**3. Die layout design**

Figure 7. The cycle of case‐based reasoning Proposed solution Revise Reuse Automotive panels can be classified into appearance parts and structure parts. Appearance parts can be seen after assembly, including door, hood, fender, roof, and trunk lid; however, structure parts cannot be seen after assembly.

Figure 7. The cycle of case‐based reasoning

Confirmed solution

Case‐based reasoning has the functions of retrieve, reuse, revise, and retain, called the 4Rs (Kendal & Creen, 2007). After retrieving the most similar case from case base, the information of this case is reused to the new case, and then the proposed solution is Design for Automotive Panels Supported by an Expert System http://dx.doi.org/10.5772/52010 191

The boundary rule result is limited by multiple number sets. For instance, if the input number is less than 6.0, 5.0 is output, and if

Rule Index: 1

Result 1

Result 3

Rule Index: 3

Rule Index: 2 Result 2

The problem of rule‐based reasoning is that converting knowledge into rules is difficult. Knowledge can be separated into explicit knowledge and tacit knowledge (Polanyi, 1958). Explicit knowledge can be converted into rules explicitly, while tacit knowledge

The knowledge database in case‐based reasoning stores previously analyzed cases. After users enter a new case, the reasoning engine compares it with all previously analyzed cases in case base, and then searches for the most similar case and reasons for

Using these two rules can increase the number of judgment modes for a system, and enhance its reasoning ability.

New case

cannot. The knowledge associated with process planning is almost always tacit knowledge.

Boundary 6.0 8.0 12.0

Index

Result 5.0 9.0 10.0 15.0

Solutions Reason based on the

revised. Finally, the new case is retained in the case base as a reference for subsequent reasoning (Fig. 7).

Figure 7. The cycle of case‐based reasoning **Figure 7.** The cycle of case-based reasoning

Figure 4. Judgment rule

Boolean

Figure 5. Boundary rule

**2.2. Case–based reasoning**

results based on the case (Fig. 6).

Case base

Figure 6. Reasoning process of case‐based reasoning

previously similar case

Find the most similar case

the input number is in the range of 6.0–8.0, 9.0 is output (Fig. 5).

Result A

Result B

Rule A

Rule B

The boundary rule result is limited by multiple number sets. For instance, if the input number is less than 6.0, 5.0 is output, and if the input number is in the range of 6.0–8.0, 9.0 is output

Index

Result A

Result B

Boundary 6.0 8.0 12.0

Result 5.0 9.0 10.0 15.0

the input number is in the range of 6.0–8.0, 9.0 is output (Fig. 5).

cannot. The knowledge associated with process planning is almost always tacit knowledge.

The problem of rule-based reasoning is that converting knowledge into rules is difficult. Knowledge can be separated into explicit knowledge and tacit knowledge (Polanyi, 1958). Explicit knowledge can be converted into rules explicitly, while tacit knowledge cannot. The

The knowledge database in case-based reasoning stores previously analyzed cases. After users enter a new case, the reasoning engine compares it with all previously analyzed cases in case base, and then searches for the most similar case and reasons for results based on the case (Fig. 6).

Find the most similar case

Using these two rules can increase the number of judgment modes for a system, and enhance

the input number is in the range of 6.0–8.0, 9.0 is output (Fig. 5).

Result A

Result B

Rule A

Rule B

Rule A

Rule B

Boolean

Figure 4. Judgment rule

Figure 5. Boundary rule

The boundary rule result is limited by multiple number sets. For instance, if the input number is less than 6.0, 5.0 is output, and if

Index

Rule Index: 1

Result 1

Result 3

Rule Index: 2 Result 2

Result 1

Result 3

Rule Index: 1

Rule Index: 3

Rule Index: 3

Rule Index: 2 Result 2

The boundary rule result is limited by multiple number sets. For instance, if the input number is less than 6.0, 5.0 is output, and if

The problem of rule‐based reasoning is that converting knowledge into rules is difficult. Knowledge can be separated into explicit knowledge and tacit knowledge (Polanyi, 1958). Explicit knowledge can be converted into rules explicitly, while tacit knowledge

The knowledge database in case‐based reasoning stores previously analyzed cases. After users enter a new case, the reasoning engine compares it with all previously analyzed cases in case base, and then searches for the most similar case and reasons for

The problem of rule‐based reasoning is that converting knowledge into rules is difficult. Knowledge can be separated into explicit knowledge and tacit knowledge (Polanyi, 1958). Explicit knowledge can be converted into rules explicitly, while tacit knowledge

The knowledge database in case‐based reasoning stores previously analyzed cases. After users enter a new case, the reasoning engine compares it with all previously analyzed cases in case base, and then searches for the most similar case and reasons for

Using these two rules can increase the number of judgment modes for a system, and enhance its reasoning ability.

Case‐based reasoning has the functions of retrieve, reuse, revise, and retain, called the 4Rs (Kendal & Creen, 2007). After retrieving the most similar case from case base, the information of this case is reused to the new case, and then the proposed solution is

New case

revised. Finally, the new case is retained in the case base as a reference for subsequent reasoning (Fig. 7).

The most similar case

Retrieve i

Case‐based reasoning has the functions of retrieve, reuse, revise, and retain, called the 4Rs (Kendal & Creen, 2007). After retrieving the most similar case from case base, the information of this case is reused to the new case, and then the proposed solution is

> The most similar case

revised. Finally, the new case is retained in the case base as a reference for subsequent reasoning (Fig. 7).

Solutions Reason based on the

Retrieve i

New case

Case base

Proposed solution

Revise Reuse

New case

Case-based reasoning has the functions of retrieve, reuse, revise, and retain, called the 4Rs (Kendal & Creen, 2007). After retrieving the most similar case from case base, the information of this case is reused to the new case, and then the proposed solution is revised. Finally, the

Solutions Reason based on the

previously similar case

Figure 6. Reasoning process of case‐based reasoning

knowledge associated with process planning is almost always tacit knowledge.

Case base

new case is retained in the case base as a reference for subsequent reasoning (Fig. 7).

Proposed solution

Automotive panels can be classified into appearance parts and structure parts. Appearance parts can be seen after assembly, including door, hood, fender, roof, and trunk lid; however,

Retain

Revise Reuse

Using these two rules can increase the number of judgment modes for a system, and enhance its reasoning ability.

Result 5.0 9.0 10.0 15.0

Boundary 6.0 8.0 12.0

New case

cannot. The knowledge associated with process planning is almost always tacit knowledge.

(Fig. 5).

**Figure 5.** Boundary rule

its reasoning ability.

Figure 4. Judgment rule

Boolean

190 Advances in Industrial Design Engineering

Figure 5. Boundary rule

**2.2. Case–based reasoning**

results based on the case (Fig. 6).

Case base

**2.2. Case–based reasoning**

Figure 6. Reasoning process of case‐based reasoning

Case base

previously similar case

results based on the case (Fig. 6).

Find the most similar case

**2.2. Case–based reasoning**

Figure 7. The cycle of case‐based reasoning

structure parts cannot be seen after assembly.

