Finite Element Analysis of Electrically-Powered Cable Stripper

Finite Element Analysis of Electrically-Powered Cable Stripper* 1 A. Simons, 1D. Amankwah, 1K. L. M. Avegnon, 1E. Adaze 1 University of Mines and Technology, Tarkwa, Ghana Simons, A., Amankwah, D., Avegnon, K. L. M. and Adaze, E., (2018), “Finite Element Analysis of ElectricallyPowered Cable Stripper”, Ghana Journal of Technology, Vol. 3, No. 1, pp. 1 - 8. Abstract Presented in this paper is a proposed design of a user friendly electrically-powered cable stripper for electrical cable producing companies. Design construction was achieved using SOLIDWORKS (2016 version) software. Data on cable specifications were gathered from Nexans KabelMetal Ghana Limited to assist in the determination of the specific insulation thicknesses of the cables under study. The design has an adjustable blade that ensures the stripping of the various cables irrespective of their insulation thicknesses. Powered by a 15 hp (11 kW) three-phase (3ϕ) induction motor, the device can strip 0.5 metres of cable per second and of diameter up to 37.50 mm. A finite element analysis was performed on the stripping blade, the roller and the base plate to determine the stress boundaries during operation. The results showed that the maximum induced stress (207.871 MPa) in the cutting blade is less than the yield strength of the cutting blade (234.422 MPa). Similarly, the maximum induced stresses in both the roller and the base plate were found to be less than their yield strengths respectively. Keywords: Design, Cable Stripper, Finite Element Analysis, Simulation, Nexans KabelMetal cables, such as fibre optic cables, are difficult to strip using conventional means such as knives or tools with enclosed blades. 1 Introduction Cables are very essential in any society for their infrastructural development such as transmission and distribution of electrical power and wiring of building such as hospitals, schools, homes, factories, etc. Industries like Nexans KabelMetal Ghana Limited are into the production of such cables. Defect cables are also generated during the manufacturing process. These companies are always faced with the challenge of how to recycle the scrap generated. The initial attempt to take off the insulation was through manual methods. These methods of cable stripping are time and energy consuming. In addition to normal knife, some manual designs of cable strippers have been presented in the past to curb this problem. Furthermore, Cheng (2002) also designed and developed a cable stripper that includes a housing and a cutter blade mounted in a top open chamber with sliding pressure plate. It can be adjusted to the diameter of the electrical wire to be stripped. The stripper could be used for cutting the insulation of any variety of electrical cable of different diameters. However, these methods of cable stripping are time and energy consuming. One needs a lot of manpower to initiate and maintain the motion of these devices through their entire operation. Some challenges associated with the manually operated cables strippers and knife usage are low operating pace, difficulty in operation and they are limited to smaller sizes of cable diameters. The depth of cut in these cases generally depends on the applied forces from the human arm to the knife against the insulation material. Hence, the depth of cutting is inconsistent and inaccurate, for which the conductor can be affected. This work seeks to design cable stripper for removing damaged insulations on cables at cable manufacturing companies such as Nexans Kabelmetal Ghana Limited, etc. Luka (1985) invented a cable stripper for stripping the protecting jacket from the end of a cable. His design was basically to expose the individual conductor ends of the cable to enable connection. He reaffirmed that, the problem encountered with manual peeling is the slow rate of removal of these jacket ends and the care needed to avoid cutting into the conductive wires. In 1997, Wall designed a cable stripper which rotates about the axis of the cable to make a peripheral cut. It is then moved lengthwise of the cable to make a corresponding slit along the sheath, which enables the sheath to be peeled off the core or conductors of the cable. 