The Three Core Operations
A packaging line has three core operations in sequence: filling, sealing, and labeling. Everything else exists to support these three. Filling puts product into the package. Sealing closes the package so product cannot escape or spoil. Labeling identifies the package with brand, regulatory, and supply chain information.
The challenge is integration. Each operation has its own machine, its own cycle time, its own requirements for upstream handoff and downstream delivery. A line that has good individual machines but poor integration runs slower, scraps more, and breaks more often than a line with average machines and excellent integration.
This article covers the technology choices for each operation and how to integrate them. For the broader line context see the Production Line pillar. For layout and floor plan see line layout and floor plan design, and for what happens after labeling see end-of-line automation.
Filling Technology Selection
Filling technology is selected first because the filler sets the pace for the line. Four families dominate packaging.
Volumetric cup fillers meter by volume. A rotating cup of known volume fills with product, then dumps into the package. Cup fillers are simple, fast (60-120 BPM in multi-lane configurations), and cheap ($5,000-$20,000). They suit free-flowing granular products where density is consistent: rice, beans, candy, pet food. Accuracy is plus or minus 2-3% of target weight because density variation translates directly to weight variation.
Gravimetric net weighers and multihead weighers meter by weight. Net weighers use a single weigh hopper that fills to target. Multihead weighers use 10-16 weigh heads and a computer that combines 2-5 heads to hit target weight within tolerance. Multihead weighers are the standard for snack food, frozen vegetables, coffee beans, and any granular product where weight accuracy matters. Accuracy is plus or minus 0.5-1.5g at 60-120 BPM. Cost is $25,000-$60,000.
Auger fillers meter by screw rotation. An auger is a vertical screw that rotates a precise number of turns to dispense a known volume. Augers suit free-flowing powders: flour, sugar, protein powder, instant coffee, ground spices. Accuracy is plus or minus 1-2% of target weight. Speed is 40-80 BPM on a single lane. Cost is $15,000-$40,000 standalone, $35,000-$70,000 integrated with a VFFS bagger.
Flow meter fillers meter by mass using Coriolis or electromagnetic flow meters. They suit thin liquids: water, juice, edible oils, solvents. Accuracy is plus or minus 0.5% of target weight. Speed is 50-100 BPM on thin liquids. Cost is $45,000-$90,000 integrated.
For pastes (sauces, gels, toothpaste, adhesives above 5,000 centipoise), use piston fillers. Piston fillers meter by positive displacement and handle viscosities from water-thin to heavy paste. Cost is $40,000-$85,000.
The filler determines line speed. A multihead weigher feeding a VFFS at 100 BPM sets the line pace. Downstream stations must keep up.
Sealing Technology
Sealing closes the package. The sealing method depends on package material and product sensitivity.
Heat sealing is the standard for flexible film packaging. Two layers of film with heat-sealable coatings are pressed between heated bars or jaws. Heat melts the sealant layer, pressure bonds the layers, and dwell time allows the bond to set. Typical parameters: 140-180 degrees Celsius, 0.2-0.5 MPa pressure, 0.3-1.0 seconds dwell. Servo-driven heat sealers hold temperature to plus or minus 2 degrees and deliver the most consistent seals at high speed.
Ultrasonic sealing uses high-frequency vibration (20-40 kHz) to generate frictional heat at the seal interface. Advantages: works through contamination (powder in the seal area), works on difficult materials, no warm-up time. Disadvantages: 2-3x the cost of heat sealing, more complex maintenance. Ultrasonic is reserved for products where contamination in the seal is unavoidable, like powders that dust heavily, or for medical and pharmaceutical packaging where seal integrity is paramount.
Induction sealing applies a foil inner seal to a rigid container (bottle, jar) by electromagnetic induction. The induction coil heats the foil, which bonds to the container mouth. Induction sealing is for tamper-evident caps on bottles of liquid: pharmaceuticals, sauces, motor oil. It is not used on flexible film.
