2。2 Injection moulding machine

The small vertical injection moulding machine LS-300, supplied by Canon Electronics Inc。, was used in the experiment。 The size of the machine is 52×46×163 cm。 A standardized mould was installed withdimensionsof90×90×115mm。 The injection moulding cycle was controlled by injection speed, injection/hold pressure and their  durations, cooling time, and mould/melt temperatures。 The specifications of the injection moulding machine are presented in Table 1。

Table 1 Specifications of injection moulding machine

2。3 Part geometry and mould design

Figure 1 shows the entire part geometry。 A cylindrical, pinpoint gate is located in the tab at the  back of the main body whose dimensions are approximately 16 mm×8 mm×1 mm。 At the front edge of the main body, there are six symmetric microcantilevers of the same length (2 mm) and thicknesses (50 or 100  μm), but three different widths (100, 200, and 300 μm)。 The melt starts to flow into the microchannels at the end of the filling step。 Point A indicates the position of pressure measurement。

The fabricated mould for the part geometry is presented in Fig。 2。 The two inserts (50 mm×50 mm×10 mm)  made of beryllium copper, which has a high thermal conductivity, are fixed at the upper and lower mould plates, but with small contact areas to minimize heat transfer between the inserts and the mould plates。 The main body cavity is machined on the lower insert。 To build the entire  part cavity, including microcantilevers, a stainless steel 316L shim from which the outer border of the part in Fig。 1 is cut out by laser micromachining is fixed onto the lower insert with multiple pins。 Compared to the direct machining of the insert using

milling or laser machining, precise cavities for microcantilevers can be simply produced as shown in  Fig。

3。 Although the use of the shim is not recommended for mass production processing, because the shim is fractured at the internal edge as the moulding cycle repeats, roughly several tens of shots could be moulded successfully。

2。4 Mould temperature control

In microinjection moulding, the mould temperature control system that varies the mould temperature between the ejection temperature (lower) and the temperature above the freezing temperature (upper) during the injection moulding cycle has been applied to improve filling in the microchannels, resulting in minimum cycle times [2]。 In this study, the mould is warmed by the injection moulding machine for a classical thermal process, whereas the dynamic control temperature is regulated by the additional heating and cooling system。 Below the cavity surface in the insert, an electric heater rod (6。5 mm diameter, 140 W power) is put in across the main cavity along a centre line。 Water circulation channels (6 mm diameter, 96 mm length) are provided in the shape of a ‘U,’ and water is pumped and cooled by the external, commercial water cooler unit for a desktop PC。 The thermocouple is plugged very close to the microcantilever cavity surface。 The image of the mould installed in the injection moulding machine with the heater rod and the cooling tube inserted in its front face is shown in Fig。 4。

Because the freezing temperature of the polystyrene material used was 117 °C, temperature control was attempted for temperatures over 120 °C。 First, the inserts were heated by the electric heater rod。 When the mould wall temperature reached the target temperature, the heater was turned off and the melt

296 Int J Adv Manuf Technol (2014) 75:293–304

Fig。 1 Illustration of moulded part Fig。 2 Schematic of injection mould