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5 key performance indicators to track in molding machine production

2025/10/15 By le zhan

5 key performance indicators to track in molding machine production

Inadequate monitoring of molding machine performance in injection molding production can lead to scrap, rework, and financial losses. As a Topstar injection molding machine user, you are responsible for your production results when using our machines. Therefore, we have leveraged our experience as a manufacturer to provide you with five performance indicators to track during production.

Observing Cycle Time Consistency: The Foundation of Efficient Molding Machine Production

Cycle time in a molding machine is the time it takes to complete injection, cooling, and ejection. Even slight variations can have a significant cumulative impact: a 2-second cycle delay on a Topstar TEll 160t injection molding machine producing 10,000 parts per day can result in a loss of 5,500 parts per week.

How to Track on Your Injection Molding Machine:
Access real-time cycle time data directly from the Topstar HMI. Most models record the time for each cycle and display an average of 10, 50, or 100 parts. Set a target cycle time and flag any deviations exceeding ±1 second.

Tracking is crucial because it can identify issues that could lead to inconsistent cycle times, such as clogged cooling lines (extended cooling time), worn ejector pins (slower ejection speed), or incorrect injection speed, allowing for timely replacement.

Injection molding cycle time

Ensuring shot weight accuracy: Ensures the molding machine can deliver accurate shot weight.

Shot weight determines part size and integrity. A deviation of even 0.5 grams from the target value can result in overfill (flash) or underfill (voids), both of which require scrap or rework.

Topstar molding machines have built-in load cells that measure shot weight during each cycle. This data is viewed on the HMI, and tolerances are set to ±0.1 grams for critical parts and ±0.3 grams for less precise parts. For more stringent requirements, “shot weight verification” can be performed every two hours: five parts are weighed consecutively on a precision scale and compared to the data recorded by the machine.

molding machine 1

Observing Injection Pressure Stability

In injection molding, consistent injection pressure is crucial to avoid part defects. Voids, flash, or uneven filling can impact final product quality. Topstar’s injection molding machines all utilize proportional backpressure control to maintain stable pressure, but wear or incorrect settings can affect this stability. During production, you can monitor the real-time pressure during the injection process by tracking the pressure curve on the injection molding machine’s HMI. A stable curve should have smooth peaks and align with the target pressure. For example, PC resin should be at 1,800 bar. Record pressure data daily and note any deviations exceeding ±50 bar, as this is the typical defect threshold.

A packaging customer using a Topstar TMll series injection molding machine noticed pressure spikes as high as 2,100 bar (target pressure: 1,900 bar), resulting in flash on bottle caps. After inspecting the mold, they discovered a clogged vent. After cleaning, the pressure stabilized, and flash defects were reduced by 85%.

Observing Injection Pressure Stability

Monitor temperature uniformity to maintain resin quality in the barrel and mold

Uneven temperatures within the molding machine barrel or mold can lead to resin degradation or flow problems. Topstar injection molding machines utilize zone-controlled barrel heating and mold temperature controllers with PID control. Regular monitoring ensures temperature consistency. During daily production, each heating zone is checked via the HMI, with a reasonable target deviation of ±1°C. Thermal sensors are also used to measure the temperature at four points on the mold surface (top, bottom, left, and right). The target temperature deviation is also ±1°C.

A toy manufacturer experienced part cracking during assembly. Tracking revealed that the temperature in barrel zone 3 reached as high as 240°C (target: 230°C), causing ABS resin degradation. Lowering the temperature in this zone resolved the brittleness issue and eliminated part failures.

Record the defect rate for each batch

The percentage of defective parts per batch is the ultimate key metric, as it links all other metrics to actual quality. Tracking the defect rate helps pinpoint the issue with the molding machine. For example, you can conduct a “100-part audit” every shift: inspect parts for common defects (flash, voids, warpage) and record the number of defects found. Use Topstar’s data logging capabilities to correlate defects with other KPIs. For example, “90% of warped parts occur when cycle times are > 32 seconds.” For one furniture parts client we work with, they tracked a 2.5% defect rate for warped parts. Cross-referencing cycle time data, they found that warpage increased dramatically when cooling times fell below 15 seconds. Increasing the cooling time to 18 seconds reduced the defect rate to 0.3%.

Take Control of Your Injection Molding Production

Tracking these five KPIs is more than just a task; it is about taking control of the quality of your injection molding production. When using Topstar injection molding machines, the built-in HMI simplifies monitoring and data logging, allowing you to identify problems early, reduce waste, and deliver consistent parts to your customers. By doing so, you ensure your molding machines are operating optimally and that your final parts meet your quality standards.

 

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