Why the 10-Point Checklist Matters

The hidden-cost asymmetry between new and used IMMs

For a small-tonnage servo-hydraulic IMM in the 90 to 250 ton range, a new machine from a Chinese supplier typically lands between between 100 percent of new price for a baseline configuration and a higher bracket for larger screw and platen configurations, platen size, and controller specification. A comparable used machine in good condition trades at between 40 and 55 percent of new price on the secondary market—often 40 to 55 percent of new price. That gap looks like an obvious win for the buyer, but the gap is real only if the used machine passes a structured inspection. A used machine with hidden defects consumes the apparent savings inside the first six months through emergency service calls, replacement parts, and lost production hours.

For procurement teams comparing new injection molding machines against equivalent used inventory on the resale market, the financial question is not “new vs used price” but “new vs used total cost of ownership across years one through five.” The checklist below turns that question into a measurable one.

What a buyer’s engineer actually checks on a used IMM

A seller’s photo gallery shows the machine looking clean—a surface that is independently verified through third-party inspection services like Intertek or SGS. A buyer’s engineer, by contrast, walks around the machine with a flashlight, a dial indicator, a multimeter, and a stopwatch. They measure platen parallelism, listen to the hydraulic pump, count the shot hours on the controller, sample the hydraulic oil, open the electrical cabinet to read the component date codes, and look for telltale repair patches that indicate prior failure. None of these inspections requires disassembling the machine. All of them take roughly 60 minutes per machine. All of them produce information that determines whether the price is fair.

New vs Used: The Real Cost Comparison

The table below summarizes the cost components that buyers typically forget when comparing a new IMM to a used IMM. The new machine column reflects real procurement data from new injection molding machines transactions across 2024 and 2025. The used machine column reflects post-acquisition cost data from service calls on machines sold without inspection.

The right column—used IMM with inspection—shows what the buyer actually achieves when the 10-point checklist is run before payment. The purchase price remains at 40-55% of new, but the first-year surprise cost drops to near zero because screw condition, controller version, and documentation are negotiated before the deposit clears.

Mechanical Inspection (Points 1-3)

The three mechanical inspection points cover the structural condition of the machine: platen and tie-bar geometry, screw and barrel wear, and toggle or direct-clamp linkage condition. None of these can be assessed from a photo. All three require the machine to be accessible with the guard open and a basic measurement toolkit.

Point 1 — Platen parallelism and tie-bar condition

Platen parallelism determines whether the mold will close evenly. A platen that has drifted out of parallel—common on machines above 30,000 hours—will produce flash on one side of the part and short shots on the other. Mount a dial indicator on the stationary platen and traverse the moving platen face at four points (top, bottom, left, right). Tolerance: maximum deviation under 0.05 mm per 300 mm of platen length. Any deviation greater than 0.10 mm per 300 mm indicates worn toggle bushings or bent tie bars and warrants a price renegotiation.

Tie-bar condition matters equally. Chrome wear on the tie bar surface—visible as vertical scoring—indicates inadequate lubrication or seal failure on the bushing. Try rotating each tie bar by hand inside its bushing. A binding bar signals bushing wear that the seller is unlikely to disclose. On a used machine, plan for tie-bar bushing replacement at 10 to 20 percent of machine value within the first 24 months if any bar shows binding.

Point 2 — Screw and barrel wear measurement

Screw and barrel condition determines shot weight consistency, melt homogeneity, and processing window for engineering plastics. A screw that has processed 500,000 shots or more typically shows wear on the flight edges, reducing its compression ratio and degrading mixing performance. To check it without disassembly, request a barrel pressure trace from the seller during a recent production run. A trace that shows pressure decay longer than 0.5 seconds at hold pressure indicates worn non-return valve or screw flight wear.

If the seller cannot produce a recent pressure trace, negotiate screw-and-barrel replacement into the purchase contract at the seller’s cost if the first 90 days of production show weight variation exceeding 1.5 percent. This single negotiation typically saves the buyer the cost of an unplanned screw-and-barrel replacement inside the first year of ownership.

Point 3 — Toggle linkages and clamp mechanism (hydraulic toggle machines)

For IMMs using a hydraulic toggle clamp mechanism—common on machines built before 2015—the toggle linkages carry the full clamp tonnage through mechanical advantage. Worn toggle bushings or pivot pins produce both platen drift and noise during clamp motion. Visually inspect the toggle pivots for grease migration, which indicates seal failure. Manually cycle the machine in setup mode and listen for knocking sounds at the toggle pivots during the high-pressure transition.

For servo-hydraulic and direct-clamp machines—newer designs—toggle wear is replaced by linear-position transducer and servo-valve health, which falls under the hydraulic inspection (Point 4). Always confirm which clamp mechanism the machine uses before inspecting; the failure modes and the inspection checklist items differ.

Hydraulic and Lubrication (Points 4-5)

Hydraulic system condition determines both the energy efficiency of the machine and the reliability of every motion—clamp, injection, ejector, carriage. On a used IMM, the hydraulic system typically accounts for the majority of post-purchase service cost if it has not been maintained. Two inspection points cover the high-leverage items: pump and valve health, and oil analysis.

