Visual design system for cooling systems is designed to generate, edit, and optimize cooling systems. Each step centers around cooling circuit, requiring a unified representation method and a standardized data model to facilitate solid model generation, data access, and modification.
Common cooling channel types include linear, spiral, baffle, and jet pipe, as shown in Figure 1.

 

Figure 1 Cooling Channel Types
Straight cooling channels are the simplest and most frequently used cooling method because they are easy to design and process, making them suitable for general cooling of most products. Spiral cooling channels are generally used for slender, small-sized products. Channel spirals around product, but this type of cooling channel requires specialized processing and has limited applicability. They are primarily used for small injection molding products, such as ballpoint pen refills. For injection molding products with deep cavities, conventional straight cooling channels can damage cavity wall, reducing product's surface quality. In these cases, baffle cooling channels and jet cooling channels, which are also drilled, are more suitable. In baffle cooling channels, a baffle divides channel into two. Coolant enters from one side, bypasses baffle, and exits from the other side. In jet cooling channels, coolant enters through nozzle and exits through cavity formed between nozzle's outer surface and drilled hole. Both types of cooling channels effectively remove heat. Conformal cooling channels have been a hot topic of research in recent years. However, their design and manufacturing are unique, have not been widely adopted by enterprises, so they are not discussed here.
Although cooling channels come in various forms, their structural characteristics can all be abstractly represented by channel's centerline. Centerline consists of a starting point (A), a line segment, and an ending point (B), as shown in Figure 1. For linear, baffle, jet-tube cooling channels, this can be abstracted as centerline of channel cylinder. Spiral cooling structures can be abstracted as centerline of spiral. Channel type and parameters can be attached as attributes to centerline. Based on object-oriented programming principles, these cooling channels are modeled using a UML class diagram, as shown in Figure 2. Figure 3 shows a schematic diagram of corresponding dimensional parameters. Table 1 provides an explanation of fields in Figures 2 and 3.

 

Figure 2 UML Class Diagram for Cooling Channel Modeling

 

Figure 3 Schematic Diagram of Cooling Channel Dimensional Parameters

 

Table 1 Description of Cooling Channel Modeling Parameters

Most CAD software programs have a preview function. There are two main ways to implement this feature in secondary development programs: solid preview and wireframe preview. Solid preview uses modeling-related APIs to create entities. During design process, entities can be edited in real time to achieve a real-time preview, as shown in Figure 4(a). While this method offers good preview results, it involves creating, deleting, and modifying 3D entities, resulting in slow processing speed and prone to lag in complex mold structures, impacting user experience. Using NX Curve object, a wireframe model of cooling circuit (Figure 4(b)) is created, enabling real-time preview of cooling circuit during design and editing process.
Figure 4 Cooling Circuit Preview
NX Curve is a curve-type object in NX, including lines, conic curves, and splines. It is fast to create and destroy, consumes minimal resources, and is suitable for creating wireframe models that change in real time. A wireframe composed of two arcs and 16 straight lines can be used as a preview for a water channel. When water channel is modified, previous preview wireframe is deleted and a new one is created. Due to rapid creation and destruction of wireframes, a "real-time" preview of water channel can be achieved. Same applies to other wireframe models that require real-time preview.

A model with a unified representation of cooling circuit structure has been established. Initial design process for cooling circuit can be divided into three steps: centerline - parameters - circuit entity. Automatically generating cooling circuit entities based on cooling circuit parameters is easily accomplished through automated programs. Therefore, how to quickly design cooling circuit centerline is a key step in achieving rapid cooling circuit design.

Drawing cooling circuit centerlines in NX software can be done using sketching tool. However, until sketch is completed, water channel preview and interference preview cannot be dynamically generated based on currently drawn lines. Therefore, other centerline generation methods are required. NX Open.Line is a simple straight line object in NX. It can be generated through API function "theUfSession.Curve.CreateLine(ref UFCurve.Line line_coords, out Tag line)". Function passes in coordinates of two end points of line specified in line_coords and returns unique tag of generated line (Tag is identity of NX object in NX software. Most APIs obtain and operate NX object itself through tag value). "Manipulator" is an interactive control in NX that specifies coordinates and orientations. Position and coordinate system orientation of control in three-dimensional space can be adjusted by clicking, dragging, rotating, etc. Based on above two elements, dynamic and fast drawing of cooling water channels can be achieved. Algorithm flow is shown in Figure 5. Specific steps are as follows.

