modeling%20Part%20B_865_1.htm

Introductory FLUENT Training-Turbulence Modeling Part A

Introduction to Turbulence Modeling

-Characterization of Turbulent Flows

-From Navier-Stokes Equations to Reynolds-Averaged Navier-Stokes (RANS) Models

-Reynolds Stress Tensor and the Closure Problem

-Turbulence Kinetic Energy (k) Equation

-Eddy Viscosity Models (EVM)

-Reynolds Stress Model

-Near-wall Treatments Options and Mesh Requirement

-Inlet Boundary Conditions

-Summary: Turbulence Modeling Guidelines

-Appendix

Characteristics of Turbulence

-Inherently unsteady, three dimensional and aperiodic swirling motions (fluctuations) resulting in enhancement of mixing, heat transfer and shear.

-Instantaneous fluctuations are random (unpredictable) both in space and in time. But statistical averaging of turbulence fluctuations results in accountable transport mechanisms

-Wide range of length scales (vortices or eddies) exist in all turbulent flows (from very small to very large).

-Very sensitive to (or dependent on) initial conditions.

Turbulent Flow Structures

Is the Flow Turbulent?

Reynolds Number Effects

Backward Facing Step

Plume in Cross Flow

On the left is an instantaneous snap shot of a plume, on the right is a time-lapse picture which smoothes out the detailed structures (vortices) and shows only the averaged, diffused state of the same flow

RANS Equations and the Closure Problem

The time-averaging is defined as

The instantaneous field is defined as the sum of the mean and the fluctuating component, such as

By averaging the Navier-Stokes equations, we obtain the Reynolds averaged Navier-Stokes (RANS) equations:

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Turbulence%20Modeling%20Part%20A_864_1.htm

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Turbulence%20Modeling%20Part%20A_864_2.htm

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Turbulence%20Modeling%20Part%20A_864_3.htm

Introductory FLUENT Training-Boundary Conditions

Defining Boundary Conditions

To define a problem that results in a unique solution, you must specify information on the flow variables at boundaries.

– Specify fluxes of mass, momentum, energy, etc. into the domain.

Defining boundary conditions involves:

– Identifying the boundary locations

– Supplying information at the boundaries

The data required at a boundary depends upon the boundary condition type and the physical models employed.

You must be aware of the information that is required of the boundary condition and locate the boundaries where the information on the flow variables are known or can be reasonably approximated

– Poorly defined boundary conditions can have a significant impact on your solution

Cell Zones – Fluid

A fluid cell zone is a group of cells for which all active equations are solved.

Fluid material selection is required.

– For multiple species or multiphase
flows, the material is not shown.
Instead, the fluid zone consists of the
mixture of the phases.

Optional inputs

– Porous region

– Source terms

– Laminar region

– Fixed Values

– Radiation

Porous Media

A porous zone is a special type of fluid zone.

– Enable Porous Zone option in the Fluid panel.

– Pressure loss in flow determined via user inputs of resistance coefficients to lumped parameter model

Used to model flow through porous media and other uniformly distributed
flow resistances.

– Packed beds

– Filter papers

– Perforated plates

– Flow distributors

– Tube banks

Inputs are directional viscous and inertial resistance coefficients.

Cell Zones – Solid

-A solid zone is a group of cells for which only heat conduction problem solved. Flow equations are not solved.

-Only required input is the material name (defined in the Materials panel).

-Optional inputs allow you to set volumetric heat generation rate (heat source).

-Need to specify rotation axis if rotationally periodic boundaries adjacent to solid zone.

-Can define motion for a solid zone

Locating Boundaries – An Example

Three possible approaches in locating inlet boundaries for this example:

Upstream of manifold

-Can use uniform profile.

-Properly accounts for mixing.

-Non-premixed reaction models

-Requires more cells.

Nozzle inlet plane

-Non-premixed reaction models.

-Requires accurate inlet profile.

-Flow is still non-premixed.

3 Nozzle outlet plane

-Premixed reaction model.

-Requires accurate profile.

-Not generally recommended since inlet BCs may drive the interior solution.

General Guidelines

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Boundary%20Conditions_862_1.htm

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Boundary%20Conditions_862_2.htm

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Boundary%20Conditions_862_3.htm

Introductory FLUENT Training-Solver Settings

Outline

Using the Solver (solution procedure overview)

– Setting Solver Parameters

– Convergence

Definition

Monitoring

Stability

Accelerating Convergence

– Accuracy

Grid Independence

Grid Adaption

– Unsteady Flow Modeling (covered in a later lecture)

Unsteady-flow problem setup

Unsteady flow modeling options

– Summary

– Appendix

Solution Procedure Overview

Solution parameters

– Choosing the solver

– Discretization schemes

Initialization

Convergence

– Monitoring convergence

– Stability

Setting Under-relaxation

Setting Courant number

– Accelerating convergence

Accuracy

– Grid Independence

– Adaption

Available Solvers

There are two kinds of solvers available in FLUENT – Pressure based and Density based.