Confirmed solution

**Figure 6.** Reasoning process of case-based reasoning

**3. Die layout design**

Retain

Confirmed solution

Figure 7. The cycle of case‐based reasoning

First, this study uses the left side of a fender (Fig. 8) to illustrate the die layout design process (Fig. 9), including feature recognition, machining center searching, drawing direction optimi‐ zation, and process planning.

**Figure 8.** Left side of fender

Fig. 8 Left side of fender

**3.1 Feature Recognition**

Fig. 9 Die layout design process **Figure 9.** Die layout design process

#### The purpose of feature recognition is to categorize a panel into different sections to **3.1. Feature recognition**

establish a bridge between a CAD model and the CAPP system (Zheng et al., 2007) because a panel model without feature recognition is merely unsorted surface data. The purpose of feature recognition is to categorize a panel into different sections to establish a bridge between a CAD model and the CAPP system (Zheng et al., 2007) because a panel model without feature recognition is merely unsorted surface data.

> If the curvature of single surface exceeds a critical value, it is called a bend surface; otherwise, it is called a flat surface. Bend surface whose curvatures in two domains both

exceed critical values is also called a corner surface (Fig. 10).

7

If the curvature of single surface exceeds a critical value, it is called a bend surface; otherwise, it is called a flat surface. Bend surface whose curvatures in two domains both exceed critical values is also called a corner surface (Fig. 10).

**Figure 10.** Bend, flat, and corner surface

A group contains parts with the same surface type that are in contact. A panel can be separated into several groups. The group that is shaped during the drawing operation is called the product-in group or main group (Zheng et al., 2007), and the other groups are collectively called the product-out group, which is separated into corners and subgroups (Fig. 11).

Single edge

Figure 13.Single edge and shared edge

Single edge

Figure 12.Framework of features

Product-in group

**Figure 13.** Single edge and shared edge

**Figure 12.** Framework of features

G5 : Nose Side

G5 : Nose Side

**Figure 14.** Feature recognition result for fender

**3.2. Machining center searching**

Shared edge

Shared edge

The final step in feature recognition is to search for hole features. After finding all edges of a surface, edges shared with another surface are called shared edges; otherwise, they are called single edges (Fig. 13). All single edges for a closed‐loop comprise a hole

Main flat Bend Flat …

Architecture of group

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The flat group with the largest area is a product‐in group, and the bend group in contact with the product‐in group is the main bend group. Corner surfaces are used to separate the main bend group into several smaller main bend groups, and the flat groups in contact with the main bend groups are the main flat groups. If other groups are in contact with the main flat groups, they are

G2 :

The file of a panel from a car company is related to the origin of a car (always at the center of the left front wheel, but differs among car companies). Before deciding the drawing direction, one should first search for the machining center as a new origin, which is a

The method of searching for the machining center is to find the minimum bounding box first, and to define the longest side to the shortest side as the x‐, y‐, and z‐axis in sequence. The direction of the x‐axis is used as a reference when designing the longest side

reference point of dimensions marked while designing the die and a machining center while assembling the die.

G6 : A-pillar Side

G6 : A-pillar Side

G2 :

Finally,thefeaturerecognitionresultforthissamplepanelhassixgroupsandsixcorners(Fig.14).

Finally, the feature recognition result for this sample panel has six groups and six corners (Fig. 14).

feature; however, the longest closed‐loop of single edges is the outer boundary of a panel.

regarded according to the order of bend groups and flat groups (Fig. 12).

Product-out group

Corner Group

Main bend Contact

Surface model of panel

Contact Contact

Door Side G3 :

Door Side G3 :

G4 : Bottom Side

G4 : Bottom Side

The file of a panel from a car company is related to the origin of a car (always at the center of the left front wheel, but differs among car companies). Before deciding the drawing direction,

G1 : Hood Side

G1 : Hood Side

Wheel Side

Wheel Side

Figure 14.Feature recognition result for fender

**3.2. Machining center searching**

**Figure 11.** Relationship between features

The flat group with the largest area is a product-in group, and the bend group in contact with the product-in group is the main bend group. Corner surfaces are used to separate the main bend group into several smaller main bend groups, and the flat groups in contact with the main bend groups are the main flat groups. If other groups are in contact with the main flat groups, they are regarded according to the order of bend groups and flat groups (Fig. 12).

The final step in feature recognition is to search for hole features. After finding all edges of a surface, edges shared with another surface are called shared edges; otherwise, they are called single edges (Fig. 13). All single edges for a closed-loop comprise a hole feature; however, the longest closed-loop of single edges is the outer boundary of a panel.

regarded according to the order of bend groups and flat groups (Fig. 12).

Figure 12.Framework of features **Figure 12.** Framework of features

If the curvature of single surface exceeds a critical value, it is called a bend surface; otherwise, it is called a flat surface. Bend surface whose curvatures in two domains both exceed critical

Bend Surface Flat Surface Corner Surface

A group contains parts with the same surface type that are in contact. A panel can be separated into several groups. The group that is shaped during the drawing operation is called the product-in group or main group (Zheng et al., 2007), and the other groups are collectively called the product-out group, which is separated into corners and subgroups (Fig. 11).

Corner3

The flat group with the largest area is a product-in group, and the bend group in contact with the product-in group is the main bend group. Corner surfaces are used to separate the main bend group into several smaller main bend groups, and the flat groups in contact with the main bend groups are the main flat groups. If other groups are in contact with the main flat groups, they are regarded according to the order of bend groups and flat groups (Fig. 12).

The final step in feature recognition is to search for hole features. After finding all edges of a surface, edges shared with another surface are called shared edges; otherwise, they are called single edges (Fig. 13). All single edges for a closed-loop comprise a hole feature; however, the

Product-in group

Group1 Group3

Corner2 Corner3

Group2

Corner1

Group2

longest closed-loop of single edges is the outer boundary of a panel.

values is also called a corner surface (Fig. 10).

Product-in group

Group3

**Figure 10.** Bend, flat, and corner surface

192 Advances in Industrial Design Engineering

Corner1

Group1

Corner2

**Figure 11.** Relationship between features

The final step in feature recognition is to search for hole features. After finding all edges of a surface, edges shared with another

**Figure 13.** Single edge and shared edge

Figure 13.Single edge and shared edge

Finally,thefeaturerecognitionresultforthissamplepanelhassixgroupsandsixcorners(Fig.14).

Finally, the feature recognition result for this sample panel has six groups and six corners (Fig. 14).

