Can new CAD tools improve
geometric modelling of tyre
tread?
Student
Ricardo Felipe Vargas De la Hoz MSc. Design & Engineering
10555456-872095
Supervisor
Professor Giorgio Colombo Mechanical Engineering Department
Co-Supervisor
Alessio Casali
Mechanical Engineering Department
A.A. 2017/2018
ABSTRACT ENGLISH
It is estimated that around half of the time required to develop a tyre mould is used in the tyre tread modelling process. [1] Therefore, it has become important for companies to find new ways to elaborate and model them in such a way that the process speeds up and the outcome turns out to be more accurate. In this thesis three modern CAD tools (ANSYS Spaceclaim, Solidthinking Evolve and Onshape) are evaluated regarding its capabilities and limitations for the tyre tread modelling. To do this, different modelling techniques are studied and used on each software. The outcomes are compared with the outcome of a traditional CAD tool (Siemens NX) to understand if with the new software it is possible to precisely obtain all the tread geometries and how easy (or complex) is to do so. Then, this study continuous by evaluating the usefulness of these tools for a tyre a company. The features with which to compare the selected CAD software are: the ease of learning, the implementation cost and the availability of relevant modelling features for the tyre tread design (like curves projection, surface creation and boolean operation). Additionally, the integration possibilities between the analysed CAD modelling software and finite element simulation (FEA) tools, CAM software and render engines are investigated, since this tools are useful for the tyre tread development and production process. Thanks to all this process, it can be concluded that the developed procedures for each of the software offer results similar to those obtainable with traditional CAD tools, besides they are more user-friendly and affordable. However, proposed solutions have some limitations, mainly related to the lack of parameterization, which leads to a longer modelling process and this makes the use of these solutions less appealing in big tyre companies.
ABSTRACT ITALIAN
Si stima che più della metà del tempo gestito per lo sviluppo di uno pneumatico, è impiegato nella modellazione del battistrada. [1] Quindi per le aziende diventa sempre più importante trovare nuovi metodi per il loro sviluppo e la creazione, al fine di ridurre i tempi di modellazione ed avere risultati migliori. In questa tesi vengono valutati tre strumenti di modellazione CAD moderni (ANSYS Spaceclaim, Solidthinking Evolve e Onshape), analizzando le rispettive capacità e limiti nella modellazione del battistrada. Per fare ciò, vengono studiate diverse tecniche di modellazione su ciascun software. I risultati vengono comparati con il risultato di un software CAD tradizionale (Siemens NX), per capire se con i nuovi software è possibile ottenere con precisione tutte le geometrie del battistrada e quanto sia facile (o complesso) farlo. Questo studio continua valutando l’utilità di questi strumenti per le aziende produttrici di pneumatici. Le caratteristiche con cui comparare i software CAD scelti sono: la facilità di apprendimento, i costi di implementazione e la disponibilità di operazioni di modellazione utili per il disegno del battistrada (come proiezione di curve, creazione di superficie e operazioni booleana). In oltre vengono investigate le possibilità di integrazione tra i software selezionati e strumenti per la simulazione ad elementi finiti (FEA), piattaforme CAM e software per il render 3D, utili per il ciclo produttivo del prodotto. Grazie a questo percorso si può concludere che le procedure elaborate per ciascuno dei software offrono risultati assimilabili a quelli ottenibili con strumenti tradizionali. In aggiunta includono costi più bassi e sono di facile utilizzo. Tuttavia, le soluzioni proposte hanno alcune limitazioni, principalmente legate alla mancanza di parametrizzazione, che comporta tempi elevati e non le rende appetibili per l’utilizzo nelle grandi aziende.
I will like to thank the following people who have supported me, not only during the course of this thesis, but throughout my Masters degree.
Firstly, I would like to express my gratitude to my supervisor Giorgio Colombo and my co-supervisor Alessio Casali, for their unwavering support, guidance and insight throughout this project.
I would also like to thank my family and friends in Milan who encouraged and supported me during the whole Masters degree and specially during the period that I did this thesis. I am immensely grateful to all of you.
Finally, I would like to thank God for the opportunity to do this master course and to lives all the experiences that will make me a good engineer and designer.
CONTENTS
INTRODUCTION 1.1 Tyre Tread Introduction 1.2 Main Objective 1.3 Specific Objectives
DESIGN OF TYRES 2.1 Tyre General Overview: Functions and Components 2.2 Tyre Design Process 2.3 Tread Design = Core of Tyre Design Process
CAD TOOLS 3.1 History-Based or Parametric CAD Tools 3.2 History-Free or Direct CAD Tools 3.3 Pros and Cons: Direct / Parametric CAD Modelling 3.4 CAD after modelling… 3.5 CAD/FEA Integration 3.6 CAD/CAM Integration 3.7 CAD/Render Integration
MODELLING PROCESS ANALYSIS
SIEMENS NX MODELLING PROCESS 4.1 Software Overview 4.2 Modelling Process
ANSYS SPACECLAIM MODELLING PROCESS 5.1 Software Overview 5.2 Modelling Process
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08 12 13 28 15 29 16 30 09 11 11 20 21 22 23 24 24 25 40 25 41 42SOLIDTHINKING EVOLVE MODELLING PROCESS 6.1 Software Overview 6.2 Modelling Process
ONSHAPE MODELLING PROCESS 7.1 Software Overview
7.2 Modelling Process
COMPARISON BETWEEN NEW CAD TOOLS AND NX 8.1 Implementation 8.2 Learning Process 8.3 Modelling Process 8.4 CAD/FEA Integration 8.5 CAD/CAM Integration 8.6 CAD/RENDERER Integration CONCLUSIONS RECOMMENDATIONS LIST OF FIGURES LIST OF TABLES LIST OF REFERENCES
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52 78 64 65 66 97 100 53 79 81 91 102 54 80 88 94 106 107As vehicles become more available in the developing countries thanks to higher incomes and the commuting distances rise all around the world fuelled by expanding economic activities (Figure 1), the demand for tyres grows by big steps (4,1% annually) and is projected to reach the 3 billion units on 2019. [4] This growth on the demand is accompanied by a growth on tyre manufacturing companies (competitors) and on user requirements. That is why the leading companies on the tyre market must continuously develop more and more advanced and appealing tyres. Nowadays, the design of the tyre have turned out to be a very important factor while developing a tyre. This is especially true for the tyre tread (Figure 2), the part that is in contact with the ground.
The design of this element influences the performance of the tyre in several aspects, like the noise, the comfort (vibrations) and the car efficiency (wear and power transmission). Its design (Figure 3) also allows to communicate the character of the tyre to the user, thus making the product more appealing. But it has many complexities too, since most of its shapes are free-form geometries that are not easy to parameterize. This last aspect is especially tricky when creating the mould to produce the tyre, as very complex manufacturing tools are required to obtain a good result. With the availability of 3D metal printing some of the limitations disappear, but the design of the tread still be a very time-consuming task. [5] It is estimated that around half to two thirds of the time required to develop a tyre mould is used in the CAD modelling process. [1] Hence, it has become relevant for companies to find new ways to develop and model tyres tread, so that the process speeds up and the outcome gets more accurate.
