Integrated CAD/CAM Approach for Parametric Design and High-Precision Microfabrication of Planar Functional Structures Comprising Radially Oriented V-Grooves

Abstract

High-precision microfabrication is essential for enhancing or enabling new functionalities in parts and tooling surfaces. V-groove structures are commonly used in surface engineering for diverse applications. Selecting the optimal V-groove shape, array, and fabrication method is crucial for achieving the desired performance. This study integrates the parametric definition of V-groove structures in both design and fabrication modules using three main function blocks (MFBs). MFB1 defines a single V-groove’s parametric model using specific input parameters. MFB2 transforms these parameters into equations to generate a CAD model of the surface. MFB3 combines inputs from MFB1 with parameters related to cutting tool geometry, cutting strategy, and process planning, producing functional NC code for the machine tool. The approach focuses on micromachining radial V-grooves on planar surfaces, requiring precise alignment and multi-axis single-point diamond cutting (SPDC) with rotation tool center point (RTCP) support. Testing on acrylic samples achieved ±0.1° orientation accuracy and ±2 μm positional accuracy, demonstrating potential for applications in drag reduction, fouling resistance, light guiding, and open microfluidics.

1. Introduction

A wide range of functional parts and tooling surfaces have been made available for augmented functionality through the use of high-precision and high-accuracy microfabrication technologies [1]. The addition of advanced modeling for functional micro-/nano-scale geometric structures can provide surfaces with enhanced and/or novel functionalities for numerous applications, such as control of light-guiding [2,3], micro-fluidics [4], friction [5], MEMS [6], and aero- and hydro-dynamics [7,8].

Among the most common types of micro-/nano-scale geometric structures, V-grooves are one of the most versatile structures to achieve the intended augmented surface functionality. V-groove geometry typically resembles an isosceles triangle whose apex constitutes the lowest point of the groove [9]. V-grooves can be engineered, but they can also be found in nature. V-grooves are commonly used to produce prototypes based on a bio-inspired surface [7]. One of the most exceedingly studied, naturally structured surfaces is constituted by the skin/scales of sharks. Unlike some of the early assumptions made, the skin of a shark is not smooth but comprises many microscales. These microscales have been thoroughly studied [10], and while many attempts have been made to replicate them, only a few have been successful in reducing drag and improving maneuverability in fluid environments, opening new avenues for bio-inspired surface engineering [11].

One of the past successful trials involved the microfabrication of V-groove arrays. The bio-inspired V-groove array was successful in replicating the turbulent flow control of the shark scale [9]. Outside of bio-inspired surfaces, V-grooves can also be engineered to be tailored for specific applications including, but without being limited to, light guiding [10], energy harvesting, or lubrication. For example, V-grooves have proven to be able to enhance sunlight trapping in photovoltaic cells [12]. More specifically, the V-grooves placed on top of solar panels have been shown to improve photovoltaic energy conversion with variable amounts [13]. V-grooves can also provide friction control by allowing lubricants to flow freely along microchannels that connect the surface pockets of stochastic structures. In other words, V-grooves enable the full lubrication of surfaces, as well as the improvement of the tribological conditions of the sheet-forming process [5,14].

Many fabrication strategies have been used in the past to generate accurate and functionally viable V-groove geometries. Nonetheless, the high-precision/high-quality cost-efficient microfabrication of ultraprecise micro- and/or nano-scale structures is far from being a trivial task, particularly in the case of ferrous alloys. The fabrication approaches developed so far have relied on the use of rotational [9,15,16] or non-rotational cutting tools [17,18,19,20]. Nonetheless, some of the main technical challenges to be surpassed in the fabrication of micro-V-grooves are related to the generation of a high-quality surface (Sa < 10 nm) [18] that can be produced in a burr-free and repeatable manner [21,22].

Along these lines, single-point diamond cutting (SPDC) is one of the most effective V-groove fabrication methods. SPDC is commonly used in the fabrication of micro-V-grooves on non-ferrous materials [18]. Advanced SPDC can be employed with six-axis motion control to produce highly precise and accurate micro-V-grooves [17]. SPDC-generated V-grooves are a “negative” replica of the cutting tool geometry. Several different SPDC strategies can be used to avoid the breakage/bending of the tool and/or the high-aspect-ratio V-grooves generated with it [7]. The strategy proposed in the past relied on constant chip thickness or constant cutting area/force implementations [19]. Recent advancements, such as single-flank cutting strategies, have demonstrated significant improvements in surface quality and tool wear management [20].

