Electromagnetic Sheet Forming by Uniform Pressure Using Flat Spiral Coil
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materials Article Electromagnetic Sheet Forming by Uniform Pressure Using Flat Spiral Coil Xiaohui Cui 1,2,3,*, Dongyang Qiu 2, Lina Jiang 4, Hailiang Yu 1,2,3, Zhihao Du 1 and Ang Xiao 1 1 Light alloy research Institute, Central South University, Changsha 410083, China; [email protected] (H.Y.); [email protected] (Z.D.); [email protected] (A.X.) 2 College of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China; [email protected] 3 State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha 410083, China 4 Shandong North Binhai Machinery Company, Zibo 255201, China; [email protected] * Correspondence: [email protected]; Tel.: +86-15388028791 Received: 13 May 2019; Accepted: 13 June 2019; Published: 18 June 2019 Abstract: The coil is the most important component in electromagnetic forming. Two important questions in electromagnetic forming are how to obtain the desired magnetic force distribution on the sheet and increase the service life of the coil. A uniform pressure coil is widely used in sheet embossing, bulging, and welding. However, the coil is easy to break, and the manufacturing process is complex. In this paper, a new uniform-pressure coil with a planar structure was designed. A three-dimensional (3D) finite element model was established to analyze the effect of the main process parameters on magnetic force distribution. By comparing the experimental results, it was found that the simulation results have a higher analysis precision. Based on the simulation results, the resistivity of the die, spacing between the left and right parts of the coil, relative position between coil and sheet, and sheet width significantly affect the distribution of magnetic force. Compared with the structure and magnetic force on a traditional uniform pressure coil, the planar uniform pressure coil can produce a uniform magnetic force distribution on the sheet, reduce the manufacturing difficulty, reduce manufacturing cost, and enhance the service life for the coil. Keywords: electromagnetic sheet forming; uniform pressure; numerical simulation 1. Introduction In electromagnetic forming (EMF), the coil is a key component that converts the electrical energy stored in a capacitor into the kinetic energy required for the deformation of a workpiece. The shape of the coil determines the distribution of electromagnetic force, affecting the forming result of the workpiece. According to the deformed shape of a workpiece, the forming coil can be divided into two types: (1) The forming coil for a tube; (2) the forming coil for a flat sheet. The tube forming coils have a solenoid structure, mainly used to achieve tube bulging and tube compression. For example, Cui et al. [1] found that electromagnetic tube bulging with multidirectional magnetic pressure can decrease the tensile stress and thickness at the easily broken position on a tube. Yu et al. [2] predicted electromagnetic tube compression and evaluated the optimum current frequency using a finite element model (FEM). Compared with electromagnetic tube forming, electromagnetic sheet forming is more complex. Thus, there are many coil structures for sheet deformation. Cui et al. [3] accurately predicted sheet bulging using a flat spiral circular coil. Li et al. [4] obtained the biaxial tensile stress state on a sheet by using flat spiral circular coils. It was found that the forming limit of Ti–6Al–4V sheets increased by Materials 2019, 12, 1963; doi:10.3390/ma12121963 www.mdpi.com/journal/materials Materials 2019, 12, 1963 2 of 16 24.37% when subjected to electromagnetic sheet bulging compared with the quasi-static condition. Cui etMaterials al. [5 2019] used, 11, x the FOR electromagnetic PEER REVIEW incremental forming (EMIF) method to produce a large2 of 17 part using a small flat spiral circular coil under the condition of a small discharge energy. Cui et al. [6] placed a flatby spiral 24.37% circular when coil subjected at the sheet-metal to electromagnetic end to generatesheet bulging radial magneticcompared pressure.with the Severalquasi-static steps of quasi-staticcondition. stamping Cui et al. and [5] magnetic-pulse used the electromagnetic forming withincremental radial forceforming improve (EMIF) the method forming to produce depth bya 31% comparedlarge part to quasi-static using a small stamping. flat spiral Cui circular et al. coil [7] usedunder two the flatcondition spiral-waisted of a small coils discharge and a energy. small discharge Cui et al. [6] placed a flat spiral circular coil at the sheet-metal end to generate radial magnetic pressure. energy to manufacture a large-size part after 36 discharging and six stretching steps. Cui et al. [8] Several steps of quasi-static stamping and magnetic-pulse forming with radial force improve the used the spiral circular coil with tower type and multidirectional magnetic pressure to reduce the forming depth by 31% compared to quasi-static stamping. Cui et al. [7] used two flat spiral-waisted cornercoils radius and a of small a cylindrical