Computer Aided Parametric Design for 3D Tire Mold Production
Chih-Hsing Chu a,*
tatp
, Mu-Chi Song b, Vincent C.S. Luo c
a
Department of Industrial Engineering and Engineering Management, National Tsing Hua University, Hsinchu 300, Taiwan
b
Department of Computer Information Science, National Chiao Tung University, Hsinchu 300, Taiwan
c
STANDTECH Company, Taoyuan 330, Taiwan
Received xxxx; received in revid form xxxx; accepted xxxx
Available online xxxx
Abstract
This paper prents a parametric design system for 3D tire mold production. Tire grooves commonly ud in the current industry are classified according to their modeling procedures, and the design parameters for each groove type are characterized. The result rves as a foundation for standardization of the tire mold design. The prented system simplifies the construction of 3D groove surfaces by reducing the number of interactive modeling operations. The resultant surface model is parameterized and thus allows for rapid creation of other grooves with simple design tables. In addition, a t of geometric algorithms is propod that first detects undesired groove geometries arising in the design process, and then corrects them automatically. In this manner 3D mold models are created with minimal ur interactions. This work is implemented in an integrated CAD/CAM system for actual mold production. Test examples demonstrate that it provides an effective approach to reducing the time yet improving the quality of tire mold development.
XXXX Elvier B.V. All rights rerved.
技巧英文Keywords: Computer-Aided Design, 3D; Parametric Design; Tire Mold
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1. Introduction
shootoutThe tire industry has received much attention since the
late 60’s. Not only is there an everlastingly large demand on
tires, but the significance also lies in the fact that tire design
and manufacturing directly determine the safety and comfort
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of driving. New tire development is a highly complex
process consisting of many engineering activities such as tire
pattern design, material lection, tribological analysis,
prototyping, testing, tire mold manufacture, and mass
production [1]. Each task requires specialized technologies,
and is often performed by companies who own the required
knowledge. As a result, the tire industry has become a
globally outsourced business [2].
Tire mold development plays a key role in the tire
production. Good tire design needs high quality molds that
subquently produce the tire compliant with its
specifications. Tire mold manufacture involves different
technologies from tire production, e.g. CAD/CAM, precision
casting, multiple-axis machining, and metrology are. Hence
it is generally outsourced by most tire companies. The entry
barrier of mold making is high but its economical return is
also rewarding.
Mold design is the most important in tire mold
production. A tire is compod of many intricate grooves
specified by corresponding tire design pattern. Sometimes
the term “tread” is ud and refers to the positive shape of a
groove. The groove shape is usually reprented with free
form geometry, and the construction process of its 3D model
is time-consuming and error prone. The groove geometry
must be created on the surface of a tire without treads,
usually with multiple-axis CNC machining. This requires
proper tool path planning and preci tool motions control.
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Approximately CAD/CAM tasks consume half to two thirds
of the entire mold production time [3]. Unfortunately, there
was very few studies focud on this topic. Most of them
concerns pitch pattern arrangement and quencing. Chen et
al. [4] developed an expert system that facilitates reu of
Computers in Industry xxx (xxxx) xxx–xxx
0166-3615/$ – e front matter # 2005 Elvier B.V. All rights rerved.
doi:10.pind.2005.02.002
previous designs similar to new tread patterns. Jung et al. [5] propod a systematic approach to matching tire patterns using fuzzy methods. Different tread patterns can be effectively recognized and classified according to their design features. Chiu et al. [6] adopted Tabu arch method for optimized quencing of tire pitches. On the commercial side, most general-purpo CAD/CAM software has a lack of support to mold design or manufacturing. Tire mold production has thus become a bottleneck in new tire development.