**Figure 14.** Feature recognition result for fender **3.2. Machining center searching**

Figure 14.Feature recognition result for fender

#### **3.2. Machining center searching** The file of a panel from a car company is related to the origin of a car (always at the center of the left front wheel, but differs among car companies). Before deciding the drawing direction, one should first search for the machining center as a new origin, which is a

The file of a panel from a car company is related to the origin of a car (always at the center of the left front wheel, but differs among car companies). Before deciding the drawing direction, reference point of dimensions marked while designing the die and a machining center while assembling the die. The method of searching for the machining center is to find the minimum bounding box first, and to define the longest side to the

shortest side as the x‐, y‐, and z‐axis in sequence. The direction of the x‐axis is used as a reference when designing the longest side

one should first search for the machining center as a new origin, which is a reference point of dimensions marked while designing the die and a machining center while assembling the die.

direction affects the forming ratio of a panel and product quality, and the modeling of the die face affects the difficulty of follow-up tasks and number of operations. Only after one identifies

Drawing direction optimization can be summarized using the following three principles: minimum depth, equal angle, and without an undercut. These principles are only for the product-in group, not other groups, because forming the product-out group is not within the

Drawing depth is the distance on a panel in the drawing direction (Fig. 17). A large depth can cause cracking and increase the height of a die, thereby increasing cost. Thus, minimizing drawing depth can reduce the degree of cracking; and it means that a shallow drawing is used

direction Drawing

The method of searching the drawing direction with the minimum depth divides the range 0– 180° into five equal parts (i.e., 0°, 45°, 90°, 135°, and 180°), and the depth in each direction is calculated. If the depth in the first direction is the shallowest, then the first direction and second direction are divided into five equal portions and each depth is calculated again. If the depth in the seconddirectionis the shallowest,thenthe firstdirectionandthirddirectionaredividedinto five equal portions and each depth is calculated again (Fig. 18); this process continues until the search range converges to <0.1 to determine the angle rotated along the x-axis and y-axis, and the direction of z-axis after rotating is the drawing direction with minimum drawing depth.

depth

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the drawing direction can the die face be designed and the process planned.

scope of the drawing operation.

**1.** Minimum depth

instead of deep drawing.

**Figure 17.** Drawing depth

Drawing

**Figure 18.** Searching drawing direction with minimum depth

The method of searching for the machining center is to find the minimum bounding box first, and to define the longest side to the shortest side as the x-, y-, and z-axis in sequence. The direction of the x-axis is used as a reference when designing the longest side of a die and the direction of the y-axis is used as a reference when designing the shortest side, which is the feeding direction. Finally, the center of the upper rectangle is regarded as the machining center (Fig. 15).

**Figure 15.** Minimum bounding box and machining center of fender

**3.3 Drawing Direction Optimization**

#### **3.3. Drawing direction optimization** Before introducing the drawing direction optimization method, this study introduces the

Before introducing the drawing direction optimization method, this study introduces the drawing task. The drawing procedure differs markedly from other tasks. A plane blank is placed on the piston, and the punch drives the upper die downward to clamp the blank with the piston, and then continues its downward movement with the piston to form the blank with the lower die (Fig. 16); notably, other operations are conducted without the piston. drawing task. The drawing procedure differs markedly from other tasks. A plane blank is placed on the piston, and the punch drives the upper die downward to clamp the blank with the piston, and then continues its downward movement with the piston to form the blank with the lower die (Fig. 16); notably, other operations are conducted without the piston.

Fig. 16 Procedure of drawing operation **Figure 16.** Procedure of drawing operation

The drawing task is always the first operation, and it is the most important task because it shapes the entire product-in group and a little other groups. The key factors in the drawing task are stamping direction and modeling of the die face (You et al., 2011). The stamping The drawing task is always the first operation, and it is the most important task because it shapes the entire product-in group and a little other groups. The key factors in the drawing task are stamping direction and modeling of the die face (You et al., 2011). The stamping

direction affects the forming ratio of a panel and product quality, and the modeling of the die face affects the difficulty of follow-up tasks and number of operations. Only after one identifies the drawing direction can the die face be designed and the process planned.

Drawing direction optimization can be summarized using the following three principles: minimum depth, equal angle, and without an undercut. These principles are only for the product-in group, not other groups, because forming the product-out group is not within the scope of the drawing operation.

**1.** Minimum depth

one should first search for the machining center as a new origin, which is a reference point of dimensions marked while designing the die and a machining center while assembling the die.

The method of searching for the machining center is to find the minimum bounding box first, and to define the longest side to the shortest side as the x-, y-, and z-axis in sequence. The direction of the x-axis is used as a reference when designing the longest side of a die and the direction of the y-axis is used as a reference when designing the shortest side, which is the feeding direction. Finally, the center of the upper rectangle is regarded as the machining center

Before introducing the drawing direction optimization method, this study introduces the drawing task. The drawing procedure differs markedly from other tasks. A plane blank is placed on the piston, and the punch drives the upper die downward to clamp the blank with the piston, and then continues its downward movement with the piston to form the blank with

Before introducing the drawing direction optimization method, this study introduces the drawing task. The drawing procedure differs markedly from other tasks. A plane blank is placed on the piston, and the punch drives the upper die downward to clamp the blank with the piston, and then continues its downward movement with the piston to form the blank with the lower die (Fig. 16); notably, other operations are conducted without the

11

The drawing task is always the first operation, and it is the most important task because it shapes the entire product-in group and a little other groups. The key factors in the drawing task are stamping direction and modeling of the die face (You et al., 2011). The stamping

The drawing task is always the first operation, and it is the most important task because it shapes the entire product-in group and a little other groups. The key factors in the drawing task are stamping direction and modeling of the die face (You et al., 2011). The stamping

Lower die Lower die

Upper die

Piston Piston

the lower die (Fig. 16); notably, other operations are conducted without the piston.

Fig. 15 Minimum bounding box and machining center of fender

(Fig. 15).

194 Advances in Industrial Design Engineering

**Z**

**Z**

**3.3. Drawing direction optimization**

piston.

**Y**

**Y**

**Figure 15.** Minimum bounding box and machining center of fender

Fig. 16 Procedure of drawing operation

**Figure 16.** Procedure of drawing operation

Upper die

Piston Piston

Plane blank

**X**

**X**

**3.3 Drawing Direction Optimization**

Drawing depth is the distance on a panel in the drawing direction (Fig. 17). A large depth can cause cracking and increase the height of a die, thereby increasing cost. Thus, minimizing drawing depth can reduce the degree of cracking; and it means that a shallow drawing is used instead of deep drawing.

**Figure 17.** Drawing depth

The method of searching the drawing direction with the minimum depth divides the range 0– 180° into five equal parts (i.e., 0°, 45°, 90°, 135°, and 180°), and the depth in each direction is calculated. If the depth in the first direction is the shallowest, then the first direction and second direction are divided into five equal portions and each depth is calculated again. If the depth in the seconddirectionis the shallowest,thenthe firstdirectionandthirddirectionaredividedinto five equal portions and each depth is calculated again (Fig. 18); this process continues until the search range converges to <0.1 to determine the angle rotated along the x-axis and y-axis, and the direction of z-axis after rotating is the drawing direction with minimum drawing depth.

**Figure 18.** Searching drawing direction with minimum depth

#### **2.** Equal angle

Characteristic lines (Fig. 19) are very important in the product-in group of appearance parts. If characteristic lines are offset from the original position, it will be very obvious from the outside of a vehicle.

The first proposed method calculates the angle between all normal vectors of point data and the drawing direction. If the angle is 0–85°, the area around the point is safe without an undercut. If the angle is 85–90°, and then the area around the point is close to an undercut, such that one should pay special attention to the draft angle. If the angle exceeds 90°, the area around the point is certainly an undercut, such that this area cannot be shaped during this

Up

per die

Lo

ower die

le = 0–85°

Angle = 85–

without under

rcut

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(a) Undercut

to undercut

90° close t

undercut

Angle > 90°

This method can determine whether undercut areas exist, but cannot detect the undercut area accurately (Fig. 23). Section (a) is detected correctly as an undercut, but section (b) is not because the angle between the normal vector and drawing direction is <85°. In fact, section (b)

15

operation, and other tasks are needed to shape this undercut area (Fig. 22).

