Lesson 5: Surface Check Tools In this lesson, you will learn to check a surface for its continuity and to repair its discontinuities. You will also learn about particularities of a molded surface and how to design an extractable part using the Generative Shape Design tools. Lesson Contents: Case Study: Checking Surfaces Design Intent Stages in the Process Surface Continuity Check Surface Moldability Check Duration: Approximately 4 Hours 1 Objectives of the lesson: - Explain the continuity problems that can be encountered on surfaces - Explain the tools available to detect them - Show how to correct these defects% 1
Case Study The case study for this lesson is to analyze the geometric connections between the surfaces of a plastic part using different surface analysis tools. Design Intent 1 2 A. Check the surfaces for gaps to ensure easy machinability. Use Connect Checker. B. Check the surface for tangency and curvature continuity. Use the Tangent and Curvature analysis options of Connect Checker. C. Check the draft on the surface for better extraction of the part from the mold. Use Draft Analysis tool to measure the draft angle on the part features. D. Heal the discontinuities between the surfaces. E. Replace the undercut faces by positive draft angle. 6 5 3 4 The objectives of this case study you will practice at the end of the lesson will enable you to manipulate the tools seen in the lesson. Discuss the Design Intent of the case study. Tell the students to perform the case study, you will learn some concepts and tools and use them to perform the case study and other exercises % 2
Stages in the Process 1. Check the surface for surface gaps. 2. Check the surface for tangency discontinuities. 3. Check the surface for curvature discontinuities. 4. Perform the draft analysis. 5. Heal the surface from discontinuity problems. 6. Replace the undercut defective surface by a drafted surface. To be able to perform the case study successfully we will learn some tools of Generative shape design workbench% 3
Step 1: Surface Continuity Check In this section, you will learn how to analyze the surface continuity using the Generative Shape Design tools. Use the following steps: 1. Surface Continuity Check 2. Surface Moldability Check Objectives of the step: - demonstrate the importance of checking surfaces continuity - Show the tools that can do these checks% 4
Why Do We Check Surface Continuity? When surfaces are imported from CATIA V4 or other CAD, the following may occur: Possible loss of geometry during the importation Difference in the tolerance of the CAD When surfaces are involved in a manufacturing process: There may be perturbations in the NC path generation if there are any gaps The use of surfaces that are not continuous in tangency is not possible Surface with discontinuities when down GSD streamed to die \ product design Die\Tool Designs Tool\ Die designed using the bad surface affects the tool dimensions and leads to mismatche. Tool Path Generation Machining \ Manufacturing Component Production The tool follows the irregularities/discontinuities of the surface and leads to undesirable surface finish Due to irregularities of the surfaces the tool may tend to Gouge into the steel. The design and the actual part may not match due to the cumulative affect of the bad surface along the process of development. Surfaces generated in CATIA V5 are likely to be good continuity surfaces (V5 surfaces are based on curves that are supposed to be clean and continuous) So it is mainly important to check the surfaces that are imported from another CAD (V4 for instance): - Difference in the tolerances: as we have seen for the curves, the CAD continuity criteria depends on the tolerance of the CAD (remember the curve topology slide: CAD continuity is different from mathematical continuity A geometry is continuous if the gap size is inferior to the tolerance). So if the tolerances between the CADs are different, something that is continuous in other CADS may not be continuous in V5 if V5 is less tolerant In an integrated CADD and Manufacturing system, the surfaces used to build the design models are processed at different stages of product development. The surfaces are used in prototyping, NC path generation, manufacturing, Quality assurance and finally Production. The continuity of the surface has an impact over all these stages. Lets take an example of a bad surface (having discontinuities) of automotive panel or a molded part surface being processed in manufacturing stream line. Thus, it is very important to check the continuity of the surface in any design. User has to understand the down stream applications of the surface and use proper tools to analyze the surface continuity.% 5