To overcome this problem, this study develops an advanced CAD system that enables 3D mold design in a parametric approach. First, the groove shapes commonly ud in the current industry are analyzed and categorized into different types. The mold design process is standardized by characteri
zing the geometric parameters comprising of each type and the corresponding modeling procedure. The parameter values form a design table that allows the ur to create, delete, and modify the groove surface with minimal interactive operations. The groove pattern construction in different pitches can be performed in the similar manner. In addition, geometric algorithms are developed for detecting invalid geometries arising in the parametric design process. Automatic shape modifications are also provided to correct them. The construction process of 3D tire mold can be significantly simplified with the functions. As a result, the time of the mold design is shortened but the modeling errors are reduced. Finally, the propod system is implemented and successfully applied to actual production, demonstrating the practicality of the parametric design approach. It provides an effective solution to improving the tire mold development process.
This paper is organized as follows. The next ction describes the design and manufacturing process of tire mold and their current deficiencies. Section 3 introduces the propod system framework with a focus on the parametric design mechanism. Section 4 prents a t of geometric algorithms that automatically eliminate undesired geometries occurring during the design process. The next ction highlights the application of the system using a commercial tire mold as a test example. The final ction summarizes the contributions and future development of this work. The classification of common groove shapes is discusd in Appendix A.
2.Tire Mold Design and Manufacturing
Tire manufacturing starts with lection of rubber compounds and other additives that combine to provide the design characteristics [7]. The next step is to asmble innerliner, body piles and belts, and strands of steel wire firmly together. The result after this stage is usually called a green or uncured tire. The last step is to cure the tire, which is placed inside a mold and inflated to press it against the mold, forming a groove (or positively, a tread) and the tire information on the sidewall. It is then heated at an elevated temperature for some period of time, vulcanizing it to bond the components and to cure the rubber [8].
One important task is to make the metallic mold required in the tire curing operation. Currently two different approaches are adopted in the mold production. Grooves can be carved out of the inner surface of a metal ring, usually by multi-axis CNC machining. This method directly creates the groove pattern and thus has a shorter production time. However, the complex groove geometry increas, to a great extent, the difficulty of the machining process, which becomes requires preci process control and error-prone. The sharp corners produced from the rever shape of a groove often induce rious tool wear and collision problems during the machining. Therefore, direct machining only applies to very simple groove geometry in the current industry. A variant of this appro
ach is to machine the tread shape, which is easier to create due to its convexity. It then rves as an electrode in the subquent EDM process to form concave grooves. However, this method is very limited to complex geometries, too. The total production time is also incread becau of the relatively low material removal rate of the EDM process.
A more commonly ud method is to produce the metallic mold with precision casting [9]. It consists of veral steps shown in Fig. 1. First, groove pattern is created in a shape like the green tire but made of non-metallic
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Fig. 1. Production procedure of a gmented tire mold
material (usually epoxy or other polymers). To generate concave shapes with a sharp cutting tool is less problematic in this ca becau of the material removal nature of cutting and the lower strength of the materials. The finished part with all the grooves created rembles to an actual tire except that the groove size has been properly adjusted to account for the material shrinkage in casti
ng. It then rves as a casting mold for making a batch size of rubber patterns with the groove shapes imprinted on the surface. The patterns become a core in the following low-pressure casting process that actually produces the final metallic mold. The mold produced by this method is actually asmbled with a number of mold gments, as the process control (e.g. casting temperature and molten metal flow rate) is easier to attain in the smaller gments. This process is thus referred to as gmented tire molding in practice. Common mold materials include aluminum alloys and stainless steel. The last step is to make company logos or tire ries numbers on the side surface of the mold with multi-axis CNC engraving. Important dimensions and groove profiles need to be inspected before the final shipping.
In theory a tire mold looks like the negative shape of the tire made from it. The tire geometry consists of a donut shape (the green or uncured tire) and a ries of groove patterns on the peripheral of the shape. Fig. 2 shows typical groove patterns in a 2D drawing. The outer surface of a tire is referred to as the road surface, which is generated by revolving a given profile relating to an axis. A groove pattern (or tread pattern) contains a group of 3D grooves in various sizes and shapes that repeat at every certain distance along the tire circumference. The portion within such a distance range is called a pitch. The grooves of a given tire design can be decompod into a number of repetitive pitc
hes. Each pitch has the same number of grooves. The connectivity among the grooves remains unchanged from one pitch to another, i.e. the position of any groove relative to the others in one pitch does not change across pitches (e Fig. 2). However, their actual locations and sizes may change in different pitches. This characteristic allows for effective parametric design and manufacturing of tire mold.
