Meaning
Production delay that occurs when thick walled plastic features require additional time in the mould to solidify before the part can be ejected safely. Cycle time cooling penalty describes the economic cost and lost output caused by uneven or excessive part thickness. This penalty is most pronounced when a single thick area of a part dictates the cooling time for the entire moulding cycle.
The moulder must wait for the centre of the thickest section to reach a temperature where it is stable enough to resist the force of the ejector pins. This delay reduces the efficiency of the machine and increases the cost per part. It applies as long as the part geometry forces a cooling time that exceeds the minimum required for the thinner sections.
Thermal Latency
Polymers act as thermal insulators, meaning that heat moves slowly from the centre of a thick section to the cooled surface of the mould. When a part has a wall thickness that exceeds three or four millimetres, the time required to remove the heat increases exponentially. This thermal latency is the primary driver of the cycle time cooling penalty.
A part with a uniform wall thickness of two millimetres might cool in ten seconds, while a similar part with one five millimetre boss might require forty seconds. The extra thirty seconds is the penalty that the manufacturer pays for the inefficient design. This delay not only slows down production but also ties up the machine and the operator for a longer period.
Reducing the thickness of the part or using advanced cooling techniques can help to mitigate this effect.
Production Throughput
The number of parts produced per hour is directly inversely proportional to the cycle time. Any increase in the cooling phase reduces the total throughput of the moulding cell. This loss of production capacity is a major concern for high volume manufacturers who need to maximise the return on their capital equipment.
A cycle time cooling penalty of just five seconds can result in thousands of fewer parts being produced over the course of a week. This lost output can lead to missed deadlines and increased pressure on the supply chain. Moulders often use software simulations to identify these penalties during the design phase so that they can be addressed before the tool is built.
The goal is always to achieve the fastest possible cycle time without compromising the quality of the part.
Economic Impact
Every additional second of cycle time adds to the direct cost of the moulded component. This cost includes the machine hourly rate, the labor cost and the overhead expenses of the facility. When a cycle time cooling penalty is present, the profit margin on each part is reduced.
In some cases, the penalty can be so large that the project is no longer financially viable. To avoid this, designers must work closely with moulders to ensure that the part is optimised for cooling. This might involve coring out thick sections, adding cooling fins or using high conductivity mould materials.
The final cost of the part is a reflection of how well these thermal challenges were managed during the development process. A well designed part with minimal cooling penalties is always the most cost effective solution.