1.1 Tyre Tread Introduction
Figure 1. Demand of tyres is driven by increased car use [2] Figure 2. Tyre tread [3]
In this scenario the use of non-traditional CAD modelling tools (Figure 4) has inclined to be more interesting, because these tools provide a different approach for creating and interacting with the 3D models. Most of them are based on the concept of direct CAD modelling (Figure 5), where the user can directly change the geometry without paying too much attention to the feature tree. Nevertheless, other most advance software combine the above mentioned approach with the parametric one to obtain more powerful results. Likewise there are available tools that combine the surface modelling approach with a more solid-oriented type. All these new CAD modelling mechanisms will change the way a tyre treads and its moulds (Figure 6) are designed and modelled. In this thesis three different and brand-new modelling processes to generate tyre treads will be developed using non-traditional CAD modelling software and they will be validated by comparing them with the currently used by a tyre manufacturer. Above comparisons have been made to understand if all these processes will make sense in an industrial environment and if the results will have a similar quality than the ones obtained nowadays with the traditional software.
Figure 4. 3D CAD Modeling in AR [7]
In order to reach the objective several steps will be follow. First, the features of the three modern software will be tested and an efficient modelling process to produce a complete tyre tread on each CAD tool will be developed. Then, based on these procedures and their outcomes the capabilities of each new software will be compared and contrasted with the ones in the traditional CAD tool (NX). In this way the opportunities and limitations of each CAD software will be found. Additionally, a validation process will be done to understand if the different software are suited for an industrial use. This method will include important characteristics like: Implementation cost, ease of learning, modelling time and integration with other tools related with the product development process (FEM, CAM, Render). Finally, the results will be discussed and some conclusion will be drawn. Evaluate the capabilities and limitations of new CAD tools (ANSYS Spaceclaim, Solidthinking Evolve, Onshape) while modelling tyre treads and compare them with the ones found on a traditional CAD software (Siemens NX) in order to find particular features that can give the opportunity to reduce/simplify (or not) the modelling operations/times.
1. Develop a reasonable design process to model a complete and relevant tyre tread on each new CAD modelling software. This tyre tread should include all the complexities and features that a tyre tread can have.
2. Evaluate the modelling tools capabilities on each software and the possible opportunities or limitations that they can bring to the tyre tread design and modelling process.
3. Validate the usefulness of these CAD software on an industrial environment based on different criteria like ease to learn, usability and time required to model a tyre tread.
4. Evaluate the integration capabilities of the different software with other important tools used on the tyre developing process, like simulations (CAD/FEA), manufacturing tools (CAD/CAM) and renders (CAD/ Renderer).
1.2 Main Objective
“Tyres… round, black and expensive! That is the impression of most consumers who often consider them a low-tech commodity and make purchasing decisions based solely on price.” [11] Those with the opportunity to know more about tyre design and production are surprised to learn the great number of components of a tyre and the massive amount of machinery required to manufacture them. Tyres (Figure 7) are a highly engineered product that does not look as advance as it is. Therefore, big tyre manufacturers like Bridgestone, Pirelli and Michelin are putting big efforts into the design of the tyre. The above because it improves the performance of the tyre, but also because it communicates to the user the quality of their tyres, that usually are more expensive than other tyres with less technology. In the following lines the whole design process and their related vocabulary will be explained.
2.1 Tyre General Overview: Functions and
Components
First, let’s begin with an overview of the main function of tyres and its components. In this thesis the concept of tyre focus on a specific type of tyre, the radial passenger tyre, which is the one used in passenger and private vehicles. The tyre in these vehicles has three main functions [11]:
- Vehicle to road interface: Provide the interface between the vehicle and the highway. (Figure 8)
- Road surface friction: The ability of vehicle to start, stop and turn corners results from friction between the highway (Figure 9) and the tyres. The tyre treads designs/patterns are required to deal with the complex effects of weather conditions: dry, wet, snow-covered and icy surfaces. Tire tread designs enable water to escape from the tire-road contact area to minimize hydroplaning.
- Absorbs road irregularities: Tyres act as a spring and damper system to absorb impacts and road surface irregularities under a wide variety of operating conditions.
Bead bundles: Serve to anchor the inflated tyre to the wheel rim.
Body plies: Provide the strength to contain the air pressure and improve the sidewall impact resistance. Bead filler: It is a component use to fill the void between the inner body plies and the turned-up body ply ends on the outside. It influences the tire ride and handling characteristics.
Innerliner : Improve air retention by lowering permeation outwards through the tyre.
Steel safety belts: These are usually used to restrict expansion from centrifugal forces during high speed operation.
Nylon safety belts: These are used to restrict expansion from centrifugal forces during high speed. Subtread: This component is used to improve rolling resitance and thus improve the fuel economy. Tread: The tread must provide the necessary grip or traction for driving, braking and cornering, and the tread compound is specially formulated to provided a balance between wear, traction, handling and rolling resistance. The pattern molded into the tread is designed to provide uniform wear, to channel water out of the frootprint, and to minimize pattern noise on a variety of road surfaces. This component must also meet customer expectations for acceptable wear resistance, low noise, and good ride quality.
Sidewall: Serves to protect the body plies from abrasion, impact and flex fatigue. They are also used
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Figure 10. Tyre Components [14]
2.2 Tyre Design Process
After understanding the tyre and its function. Now it is important to understand the tyre design process (Figure 11). It begins by identifying the goals or requirements that a certain tyre must meet. Each of the requirements is set by a different entity. The sales department sets some performance targets based on consumer needs and material costs. The production department sets some processing requirements and restrictions based on the available machinery. The government sets some additional requirements based on the national/international safety standards.
Then the design process begins by designing the tread pattern based on the previous set goals and requirements. This is one of the most important parts of the process, because it affects different performance variables like the noise, the behaviour in wet/dry road, the traction, the comfort inside the vehicle and the customer perception of product performance (aesthetically).
Later the design of the mould begins by defining mould contour features. Some of the variables related with the mould like the tread, centre and shoulder radii and skid depth affect tyre performance. They influence vehicle ride and handling, tyre wear and traction.
After these two parts are designed, begins the design of the construction elements like the body ply or the belts that depend on the tread size and shape. All the construction elements are important in the performance of the tyre. For example, the number of body plies affect the strength of the tyre.
Subsequently, the materials or the compound of materials for each component are selected based on the requirements for each component and having always in mind the manufacturing process that will overcome each part. When selecting the material is also considered the durability that a certain material can provide to the tyre.
Finally, when all these steps are done the tyre is tested with finite elements analysis (FEA) and its expected performance is confirmed or not. Later experimental tyres are manufactured using CAM tools, and several tests are done to guarantee the high performance of the tyre in the weather conditions that it was designed for.