Despite advancements in CAD/CAM and micromachining techniques, current frameworks often lack the integration required to automate both the design and fabrication of complex functional surfaces. Present solutions typically involve manual intervention to generate tool paths, optimize machining strategies, or design intricate geometric features. This fragmentation not only increases the risk of errors but also reduces efficiency and scalability. Furthermore, very few methodologies address the challenges of micromachining high-precision V-grooves, such as maintaining alignment during multi-axis machining, achieving burr-free surfaces, or handling tool wear effectively. To bridge these gaps, this study proposes an integrated CAD/CAM framework capable of automating parametric design, simulation, and NC code generation for radial V-groove structures, offering a streamlined and scalable approach for both research and industrial applications. The proposed framework includes several secondary functional blocks (SFBs): (i) a parametric model of a rectangular workpiece, (ii) a parametric model of a unit V-groove, (iii) a parametric model of a flat planar functional surface as an array of specifically positioned V-grooves, (iv) cutting tool geometry and its parameters, (v) a single-V-groove cutting strategy, and (vi) an array cutting process plan.

These six SFBs are grouped into three main function blocks (MFBs): (I) the parametric model of the functional structure, (II) the CAD module, and (III) the CAM module. MFBs integrate the automated generation of the solid model and the tool path trajectory of the V-groove-based functional structures. A particular effort was applied to the automated generation of a set of radial V-grooves on a flat planar surface and their precise micromachining by multi-axis single-point diamond cutting (SPDC) supported by the rotation tool center point (RTCP) function. The proposed framework can be extended and used for various combinations of a single and/or set of linearly and spatially oriented V-grooves that can be applied to control hydro-dynamics [4], optical performance [18], aero-dynamics [7], and various other bio-inspired functionalities [8,17].

2. Integrated CAD/CAM Approach

The development of a functional structure might be a difficult and ineffective process. As a result, the fabrication of structures requires intertwined considerations of geometric design, required/optimized functionality, and high-precision and cost-effective manufacturing. These components constitute the main drivers underlying the development of an integrated approach. Once the manufacturing approach has been implemented and completed, the structure can be physically evaluated to test its functional performance. Therefore, the focus of the framework presented in Figure 1 is represented by the process of the parametric design of radially oriented V-grooves and their high-precision fabrication on planar functional surfaces. The proposed CAD/CAM-integrated approach automates the main steps using functional blocks. Each of these functional blocks (FBs) depicts a specific operation or a set of geometric parameters that defines a particular design component. The links between FBs depict the flow of information required to obtain one of two intended outputs of the framework: (a) a CAD solid model of the functional structure for its visualization and the further numerical simulation of its functional performance and (b) an NC code/program for the micromachining of the structure.

The integrated approach can be redefined using the MFBs presented in Figure 1, namely, the parametric Model, the CAD module, and the CAM module. These MFBs require input from several secondary functional blocks. More specifically, SFB 1-3 (workpiece, unit V-groove, and radial pattern) define the parameters used as inputs for MFB1. The output of MFB1 is a set of mathematical formulas that form the parametric geometric model of the functional structure to integrate the use of MFB2 (CAD module) and MFB3 (CAM module). MFB2 produces a solid model of the functional structure for further visualization and a numerical simulation of its functional performance. MFB3 additionally takes inputs from SFB 4-6 (cutting tool, cutting strategy, and process plan) and acts as a postprocessor to output the NC code/program to be used to fabricate the entire functional surface according to the predefined parameters of the cutting tool, cutting strategy, and cutting process plan.

3. Parametric Model

The parametric model constitutes the first main function block (MFB1) of the proposed integrated CAD/CAM approach. The three basic geometric components of the functional surfaces are defined in SFB 1-3 and feed into MFB1 (Figure 1). The main role of the three secondary functional blocks is to define—through dimensional and trigonometric constraints—the geometry of the workpiece (SFB1), the unit V-groove (SFB2), and the radial pattern (SFB3). A more detailed description of the three SFBs is presented in the upcoming sections.

3.1. Workpiece Geometry

The first step in parameterizing the functional surfaces requires the definition of the workpiece in SFB1 (workpiece). The main components of SFB1 are constituted by the location of the origin and definition of the workpiece coordinate system (WCS). When taken together, these elements provide the basis of the trigonometric relations used to define the other geometric components. The other SFB1 inputs are represented by the length of the workpiece along the X, Y, and Z directions (Figure 2). These three geometric parameters are used to define the parametric model and provide the sizing of the working area. A basic rectangular stock was used in this study, but this could be augmented in the future in order to encompass more complex geometries.