For flexible film at high speed (above 80 BPM), servo-driven constant-temperature heat sealing is the workhorse. Cost is integrated with the bagger ($30,000-$150,000 for a complete VFFS or pouch machine). Ultrasonic add-on systems run $20,000-$50,000 per station.
Sealing parameters must be matched to the film laminate. A PET/PE film needs different temperature and dwell than a NY/PE or a foil laminate. Mismatched parameters cause leakers, wrinkles, or cold seals. The film supplier provides seal curves showing seal strength versus temperature and dwell. Use them.
Labeling Technology
Labeling identifies the package. Three methods dominate.
Pressure-sensitive labeling applies a die-cut label with adhesive backing to the package. The label is peeled from a liner and pressed onto the package, typically by a wipe-down or tamp-blow applicator. Pressure-sensitive labeling is the most versatile: works on bags, bottles, boxes, pouches. Cost is $15,000-$50,000 per machine. Speed is 100-300 products per minute on round containers, 60-150 on flat surfaces.
Sleeve labeling applies a heat-shrink plastic sleeve over the container. The sleeve covers the entire container (full sleeve) or part (neck band, tamper-evident band). Sleeve labeling is for bottles and jars where 360-degree graphics matter: beverages, dairy, personal care. Cost is $40,000-$120,000 including the heat-shrink tunnel. Speed is 100-600 containers per minute.
In-mold labeling places the label inside the mold before blow-molding or injection-molding the container. The label bonds to the container wall during molding. In-mold labeling is for high-volume rigid containers (yogurt tubs, ice cream pails, paint cans). The label cannot peel, smear, or be removed. The container and label arrive as one piece. Cost is integrated with the molding machine.
Placement accuracy on a modern pressure-sensitive labeler with servo drive and product sensor is plus or minus 1-2mm at up to 300 products per minute. Sleeve labelers achieve similar accuracy on round containers. Vision systems verify placement and reject misapplied labels in real time.
Timing Integration: Handoff Between Stations
The integration challenge is timing. Product must hand off from filler to sealer to labeler with no collisions, no gaps that slow downstream, no bunch-ups that cause jams.
Three integration patterns dominate packaging.
Continuous motion runs all stations continuously. Product flows in a steady stream. Handoff is by synchronized timing: filler discharges at time T, sealer jaws close at time T plus delta, labeler triggers at time T plus delta plus epsilon. Continuous motion lines run 100-400 BPM and suit uniform products like candy bars, bottles, small pouches. All stations must be capable of continuous operation. Capital cost is high because every station is a continuous-motion machine.
Intermittent motion indexes product through stations in steps. Product stops at the filler, fills. Indexes to the sealer, seals. Indexes to the labeler, labels. Intermittent motion lines run 30-120 BPM and suit pre-made pouch machines, cartoners, and any product where station dwell time is required. Capital cost is lower per station because each station only needs to operate when product is present.
Buffer zones decouple stations. A buffer between filler and sealer absorbs short filler stoppages so the sealer keeps running. A buffer between sealer and labeler absorbs short labeler stoppages. Buffer sizing is 30-60 seconds of product at line speed. Larger buffers hide upstream problems and let scrap accumulate. Smaller buffers cause cascade stoppages.
The handoff signal logic is critical. The downstream station signals ready-for-product. The upstream station discharges only when the downstream is ready. If downstream is not ready (jammed, changeover, fault), upstream holds product. This prevents product pile-up at the handoff.
Modern lines use a line control PLC that coordinates all stations. The line PLC tracks product position through the line, triggers each station at the right moment, and handles faults by stopping upstream of any faulted station. This is why mixing vendors without a line control plan fails: each vendor assumes their machine is the line master.
Quality Control Between Stations
Quality control between stations catches defects before they propagate. The principle: detect and reject at the source, not at the end of the line.
