Chapter System Structure 3.1 Integrative Feature Feature-based technology has been found to be feasible for the integration of CAD/CAM/CAPP segments due to its ability to capture the designer’s intent from one stage to the other of the product development cycle (Shah, 1990). One approach is design-by-feature, which is to design a part using manufacturing features directly. This approach has some drawbacks because: 1) designers need to work in terms of functional features, which are linked to product performance requirements, 2) manufacturing features are closely tied to specific processes and therefore restrict one’s ability to select the best manufacturing methods. Another approach is feature recognition and extraction. Feature extraction is considered as a key element in linking design and process planning. It is used to recognize feature information (shape/form) and retrieve technological information (dimensions, tolerances, etc.) from a product’s solid model. The design-by-feature approach is used in most of the current commercial software tools in product development to create component models. Examples are Inventor®, UG®, Pro/ENGINEER®, SolidWorks®, SolidEdge®, etc. Their features are usually at a 36 Chapter System Structure high-level of abstraction and the commands may be very generic such as punch, extrude, cut, thicken, etc., but they are not suitable for downstream applications, and feature extraction is yet to be established in commercially available CAD tools. Researchers mostly agree that an ideal feature-based system should provide an environment for the design-by-feature approach, in combination with feature extraction and interactive feature definition. In this research, integrative features, which include machining features, fixturing features, set-up features and machine resource features, are defined to integrate the process planning and robust fixturing design processes. Integrative features, in the manufacturing view, represent shapes and technological properties associated with manufacturing (here refer to machining) operations and tools. The integrative features are obtained through a hybrid approach: feature extraction is used to extract machining/fixturing features directly from the 3D product which is modelled using a commercial CAD software, and the design-by-fixturing-feature approach is used to design fixturing features on the product model if necessary. Machine resource features represent the machining environment, and the data can be obtained from libraries. Setup features represent the possible orientations of a workpiece during the machining processes. The detailed definitions of each type of integrative feature are presented in the following sections. 3.1.1 Fixturing Feature Proper fixturing is based on features which can be considered for location, clamping, and supporting. These features, defined as fixturing features, must be present in a product. If not, then the product cannot be fixtured and hence cannot be machined 37 Chapter System Structure successfully. It would mean that the product will need to be redesigned with certain fixturing features to be included, which may or may not be part of the original shape of the product. In simple cases, the fixture layout will use datum which is a theoretical feature that is assumed to be exact (Robert 2003). A datum is an idealized plane, point, or a set of points, lines, axes, or other sources of information on a part. They are used for geometric dimensioning and frequently imply information on the locations of fixturing surfaces. However, in more complex cases, functional features, such as tooling holes, bosses, or tabs, may need to be added to the component design, providing features of sufficient size and geometric form to allow proper part fixturing. The fixture layout then takes on additional geometric characteristics in order to provide the locating and clamping surfaces necessary for workholding. It is therefore necessary either to enhance the existing features in a product to make them suitable for fixturing, or to design special fixturing features which can be removed later on. A typical example for the latter is the die casting method called FIXTUREBLOCKTM (Street, 1986), which is used to ease the machining of hard-to-clamp parts such as turbine blades. This practice is more costly and is usually avoided. To address these issues which are more likely to happen to the cast and forged parts due to their irregular shapes, fixturing feature extraction, interactive fixturing feature definition and design-by-fixturing-feature approaches are proposed to obtain fixturing features. The former is to extract fixturing features, especially for locating fixturing features, from the 3D model of a concept product design directly. The latter two let the 38 Chapter System Structure users define or design fixturing features in case the extracted fixturing features are not sufficient. It can be seen from Figure 1.1 in Chapter that the fixturing features on a cast or forged part are usually holes and tabs. Therefore in this system, these two categories of fixturing features are considered. Some possible types of holes and tabs for location and clamping on a casting are shown in Figure 3.1. For castings, there are many categories: (1) Sand casting; (2) Investment casting and (3) Die casting. Each will have slightly different characteristics. Die castings and investment castings are usually smaller with thin sections, while sand castings are usually large with thick sections. To ensure the fixturing features can be blended to the