Hot Runner maintenance for a 48-cavity injection mold at a packaging manufacturer in Thailand

How the brief came about

The challenge in this case was to get Hot Runner plastic injection moulds back into production after problems with a heating zone or temperature control cabinet. The customer is a packaging manufacturer in Thailand using several moulds, most of them 48-cavity (48 part cavities in a single mould). When any one zone cannot heat, the whole mould has to wait for repair.

The customer reported various symptoms, such as a heater zone raising a short-to-ground alarm (Short to Ground), a control cabinet screen that would not turn on, or plastic and carbon deposits building up and obstructing flow in the runners. The customer issued work orders per job according to the symptoms, over several rounds between 2021 and 2025.

Requirements and constraints

This work requires finding the right root cause before replacing parts, and testing before returning the mould. The main requirements and constraints are as follows:

• There are several moulds with different codes, most of them 48-cavity, so every job has to check the problem zone on that specific mould directly.
• The same symptom may come from the temperature control cabinet, the wiring between the cabinet and the mould, or parts inside the mould, so both sides have to be checked.
• Some work is done at the customer's factory. Other work, such as Manifold cleaning, requires removing the runner assembly from the mould and sending the parts out.
• The mould must pass testing before returning to the production line. Most jobs close with a service report, and some have an acceptance document for the customer's representative to sign.
• The work is on a per-job basis under purchase orders, not an annual maintenance contract.

Why check both the control cabinet and the mould before repairing?

Because the symptom shown on the control cabinet's screen does not tell you where the root cause is. A zone reporting a short circuit may be caused by the Back Plane (the main circuit board into which each zone's control card plugs), the wiring in the cabinet or the heater wire in the mould. If parts are replaced before finding the root cause, the same symptom may return. Fault-fixing work in this case therefore followed the checking sequence below.

1. 1

   Receive the fault report

   Record the zone raising the alarm and the symptoms found, such as a short circuit to ground, a control cabinet screen that will not turn on, or plastic not flowing freely because of deposits in the runners.

2. 2

   Check the temperature control cabinet side

   Open the cabinet and check the Back Plane, the MCU board (Microcontroller Unit, the cabinet's main processing board) and the wiring from the cabinet to the mould for short circuits or loose points.

3. 3

   Check the mould side

   Check the heaters, thermocouples and wiring of the problem zone, measure the heater resistance, and see whether any wire is touching metal parts of the mould.

4. 4

   Repair or replace parts

   Repair damaged wires and replace fuses, heaters, thermocouples, the Back Plane or Nozzle Housings (nozzle casings) according to the findings. If there are deposits, the Manifold and Cross Manifold are removed for Thermal Cleaning, then reassembled.

5. 5

   Test before return

   Test the mould's operation and carry out a Heat-up Test to confirm that every zone heats normally, before returning the mould to the production line.

6. 6

   Send the service report

   Summarise the symptoms, what was fixed, the cause when one was found and recommendations in a service report, which the production team keeps as part of the mould's history.

We take on work under the customer's purchase orders and coordinate repairs with partner technicians specialising in Hot Runner systems. Heater short circuit fixes, Back Plane replacement and Nozzle Housing replacement are done at the customer's factory. For Manifold cleaning and Cross Manifold repair, the customer sends the parts to us, then takes them back for reassembly.

Deliverables

What is delivered in each round is the repair work under the purchase order, together with a service report or job closure documents. The table below shows the work backed by job closure documents.

Results confirmed by service reports

In 2025, after all 48 Nozzle Housings were replaced, the 48-cavity mould returned to production, and the service report states that every zone could heat. On-site repair work covered by 2025 service reports included a Heat-up Test before return.

The work on zones 26 and 44 has an acceptance document (Exit Criteria Checklist) signed by the customer's representative. The Manifold cleaning report states that plastic and carbon deposits were fully removed. This case has no business metrics such as reduced machine downtime, so we report only results backed by documents.

This packaging manufacturer issued us Hot Runner maintenance work orders over several rounds between 2021 and 2025.

What we learned

The key principles of Hot Runner repair are to find the root cause before replacing parts, to take care with heater wires during disassembly and reassembly, and to close the job with a test on the actual mould.

• Find the root cause before replacing parts. The same short circuit symptom can come from several points. In this work, on one occasion the root cause was a loose wire-fastening screw in the cabinet; on another, the control cabinet had no problem but a heater wire in the mould was damaged.
• Mould disassembly and reassembly is a risk point for heater wires. A heater wire damaged during part installation that then touches the Manifold plate can cause a zone to short-circuit to ground, so the wire routing should be checked every time before turning on the heat.
• Close the job with a test on the actual mould and record the cause. A heat-up test confirms that every zone is working again, while a service report recording the cause helps the production team know where to take care in the next round.

How this approach can apply to your factory

If your factory uses Hot Runner plastic injection moulds, you can use the same checking sequence as this case: check the temperature control cabinet and wiring, then the heaters and thermocouples in the mould, before repairing and carrying out a heat-up test. What needs adjusting is the detail of each mould and control cabinet model.

• Prepare mould and control cabinet details, such as the mould code, number of cavities, control cabinet model and the zones raising alarms, to assess which spare parts need to be prepared.
• Keep the service report from each job with the mould's history, to see whether the same symptom recurs in the same zone.