Piston turning life and death unit simulation method

Abstract

The simulation method comprises the following steps: cutting simulation is performed by establishing a simplified finite element model of a tool-workpiece to obtain a cutting force; an original model of the piston is established based on the geometric characteristics of the piston; the oil groove part, the weight reduction cavity part and the non-bearing fillet part of the original model are removed to determine a simplified model of the piston; the turning area is meshed based on a structured grid, and the non-turning area is meshed based on the simplified grid; a piston grid model is established according to the meshing results of the turning area and the meshing results of the non-turning area; the cutting force is applied to the piston grid model, and the turning process is simulated by using the birth-death element method to determine the residual stress distribution of the piston along the turning path and the deformation amount of the piston. The piston turning process can be simulated efficiently.

Description

Technical Field

[0001] This disclosure relates to the field of machining technology, and more specifically, to a method for simulating the turning of a piston. Background Technology

[0002] Pistons are a core component of engines, and the residual stress and deformation generated during their turning process directly affect product performance and lifespan. Currently, piston turning simulation faces two main challenges: First, model distortion: In order to simplify calculations, existing methods often oversimplify piston geometry (such as removing non-machined areas such as the inner cavity), which leads to distortion of the structural stiffness and mass distribution of the simulation model, making it unable to reflect the mechanical response under real working conditions.

[0003] Secondly, process distortion: Although another method retains the complete model, it applies the cutting force directly to the final contour as a static load, which cannot simulate the dynamic process of "gradual material removal", and therefore it is difficult to accurately predict the residual stress field that evolves during processing.

[0004] The key feature of the birth-death element method is its ability to accurately simulate the gradual removal of material by dynamically "killing" elements while fully preserving the geometric model. This mechanism completely preserves the structural stiffness of the workpiece and can reproduce the dynamic evolution of residual stress in real time, providing a crucial technological foundation for accurately predicting machining deformation and stress distribution.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this disclosure is to provide a piston turning simulation method, thereby overcoming, at least to some extent, the problems of high cost and low efficiency in obtaining piston turning process parameters.

[0007] According to a first aspect of this disclosure, a piston turning simulation method is provided, comprising: performing cutting simulation by establishing a simplified finite element model of the tool-workpiece to obtain cutting force; establishing an original piston model based on the piston's geometric characteristics; removing the oil groove portion, weight reduction cavity portion, and non-load-bearing fillet portion of the original model to determine a simplified piston model, the simplified model including a turning region and a non-turning region; meshing the turning region based on a structured mesh, and meshing the non-turning region based on the simplified mesh; wherein the number of polyhedral faces in the structured mesh is greater than the number of polyhedral faces in the simplified mesh; establishing a piston mesh model based on the meshing results of the turning region and the non-turning region; applying cutting force to the piston mesh model, and simulating the turning process using the birth and death element method to determine the residual stress distribution of the piston along the turning path and the amount of piston deformation.

[0008] Optionally, the simplified model also includes a transition region between the turning region and the non-turning region; the transition region is meshed using a structured mesh.

[0009] Optionally, the grid cells of the structured mesh are hexahedrons; the grid cells of the simplified mesh are tetrahedrons.

[0010] Optionally, the cutting force includes the main cutting force, the back force, and the feed force; the main cutting force, the back force, and the feed force are all determined based on the reaction force of the tool reference point simulated by a simplified model.

[0011] Optionally, the turning regions corresponding to the turning process include the skirt top region, the pin hole region, and the stop region. The turning process is simulated using the birth and death element method, including: for the skirt top region, repeatedly setting the outermost mesh element of the mesh model to the kill state stiffness matrix until the mesh model reaches the ideal shape of the skirt top region; for the pin hole region, repeatedly setting the outermost mesh element of the mesh model to the kill state stiffness matrix until the mesh model reaches the ideal shape of the pin hole region; for the stop region, repeatedly setting the outermost mesh element of the mesh model to the kill state stiffness matrix until the mesh model reaches the ideal shape of the stop region.

[0012] Optionally, determining the residual stress distribution and deformation of the piston along the turning path includes: defining JC constitutive model parameters for the piston material in finite element software, calculating the deformation and stress distribution of the piston by applying a cutting force as a load; sampling the residual stress of the piston along the turning path in the depth direction; and collecting the sampling results to obtain the residual stress distribution of the piston along the turning path.

