Development of an Electro-mechanical Driven Broaching Machine

Development of an Electro-mechanical Driven Broaching Machine

Hong-Seok Park ^a , In-Soo Park ^b , Xuan-Phuong Dang ^c*

a

Lab for Production Engineering, School of Mechanical and Automotive Engineering, University of Ulsan, San 29, Mugeo 2-dong Namgu, Ulsan 680-749, Korea

b

Korea Broach Manufacture Co., LTD.,

114 Soto-ri, Sangbuk-myeon, Yangsan-si, Gyeongsangnam-do, 626-856, Korea

c

Mechanical Engineering Faculty, Nha Trang University, 2 Nguyen Dinh Chieu Str., Nha Trang City, Khanh Hoa Prov., Viet Nam

ARTICLE INFO ABSTRACT

Article history: The machine tools builders are trying to improve the efficiency and performance of the machine tools. The electro-mechanical driven broaching machine has many advantages such as lower noisy operating, higher energy efficiency, and smaller space of installation. This paper presents the structural and mechanical development of an electro-mechanical driven broaching machine that is replaced for traditional hydraulic one. The servo motor, ball screw and roller linear guide are used instead of hydraulic cylinder and translation frictional sliding guides.

The simulation method based on FEM was applied to analyze the stress, deformation of the machine for static analysis. The dynamic analysis was carried out for verifying and assessing the mechanical behavior of the developed broaching machine. This work helps broaching machine developer make a better product at the early design stage with lower cost and development time.

Received 1 February 2015 Accepted 13 February 2015

Keywords:

Broaching machine Simulation Static analysis Dynamic analysis Mechanical design

* Corresponding author. Tel.: +82-52-259-2294 Fax: +82-52-259-1680

E-mail address: [email protected] (Xuan-Phuong Dang).

1. Introduction

Currently, most of the broaching machines use a hydraulic driving system because the broaching process requires a high cutting force. Although these kinds of conventional broaching machines were widely employed, they have some disadvantages such as: noisy operating, high energy consumption, low productivity, higher cost, and larger space of installation. To reduce these disadvantages of the conventional broaching machine, new type of broaching machine is being developed in which servo motor, ball screw, and rolling element linear

motion guide are employed instead of hydraulic cylinder and sliding element linear motion rail (Fig. 1). Because the broaching process requires a large cutting force and a long stroke, the static and dynamic properties of the machine are important characteristics

that should be carefully considered. These mechanical characteristics relate to the deployment of the machine components and their physical properties.

Due to the characteristic of the broaching tool, the

working stroke of the broaching machine is very long. As

the result, the column of the machine is high. This

Fig. 1 Structural comparison of hydraulic broaching machine (a) and electrical driven one (b)

Fig. 2 The systematic procedure of the development process

Fig. 3 The main types of workpiece internal surfaces will be machined by the developed broaching machine

geometrical characteristic results in a low stiffness of the machine frame. In addition, the large cutting force with alternative cutting stroke and idling returning stroke cause the vibration during the operation of the machine. Therefore, analyzing the mechanical behavior of the machine is an important task

when developing this new kind of broaching machine. This paper presents a study on the static and dynamic behavior of a 10 tons electro-mechanical driven broaching machine.

2. Design of the Mechanical Structure of the Broaching Machine

2.1 Design and development process

Base on the identification of the need, we formulated the problem and design requirement. The background research, collection of relevant design information and feasibility study were done before goal statement. The systematic procedure of the development process is detailed depicted in Fig. 2.

However, initial conceptual design, simulation and mechanical analysis are focused in this paper. Followings are some of the main contents in some important steps.

2.2 Frame structure

Based on the conventional 7.5 tons hydraulic broaching machine, we developed a 10 tons electro-mechanical driven broaching machine. This machine is used to machine the

internal surface of the main types of workpiece are hubs, inner races, and sleeves for automotive components as shown in Fig. 3.

The developed broaching machine is a kind of table-lift one.

Fig. 4 3D model and specifications of the electro-mechanical driven broaching machine

Fig. 5 2D drawing of the broaching machine Fig. 6 The ball screw for 10 tons broaching machine The table that carries the workpiece moves from the bottom

to top across the stationary tool during the cutting process.

The advantages of the table-lift broaching machine are as follows:

 Ground-level installation of the machine without a pit or pedestal.

 High axial accuracy due to stationary shaft puller head and retriever head.

 Only the moving machined part (the lifting table) influences the accuracy of the machine.

 Short cycle time thanks to the movements of the broaching tool and the workpiece being overlapped

The specifications of the electro-mechanical driven broaching machine are shown in Fig. 4, and the construction of the machine is depicted in Fig. 5.

2.3 Design and selection of important components The most important mechanical elements of the broaching machine are the ball screw, linear guide, and RAM body.

These components play a crucial role in the accuracy and the performance of the machine.