Point 4 — Hydraulic pump, valves, and servo health

Run the machine through a complete cycle in setup mode and listen to the hydraulic pump. A healthy variable-displacement pump produces a smooth, low-frequency hum. A pump with internal wear produces a higher-frequency whine or knocking sound during pressure transitions. The same diagnostic applies to the proportional and servo valves that control injection velocity and pressure profile. A valve that produces a noticeable hiss during pressure hold indicates internal leakage, which raises energy consumption and degrades shot-to-shot consistency.

For servo-hydraulic IMMs, request the servo-motor nameplate data and the controller’s energy-consumption log if available. A servo-pump system that has logged 30,000+ hours typically shows a 10 to 20 percent rise in kWh-per-shot compared to its as-new baseline—a quiet signal of pump or motor wear that does not yet produce a service alarm.

Point 5 — Oil analysis and lubrication system

Request a hydraulic-oil analysis report from the seller dated within the last 60 days. A reputable seller will have one on file; a seller who refuses or claims “we just changed it” is signaling risk. The report should include particle count (ISO 4406), water content (ppm), and viscosity at 40°C. Particle count above ISO 4406 code 22/21/18 indicates contamination that will accelerate pump and valve wear. Water content above 500 ppm indicates seal failure or condensation—both reduce oil life and damage servo-valve spools.

Lubrication system health is checked by visually inspecting the central lubrication reservoir and the distribution lines. Low lubricant level, dried grease at any distribution point, or visibly hardened grease at the toggle pivots all indicate deferred maintenance. Budget a full lubrication-system service—typically a half-day of technician time plus lubricant—at the time of purchase for any used machine above 20,000 clamp hours.

Electrical and Control (Points 6-8)

Electrical and control subsystems determine machine reliability, process repeatability, and the buyer’s ability to integrate the IMM with downstream automation. Three inspection points cover the high-leverage items: shot hours and controller logs, controller and software version, and electrical cabinet component age.

Point 6 — Shot hours, cycle count, and controller logs

Every modern IMM controller logs shot count, clamp hours, and total machine hours. Read these directly from the controller screen during inspection. Cross-check the shot count against the seller’s stated production history. For a small-tonnage IMM in the 90 to 250 ton range, up to 40,000 clamp hours is generally considered reasonable. Once the count crosses 60,000 hours, plan for tie-bar and screw replacement within the first 12 months regardless of cosmetic condition.

Beyond the hour count, request the controller’s recent alarm log. A machine that has logged frequent alarms—particularly hydraulic-pressure-low or servo-valve-fault—within the last six months has a developing fault the buyer will inherit. A clean alarm log over the same period is a positive signal, though not a guarantee.

Point 7 — Controller generation and software support

Controller generation matters more than hour count for long-term support. An IMM running an obsolete controller—anything more than two generations behind current production—will face a parts-availability problem within 36 months. Common Chinese controllers in this risk category include early-generation models from KePlast, Keba, and B&R that have been superseded. Always ask the controller manufacturer directly whether the model is in current production and whether spare parts are stocked. If the answer is uncertain, the resale value of the IMM drops accordingly.

Software version matters equally. A controller running outdated firmware may not communicate with modern upstream MES or downstream robot-handling systems. For a factory planning to integrate the used IMM into an existing automated cell, request the controller’s communication protocol documentation before purchase and verify the protocol is current.

Point 8 — Electrical cabinet component condition

Open the electrical cabinet and inspect the major components against the UL component standards: contactors, circuit breakers, servo drives, and PLC. Read the date codes on the nameplates. Components manufactured more than 10 years ago are typically nearing end-of-life even if they appear functional. Look for signs of prior repair—mismatched replacement components, hand-written wire labels, or temporary wiring patches—which signal that the cabinet has been serviced in a non-standard way.

For Chinese-supplied new IMMs sold through export channels, the electrical cabinet is the single most likely subsystem to differ from the domestic-market version—Bureau Veritas publishes compliance guidance for industrial machinery exported from China to Europe, North America, and the Gulf states. Confirm in writing whether the cabinet meets the destination country’s electrical code (CE for Europe, UL for North America, CCC for China domestic). For a used machine, this question applies equally to its original specification.

Safety, Documentation, and Operator Access (Points 9-10)

The final two inspection points cover items that the buyer’s engineer often skips but the operator and the service team feel immediately: safety interlock function and documentation completeness. Both are checklist items that produce a clear yes-or-no answer and should be reflected in the purchase contract.

Point 9 — Safety interlock and guard function

Test every guard interlock on the machine: the movable platen guard, the hopper guard, the lubrication cabinet, and any side panels that expose moving parts. Each should stop the relevant motion within one controller scan of the guard being opened. An interlock that has been bypassed—wired permanently closed or mechanically shorted—is a serious safety violation and indicates prior operator injury risk. On a used machine, bypassing is more common than sellers admit.