[0013] Optionally, the piston turning simulation method also includes: determining the piston surface roughness based on the amount of deformation.

[0014] Optionally, the piston turning simulation method further includes: optimizing the turning process parameters based on the piston's deformation and residual stress distribution; wherein the turning process parameters include at least one of cutting speed, feed rate, and depth of cut.

[0015] In some embodiments of the present disclosure, the cutting force is first obtained, then input into a mesh model established based on the geometric features of the piston, and finally the simulation results of the turning process are determined by the birth and death element method. The present disclosure employs parametric modeling and automated simulation processes, avoiding a large amount of repetitive modeling and manual setting processes, thus exhibiting high efficiency.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0018] Figure 1 A flowchart illustrating a piston turning simulation method according to an exemplary embodiment of the present disclosure is shown.

[0019] Figure 2 A schematic diagram of the skirt top portion of a grid model of a piston according to an exemplary embodiment of the present disclosure is shown.

[0020] Figure 3 A schematic diagram of the pin hole portion of a grid model of a piston according to an exemplary embodiment of the present disclosure is shown.

[0021] Figure 4 A schematic diagram of the stop portion of a grid model of a piston according to an exemplary embodiment of the present disclosure is shown.

[0022] Figure 5 A schematic diagram of the transition region grid of the piston stop portion according to an exemplary embodiment of the present disclosure is shown.

[0023] Figure 6 The diagram schematically illustrates the skirt top profile of a piston mesh model according to an exemplary embodiment of the present disclosure at different cutting depths.

[0024] Figure 7The diagram schematically illustrates the distribution of residual stress on the skirt top machining surface along the path under different cutting depths in a mesh model of a piston according to an exemplary embodiment of the present disclosure. Detailed Implementation

[0025] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more specific details omitted, or other methods, components, apparatus, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0026] Furthermore, the accompanying drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0027] The flowchart shown in the attached diagram is merely an illustrative example and does not necessarily include all steps. For example, some steps may be broken down, while others may be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0028] The various steps in the piston turning simulation method described below are performed by electronic devices. This disclosure does not limit the type of electronic device, such as a server, personal computer, mobile device, etc.

[0029] Figure 1 A flowchart illustrating an exemplary embodiment of a method according to this disclosure is shown schematically. References Figure 1 The piston turning simulation method may include the following steps: S100. Cutting force is obtained by performing cutting simulation through the establishment of a simplified finite element model of the tool and workpiece.

[0030] The cutting forces involved in the piston turning process include the main cutting force, the back force, and the feed force. The main cutting force, back force, and feed force can all be determined based on empirical formulas. The three components of the cutting force are expressed using an exponential empirical formula:

[0031] in, , , These are the main cutting force, the back force, and the feed force, respectively. , , These are coefficients related to the metal being processed and the cutting conditions, respectively. , , , , , , , , The depth of cut in the three component force formulas are respectively , Feed rate and cutting speed The index, , , These are the products of the correction coefficients for cutting force under various factors.

[0032] According to an exemplary embodiment of this disclosure, the cutting force is obtained through a separate tool-workpiece cutting finite element simulation. The method includes: First, establish a finite element model containing a simplified cutting tool and piston workpiece (or a representative material block). The piston workpiece model here can be a local model, containing only the local area to be cut, to improve computational efficiency. Next, an accurate Johnson-Cook (JC) constitutive model and fracture criterion are defined for the workpiece material, and rigid or elastic material properties are defined for the tool. Contact pairs, including parameters such as the coefficient of friction, are also defined between the tool and the workpiece.

[0033] Then, the tool's motion trajectory and boundary conditions are set according to the actual turning process parameters (such as cutting speed, feed rate, and depth of cut).

[0034] A reference point is set on the cutting tool, coupled to the cutting section of the tool. After running the cutting simulation, the historical data of the reaction force at this reference point is directly extracted in the post-processing. This reaction force has three components (F... x F y F z These correspond to the main cutting force, the back force, and the feed force, respectively.