 

Figure 5 Dynamic drawing of water channel algorithm flow

(1) Prepare a linked list lineList to store drawn straight lines. S and E represent starting point and end point of last straight line lineList.Last (hereinafter referred to as last) in linked list lineList, and O represents origin of control manipulator (hereinafter referred to as manip).

(2) Select a starting point as starting point of cooling loop, set E equal to point selected at this time, and set origin coordinate of manip O = E.
(3) Drag manip control.
(4) Create a line EO with point E and origin O of manip at this time as end points of line, and put line EO into linked list lineList.
(5) Continue dragging manip to determine whether vector is parallel to . If not (see Figure 6 (a)), return to step 4.
(6) If vector is parallel to (see Figure 6 (b)), modify end point E of last line in linked list lineList and set E equal to origin O of current manip.
(7) If drawing of all center lines of cooling loop has been completed at this time, end process and obtain center line set lineList of cooling loop. Otherwise, return to step 5.

Dynamic water channel drawing is suitable for quickly drawing complex cooling circuits. However, in actual design, many similar cooling circuit designs are used repeatedly. Manually drawing these circuits each time would significantly reduce efficiency. Therefore, by extracting centerlines of common cooling circuits as templates, a library of commonly used cooling circuit templates can be established. When needed, corresponding templates can be directly imported. Template dimensions and parameters can then be adjusted according to actual design requirements to achieve rapid design of common cooling circuits. This not only improves design efficiency but also ensures standardization and consistency in cooling circuit design.
Cooling circuit template database consists of a centerline template file library and a dimensional control parameter table. Template file library stores the .prt files of cooling circuit centerlines and corresponding template schematics. Dimensional control parameter table stores key dimensional parameter names and their adjustable ranges associated with each template.
Cooling circuit shown in Figure 7(a) is used as an example to illustrate process of template creation, storage, and use. First, extract cooling circuit centerline and save it to a new .prt file (see Figure 7(b)). Dimensions are then assigned to key locations along centerline (see Figure 7(c)). Using NX parametric modeling technology, key dimension variables are defined and associated with dimension variables (see Figure 7(d)). Parameter names are recorded and saved in database's dimension control parameter table. During design, designer selects a template based on product requirements, sets dimensional parameters, and imports template at designated location to complete initial design of cooling circuit centerline.
In addition, designers can export custom cooling circuit designs as templates and store them in system's template database for quick access in subsequent projects. This template storage mechanism not only improves design efficiency but also enables standardized management of commonly used cooling circuit configurations. By establishing a template library, designers can easily access historical designs, avoiding duplication of effort and ensuring consistent and standardized cooling circuit design across projects.

Cooling system design requires repeated revisions and optimizations. After completing cooling circuit design based on centerline basic model, if user needs to modify cooling circuit, using NX Modify Line tool to modify centerline will not automatically modify corresponding cooling circuit entity. Furthermore, associated cooling circuit structures, such as extensions, drill bits, and other connected cooling circuits, will not automatically modify associated cooling circuit entities. Root cause is that during cooling circuit design, topology is stored in corresponding data structure in code. However, after design is completed, cooling circuit information in code is not saved to model file. While using additional files to store cooling circuit information can solve this problem, it adds additional data files to CAD model file, making it difficult for designers to migrate and manage it, and also affects corporate data file standards. Therefore, it is necessary to find other solutions to preserve circuit topology information and associate centerlines with circuit entities.
NX's Group Association technology provides a foundation for solving this problem. An NX Group is a special NX object that can store tag values of multiple other NX objects. Essentially, it's a linked list and can be nested. This not only allows for association of multiple NX objects, but also clearly expresses dependencies between complex sets of objects. Group objects are stored directly in the .prt file and persist when software is closed. Therefore, placing a cooling circuit's centerline in an NX Group object allows for association between circuit centerlines, and placing a cooling circuit's entities in an NX Group object allows for association between cooling circuit entities. Ordered nature of linked list ensures storage of cooling circuit topology information. Placing centerline Group and circuit entity Group in another NX Group object allows for association between cooling circuit centerlines and entities. Placing all cooling circuit Group objects in a single NX Group object allows for association of the entire cooling system information. This dependency relationship is shown in Figure 8.