TYRE DESIGN PROCESS
Identify Goals/Requirements
Performance Targets ManufacturingRequirements/ Processing Restrictions Interchangeability Standards,T&RA, JATMA; ETRTO National/International Standars
Select Design Features
TREAD PATTERN CONSTRUCTION MATERIALS MOLD CONTOUR
No. Ribs, Groove Spacing, Void, Shoulder Slots, No. Pitches, Sipes, Element Orientation, Noise Treatment
Body Ply Denier, Body Ply EPD, Body Ply Tie-in, Bead Filler Shape Steelcorrd Type, Belt Reinforcement Tread Compound, Subtread Compound, Bead Filler Compound, Sidedwall Compound
Skid Depth, Section Width, Tread Arc Width, Shoulder Radius, Footprint Ratio
Design Features Selected
Confirm Expected Performance Computer Modeling (FEA)
Experimental Mould Manufactured (CAM)
2.3 Tread Design = Core of Tyre Design Process
As could be seen in the previous section, the core of the design process is the tread design because it highly affects the performance of the tyre and its complexity drives the requirements in the manufacturing process. So, that’s why the focus of this thesis will be in the tyre tread design. But first let’s understand which the components (Figure 12) of the tyre tread are and what is their influence on the tyre performance.
Tread Components
Some of the tread components are [16]:
Similarly, the relationship between these void areas and the lug area influences the overall contact patch of a tyre. A larger number of voids, for instance, can diminish a tyre’s grip on dry surfaces, yet offers better performance on wet surfaces. As a result, the number of voids depends on the tyre’s purpose, as specific wet or ‘rain tyres’ may feature more tread voids.
Sipes: These are the narrow voids and passageways on the tyre lugs, usually around 0.3 - 1.5 mm thing. Their main purpose is to improve the tyre’s traction on wet surfaces, as well as snow, channelling water away from underneath the tyre. This helps build resistance to aquaplaning. Tread rib: Also, occasionally known as transverse voids, these are circumferential ribs or contact bars that run around the tyre tread.
Tread groove: These are depressed parts of the tread, like sipes but often much longer and deeper. These grooves form a specific pattern, with shapes and sizes calculated to improve a tyre’s quality in key areas. Generally, these features serve to improve the tyre’s braking effectiveness and steerability. The depth of the grooves, as well as their pattern, can also prove decisive in the rolling noise level.
Tread Channels: These voids create the space required to channel water from underneath the tyre when driving on wet surfaces. This maintains good traction, since the water is channelled through the wider voids along the axis
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Tread Components Influence on Tyre Performance
Each of these features affects the performance of the tyre. [11] The number of ribs and the groove spacing influences the way water is eliminated. The size, volume and orientation of the grooves affect the traction and handling. The number of pitches and the pitch sequence have a big influence on the noise, traction, wear, and the tendency to wear non-uniformly. For example, the use of a sequence of different pitches is mandatory to limit tone generation as the tire rotates. The sipes affect the traction and the behaviour of the tire in different environment, specially wet ones. Additionally, the design of the tread has big influence on customer’s perception of product performance, because it communicates the character of the product and its intended use.
Types of Treads
The treads are classified in different types depending on the orientation and size of the tread elements (sipes, grooves, etc.). [16] The following are the most common types of treads:
RIB PATTERN
It is characterized by parallel S-shaped voids along the axis (Figure 13).
LUG SHAPE
This pattern refers to a series of grooves perpendicular to the tyre’s circumference (Figure 14).
Advantages:
• Good steering control (thanks to lateral resistance) • Lower rolling resistance • Suitable for sustaining high speeds (thanks to low heat generation)
• Good directional stability
Disadvantages:
• Poor grip when
accelerating or braking on wet roads
• Flexing of the treads can cause excess stress, resulting in a tyre that is more
susceptible to cracking.
Uses:
These tyres are generally designed for use on hard road surfaces, such as tarmac and concrete. They are often fitted to the wheels of trucks or buses responsible for direction, depending on if the vehicle uses a front wheel steering system or rear wheel steering system, naturally.
Advantages:
• Improved traction • Excellent grip when braking and accelerating
Disadvantages:
• Excess noise at high speeds • Not suitable for high speed driving due to additional rolling resistance
Uses:
Figure 13. Rib Pattern Tyre Tread [16]
BLOCK SHAPE
A block shape pattern refers to designs with independent blocks along the tread, separated by a series of interconnected grooves (Figure 16).
MIXED, RIB-LUG SHAPE
A mixed shape pattern is a combination of the two previous shapes. It can feature varying combinations of S-shaped voids along the axis, as well as perpendicular grooves (Figure 15).
Advantages:
• The central rib provides good directional
control.
• The shoulder lugs offer good braking & driving power.
Disadvantages:
• The mixed shape offers a more balanced performance, so it is not as good in key areas as more specialised designs, such as pure rib or lug patterns.
Uses:
These tyres are good for both paved and dirt roads and can be found on a variety of trucks and buses.
Advantages:
• Good steering and stability on both wet and
snow-covered roads.
• Good water dispersal properties thanks to the numerous grooves.
Disadvantages:
• Low durability, depending on the size of the tread blocks.
Uses:
The main benefit to these tyres is their ability to perform well on snow. This makes them highly useful as winter tyres, as well as all-season tyres for passenger cars.
Figure 15. Mixed Tyre Tread [16]
ASYMMETRIC SHAPE
This refers to tread patterns that differ on each side. Typically, bigger blocks are used on the outer side, while the internal blocks are smaller, while a series of grooves help disperse water outwards (Figure 17).
DIRECTIONAL PATTERN
Directional tyre treads are also another very common tyre design and involve a series of lateral grooves positioned at the same angle on both sides of the tyre. This creates a ‘direction’ of sorts as all grooves point forward (Figure 18).
Advantages:
• Good for high speed cornering thanks to the big contact area
• Improved stability when turning, thanks to the bigger blocks
• Reduced tread wear on the outside of the tyre
Disadvantages:
• Need to be positioned correctly, due to the different sides
Uses:
These tyres offer great performance even at high speeds, making them suitable for sporting vehicles and more aggressive driving styles. Naturally, they are commonly used as motorsport tyres.
Uses:
Directional tyres have plenty of uses and are most commonly found in high speed passenger vehicles.
Disadvantages:
• Due to their directional nature, these tyres need to be installed with the correct orientation.