Undercut

Ang

16

18

(b) No und

ercut

D d rawing irection

**Figure 21.** Undercut

**Figure 22.** Detecting undercut by angle

still belongs to the undercut area.

Drawing direction

**Figure 23.** Fail to detect the undercut area by angle

#### **Figure 19.** Characteristic lines on fender

The reasons for the offset of characteristic lines are that non-uniform forces exist on both sides of characteristic lines. When the slope of one side is larger than that of the other side, charac‐ teristic lines will be offset to the more oblique side because the material flow rate is slower than that of the other side. However, automotive panels always have irregular, asymmetric, and complex shapes. The method for preventing offset of characteristic lines is to make all slopes from boundaries to characteristic lines as close as possible (Fig. 20). This study sums all normal vectors in the product-in group and calculates the average normal vector, which is the drawing direction with equal angle.

#### **Figure 20.** Equal angle

#### **3.** Without an undercut

An undercut is an area that cannot be reached by the upper die and lower die during stamping (Fig. 21), and the die will damage at that area. If an undercut area is unavoidable, cams must be used or follow-up operations are needed to shape the undercut area.

In this study, two novel methods are applied for detecting undercut areas after determining the drawing direction, and the range of detecting is not only product-in group but also productout group because some groups with simple modeling without an undercut are still shaped during the drawing operation.

**2.** Equal angle

196 Advances in Industrial Design Engineering

outside of a vehicle.

**Figure 19.** Characteristic lines on fender

drawing direction with equal angle.

**Figure 20.** Equal angle

**3.** Without an undercut

during the drawing operation.

Characteristic lines (Fig. 19) are very important in the product-in group of appearance parts. If characteristic lines are offset from the original position, it will be very obvious from the

The reasons for the offset of characteristic lines are that non-uniform forces exist on both sides of characteristic lines. When the slope of one side is larger than that of the other side, charac‐ teristic lines will be offset to the more oblique side because the material flow rate is slower than that of the other side. However, automotive panels always have irregular, asymmetric, and complex shapes. The method for preventing offset of characteristic lines is to make all slopes from boundaries to characteristic lines as close as possible (Fig. 20). This study sums all normal vectors in the product-in group and calculates the average normal vector, which is the

An undercut is an area that cannot be reached by the upper die and lower die during stamping (Fig. 21), and the die will damage at that area. If an undercut area is unavoidable, cams must

In this study, two novel methods are applied for detecting undercut areas after determining the drawing direction, and the range of detecting is not only product-in group but also productout group because some groups with simple modeling without an undercut are still shaped

Characteristic lines

Drawing direction

be used or follow-up operations are needed to shape the undercut area.

The first proposed method calculates the angle between all normal vectors of point data and the drawing direction. If the angle is 0–85°, the area around the point is safe without an undercut. If the angle is 85–90°, and then the area around the point is close to an undercut, such that one should pay special attention to the draft angle. If the angle exceeds 90°, the area around the point is certainly an undercut, such that this area cannot be shaped during this operation, and other tasks are needed to shape this undercut area (Fig. 22).

**Figure 22.** Detecting undercut by angle

This method can determine whether undercut areas exist, but cannot detect the undercut area accurately (Fig. 23). Section (a) is detected correctly as an undercut, but section (b) is not because the angle between the normal vector and drawing direction is <85°. In fact, section (b) still belongs to the undercut area.

16

**Figure 23.** Fail to detect the undercut area by angle

To overcome the detection problem, this study applies another novel method that detects all undercut areas accurately. All point data are adopted as start points and the drawing direction is adopted as the direction vector to establish a ray. If no points exist at the intersection between the ray and the panel, the area around the point is safe. If points exist at this intersection, the area around the point is an undercut (Fig. 24). Section (b) is also detected as an undercut as section (a) correctly by the intersection between the ray and the panel.

**Type Task Simplified Description**

Flanging(FL) Flange the unformed groups to position

Burring(BUR) Flange the boundary of hole feature

Trimming(TR) Cut the redundant material

Piercing(PI) Cut the hole feature

Fig. 26 Procedure of trimming task

Upper die

Pad

knife Scrap

Fig. 27 Procedure of restriking task

Lower die

(3) Flanging task

(2) Restriking task

**Figure 26.** Procedure of trimming task

**2.** Restriking task

**3.** Flanging task

Drawing(DR) Form the product-in group and some other groups

Restriking(RST) Form the groups whose precision is not enough

The trimming task is separated into two parts—one uses a trimming knife to trim outside the surface of a panel, which is called scrap material, and the other trims the scrap material into smaller pieces with the longest diagonal <500 mm to discharge from punch conveniently (Fig. 26). Based on the laws of physics, when the machining direction of the trimming knife is parallel to the normal vector of a trimmed surface, it will apply the optimal trimming force to make the situation of boundary well. If the angle between the machining direction and the normal

vector is too large, the boundary will produce deckle edges and sharp phenomenon.

Pad Trimming

The contact between the restrike knife and surface is face to face (Fig. 27). The restriking task is necessary when surfaces deform because of springback after drawing and trimming, or the accuracy requirement is high because a surface overlaps another surface of another panel during assembly. If the machining direction of the restriking knife is parallel to the

The contact between the restrike knife and surface is face to face (Fig. 27). The restriking task is necessary when surfaces deform because of springback after drawing and trimming, or the accuracy requirement is high because a surface overlaps another surface of another panel during assembly. If the machining direction of the restriking knife is parallel to the normal

The contact between the flanging knife and surface is a line contact (Fig. 28). The flanging task is necessary when the position between the surface after drawing and the final shape of a panel

Lower die Lower die

material

normal vector of a surface, the optimal restriking force is applied to the surface.

vector of a surface, the optimal restriking force is applied to the surface.

Pad Pad

Restriking

18

The contact between the flanging knife and surface is a line contact (Fig. 28). The flanging task is necessary when the position between the surface after drawing and the final shape of a panel differ, and there are the effect of restriking when flanging to the end. The machining direction of the flanging knife perpendicular to the normal vector of a surface

Lower die

knife

Upper die

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knife Restriking

Forming

Cutting

**1.** Trimming task

**Table 1.** Classification of common tasks

**Figure 24.** Detect the undercut area correctly by intersection of ray

The drawing direction result for a fender (Fig. 25) is determined from the half minimum depth and half equal angle methods.

**Figure 25.** Drawing direction of fender

#### **3.4. Process planning**

The purpose of process planning of automotive panels is to identify the number of operations, the tasks in each operation, and the content of each task. This researching proposes an automatic reasoning procedure based on expert experience and the laws of physics. First, the essential tasks based on the feature recognition and drawing direction results are searched and reasoned and then arranged in each operation. Finally, the most suitable stamping direction of each operation is analyzed, and the machining direction of each task is based on the stamping direction.