 

Figure 8: Cooling System Group Association Organization Structure

Based on this association technique, color, size, attributes of cooling circuits can be easily modified and updated uniformly. This is achieved by leveraging parametric modeling capabilities of NX software and will not be detailed here. Thanks to linked list nature of NX Group, operations such as adding, inserting, and deleting channels within cooling circuits can be easily performed while maintaining integrity of cooling circuit topology.
Editing a cooling circuit layout typically involves moving the entire circuit or a specific channel. Moving the entire circuit does not involve any interaction with other components and can be accomplished using NX's native move editing functionality. However, editing a specific channel requires associative editing of its connected channels, ensuring integrity of circuit's topology.
Based on centerline model, editing a cooling circuit layout can be translated into editing centerline position. Editing a cooling channel centerline requires corresponding modifications to centerlines of its connected channels. When a channel's position coordinates change, following must be ensured for other channels: 1) circuit connectivity is maintained; 2) channel direction remains unchanged (generally, processing direction of a channel is determined during initial design and cannot be arbitrarily modified). Based on above, editing centerline position of a waterway can be converted into extending or contracting an endpoint of that waterway or its adjacent waterways. Reasoning is as follows: for centerline l1, editing its length is equivalent to extending or contracting its two endpoints (see Figure 9(a)); editing position of l1 can be converted into extending or contracting endpoints connected to l2, because direction of l2 must remain unchanged when position of l1 changes (see Figure 9(b)).
Therefore, for more complex cooling circuits, editing a section of a waterway will cause corresponding modifications to other waterways in circuit. For example, in cooling circuit in Figure 10(a), extending endpoint E0 of waterway l0 to E0' results in resulting cooling circuit shown in Figure 10(b).

 

Figure 10 Cooling Circuit Associative Editing
This study implements a general centerline associative editing algorithm. Using cooling circuit shown in Figure 10 as an example, detailed steps of algorithm are described below.
(1) Select water channel centerline l0 to be edited, and obtain lineList of all centerlines of cooling circuit where l0 is located through NX Group.
(2) Traverse lineList from edited endpoint, search for lines affected by edit, and store them in editList for subsequent processing. Search steps are: skip line l1 on edited endpoint side adjacent to l0, and traverse downward until traversed line li is coplanar with l0, or li is last line at this end of linked list lineList, then stop traversing. At this time, l1, l2, ...li are lines affected by edit. In Figure 10, starting from l0, skipping l1, traversing begins, traversing until l4 is the first line coplanar with l0, and stopping traversing. Obtained lines l1, l2, l3 and l4 are lines to be processed and stored in editList set.
(3) Update position of lines in editList.
For n lines in editList, it is necessary to determine their updated positions, that is, it is necessary to calculate coordinates of two end points of each line after update. Since n lines are connected end to end, it is only necessary to calculate coordinates of (n+1) points.
(1) First calculate coordinates of two points E0' and Sn' (since line segments are connected end to end, coordinates of common endpoints of adjacent line segments are same, Sn' is En-1', but for convenience, a point is only marked with one letter in figure, same below). Relationship between l0 and ln is shown in two cases in Figure 11. Coordinate calculation formula of E0' is:
 
Figure 11 Relationship between l0 and ln
Coordinate calculation formula of Sn' is:
 
Among them, value of p corresponds to two cases in Figure 11, that is, when inflection point directions of E0 and Sn are same, p takes -1, and when they are different, p takes 1. Inflection point direction can be uniformly described by multiplying two vectors, that is:
 

(2) Calculate coordinates of remaining points. Starting from E0, remaining points are named E1, E2…En-2 in order, and updated positions are E1', E2'…En-2'. To ensure that direction of cooling circuit remains unchanged, that is, corresponding center lines before and after editing should remain parallel, we can get:

 

Substitute coordinate points into equation (4) and solve equation to obtain coordinates of points E1', E2'…En-2'. Update position of water channel center line according to new coordinate values.
(4) Regenerate new water channel entity and auxiliary structure based on new water channel center line and water channel properties, and complete Group association structure of new water channel.