3.2. Unit V-Groove Geometry

The parameters of the “base” or “unit” V-groove geometry with a triangular cross-section are defined in SFB2 (unit V-groove). It is necessary to emphasize that in this work, the cross-section of the unit V-groove is defined by the shape of the diamond-cutting tool. Because of this geometric constraint, no spatial movements or alignments of the cutting tool are required. SFB2 and SFB3 work closely together to allow for several variable inputs that provide the near-complete customization of the set of unit V-grooves in accordance with the required radial pattern.

The number of radial sets is defined as $j=\overline{1\dots N}$, where each set includes $i=\overline{1\dots n}$ V-grooves. Figure 3 shows the parameterization of the unit V-groove that is generally defined by its triangular cross-section, $\{A_{j,i}(x,y,z),B_{j,i}(x,y,z),C_{j,i}(x,y,z)\}$, at the j-th axis of rotation and its total length.

The first of the five input parameters is groove depth (h_j,i), which is defined by the Z-coordinate of the apex point, A_j,i(z), and located on the vertical axis of rotation of the j-th radial pattern set. The next two inputs are represented by the left and right facet angles (${\beta }_{j,i}^{left}$ and ${\beta }_{j,i}^{right}$). These three inputs (h_j,i, ${\beta }_{j,i}^{left}$, and ${\beta }_{j,i}^{right}$) completely define the triangular cross-section of each i-th V-groove, $\{A_{j,i},B_{j,i},C_{j,i}\}$. The two components of the total length (LengthStart_j,i and LengthEnd_j,i) set the start and end positions, as well as the length to be cut.

3.3. Radial Pattern

SFB3, referred to as the radial pattern, is responsible for defining the parametric model of the radially distributed V-grooves within each set of radial grooves (Figure 4). The radial pattern is meant to exemplify the use of the rotation tool center point (RTCP) function when V-grooves are to be fabricated via single-point diamond cutting (SPDC). As suggested by Figure 4, several more geometric parameters are required to define the radial pattern. More specifically, two offsets are required to define R_j(x) and R_j(y). These two offsets essentially enable a fully constrained center of rotation with respect to the origin of the WCS. An additional input parameter is the radial orientation angle, α_j,i, which defines the direction of the i-th V-groove with respect to the center of rotation around the Z-axis for each j-th set. The radial angle, α_j,i, is then used to define the unique spatial orientation for each i − j V-groove. This geometric definition of each i − j V-groove is the most appropriate since these parameters can be directly used for CNC postprocessing and programming in absolute coordinates.

In cases of the uniform radial distribution of n V-grooves, their radial orientation can be defined as

$${\alpha }_{j,i}={\alpha }_j^{ini}+i\cdot {\alpha }_j^{\Delta }\mathrm{for}i=\overline{1\dots n},$$

(1)

where ${\alpha }_j^{ini}$ is the initial radial offset, and ${\alpha }_j^{\Delta }$ is the radial pattern step between each groove within each j-th set of V-grooves. The number of grooves is determined by the values of the parameters shown in Eq. 1. The final input parameter required to fully define the entire distribution pattern is represented by the number, N, of radially distributed V-groove sets and their corresponding rotational centers, R_j.

Once the parametric model is fully defined, the aforementioned inputs will facilitate the definition of a set of unit V-grooves from each of their start points to each of their endpoints. This creates a set of data (R_j, A_j,i, $A_{j,i}^{start}$, $A_{j,i}^{end}$, ${\beta }_{j,i}^{left}$, ${\beta }_{j,i}^{right}$, and α_j,i) as the parametric definition of each i − j V-groove. This information will become the input for MFB2 and MFB3 and will be used further in an integrated CAD/CAM approach for the CAD solid modeling of the functional structure and CAM postprocessing for microfabrication.

4. CAD Module

The developed CAD macro constitutes the core of the CAD module (MFB2). Within this function block, a script was developed to automatically generate a solid model of the functional structure based on the input parameters. The macro/script enables the user to design different structures with systematically or heuristically varied parameters whose goal is the optimization of the functional performance of the structure.