Advantages:
• Very good traction and braking
• Good water dispersal for stability on wet roads • A good choice for fast driving styles
Figure 18. Directional Pattern Tyre Tread [16]
Figure 17. Asymmetric Shape Tyre Tread [16]
Computer Aided Design (CAD) allows engineers to create detailed designs of parts with maximum efficiency and minimal cost. The days of the drawing boards are essentially over with the release of affordable and easily used 2D and 3D CAD packages. The aim of CAD is to apply computers to both the modelling and communication of designs. This includes automating such tasks as the production of drawings or diagrams and the generation of lists of parts in a design and providing new techniques which give the designer enhanced capabilities to assist in the design process. [17]
At the same time the diversity in design processes and ways of designing have created an equally diverse number of CAD tools. These CAD tools vary a lot between themselves, but they can be classified as shown in the next figure in two big families: History-based CAD tools and History-Free CAD tools.
3.1 History-Based or Parametric CAD Tools
This approach has a structured modelling process with hierarchy (Parent-Child) inside it. It begins with constrained sketches, that are the base of features. These features create parts than then should be assembly to create the different objects. In this approach to edit a part it is not possible to directly edit the part’s geometry, but it is necessary to edit the different sketches or features to obtain the change in the geometry. All these gives the possibility to create linear parameters that facilitate replication of a certain part with some small changes. [18] So, it is possible to create many similar parts where just a simple feature change.
Some of the CAD technologies that use this approach are: • Constructive Solid Geometry (CSG) Modelling:
It uses solid primitives (rectangular prisms, spheres, cylinders, cones, etc.) and boolean operations (unions, subtractions, intersections) to create the solid model (Figure 19). The main drawback to this type of modelling is the lack of editing or re-dimensioning capabilities. If there is a change in the design, the model, in most cases, will have to be reconstructed. [17]
•Parametric Solid Modelling: In a parametric model (Figure 20), each entity, such as a boolean primitive, a line or arc in a wireframe, or a filleting operation, has parameters associated with it. These parameters control the various geometric properties of the entity, such as the length, width and height of a rectangular prism, or the radius of a fillet. They also control the locations of these entities within the model. All these parameters are changed by the designer to obtain the desired part. Parametric modelling is most efficient working with designs which only undergo dimensional changes rather than gross geometric ones such as removal of a feature. [17]
Figure 19. Model made by CSG Modelling [17}
Figure 20. Model made by Parametric Modelling [17]
3.2 History-Free or Direct CAD Tools
On the opposite, the direct modelling approach provides a more flexible modelling process where there are no hierarchies and the master is the final geometry. In this approach every change is directly done on the final object and there are no differentiation between a part and an assembly. So, a document can include many different parts placed together as the user ones, without too many constraints. Sometimes this approach also includes the possibility of parametrization, but it usually limits the parameters to some final geometry dimensions. Some of the CAD technologies included in this approach are:
•3 D Boundary Representation (B-Rep): It starts with one or more wireframe profiles (Figure 21), and create a solid model by extruding, sweeping, revolving or skinning these profiles. The boolean operations can also be used on the profiles themselves and the solids generated from these profiles. Solids can also be created by combining surfaces, which often have complex shapes, through a sewing operation. This can be used, for example, to create the body of an aerodynamic vehicle such as an airplane, with its carefully designed wing profiles. [17]
• 3 D Direct Modelling: It uses flexible model creation
and refinement concepts to allow designers to capture ideas and detail models quickly, without focusing on the models' underlying history. Basically, it allows creation of features that are not fully dimensionally constrained. (Figure 22) CSG CSG+B-Rep Primitives Parametric Modelling I-DEAS CATIA V4 Pro/Engineer (Wildfire) Creo Parametric NX CATIA V5 SolidWorks Solid Edge Inventor IronCAD B-Rep B-Rep + Local Ops Direct Modelling Anvil Graftek UniGraphics SolidDesigner (CoCreate) CoCreate SpaceClaim KeyCreator Fusion NX (History-Free Mode) 3D Sync
History-Free
History-Based
V S .
Figure 21. Model made by B-Rep Modelling [17]
Figure 22. Model made by DirectModelling [17]
3.3 Pros and Cons: Direct / Parametric CAD
Modelling
Both approaches have many advantages and disadvantages that limit their use to certain applications and kind of products.
DIRECT MODELLING
Advantages:
- Easy to learn, because they have less features and the way to change them is more intuitive. “What you see is what you get” ( - Geometries can come from any source (other CAD files are easily converted) and can be directly edited without problems. - Lightweight files, usually they are around 70 to 90% smaller than parametric files. - STEP and IGES data works as native data thus facilitating the co-working with suppliers.
- Independent from how geometry is created, so they allow are more free and faster design process. [19]
Disadvantages:
- Many immature representations of direct modelling on the market, there are not many powerful software that fully used this kind of approach.
- It is hard to create dies, because usually there are not native add-ins for this kind of application.
- Less optimized for design optimization and automation
- No parent/child relationship, i.e. no inherent feature to feature associativity. This makes hard to create patterns and other kind of repetitive operations.
PARAMETRIC MODELLING
Advantages:
- Many mature CAD modelling tools include this approach and there are many add-ins for different applications (like die design). All these make the parametric model more robust.
- Develop reconfigurable intelligent
“platforms” and reuse, that makes easy to create templates that can be used to create several similar products.
- Many designers with experience in one or more of these tools, that makes it easier to solve problems when they appear.
- Growing direct editing capabilities for improved flexibility. [20]
Disadvantages:
- Long learning curve, the process can become very complex to achieve proficiency. - Data exchange at the “history” or feature level is extremely complex and becomes a big problem when exporting files between different CAD tools.
- Designer must follow good modelling practices to obtain a stable model. - Large file size and potential slow performance.
As shown above, each of the approaches has many advantages and some disadvantages. Therefore, in the last years there have been created different CAD tools that combine both approaches in some degree. In this way, it iz possible to achieve more complete and powerful CAD modelling tools. In this thesis the idea is to use this kind of tools to model tyre treads, so that it will be possible to understand the advantages and limitations that this kind of tools can have in the developing process of tyre treads. For
In order to have a complete product it is required not only a well-modelled 3D model, but also a well designed one. To have a well designed product, its endurance to working conditions, its manufacturing feasibility and its aesthetic attributes should be tested. All these cannot be done by the CAD tool alone, so other tools – FEA, CAM and Render- are required to perform these tasks.
The finite element method analysis is an important step when developing products, because it allows test the structural behavior of an object under its required conditions. Therefore, it provides information about problematic features in the object. Usually, the process to apply a FEM Analysis to a CAD model requires the following steps [21]:
- Transformation of the model for FEA - Mesh Generation
- Constraints Definition - FE Solution (Figure 24)
All these steps are important for the FEM analysis, but the one that nowadays gives more problems is the transformation of the model for FEA (Figure 25). Usually, the model is redrawn based on technical drawings in order to make it suitable for the meshing. The above due to two main problems in the translation.
The first, happens when the CAD software and the FEA software work with different types of files. In this case, it is necessary to convert the model into a standard file like STEP or Parasolid. The problem with this file is that many times during the conversion some geometries get distorted or disappear creating many problems during the FEA.
