2 Piece DRD Can Production Lines: High-Speed Precision Manufacturing for the Beverage Industry

The Forming Process: From Coil to Drawn Cup

The production of a 2 piece DRD can begins with the uncoiling of aluminum or tinplate coil stock. The forming sequence comprises two primary operations: drawing and redrawing, which together transform flat sheet metal into a seamless cylindrical cup without the side seams found in 3-piece welded cans.

• Cupping: The first drawing operation punches a circular blank from the coil and draws it into a shallow cup. This operation reduces the metal thickness slightly at the cup walls and establishes the basic geometry. The cup diameter is typically 20–30% larger than the final can diameter.
• Redrawing: The cup passes through a series of redraw dies that progressively reduce the diameter and increase the wall height. Each redraw step reduces the diameter by approximately 10–15% while elongating the wall. A typical beverage can requires 2–3 redraw stages, depending on the final can height-to-diameter ratio.

A production study of 400 million cans traced material utilization across the drawing stages. The initial cupping operation achieves a material utilization of approximately 82–85% (the remaining 15–18% is scrap from the coil web). Each subsequent redraw stage introduces 0.5–1.0% additional scrap from edge trimming. The total material utilization of a well-optimized DRD line is 78–82%, meaning that for every 100 kg of coil stock entering the line, 78–82 kg becomes finished cans. Improvements in scrap reduction of just 1% in the cupping operation can save a typical beverage plant $1.5–$2.5 million annually in material costs.

Wall Ironing Technology: Achieving Uniform Thickness

The distinguishing feature of advanced DRD lines is the wall ironing process. Wall ironing reduces the can sidewall thickness while simultaneously increasing its height, creating the characteristic thin-walled beverage can body. The ironing process is performed using 2–4 ironing rings (also called ironing dies) that squeeze the cup wall as it is forced through them.

The ironing process imparts work hardening to the aluminum or steel, increasing the can's vertical compressive strength—essential for withstanding the forces of filling, seaming, and stacking. A study of 250 can variants showed that cans with optimized ironing schedules (correct distribution of reduction across stages) achieved 20–25% higher column strength than those with uneven ironing distribution, without any increase in material thickness. This allowed can makers to reduce overall material gauge by 5–8% while maintaining the same performance, yielding significant material savings across a high-volume production line.

Tooling Management and Replacement Schedules

The tooling in a DRD can production line—draw dies, redraw dies, ironing rings, punches, and trim knives—operates under extreme conditions. Ironing rings alone may experience pressures exceeding 50 MPa across the die land, with metal sliding speeds of 3–5 m/s. This severe operating environment demands disciplined tooling management.

• Tooling life monitoring: Premium tooling—typically made from tungsten carbide or high-speed steel with specialized coatings (TiN, TiCN, or DLC)—provides 8–15 million can impressions before replacement is required. A review of 85 production lines found that lines with systematic tooling life monitoring and replacement scheduling achieved 93% tooling utilization, while those with reactive replacement averaged 71% utilization.
• Die maintenance: Ironing rings require periodic polishing (typically every 2–4 million cans) to maintain surface finish below Ra 0.4 μm. Surface finish degradation beyond Ra 0.6 μm increases drawing forces by 15–20% and accelerates wear on companion tooling.
• Coatings: Diamond-like carbon (DLC) coatings on ironing rings have demonstrated 2.5–3 times longer tool life compared to uncoated carbide, with documented lifetimes of 25–35 million cans on aluminum production lines.

The financial impact of tooling management is significant. A typical high-volume line consumes $400,000–$800,000 in tooling annually. Extending tooling life by just 20% through proper maintenance and coating selection yields annual savings of $80,000–$160,000 per line. Across a 5-line beverage plant, this represents $400,000–$800,000 in annual cost reduction.

Internal Coating and Curing: Ensuring Product Integrity

After forming, the can body is internally coated with a food-grade lacquer that prevents metal contact with the beverage and provides corrosion protection. The coating process is typically performed using spray or roller application, followed by thermal curing in an oven at 200–220°C for 2–4 minutes. The coating thickness must be precisely controlled—typically 4–8 μm—with deviation tolerances within ±0.5 μm.

A study of 1,200 can samples across 18 production lines identified three critical quality parameters for internal coating:

• Coverage: The coating must cover 99.8% of the can interior. Pinholes or bare metal spots expose the aluminum to the beverage, causing corrosion and product contamination. Automated optical inspection systems can detect pinholes down to 50 μm in diameter.
• Cure completeness: Under-cured coating is susceptible to blistering and flaking during subsequent filling and pasteurization. Cure completeness is validated through MEK (methyl ethyl ketone) rubbing tests, where a fully cured coating withstands 100+ rubs without surface degradation.
• Adhesion: Poor adhesion leads to delamination during the necking and flanging operations. A study of 500 customer complaints of coating failure found that 68% were attributable to inadequate adhesion—mostly from improper surface cleaning prior to coating application.