For the emergency-stop circuit, press every e-stop button on the machine and verify that the relevant motion stops within the response time specified by the controller manufacturer. A delayed e-stop response indicates a contactor or safety-relay that is at end-of-life. This is a a modest-cost replacement part but signals deferred maintenance across the cabinet.

Point 10 — Documentation package completeness

The documentation package is the single highest-leverage inspection item on a used IMM. Without it, a controller failure in month three can halt production for six weeks while parts are reverse-engineered. The minimum package should include: (1) electrical schematic, (2) hydraulic schematic, (3) mechanical assembly drawing, (5) original controller manual and current firmware version, (6) lubrication and maintenance schedule, (7) spare parts list with current OEM order codes.

Request the documentation package in writing before payment. Walk away from any seller who refuses—this is non-negotiable. The cost of compiling a missing documentation package post-purchase typically runs a substantial technician-time cost that is avoidable by a single written clause in the purchase contract. For buyers evaluating servo injection molding machine lineup options from the original equipment manufacturer, the documentation is included by default and represents one of the strongest arguments for buying new.

Decision Framework: When to Buy Used vs New

The decision between used and new is not a single threshold; it is a set of conditional recommendations based on application, cycle rate, and integration requirements. The matrix below summarizes nine common scenarios and the recommended path.

The matrix shows—per industry guidance from Plastics Industry Association and Plastics Technology—that used IMMs are best suited to low-cycle-rate, prototype, sample, training, and R&D environments where capital efficiency dominates and downtime is tolerable. For high-cycle-rate, engineering-plastic, medical, or fully-automated cell applications, the documentation, controller-version, and screw-condition risks of a used machine typically outweigh the headline price advantage.

Buying Checklist and Contract Clauses

Eight contract clauses should appear in any used-IMM purchase agreement. Each clause is negotiable; a seller who refuses any one is signaling risk that the buyer’s inspection uncovered. The clauses below are written for cross-border procurement and apply to both CIF and FOB terms.

Clause 1 — Documentation package delivery

Specify that the documentation package (electrical schematic, hydraulic schematic, mechanical assembly drawing, controller manual, maintenance schedule, spare-parts list) is a contractual deliverable. Payment of the final 20 percent should be contingent on receipt and verification of the documentation. Walk away from any seller who refuses this clause.

Clause 2 — Hour-count and alarm-log disclosure

Require the seller to disclose the controller’s logged clamp hours, shot count, and last-six-month alarm log in writing, signed by an authorized representative. Any discrepancy between disclosed and actual hours discovered during pre-shipment inspection entitles the buyer to a price reduction or contract termination.

Clause 3 — Screw-and-barrel condition warranty

Include a clause that the screw and barrel are warranted against weight-variation defects exceeding 1.5 percent for the first 90 days of operation. If the seller cannot warrant this, the buyer should budget screw-and-barrel replacement as part of the acquisition cost and negotiate accordingly.

Clause 4 — Controller version and spare-parts availability

Require the seller to disclose the controller model, firmware version, and a written statement of spare-parts availability for at least five years from the date of purchase. Controllers in current production at major manufacturers are typically supportable for five to seven years after the model is superseded.

Clause 5 — Pre-shipment inspection right

Retain the right to inspect the machine on the seller’s premises before final payment and before crating—a practice codified in the Society of Plastics Engineers buyer-engineer inspection guidelines. The cost of inspection—typically a small fraction of the purchase price for a qualified third-party inspector—is small relative to the risk of receiving a machine whose condition does not match the contract. For high-value purchases above the high-value threshold, this clause is non-negotiable.

Clause 6 — Installation, commissioning, and training

Specify whether installation, commissioning, and operator training are included in the purchase price. For a Chinese-supplied machine, commissioning is often quoted separately as a meaningful percentage of machine cost, depending on tonnage and integration complexity. Clarify in writing whether the seller’s technician will travel to the buyer’s site or whether commissioning will be conducted remotely via video.

Clause 7 — Warranty scope and duration

Standard used-IMM warranty from a Chinese supplier is 6 to 12 months on mechanical components, 3 to 6 months on electrical components. Warranty exclusions typically include consumables (screw, barrel, heaters, nozzles) and software. Read the warranty exclusions carefully. For critical applications, consider purchasing an extended warranty from the seller or from a third-party service provider.

Clause 8 — Spare-parts kit inclusion

A small spare-parts kit—contactors, relays, heaters, thermocouples, seal kits for the toggle linkages, and one spare proportional-valve solenoid—should accompany the machine. The cost is small relative to machine value, and the operational value is substantial, because shipping a single replacement part from China to a buyer’s factory typically takes 5 to 10 days. The kit converts that wait into a planned swap.

For buyers ready to evaluate servo injection molding machine lineup options side-by-side against the used inventory they are considering, the production line at ROBOT Ningbo is open to qualified buyers for an in-person walk-through. inspect our factory before you buy to schedule a visit; our engineering team will run a live molding demonstration and walk through the documentation package that accompanies every new machine.

Frequently Asked Questions