What steps are involved in the manufacturing process for metal cans?

From raw material selection to the finished metal cans reaching store shelves, the entire process involves a series of precise, interconnected stages. Each stage integrates advanced machinery, rigorous quality inspections, and meticulously controlled process conditions to create high-performance packaging. Metal can production is divided into several key steps, and understanding these processes can help brands appreciate the technological expertise and scale efficiencies that underpin today’s metal can packaging solutions.

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Raw Material Sourcing and Pretreatment for Metal Cans

The first step in manufacturing metal cans is sourcing high-quality raw materials. Most metal cans are made from either cold-rolled steel sheet (tinplate) or aluminum coil, with the choice of these two materials determined by their mechanical properties, corrosion resistance, and cost-effectiveness. Suppliers typically provide coils with thicknesses ranging from 0.12 mm to 0.30 mm, depending on the intended use of the can. Beverage cans normally use 0.12 to 0.15 mm aluminum, while food cans may require 0.20 to 0.30 mm steel.

Upon arrival, the metal coils require surface cleaning to remove oil, dirt, and mill scale. An automated cleaning machine sprays an alkaline or acidic solution, followed by a rinse with deionized water. The coil then enters a tempering furnace, where a precise heating profile optimizes yield strength and ductility. Proper pretreatment ensures uniform formability in subsequent processing steps, resulting in up to a 15% reduction in scrap.

Sheet Forming for Metal Cans: Rolling and Slitting

Next, the pretreated coil enters the rolling mill, where heavy rollers gradually reduce the thickness and refine the grain structure. The multi-stand cold rolling mill applies up to 500 tons of pressure per stand to achieve tight thickness tolerances (±0.002 mm). This controlled reduction process improves surface finish and mechanical uniformity.

After rolling, a high-precision slitting machine cuts the parent coil into narrower strips—typically 520-580 mm for standard food cans and 153-156 mm for two-piece beverage can bodies. The slitting machine uses a laser-guided blade to minimize burr formation. Furthermore, proper slitting width and edge quality are crucial for efficient downstream stamping and forming, directly impacting line uptime.

Drawing Process

The deep-drawing and indenting (D&I) process transforms flat blanks into tall, seamless can bodies—the hallmark of two-piece can production. First, a blanking press, using a die diameter customized to the desired can outer diameter, cuts discs from the cut strip at a rate of up to 500 blanks per minute. Then, a deep-drawing die draws each blank into a cup shape using a hydraulic or mechanical press.

Next, a series of reducing rings gradually reduces the can wall thickness from the base to the open end, achieving uniform wall thickness. Can-reducing lines operate at speeds of 450-650 cycles per minute, producing thousands of metal tins per hour. Finally, a trimming cutter cuts the can specification body and forms a flange in preparation for sealing.

Strike and Stretch Process

When the two-piece can body is terminated, different lines produce the “can lid” or “can base” through stamping or stretching. During the stamping process, a coil-fed press forms the can base in a single pass, creating a double seam for subsequent end-joining. Stretched can bases for food cans utilize a progressive stamping process—first stretching, then flanging and curling, before finally forming the base and creating the curled seam. Quality is paramount: end concentricity tolerances must be maintained within ±0.10 mm to ensure a leak-free seam. Automated vision systems inspect thousands of ends per minute, detecting defects such as irregular end curling or coating imperfections.

Surface Treatment and Decoration

After forming the cans body and base, manufacturers coat and print the metal cans. They apply the inner coating (typically epoxy, phenolic, or polymer lacquer) using a spray or roller system and then cure it in an induction or convection oven at 180–200°C. These coatings prevent corrosion and ensure food safety, meeting FDA and EU food contact standards.

Manufacturers perform exterior printing using digital or UV offset printing, allowing them to apply full-package, high-resolution graphics. They can equip modern production lines with up to eight color stations, producing vibrant, durable graphics at line speeds of up to 300 metal cans per minute. They also add overprint varnish and anti-tamper inks to enhance brand protection and consumer appeal.

Inspection and Quality Control

Rigorous inspection procedures ensure product quality throughout the entire production process. Online thickness gauges, eddy current sensors, and laser micrometers control wall and base thickness to within ±0.01 mm. Meanwhile, vision systems check coating uniformity and print registration to within ±0.2 mm. Statistical process control (SPC) charts track key metrics—drawing force, ironing pressure, and coating weight—to detect trends and initiate corrective actions before defects accumulate. As a result, modern metal cans production lines achieve defect rates of less than 50 ppm, ensuring consistent high performance and reducing costly recalls.

Ultimately

Metal cans manufacturing involves seven closely linked steps: raw material pre-processing, sheet rolling and slitting, stretch forming, final production, coating and printing, comprehensive quality control, and automated packaging and distribution. Each stage requires specialized equipment, precise control, and continuous monitoring to achieve the performance, safety, and aesthetic standards expected by brands and consumers. By mastering these processes, metal cans manufacturers can provide cost-effective, sustainable packaging solutions that maintain product integrity and brand impact.