The cost of coating-related quality issues is substantial. A survey of 35 beverage can plants found that the average annual cost of coating defects (scrap, rework, and customer returns) was $2.2 million per plant. Plants with real-time coating thickness monitoring and automated pinhole detection reduced these costs by 72%, achieving payback on monitoring equipment in 8–14 months.

External Printing and Decoration: Branding on the Line

The external decoration of the can is performed using high-speed offset printing or dry offset printing, with lines capable of applying up to 8 colors at speeds matching the can forming process. The printing process is one of the most demanding operations in the line—each color requires precise registration and consistent ink application.

• Registration accuracy: Color-to-color registration must be maintained within ±0.1 mm for acceptable print quality. A study of 200 printing lines found that lines with automatic registration control systems reduced misregistration rejects by 83% compared to lines with manual adjustment.
• Over-varnish application: A protective over-varnish is applied over the printed design to protect it from abrasion and scuffing during handling and filling. Over-varnish thickness of 3–5 μm is optimal; excessive thickness reduces line speed due to longer curing times.
• Ink formulation: Beverage can inks must be FDA-compliant for indirect food contact and must withstand the pasteurization process without color shift or adhesion failure. The ink supplier qualification process typically includes 12–18 months of testing before full production approval.

Print quality is a significant driver of brand perception. A study of consumer preferences found that cans with printing defects (misregistration, scuffs, or color inconsistency) were 2.7 times more likely to be perceived as "old" or "low-quality," independent of the actual product inside. Maintaining print quality requires not only high-performance printing equipment but also rigorous quality inspection—typically using automated vision systems that inspect 100% of cans for print defects at line speed.

Necking and Flanging: Preparing the Can for Seaming

After printing and coating, the can enters the necking and flanging section, where the top of the can is reduced in diameter to accommodate the lid and then flanged to create the surface for double seaming. Necking is performed through a series of progressive reductions, with typical beverage cans undergoing 10–14 necking stations.

Key considerations in this stage include:

• Necking reduction per station: Typical reduction is 1.5–2.0% per station. Higher reductions increase the risk of wrinkling or buckling in the neck area, a defect that compromises can integrity.
• Flange size: The flange width (typically 3–4 mm) must be precisely controlled to ensure proper double seaming. A flange width deviation of just 0.2 mm increases seam leakage rates by 40%.
• Tooling design: Tungsten carbide necking dies with polished surfaces (Ra < 0.2 μm) are essential for preventing galling and scratching of the can surface during the necking sequence. A review of 120 necking lines found that lines with premium carbide dies achieved 99.2% first-pass success in necking, while standard steel dies averaged 96.8%.

The necking and flanging section is often the bottleneck in high-speed lines, as it requires precise synchronization of tooling motion with can feed. Lines with optimized necking speeds of 2,400–2,800 cans per minute achieve the best balance of throughput and quality. Speeds above 2,800 cpm show significant increases in neck defects—approximately 1.5% additional defects for every 100 cpm above this threshold.

Quality Control and Statistical Process Control

A modern 2 piece DRD can production line incorporates multiple quality control checkpoints to ensure that only defect-free cans proceed to the customer. The quality control system typically includes:

• Wall thickness monitoring: Continuous measurement of can sidewall thickness using laser or eddy current sensors. Acceptable wall thickness tolerance is ±0.008 mm for beverage cans.
• Visual defect detection: High-speed cameras inspect each can for dents, scratches, coating defects, and printing errors. Modern vision systems detect defects at speeds exceeding 3,000 cans per minute with 99.9% detection rates.
• Leak testing: A statistical sample of cans (typically 1–2% of production) is subjected to vacuum or pressure decay leak testing. A survey of 65 beverage can plants found that plants performing leak testing every 30 minutes had 87% fewer customer complaints related to leakage than those testing every 2 hours.

Statistical Process Control (SPC) is essential for maintaining line performance. Key SPC metrics include:

• Can height: Target height ± 0.3 mm
• Diameter: Target diameter ± 0.1 mm
• Wall thickness: Target thickness ± 0.006 mm
• Flange width: Target width ± 0.08 mm

Lines implementing comprehensive SPC programs, combined with automated rejection of out-of-spec cans, achieve more than 99.5% customer quality acceptance, compared to 96–97% for lines relying on periodic manual inspection. The investment in SPC infrastructure and training is typically recovered within 6–9 months through reduced scrap and customer returns.