Flaws that can be Detected and Corrected The following table discusses the types of flaws which are commonly detected between surfaces. Fault Category Surface continuity faults Description Gaps between surfaces. Illustration Overlapping surfaces. Tangency and Curvature discontinuities. Irregular surface boundaries Sharp variation in the surface boundaries curvature. Surface Inflections Formation of bump in the surface. In the following slides, we ll see the types of defects that can be detected by CATIA V5. - Continuity faults: 4 types can be detected on surfaces: points, tangency, curvature but also overlapping These defects can be detected using the dedicated tool: connect checker Explain also that the analysis can be done internally to a surface or between surfaces - Boundaries checks: surfaces quick curvature variations can be detected by checking the curvature evolution on the boundaries of the surfaces. The tool to do this is porcupine curvature analysis As we said before: the curvature evolution has a big impact on the aspect of the parts: so porcupine analysis is used to detect visual defaults that most of the time do not induce that the surface is bad: it is simply not nice enough for external shapes - Surfaces inflexions: the same way as porcupine: this analysis is done to detect inflection problems on surfaces% 6
Tools to Detect the Geometric Connection in Surfaces The following analysis tools give you visual information, in the form of color codes, helping you to differentiate good areas from bad areas depending upon the standards set. A. Tool to detect surface connection faults: Connect Checker A B. Tool to detect irregular surface boundaries: Porcupine Analysis B C. Tool to detect surface inflections: Surfacic Curvature Analysis C Tools to Detect the Geometric Connection in Surfaces Performing Porcupine Analysis on Surfaces Let us see the Connect Checker and the porcupine analysis (L5.CATPart/CHECKS) $Show: DEMONSTRATE : show the different modes of check on the surface. Explain the maximum gap concept (using the hole left on the surface) and show how to interpret the result of the quick mode.% explain how to interpret the resulting analysis curvature discontinuities detection = porcupine analysis not continuous. Explain that what s important also is the evolution of the curvature that should not be too brutal. Sometimes it s better to have a little curvature discontinuity better than a continuity but with big curvature variations (use surface Auto to demonstrate this surface taken from the external skin of a car).% 7
Correcting Defects in Surfaces with Healing The Heal tool is used to correct the defects found by performing an analysis between the surfaces. Before Healing After Healing Choice of the threshold values: Distance Objective Gap Not healed Gap Healed Not considered as a gap Correcting Defects in Surfaces with Healing Impact of Healing Operation on Surface Merging distance Gap value Let us see the healing tool (L5.CATPart/HEAL) Among the defaults we have seen just before, the discontinuities are the only ones that can be corrected using a GSD tool: healing tool. So here we ll come back to the connection analysis we have seen before and we ll see how to deduce from this analysis the use of the healing tool Healing is a process by which one surface is deformed at a boundary to form a smooth transition into another surface. It will mathematically deform the shape of surfaces at boundary areas so they smoothly blend into one other. % $Show: Use the demonstration data to show the healing tool% 8
Exercises Overview 5A Start You will practice what you have learned by working through exercises 20 min Exercise 5A-start You can also practice on the demonstration data that are provided Present the exercise Have the students begin the exercise and note the time Assist students as needed with the exercise% 9
Exercise 5A-Start: Recap Check the surfaces for gaps using distance option in surface connection checker. Check the tangency and curvature continuities between two surfaces. Heal the surfaces Review the Exercise Recap slides after the students have attempted the exercises. Try to encourage group discussion on the exercises they have just completed. Discuss the different tools used.% $Ask: Ask if there are any questions about this exercise, any difficulties?% 10
Step 2: Surface Moldability Check In this section, you will learn about the particularities of a molded surface and how to achieve them using the Generative Shape Design Tools. Use the following steps: 1. Surface continuity Check 2. Surface Moldability Check Objectives of the step: - Talk about the molded surfaces - What are the criteria they have to respect - How GSD offers the tools to check that these criteria are respected - If not, how can these surfaces be solved NOTE: GSD is not a workbench dedicated to the creation of molds. So what we re going to see is limited compared to workbenches dedicated to the molds creation. But GSD can help produce surfaces that will be easier to use when the time to create the mold will come% 11