existing dimensions of these castings, they are to be parametrically defined, and their sizes can be varied according to the different castings. Their properties are listed in Table 3.1. Fixturing Feature Fixturing Feature Fixturing Feature Fixturing Feature Fixturing Feature Figure 3.1 Examples of fixturing features for location and clamping 39 Chapter System Structure The fixturing method may vary based on the distribution and types of fixturing features. For instance, if there are small hole fixturing features on a precision die casting, holelocating method may be considered. If the fixturing features are plane surfaces, 3-2-1locating method is selected. If the base surface is large, 4-2-1-locating type can be selected. If a cylinder fixturing feature is obtained, v-block locating is usually used. Table 3.1 Properties of integrative features Integrative Features Small Machining Hole Feature Large Hole Plane Hole Fixturing Feature Cylinder Plane Set-up Feature Machine Resource Feature Properties Id, Diameter, Position, TAD, Diameter_tol, Depth_tol, Fixturing Features, Operation, Set-up, Machine Resource Id, Diameter, Position, TAD, Diameter_tol, Depth_tol, Fixturing Features, Operation, Set-up, Machine Resource Id, Length, Width, Depth, Position, TAD, Length_tol, Width_tol, Depth_tol, Fixturing Features, Operation, Setup, Machine Resource Id, Diameter, Position, Dir, Diameter_tol, Depth_tol, Setup, Machining Feature, Fixturing Method Id, Diameter, Position, Dir, Diameter_tol, Depth_tol, Setup, Machining Feature, Fixturing Method Id, Area, Position, Dir, Length_tol, Width_tol, Depth_tol, Machining Feature, Fixturing Method Id, Dir, Machining Features, Fixturing Features Id, Axis (3-/4-/5-axis), orientation(horizontal or vertical), set-up, schedule, tooling, operation cost Each fixturing feature will have a link to the machining features and set-up features, and have a unique fixturing function, i.e., location, clamping or supporting. An example to show the links among these integrative features is illustrated in Section 3.1.5. 40 Chapter System Structure The application of fixturing features may vary according to different machining environment, e.g. 3-, 4- or 5-axes machining centre, vertical or horizontal, etc. Some optimizing strategies will be required in applying these fixturing features, e.g. whether it is meant for minimum number of set-ups and minimum tool changes, which are realized using a cost model, while satisfying tolerance requirements with respect to some datum definition during machining, etc. The extracted/designed fixturing features will be stored in the information structure which can be accessed by each segment of the product development cycle. 3.1.2 Machining Feature A machining feature can be considered as the portion of a part having some functional significance and can be created by common machining operations, such as drilling, boring, reaming, milling, shaping, planning, broaching, etc. In this research, castings are considered as raw workpieces, and machining features usually represent holes or planes in a casting. Therefore, hole and plane features, which commonly exist on a cast part, are considered, and they are shown in Figure 3.2. Their properties are listed in Table 3.1. There are two types of hole features. One is a smaller hole feature which is generated purely by machining, and it is the “Small Hole” shown in Table 3.2. The other is the larger hole generated by casting and requires finish machining. This type of hole is usually quite large, and it is the “Large Hole” shown in Table 3.2. The TAD of a feature is determined by searching whether there are any intersection entities in the candidate direction with a ray which has a radius similar to the cutter. If the result is negative, the candidate direction can be considered as a TAD. Otherwise, this candidate direction should be discarded. For a hole feature, the candidate directions are 41 Chapter System Structure the two directions of the hole axis. For a plane feature, the candidate direction is the direction of the face normal. Figure 3.2 Hole and plane machining features An extracted machining feature will be assigned a machining operation automatically based on its type and tolerances. For example, rough or finish machining is assigned to a plane feature, drilling assigned to a small home, and reaming assigned to a larger hole. Each machining feature will finally be produced using a feasible machining operation within a set-up with an appropriate fixturing method and on a suitable machine. Except for the properties which describe its shape, tolerance and material, it must have the link to the fixturing feature, set-up feature, operation and machine resource feature. The machining features are obtained using feature extraction. The heuristics used for reasoning the hole and plane features are shown in Table 3.2. The inputs to the feature 42 Chapter System Structure extractor are the 3D cast part model and the 3D machined part model. Both of them are designed using part features available in Inventor®. Part feature in Inventor® has the geometrical and dimensional information. Boolean operation will be performed on the two models, and the excess material of the cast part which represents the volumes of material to be removed can be obtained. The excess material has only geometrical information. By reasoning the geometrical information on the excess material and the part features in the machined part model, the excess material can be linked to a part feature in the machined part model. In this way, the machining feature can be obtained by analyzing the linked part feature. The extracted machining features will be stored in the information structure which can be accessed by each segment of the product development cycle. Table 3.2 Reasoning heuristics for machining features Small Hole Large Hole 1. It has three 1. It has four faces: one faces, two cylinder face cylinder faces Reasoning and two plane and two plane faces; faces; Heuristics 2. The cylinder 2. The outer face is cylinder face is machined. machined. 