2 Resources and Methods Used 2.1 Proposed Design Ducret (1998) invented a cable stripping device which is capable of removing the jacket (armoured steel shields) from cables. They stated that, coaxial *Manuscript received June 20, 2018 Revised version accepted September 19, 2018 Taking cognisance of the shortfalls of the existing cable strippers, a new design which is electrically driven is being proposed as shown in Fig. 1 1 GJT Vol. 3, No. 1, September, 2018 (exploded view). Table 1 shows the component part list. Fig. 2: Proposed Design of Cable Stripper Fig. 1 Exploded View of the Proposed Design 2.2 Design Calculations Table 1 Components Part List Design calculations were computed in the following areas and parameters: motor selection, components design, pulley and belt parameters. The diameters of cables considered range between 10.86 mm and 37.38 mm with 1.00 mm to 2.40 mm insulation thicknesses. Cutting Operation Area The Circumference (C) of the space where the cable is held is given by equation (1). C = 2π (r + t) (1) where, C = Circumference r = radius of largest cable under review t = tolerance Cutting Blade Height and Thickness This blade is a cylindrical bar engraved with dimensions in millimetres. One of its ends is sharpened to a chisel edge. In order to avoid the cutter getting stuck in the insulating material, the thickness of the cutting edge increases in size away from the first point of contact. The area of the cutting edge is given as: 2.2 Mode of Operation The cable is fed in the direction of motion of the rotating roller (8). In order not to interrupt the conductor material, an allowance is given between the tip of the blade (3) and the conductor. With drive power from the motor (7), transmitted through the belt (5), the cables run past the adjustable blade (3) by the aid of the pulling actions from the roller (8) and flange wheel (4). The wheels in the cutter assembly (2) allow for self-positioning of the cable per its size, by the help of springs. Area = (2) where, d = diameter Pulleys and Belt Parameters According to Khurmi and Gupta (2005), the length of belt used is calculated as follows: This machine as shown in Fig. 2 should be placed between the pay-off machine and the insulation or extrusion for the stripped cable to insulated. (3) L= 2 GJT Vol. 3, No. 1, September, 2018 where, x = centre-to-centre distance of the driver and driven pulley = radius of the driver pulley = radius of the driven pulley Tm = k CMA (12) where, k = a constant; 0.008 and 0.006 for copper and aluminium conductors, respectively n = number of conductors CMA = circular mil area for one conductor. (1CMA is equivalent to 5.067 mm2) The belt speed is computed as follows: (4) V= n where, N1 = Driver pulley speed d1 = Driver pulley diameter Roller Velocity (Vr) of roller is calculated as: sin α = where, (5) N = the speed of roller r = the roller radius. where, d2 = Driven pulley diameter Selection of Compression Spring The angle of contact (θ) is given as θ1 = 180° 2α (6) θ2 = 180° 2α (7) The Spring Constant (k) is given as (Khurmi and Gupta, 2005a): G = Modulus of shear d = Thickness of wire D = Mean diameter n = Active coils (Nt – 2) d = 2 mm, OD (Outside diameter) Assuming the coefficient of friction ( ) between the belt and pulley is 0.28, the Belt Tension is determined from the equations (8) and (9): 2.3 log V The spring index (C) is calculated as: C= (8) = (14) k= where, for the smaller (θ1) and bigger (θ2) pulleys respectively (Khurmi and Gupta, 2005). Power (P) = (T1 T2) (13) Vr = The angle of wrap (α) for open belt drive is given as: (15) (9) Let W = Axial load, and = Deflection per active turn (16) where, = groove angle T1 = tension in the tight side of the belt T2 = tension in the slack side of the belt V = belt speed Considering the effect of curvature, we know that Wahl’s stress factor (K) is given by (Khurmi and Gupta, 2005); The Number of Belts (nb) Required is computed as follow (Khurmi and Gupta, 2005): nb = (17) K= The spring deflection (δ) δ= (10) (18) The solid length (Ls) of the spring is computed as follows: Ls = n` x d (19) where, n = total number of coils d = diameter of the wire The width pulley (B) is taken as 25% greater than the belt width (b). B = 1.25b (11) Maximum Cable Pulling Tension (Tm) The free length (Lf) of the unloaded spring Lf = n' × d + δmax + 0.15 δmax Lf = Ls + δmax + 0.15 δmax The maximum cable pulling tension (T m) is given as: 3 GJT (20) Vol. 3, No. 1, September, 2018 Table 2 Values of Parameters from Design Calculations Parameter Description Unit Value C Circumference mm 368.76 Height of mm 200 cutter d1 Driver pulley mm 76 diameter d2 Driven pulley mm 194 diameter N1 Driver pulley rpm 318 speed N2 Driven pulley rpm 119 speed L Belt length mm 1431 x Centre to mm 0.55 centre distance V Belt Speed m/s 1.2654 β Groove angle ° 16 α Angle of wrap ° 6.158 θ1 Angle of ° 167.7 contact of smaller pulley θ2 Angle of ° 192.3 contact of the greater pulley T1 Tension in the N 3310 N tight side of the belt T2 Tension in the N 149 slack side of the belt nb Number of 1 Belts B Width of mm 21.25 pulley Tm Maximum kN 2.086 Cable Pulling Tension Vr Velocity of N/mm 0.904 roller Cs Spring Index 11.5 δ Spring mm 13.429 deflection Ls Solid Length mm 20 Lf Free length mm 35.443 P Power Supply kW 4.0 Power Supply Based on design calculations and recommendations from engineers both at Nexans KabelMetal Ghana Limited and at University of Mines and Technology (UMaT), a 15 hp (11 kW) three-phase (3ϕ) induction motor is selected to serve as the design’s prime mover. 2.3 Application of Theory to Proposed Design After going through the design calculations, the computed values of parameters are shown in Table 2. 3 Results and Discussion 3.1 Finite Element Analysis and Simulation A finite element analysis was performed on the stripping blade, the roller and the base plate to determine the stress boundaries during operation. The analysis was done using SOLIDWORKS simulation version 2016 using the explicit static option. For simplicity of the simulation, just the above mentioned components (stripping blade, roller and base plate) were used. Stripping Blade Depicted in Fig. 3 is the stripping blade as being used the simulation setup. The strip force of a wire varies with length of slug, wire size, insulation type, type of stranding and other variables, but it is typically in the range of 5 to 25 pounds (22 N to 111 N). In the analysis settings, the blade was constrained at the portion where it will be held against the cutter assembly. 111 N was applied 90° to the axe of the blade. The anticipated deformation of the blade and a graphical representation of the simulation result are shown in Fig. 4 and 5 respectively. Fig. 3 Simulation Domain 4 GJT Vol. 3, No. 1, September, 2018 Fig. 4 Anticipated Deformation of the Blade Fig. 5 Shear Stress Distribution at the end of the Simulation 207.871 MPa. This maximum induced stress is less than the Yield strength of the blade. This means the blade can strip cables up to 37.50 mm diameter. It was observed from the deformation graphs that the cutting blade will be stressed closer to where it is held stable. The yield strength of the blade depends on the material selection. In this case, the material selected for this analysis is AISI 321 annealed stainless steel with a yield strength of 234.422 MPa. Roller The roller as modeled in the simulation is presented in Fig. 6. For simplicity of the simulation, just the roller was used as mentioned earlier. When applying 111 N at the tip of the Blade, the maximum stress being induced in the blade is 5 GJT Vol. 3, No. 1, September, 2018 rotational speed of 12.5 rad/s. In the analysis settings, the roller was constrained like a hinge at the portion where it will be supported by bearings attached to the frame. The roller was given a speed of 12.5 rad/s. Also, the maximum pulling force to drag the cable against the blade will be facing an equal reaction at the surface of the roller in form of friction. The maximum friction obtained is of magnitude 111 N. Fig. 6 Roller in Simulation Setup The anticipated strain graph of the roller and a graphical representation of the simulation result are shown in Fig. 7 and 8 respectively. The motor is to cause the roller to rotate at a speed of 0.5 m/s and the roller radius is 0.04 m giving a Fig. 7 Anticipated Strain in the Roller Fig. 8 Stress Distribution in the Roller 6 GJT Vol. 3, No. 1, September, 2018 weight of the cutter assembly. From the graphs, the maximum allowable stress under which the roller will break is 4.127 MPa. The material selected for this analysis is low density