Due to the high load of the broaching force, a customized THK ball screw model HBN10025S-7.5RRG2+2460L C5 (Fig. 6) was selected. This is a caged-ball high-load ball screw with high load capacity, low torque fluctuation, low noise and long-term maintenance-free operation. Caged-Ball high-load ball screw model HBN is characterized by its internal structure design optimum for operation under high-load conditions and, thus, by a significantly enhanced load rating as compared with conventional ball screws. The permissible axial fore is approximate 179 KN. Therefore, it can endure the allowable broaching force of 10 tons.

The linear guide is also an important component. Because of high cutting force, the moment acting on the RAM body is very large. This moment acts on the linear rails and linear blocks; therefore, four blocks are used to ensure the strength of the linear guide (Fig. 7).

To calculate the maximum normal force acting on the block of the linear guide, we used the equation of moment equilibrium with an assumption R

= R

= 2 R

= 2 R

:

L

* R

+ L

/2 * R

= L

* N

⇔ 885*R

+ 885/2 * R

= 425* N (1)

where R

, R

, R

, and R

are reaction forces at four linear

N=100kN

Cutting force N

R1= 38.5kN 38.5kN R4 =

R2 19.25kN R3 =

Frictional Force

F Joint reaction

force Pulling force

caused by ball screw

L1 = 88 5

L2 = 425

Fig. 7 Force diagram for checking the performance of linear

guide of the ball-screw driven broaching machine Fig. 8 Structure and load capacity of linear guide model SHS 45R

Front side Back side

Fig. 9 Construction of the RAM body guide blocks; L

and L

are the lever arms of the moments.

Solving this system of equation yields R

= R

= 19.25 kN and R

= R

= 38.50 kN.

We chose THK linear guide with balls roll in four rows of raceways precision-ground on an LM rail and an LM block model SHS 45R (Fig. 8) that replaces for the traditional sliding guide of the conventional hydraulic broaching machine.

The advantages of the ball cage linear guide are as follows:

 Service life and long-term maintenance-free (lubrication- free) operation.

 The absence of ball-to-ball collision achieves low noise and acceptable running sound.

 The absence of friction between balls achieves low heat generation and high speed operation.

 The absence of friction between balls allows high grease retention and low dust generation.

With this kind of linear guide, the permissible normal force is 50.2 kN. It can be seen that the linear guide block works safely with the maximum value of 38.5 kN calculated by Eq. (1).

The RAM body (lift table) is the third important part of the ball screw driven broaching machine. It construction is different from the conventional hydraulic broaching machine.

Figure 9 shows the construction of the RAM body. Two sliding groves are replaced by two planes where the linear

guides are assembled. The joint between the ball screw and the RAM body is designed according to the standard shape and geometry of the nut. Due to large cutting fore, RAM body is made by casting steel with solid state in order to ensure a minimum deformation. The back side of the RAM body is designed with ribs to increase the stiffness. These factors meet the accuracy requirement of the machine tools.

3. Static Analysis

A static analysis calculates the effects of steady load

Simplify

the model Meshing

Virtual

3D model Geometry

model

FEM model

Define materials

Load

& boundary condition Deformation

and stress

Analysis Results

Fig. 10 Systematic procedure for static analysis

Fig. 11 Force flow loop in the ball screw (electro-mechanical) driven broaching machine

conditions on a structure, while ignoring inertia and damping effects caused by time-varying loads. Static analysis is used to determine the displacements, stresses, strains in whole structures or components caused by assumed steady loads state.

For a machine tool, the static analysis that calculates the stress and deformation is a crucial task in order to ensure the allowable deformation of the machine tools. Because the mechanical construction of the broaching machine is complex, we use Abaqus 6.7 FEM (finite element method) tool to analyze its strength. This is the best way to verify the mechanical properties of the machine at the early design stage

.

The procedure of static analysis includes following steps as shown in Fig. 10.

 Modeling the 3D model of all the important component of the machine,

 Define the materials properties,

 Mesh the model with C3D10 element (a 10-node quadratic tetrahedron),

 Define load and boundary condition,

 Solve,

 Visualization and read the results,

 Improve the structure if necessary,

To perform the static analysis for the whole machine, we used the force flow loop concept for identifying the action forces and reaction forces (Fig. 11). The fore caused by cutting process transferred from cutting tool to the workpiece, then to the table, to ball screw, and to the main frame. They

form a close loop within the machine. It can be seen that the base frame does not carry the cutting load. Therefore, it is no need to make a strong base frame for the machine, and the material can be saved. This is the advantage of the table-lift broaching machine.

The static analysis is used to calculate both stress and deformation of the machine under the static force condition.

The analysis results show that the maximum stress is very low (7 MPa on RAM body and 18 MPa on the frame) because the construction of the machine must be thick in order to ensure a high stiffness. The deformation of the machine is the important criteria. This deformation partly shows the static accuracy of the machine

. We found that the deformation of the broaching machine is varied when the table is at different height due to the flexible of column. When the RAM body is at the top position or full stroke, the displacement of the frame reaches the largest value as shown in Fig. 12.

