Speed of mold replacement in workshop directly determines efficiency of equipment operation and flexibility of production scheduling. A usable and practical mold replacement operation process is not simply about breaking down a few steps; it involves many intricacies such as force balance, temperature preheating, hydraulic and electrical interlocking protection.

 

Actually, whether a mold replacement can be completed smoothly in one go doesn't depend on starting work after machine stops. What truly saves time and reduces problems is preparatory work done before shutdown. Those who have worked in this field for a long time understand this.
1.1 First, verify mold to be installed
First, check if mold to be installed has been properly maintained and if all qualification marks are complete. Then check if there is a thick layer of anti-rust oil on mold parting surface, whether high-temperature grease has been applied, properly maintained for moving parts such as slides and slides.
While checking machine, verify mold's closed height, locating ring size, ejector pin hole arrangement, and the overall weight of mold set. Make sure injection molding machine can accommodate mold thickness and that clamping force is perfectly matched; otherwise, there will be numerous problems later on.
1.2 Prepare Piping and Tools in Advance
Gather all necessary tools beforehand: hydraulic connectors, uniformly sized cooling water pipes, high-strength thickened pressure plates, and torque wrenches. Keep everything readily available so you don't waste time searching and disrupt your workflow.

Proper handling of mold removal directly affects its lifespan and prevents unexpected malfunctions. Don't be lazy or careless about this.
2.1 First, empty the barrel of residual material and properly handle injection section.
If two raw materials are incompatible, you must first use a cleaning agent or a material with similar viscosity and mild properties to completely replace old material in barrel and seal it. Otherwise, residual material, trapped in high temperature of barrel for a long time, will easily carbonize and clump together, making subsequent cleaning extremely difficult.
Retract the entire injection unit completely to back, ensuring front nozzle is far away from mold sprue bushing to avoid collisions and scratches during mold disassembly and movement.
2.2 Properly disassemble mold step by step.
Before loosening pressure plate, always slowly close mold, maintaining a low-pressure, lightly locked state. Do not force it open directly. Disconnecting water, electricity, and pipelines must also be done in a fixed order:
First, turn off cooling water switch and use an air gun to blow out all residual water from water pipes inside mold to prevent rust and corrosion caused by water accumulation in water lines when mold is stored in warehouse.
Second step is to unplug hot runner connector. Make sure power is completely disconnected before proceeding, otherwise sparks may occur, burning out connector terminals.
Finally, disconnect side-mounted hydraulic cylinder line and signal line of limit switch.
When lifting mold, be careful. Lifting ring must be fully screwed into screw hole; a sufficient engagement depth is crucial for stability. Lifting chain should be pulled vertically upwards as much as possible; avoid applying force at an angle, as this can easily deform or damage mold's front positioning ring.

Mold installation is the most critical step in the entire mold change process. Force balance and precise alignment all depend on this step; carelessness will lead to numerous problems later.
3.1 Lifting Mold and Finding Center for Alignment
Use positioning hole in the center of machine's mounting plate to align and center mold.
Before lifting mold, confirm that number and position of ejector pins on injection molding machine match ejector pin holes on mold. Large molds should not have only one central ejector pin; otherwise, uneven ejection force may occur, ejector pins may get stuck and fail to eject. In principle, ejector pins should be installed on machine at corresponding positions of ejector pin holes on mold. Position and number of ejector pin holes on mold must align with ejector pins on machine.
Confirm that ejector pins on machine do not retract higher than fixed mold platen. Ejector pins that are too high will block mold and prevent mold closing.
Confirm that ejector pins are all same length when retracted and tighten ejector pin screws. Otherwise, uneven ejector pin lengths will cause uneven force on ejector platen, leading to ejector pin jamming.
When lifting mold, pay attention to "head higher than tail" principle. Side with locating ring is "head," and side with moving mold fixing plate is "tail." "Head" should be approximately 1-3 cm higher than "tail." (This is self-explanatory.)
When lifting mold, be careful to "prevent front and rear molds from separating in mid-air." Use two lifting rings if possible, one for front and one for rear molds. Some molds can only accommodate one lifting ring; in such cases, a connecting module must be installed.
Except for molds with only one ejector pin hole in the center, ensure mold is level left and right when lifting it. Non-operating side is "left," and operating side is "right." If left and right sides are uneven, mold's ejector pin hole will not align with injection molding machine's ejector pin, causing ejector pin to hit mold platen and preventing ejector pin from ejecting.
Confirm that locating ring matches machine's locating hole. If mold's locating ring is smaller than machine's locating hole, a suitable locating ring needs to be added.
Before lifting mold, ensure it is stable and does not touch injection molding machine, robotic arm, or anything else. If you are unsure of direction, jog movement first. After lifting mold next to machine, it must be higher than injection molding machine's height before entering injection molding machine area; it must not collide with machine.
Stand in the middle of rear of injection molding machine and check if mold is centered within machine. Then, stand on operating side of injection molding machine and jog overhead crane to move mold between moving and stationary mold plates.
Slowly lower mold, ensuring it does not touch anything.
After mold descends to midpoint between upper and lower support columns, rotate mold to align positioning ring with machine's positioning hole.
Jerk overhead crane to move mold towards machine's fixed platen. Because mold is "higher at head and lower at tail," it's easier for mold to align with machine's fixed platen, and positioning ring will easily enter positioning hole.
After closing mold, straighten boom. If moving platen is far from mold, adjust "mold thinning" setting until moving platen is close to mold.
If boom is not straightened after closing mold and has already hit mold, adjust "mold thickness" setting until boom is straight.
3.2 Locking plate requires careful attention; even force distribution is crucial for safety.
Front end of locking plate should not press against mold (for three-plate molds, stripper plate).
Vertical distance between locking plates should not be too close, otherwise force will be uneven.
Screws should be placed as close to mold as possible; the closer they are, the greater force.
Locking plate must be placed flat and straight. Thickness of shim underneath should match thickness of mold's back plate. Never tighten bolts at an angle, with one side higher than the other. Over time, this will cause bolts to be subjected to shear stress, easily leading to breakage and damage.
Choose an appropriate torque wrench based on machine size. Don't rely on feel to apply force when tightening bolts; use a torque wrench to tighten them to standard torque for safety and durability.
When tightening pressure plate bolts, always tighten them in a diagonal, crisscrossing sequence. Do not tighten them all the way down one side, as this will cause uneven stress.
After tightening pressure plate, remember to disassemble connecting modules. For large molds, check connecting modules on all four sides.
Use overhead crane to lower machine and remove hook before opening mold; otherwise, crane may be damaged.
3.3 Connect ejector structure and side oil circuits.
If machine has a built-in mechanical linkage ejector pin structure, check connection between machine ejector rod and mold ejector plate to ensure it is secure and that stress on both sides is balanced. Avoid tightening one side while loosening the other.
Slowly open mold and slowly eject ejector pins, confirming ejection action to prevent missing or incorrect ejector pins. Reconnect water and oil lines before reworking and disassembling.
Connect water pipes according to water circuit diagram. Before connecting, blow water lines with an air gun to ensure they are clear.
For machines with side-mounted core-pulling cylinders, connect oil pipes according to pipe inlet and outlet markings. Immediately after connection, perform a few idle movements to check if limit sensor signals are transmitted correctly to machine control panel, and whether there are any signal abnormalities or movement jams.
Connect two ejector pin signal leads to machine's ejector pin signal. This prevents ejector pin from hitting slide block or front mold before mold closes.
Plug hot runner connector into hot runner interface, fully inserting it and securing clip. If there is a small connector for solenoid valve, plug valve needle signal into that connector. Connect air pipe to air pipe interface. If valve needle is hydraulically controlled, connect oil pipe according to valve needle's action. Connect the other end of hot runner cable to hot runner temperature control box. Set hot runner temperature according to molding conditions.
After connecting all signals and piping, close mold, leaving approximately 1 cm between front and rear molds. Raising mold temperature while mold is open may prevent it from closing properly.

