Line ar guide pairs are the main part of the CNC machine tools. The dynamic behaviours are the main properties of the linear guide. These properties can mainly increase the service life of linear guide pairs. The main propose of this study is the comparison of stiffness of linear guide pairs by FEA and experiment. Measure the stiffness experimentally and, compare the results with FEA to prove the correctness of FEA model. For studying was chosen three linear guides: Chinese company-1, Chinese company-2 and abroad company. The results of this study are (1) Set up the finite element model of linear guides with different geometrical parameters. (2) Comparison of FEA and experiment results shows almost same results. (3) The FEA results show correctness of analysis. These studies are useful for establishing the stiffness on different structures of linear guides.
Rolling element linear motion bearings are widely used to guide, support, locate, and accurately move machinery components and products in a wide range of automation applications. Rolling element linear bearings and guides provide low friction, smooth, accurate motion for nearly any moment or normal loading condition. Major applications include factory automation, medical, packaging, machine tool, semiconductor, printing, automotive assembly, aerospace and food processing [
Geometrical differences of linear guides effect on properties. The structure and geometrical parameters have differences. LM guides supported by non-contact bearings require complex and expensive fabrication process [
James Shih-Shyn Wu studied contact stiffness and dynamic characteristics of linear guide under moment load by finite element method and experimentally [
Three linear guide pairs are chosen for studying. They are abroad company, Chinese company-1 and Chinese company-2. The differences between them are in geometrical parameters.
Linear guide pair application is the same. These types of linear guides are the most widely used guide pairs. Contact angle designed with equal 45˚ (
equal load in four directions―vertical upside, vertical downside, horizontal left and right. It transports an LM block by use of four rows of recirculating balls.
The procedures of the finite element analysis are as shown in
Pre-process performed:
CAD model is set up according the parameters as in company’s handbook. The FE model consist of three parts, to get the accurately results respectively to experiment data. The model is set up in Proengineer. The geometric parameters for linear guides are shown in
Parameters | Abroad company | Chinese company-1 | Chinese company-2 |
---|---|---|---|
D a/mm | 6.54 | 6.54 | 6.54 |
φ1 /˚ | 45˚ | 45˚ | 45˚ |
H1/mm | 32 | 38 | 38 |
H/mm | 60 | 70 | 70 |
K/mm | 44.6 | 59 | 60.5 |
B4/mm | 43.717 | 45 | 45 |
B1/mm | 80.6 | 86 | 86 |
L/mm | 106 | 105 | 103 |
For finite element analysis is taken the simplify model of linear guide pair, ignore other elements are taken the main components: balls, guide and slider. The whole linear guide is shown in
Boundary conditions
The second step is input CAD model into ANSYS Workbench (
The material is a structural steel. Material properties are for structural steel such as, elastic modulus E = 206 GPA, density ρ = 7800 kg/m3 and, a Poisson’s ratio is 0.3. Contact with friction is assigned in the joints. The friction coefficient is F = 0.1. The mesh generation is a Multizone. In Multizone zones should be mesh-conformal, and all the mesh should be high quality. The rail and slider set grid 2 mm, the arc contact surface and the surface of the ball set the grid size is 0.5 mm. The arc zone meshed less than other zones to see correctly the deformation in zones. The resulting mode contained 120894 elements. The meshing model of linear guide is shown in
The boundary conditions for three linear guides are identical (
For Chinese company: 1―563 N.
For Chinese company: 2―1156 N.
For abroad company: 719 N.
The load is chosen 563 N as average load for three linear guide pairs, so as further linear guide pairs will compare with each other. The downward load is applied on slider. The contact between ball and groove is: the ball is contact, and groove and the point in slider is a target. The bottom of the guide is chosen as a fixed support.
Post-process performed: After solving process for FE model was finished, the graphic results of deformation and modal animation of guide pairs were performed by ANSYS Workbench. The measurement results of deformation can compare with the displacement of the node at the central of block.