Characteristics of a Molded Part and a Draft Analysis Let us understand the particularities of molding a surface: Pulling Direction Parting plane Generative Shape design workbench provides with the draft analysis tool. Using this draft analysis tool you can check whether or not the part is extractible from the mold at a given angle of the draft. Pulling Direction Draft Angle Draft Angle First we ll see what are the necessary characteristics of a molded part: - Pulling direction: it is the direction in which the mold will go. - Draft angle: at any point of the surface, it is the angle formed between the plane tangent to the surface and the pulling direction. If this angle is inferior to a certain value, then their will be problems when the mold will go away to free the molded part: the plastic material is going to stick to the mold and the material is going to be deteriorated (due to friction) DRAW on a paper board if necessary or show with the hands... - Parting element: the surface that separates the 2 parts of the mold. This is also important because the pulling direction is inverted when you pass this surface element (for instance: upper part of the mold to +Z and lower part of the mold to Z) and so the minimum draft angle we talked about just before is also inverted. In GSD: the draft analysis tool gives the possibility to check that at each point of the surface, this minimum draft angle is respected% 12
How a Draft Analysis is Computed At these points, the angle between the planes tangent to the surface and the mold direction is higher than the specified angle threshold These areas will not be a problem during mold extraction Negative angle Pulling Direction At these points, the angle between the planes tangent to the surface and the mold direction is under the specified angle threshold These areas may be a problem during extraction from the mold The objective of the draft analysis is to detect these areas How a Draft Analysis is Computed Using the Draft Analysis Tool In this slide, we see how this draft analysis is done by CATIA: - You take each point of the surface - You do a line that passes by this point and that is parallel to pulling direction - You measure the angle between this line and the plane tangent to the surface at this point And you know in regards to this angle value if you re in a zone that can be extracted from the mold% 13
Methods to Make the Part Extractable A. By modifying the inputs of existing surface. B. By removing the erroneous area of the part and building a replacing drafted surface. Draft Analysis is updated and shows green color now this portion will be extracted from the mold Apply a draft greater than 5deg here Let us see the draft analysis (L5.CATPart/DERAFT/DRAFT ANALYSIS) Explain that GSD allows the creation of surfaces with an history. And so sometimes you can edit the input of the features or the features themselves to solve the problems. Sometimes, you cannot do this (datum surface for instance) and so you need to replace the erroneous area by a moldable surface. Now we ll see the tools to do this with the next slide % 14
What is a Reflect Line? Inputs required: a pulling direction and an angle value. The reflect line is the curve on the surface corresponding to the points where the draft angle with regard to the pulling direction is equal to the specified angle value. What is a Reflect Line How to Find a Reflect Line? Let us see the draft analysis (L5.CATPart/DERAFT/REFLECT LINE) In the illustration: the specified angle is 5 degrees: all that is in blue has a draft angle inferior to 5 degrees in regards to the pulling direction. On the right: the reflect line that has been computed with 5 degrees as draft angle in regards to the same pulling direction: it corresponds to the blue limit% $Show: DEMONSTRATE the calculation of the reflect line and show that a reflect line is often divided in non connex parts and so that you have the possibility to extract the necessary elements Do the manipulation: - Reflect line + extract + connect + smooth + project + split And stress the fact that it requires a lot of work This is far from being automatic you ll be able to practice it in one of the following exercise with a draft angle = 0 degree to find the parting line% 15
Use of Draft Sweep to make the Part Extractable Replacing erroneous area by drafted swept surface. Use of Draft Sweep to make the Part Extractable Creating Line Sweep - with Draft Direction (2/2) In GSD, we have the possibility to create draft linear surfaces that runs along a curve: the draft sweep useful to create surfaces with respect to a minimum draft angle in regards to a pulling direction. We ll use this to repair the bad area of the surface we ve seen before. But to create a sweep, you need a guide curve. You need also to determine the limit of the bad area (the analysis gives a visualization of this limit but does not concretely create it). So now we ll see what is a reflect line. And after, we ll see how to combine both reflect line and draft sweep.% 16
V5 Surface Design To Sum Up In the following slides you will find a summary of the topics covered in this lesson. 17
Surface Continuity Check We need to perform surface connection analysis when surfaces from CATIA V4 or other CAD packages are imported into CATIA V5. This ensures that good quality surface is provided for further processing. Following are the flaws that can be detected between surfaces: A B Gap A. Surface continuity faults like gaps, overlapping surfaces and tangency and curvature discontinuities. B. Irregular surface boundaries. C. Surface Inflections. C Bump 18