The material properties with yield strength vary from 350

to 550 MPa and elastic modulus of 200 GPa. The boundary

condition is that the base of the machine is fixed on the

ground. The column of the machine reacts as a beam which

is fixed at on end. Therefore, the large bending zone occurs

at the bottom position of the column. The upper portion of

the column is nearly straight under the cutting fore. Base on

Low position of RAM body Middle position Top position (full stroke)

Displacement magnification: 1000 times

Low bending zone Low bending zone Low bending zone

Large bending

zone

Large bending

zone

Large bending

zone

0.17

mm

0.24 mm

0.30 mm

Fig. 12 Static analysis results

0.21 mm displacement Increase the thickness

of these walls 8 mm more

Fig. 13 Increase the stiffness at the lower portion of the fame

Table 1. The free vibration modes of the machine

No. Mode Frequency

(cycles/sec) 1 Mode 1 (bending in X axis) 18.5 2 Mode 2 (bending in Y axis) 21.4 3 Mode 3 (jumping in Z axis) 83.7 4 Mode 4 (twisting in Z axis) 87.4 5 Mode 5 (high order bending) 102.9 6 Mode 6 (high order bending) 105.7

The cutting force progressively increased to a steady -state force

when all the teeth were engaged in the work piece.

Approximate cutting force

Fig. 14 A typical cutting force profile of the broaching process and transient analysis result of deformation

this analysis result, it is recommended that the stiffness of the large bending zone should be increased by thicken the wall thickness of the column as shown in Fig. 13. The displacement at the top of the column decrease from 0.30 mm down to 0.21 mm when increase the wall thickness 8 mm more at the lower portion. This result satisfies the desire of the machine tools developer based on the comparison to the existent hydraulic machine.

4. Dynamic Analysis

Dynamic analysis includes: find dynamic displacements, time history, and modal analysis

. Modal analysis is the study of the dynamic properties of structures under vibrational excitation. Modal and harmonic analyses corresponding natural frequencies of the machine were analyzed by FEM method. This simulation method is certainly more appropriate for the analysis of complex compliant systems, providing a model with an arbitrarily high level of detail

.

To reduce the computation time, the model is simplified by removing small holes and small component. After simplifying

the 3D model, we mesh the model using tetrahedral elements.

The boundary condition is that the machine is fixed to the ground at six mounting elements.

The modal analysis results are shown in Table 1 in which Z, Y, and X are vertical (up-down), forward-back, and left-right axis, respectively. We consider six vibration modes at the lower range of the frequency. The purpose of modal analysis is to verify whether or not the frequency of exciting fore is coincided with nature frequency in order to avoid the resonance. Fortunately, the free vibration frequencies are higher than the machining cycle (1/9 cycle/sec). Therefore, there will be no resonant vibration.

Another dynamic simulation is the transient analysis. The

transient dynamic analysis of the broaching machine was done

using Ansys software. Transient dynamic analysis (sometimes

called time-history analysis) is a technique used to determine

the dynamic response of a structure under the action of any

general time-dependent loads. In this work, we assume that

the load increases linearly from 0 to a defined value (100,000

N or 10 tons) according to a typical cutting force profile of

the broaching process

(Fig. 14). Displacements, strains,

stresses, and forces in a structure as it dynamic responds are

obtained from this kind of analysis.

Fig. 15 The deformation history in the transient analysis

Fig. 16 Prototype making of mechanical parts

Fig. 17 Electronic and control system development

Displacement is the most considered information for machine tools. Fig. 15 shows deformation of the analysis results. The maximum displacement at the top of the broaching machine fluctuates with a magnitude about 0.1 mm around the displacement caused by static load. This vibration decreases continuously after 0.7 s due to the damping effect.

These values satisfy the requirement of the machine builder based on their experience and on the comparison with the hydraulic broaching machine with the same cutting load that

has been manufactured before. The modal analysis shows that the machine is safe in terms of dynamic behavior.

5. Prototype Making

The prototype machines were made based on the design and modification according to the analysis results. Base frame, column, and RAM body were manufactured by the machine developer (Fig. 16). Other components such as motor servo, driver, controller hardware, ball screw, linear guide were supplied be professional manufacturers. The prototype components will be assembled and ready for testing in the future works.

6. Conclusion

This study carried out the static and dynamic behavior of an electro-mechanical driven broaching machine. Through this work, the machine tools builder can assess the new product at the early design state. Compared to conventional broaching machine, new type broaching machine has several advantages:

 Higher cutting speed due to low friction in ball screw and linear guide,

 New driving system requires smaller installing space. All components of the hydraulic system such as cylinder, pump, and tank oil will be removed,

 Reducing the time for maintenance and replacement of components,

 The operating noise is reduced, better environment and greener technology.

We analyzed the deformation of important parts in the machine and assess their effect to the geometrical accuracy of the machine. This work contributes to the development of an advanced broaching machine. Although a lot of attempts were made, this work mainly used simulation method.

Therefore, the physical experiments are required to verify the results after building the prototype machine. The broaching machine will be improved completely after real testing.

Acknowledgements

This research was financially supported by the Ministry of

Trade, Industry & Energy (MOTIE) Korea Institute for Advancement of Technology (KIAT) and Dongnam Institute for Regional Program Evaluation through the Leading Industry Development for Economic Region.

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