Redraw Training Course: Mastering the Art of Cup Resizing

This Redraw Training Course, created by Sirack Yohannes of Clever Can Solutions, provides an in-depth guide to the redraw process in can manufacturing. By mastering this foundational stage, operators can help ensure that every cup smoothly transitions into a perfectly formed can.


Course Outline


  • About Redraw: Understanding the importance of the redraw process.

  • System Components: An overview of essential components and their functions.

  • Redraw Defects: Common defects, their causes, and how to prevent them.


Key Objectives in the Redraw Process


The primary goal of the redraw stage is to resize the cup to match the final can diameter, ensuring uniform wall thickness and height. During this step, the cup is securely clamped to prevent movement, keeping it perfectly aligned with the forming tools.

System Components and Their Functions

  • Airbags: Responsible for applying uniform pressure to keep cam followers in stable contact with cams. The rear airbags inflate to press the cam followers against the cams, ensuring a stable and precise operation.

  • Hold Down Lever: Converts rotational motion into linear movement. As the cams rotate, cam followers move along the cam’s surface, allowing the hold-down lever to pivot, converting the rotational motion into linear motion.

  • Cams: The cam profiles determine movement patterns in the redraw process. The shape of each cam profile controls timing and motion, guiding how the cam followers move.

  • Connecting Links: These transfer motion between the rear hold-down lever and push rods, and in some cases assist with front piston alignment.

  • Push Rods: Transmit force from the rear hold-down lever to the front piston via connecting links. As the cam rotates, push rods are engaged, pushing or pulling the front piston.

  • Front Hold Down: This mechanism holds the cup in place against the redraw die, preventing movement during forming and ensuring alignment.


Sustainable Success Through Wear and Maintenance

To ensure the redraw process operates smoothly and reliably, regular maintenance is crucial:

  • Inspection: Regularly check for wear, damage, and misalignment.

  • Lubrication: Proper lubrication reduces friction and wear.

  • Adjustment: Make adjustments as necessary to maintain optimal operation.

  • Replacement: Promptly replace worn parts to prevent damage to other components.


Common Redraw Defects and Their Causes

The course also addresses frequent redraw defects and their potential causes:

  • Punch Through at Start of Redraw: May result from scrap in the forming area, insufficient overtravel on the front piston, worn redraw die, or a worn redraw sleeve.

  • Punch Through Partial Form: Possible causes include excessive redraw clamping pressure, incorrect tooling geometry, or cans caught between the redraw die and 1st iron stage.

  • Folded Over Cup Sidewall: Can occur due to a mis-fed cup, cup feed timing issues, or out-of-spec cup ovality.

  • Redraw Wrinkles: Often due to insufficient overtravel or worn parts causing a loss of overtravel.

  • Ears/Clip Outs: May be caused by the cup being pinched in the redraw area, due to insufficient clearance between the cup feed cam, cup locator, and cup.