discharge part.energy Li to et manufacture al. [9] designed a large-size special part specimens after 36 discharging to obtain theand uniaxialsix tensionstretching state by steps. EMF Cui using et al. a single-turn[8] used the coil. spiral Oliveira circular et coil al. [with10] designedtower type a doubleand multidirectional spiral square coil to makemagnetic sheet-free pressure bulging to reduce and the formed corner a radius flat insert of a cavity.cylindrical However, part. Li aet “dead al. [9] spot”designed (region special of low magneticspecimens pressure) to obtain occurred the uniaxial on the sheet,tension corresponding state by EMF using to the a centersingle-turn of winding coil. Oliveira of the et flat al. spiral [10] coil. Therefore,designed traditional a double flat spiral actuators square producecoil to make a non-uniform sheet-free bulging pressure and distribution, formed a flat limiting insert thecavity. types of partsHowever, that can bea “dead formed. spot” (region of low magnetic pressure) occurred on the sheet, corresponding to Thus,the center a new of type winding of actuator of the that flat provided spiral coil. a uniform Therefore, pressure traditional distribution flat actuators on a sheet produce was proposed a non-uniform pressure distribution, limiting the types of parts that can be formed. by Kamal et al. [11]. Figure1a shows the design principle of a uniform-pressure coil. The outer Thus, a new type of actuator that provided a uniform pressure distribution on a sheet was channel is in close contact with the sheet metal, generating the induced current on an outer channel proposed by Kamal et al. [11]. Figure 1a shows the design principle of a uniform-pressure coil. The and sheetouter metalchannel composed is in close ofcontact a closed with circuit the sheet after me coiltal, generating discharge. the Manish induced et al.current [12] usedon an aouter two-step formingchannel process and tosheet manufacture metal composed a good of phone a closed face circuit by using after acoil uniform-pressure discharge. Manish coil. et al. Golowin [12] used et al.a [13] demonstratedtwo-step forming that the process uniform to pressuremanufacture actuator a good can phone form face a sheet by using metal a withuniform-pressure a complex shape coil. and obtainGolowin fine surface et al. [13] features. demonstrated Kinsey that et al. the [14 uniform] established pressure the actuator electromagnetic-mechanically can form a sheet metal with coupled a numericalcomplex model shape to predict and theobtain forming fine pressuresurface andfeat mechanicalures. Kinsey deformation et al. [14] using established a uniform pressurethe actuator.electromagnetic-mechanically Weddeling et al [15] proved coupled the magneticnumerical pulsemodel welding to predict is feasible the forming and applicable pressure byand using the uniformmechanical pressure deformation electromagnetic using a uniform coil. Thibaudeaupressure actuator. et al. [Weddeling16] proposed et al an [15] analytical proved modelthe to magnetic pulse welding is feasible and applicable by using the uniform pressure electromagnetic design the uniform pressure coil. The designed coil can be used for electromagnetic forming and coil. Thibaudeau et al. [16] proposed an analytical model to design the uniform pressure coil. The magneticdesigned pulsed coil welding.can be used Cui for etelectromagnetic al. [17] analyzed forming the distributionand magnetic ofpulsed magnetic welding. force Cui on et aal. sheet [17] and coil usinganalyzed a uniform the distribution pressure of coil.magnetic It was force found on a thatsheet a and uniform coil using pressure a uniform is distributed pressure coil. in It the was region correspondingfound that a to uniform the under-surface pressure is distributed of the coil. in th Thus,e region the corresponding coil undergoes to the a complexunder-surface state of ofthe stress, whichcoil. may Thus, cause the coil coil failure. undergoes Figure a 1complexd shows state that of a bulgestress, appears which may in the cause bottom coil surfacefailure. ofFigure the coil1d [ 18]. Therefore,shows comparedthat a bulge to appears a flat spiral in the coil,bottom the surface uniform-pressure of the coil [18]. coil Therefore, in Figure compared1 has two to maina flat spiral problems: (1) Thecoil, coil the can uniform-pressure easily break, andcoil in (2) Figure the coil 1 has has two a complex main problems: structure. (1) The coil can easily break, and (2) the coil has a complex structure. FigureFigure 1. Traditional 1. Traditional uniform-pressure uniform-pressure coil. (a ()a Design) Design principle, principle, (b) magnetic (b) magnetic force on force sheet on [17], sheet (c) [17], (c) magneticmagnetic force force onon a coil [17], [17], and and (d ()d failure) failure of ofa coil a coil [18]. [18 ]. Materials 2019, 11, x FOR PEER REVIEW 3 of 17 Therefore, a new uniform-pressure coil with a planar structure was designed in this study. A three-dimensional (3D) FEM was established to analyze the effect of the main process parameters on magneticMaterials 2019 force, 12, 1963distribution.