This module takes in the output defined within the parametric model (R_j, A_j,i, $A_{j,i}^{start}$, $A_{j,i}^{end}$, ${\beta }_{j,i}^{left}$, ${\beta }_{j,i}^{right}$, α_j,i, $i=\overline{1\dots n}$, and $j=\overline{1\dots N}$) alongside the defined workpiece size (LengthX, LengthY, and LengthZ) and origin of the workpiece coordinate system. These inputs are then converted into $A_{j,i}^{start}$, $B_{j,i}^{start}$, and $C_{j,i}^{start}$ and $A_{j,i}^{end}$, $B_{j,i}^{end}$, and $C_{j,i}^{end}$ coordinates within the CAD software (AutoCAD 2023 version 24.2). As shown in Figure 5, this module takes in the design parameters in the form of a text file. Following this, the parametric model is defined as a sequence of CAD operations that include the generation of the blank, the sketching of the grooves, and their three-dimensional modeling through a loft-cut operation. These operations are then repeated for each j-th rotational center. A generated 3D model can be used in its digital form primarily for simulation purposes. As shown in Figure 1, the CAM module integrated into the proposed framework does not need a solid model since all of its input parameters constitute the output of MFB1, which feeds into both the CAD (MFB2) and CAM (MFB3) modules.

The effectiveness of the CAD module is depicted in Figure 6. The examples presented demonstrate the effect of altering the center of rotation, depth, and radial angle. The developed module can be used to produce multiple V-grooves on a single planar surface, thus allowing the user to produce the final desired structure without the trial and error of manually designing each new iteration.

5. CAM Module

The CAM module (MFB3) constitutes the most complicated and final step of the developed integrated CAD/CAM approach. MFB3 takes in the output from the parametric model, MFB1 (R_j, A_j,i, $A_{j,i}^{start}$, $A_{j,i}^{end}$, ${\beta }_{j,i}^{left}$, ${\beta }_{j,i}^{right}$, α_j,i, $i=\overline{1\dots n}$, and $j=\overline{1\dots N}$), alongside three other outputs of secondary blocks to generate the NC code needed to fabricate the physical replica of the CAD model. Unlike most commercial CAM software, this CAM module does not include visualization capabilities since they were simply not needed. The three SFBs feeding into the CAM module are focused on the geometry of the cutting tool (SFB4), the V-groove cutting strategy (SFB5), and the overall cutting process plan (SFB6), and they will be detailed in the upcoming sections.

5.1. Tool Geometry

The first additional secondary functional block is SFB 4 (tool geometry), in which the geometry of the cutting tool is defined. Depending on the application and the micromachining system used, a wide range of cutting operations can be chosen. In the past, V-grooves have been produced either through single-point cutting [19] or micromilling [23]. As indicated above, the focus of the present study is represented by functional structures involving symmetric radial V-grooves to be generated through a single-point cutting operation. One of the advantages of this manufacturing approach is that V-grooves can have smaller than 90° angles, whereas the use of rotational tools generally implies that the two lateral facets of the groove are highly constrained to the geometry of the tool. The cutting tool typically used in single-point cutting operations is a V-shaped monocrystalline diamond insert fused to a carbide holder (Figure 7).

The most important input of SBF 4 is represented by the included angle since V-grooves are inverse “replicas” of the diamond insert geometry. The included angle (θ) defines how the V-groove facets will be oriented with respect to each other. Additional parameters that might be specified include rake and clearance. For instance, the cutter shown in Figure 7 is characterized by a rake angle of 0°, whereas side and bottom clearance angles were 10° on both cutting faces. The diamond insert was ground and lapped to obtain a symmetrical included angle of 30°. Once the tool geometry is defined, the output of SBF4 can be passed to SBF5.

5.2. Cutting Strategy

SFB5 represents a technical challenge when aiming to achieve a high surface quality (S_a < 10 nm) through precise and burr-free form geometry. SFB5 aims to provide multiple cutting strategies to address the need for efficiency, reliability, repeatability, breakage prevention, and precision. There are several strategies to choose from [19,22], but for the purposes of this function block, two specific strategies were selected to demonstrate the difference between productivity and quality. Figure 8 depicts two strategies, referred to as constant cutting area (CCA) and constant chip thickness (CCT). Both strategies presented in Figure 8 represent implementations of symmetrical double-flank axial cutting in the sense that both V-groove facets are cut at the same time. Single- or alternate-flank cutting strategies have been proposed as well [22].

