2.2 Mold Design and Manufacturing

When producing a plastic part, the molds must be designed and manufactured using various machines. In this study, the steps applied for manufacturing the plastic product of the DVD-ROM cover are described and shown in Fig. 1. In the plastic injection molding, the CAD model of the plastic product of the DVD-ROM cover was designed in the Pro/Engineer Wildfire CAD/CAM program. Also, the mold designed for the DVD-ROM cover consisted of two clamping plates, a core plates, and pins.

In fabricating the mold components, some machines such as CNC milling, EDM machining, drilling, and grinding were employed. The material utilized for the mold components was selected as DIN 1.2738 (IMPAX) steel. This material’s hardness was measured to be 31 HRC with a Wolpert Instron Instrument and its chemical composition is presented in Table  3.

2.3 Finite Element (FE) Analysis and Molding Cycle

2.3.1 FE Pre-Processing of the DVD-ROM Cover. The 3D model of the DVD-ROM cover part was imported into the Moldflow Plastic Insight 5.0 (MPI 5.0) (Ref 18). The DVD-ROM

Fig. 1    The steps applied for producing the plastic product of the DVD-ROM   cover

Table 3   DIN 1.2738 (IMPAX) material’s chemical composition (%)

Table 4    The material properties of ABS  polymer

Commercial  product name LG Chemical (HI-121)

Melt density, g/cm3 0.91459

Solid density, g/cm3 1.0175

Material structure Amorphous

Moldflow viscosity index VI (240) 142

Thermal conductivity, W/m °C 0.1960

Specific heat, J/kg °C 2449

Modulus of elasticity, MPa 2240

Shear modulus, MPa 805

Poisson ratio 0.392

cover part has dimensions of 153, 45.17, and 7 mm. The polymer material (ABS) for the DVD-ROM cover part was composed of CMOLD generic estimates, and its material properties are listed in Table 4. The ABS polymer material was also dried for 4 h using a drier before the molding cycle. The FE model of the DVD-ROM part was created by discretizing the geometry into the smaller simple elements. The FE fusion mesh model, as shown in Fig. 2, consisted of 2726 nodes, 69 beam elements, and 5318 triangular elements.

2.3.2 Molding Cycle of  the  DVD-ROM  Cover.  The mold components were designed and manufactured to inject the plastic material of the DVD-ROM cover part, which is mounted

Fig. 2    The FE mesh model of the DVD-ROM cover   product

on the front of a computer body to fix a DVD within a DVD-ROM. The plastic injection machine which is used in this study was a NETSTAL (600 H-110 60 tons 1.66 oz (25 mm)) made in Switzerland. This plastic injection machine has the technical specifications of a maximum clamp force of 543 tons,

a maximum injection pressure of 243 MPa, a maximum injection rate of 491 cm3/s, a screw diameter of 25 mm, and machine hydraulic response of 0.2 s.

3. Statistical Methodology

yi  ¼ b0 þ b1xi1 þ b2xi2 þ ··· þ bk xik  þ ei ðEq 8Þ

The least square method selects the b coefficients for minimizing the sum of the squared of the errors, ei. The final least square function can be written as  follows: