Basics of CAD, CAM, and CAE

The major topics covered in this chapter are:

• Introduction to CAD
• Introduction to CAM
• Introduction to CAE

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Introduction to CAD

In earlier days of Mechanical industry, designer engineers had to draw every mechanical component on paper or cloth using drafter and geometry tools like pencils, markers, scale, erasers, and so on. But the age of manually drawing is gone and now a days, we use CAD (Computer Aided Design) software to create engineering drawings. There is a long list of CAD software available in market like Autodesk Inventor, SolidWorks, Creo Parametric, and so on. Broadly there are two ways in which CAD software perform 3D modeling:

• Parametric Modeling
• Direct Modeling

Parametric Modeling V/S Direct Modeling

In Parametric Modeling, the model is create based on parameters. All the parameters that you specify while creating the model are recorded and can be changed any point of time while working on the model. Like, if you are creating a box in parametric modeling then its length, width, and height will be recorded with model and can be changed anytime. AutoCAD, Autodesk Inventor, SolidWorks, Creo Parametric are name of some of the software capable of performing Parametric modeling.

In Direct Modeling, the model is created by direct approach rather than specifying parameters for model. To create a model with direct modeling approach, you place primitive shapes and them drag-drop the key points to change the shape of model. Although Direct Modeling is a nice approach to create models for animators but for Mechanical Engineers, Parametric modeling is an important requirement.

 

2D Drawing

2D Drawings are used to represent 3D objects on paper for manufacturing. 2D drawings are still the requirement of manufacturers for manufacturing any engineering product. There are various symbols and standards established to created 2D drawing for engineers. These drawings can be furthers divided into different categories based on their application areas like mechanical drawing, electrical drawing, electronic drawing, civil drawing and so on. Our concern for this book is mechanical drawings. For representing objects in mechanical 2D drawings, we use two type of projects of objects on paper: First Angle Projection and Third Angle Projects.

Drafting Standards

Drafting Standards are the collection of rules defined for creating 2D drawings. In CAD software 2D drawings, following parameters are controlled by Drafting Standards:

• Mechanical object behavior.
• What layers Mechanical Objects are created on.
• The properties of these layers.
• Text heights and colors.
• Projection settings for use with Power View.
• Dimension styles.
• Hole chart settings and formats.
• Centerline format.
• Section line format.
• Thread line format.
• Note text and leader formats.
• Symbology formats.
• Bill of Materials (BOM), parts list and balloon formats.

There are various standards followed by different countries for drafting like, ANSI, BSI, CSN, DIN, GB, ISO JIS, GOST, and so on. ANSI drafting standard was developed by American National Standards Institute. This drafting standard is widely used by American manufacturers. ISO drafting standard was developed by International Organization for Standardization. ANSI and ISO are two most popular standards for drafting engineering drawing. Following are some of the major differences between the two standards:

• ANSI dimensions are read horizontally. ISO dimensions are parallel to the dimension line.
• ANSI dimensions are centered on the dimension line. ISO dimension are placed above the dimension line.
• ANSI tends to use abbreviations. ISO uses symbols. (example: RAD, DIAM, 3 PLACES versus R, Ø, 3X)
• Dimensions have a different syntax. ANSI: 1.000 DIAM 3 PLACES and ISO: 3X Ø 1.000

3D Modeling

The time when first CAD software was developed, manufacturers were using geometry tools like pencil, scale, drafter, and so on to create drawings. Since that time the CAD software have developed a lot and so has the requirement of manufacturers. Now, 3D replication of object is created in the computer using various 3D Modeling tools and later the model is used to generate different views with annotations, perform analysis, or generate programs for CNC machines. There is a very long list of CAD software available in market.

Following are some of the functions that can be performed using Latest CAD software:

• 3D Modeling
• Drafting (2D Drawing Creation and generation
• Assembly (Top-Down Approach and Bottom-Up Approach)
• 3D Printing
• Computer Aided Manufacturing (CAM)
• Computer Aided Engineering (CAE)

You will learn about various aspects of CAD software later in this book. Now, we will discuss the role of CAD Engineer in mechanical industry.

Role of CAD Engineer in Industry

Following are some of the roles and responsibilities of a CAD engineer:

• Configure, deploy, maintain, and upgrade CAD models as per the client requirement.
• Design, develop and engineer high quality models using 3D and 2D CAD tools for manufacturing and analysis.
• Produce designs that meet targets for feasibility, performance, costs, quality, safety, legislation and timing.
• Ensure that all work carried out is in compliance with company design, safety, quality, environmental compliance and procedural standards.
• Interact with architect and client, as necessary to obtain critical design information necessary to complete project within intended time frame.
• Update and maintain product design files.
• Assist in improving daily processes to ensure that the CAD systems meet customer requirements.
• Train and guide Production Engineers on engineered design.
• Determine limitations, assumptions and solutions in the design and development of CAD models.
• Assist in implementation of CAD engineering applications.
• Determine design specifications and parameters for CAD models.