The CCT strategy has a facile implementation, making it one of the most practical strategies employed in SPDC. As its name implies, the core characteristic of CCT (Figure 8a) is that the uncut chip thickness is held constant throughout the entire cut (δ_k = const). The constant uncut chip thickness correlates with a constant depth of cut—represented by P₁, P₂, P₃, and P₄—providing control over the thickness of the chips. The final depth (P₄) correlates with the A_j,i(z) coordinate. While a constant depth of cut is maintained, the area and, consequently, the volume of the material removed will increase per cut. This increase in the cutting area removed leads to an increase in the cutting force. This has a negative impact on the cutting process by reducing the tool life, wear, and surface quality. Furthermore, if the depth of cut is not kept at a low enough value, the tool could break, and V-groove tips could also deform and/or break. The main benefit of the CCT approach is represented by its simplicity and productivity. Of note, the four passes illustrated in Figure 8 are just an example; the actual number of cuts is dependent on the actual machining constraints set in the CCA or CCT strategies.

The CCA strategy can address some of the negative consequences of CCT but could also require more time, depending on the constraints/requirements of the cutting process. According to its definition (Figure 8a), the area of cut during CCA is held constant (A_k = const). The constant cutting rate enables a constant material removal rate, and this, in turn, leads to a constant cutting force. The amount of material removed in the CCA strategy can be limited either by the cutting force magnitude or area value. In this regard, the limitation of the cutting force can avoid tool breakage or the deformation of the V-groove tips such that CCA could sometimes be preferred over CCT.

Depending on the requirements of the desired functional structures, either cutting strategy can be chosen with the proposed integrated approach. This enables the use of different fabrication strategies depending on the application of the functional surface to be generated. Evidently, other cutting strategies can also be integrated into the framework in order to provide more choices with respect to the quality of the surface or the rapidity of fabricating the surface [22]. It is also important to note that at the end of SFB5, strategy-specific cutting points (P₁, P₂, P₃, and P₄) are ready to be transferred to SFB6 for the purpose of developing an efficient cutting process plan.

5.3. Cutting Process Plan

The last component of the CAM Module is represented by the actual fabrication of the functional surface. Referred to as the process plan, SFB6 enables the selection of the method used to fabricate the entire functional surface. With respect to SPDC, the postprocessing of the cutting tool path trajectory requires that the orientation of the surface is continuously adjusted such that the normal to the primary rake face of the tool remains contained in the vertical plane enclosing the feed direction for each radial groove.

To achieve a change in V-groove orientation, one of the machine tool axes is required to rotate. For instance, to generate V-grooves in the horizontal XY-plane (Figure 9), the C-axis is required to rotate incrementally in agreement with the radial angles α_j,i, $i=\overline{1\dots n}$, and $j=\overline{1\dots N}$, as defined in SFB3 and MFB1. One of the main issues associated with five-axis machining is related to the fact that any point on the machined surface will change its location with respect to the machine coordinate system as a result of the aforementioned rotation. Because of this, if the rotation point, R_j, of the j-th V-groove set does not coincide with the center of the rotary axis, then the intersection point will have to be redefined after each incremental rotation.

At least two main ways to redefine the center of rotation exist: the general coordinate transformation matrix (GCTM) and rotation tool center point (RTCP). While the second option is only available on some of the more advanced CNC controllers, the first option can be used on virtually all controllers, including those without RTCP capabilities. GCTM is inherently linked to the kinematic configuration of the five-axis machine tool and has to be determined and defined by the user. The main role of the coordinate transformation matrix is to convert the tooltip—tracked by the controller—from the default tool coordinate system into the workpiece coordinate system. On the other hand, RTCP could be conceived as a function according to which the controller “follows the tooltip”. This happens because the coordinate transformation matrix—while not transparent to the user/CAM programmer—is already built into and known to the controller itself.

If RTCP is activated, when the workpiece is rotated around the Z-, X-, or Y-axis, the tooltip maintains its position relative to the WCS and rotates with the workpiece. In this case, all coordinates of the cutting tool location and path trajectory are automatically recalculated by the CNC controller. By contrast, when RTCP functionality is not available, all components of GCTM must be determined based on the kinematic structure of the five-axis machine tool. After that, GCTM is integrated into the postprocessor. This approach does not need to be external to controller calculations since cutting motions will rely on coordinates that have already been converted via GCTM. Nonetheless, the use of RTCP implies the permanent use of the work coordinate system (WCS), which simplifies the entire programming activity.

