Computer simulation and automated calculation of parameters for process and receipt of deformed semi-finished products of new precious metals alloys for jewelry chains production

Mechanical testing of deformed semi-finished products were carried out on the electromechanical universal testing machine «LFM-400» (Walter + Bai AG, Switzerland) and on the universal tensile testing machine «H5K-S» (Hounsfield teste equipment ltd, UK). Research showed that unlike the processing by conventional technology, the current level of this alloy properties [2] allows to eliminate the preliminary and intermediate annealing between the stages of bar rolling without the risk of cracks and breaks.

Next stage of work was the computer simulation of bar rolling and drawing processes, which was conducted with the help of the DEFORM 3D package. In the simulation cold deformation of elastoplastic medium by incompressible tool was considered at 20 °С. For bar rolling (60000 items) rolls rotation frequency in accordance with the technical specifications of the equipment used in manufacturing was 33.3 rev/min, and the rate of friction was assumed equal to 0,12. In drawing (20,000 items) gripper was moving with speed of 1 m/s, and the friction rate was equal to 0,08. The rheological characteristics of the material accepted based on the results of mechanical properties studies of new alloy 925 standard silver semi-finished products. Received models (Fig. 2) allowed to estimate the feasibility of bar rolling and drawing on the proposed routes, metal forming during processing and power parameters.

а

Fig. 1. The microstructure of new 925 standard silver alloy in cast (a) and in deformed (b) condition; × 1000

b

b

Fig. 2. Models of bar rolling (a) and drawing (b) in the DEFORM 3D package

Analysis of the simulation results showed that the required shape and dimensions of the cross section of 0,25 mm wire are achieved in 16 bar rolling and 10 drawing passes. Forming of metal till the set parameters going without destroying, the values of the rolling and drawing force reduced gradually during the process.

Using the results of computer modeling in FeatureCAM system the working drawings of bar rolls created, their processing simulated and control programs code generated for roll tool manufacturing on CNC mills (Fig. 3).

The third phase in acting of research was the calculation of rolling and drawing technological modes with the help of “PROVOL” computer-aided design system [11].

Calculation was carried out for available at «Krastsvetmet» JSC equipment and in accordance with applicable in manufacturing technological scheme:

rolling of continuously cast billet with a diameter of 8 mm in three stages with intermediate annealing till receiving of bar close to the square cross-section with a side of 1 mm on continuous mills of Famor and BILER types;

drawing of rods till wire with a diameter of 0,25 mm on COMEVI bull-block wire-drawing machine.

The calculated modes took into account the increased alloys mechanical properties, their hardening during processing, as well as limitations on the power parameters caused by the characteristics of used equipment.

Fig. 4 shows the diagram of force variation during rolling process with the given unit reduction in comparison with the existing bar rolling route at the plant for obtaining of deformed semi-finished products of new 925 standard silver-based alloy.

The calculated rolling modes significantly reduce the number of passes, provide more evenly distribution of passages reduction, thereby creating favorable conditions for metal processing and minimize the potential defects of finished products. The ductility of the alloy allows to eliminate intermediate annealing operations between rolling stages, while force does not exceed permissible (50,3 kN).

Fig. 3. Simulation of bar rolls and their processing in FeatureCAM system

Fig. 4. Changing of unit reduction ( a), force (b) and torque (c) of rolling the aisles for the proposed (1) and existing (2) processing of new 925 standard silver alloy routes

Based on developed route in the “PROVOL” program rolls calibration was designed and the working drawings of all calibers the aisles were produced (Fig. 5).

Analysis of the drawing modes (Fig. 6) showed that, unlike used, there is a more evenly reduction change the passages, as well as reducing their value as metal hardening.

The calculated drawing mode is presented in Table 1, its analysis showed that the values of the safety factor changing without peaks and increasing gradually to the last pass.

To verify the adequacy of developed models experimental studies in laboratory conditions were carried out. The cast billet with a diameter of 8 mm was subjected to bar rolling by the proposed route on the AMBIFILO VELOCE ROSEN 180+200×ø130 mill of Mario Di Maio company till receiving of bar close to the square cross-section with a side of 1 mm. Wire drawing to a 0,25 mm diameter was carried out on 10 NFS TRONIC bull-block wire-drawing machine.

a

b

Fig. 5. The program «PROVOL» windows for the rolling tool calibration design

From the obtained semi-finished products (Fig. 7) samples for mechanical testing and metallography studies were collected. Alloy ductility allowed to carry out bar rolling and wire drawing without intermediate annealing. Forming of metal on the proposed route passed without the formation of cracks in the bars and wire breaks. For bar rolling billet of 4×4 mm side size used to obtain bars with 1×1 mm dimensions.

During the physical modeling of deformed semi-finished products for jeweler chains obtaining process with strain-gauge indicators and strain-gauge station ZET 017-T8 changing – 637 –

Number of aisles

b

Fig. 6. Changing of unit reduction (a) and force of drawing (b) the aisles for the proposed (1) and existing (2) processing routes for new 925 standard silver alloy

Table 1. Developed mode of new 925 standard silver alloy drawing

Number of aisles Diameter, mm Unit reduction The total deformation degree, % Drawing stress, MPa Safety factor Drawing force, N 1 0,89 1,57 36,3 186,7 1,60 117,1 2 0,74 1,47 56,7 240,2 1,50 102,5 3 0,62 1,42 69,5 256,2 1,55 77,0 4 0,53 1,38 77,9 256,8 1,63 55,9 5 0,46 1,33 83,4 242,2 1,78 39,7 6 0,40 1,31 87,3 238,2 1,85 29,8 7 0,35 1,28 90,0 226,0 1,98 22,1 8 0,31 1,26 92,1 217,7 2,08 16,9 9 0,28 1,25 93,7 214,0 2,13 13,3 10 0,25 1,23 94,9 204,0 2,25 10,3 of the force of bar rolling the aisles was registered. Compare the values of forces obtained by calculation and experimentally demonstrated that calculation error does not exceed an average of 5-7 % (Fig. 8).

Thus, with the help of the developed software rational modes of deformed semi-finished products processing were designed for the manufacture of jewelry chains from new alloys based on precious metals. The analysis showed that in comparison with existing they allow to reduce amount of – 638 –

Fig. 7. Cast blank (a), bars (b – d) and wire (e) from the new 925 standard silver alloy

Fig. 8. Changing the experimental (1) and calculated (2) rolling force the aisles technological processes, energy-power load of equipment and the probability of occurrence finished product defects.

The feasibility of bar rolling and drawing processes on the proposed routes has been confirmed by simulation in a specialized software system using the method of finite element analysis. Designed modes were tested during physical modeling. Results of experimental studies allow to recommend them to introduction in the jewelry chains manufacture at “Krastsvetmet” JSC.

Used complex of software tools and developed computer models of bar rolling and drawing can be recommend for analysis of existing technologies and creation of processing modes for new alloys based on gold, palladium and silver.