Documents Prepared by CAD Engineers in Automobile Industry

A CAD Engineer is involved in designing of new parts and very soon gets involved in Design Engineer’s work. There are various documents that are prepared by CAD/Design Engineers in mechanical industries for development of new parts and processes. Automotive Industry Action Group (AIAG) has developed a standard packages of documentation for Automotive industries world-wide called PPAP. Production Part Approval Process (PPAP) is used in automotive industry supply chains to establish confidence between supplier. Various documents that are prepared in PPAP package are given next.

Design Records

Design records means printed copy of engineering drawings of components to be manufactured. If the customer is responsible for designing, this is a copy of customer drawing that is sent together with the Purchase Order (PO). If supplier is responsible for designing then these drawings are released in supplier’s release system. “Each and every feature must be “ballooned” or “road mapped” to correspond with the inspection results (including print notes, standard tolerance notes and specifications, and anything else relevant to the design of the part).”

Authorized Engineering Change (note) Documents

The Authorized Engineering Change Documents (notes) are used to convey changes in original design. The detailed description of changes is noted in this document. Usually this document is called “Engineering Change Notice”, but it may be covered by the customer PO or any other engineering authorization.

Engineering Approval

This approval is usually the Engineering trial with production parts performed at the customer plant. A “temporary deviation” usually is required to send parts to customer before PPAP. Customer may require other “Engineering Approvals”.

DFMEA

A copy of the Design Failure Mode and Effect Analysis (DFMEA) is reviewed and signed-off by supplier and customer. If customers are design responsible then customers may not share this document with the supplier. However, the list of all critical or high impact product characteristics should be shared with the supplier, so they can be addressed on the PFMEA and Control Plan.

Process Flow Diagram

A copy of the Process Flow, indicating all steps and sequence in the manufacturing process including incoming components.

PFMEA

A copy of the Process Failure Mode and Effect Analysis (PFMEA), reviewed and signed-off by supplier and customer. The PFMEA follows the Process Flow steps, and indicates “what could go wrong” during the manufacturing of each component.

Control Plan

A copy of the Control Plan, reviewed and signed-off by supplier and customer. The Control Plan follows the PFMEA steps, and provides more details on how the “potential issues” are checked in the incoming quality, assembly process or during inspections of finished products.

Measurement System Analysis Studies (MSA)

MSA usually contains lists of Gauges and other measuring instruments required to measure critical or high impact characteristics, and a confirmation that gauges used to measure these characteristics are calibrated.

Dimensional Results

A list of every dimension noted on the ballooned drawing. This list shows the product characteristic, specification, the measurement results and the assessment showing if this dimension is “OK” or “not OK”. Usually a minimum of 6 pieces are reported per product/process combination.

Records of Material / Performance Tests

A summary of every test performed on the part. This summary is usually on a form of DVP&R (Design Verification Plan and Report), which lists each individual test, when it was performed, the specification, results and the assessment pass/fail. If there is an Engineering Specification, usually it is noted on the print. The DVP&R shall be reviewed and signed off by both customer and supplier engineering groups. The quality engineer will look for a customer signature on this document. In addition, this section lists all material certifications (steel, plastics, plating, etc.), as specified on the print. The material certification shall show compliance to the specific call on the print.

Initial Sample Inspection Report

The report for material samples which is initially inspected before prototype made.

Initial Process Studies

Usually this section shows all Statistical Process Control charts affecting the most critical characteristics. The intent is to demonstrate that critical processes have stable variability and that is running near the intended nominal value.

Qualified Laboratory Documentation

Copy of all laboratory certifications (e.g. A2LA, TS, NABL) of the laboratories that performed the tests reported in this section.

Appearance Approval Report

A copy of the AAI (Appearance Approval Inspection) form signed by the customer. Applicable for components affecting appearance only.

Sample Production Parts

A sample from the same lot of initial production run. The PPAP package usually shows a picture of the sample and where it is kept (customer or supplier).

Master Sample

A sample signed off by customer and supplier, that usually is used to train operators on subjective inspections such as visual or for noise.

Checking Aids

When there are special tools for checking parts, this section shows a picture of the tool and calibration records, including dimensional report of the tool.