The tool path trajectory for cutting a 0 deg V-groove is graphically presented in Figure 9. Let us assume that this is the very first cut of a V-groove with a 0-degree rotation angle. In this case, this groove will be oriented along the Y-axis, and therefore, it does not require the use of RTCP. After preliminary functions are completed, the tool is brought to location L₁, a preset distance above the location of the radial intersection of each groove. Next, the tool is brought back to L₂ and lowered to L₃ in a circular move to avoid interrupted linear motions. Locations L₂ and L₃ depend on the location of $A_{j,i}^{start}$, as they may end up within the boundaries of the workpiece. L₃ is set to the P₁ depth of the cutting strategy chosen. Then, the first cut takes place between L₃ and L₄. L₄, like L₃, depends on the location of $A_{j,i}^{end}$. The following three moves return the tool to L₃’s location. These three moves ensure the smooth movement of the tool, optimizing the process, and they aid in the removal of chips and the motion control of the tool [19]. If L₄ is found within the boundaries of the workpiece, the tool’s movement will be squarer to provide a finer end to the groove. The cutting pass will then be repeated as many times as required for the cutting strategy. After the last pass of the cutting strategy is completed, the tool returns to L₁. The typical structure of the CNC code for this process implementation is also presented in Figure 9.

Once the first groove is cut (if the radial offset angle is equal to zero), the workpiece must be reoriented such that the normal of the primary rake face remains within the vertical plane determined by the direction of the feed for the next radial V-groove with any arbitrary angle, α_j,i. The tool path trajectory of this operation is shown in detail in Figure 10. When the cutting tool is located at L₁, the RTCP function is activated, and the workpiece is rotated by α_j,i degrees around the Z-axis (C rotation). However, because RTCP is active, the tool maintains its L₁ location above the workpiece. Once the rotation is complete, the RTCP function is deactivated, and a cutting move can be performed for a specific radial V-groove. The cutting motions repeat until all radial V-grooves are produced. The use of the RTCP function with this array of radial V-grooves is necessary to ensure that the normal of the primary rake face remains within the vertical plane and to ease the process of cutting the radial functional structures.

It is also necessary to note that the cutting process plan defined in SFB6 also includes a sequence for producing radial V-grooves. For instance, the grooves can be produced sequentially one-by-one in accordance with an increasing α_j,i. However, the grooves can be machined in alternating order and, in a general case, in any random arrangement. This type of organization of the cutting plan as a sequence of the radial grooves can be important in achieving desired and/or optimal quality of the entire functional structure can be important in achieving the desired and/or optimal quality of the entire functional structure, for example, with respect to the deformation of riblets, burr-free/minimum edges, high surface quality, and other characteristics that may significantly affect functional performance, e.g., aero- or hydro-dynamics, flow control, and optical performance.

Once the cutting process has been defined alongside SFB4, SFB5, SFB6, and the MFB1 parametric model, the NC code can be generated by the MFB3 CAM module. The NC code includes the location of all points presented in Figure 9 and Figure 10 but is replicated to the i-th groove and the j-th rotational point, R_j. Clearly, the use of RTCP considerably simplifies the generation of the NC code, specifically when working with the WCS. If RTCP can be invoked upon the controller, no work is required by an outside programmer. If not, then a transformation matrix based on the specific machining system must be integrated into MFB3 to define the new locations of each point, requiring external work by the user. By allowing for the use of the RTCP function, the integrated CAD/CAM approach becomes easier to implement in micromachining systems that have an RTCP-compatible controller. This culminates in the final main function block, MFB3, allowing for the integrated CAD/CAM approach to be implemented in the fabrication of radial-V-groove-based functional surfaces. The next section provides a practical application of this proposed integrated approach and a demonstration of its implementation.

6. Application and Implementation of the Proposed Approach

To demonstrate the applicability and functionality of the proposed integrated approach, the functional radial structure depicted in Figure 11 was fabricated from an acrylic workpiece with dimensions of 50 mm × 50 mm × 5 mm (length × width × depth). The number of rotational centers was set at 1 (N = 1), and this rotation point was placed at R_1,const(x) = 25 mm and R_1,const(y) = 5 mm. The depth of each groove was provided as h_1,const = 0.1 mm (n = const), with angles of ${\alpha }_{1,1\text{–}7\&10\text{–}14}^{left}=10°$, ${\alpha }_{1,8\&9}^{left}=20°$, and ${\beta }_{1,const}^{left}$ = ${\beta }_{1,const}^{right}$ = 60°, with the length start and end held constant at the maximum diagonal size of the workpiece, clearing the workpiece after each cut. The cutting tool used had an included angle of 30° and a clearance angle of 10°. These inputs were taken in the CAD macro, where all the points of a unit V-groove were created. These inputs were fed to the CAD macro. For this purpose, all points of a unit V-groove were created as explained previously in the CAD module section whereas the unit V-groove was used to create the radial array of V-grooves (Figure 11a).