[0035] Finally, the cutting force obtained by the above method is applied as a concentrated load or a distributed load to the piston mesh model in the subsequent main simulation.

[0036] S102. Establish the original model of the piston based on its geometric properties.

[0037] According to an exemplary embodiment of this disclosure, an original model can be established based on the geometric features of the piston. By eliminating the oil groove portion, the weight reduction chamber portion, and the non-load-bearing fillet portion in the original model, a simplified model can be obtained.

[0038] S104. Eliminate the oil groove, weight reduction chamber, and non-load-bearing fillet parts of the original model to determine the simplified model of the piston. The simplified model includes the machined area and the non-machined area.

[0039] According to an exemplary embodiment of this disclosure, the cutting region of the simplified model is divided based on a structured mesh, and the non-cutting region of the simplified model is divided based on the simplified mesh to establish a mesh model.

[0040] S106. The turning region is meshed based on a structured mesh, and the non-turning region is meshed based on a simplified mesh; wherein the number of polyhedral faces in the structured mesh is greater than the number of polyhedral faces in the simplified mesh.

[0041] In the simplified model, the skirt top, pin hole, and stop can be defined as the cutting area, while the rest of the simplified model are non-cutting areas. The mesh elements of the structured mesh can be hexahedral, while the mesh elements of the simplified mesh can be tetrahedral.

[0042] According to an exemplary embodiment of this disclosure, the simplified model also includes a transition region between the turning region and the non-turning region. The transition region has fewer cell layers and is meshed using a hexahedral structured mesh to obtain more accurate simulation results after the turning simulation of the turning region is completed.

[0043] According to an exemplary embodiment of this disclosure, the cutting region of the piston can be modeled and meshed separately using the Abaqus birth and death element technique, which is used to model three typical parts separately. Figure 2 A schematic diagram of the skirt top portion of a piston mesh model according to an exemplary embodiment of the present disclosure is shown, along with a mesh unfolded view of the curved surface portion of the skirt top portion. 4000 hexahedral elements are used at the top of the piston skirt, and 1000 hexahedral elements are used at the bolt opening and stop positions. The mesh size of the skirt top region can be 0.1 mm, and the boundary layer can be refined to 3 layers to capture surface stress gradients.

[0044] S108. Establish a piston mesh model based on the meshing results of the turning area and the non-turning area.

[0045] According to an exemplary embodiment of this disclosure, the pin hole portion of the piston's mesh model is as follows: Figure 3 As shown, the mesh development of the curved surface portion of the pin hole is presented. The stop portion of the piston mesh model is shown below. Figure 4 As shown, Figure 4 The mesh unfolded diagram of the curved surface of the stop portion is presented. The mesh size for the pin hole and the stop portion can be 0.2 mm.

[0046] Figure 5 A schematic diagram of the transition region mesh of the piston stop portion according to an exemplary embodiment of the present disclosure is shown. The transition region is connected by hexahedral elements, and the global mesh element count can be set to approximately 1 million to achieve a balance between computational accuracy and efficiency.

[0047] The test specimen is fixed and connected to the vibrator according to the fixture and clamping principle designed above. Careful installation is required to ensure the test specimen is positioned between the upper and lower clamps to apply axial force and a predetermined stress pattern. For piston test specimens, ensure the force is evenly distributed across the clamping section of the specimen.

[0048] S110. Apply cutting force to the piston mesh model and use the birth and death element method to simulate the turning process to determine the residual stress distribution of the piston along the turning path and the amount of piston deformation.

[0049] According to an exemplary embodiment of this disclosure, firstly, the simulation process is divided into three steps according to the actual process route. The three steps may include turning the skirt top step, boring the pin hole step, and turning the stop step. Each step corresponds to the processing of a feature part. Taking the stop step as an example, the transition area mesh is shown.

[0050] Next, the logic control for the birth and death of the units is implemented. In each process, the outermost ring of units is selected, and its stiffness coefficient is set to 1×10. -6 This avoids matrix singularities and simulates the material removal process. Here, [K]0 is the original stiffness matrix of the element, and [K]0 is the elastic stiffness matrix of the element obtained by integrating the element's geometric function and material constitutive relations. In the actual calculation, the elastoplastic tangential stiffness matrix related to the current strain, strain rate, and temperature is used. The kill-state stiffness matrix of [K]0 can be expressed as [K]. killed =10 -6 ×[K] = 0, the activation state stiffness matrix can be represented as [K]. active =[K]0.