20 Common tasks in die layout of automotive panels are drawing, trimming, restriking, flanging, piercing, and burring (Table. 1). These tasks are characterized as follows:


**Table 1.** Classification of common tasks

#### **1.** Trimming task

To overcome the detection problem, this study applies another novel method that detects all undercut areas accurately. All point data are adopted as start points and the drawing direction is adopted as the direction vector to establish a ray. If no points exist at the intersection between the ray and the panel, the area around the point is safe. If points exist at this intersection, the area around the point is an undercut (Fig. 24). Section (b) is also detected as an undercut as

section (a) correctly by the intersection between the ray and the panel.

(b) Und

ercut

The drawing direction result for a fender (Fig. 25) is determined from the half minimum depth

(a) Undercut

20

piercing, and burring (Table. 1). These tasks are characterized as follows:

Common tasks in die layout of automotive panels are drawing, trimming, restriking, flanging,

The purpose of process planning of automotive panels is to identify the number of operations, the tasks in each operation, and the content of each task. This researching proposes an automatic reasoning procedure based on expert experience and the laws of physics. First, the essential tasks based on the feature recognition and drawing direction results are searched and reasoned and then arranged in each operation. Finally, the most suitable stamping direction of each operation is analyzed, and the machining direction of each task is based on the stamping

Drawing direction

**Figure 24.** Detect the undercut area correctly by intersection of ray

and half equal angle methods.

198 Advances in Industrial Design Engineering

**Figure 25.** Drawing direction of fender

**3.4. Process planning**

direction.

The trimming task is separated into two parts—one uses a trimming knife to trim outside the surface of a panel, which is called scrap material, and the other trims the scrap material into smaller pieces with the longest diagonal <500 mm to discharge from punch conveniently (Fig. 26). Based on the laws of physics, when the machining direction of the trimming knife is parallel to the normal vector of a trimmed surface, it will apply the optimal trimming force to make the situation of boundary well. If the angle between the machining direction and the normal vector is too large, the boundary will produce deckle edges and sharp phenomenon.

Fig. 26 Procedure of trimming task **Figure 26.** Procedure of trimming task

Fig. 27 Procedure of restriking task

Lower die

(3) Flanging task

#### (2) Restriking task **2.** Restriking task

The contact between the restrike knife and surface is face to face (Fig. 27). The restriking task is necessary when surfaces deform because of springback after drawing and trimming, or the accuracy requirement is high because a surface overlaps another surface of another panel during assembly. If the machining direction of the restriking knife is parallel to the normal vector of a surface, the optimal restriking force is applied to the surface. The contact between the restrike knife and surface is face to face (Fig. 27). The restriking task is necessary when surfaces deform because of springback after drawing and trimming, or the accuracy requirement is high because a surface overlaps another surface of another panel during assembly. If the machining direction of the restriking knife is parallel to the normal vector of a surface, the optimal restriking force is applied to the surface.

#### **3.** Flanging task

Pad Pad Restriking knife Restriking The contact between the flanging knife and surface is a line contact (Fig. 28). The flanging task is necessary when the position between the surface after drawing and the final shape of a panel

> Lower die

knife

18

The contact between the flanging knife and surface is a line contact (Fig. 28). The flanging task is necessary when the position between the surface after drawing and the final shape of a panel differ, and there are the effect of restriking when flanging to the end. The machining direction of the flanging knife perpendicular to the normal vector of a surface (2) Restriking task

Fig. 26 Procedure of trimming task

Upper die

Pad

knife Scrap

The contact between the restrike knife and surface is face to face (Fig. 27). The restriking task is necessary when surfaces deform because of springback after drawing and trimming, or the accuracy requirement is high because a surface overlaps another surface of another

Lower die Lower die

material

Pad Trimming

Upper die

normal vector of a surface, the optimal restriking force is applied to the surface.

**Figure 27.** Procedure of restriking task

Fig. 27 Procedure of restriking task

differ, and there are the effect of restriking when flanging to the end. The machining direction of the flanging knife perpendicular to the normal vector of a surface will apply the optimal flanging force for a surface. will apply the optimal flanging force for a surface. (3) Flanging task The contact between the flanging knife and surface is a line contact (Fig. 28). The flanging task is necessary when the position between the surface after drawing and the final

shape of a panel differ, and there are the effect of restriking when flanging to the end. The

**Figure 28.** Procedure of flanging task

Fig. 28 Procedure of flanging task

(4) Piercing task **4.** Piercing task

Each hole feature requires a piercing task (Fig. 29). Hole features can be classified as basic holes, lock holes, and enlarge holes based on their different functions during assembly. A basic hole is for locating the panel, and a lock hole is for locking panels. The accuracy requirement of both holes is high. A enlarged hole whose accuracy requirement is low for passing through the machining tools during assembly. The piercing principle is similar to that of trimming. The machining direction of a drill parallel to the normal vector of a hole feature will also make the situation of boundary of hole well, and the allowed angle is based Each hole feature requires a piercing task (Fig. 29). Hole features can be classified as basic holes, lock holes, and enlarge holes based on their different functions during assembly. A basic hole is for locating the panel, and a lock hole is for locking panels. The accuracy requirement of both holes is high. A enlarged hole whose accuracy requirement is low for passing through the machining tools during assembly. The piercing principle is similar to that of trimming. The machining direction of a drill parallel to the normal vector of a hole feature will also make the situation of boundary of hole well, and the allowed angle is based on the size of the hole feature.

on the size of the hole feature. **5.** Burring task

Pad Pad The burring task is necessary when bending shapes exist at the boundary of a hole feature after piercing. The burring procedure resembles that of flanging (Fig. 30). The best machining direction is the same as the piercing direction.

This study now introduces the relationships among all tasks and specification of planning.

Lower die

If trimming is performed after restriking and flanging, residual stress will cause severe

This study now introduces the relationships among all tasks and specification of planning.

19

The burring task is necessary when bending shapes exist at the boundary of a hole feature after piercing. The burring procedure resembles that of flanging (Fig. 30). The best

Pad Pad

Pad Pad

Lower die

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Lower die

Each hole feature requires a piercing task (Fig. 29). Hole features can be classified as basic holes, lock holes, and enlarge holes based on their different functions during assembly. A basic hole is for locating the panel, and a lock hole is for locking panels. The accuracy requirement of both holes is high. A enlarged hole whose accuracy requirement is low for passing through the machining tools during assembly. The piercing principle is similar to that of trimming. The machining direction of a drill parallel to the normal vector of a hole feature will also make the situation of boundary of hole well, and the allowed angle is based

Pad Pad

Lower die

Flanging knife

As the number of pieces of scrap metal is typically excessive, they could not be discharged from the punch easily, and the difficulty in die design will increase; however, if trimming tasks are arranged in a backward order, then the restriking and flanging tasks will also be arranged in a backward order, such that the number of operations will increase, thereby increasing

(2) As many trimming tasks as possible are arranged in the same operation

If trimming is performed after restriking and flanging, residual stress will cause severe

As the number of pieces of scrap metal is typically excessive, they could not be discharged from the punch easily, and the difficulty in die design will increase; however, if trimming tasks are arranged in a backward order, then the restriking and flanging tasks will also be arranged in a backward order, such that the number of operations will increase, thereby

Positional errors always exist in each piercing task. If piercing tasks are conducted in different operations, and then the error among all holes will likely increase because offset directions differ. Thus, arranging piercing tasks in the same operation can reduce error because all offset

When restriking or flanging, the position, shape, and size of a pierced hole will change; thus, piercing tasks are usually arranged after restriking and flanging. However, enlarge holes whose accuracy is low are acceptable before restriking and flanging to prevent generating an

20

Positional errors always exist in each piercing task. If piercing tasks are conducted in different operations, and then the error among all holes will likely increase because offset

excessive amount of scrap material from holes, which increases discharge difficulty.