Customer-Specific Requirements

Each customer may have specific requirements to be included on the PPAP package. It is a good practice to ask the customer for PPAP expectations before even quoting for a job. North America auto makers OEM (Original Equipment Manufacturer) requirements are listed on the IATF website.

Part Submission Warrant (PSW)

This is the form that summarizes the whole PPAP package. This form shows the reason for submission (design change, annual revalidation, etc.) and the level of documents submitted to the customer. There is a section that asks for “results meeting all drawing and specification requirements: yes/no” refers to the whole package. If there is any deviations the supplier should note on the warrant or inform that PPAP cannot be submitted.

Augmented Reality and Virtual Reality

Augmented Reality

Augmented Reality is a way to project information on different displays. Augmented Reality has vast application area from social media and entertainment industry to surgical procedures in hospitals; refer to Figure-8. The game Pokemon Go is an example of AR.

Augmented Reality also finds applications in CAD. Although for mechanical engineers it has applicable than civil engineers. Civil engineers can project the image of a whole building designed in computer to the customers while there is no building at all. This way they can collect funding for a building project.

Mechanical Engineers can show their final CAD design of a product to their customer without even starting a manufacturing step; refer to Figure-9. If customer approves the design then they can start manufacturing.

Virtual Reality

Virtual Reality is a computer simulated environment to show different types of objects and project real experience through our sensory system. Virtual Reality shuts you from real world and keeps you inside a computer simulated environment. VR is very common with smart phones these days. For CAD engineer, VR can be a life saver sometimes. Using Virtual Reality, you can assemble different components of a large machine virtually and then find any shortcoming based on the experience.

Introduction to CAM

The story of CAM starts with CNC machines. CNC represent Computer Numeric Control. CNC machines used numeric codes generated by CAM software to perform various operations. A CAM software takes the input from user and based on specified parameters, it generates CNC programs with G-codes and M-codes. There are various software available for CAM like MasterCAM, BobCAM, EdgeCAM and so on. These software are specialized for CAM. Now a days, most of the CAD software also come with CAM modules like SolidWorks, Creo Parametric, and so on. The NC codes generated by these CAM software depend the controller hardware installed on your machine. There are various controllers available in the market like Fanuc controller, Siemens controller, Heidenhain controller, and so on. The numeric codes change according to the controller used in the machine. These numeric codes are compiled in the form of a program, which is fed in the machine controller via a storage media. The numeric codes are generally in the form of G-codes and M-codes. For understanding purpose, some of the G-codes and M-codes are discussed next with their functions for a Fanuc controller.

Code Function

G00 – Rapid movement of tool.

G01 – Linear movement while creating cut.

G02 – Clockwise circular cut.

G03 – Counter-clockwise circular cut.

G20 – Starts inch mode.

G21 – Starts mm mode.

G96 – Provides constant surface speed.

G97 – Constant RPM.

G98 – Feed per minute

G99 – Feed per revolution

M00 – Program stop

M02 – End of program

M03 – Spindle rotation Clockwise.

M04 – Spindle rotation Counter Clockwise.

M05 – Spindle stop

M08 – Coolant on

M09 – Coolant off

M98 – Subprogram call

M99 – Subprogram exit

Once you have created an NC program in CAM software, you can simulate the cutting operations in software to check the toolpaths; refer to Figure-10.

Role of CAM Engineer

A CAM engineer works closely with CAD engineer and in most of the small industries, CAD engineer and CAM engineer is the same person. Various tasks that a CAM engineer perform in industry are given next.

• Modifying model as per the customer requirement.
• Deciding machining strategy and tools required for machining the part.
• Creating CNC programs depending on NC controller for the machine.

Introduction to CAE

CAE means Computer Aided Engineering. Software like Ansys, Cosmol, SolidWorks Simulation, and so on are dedicated to perform different types of analyses. The types of analyses that can be performed using CAE software are given next.

• Structural Analysis
• Thermal Analysis
• Computational Flow Analysis
• Mold Flow Analysis
• Electronic Circuit Analysis
• Topology Optimization and many others.

Static Analysis

This is the most common type of analysis we perform. In this analysis, loads are applied to a body due to which the body deforms and the effects of the loads are transmitted throughout the body. To absorb the effect of loads, the body generates internal forces and reactions at the supports to balance the applied external loads. These internal forces and reactions cause stress and strain in the body. Static analysis refers to the calculation of displacements, strains, and stresses under the effect of external loads, based on some assumptions. The assumptions are as follows.