3.1.3 Plane 1. It has one machined plane face. Set-up Feature The features of a workpiece are machined in a certain sequence, as given in its process plan. These features (planes, slots, holes, etc) are usually located on the different sides 43 Chapter System Structure (faces) of the workpiece and not all the features can be accessed (machined) while the workpiece is in a given orientation. An orientation, or a set-up, refers to a unique location, clamping and supporting configuration. Every machining operation has a fixturing configuration that is best for the operation, but may not be a practical one. One would like to find subsets of such feasible fixturing configurations whereby all the operations can be performed within those configurations. Therefore, it is necessary that the machining operations can be grouped into set-ups. Each set-up will have a unique location/clamping/supporting scheme, and requires a separate fixture in most cases. The set-up feature is a segment of the integrative features. It represents a particular orientation of a workpiece during a machining process. Its properties are shown in Table 3.1. Each set-up has a link to the machining features which will be machined in this set-up, and also has a unique fixturing configuration, i.e., basing on particular fixturing features. Set-up planning relies on the geometry, dimension and tolerance of the individual machining features and the fixturability of fixturing features (Ong and Nee, 1994, 1996, 1997, 1998). It must also be based on the availability and the specification of the machine tools. A different machine tool would have a different effect on set-up planning, and therefore the fixture plan. The operations that can be performed depend on the number of axes of a machine. Many CNC machines, especially machining centres, can perform a variety of operations in one set-up position. A machining centre with five axes would be able to perform more operations in one set up. The fixture must then be designed to the requirements of all the specified operations. 44 Chapter System Structure 3.1.4 Machine Resource Feature Common job shops are assumed to have 3- to 5-axis vertical and horizontal machining centres. These machining centres can be distributed and located in different places. Each machining centre has its own tools with their corresponding capabilities. Each machine has its ID, axis (3-, 4- or 5-axis), location, orientation (vertical or horizontal), power, set-up, schedule, tooling, operation cost, etc., which are listed in Table 3.1. Each tool has its ID, geometry, material, hardness, potential operations, tolerance specification, etc. It is also assumed that there are always available tools to machine the part, i.e., each machining operation can be processed on a certain machine. As stated before, machining features considered for cast parts in this system are mainly hole and plane features, correspondingly, several possible operations to machine them are considered. They are rough and finish milling of faces, drilling, boring and reaming of holes. Five axis machining is most commonly used to make highly contoured part, such as aircraft components, dies/molds, and engine components in the automotive industry. Machining with 5-axis machines could help manufacturers enhance productivity with far fewer set-ups on a smaller number of machines. Doug Gale, vice president and general manager, Handtmann CNC Technologies (Buffalo Grove, IL) noted "The true beauty of the five-axis machine is the quick set-ups, for low-volume work." (Patrick, 2004) As castings have irregular shapes and low production volumes, they are more likely to be machined using a 5-axis machining centre, so as to reduce the set-ups and thus improve the machining quality due to the ability to control a tighter tolerance arising from fewer set-ups. 45 Chapter System Structure 3.1.5 An Example Here, an example is used to explain the links of integrative features. The part used here is a water outlet (Figure 3.3a). Its material is aluminum. The raw part is made using the die casting process. The secondary machining operations are to drill the two holes (Hole and Hole 2) and mill the face (Plane) as indicated in Figure 3.3a. These two types of operations can be performed on a 3-axis vertical machine center in one set up. For proper location, it uses the inner and outer cylinder surfaces indicated in Figure 3.3a as the fixturing features. The links of these integrative features can be illustrated in Figure 3.3b. a. Part Model Machine Resources Operations Machining Features Set-ups Fixturing Features 3-axis vertical machine center Drilling Hole1 Set-up1 Surface1 Milling Hole2 Surface2 Plane b. Links of Integrative Features Figure 3.3 Links of integrative features 46 Chapter System Structure 3.2 Optimizing Integration In the optimizing integration, product design, machine resource and process planning are embodied in the modules. These modules are assumed to have been distributed in geographically different places. They execute their tasks under the management and supervision