(3) As many piercing tasks as possible are arranged in the same operation

**2.** As many trimming tasks as possible are arranged in the same operation

Lower die

(1) Trimming is arranged before restriking and flanging

Lower die

machining direction is the same as the piercing direction.

will apply the optimal flanging force for a surface.

Flanging knife

Fig. 28 Procedure of flanging task

Lower die

on the size of the hole feature.

Punch

Punch

(5) Burring task

**Figure 29.** Procedure of piercing task

Fig. 29 Procedure of piercing task

Fig. 30 Procedure of burring task

deformation after trimming.

increasing production cost.

(4) Piercing task

**3.** As many piercing tasks as possible are arranged in the same operation

**4.** Piercing is arranged after restriking and flanging

**5.** Cutting tasks are not arranged with upward flanging tasks

deformation after trimming.

**Figure 30.** Procedure of burring task

production cost.

directions are the same.

19

Lower Punch **1.** Trimming is arranged before restriking and flanging

die

Fig. 29 Procedure of piercing task

Lower die

Flanging knife

after piercing. The burring procedure resembles that of flanging (Fig. 30). The best

Each hole feature requires a piercing task (Fig. 29). Hole features can be classified as basic holes, lock holes, and enlarge holes based on their different functions during assembly. A basic hole is for locating the panel, and a lock hole is for locking panels. The accuracy requirement of both holes is high. A enlarged hole whose accuracy requirement is low for passing through the machining tools during assembly. The piercing principle is similar to that of trimming. The machining direction of a drill parallel to the normal vector of a hole

Pad Pad

will apply the optimal flanging force for a surface.

Flanging knife

Fig. 28 Procedure of flanging task

Lower die

on the size of the hole feature.

Fig. 29 Procedure of piercing task

(4) Piercing task

**Figure 29.** Procedure of piercing task machining direction is the same as the piercing direction.

differ, and there are the effect of restriking when flanging to the end. The machining direction of the flanging knife perpendicular to the normal vector of a surface will apply the optimal

The contact between the flanging knife and surface is a line contact (Fig. 28). The flanging task is necessary when the position between the surface after drawing and the final shape of a panel differ, and there are the effect of restriking when flanging to the end. The machining direction of the flanging knife perpendicular to the normal vector of a surface

The contact between the restrike knife and surface is face to face (Fig. 27). The restriking task is necessary when surfaces deform because of springback after drawing and trimming, or the accuracy requirement is high because a surface overlaps another surface of another panel during assembly. If the machining direction of the restriking knife is parallel to the

Lower die Lower die

material

Pad Trimming

normal vector of a surface, the optimal restriking force is applied to the surface.

Pad Pad

Restriking

18

Pad Pad

Each hole feature requires a piercing task (Fig. 29). Hole features can be classified as basic holes, lock holes, and enlarge holes based on their different functions during assembly. A basic hole is for locating the panel, and a lock hole is for locking panels. The accuracy requirement of both holes is high. A enlarged hole whose accuracy requirement is low for passing through the machining tools during assembly. The piercing principle is similar to that of trimming. The machining direction of a drill parallel to the normal vector of a hole feature will also make the situation of boundary of hole well, and the allowed angle is based

Each hole feature requires a piercing task (Fig. 29). Hole features can be classified as basic holes, lock holes, and enlarge holes based on their different functions during assembly. A basic hole is for locating the panel, and a lock hole is for locking panels. The accuracy requirement of both holes is high. A enlarged hole whose accuracy requirement is low for passing through the machining tools during assembly. The piercing principle is similar to that of trimming. The machining direction of a drill parallel to the normal vector of a hole feature will also make the situation of boundary of hole well, and the allowed angle is based on the size of the hole feature.

The burring task is necessary when bending shapes exist at the boundary of a hole feature after piercing. The burring procedure resembles that of flanging (Fig. 30). The best machining

This study now introduces the relationships among all tasks and specification of planning.

Lower die

Lower die

knife

Upper die

knife Restriking

Flanging knife

19

Pad Pad

Lower die

flanging force for a surface.

(3) Flanging task

**Figure 27.** Procedure of restriking task

will apply the optimal flanging force for a surface.

Fig. 27 Procedure of restriking task

Lower die

Fig. 26 Procedure of trimming task

Upper die

Pad

knife Scrap

(2) Restriking task

200 Advances in Industrial Design Engineering

Flanging knife

Fig. 28 Procedure of flanging task

Lower die

on the size of the hole feature.

direction is the same as the piercing direction.

Punch

Fig. 29 Procedure of piercing task

**1.** Trimming is arranged before restriking and flanging

Lower die

(4) Piercing task

**Figure 28.** Procedure of flanging task

**4.** Piercing task

**5.** Burring task

Fig. 30 Procedure of burring task **Figure 30.** Procedure of burring task

If trimming is performed after restriking and flanging, residual stress will cause severe deformation after trimming. This study now introduces the relationships among all tasks and specification of planning.

**2.** As many trimming tasks as possible are arranged in the same operation (1) Trimming is arranged before restriking and flanging

As the number of pieces of scrap metal is typically excessive, they could not be discharged from the punch easily, and the difficulty in die design will increase; however, if trimming tasks are arranged in a backward order, then the restriking and flanging tasks will also be arranged in a backward order, such that the number of operations will increase, thereby increasing production cost. If trimming is performed after restriking and flanging, residual stress will cause severe deformation after trimming. (2) As many trimming tasks as possible are arranged in the same operation As the number of pieces of scrap metal is typically excessive, they could not be discharged

**3.** As many piercing tasks as possible are arranged in the same operation from the punch easily, and the difficulty in die design will increase; however, if trimming

Positional errors always exist in each piercing task. If piercing tasks are conducted in different operations, and then the error among all holes will likely increase because offset directions differ. Thus, arranging piercing tasks in the same operation can reduce error because all offset directions are the same. tasks are arranged in a backward order, then the restriking and flanging tasks will also be arranged in a backward order, such that the number of operations will increase, thereby increasing production cost.

**4.** Piercing is arranged after restriking and flanging (3) As many piercing tasks as possible are arranged in the same operation Positional errors always exist in each piercing task. If piercing tasks are conducted in

When restriking or flanging, the position, shape, and size of a pierced hole will change; thus, piercing tasks are usually arranged after restriking and flanging. However, enlarge holes whose accuracy is low are acceptable before restriking and flanging to prevent generating an excessive amount of scrap material from holes, which increases discharge difficulty. 20 different operations, and then the error among all holes will likely increase because offset

**5.** Cutting tasks are not arranged with upward flanging tasks

If upward flanging tasks exist, the pad is mounted on the lower die. However, it is relatively unstable during production, such that arranging cutting tasks, such as trimming and piercing, will increase the magnitude of errors.