The second problem is related with the quality of the result produced by the CAD modelling tool, sometimes the problem begins in the CAD model, because it has too small edges or too complex geometries that are not easy to mesh. So, in both cases the geometry is so complex to fix that it is better to remodel it on the modelling tool of the FEA software. Unfortunately, these tools usually do not provide the same capabilities than CAD modelling tools. [22]
Therefore, it is important that future CAD tools provide a good integration with the FEA tools. To reach a high integration level, these tools should offer reliable conversion tools that allow to save files in many different file formats (not only standard ones). They should also include repairing or simplification tools that make the 3D model de-featuring for FEA easy and reliable. [23] Finally, the tool should allow real-time updates in the behavior of a model under certain conditions, when a specific geometry is changed. In this way, the development of a product is fully simulation driven and the modelling process becomes shorter.
3.4 CAD after modelling…
Historically, CAD (Computer Aided Design) and CAM (Computer Aided Manufacturing) have been considered two distinct and independent technologies. This has created a lack of integration between these two worlds that with the rise of new manufacturing technologies like CNC or 3D printing is becoming a big problem for companies. In the tyre industry most of the moulds used to manufacture the tyre tread are developed with CNC machines (Figure 26) and in the future, it is expected that they will also be manufactured by 3D printing technologies. [26]
The main problems in the integration of these tools are found in the transfer of data between the CAD modelling tool and the CAM tool. Nowadays this transfer is mostly done with technical drawing or incomplete CAD models that usually drive to errors in the 3D model of the CAM tool. These errors are extremely expensive, because they produce waste of material if they drive to incorrect/undesired geometries in the product.
Therefore, a good CAD modelling software should provide integration with a CAM tool, whether easily translating the information to an external CAM software or having built-in CAM tools. Some of the features that a software should provide for an efficient and worthy integration are good file geometry translation, possibility to transfer manufacturing data from the native model and possibility to make simulations. The first feature is important because many times the geometry is correctly translated, but the centre of coordinates is set in a wrong position causing an incorrect manufacturing process. That is why it is important that the file translation also provides this kind of information. The manufacturing data (like the tool path, type of tool and surface finishing) associated with the model should also be translated from CAD to CAM tool.
Finally, the simulations are also an important part in the integration. For example in the tyre industry it is important to understand how the variations in the tread design influence the flow of material inside a mould (Figure 27). If this influence is understood in real-time during the manufacturing process, a lot of time and money is saved. [27]
Until recent years the integration between CAD tools and renderers was seen an optional eye candy, but it is becoming an essential tool for the evaluation of the aesthetic appeal and commercial prospect of any product. In the tyre industry, it is specially relevant because the design of the tyre treads has become one of the main elements that give value and transmit the performance of a tyre to the user (Figure 28). Unfortunately, to test different kind of tyres with realistic models is expensive because they require special tools like moulds.
Therefore, it is important that the CAD modeller allows some integration with a render engine. To do this it should include some render features that allow to create photorealistic renders directly in the software. Some of these features are cameras, lights, environments and different textures that will give a sense
3.6 CAD/CAM Integration
3.7 CAD/Render Integration
MODELLING PROCESS
ANALYSIS
To reach the main objective, a process with four main steps is followed.
First, the modelling process in NX (the traditional CAD tool) is studied using a winter tyre because this kind of tyres includes the biggest variety of features on their treads, for example it contains sipes, a feature that requires modelling proficiency due to its high geometric complexity.
Secondly, the winter tyre tread is modelled in Evolve, Spaceclaim and Onshape (modern-CAD software) using technical drawings provided by a tyre company. During the modelling process different procedures are tested to understand the capabilities of each CAD tool. Then the best solution on each case is selected, the complete tyre tread is modelled, and the modelling time is measured.
Thirdly, the capabilities and limitations of the new CAD tools are compared with the ones in NX. The different software are compared based on different characteristics like the implementation, the ease to learn, the capabilities of the modelling features included on each software, the modelling time and steps.
Finally, the integration between the CAD software and other tools required for the product development process is explored. To do this, the integration possibilities between each software and some simulation environments, CAM tools and render engines are investigated and analysed.
4. SIEMENS NX MODELLING
PROCESS
To design all these tyres the most commonly used CAD modelling tool is SIEMENS NX. Siemens NX software is a flexible and powerful integrated solution that provides not only a CAD modeler, but also a simulation environment (for structural tests and manufacturing) and a renderer. Supporting every aspect of product development, from concept design through engineering and manufacturing, NX gives the user an integrated toolset that coordinates disciplines, preserves data integrity and design intent, and streamlines the entire process. [33] Some of its advantages are:
- Complete 2D & 3D CAD Modelling Tools: NX combines wireframe, surface, solid, parametric, and direct modelling (synchronic mode) in a single modelling software solution that allows the user to choose the best tool for the task at-hand. In addition, Convergent Modelling technology in NX gives the ability to combine these approaches with faceted-based modelling without the need for data conversion. [34]
- Assembly Design: NX is optimized to manage very big assemblies without crashes or many problems in the constraints.
- Feature Modeling: NX combines comprehensive high-performance parametric wireframe, surface, solid, and facet modelling with the power of synchronous technology's direct modelling in a single modelling solution.
- Free Form Design: NX provides more possibilities than its competitors when speaking about free form features. A versatile, integrated toolset combines 2D or 3D curves, surface, solid, facet, and synchronous modelling for fast and easy shape creation, evaluation and editing.
Although this is one of the most powerful CAD tools available nowadays NX also has some disadvantages.
- Long learning curve, because of the big number of tools that NX has that make it complex for beginners to use the software with confident.
- Not previous knowledge about it. NX does not have a free student version, so it is not common that recently graduated designers and engineers are familiar with the software. Additionally, it requires constant use to get use to it and become highly productive with it.
- High license cost. The cost is a big barrier for the use of this software outside of big companies. - Interface is not as user-friendly as in other CAD tools.
4.2 MODELLING PROCESS
In the following pages the modelling process of tyre treads will be explained using as model a winter tyre. The steps are based on the guidelines for modelling a tyre found in a book about tyre design [11] and a research paper about parametric tread design for efficient tyre mould production [1].
The modelling process begin with the creation of parameters. Unlike other software in NX it is possible to create at the beginning all the required variables and then use them when sketching or modelling. On the “User Expressions” tab (Figure 30) it is possible to add formulas or just numerical values on each expression. NX also allows to change the units and type of dimension for each variable. The main variables that should be created on this stage are the lateral grooves width, the central grooves width, the pitch length and some sipe distribution parameters like the length and the space between sipes.
When all the variables are created the sketching process begins. To create a sketch, a plane, a face or a CSYS (absolute coordinate system) are required. NX provides all the common simple curves (line, arc, circle, polyline, square) and some splines that are powerfull enough to sketch almost any form. Arcs (and other simple curves) are the most common choice when sketching the tread and grooves profiles. These curves are completely parametric and stable, which makes them perfect for the use on CAM models that require smooth tool paths. Additionally, NX provides a powerful handset of constraints (Figure 31) that makes it easy to obtain smooth surfaces, even when using several tangent arcs. These contraints make the sketching process fast and intutive because they directly change the shape to fit the requirements. So, it is not necessary to set all the dimensions of the curves, some of them will be automatically calculated by the software to comply the constraint.