Three linear guides with different geometric parameters under one load were investigated. Further compare the results with experiment the load was applied on slider and, got results of simulation: total deformation.
other two linear guide pairs are similar, so no need show the other results. The results of the simulation are shown in
In
Stiffness of Chinese company-1: k = 25.157 N/μm.
Stiffness of Chinese company-2: k = 25.313 N/μm.
Stiffness of abroad company: k = 22.947 N/μm.
The stiffness of abroad company is 22.947 N/μm was the minimum. The stiffness of Chinese company-2 is 25.313 N/ was the maximum value. The maximum load for every company is different. The 563 N is the maximum load for one ball of Chinese company-1. The maximum load for one ball for Chinese company-2 is 1203 N and for abroad company is 750 N. The FEA verified that the theory on linear guide is applicable, also illustrated the finite element model’s contact modelling is correct and feasible.
The amplitude properties of linear guides were measured in stiffness measurement test- bed shown in
The value of maximum load is taken from every company’s handbook. The maximum load for abroad country―24,000 N, Chinese company-1―18,000 N and, Chinese company-2―38,500 N.
Load | Deformation | |
---|---|---|
Chinese company-1 | 563 N | 22.379 μ/m |
Chinese company-2 | 563 N | 22.241 μ/m |
Abroad company | 563 N | 24.535 μ/m |
In
where, F―is the force applied on the body,
Stiffness of Chinese company-1 k = 789.474 N/μm.
Stiffness of Chinese company-2 k = 857.143 N/μm.
Stiffness of abroad company k = 705.882 N/μm.
In additional, the stiffness obtained from finite element simulation and experiment need to compare. The measured linear guides by experimentally have 16 balls on each row of groove, it means on the upper rows 32 balls. Therefore, the defined stiffness should be 32 times in FEA model.
Load | Deformation | |
---|---|---|
Chinese company-1 | 18,000 N | 22.8 μm |
Chinese company-2 | 18,000 N | 21.2 μm |
Abroad company | 18,000 N | 25.5 μm |
FEA | experiment | |
---|---|---|
Chinese company-1 | 22.379 μm | 22.8 μm |
Chinese company-2 | 22.241 μm | 21.2 μm |
Abroad company | 23.535 μm | 25.5 μm |
load is chosen 18,000 N for every linear guide pairs further to compare with each other. The load for FEA analysis is chosen 563 N for one ball of linear guide pair. The result of experiment and FEA shows almost the same results. According to the stiffness measurement, the Chinese company-2 linear guide pair has high stiffness. The maximum load for this linear guide pair is 38,500 N. For Chinese company-1 F = 18,000 N is the maximum load. And, the maximum load for the abroad company is 24,000 N. And the length of slider of Chinese company-2 is higher than the other two companies linear guide pairs. The structure of Chinese company-2 is suitable for the service under the big load. According to the FEA and experiment analysis, the Chinese company’s structure obtained like suitable one for creating the linear guide pairs.
In this paper, we obtained effect of different structures of linear guides on properties. Three linear guides examined: Chinese company-1, Chinese company-2 and abroad company.
The stiffness was measured by experimentally and also for comparison the finite element simulation is done in ANSYS Workbench for three linear guides. The study has following conclusion:
1) The finite element analysis shows good results in the prediction of the dynamic behaviours of the linear guides comparing the experimental results.
2) FEA results show the maximum deformation was in the down of slider and the minimum deformation was in guide for all linear guides.
3) FEA results show the maximum stress and strain was in the upper ball and the minimum stress and strain in the down ball for all linear guides. Contact between ball and groove is not changed.
4) The analysis is showed that the different structure of linear guide pairs effect to the stiffness property of linear guide pair.
5) According to the analysis, the linear guide pair with good structure is obtained.
Shaukharova, A., Liang, Y., Feng, H.T. and Xu, B. (2016) Study of Stiffness of Linear Guide Pairs by Experiment and FEA. World Journal of Engi- neering and Technology, 4, 115-128. http://dx.doi.org/10.4236/wjet.2016.43D015