**6.** Burring is arranged after piercing

A hole feature with a bending boundary requires two tasks. Although a new task combining piercing and burring exists, it is used rarely as it is associated with increased cost and a short service life; thus, it is not considered by this study.

**7.** Determining the machining direction of each task

Using cams increases production cost, such that using the stamping direction as the machining direction is best. Additionally, if difficulty is associated with the stamping direction, cams can be used to change the machining direction. Cams are generally classified as suspension cams and non-suspension cams (Fig. 31). The knife of the former is mounted on the upper die, increasing cost and reducing service life. Thus, this study first considers non-suspension cams. However, if problems in discharging scrap material or feeding the blank exist, then suspension cams are used to increase the space of the lower die.

22

Because drawing and trimming results affect the assessment of forming tasks, this study arranges drawing and trimming operations first. The first operation is only for the drawing task, such that other tasks are not arranged. In addition to trimming tasks around the panel, this study also considers all piercing tasks of enlarge holes of the product-in group in the second operation, and searches for the stamping direction that maximizes the number of piercing tasks without cams. If any piercing task of an enlarge hole cannot be conducted in the stamping direction, it should be arranged in follow-up operations because cams will

Hole feature classification is based on the product drawing from a car company. However, this study simplifies this classification to a enlarge hole with a lower accuracy when the boundary length exceeds 50 mm because the area of enlarge holes is much larger than that

Hole feature classification is based on the product drawing from a car company. However, this study simplifies this classification to a enlarge hole with a lower accuracy when the boundary length exceeds 50 mm because the area of enlarge holes is much larger than that of

Because drawing and trimming results affect the assessment of forming tasks, this study arranges drawing and trimming operations first. The first operation is only for the drawing task, such that other tasks are not arranged. In addition to trimming tasks around the panel, this study also considers all piercing tasks of enlarge holes of the product-in group in the second operation, and searches for the stamping direction that maximizes the number of piercing tasks without cams. If any piercing task of an enlarge hole cannot be conducted in the stamping direction, it should be arranged in follow-up operations because cams will interfere

If some groups cannot be shaped while drawing (e.g., undercuts exist in the drawing direction or the draft angle is too small), this study designs the die face with a shape that can be drawn successfully and the follow-up flanging task is used to shape the groups. Even when groups can be drawn successfully, they cannot be trimmed in the trimming direction because of the normal vector of the trim line, and they still need a flanging task by designing the die face with

the die face with a shape that can be drawn and trimmed successfully (Fig. 34).

Drawing direction

If some groups cannot be shaped while drawing (e.g., undercuts exist in the drawing direction or the draft angle is too small), this study designs the die face with a shape that can be drawn successfully and the follow-up flanging task is used to shape the groups. Even when groups can be drawn successfully, they cannot be trimmed in the trimming direction because of the normal vector of the trim line, and they still need a flanging task by designing

23

If a group can be drawn and trimmed successfully, restriking tasks are only needed to increase accuracy. The complexity of modeling of a group affects the forming result. Applying a flanging task to groups whose modeling is complex will result in cracking or wrinkling easily.

Product

(b) Draft angle

Die face

Trimming direction

Die face

Product

(c) Cannot be trimmed

Normal vector of trim line

Fig. 31 Suspension cams and non-suspension cams

Cam Base

still be confirmed according to the panel models.

Knife

Fig. 32 The sequence among all tasks

**Figure 33.** Reasoning whether the hole feature requires a burring task

a shape that can be drawn and trimmed successfully (Fig. 34).

Die face

Fig. 34 Some reasons for flanging task

Product

(a) Undercut

other holes.

with trimming knives.

Drawing direction

**Figure 34.** Some reasons for flanging task

interfere with trimming knives.

of other holes.

Based on the specifications described above, this study summarizes the sequence of all tasks (Fig. 32). However, the stamping direction and detailed tasks in each operation must

Suspension cam Non-suspension cam

Driver

Knife

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Driver

Cam Base

Before arranging tasks into operations, one must determine which tasks are needed. Piercing and burring tasks are easier than other tasks to reason. Each hole feature needs a piercing task, and when the normal vector of a hole is not parallel to the normal vector of

Trimming Piercing Restriking and Flanging Drawing Burring

of hole Normal vector of

boundary

the boundary, the hole feature also requires a burring task (Fig. 33).

Fig. 33 Reasoning whether the hole feature requires a burring task

Normal vector

**Figure 31.** Suspension cams and non-suspension cams Fig. 31 Suspension cams and non-suspension cams

Fig. 32 The sequence among all tasks

Based on the specifications described above, this study summarizes the sequence of all tasks (Fig. 32). However, the stamping direction and detailed tasks in each operation must still be confirmed according to the panel models. Based on the specifications described above, this study summarizes the sequence of all tasks (Fig. 32). However, the stamping direction and detailed tasks in each operation must still be confirmed according to the panel models.

**Figure 32.** The sequence among all tasks

Before arranging tasks into operations, one must determine which tasks are needed. Piercing and burring tasks are easier than other tasks to reason. Each hole feature needs a piercing task, and when the normal vector of a hole is not parallel to the normal vector of the boundary, the hole feature also requires a burring task (Fig. 33). Before arranging tasks into operations, one must determine which tasks are needed. Piercing and burring tasks are easier than other tasks to reason. Each hole feature needs a piercing task, and when the normal vector of a hole is not parallel to the normal vector of the boundary, the hole feature also requires a burring task (Fig. 33).

of hole Normal vector of

boundary

28

Fig. 33 Reasoning whether the hole feature requires a burring task

Normal vector

Knife

Driver

Cam Base

Before arranging tasks into operations, one must determine which tasks are needed. Piercing and burring tasks are easier than other tasks to reason. Each hole feature needs a

Trimming Piercing Restriking and Flanging Drawing Burring

the boundary, the hole feature also requires a burring task (Fig. 33).

Based on the specifications described above, this study summarizes the sequence of all tasks (Fig. 32). However, the stamping direction and detailed tasks in each operation must

Suspension cam Non-suspension cam

Driver

Fig. 33 Reasoning whether the hole feature requires a burring task **Figure 33.** Reasoning whether the hole feature requires a burring task boundary length exceeds 50 mm because the area of enlarge holes is much larger than that

of other holes.

Fig. 31 Suspension cams and non-suspension cams

Cam Base

still be confirmed according to the panel models.

Knife

Fig. 32 The sequence among all tasks

If upward flanging tasks exist, the pad is mounted on the lower die. However, it is relatively unstable during production, such that arranging cutting tasks, such as trimming and piercing,

A hole feature with a bending boundary requires two tasks. Although a new task combining piercing and burring exists, it is used rarely as it is associated with increased cost and a short

Using cams increases production cost, such that using the stamping direction as the machining direction is best. Additionally, if difficulty is associated with the stamping direction, cams can be used to change the machining direction. Cams are generally classified as suspension cams and non-suspension cams (Fig. 31). The knife of the former is mounted on the upper die, increasing cost and reducing service life. Thus, this study first considers non-suspension cams. However, if problems in discharging scrap material or feeding the blank exist, then suspension

will increase the magnitude of errors. **6.** Burring is arranged after piercing

202 Advances in Industrial Design Engineering

service life; thus, it is not considered by this study.