The parametric inputs were also transferred to an in-house-developed MATLAB program (R2023b) as a mathematical postprocessor where the NC code was generated and further tested using the CNC machining simulation software Vericut. After confirmation within the Vericut software (9.5.2), which showed the actual cutting plan in action, the NC code was run on the multi-process multi-axis CNC micromachining system Microgantry Nano 5x (by Kugler GmbH, Nagold, Germany), shown in Figure 12a. This micromachining center has a positioning accuracy of <± 1 µm and a max feed rate of 10,000 mm/min. A more detailed description of this micromachining system and its advanced capabilities in micromilling, SPDC, and picosecond laser polishing can be found in [24]. The fabrication setup is detailed in Figure 12b, where microfabrication by SPDC was performed using an A-C rotary/tilt table mounted on a Y-axis.

The CCT strategy shown in Figure 8a was used to produce each radial V-groove with a constant chip thickness of δ = 10 µm and a cutting speed of 1800 mm/min. CCT was chosen over CCA due only to the simplicity of the machining operation programming as a demonstrated example of the applicability and implementation of the developed integrated CAD/CAM approach. The fabricated prototype of the designed functional structure is presented in Figure 13b. The cross-section of the fabricated V-grooves is shown in Figure 13a with their intersection/rotation point illustrated in Figure 13b, where the RTCP function is activated and deactivated. As can be seen, the accuracy of the radial orientation of the V-grooves was within ±0.1°, and the intersection point positional accuracy was within ±2 µm. Also, the depths of all fabricated V-grooves were measured using replicate measurements (at least five) performed with a Keyence digital microscope that demonstrated a dimensional accuracy of ±2 µm.

To demonstrate the functionality of the prototype, a green laser beam was directed to the side of the sample and was focused on the rotational center point (Figure 14b). As the figure suggests, the radial grooves fabricated with the proposed framework enabled strong light dissemination along their pathways. Figure 14c illustrates the mechanism of total internal reflection that constitutes the basis of light propagation. This approach has been used in the past to increase the performance of edge-lit backlights [25].

7. Summary and Conclusions

This study introduced a completely integrated CAD/CAM approach for the parametric design and fabrication of radial-V-groove-based functional structures. The approach incorporates three main function blocks—a parametric model, a CAD module, and a CAM module—that take in input parameters from six secondary function blocks attributed to the workpiece dimensions, design of a unit V-groove, radial pattern, cutting tool geometry, cutting strategy, and process plan. The developed integrated approach outputs a parametric model of the functional structure, its solid model, and NC code for its SPDC-based fabrication. The applicability and functionality of the proposed integrated CAD/CAM approach were demonstrated through the generation of a functional prototype whose light-dispersing capabilities could be employed in microfluidic applications.

It is necessary to note that the CAD/CAM approach presented is only applicable in its current form when the cross-section of the V-groove generated replicates the geometry of the diamond insert. When the geometry of the groove to be fabricated is different from that of the insert, an additional module will need to be added to the proposed framework. More specifically, this new module could define—for instance—the directionality, shape, and direction of each groove to be generated. In a more general sense, as long as the geometry of the cutting insert is dimensionally compatible with (but without matching) that of the groove to be machined with it, the groove can still be generated, but more passes and/or relative orientations between the tool and workpiece will likely be required.

Future extensions of this work will present other possible applications for the framework, whose results will include both geometric and physical embodiments of V-groove-based functional surfaces. One of the immediate applications of the framework will be represented by the fabrication of functional surfaces for drag reduction, fouling resistance, light guiding, and open microfluidics. Following this, the next developmental step will be constituted by the development of curvilinear V-groove patterns, with an emphasis on sinusoidal wave patterns. Over the long term, this research aims to develop a flexible CAD/CAM solution capable of designing and recommending automated fabrication strategies for complex micro-/nano-scale structures to be placed on a wide range of freeform surfaces.