PARAMETRIZATION
SKETCHES CREATION
Another important command is “Rapid Dimension” (Figure 32) that allows to dimension the different curves or sketch entities. In the case that one of the sketch entities dimension is variable, it is possible to change its value for the name of one of the variables created as User Expression.
For the design of the tyre tread several sketches are necessary. These sketches change depending on the type of tyre and the tread design. Some sketches that are usually necessary are:
- Tyre tread outer shape: This sketch is used to created the the tyre tread solid.
- Pitch lenght references: In this sketch are referenced the positions of the different tread elements like
the grooves and the channels.
- Lateral/Central Grooves: This sketch includes all the curves that will work as path to create the
grooves walls.
- Block cutting edge: This sketch includes the curves that will work as path to create a surface to cut the
tyre tread block.
Figure 31. NX References & Constraints in the sketching mode
After creating all the sketches the first solid is generated. This solid (Figure 33) is created by revolving the tyre tread profile. It is important to create a solid bigger (revolve with a 25% bigger angle) than the final tread block to be able to cut the block edges. Before creating this revolution it is suggested to set an additional CSYS (absolute coordinate system) in the coordinates of the revolution axis, this CSYS will be useful for the creation of the complete tyre and for the FEM analysis simulations.
When all these is done, an off-set surface based on the upper surface of the solid is created. This surface will be the main reference for projecting the sketches on the curved tread profile. It is used an offset surface because using directly the surface of the solid will create some problems when executing further operations. On this surface the reference lines for the channels that are sketched in the Pitch Reference’s Lines Sketch are projected using the option equal arc lenght projection. These projected lines are used as reference for the following sketches.
To create the different channels that a tyre tread can have the process is very simple. First, the cross-section of the different radial channels have to be sketched using as reference the tread outer shape. Later these sketches are revolve as surfaces. It is important to revolve them for a bigger angle than the tyre tread block, because these surfaces will be intersect and merge with the grooves surfaces.
CREATING THE TYRE TREAD PROFILE
CREATING THE CHANNELS
When the channels are created it is time to create the grooves bottom (Figure 34). Usually the grooves bottom consists on different pieces because the central and the lateral grooves require different depths. These segments should be sketched a little longer that the final result because it is important that the revolved surfaces created by these segments intersect between themselves in order to produce a uniform bottom surface without gaps or inexact edges.
The tread under-cut is sketched using as reference the outer tread sketch. Then, it is revolved to obtain a surface that will be used to split the tyre tread solid and remove the material under this surface (Figure 35).
CREATING THE GROOVES BOTTOM
CUTTING MATERIAL FROM THE TYRE TREAD PROFILE
To create the grooves and all the details a process of six steps is followed.
Projection
First all the curves on the previously created sketches are projected (Figure 36). Projection tools are different from the wrapping tool because the wrapping tool is primarly designed for euclidean surfaces like the cylindrical surfaces. On the opposite, tyre treads are toroidal surfaces that are non-euclidean, so they can not be flattened. Therefore, it is not advised to use wrap tool to project the sketches on the tread surface.
Surface Sweep
These projections are used as the path for new surfaces produced by sweep operations. The sweep command used (Figure 37) is an add-in command created with script that allows to directly set the width and inclination of the surface. It creates surfaces completely normal to the surface where the path is drawn. Additionally, it allows to extend the surface some milimeters from the curve.
CREATING THE GROOVES AND ALL THE DETAILS
Cutting Edge Creation
When all surfaces are created, the block lower edge’s surfaces are selected (Figure 38). Usually all of them are not connected in the part where the radial channels intersect them. So, a new surface is created by revolving the central axis of the big channel cross-section. This revolution surface intersects the block lower edge’s surfaces. So, the trim operation is used to intersect them and create the connecting surfaces between the block edge swept surfaces. The result is sewed and a new surface is created. Then this new surface is patterned using a circular pattern. The angle between the surfaces will depend on the block length (also on the pitch lenght) and on the tyre radius. It can be calculated with the formula:
Angle = L_block/r_tyre *180/pi
Grooves Surface Mani pulation (Intersect, Extend & Trim)
After generating all the surfaces required to create the grooves, it is possible to see that most of them have material in excess. This is a problem because in order to trim the tyre tread solid it is necessary to have a set of surfaces that share edges. Therefore, different operations should be use to remove the excess material (Trim) or to extend surfaces (Extend), so that they intersect another one.
Grooves Surface Blend
Sometimes it is necessary to create rounded edges and NX gives the possibility to create them directly in the intersection between two surfaces. The tool called “Face Blend” directly combines the two surfaces with all the required parameters on its intersection. It is a very useful tool that allows more precise results that the rounded tool that can be used only on solids.
Figure 38. NX Cutting edge creation through pattern operation.
Surface Sew
When all the manipulation of the surfaces is finished and all of them are intersecting between themselves without gasps or inexact edges, it is possible to use the surface “Sew” command that will join them in a smooth way. Usually it is necessary to use the Sew command several times. The final result should be made only of walls and bottoms as shown in figure 39.
Trim/Boolean operation
Finally, the sewed entity obtained in the former step is used to split the tread profile solid. In this operation the upper part is removed and in this way the detailed block is obtained (Figure 40).
After obtaining the tread block the document is save. Then the User Expresion variables are changed to obtain the different blocks. The user expressions can be manipulated and grouped in tables so that all the results can be directly changed associated by the tread block name.
The process to obtain the sipes is the most time-consuming step in the whole modelling process of tread profile. It requires similar steps to the ones used for the grooves, so it is like modelling hundred of small
CREATING THE SIPES
Figure 39. NX Grooves surfaces sew
Sketch Projection & Surface Creation
The sipe’s profile sketch is projected using “Equal Arc Length” projection over the face where the sipes will be created. Then, a surface is created using the sweep operation. (Figure 43) This operation has some limits, like the requirement that the curve that will be sweep should intersect the curve that will be the path.
Sketch Creation
When all the reference are created, it is possible to create the sketches (Figure 42). NX offers some features that make this process easier. For example, it allows to edit each curve separately, which gives a higher control on the curve’s shape, and to create patterns with a direction defined by a curve, which is helpful in these repeating elements.
Reference Creation
The sipes are created over each of the tread upper faces and intersect the grooves. So, to draw the sipes precisely some references (Figure 41) based on the grooves edges should be created. These reference are useful when giving the length and direction to each sipes. Also, they help on defining the areas where the sipe’s depth changes. This characteristic is necessary to preserve the tyre stiffness.