 

Mounting mold is not the end; subsequent system debugging and process matching are crucial to ensuring no defective products are produced.
4.1 Adjusting Low-Pressure Mold Closing Protection: Anti-Collision is Paramount
This step is crucial to prevent debris or cold material from getting caught during mold closing, directly damaging precision mold. It's a life-saving step.
Just before front and rear molds touch during mold closing, allow a short distance and switch to low-pressure monitoring mode.
Adjust pressure to minimum force required for a smooth mold closing; do not increase it further.
Low-pressure protection monitoring time should also be slightly longer than normal mold closing time to allow for a buffer.
4.2 Activate Water Circuit Temperature Control and Gradually Increase Temperature
After connecting water circuit, check water flow in each group of water circuits to ensure there are no blockages, cross-contamination, or mixing of water flow between pipes.
Hot runner temperature should not be increased abruptly; it should be increased gradually in stages, with pauses for heat preservation in between. First, heat middle distribution area, then slowly heat front outlet to prevent uneven thermal expansion that could cause outlet to crack and leak material.
4.3 Run Machine Without Filling to Check for Hidden Problems
Without injection or adding raw materials, manually run the entire fully automatic process several times. Repeat mold opening and closing, core pulling, and ejector pin retraction processes several times, carefully listening for any abnormal noises and checking for any false fault signals. Address any minor issues proactively.

After completing all preceding processes, the first sample is used to determine whether machine can be put into full production.
5.1 Sampling and Dimensional Inspection
After machine has continuously and stably produced several molded products, take one out as first sample and carefully inspect it. Visually inspect for shrinkage, dents, burrs, burnt or yellowed areas—any obvious defects. Verify that key dimensions conform to drawings and standards.
Simultaneously weigh and compare weight of each individual product to see if fluctuation error is within allowable range. Weight stability directly reflects stability of the entire molding process.
5.2 Site Cleanup and Handover Records
Replaced old molds, idle pressure plates, and excess water pipes and lines, and neatly place them in designated area, keeping site clean and tidy.
Furthermore, carefully fill out mold change registration form, clearly recording start and end times of mold change, any minor anomalies encountered, and final adjusted process parameters. This information will facilitate subsequent shifts and troubleshooting.
Chapter Six: Strictly Adhered Safety Rules Throughout Mold Change Process
No one is allowed to stand under suspended mold; safety baseline must not be crossed.
All live connectors for heating coils, temperature probes, and hot runners must be plugged in or unplugged only after temperature control power is switched off. Operating with power on can easily burn wires and cause electric shock.
If machine trips a low-voltage protection alarm, it indicates that there is a foreign object stuck in mold or that mold is interfering. Machine must be stopped immediately to investigate cause. Never force mold to close by applying pressure, as this will damage mold and result in significant losses.
In summary, mold changing is not a simple, labor-intensive task; it is a systematic process that requires careful attention to detail and proper procedures. By diligently following these steps, you can save considerable time on mold changing and reduce damage caused by improper mold installation.
A truly effective mold changing approach involves meticulous preparation beforehand, following standard installation procedures on machine, and ensuring seamless transitions between actions. Tightness of every screw and smoothness of every water pipe may seem insignificant, but they are fundamental to stable production and production of qualified products.