Does Case Trial Moulding always need a short-shot series?

Yes. Without the fill threshold, packing pressure cannot tell you whether the melt reached the far end.

Is a short first shot scrap?

No. Its value is the measurement: logging the injection position starts the curve.

How do I know packing time is long enough?

A gain under 0.5 g between steps means the gate has sealed; take the knee plus one second.

How many shots does a trial take?

Case Trial Moulding takes about fifty: eight for the first shot, fifteen for short-shot steps, twenty-five for packing.

Can trial settings be used for mass production?

Yes, as a range. Any change of mould, melt temperature or resin lot needs three verification shots.

Case Trial Moulding: First Shot, Short Shot and Packing

Quick answer: Case Trial Moulding runs in three stages. The first shot judges fill and appearance, the short-shot series finds the position where the cavity just fills, and packing locates the gate-seal point by weight. Each has a written stop criterion.

Why Case Trial Moulding Runs in Three Stages
First Shot: Fill and Appearance Only
Short Shots: Climbing from Sixty Percent
Packing: Timing It with a Weight Curve
Recording the Three Stages on One Card
FAQ

1. Why Case Trial Moulding Runs in Three Stages

A single-pass trial yields numbers that worked once, not a window anyone can reproduce. Splitting Case Trial Moulding into fill, threshold and compensation gives each number a reason.

The stages build on each other: does a whole part exist, where does the melt front stop filling, how much material must be added. Skipping it brings both defects at once: a short far end at low pressure, a lifted parting line at high pressure.

Fix the machine first: 45 °C mould held 40 minutes, cavity and core within 3 °C, polypropylene dried one hour at 80 °C, three dry cycles.

Stage	Question	Stop criterion	Time
First shot	Can it make a whole part	Full fill, no flash	30 min
Short shot	Where the cavity fills	Far-end haze disappears	60 min
Packing	How long to pack	Gain under 0.5 g per step	45 min

2. First Shot: Fill and Appearance Only

Start Case Trial Moulding by sampling between shot 5 and shot 8, when mould temperature sits within 2 °C of setpoint. On a 650-tonne press running a 520 × 380 × 220 mm case, start at 90 MPa, velocity 45, 60 and 35 percent.

At 380 mm opposite the gate, missing material is a short shot and stage three's first data point. A fingernail dragged across the long-side weld line should not catch. A 0.03 mm feeler should not enter the parting line; ejector pins should show no whitening.

Measure wall thickness at three points, base centre, long-side middle and one corner, against 3.5 ± 0.2 mm; 0.25 mm out sends you back to packing.

3. Short Shots: Climbing from Sixty Percent

Injection volume starts at 60 percent, rising 5 percent per step, three parts per step, missing length measured with a caliper, mould temperature settling between steps.

Near 97 percent fill a haze appears where the melt front meets itself. Add 3 percent and weight and appearance both stop moving. Record an injection position of 62 mm and a peak pressure of 78 MPa, then control by position, not pressure, which drifts with melt temperature.

Volume	Fill	What you see	Next step
60%	85%	Gap at the corner	Add 5%
65%	97%	Haze band at far end	Add 3%
68%	Complete	Far end solid	Record

Melt temperature is underestimated: from 215 °C to 235 °C the same position fills 8 percent more volume.

4. Packing: Timing It with a Weight Curve

Packing in Case Trial Moulding is timed from a balance. Start at 6 seconds, step by 2 seconds, weigh five parts per step on a 0.1 g scale. When the gain falls below 0.5 g the gate has sealed.

Packing pressure sits at 60 to 70 percent of injection pressure, 54 to 63 MPa. At 90 percent, residual stress rises and a case dropped from 1.2 m splits at the corner; below 50 percent, base flatness drifts past 1.5 mm.

Time	Weight	Gain	Reading
6 s	948.3 g	—	Sinks visible
8 s	957.6 g	+9.3 g	Still short
12 s	963.4 g	+5.8 g	Near plateau
14 s	964.2 g	+0.8 g	Knee
16 s	964.3 g	+0.1 g	Sealed

5. Recording the Three Stages on One Card

Write ranges, not single values: 45 ± 3 °C mould, 225 ± 10 °C melt, 88 to 95 MPa injection. A single value closes the window. Add mould number, press tonnage, resin lot and photo numbers.

Keep twenty parts, 001 to 020: four for dimensional approval, three for drop and stack tests, the rest in the file. At shift change the incoming operator repeats three shots; a weight spread within 1 g proves the settings travel, and that is the real test of whether Case Trial Moulding produced a window.

Conclusion

Case Trial Moulding leaves three boundaries behind: appearance and fill from the first shot, injection position from the short-shot series, pressure and time from the packing curve. Written as ranges on one card, they turn a personal feel into a window the whole shift can use.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.