Figure 41. NX Reference creation for the sipes generation
Si pe’’’s Solid Creation
Due to the variation in the sipes depth it have been seen that the best method to obtain the desired geometry requires to first create the sipe’s bottom profile. This profile is revolved to obtain a surface. It is necessary that this surface and the one created by the sweep intersect themselves. In this way they can be trimmed, and the result will have the shape of the sipe. So, to obtain a solid the only step necessary is to thicken this surface. (Figure 44)
Boolean Operation
When the solid of the sipe is created, it is possible to subtract (Figure 45) this solid from the detailed tyre tread solid.
All this process should be done for each sipe, so it becomes a very long and time-consuming process. One strategy that can be applied to make the process more efficient is to create a User Defined operation that includes and executes all the commands to generate a sipe. The problem with this operation is that sometimes if the sipe is to big, it will intersect not only the required faces, but other faces. So, it is advised
Figure 44. NX Sipes Solid Creation
The process to create the whole tyre tread (Figure 46) is simple in NX. It requires the creation of an assembly file, where all the tread blocks will be placed. A very helpful feature that offers NX is the block selection. When all the configurations are saved, it is possible to select any of them when placing them on the assembly. All of them should be combined to obtain better results during the FEM Analysis.
CREATING THE COMPLETE TYRE TREAD
5. ANSYS SPACECLAIM
MODELLING PROCESS
ANSYS Discovery SpaceClaim is a multipurpose 3D modelling application created by Mike Payne, founder of PTC and Solidworks. Spaceclaim provides efficient solutions to common modelling tasks. Built on the direct modelling technology approach, Discovery SpaceClaim removes geometry problems associated with various 3D CAD operations, such as design or concept modelling, repair of translated CAD files, general model defeaturing, and complete model editing. [35]
Some of its key features include:
- Full part and assembly modelling
- Detailed drawings including full 2-D/3-D GD&T - Photorealistic rendering capabilities with Keyshot - Open/edit files from neutral and native CAD systems - Open/edit drawings from neutral and native CAD systems - Complete help guide and tutorials for a rapid start
Additionally, SpaceClaim was built to allow easy modification and optimization of CAD files. Whether modifying existing geometry or creating simplified representations, SpaceClaim removes the geometry bottleneck and lets engineers focus on the physics. True simulation-driven product development is possible with SpaceClaim, because it has a bidirectional linkage to ANSYS Workbench. So, it is possible to take advantage of design iteration studies, and the seamless integration of geometry to other ANSYS products.
With SpaceClaim it is possible also to parameterize any model. This means rapid changing of dimensions as the design needs change. SpaceClaim also supports scripting functionality for the
5.2 MODELLING PROCESS
In Spaceclaim it is not necessary to have a previously created plane to draw a sketch on it. Instead of that it is possible to create a sketch just touching any reference and activating the “Sketch” mode. Spaceclaim has three modelling modes: “Sketch”, “Section” and “3D”. All these makes the creation of sketches very intuitive because it is possible to change several times the desired sketch plane, without the need of many plane entities as in other software. For the people that like to first define the sketch plane (Figure 47), there is also the possibility to do so.
When drawing the curves, it is better to set all the dimension from the beginning because there is not any dimensioning tool that works after the curve is created. There is the possibility to manipulate the shapes dimensions by using the pull or move operations, but these tools are complex to use with curves because they sometimes distort the curves.
In Spaceclaim is not possible to add constraints to the curves, which makes the sketching process longer than in parametric CAD tools. The above because the creation of many tangent arcs or other simple curves requires more specific dimensions (like the coordinates of the intersecting points that in parametric CAD tools are calculated automatically). Additionally, it is important to know that each created curve is a different and independent entity, so it can be move and pull as any other entity. The last has a hidden problem, it is that Spaceclaim automatically splits the entities when in the 3D mode if there is any surface or solid that intersects that entity. This creates many problems with the resulting geometries. So, it advise to avoid this kind of cases. A way to avoid it is to create different layers (Figure 48). When modelling the tyre tread, different layers were created in order to avoid this problem.
SKETCHES CREATION
Figure 47. Spaceclaim (Left) Sketch Mode Overview / (Right) Plane Creation
So, to draw the different sketches a good procedure begins by creating all the layers. Then sketches are drawn, and when they are finish all its curves are selected and assigned to one layer. Later the layer is hidden by clicking on the light bulb besides the layer’s name. It is important to hide it because if it is shown and the user creates a surface that intersects that sketch, it will be split creating the problems explained before. To summarize, the sketches that should be created on this stage are:
- Tread Outer Shape - Pitch Reference’s Lines - Lateral Grooves - Central Grooves
- Central/Lateral Grooves Details - Grooves Bottom
To create the tyre tread main solid, first it is necessary to set an axis (Figure 49). In Spaceclaim, axes can only be created on the CSYS axes. So, after generating the axis, it is always necessary to move it with the move command into the correct position. It is suggested to always use the ruler included in the “Move” tool to have precise results.
When the axis is created it is possible to select the “Tread Outer Shape” sketch and revolve it around this axis (Figure 50). In Spaceclaim most of the solid creation operations are included into the “Pull” tool. To have only one tool that makes everything, provides a cleaner interface and a smoother user experience. Despite this, sometimes problems can arise because the function requires more steps and more feeds. Also, there is something odd in the way that the parameters of the function are set, because some of them like the dimensions can only be accessed by keyboard keys (like “Spacebar” to set the parameters) and others can only be changed in “Options” on the lower part of the Control Panel.
For creating the tread profile, it is suggested to use the “Pull both sides option” because the results will be centred. The “Revolve” option in the “Pull” operation also allows to remove material and to create independent solids (Option “No merge”).
CREATING THE TYRE TREAD PROFILE
When the solid is created, select the upper face and press CTRL+C and then out of the solid and press CTRL+V. In this way a new surface is created in the same position of that Face. That surface will be useful to draw and project the grooves sketches. The last is a useful that Spaceclaim includes, it is possible to copy any entity of a solid, surface or curve and paste them as a completely independent feature. So, it is not necessary to have off-set operations, just copy/paste and move if necessary.
Then the block lower edge is drawn. The procedure to draw it is completely different from the one in NX because Spaceclaim does not have the option of “Arc Length Projection”. So, it is not possible to project the sketches based on the technical drawings on the upper surface because the results are completely different. It was looked for another operation that could do something similar like wrapping. There is a tool that wraps the curves, surfaces or solids around rounded surfaces. It can be found in Prepare tab in the Analysis section. The name of the function is “Wrap” (Figure 51). This tool is more powerful than other wrapping tools in other CAD software, because it can be used on non-Euclidean surfaces. Unfortunately, the geometries that it produces are different and less accurate than the ones that produces the “Equal Arc Length” projection in NX.
The last is more evident when a curved surface like the grooves is wrapped because the results with the two tools are completely different. Therefore, it was decided that this tool cannot be used in this case, because it does not allow to translate the information from the technical drawings to a correct geometry.