**7.** Determining the machining direction of each task

cams are used to increase the space of the lower die.

Cam

Base

Cam Base

Knife

Knife

Suspensio

still be confirmed according to the panel models.

Fig. 32 The sequence among all tasks

hole feature also requires a burring task (Fig. 33).

**Figure 31.** Suspension cams and non-suspension cams

confirmed according to the panel models.

**Figure 32.** The sequence among all tasks

n cam

Fig. 31 Suspension cams and non-suspension cams

Drive

Driver

r

Based on the specifications described above, this study summarizes the sequence of all tasks (Fig. 32). However, the stamping direction and detailed tasks in each operation must still be

Suspension cam Non-suspension cam

Before arranging tasks into operations, one must determine which tasks are needed. Piercing and burring tasks are easier than other tasks to reason. Each hole feature needs a piercing task, and when the normal vector of a hole is not parallel to the normal vector of

Before arranging tasks into operations, one must determine which tasks are needed. Piercing and burring tasks are easier than other tasks to reason. Each hole feature needs a piercing task, and when the normal vector of a hole is not parallel to the normal vector of the boundary, the

Trimming Piercing Restriking and Flanging Drawing Burring

of hole Normal vector of

boundary

the boundary, the hole feature also requires a burring task (Fig. 33).

Fig. 33 Reasoning whether the hole feature requires a burring task

Normal vector

Based on the specifications described above, this study summarizes the sequence of all tasks (Fig. 32). However, the stamping direction and detailed tasks in each operation must

N

on-suspension

Cam Base

Cam Base

Kn

nife

Knife

cam

Driver

Driver

28

22

22 Hole feature classification is based on the product drawing from a car company. However, this study simplifies this classification to a enlarge hole with a lower accuracy when the boundary length exceeds 50 mm because the area of enlarge holes is much larger than that of other holes. Because drawing and trimming results affect the assessment of forming tasks, this study arranges drawing and trimming operations first. The first operation is only for the drawing

Because drawing and trimming results affect the assessment of forming tasks, this study arranges drawing and trimming operations first. The first operation is only for the drawing task, such that other tasks are not arranged. In addition to trimming tasks around the panel, this study also considers all piercing tasks of enlarge holes of the product-in group in the second operation, and searches for the stamping direction that maximizes the number of piercing tasks without cams. If any piercing task of an enlarge hole cannot be conducted in the stamping direction, it should be arranged in follow-up operations because cams will interfere with trimming knives. task, such that other tasks are not arranged. In addition to trimming tasks around the panel, this study also considers all piercing tasks of enlarge holes of the product-in group in the second operation, and searches for the stamping direction that maximizes the number of piercing tasks without cams. If any piercing task of an enlarge hole cannot be conducted in the stamping direction, it should be arranged in follow-up operations because cams will interfere with trimming knives.

If some groups cannot be shaped while drawing (e.g., undercuts exist in the drawing direction or the draft angle is too small), this study designs the die face with a shape that can be drawn successfully and the follow-up flanging task is used to shape the groups. Even when groups can be drawn successfully, they cannot be trimmed in the trimming direction because of the normal vector of the trim line, and they still need a flanging task by designing the die face with a shape that can be drawn and trimmed successfully (Fig. 34). If some groups cannot be shaped while drawing (e.g., undercuts exist in the drawing direction or the draft angle is too small), this study designs the die face with a shape that can be drawn successfully and the follow-up flanging task is used to shape the groups. Even when groups can be drawn successfully, they cannot be trimmed in the trimming direction because of the normal vector of the trim line, and they still need a flanging task by designing the die face with a shape that can be drawn and trimmed successfully (Fig. 34).

Fig. 34 Some reasons for flanging task **Figure 34.** Some reasons for flanging task

23 If a group can be drawn and trimmed successfully, restriking tasks are only needed to increase accuracy. The complexity of modeling of a group affects the forming result. Applying a flanging task to groups whose modeling is complex will result in cracking or wrinkling easily. The restriking task result is better than that of flanging task because most modeling is done while drawing. modeling is done while drawing.

If a group can be drawn and trimmed successfully, restriking tasks are only needed to

Applying a flanging task to groups whose modeling is complex will result in cracking or wrinkling easily. The restriking task result is better than that of flanging task because most

When a group cannot be drawn or trimmed successfully and modeling is complex, the group is shaped by two forming tasks. A flanging task is first used to bend the die face into a transitional shape and the restriking task is then used to form the transitional shape to product shape (Fig. 35). When a group cannot be drawn or trimmed successfully and modeling is complex, the group is shaped by two forming tasks. A flanging task is first used to bend the die face into a transitional shape and the restriking task is then used to form the transitional shape to product shape (Fig. 35).

Fig. 35 Two forming tasks: restriking after flanging **Figure 35.** Two forming tasks: restriking after flanging

After drawing and trimming operations, each group requires at least one forming task, such that all remaining piercing tasks are not considered currently, but burring tasks, whose hole features are already pierced, are arranged. The best stamping direction of the forming After drawing and trimming operations, each group requires at least one forming task, such that all remaining piercing tasks are not considered currently, but burring tasks, whose hole features are already pierced, are arranged. The best stamping direction of the forming operation minimizes the number of cams needed and has the best forming effect.

operation minimizes the number of cams needed and has the best forming effect. If other second forming tasks exist, they should be arranged after the forming operation. If all forming tasks are arranged, then one must consider the remaining tasks of the hole If other second forming tasks exist, they should be arranged after the forming operation. If all forming tasks are arranged, then one must consider the remaining tasks of the hole feature according to the order of piercing and burring tasks, and the best stamping direction for followup operations is the same as that in the forming operation.

feature according to the order of piercing and burring tasks, and the best stamping direction for follow-up operations is the same as that in the forming operation. The sample fender requires five operations in the result of process planning. First two operations are for drawing and trimming, and suitable standard cams are chosen or the size of homemade cams is reasoned based on features (Fig. 36).

24 The operating time of this example is taken about twenty minutes, and it will change with the file size and panel shape. The actual cost time except die face design from the experience engineers on the factory is taken about three to five days.

structure parts is strength and rigidity, not appearance, such that the offset of characteristic lines is not important. Thus, the equal angle principle is not used to search the drawing

and cam-pierc

Furthermore, feature recognition procedure differs from the appearance parts and structure parts because structure parts do not have the constant modeling rules that appearance parts have. For instance, the area of the product-in group may not be the largest; the main bend group may not constitute a closed-loop; corner surfaces for separating the main bend group into smaller pieces may not exist; and the single surface, even when its curvature exceeds a critical value, should be classified as a flat surface. Thus, the automatic recognition procedure

32

Although this system supports manual feature recognition, too much time is needed to click on all surfaces. Thus, this study applies a novel procedure that uses both automatic and manual operations for feature recognition for structure parts. Users must establish only the framework

direction of structure parts.

**Figure 37.** Sample of structure parts

for appearance parts does not apply to structure parts.

4th operation: cam-restriking

**Figure 36.** Process planning result for fender

Home

made cam

3rd operation: cam-rest

flanging and triking

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http://dx.doi.org/10.5772/52010

205

th operation: cam-piercing

cing 5