polyethylene (very low PE(SS)) and the yield strength is 6.895 MPa. This maximum induced stress is less than the yield strength of the roller. This means the roller can withstand the operation at the design speed. Base Plate. Analysing the base plate in a similar manner as the stripping blade and the roller, the simulation model adopted for the base plate is shown in Fig. 9. The weight of the cutter assembly is found to be 88.1 N. Hence, in the analysis settings, the base plate was constrained where it is supported by the frame. The base plate was acted upon by a force equal to the Fig. 9 Base Plate in Simulation Setup The anticipated deformation of the base plate and a graphical representation of the simulation result are shown in Fig. 10 and Fig. 11 respectively. Fig. 10 Anticipated Deformation of the Base Plate Fig. 11 Stress Distribution in the Base Plate 7 GJT Vol. 3, No. 1, September, 2018 Transfer, Fuels and Internal Combusting Engines, Machine Design, Maintenance Engineering, Accident Vehicle Assessment, Factory Technical Audit and Non-Destructive Testing (NDT). It was observed from the deformation graphs that the cutter assembly will be stressed quite evenly. The yield strength of the blade is dependent on the material selection. The material selected for this analysis is aluminium (1060 alloy) and the yield strength is 27.574 MPa. D. Amankwah holds BSc. Mechanical Engineering from the University of Mines and Technology (UMaT) Tarkwa, Ghana. His research areas cover Design and Manufacturing. When applying 88.1 N on the base plate, the maximum stress being induced in the blade is 3.25 MPa which is less than the yield strength of the base plate (27.574 MPa). K. L. M. Avegnon holds a BSc in Mechanical Engineering from the University of Mines and Technology, Tarkwa, Ghana (UMaT). He is currently serving as a Teaching Assistant and lab technician in the Mechanical Department of UMaT. His research interests are in 3D printers, CAD design, manufacturing, mechatronics, structures and robotics. 4 Conclusions A user-friendly cable stripping device has been designed with its blade capable of withstanding the stress from the cable insulation. The device can strip 5 m of cable per second and of diameter up to 37.50 mm. The device is powered by a 15 hp (11 kW) three-phase (3ϕ) induction motor. E. Adaze is currently an Assistant Lecturer at University of Mines and Technology, Tarkwa, Ghana. He holds an MSc degree in Mechanical Engineering (Thermo-Fluid Sciences) from King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia and a BSc degree in Mechanical Engineering from University of Mines and Technology. His research interests include Computational Fluid Dynamics, TwoPhase Flow modeling, Thermodynamics and Heat Transfer. The results from the finite element analysis showed that the maximum induced stress (207.871 MPa) in the cutting blade is less than the yield strength of the cutting blade (234.422 MPa). Similarly, the maximum induced stresses in both the roller and the base plate were found to be 4.127 MPa and 3.25 MPa respectively. These values were found to be less than the yield strengths of both the roller (6.895 MPa) and the base plate (27.574 MPa) References Cheng, Y. H., (2002), Adjustable wire stripper. U.S. Patent 6,334,253, http://patents.com/us6334253.html Ducret, L. C., (1998), Cable stripping device, U.S. Patent 5,809,652, https://patents.justia.com/p atent/5809652 Luka, R. E., (1985), Cable stripper, U.S. Patent 4,543,717, http://www.freepatentsonline.com/4 543717.html Khurmi, R. S. and Gupta, J. K. (2005), Machines Design, Eurasia Publishing House (Pvt.) Ltd. Ram Nagar, New Delhi-110 055, India, 1230pp. Wall, J. R., (1997), Cable stripper. U.S. Patent 5,653,027, https://patents.google.com/patent/US 5653027 Authors A. Simons is an Associate Professor of Mechanical Engineering and a Consulting Engineer currently working at University of Mines and Technology, Tarkwa, Ghana. He holds the degrees of MSc from the Belarusian-Russian University, Magilev, Belarus, PhD from St. Petersburg State Mining Institute St. Petersburg Russia and ASNT NDT Level II from Trinity NDT College Bangalore, India. He is a member of America Society of Mechanical Engineers. His research and consultancy work covers Heat 8 GJT Vol. 3, No. 1, September, 2018