The pressure-based solvers take momentum and pressure (or pressure correction) as the primary variables.

– Pressure-velocity coupling algorithms are derived by reformatting the continuity equation

Two algorithms are available with the pressure-based solvers:

– Segregated solver – Solves for pressure correction and momentum sequentially.

– Coupled Solver (PBCS) – Solves pressure and momentum simultaneously.

Density-Based Coupled Solver

– Equations for continuity, momentum, energy and species (if required) are solved in vector form.

– Pressure is obtained through an equation of state.

– Additional scalar equations are solved in a segregated fashion.

The DBCS can be run either explicit or implicit.

– Implicit – Uses a point-implicit Gauss-Seidel / symmetric block Gauss-Seidel / ILU method to solve for variables.

– Explicit: uses a multi-step Runge-Kutta explicit time integration method

Choosing a Solver

The pressure-based solver is applicable for a wide range of flow regimes from low speed incompressible flow to high-speed compressible flow.

– Requires less memory (storage).

– Allows flexibility in the solution procedure.

The pressure-based coupled solver (PBCS) is applicable for most single phase flows, and yields superior performance to the standard pressure-based solver.

– Not available for multiphase (Eulerian), periodic mass-flow and NITA cases.

– Requires 1.5–2 times more memory than the segregated solver.

The density-based coupled solver (DBCS) is applicable when there is a strong coupling, or interdependence, between density, energy, momentum, and/or species.

– Examples: High speed compressible flow with combustion, hypersonic flows, shock interactions.

The implicit option is generally preferred over explicit since it has a very strict limit on time step size

The explicit approach is used for cases where the characteristic time scale of the flow is on the same order as the acoustic time scale. (e.g.: propagation of high-Ma shock waves).

Discretization (Interpolation Methods)

Field variables (stored at cell centers) must be interpolated to the faces of the control volumes.

Interpolation schemes for the convection term:

– First-Order Upwind – Easiest to converge, only first-order accurate.

– Power Law – More accurate than first-order for flows when Recell < 5 (typ. low Re flows)

– Second-Order Upwind – Uses larger stencils for 2nd order accuracy, essential with tri/tet mesh or when flow is not aligned with grid; convergence may be slower.

– Monotone Upstream-Centered Schemes for Conservation Laws (MUSCL) – Locally 3rd order convection discretization scheme for unstructured meshes; more accurate in predicting secondary flows, vortices, forces, etc.

– Quadratic Upwind Interpolation (QUICK) – Applies to quad/hex and hybrid meshes, useful for rotating/swirling flows, 3rd-order accurate on uniform mesh.

Interpolation Methods (Gradients)

Gradients of solution variables are required in order to evaluate diffusive fluxes, velocity derivatives, and for higher-order discretization schemes.

The gradients of solution variables at cell centers can be determined using three approaches:

– Green-Gauss Cell-Based – The default method; solution may have false diffusion (smearing of the solution fields).

– Green-Gauss Node-Based – More accurate; minimizes false diffusion; recommended for tri/tet meshes.

– Least-Squares Cell-Based – Recommended for polyhedral meshes; has the same accuracy and properties as Node-based Gradients.

Gradients of solution variables at faces computed using multi-dimensional Taylor series expansion.

Interpolation Methods for Pressure

Interpolation schemes for calculating cell-face pressures when using the segregated solver in FLUENT are available as follows:

– Standard – The default scheme; reduced accuracy for flows exhibiting large surface-normal pressure gradients near boundaries (but should not be used when steep pressure changes are present in the flow – PRESTO! scheme should be used instead.)

– PRESTO! – Use for highly swirling flows, flows involving steep pressure gradients (porous media, fan model, etc.), or in strongly curved domains

– Linear – Use when other options result in convergence difficulties or unphysical behavior

– Second-Order – Use for compressible flows; not to be used with porous media, jump, fans, etc. or VOF/Mixture multiphase models

– Body Force Weighted – Use when body forces are large, e.g., high Ra natural convection or highly swirling flows

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Solver%20Settings_863_1.htm

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Solver%20Settings_863_2.htm

http://www.cadfamily.com/html/Article/Introductory%20FLUENT%20Training-Solver%20Settings_863_3.htm