Between filling and sealing: weight verification. A checkweigher or load cell confirms fill weight. Overfills cost product giveaway. Underfills risk consumer complaints and regulatory action. Reject limits are typically plus 2 sigma to minus 1 sigma of the target. The checkweigher rejects out-of-spec packages before they reach the sealer.
Between filling and sealing: contaminant detection. A metal detector or X-ray system detects metal, glass, dense plastic, and bone fragments. The detector rejects contaminated packages before sealing. Post-seal detection is possible but sealing in contamination is worse than catching it pre-seal.
Between sealing and labeling: seal integrity check. A vision system inspects every seal for leakers (grease wicking, drip staining), wrinkles, cold seals (discolored seal area from inadequate heat), and contamination in the seal. Reject rates above 1% indicate a sealing problem that needs immediate attention.
After labeling: label presence and placement. A vision system verifies the label is present, readable, and within placement tolerance. Code date (lot, expiry) must be present and legible. Auto-reject any package with missing, misapplied, or unreadable labels.
Each QC station should auto-reject. Operator-pulled samples every Nth package are QC theater, not QC. Real QC is 100% inspection with automatic reject.
Worked Example: 120-CPM Snack Line Integration
A 120-counts-per-minute snack line packaging potato chips into 50g stand-up pouches. The integration story.
Filling: 14-head multihead weigher. Selected for plus or minus 0.8g accuracy at 120 BPM. The weigher discharges into a VFFS that forms the stand-up pouch. Weigher discharge is timed to the VFFS film pull: weigher dumps as the film pull completes, product drops into the formed pouch.
Sealing: VFFS with servo-driven heat sealing. Jaws at 165 degrees Celsius, 0.4 MPa pressure, 0.6 seconds dwell. Top and bottom seals on the pouch, plus a bottom fin seal. The VFFS servo pulls film at 120 cycles per minute, synchronized to the weigher discharge.
Labeling: pressure-sensitive labeler after the VFFS. Pouches exit the VFFS on a conveyor, single-file. The labeler has a product sensor that triggers label dispense when each pouch is in position. Label placement is on the front face of the pouch, plus or minus 1.5mm at 120 pouches per minute.
Between filling and sealing: checkweigher. A checkweigher sits between the multihead weigher and the VFFS discharge point, weighing each pouch as it exits the VFFS. Rejects plus 3g and minus 1.5g from target. Rejects go to a locked reject bin for rework or scrap.
Between filling and sealing: metal detector. A metal detector sits after the checkweigher, before the labeler. Detects ferrous, non-ferrous, and stainless steel contaminants down to 1.5mm. Auto-reject.
Between sealing and labeling: vision system. A vision system inspects each pouch for seal integrity (no wrinkles, no cold spots), print registration, and code date legibility. Auto-reject on any defect.
Buffer zones: minimal. A 30-second buffer between VFFS and labeler absorbs short labeler stoppages without stopping the VFFS. No buffer between weigher and VFFS: they run synchronized.
Line control: one line PLC. A line control PLC coordinates weigher discharge, VFFS cycle, checkweigher, metal detector, vision system, and labeler. The PLC tracks each pouch through the line by position and triggers each station at the right moment. Any station fault stops upstream stations.
Performance: 120 CPM sustained, 2-3% reject rate, 92% OEE. The line runs 120 pouches per minute with 2-3% auto-rejected (mostly overfills and the occasional cold seal). Overall equipment effectiveness is 92%, well above the industry average of 60-70% for snack lines.
Capital cost: $380,000. Multihead weigher $45,000. VFFS with servo sealing $120,000. Checkweigher $25,000. Metal detector $18,000. Vision system $45,000. Labeler $35,000. Conveyors and line control $40,000. Installation and commissioning $12,000.
This is a well-integrated line. The integration, not the individual machines, is what delivers 92% OEE. The same machines integrated poorly would deliver 65-70% OEE at the same capital cost.
The lesson: spend engineering time on integration, not just on machine selection. The 25-point OEE gap between well-integrated and poorly integrated lines of equivalent hardware is the largest single lever in packaging line performance.