of a central Managing Module (MM) through the Internet. The integration framework, as depicted in Figure 3.4, consists of one MM and several modules, viz., the Product Modules (PM), Machine Tool Modules (MTM) and Process Planning Module (PPM), which is located inside the MM. … Product Module (PM2) … Product Module (PM1) Product Module (PM3) Managing Module (MM) Process Planning Module (PPM) 5-axis vertical machine centre (MTM1) 3-axis vertical machine centre (MTM3) … 4-axis vertical machine centre (MTM2) … Figure 3.4 System architecture 47 Chapter System Structure 3.2.1 Product Module (PM) The PM contains all the details of a cast part, e.g., material, dimensions, tolerances, CAD models of the finished part and the cast part. It compares the two CAD models, and the excess material of the cast part represents volumes of material to be removed. At the same time, fixturing and machining features are extracted. The machining features are obtained by reasoning the volumes of material to be removed using the rules described in Table 3.2. Based on the availability of fixturing features, the cast part may need to be modified or can be accepted as it is. The PM also functions as a design module to allow a planner to design a new cast part correctly to ensure its fixturability, i.e., to add fixturing features. All the characteristics of a cast part would need to be considered carefully, e.g. cores, inserts, parting directions, draft angles, etc. Fixturing features are designed based on the rules of minimum production cost and at the same time to satisfy the critical tolerances. These targets are achieved by optimizing set-up planning and scheduling based on the available machine resources. Upon doing so, the product module registers with MM. After successful registration, it posts the product design, which contains the information of machining features, fixturing features, material and due date, to the MM. The methodologies that PM uses to extract and design fixturing feature will be addressed in Chapter 4. 3.2.2 Managing Module (MM) The MM is the center of the modular system and it is responsible for receiving product information from the PM, and broadcasting the received product information to the MTM to check which machine can make this part (based on availability and capability). MM shall also perform negotiation, based on pricing and schedules of the various 48 Chapter System Structure MTM, using an optimization criterion of minimum cost. This task is performed by the PPM located inside the MM. The MM has a knowledge base in which the logics and rules for guiding the management of the modules are defined and stored. In addition, when a module enters or leaves this system, it will register or deregister with the MM. Once a PM or a MTM registers with the MM, its information and functions will be stored in the database in MM. Therefore, the MM knows the modules that are available and the functions of each module. Based on its knowledge of the capabilities of each module, it requests/sends the necessary messages from/to other functional modules to co-ordinate their operations. For example, after a PM registers with the MM, the MM knows that this product has the designed fixturing features, for example, for 5-axis machine center, so it checks the registered MTMs list, locates the 5-axis MTMs, and then sends the detailed product information and the 5-axis MTMs information to the PPM to perform process planning, and at the same time it requests the feedback from the PPM and negotiates with the PPM to determine the optimum machine resources allocation to carry out the machining processes. The determination is made based on the criterion of minimum cost. 3.2.3 Machine Tool Module (MTM) The MTM contains the specifications and configuration of a particular machine tool (cutting tools being part of this system as standard cutting tools are usually available in the tool carousel). Each MTM has its current schedule (availability of machine time) 49 Chapter System Structure and overhead costs. This information is used by the MM for the necessary negotiation and allocation. The MTM does not make decisions but maintains two parts of information: one is a time-invariant part (number of axes, machining volume, accuracy, etc.); the other part is dynamic (schedules, overhead rates, maintenance periods, etc.). 3.2.4 Process Planning Module (PPM) The PPM is located inside the MM. It can access the database of modules registered with the MM. Therefore it knows the modules that are available and the functions of each module as well. It knows the type, geometry, material, hardness of each available MTM, and the potential operation(s) each available MTM can be performed. It also knows that when processing some type of operation on a particular machine, with a particular work material having certain hardness, under certain process parameters, the machine can achieve certain tolerance specifications. Upon receiving the part and machine resource information from the MM, the PPM starts process planning. It examines the extracted machining features which contain tolerance requirements and the fixturing features of the part, feature by feature, and checks its tool accessibility and determines if the feature can be machined. Next it chooses an operation to machine the feature depending on the feature type, and evaluates the MTMs that can perform this operation. Since the PPM can access the database and match which machine can achieve certain tolerance specifications, when working with a particular type of work material having certain