• All loads are applied slowly and gradually until they reach their full magnitudes. After reaching their full magnitudes, load will remain constant (i.e. load will not vary against time).
• Linearity assumption: The relationship between loads and resulting responses is linear. For example, if you double the magnitude of loads, the response of the model (displacements, strains and stresses) will also double. You can make linearity assumption if:

1.All materials in the model comply with Hooke’s Law that is stress is directly proportional to strain.

2.The induced displacements are small enough to ignore the change is stiffness caused by loading.

3.Boundary conditions do not vary during the application of loads. Loads must be constant in magnitude, direction, and distribution. They should not change while the model is deforming.

If the above assumptions are valid for your analysis, then you can perform Linear Static Analysis. For example, a cantilever beam fixed at one end and force applied on other end; refer to Figure-1.

If the above assumptions are not valid, then you need to perform the Non-Linear Static analysis. For example, force applied on an object attached with a spring; refer to Figure-3.

Modal Analysis (Vibration Analysis)

By its very nature, vibration involves repetitive motion. Each occurrence of a complete motion sequence is called a “cycle.” Frequency is defined as so many cycles in a given time period. “Cycles per seconds” or “Hertz”. Individual parts have what engineers call “natural” frequencies. For example, a violin string at a certain tension will vibrate only at a set number of frequencies, that’s why you can produce specific musical tones. There is a base frequency in which the entire string is going back and forth in a simple bow shape.

Harmonics and overtones occur because individual sections of the string can vibrate independently within the larger vibration. These various shapes are called “modes”. The base frequency is said to vibrate in the first mode, and so on up the ladder. Each mode shape will have an associated frequency. Higher mode shapes have higher frequencies. The most disastrous kinds of consequences occur when a power-driven device such as a motor, produces a frequency at which an attached structure naturally vibrates. This event is called “resonance.” If sufficient power is applied, the attached structure will be destroyed. Note that armies, which normally marched “in step,” were taken out of step when crossing bridges. Should the beat of the marching feet align with a natural frequency of the bridge, it could fall down. Engineers must design in such a way that resonance does not occur during regular operation of machines. This is a major purpose of Modal Analysis. Ideally, the first mode has a frequency higher than any potential driving frequency. Frequently, resonance cannot be avoided, especially for short periods of time. For example, when a motor comes up to speed it produces a variety of frequencies. So, it may pass through a resonant frequency.

Thermal analysis

There are three mechanisms of heat transfer. These mechanisms are Conduction, Convection, and Radiation. Thermal analysis calculates the temperature distribution in a body due to some or all of these mechanisms. In all three mechanisms, heat flows from a higher-temperature medium to a lower temperature one. Heat transfer by conduction and convection requires the presence of an intervening medium while heat transfer by radiation does not.

There are two modes of heat transfer analysis.

Steady State Thermal Analysis

In this type of analysis, we are only interested in the thermal conditions of the body when it reaches thermal equilibrium, but we are not interested in the time it takes to reach this status. The temperature of each point in the model will remain unchanged until a change occurs in the system. At equilibrium, the thermal energy entering the system is equal to the thermal energy leaving it. Generally, the only material property that is needed for steady state analysis is the thermal conductivity.

Transient Thermal Analysis

In this type of analysis, we are interested in knowing the thermal status of the model at different instances of time. A thermos designer, for example, knows that the temperature of the fluid inside will eventually be equal to the room temperature(steady state), but designer is interested in finding out the temperature of the fluid as a function of time. In addition to the thermal conductivity, we also need to specify density, specific heat, initial temperature profile, and the period of time for which solutions are desired.

Thermal Stress Analysis

The Thermal Stress Analysis is performed to check the stresses induced in part when thermal and structural loads act on the part simultaneously. Thermal Stress Analysis is important in cases where material expands or contracts due to heating or cooling of the part to certain temperature in irregular way. One example where thermal stress analysis finds its importance is two material bonded strip working in a high temperature environment.

Event Simulation

The Event Simulation analysis is used to study the effect of object velocity, initial velocity, acceleration, time dependent loads, and constraints in the design. The results of this analysis include displacements, stresses, strains, and other measurements throughout a specified time period. You can perform this analysis when you need to check the effect of throwing a phone from some height or similar cases where motion is involved.

Shape Optimization

The Shape Optimization is not an analysis but a study to find the shape of part which utilizes minimum material but sustains the applied load up to required factor of safety.

There are various equations and parameters involved in analysis by CAE software and results are displayed in the form of tables & graphical representations.

Role of CAE Engineer

The CAE engineer performs many tasks related to analyses like checking and deciding material of product, defining real-world scenario for the analysis in software, preparing mesh model of product for analysis, running different types of analyses, and analyzing the results.

 

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