Tools to Detect Geometric Connection Following are the tools to detect geometrical connection faults: A. Connect Checker: It is used to check connections between two or more surfaces. The tool gives a measure of Distance (mm), Tangency (degrees), and Curvature (percentage) between the edges of the surfaces. B. Porcupine Analysis: It is used to detect the imperfections in the boundaries of a surface which cannot be seen with the naked eye. The result is shown in the form of spikes. C. Surfacic Curvature Analysis: It is used to detect curvature changes on a surface or group of surfaces. A B C 19
Correcting Defects in Surfaces The Heal tool is used to correct the defects (gaps, continuity problems) found by performing an analysis between the surfaces. Heal deforms the surface to fill up the gaps and reduces the tangency and the curvature discontinuities. To heal the surfaces, you need to enter healing parameters. These parameters are threshold values and must be deduced from the results of the analysis. Parameters allow you to: Before Healing After Healing A. Define the discontinuities which are important and must be healed: Merging distance and Tangency angle parameter values must be greater than the maximum value you get from the connect checker analysis. B. Define the discontinuities which are not important and must not be healed: The magnitude of distance objective or tangency objective parameters must be set less than the discontinuity that you desire to heal. In other words, discontinuities less than these values are not considered as gap. 20
Surface Moldability Check A certain value of draft angle is provided on the walls of a part to be molded. This is done for easy extraction of the part from the mold. Using the Draft Analysis tool, you can check whether the part is extractible from the mold at the given draft angle. In case of huge parts reflect line helps you to divide a part into two or more smaller parts which can be easily retractable. It helps in determining the parting line of a part. Pulling Direction Draft Angle 21
Main Tools Analysis Toolbar 1 2 3 4 Connect Checker Analysis: Checks connections between two or more surfaces. Feature Draft Analysis: Analyzes the draft direction on selected surfaces. Surfacic Curvature Analysis: Analyzes the Gaussian curvature on shape. Porcupine Curvature Analysis: Detects the imperfections in boundaries of the curve. 1 2 3 4 Wireframe Toolbar 5 5 ReflectLine: Creates a reflect line. Operations Toolbar 6 Healing: Heals the surface. 6 22
Exercises Overview 5A End, 5B and 5C You will practice what you have learnt by working through exercises: Exercise 5Aend Exercise 5B Exercise 5C You can also practice on the demonstration data that is provided. Present the exercise Have the students begin the exercise and note the time Assist students as needed with the exercise 5A: heal and draft management in the same part 5B: simple draft analysis 5C: find the reflect line of a part and split it in 2% 23
Case Study: Surface Check Tools Using the techniques you have learned in this lesson and previous exercises, create the model without detailed instruction. Check the surfaces for the gaps to ensure the easy machinability. Check the surface for tangency and curvature continuity. Check the draft on the surface for better extraction of the part from the mold.. Heal the discontinuities between the surfaces. Replace the undercut faces by positive draft angle. Using the techniques you have learned in this lesson and previous exercises, create the model without detailed instruction. Present the recap exercise. The same manipulations as before are done except that now, you have less instructions They have 30 minutes to do this.% 24
Exercise 5A-End: Recap Check the draft on the part. Review the Exercise Recap slides after the students have attempted the exercises. Try to encourage group discussion on the exercises they have just completed. Discuss the different tools used.% $Ask: Ask if there are any questions about this exercise, any difficulties?% 25
Exercise 5B: Recap Analyze the draft on the part using the draft analysis tool. Review the Exercise Recap slides after the students have attempted the exercises. Try to encourage group discussion on the exercises they have just completed. Discuss the different tools used.% $Ask: Ask if there are any questions about this exercise, any difficulties?% 26
Exercise 5C: Recap Determine the parting line using Reflect line. Review the Exercise Recap slides after the students have attempted the exercises. Try to encourage group discussion on the exercises they have just completed. Discuss the different tools used.% $Ask: Ask if there are any questions about this exercise, any difficulties?% 27
Case Study: Surface Check Tools Recap Check the surfaces for the gaps to ensure easy machinability. Check the surface for tangency and curvature continuity. Check the draft on the surface for better extraction of the part from the mold. Heal the discontinuities between the surfaces. Replace the undercut faces by positive draft angle. Recap what has been seen in the lesson% 28