hardness, using certain process parameters for a particular type of operation, it evaluates an MTM with respect to the tolerance requirements of the feature. The MTM 50 Chapter System Structure that can achieve the tolerance specification is chosen as a candidate. If the tolerance requirements are not completely satisfied, the PPM considers the feature for the secondary operations it can perform. If one such operation exists, then it is chosen. The next task is set-up planning. The PPM uses ACO to search for the optimal set-up plan based on the candidates of the machine resources. The set-up planning process can be divided into three stages: preliminary set-up planning, tolerance planning and optimal set-up planning. During the preliminary set-up planning stage, each machining feature is assigned certain machine resource based on its TAD and the TOS of the candidates of the machine resources. During the tolerance planning stage, machining features are grouped into set-ups based on the machine tools assigned and their TADs, and the machining datum for each set-up is determined. The set-ups are next sequenced. For a set-up, tolerances on the sequence of operations resulting in the specific design tolerance are added together. In particular, multiple, interrelated datum would introduce unavoidable tolerance stack-ups. So when performing the planning, tolerance achievement will be of the greatest concern here. The sequence of set-ups is determined based on the following rules. The first set-up is selected such that the datum faces required for the maximum number of subsequent operations are machined. The subsequent set-up is selected by determining the one in which the maximum number of operations can be performed. Then the blueprint tolerances of the machining features are checked based on their ideal set-up datum, and a tolerance cost factor is generated accordingly. 51 Chapter System Structure Next, the PPM sequences the operations for each set-up to minimize the number of tool changes. As stated before, for castings, the machining operations performed are usually drilling of small holes, enlarging pre-cast holes and milling of faces. Some common operations related to making holes and planes will therefore be considered in this system, that is, rough/finish machining of faces, drilling/reaming of holes. Therefore the PPM sequences the operations according to the following manufacturing logic: 1) Rough machining of faces 2) Drilling of holes 3) Reaming of holes 4) Finish machining of faces The PPM then checks for adjacent operations requiring similar type of tools if one of the tools can perform both the operations. During the optimal set-up planning stage, the manufacturing cost of each set-up plan is evaluated based on the cost model, in which, multiple objectives (set-up change cost, machine tool cost, cutter change cost, etc) that are possibly in conflict with each other are combined through the use of a weight vector and an aggregation function. The set-up plan which incurs the least cost is taken as the final result. The PPM performs the set-up planning task in the way as described above. When the task is completed, it sends feedback to the MM. If all the MTMs cannot satisfy the part requirements completely, the feedback to the MM is negative. Otherwise, the feedback is positive with a minimum cost value, together with the corresponding optimal set-up plan. The MM then asks the selected MTMs in the optimal set-up plan to commit 52 Chapter System Structure themselves. The selected MTMs commit themselves for the job by updating their schedules accordingly and pass on this information down the line to each tool selected. Thus the scheduling is accomplished. The PPM has now obtained the best set-up plan with the minimum cost. That process plan may have a set of set-ups and each has the determined fixturing faces. Next, the PPM performs the fixture layout planning based on the fixturing faces for each set-up in the selected process plan. The process planning procedure that the PPM follows is shown in Figure 3.5. A cost model is used for evaluation purposes. The tasks of optimal set-up planning and optimal fixture layout are addressed in detail in Chapter and Chapter respectively. Information of a part and machine tools Check accessibility of each machining feature Rules Check machinability of each machining feature Perform optimal set-up planning Perform robust fixture layout planning Tolerance requirements Cost model Location requirements A set-up plan with minimum cost Figure 3.5 Procedure of process planning 53 Chapter System Structure 3.2.5 Data Flow The data flow of the system is shown in Figure 3.6. The input to the system is a 3D CAD model which represents a tentative concept product design and it will be modeled using Inventor®. It is a combination of the cast part model and the machined part model, i.e., it is the starting workpiece but contains the machined product information. The output is a final concept product design. CAD Models (Tentative Design Concept) Extract Machining & Fixturing Features Design Fixturing Features Product Module (PM) Managing Module (MM) Machine Tool Module (MTM) Process Planning Module (PPM) Final Concept Product Design Figure 3.6 Data flow 3.3 Summary Integrative features, i.e., machining features, fixturing features, set-up features and machine resource features (to be explained later), are defined and used as the link 54 Chapter System Structure between the two functions of product design and manufacturing. They capture the designer’s intent from the initial