Traditional cooling system interference check is generally performed after cooling circuit design is completed. Interference check tool provided by CAD software is used to check whether there is interference between cooling circuit entities, between circuit entities and other structures of injection mold, such as cavity plate and push rod hole. However, actual cooling system not only requires avoiding such errors as interference, but also requires a certain safety distance to be reserved between various structural holes to avoid generation of too thin walls. Figure 12 shows positional relationship between cooling circuit and other mold structures. Interference (Figure 12(a)) and spacing less than safe distance (Figure 12(b)) are both situations that should be avoided.

 

Figure 12 Positional relationship between cooling channels and other mold structures
(a) Interference (b) Less than the safe distance (c) Greater than the safe distance
A real-time interference detection algorithm based on ray tracing method provided by NX software has been implemented. This algorithm offers high accuracy and efficiency. When designing and editing cooling systems using this system, it can detect interference and safety distance violations in circuit in real time, displaying aforementioned wireframe model to alert user.
TraceARay is a ray tracing API function provided by NX Open. By specifying a ray source point (origin), a ray direction vector (direction), and participating NX objects (no actual ray creation), it calculates intersection information between ray and specified NX objects. Returned hit point information includes its 3D coordinates, identifier of solid object it is located on, and identifier of surface object it is located on.
Using a cooling channel as an example, steps for implementing real-time interference detection algorithm for cooling channels based on TraceARay are as follows.

(1) Calculate coordinates of the ray set's source points. Figure 13 (a) shows a schematic cross-section of one end of a cooling water channel. Center is starting point S of cooling water channel's centerline, channel diameter is D, and interference check safety distance is L. Point set OriginSet is obtained by offsetting point set outward by L at every angle θ on circumference. To improve comprehensiveness of detection, point S is also added to OriginSet. Size of θ also affects the comprehensiveness of detection. In theory, the smaller θ is, the closer point set is to arc, and interference check result is more comprehensive, but number of calls to TraceARay method will increase, and time consumption will also be longer. To balance performance and accuracy, following formula is used to determine θ:

 

(2) As shown in Figure 13 (b), traverse OriginSet. For each source point, call TraceARay method twice to perform ray detection in two ends of cooling water channel (in program implementation, source point can be translated a certain distance along water channel direction to pass over all NX objects to be detected, then only call TraceARay method once in opposite direction of translation to achieve same detection effect).

(3) All hit point results hitSet are obtained from step (2) (taking result shown in Figure 14 (a) as an example, for ease of processing, it is illustrated here in a plane perspective and only two rays are shown, same below). In order to reduce number of interference warning wireframes finally created, hit point data needs to be processed. First, group points according to surface object where hit points are located, that is, points that hit same surface are grouped together (see Figure 14 (b)); then, for each set of data, take two points that are farthest apart along waterway direction and discard the rest of data (see Figure 14 (c)); use "merge interval algorithm" to merge data groups with overlapping ranges (see Figure 14 (d)).

 (4) Create an interference reminder wireframe with final point data. Use each pair of points as endpoints and (D+2L) as diameter to create a wireframe cylinder (set a minimum length minLength. If distance between two points is less than minLength, or there is only one point in regrouped data, create a wireframe cylinder with a length of minLength), as shown in Figure 14 (e). Final effect of interference check and reminder in NX is shown in Figure 14 (f).

Cooling system design of product shown in Figure 15 is carried out using developed system. Steps are as follows.

 

Figure 15 Product CAD model
(1) First, use "Template Water Channel" tool to import two simple cooling circuits and complete initial design of circuit on upper left part of product, as shown in Figure 16 (a).
(2) Use "Dynamic Water Channel" tool to manually draw part of water channel on lower side of product, as shown in Figure 16 (b).
(3) Use "Water Channel Transformation" tool to complete design of remaining cooling system through mirror and copy functions, as shown in Figure 16 (c).
(4) Use "Standard Part Addition" tool to add standard parts such as plugs, gaskets, inlets and outlets, as shown in Figure 16 (d).
Final cooling system design result is shown in Figure 17.

 

Figure 17 Application example results