Another solution that was studied was to draw curves directly on the surface using the command “Face Curve” in the sketch section. Unfortunately, it was found that this command does not allow to create editable curves and require too many control points to satisfy the geometry requirements. Therefore, it was discarded for most of the sketches. It should be use, only if a surface that intersects the tread profile is required. The last is the case of the block lower edge. So, this tool was used to draw all the curves (Figure 52).
The process to create all the block lower edge’s surfaces is different and longer than the one in NX, because in this case there is not a customized function that does it. So, it was found that the best way to do it was following a process of three steps. First, planes on the end point of the curves are created. These planes should be normal to the curve. Then, a line is sketched on each plane. (Figure 53) Later these lines are sweep using the “Pull” operation. (Figure 54) This operation has a limitation because it does not produce a surface normal to the sweep path surface. So, it is advised to change several times the inclination of the sketched lines in order to obtain better results.
The resulting surfaces should be combined using the “Combine” operation. This operation convert all the surfaces into one entity. Unfortunately, sometimes it leaves gaps or inexact edges in the intersection of the different surfaces. So, it is advised to go to the “Repair” tab and check the quality/continuity of the combined surface. Some tools that detect and fix problems with surfaces are “Gasps” or “Simplify”. The last is an important step because the “Split Body” operation that splits solid using a surface only allows to use as cutting tool a unique continuous surface.
When the unique surface is created, it is used the “Circular Pattern” operation as in NX to create the block upper edge surface. These surfaces are used to split the tyre tread solid and then the edges are removed (Figure 55).
Figure 53. Spaceclaim Profile Sketch Creation for the Sweep. (Left) Plane is created (Right) Sketch is drawn.
The grooves bottom is created by revolving the grooves bottom sketch curves (Figure 56). The result should be different intersecting surfaces.
The lateral grooves can be done using the Face Curve operation, as in the case of the block edges surface. That was the first procedure tried to develop them, but when creating the sweep, the geometry failed to resemble the one of NX. The above because the sweep operation does not work well on a curve with many control points. Unfortunately, due to the curvature of the grooves, it is necessary to create a face curve with many control points. Therefore, this kind of solution was abandoned. So, to obtain the same results as in NX. The process that was done, was to select all the splines resulting from the equal arc length projection of the different sketches and project them back to a plane using the normal projection (not equal arc length). In this way all the sketches were converted, so that a normal projection will give an accurate result.
When all the sketches are adjusted, they can be projected back on a copy of the tyre tread off-set surface. It is important that each groove’s projection is a closed loop. To guarantee this, close all the grooves profiles thus that when the 3D mode is activated they are converted into surfaces. These surfaces are projected into the off-set surface (Figure 57). If there is any error in the projection, it is possible to change the direction of the projection, the target face and the type of projection by changing the options inside the function. Another advise, is to make a copy of this off-set surface before projecting the curves because the projection will split the surface and make impossible to use it for further projections.
CREATING THE GROOVES BOTTOM
CREATING THE LATERAL/CENTRAL GROOVES
Then when the projection is done it is possible to extrude them with the “Pull” operation (Figure 58). This operation will extrude the object in a way that all the faces will be normal to the face. In Spaceclaim this is the way that gives the best results, because it is the only one that creates walls completely normal to the off-set surface. These walls usually have an angle with respect to the surface normal and in Spaceclaim this angle can be added with the draft mode in the “Pull” operation (Figure 58). In this way the same result as in NX can be obtained with less steps and a simpler process. The outcome of this process are different solids that will be use as cutting tool in a boolean operation to remove material from the tyre tread solid.
Sometimes it is necessary to remove additional material from these solids to obtain the desired shape. For example, it can be necessary to remove material from the bottom to obtain the desired curvature. The “Combine” or the “Split Body” operations can be used to do this. Both operations allow to split a body using a face or surface, but the “Combine” operation can be use when several bodies should be split at the same time by a surface (Figure 59). This is the case of the lateral grooves, so this is the operation used. The last step of this operation allows to remove the undesired volumes of the split solid.
After creating the lateral and central grooves, usually it is required to create some details related with them. These details are created on the walls that intersect them with the big channels. The procedure to create them is the same that was used to create the grooves. The projected curves are extruded, and a draft angle is created on the wall that intersect the grooves. The final solid is shown in figure 60.
Figure 58. Spaceclaim Lateral Grooves (Left) Solid creation through normal extrusion (Right) Drafting operation for the walls
To create the radial channels the procedure requires few steps. First, the channel cross-section curves are revolved. Then, the volume is split where it is necessary using surfaces. These surfaces are generated by extrusion or sweep operations. To split them, the function “Split Body” can be used. With this function is possible to remove the unnecessary volumes directly inside the function control panel. The final result is shown in figure 61.
To create the final solid a boolean subtraction is executed (Figure 62). This is done with “Combine” command. The the tread profile is used as target and all the other components as the cutting tools. It is advised to hide all the layers different from the one containing the target object, because in this way it is easier to remove all the undesired volumes.
CREATING THE CHANNELS
CREATING THE DETAILED SOLID
Figure 61. Spaceclaim big and small channels
In Spaceclaim it is possible to parametrize the sketches by creating group of variables or simply by pressing the P icon that appears whenever a dimension should be set. Unfortunately, the sketch and its parameters are deleted when the sketch is used in any other operation that convert it into a surface or a solid. So, basically it does not make sense to parametrize anything but the ultimate result of the whole design process. However, to do this on a model with many inclined walls like the tyre tread turns out to be tricky due to the lack of a good reference system that will make that all geometries remain constrained. It was tried to parametrize the model, but when the dimensions changed, most of the time the final inclination of the walls also changed. Therefore, it was decided that it is not possible to parametrize the model.
The sipes are one of the most complex elements in the tyre tread developing process because they have complex geometries and should be patterned. In Spaceclaim the process to make the sipes is time-consuming and requires several steps. It can be divided in five phases: pattern creation, projection, solid creation, cutting surfaces creation, boolean subtraction.
PATTERN CREATION
The pattern can only be created through curves. When the first curve is created it is possible to pattern it using the linear pattern feature (Figure 63), this feature requires a reference to have a direction. Therefore, it is important to draw a line with the desired direction for the pattern. The created pattern will be defined as a parametric entity (it is one of the few cases in Spaceclaim that is fully parametric). This entity can be copied to apply it to a different face, when this is done it is important to right-click on the pattern and select “Source”, “Make Independent”. In this way each of the copies have independent parameters.
PROJECTION
When the pattern is created it is possible to project it onto the surface (Figure 64). It is advised to create an offset of just the surface that will be covered by the same pattern. In this way, it is possible to select only this surface when projecting and the pattern will be applied only in the small patch selected. Sometimes only a small part of the surface should have sipes, for this cases Spaceclaim offers the Split tool that allows to split any surface by using its u, v coordinates. Then the required patch can be selected as the target for the projection.