The groove shape is determined by factors from many aspects such as tribology, heat transfer, fluid dynamics, and aesthetics. The shape becomes highly complex in certain occasions. Parametric design of tire mold starts with standardization of the geometric modeling procedure of the grooves. A classification scheme for different grooves is a priori, which unfortunately does not exist. In addition, it is Fig. 2. Three pitches (small, medium, and large) in a tire design not clear which portions of the mold design process can be parameterized and how the parameterization should be conducted.
One critical issue in any parametric design system is to identify a proper t of variables that construct the design model in a parameterized manner. It is also important to characterize how the modeling operation is conducted for each design and the commonalities among the different operations. The focus is to derive certain patterns that support reu of an existing model and/or its operation procedure in different designs. An effective approach is to classify the design models, anal
yze the parameters comprising them, synthesize the results, and deduce possible generalization [10]. Following the same concept, we first categorize the groove shapes that are commonly ud in practice. Appendix A illustrates the classification result in detail.
3. System Architecture
Fig. 3 illustrates the software framework for the propod design system. It consists of two major parts −Interactive Design and Parametric Design modules. The former contains three functions with which the ur can interactively construct 2D geometric entities required for the 3D mold design. The Parametric Design module consists of a number of tools that facilitate the construction of 3D tire mold in a parametric fashion. Each function is described as follows:
Fig. 3. Framework of the parametric design system
3.1 Tire Design Importer
Currently most tire designs are specified with 2D engineering drawings. Tire mold design and manufacturing, on the other hand, have adopted 3D CAD/CAM software since the late 90’s. To import the tire design data into the mold production remains a manual and tedious process. In contrast, the propod system acquires the 2D design information (including tire profile, guide curves for the groove pattern, and cross-ction profiles of each groove) with the assistance of an intelligent software program − Tire Design Importer. This program assures two critical issues during the data importing process. First, the number of guide curve gments for any given groove does not change across different pitches. A guide curve is normally approximated by a ries of discrete points in the 2D tire design. They are interpolated with spline curves under some tolerance control for the 3D mold modeling. The number of the interpolating curves has to remain the same for every pitch. Second, the connectivity of the grooves in one pitch should be retained. Fig. 4 shows that the connectivity relationship is reprented by a non-directional graph [11].
3.2 Road/Bottom Surface Constructor
A tire mold normally contains one road surface and
veral bottom surfaces corresponding to different groove
depths. Revolving a cross-ctional profile along a coordinate axis with a given extended angle generates the核心价值观演讲稿
road surface, as shown in Fig. 5. The profile can be highly
complex and consist of many line/curve gments with
geometric constraints (e.g. positional and tangent continuities) among them. The ur has to interactively
specify the relationships until the resultant shape becomes
fully constrained with no degrees of freedom. It is important
to maintain the fully constrained condition, which ensures
intact of the parametric design form.考研预报名时间
Fig. 4. Connectivity of a groove pattern in one pitch
and its non-directional graph
3.3 Groove Design Enabler
The groove geometry is characterized with a number of cross-ction profiles along a guide curve (or guide curves). Fig. 6 shows a typical example. The guide curve(s)
determines the location and orientation of a groove on the road surface. It can be the boundary curves of the grooves with varying width. The center curve is ud in the ca of fixed width. The cross-ctional profiles describe the groove shape at a number of positions along the guide curve. Groove Design Enabler imports the profile information and provides a table for the ur to lect at each position. The matching process between each groove and its constructing profiles is simplified and the matching errors are reduced. The matching relationship is stored in Groove Design Enabler and becomes an integral part of the parameterized groove model. 3.4 Groove Modeling Knowledge Ba
General groove shapes have been analyzed and classified into various categories (e Appendix A). The focus is to obtain the design parameters comprising each different groove and the geometric operations required in the corresponding modeling process. They rve as a ba for standardization of the 3D groove construction. The pieces of information are stored in the form of templates. Totally thirty types of groove are stored in the current knowledge
