250 2。186 0。263

Injection pressure (MPa) 70 5。379 0。087

80 1。091 0。051

90 1。578 0。064

100 1。622 0。159

Switchover position (mm) 6 1。261 0。022

6。12 1。091 0。051

6。24 1。367 0。293

Cooling time (s) 5 3。970 0。091

10 1。091 0。051

15 1。082 0。130

20 1。072 0。112

Packing time (s) 0。5 4。828 0。028

1 2。355 0。262

2 1。091 0。051

3 2。669 0。374

4 3。141 0。193

5 3。664 0。127

Parking pressure (MPa) 75 1。632 0。240

85 1。091 0。051

95 1。818 0。269

105 1。465 0。264

Mold temperature (°C) 70 4。874 0。369

80 1。091 0。051

90 4。084 0。754

100 4。936 0。051

Injection speed (mm/s) 70 1。368 0。132

80 1。091 0。051

90 1。161 0。012

100 1。295 0。059

obtained at the cooling stage。 In addition, as the sensor mount- ing location in the runner affects the pressure profile, the

4。4 Difference between runner and cavity pressures

The optimal parameters were used, as obtained by Taguchi experiments, and the pressure sensor top was mounted 2 mm at the lower outside diameter of the runner for experiment。 Injection’s experimental results showed the pressure history profiles of the cavity and runner, as seen in Fig。 8。 At the packing stage, the pressure profiles of the secondary runner and tertiary runner were scalariform and different from the cavity。 As the secondary runner and tertiary runner contacted the melt earlier, the pressure increased sharply。 When the melt filled the cavity, the runner pressure was similar to the cavity pressure, which increased slowly, and the pressure of the secondary runner was higher than the pressure of the tertiary runner。 At the packing stage, the pressure profiles of runners declined approximately horizontally, which is identical to the results proposed by Collins [38]。 The pressure profile at the packing stage was more explicit than that in the cavity。 However, the pressure inside the cavity was higher than that in the runner, as the pressure sensor in the runner adheres to the runner surface。 As the melt  flows,  the sensor in the runner cannot directly sustain the pressure of the melt, whereas, the pressure sensor  in  the  cavity can。 Therefore, the pressure inside the cavity  is  higher than that in the runner。 At  the  cooling  stage,  the pres- sure profiles of the runners have a trend similar  to the cavity  pressure drop。