[0051] According to an exemplary embodiment of this disclosure, determining the residual stress distribution and deformation of the piston along the turning path includes: performing layered sampling of the residual stress of the piston along the turning path in the depth direction; and fitting the results of the layered sampling to output the residual stress distribution of the piston along the turning path. First, after completing the simulation process of birth and death elements, the residual stress of the surface elements of the mesh model can be extracted, and a sampling layer can be divided every 0.05 mm along the depth direction. Among them, the depth of the surface element is less than or equal to 0.2 mm.

[0052] Applying a cutting force (F) to the tool contact area x F y F z The plastic deformation of the material was calculated using the Johnson-Cook constitutive model: σ=(A+Bε n )(1+Cln (1-T) m ) Where σ is the flow stress, A is the yield stress, B is the hardening modulus, n is the hardening exponent, ε is the equivalent plastic strain, and C is the strain rate sensitivity coefficient. T is the dimensionless strain rate. The dimensionless temperature is given by m, where m is the thermal softening index, (A+Bε) n (1+Cln) represents the strain hardening term, describing the stress-strain response of the material under quasi-static, room-temperature conditions. (1-T) is a strain rate sensitive term, describing how the material strength increases with increasing deformation rate. m The term "thermal softening" describes how material strength decreases with increasing temperature. In Abaqus, after defining the Johnson-Cook constitutive model parameters for the piston material, the cutting force is applied to the model as an external load. The solver performs iterative calculations based on the principle of virtual work: the load induces strain in the model, and the JC model calculates the stress that the material resists deformation based on this strain; when the unbalanced forces of the system approach zero, the solution converges, and the final output nodal displacement result is the deformation.

[0053] According to an exemplary embodiment of the present disclosure, after determining the residual stress distribution of the piston along the turning path and the amount of deformation of the piston, the piston turning simulation method may further include: obtaining the surface roughness of the piston. The calculation steps for piston surface roughness under discrete data are as follows: Sort the exported node data by X-coordinate; determine the sampling length, calculate the arithmetic mean of all Y-coordinate values ​​within the selected length (this mean is the Y-coordinate of the centerline); subtract the centerline value from the Y-coordinate of each point and take the absolute value; average all absolute deviation values ​​to obtain R. a .

[0054]

[0055] Next, an orthogonal experiment can be designed. The orthogonal experiment selects the cutting speed v, feed rate f, and depth of cut a. p For each target variable, three data levels are set. Table 1 illustrates this example: Table 1

[0056] Based on Table 1, a response surface model of the objective function can be constructed, taking the piston material as an example: ∣σ min | = 280 - 18v + 25f + 12a p +10v 2 +8f 2 R a =0.8 + 0.05v + 0.2f + 0.1a p +0.03v·f Wherein, the minimum residual stress σ min and minimizing roughness R a The physical meaning is as follows: residual compressive stress (usually negative) helps to suppress the initiation and propagation of microcracks, and optimizing its value helps to improve the fatigue resistance of the piston; while surface roughness R a The lower the value, the higher the surface finish, which helps reduce friction and wear and improve piston performance.

[0057] In one specific embodiment, to verify the effectiveness of the simulation method, the spindle speed was fixed at 150 r / min and the feed rate was 0.1 mm / r. The deformation and residual stress distribution at the top of the cast iron piston skirt were analyzed using the simulation method when the cutting depths were 0.25 mm, 0.35 mm, 0.45 mm and 0.55 mm, respectively, thereby revealing its variation law.

[0058] Figure 6The diagram schematically illustrates the skirt top profile of a piston model according to an exemplary embodiment of the present disclosure at different cutting depths. As can be seen from the profile, deformation increases steadily when the cutting depth is 0.25 mm, 0.35 mm, and 0.45 mm, while deformation increases significantly when the cutting depth is 0.55 mm. Specifically, the deformation at the piston skirt top is greatest when the cutting depth is 0.55 mm, and smallest when the cutting depth is 0.25 mm.