design stage to the final manufacturing stage of product development and therefore can integrate the design and manufacturing feasibly. Functional modules are used to represent currently distributed design and manufacturing environment, and to search for the optimum machine resource which can machine the product with minimum production cost while satisfying the critical tolerances, which will greatly improve the flexibility and adaptability of the integration of design, manufacturing and process planning. The tasks of each functional module are defined. Three core tasks, i.e., the hybrid fixturing-feature-based approach to obtaining the fixturing features in the product module, and the optimal set-up planning approach and the robust fixture layout approach implemented in the process planning module are presented in detail in Chapter 4, Chapter and Chapter respectively. 55 [...]... set-up planning The PPM uses ACO to search for the optimal set-up plan based on the candidates of the machine resources The set-up planning process can be divided into three stages: preliminary set-up planning, tolerance planning and optimal set-up planning During the preliminary set-up planning stage, each machining feature is assigned certain machine resource based on its TAD and the TOS of the candidates... later), are defined and used as the link 54 Chapter 3 System Structure between the two functions of product design and manufacturing They capture the designer’s intent from the initial design stage to the final manufacturing stage of product development and therefore can integrate the design and manufacturing feasibly Functional modules are used to represent currently distributed design and manufacturing... Location requirements A set-up plan with minimum cost Figure 3. 5 Procedure of process planning 53 Chapter 3 System Structure 3. 2.5 Data Flow The data flow of the system is shown in Figure 3. 6 The input to the system is a 3D CAD model which represents a tentative concept product design and it will be modeled using Inventor® It is a combination of the cast part model and the machined part model, i.e.,... contain tolerance requirements and the fixturing features of the part, feature by feature, and checks its tool accessibility and determines if the feature can be machined Next it chooses an operation to machine the feature depending on the feature type, and evaluates the MTMs that can perform this operation Since the PPM can access the database and match which machine can achieve certain tolerance specifications,... Figure 3. 5 A cost model is used for evaluation purposes The tasks of optimal set-up planning and optimal fixture layout are addressed in detail in Chapter 5 and Chapter 6 respectively Information of a part and machine tools Check accessibility of each machining feature Rules Check machinability of each machining feature Perform optimal set-up planning Perform robust fixture layout planning Tolerance... 3 System Structure 3. 1.5 An Example Here, an example is used to explain the links of integrative features The part used here is a water outlet (Figure 3. 3a) Its material is aluminum The raw part is made using the die casting process The secondary machining operations are to drill the two holes (Hole 1 and Hole 2) and mill the face (Plane) as indicated in Figure 3. 3a These two types of operations can... Surface2 Plane b Links of Integrative Features Figure 3. 3 Links of integrative features 46 Chapter 3 System Structure 3. 2 Optimizing Integration In the optimizing integration, product design, machine resource and process planning are embodied in the modules These modules are assumed to have been distributed in geographically different places They execute their tasks under the management and supervision... material and due date, to the MM The methodologies that PM uses to extract and design fixturing feature will be addressed in Chapter 4 3. 2.2 Managing Module (MM) The MM is the center of the modular system and it is responsible for receiving product information from the PM, and broadcasting the received product information to the MTM to check which machine can make this part (based on availability and capability)... accordingly and pass on this information down the line to each tool selected Thus the scheduling is accomplished The PPM has now obtained the best set-up plan with the minimum cost That process plan may have a set of set-ups and each has the determined fixturing faces Next, the PPM performs the fixture layout planning based on the fixturing faces for each set-up in the selected process plan The process planning. .. supervision of a central Managing Module (MM) through the Internet The integration framework, as depicted in Figure 3. 4, consists of one MM and several modules, viz., the Product Modules (PM), Machine Tool Modules (MTM) and Process Planning Module (PPM), which is located inside the MM … Product Module (PM2) … Product Module (PM1) Product Module (PM3) Managing Module (MM) Process Planning Module (PPM) 5-axis . hole and plane features are shown in Table 3. 2. The inputs to the feature Figure 3. 2 Hole and plane machining features Chapter 3 System Structure 43 extractor are the 3D cast part model and. features and machine resource features, are defined to integrate the process planning and robust fixturing design processes. Integrative features, in the manufacturing view, represent shapes and. set-up planning, tolerance planning and optimal set-up planning. During the preliminary set-up planning stage, each machining feature is assigned certain machine resource based on its TAD and