ba. In addition, it compiles the shrinkage factors in casting, engineering change records, important inspection dimensions, and special treatments for each groove type. The ur can query the knowledge ba about all the
production information. More importantly, the other software modules can programmatically access necessary templates during the design process. Fig. 5. Construction of the road/bottom surface by revolving a profile along a given axis
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Fig. 6. Design specifications of a groove pattern
3.5 Groove Shape Generator
Groove Shape Generator performs the actual 3D modeling process for tire mold. A groove cross-ctional profile is specified with two ts (right and left) of design parameters. Each t contains the top point, wall angle, and rounding radius. The corresponding guide curve has been in place with the aid of Groove Design Enabler. Next, this module queries the knowledge ba and obtains the template for the constructing groove. All the geometric operations are wrapped up into one command, and thus hide the design complexity from the ur. The 3D CAD model is created automatically without the ur’s interactions after the required parameters have been chon. If the modeling process fails, error messages will be logged into Program Coordinator for prompting the ur for the command status. 3.6 Design Table Constructor
The ur needs to interactively perform some design tasks, mainly in Road/Bottom Surface Constructor and Groove Type Preparatory. However, after a first pitch has been constructed, the system stores the resultant grooves according to their parameterized, which accelerates the pattern creation in other pitches. Design Table Constructor outputs the parameters into the form of design tables. The following information is recorded for a groove surface: the type, guide curves, cross-ctional profiles, connectivity to other grooves, and all the values of the geometric elements constru
cting the groove. Note that the number of the parameters remains the same across pitches, but their values may change. The table can exist in a text file, Excel document, or PDM (Product Data Management) system. The ur only needs to modify the parameter values for the next pitch design and input the file back into the system. The corresponding 3D grooves are then automatically generated without the ur interaction.
3.7 Invalid Groove Corrector
The propod system allows the ur to design the entire t of grooves in a next pitch by modifying the parameter values from an existing one. This function is bad on the fact that any given groove is geometrically constructed in the same manner at different pitches. However, the change of the parameter values may induce invalid groove shapes or cau geometric operations to fail during the design process. Geometric algorithms are needed to detect the problematic situations and correct them automatically. Invalid Groove Corrector is mainly responsible for such an auto-correction mechanism. The later ction will discuss in detail when the problems occur and how they can be resolved.
3.8 Parametric Design Coordinator
This module rves as a coordinator among the other modules. It pars the design tables from an external medium for the groove pattern of a new pitch; then interrogates with Groove Modeling Knowledge Ba for the modeling procedure of each groove. The next step is to invoke Groove Shape Generator and produces a t of 3D groove surfaces with the new parameter values. Invalid Groove Corrector handles the invalid geometries when they occur during the design process. The coordinator is also responsible for error logging, exceptional handling, and interactions with the ur.
4.Geometric Algorithms for Correcting Invalid Groove Geometries
One major problem in any parametric design process is to assure the validity of the resultant geometries, as the ur interaction has been minimized and it is no longer possible to prevent the modeling errors with manual handling. Invalid CAD models often take place in the mold design due to the poor interface with the tire design. One major problem is that most of the tire design activities such as creation of the groove pattern, guide curves, and cross-ctional profiles are conducted in 2D CAD. The design engineer has difficulties in visualizing the corresponding 3D models. It is inevitable that the models often become invalid or simply cannot be created in 3D space. Intelligent algorithms are required to automatically the occurrence of the errors, adjust the related geometric operations, and subquently generate correct results. The invalid groove geometries ma
y ari in a number of conditions, which are analyzed and described as follows.