[0059] According to an exemplary embodiment of this disclosure, with a spindle speed of 200 r / min, a feed rate of 0.15 mm / r, and a depth of cut of 0.2 mm, results are extracted at three typical locations. On the machined surface, residual stress is formed along the tool's movement trajectory. Taking the skirt top as an example, in the skirt top simulation, a series of reference points are sequentially selected at 0.005 mm, 0.008 mm, and 0.01 mm below the machined surface according to the cutting path, and the residual stress distribution at these reference points is obtained as follows: Figure 7 As shown, Figure 7 The horizontal axis represents the distance of the cutting path, and the vertical axis represents the residual stress.

[0060] Regarding residual stress, the average values ​​for 0.25mm, 0.35mm, 0.45mm, and 0.55mm are 251.75MPa, 283.56MPa, 298.68MPa, and 312.48MPa, respectively. The differences in residual stress between adjacent process parameters are 31.81MPa, 15.12MPa, and 13.18MPa, respectively. This indicates that the residual stress gradually increases with the increase of cutting depth.

[0061] It should be noted that although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0062] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of the present invention, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0063] It should be noted that although several modules or units for the device used to perform actions have been mentioned in the detailed description above, this division is not mandatory. In fact, according to embodiments of this disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided and embodied by multiple modules or units.

[0064] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0065] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A piston turning simulation method, characterized in that, include: Cutting forces are obtained by performing cutting simulations using a simplified finite element model of the tool and workpiece. The original model of the piston is established based on its geometric properties; The oil groove, weight reduction cavity, and non-load-bearing fillet parts of the original model are removed to determine a simplified model of the piston, which includes a machined area and a non-machined area. The turning region is meshed based on a structured mesh, and the non-turning region is meshed based on a simplified mesh; wherein the number of polyhedral faces of the structured mesh is greater than the number of polyhedral faces of the simplified mesh. A piston mesh model is established based on the meshing results of the turning region and the meshing results of the non-turning region; The cutting force is applied to the piston mesh model, and the turning process is simulated using the birth and death element method to determine the residual stress distribution of the piston along the turning path and the amount of deformation of the piston.

2. The piston turning simulation method according to claim 1, characterized in that, The simplified model also includes a transition region between the turning region and the non-turning region; the transition region is meshed using the structured mesh.

3. The piston turning simulation method according to claim 1, characterized in that, The structured mesh has hexahedral mesh elements; the simplified mesh has tetrahedral mesh elements.

4. The piston turning simulation method according to claim 1, characterized in that, The cutting force includes the main cutting force, the back force, and the feed force; the main cutting force, the back force, and the feed force are all derived from the reaction force at the tool reference point extracted by finite element simulation of the tool-workpiece cutting simulation model.

5. The piston turning simulation method according to claim 1, characterized in that, The turning area corresponding to the turning process includes the skirt top area, the pin hole area, and the stop area; wherein, the turning process is simulated using the birth and death element method, including: For the skirt top region, the outermost mesh cells of the mesh model are set as dead cells until the mesh model reaches the ideal shape of the skirt top region; For the pin hole region, the outermost mesh cells of the mesh model are set as dead cells until the mesh model reaches the ideal shape of the pin hole region; For the stop region, the outermost mesh cells of the mesh model are set as dead cells until the mesh model reaches the ideal shape of the stop region.

6. The piston turning simulation method according to claim 1, characterized in that, Determining the residual stress distribution of the piston along the turning path and the amount of deformation of the piston includes: In the finite element software, JC constitutive model parameters are defined for the piston material. By applying a cutting force as a load, the deformation and stress distribution of the piston are calculated. The residual stress of the piston along the turning path is sampled in the depth direction; The results of the sampling are collected to obtain the residual stress distribution of the piston along the turning path.

7. The piston turning simulation method according to claim 1, characterized in that, The piston turning simulation method also includes: The surface roughness of the piston is determined based on the amount of deformation.

8. The piston turning simulation method according to claim 1, characterized in that, The piston turning simulation method also includes: Based on the deformation of the piston and the residual stress distribution, the turning process parameters are optimized; wherein the turning process parameters include at least one of cutting speed, feed rate and depth of cut.

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