High NG Rate When Printing a Logo on Curved Workpieces: How to Reduce the Number of NG Parts

Printing a logo on a curved workpiece is often more difficult to control than printing on a flat surface because the Silicone Pad must make contact with the entire printing area, while the jig must support the workpiece in the same position every time. If these elements do not correspond with one another, problems may occur, including incomplete printing, unclear edges, positional deviation, or different printing results between workpieces.

Reducing NG parts should therefore not begin by adjusting several machine settings at the same time. The symptoms should be separated, and each part should be inspected individually, from the Pad shape, workpiece holding, and plate to the printing conditions.

Table of Contents

• Why curved workpieces are more likely to produce NG parts
• Begin by examining the pattern of the symptoms
• Check the shape and hardness of the Silicone Pad
• The jig must support the workpiece and allow repeatable positioning
• Check the plate before adjusting the printing conditions
• A step-by-step approach to reducing NG parts
• Which parts of the problem Tokuabe (Thailand) can help inspect
• FAQ
• Key terms for understanding this article

■　Why curved workpieces are more likely to produce NG parts

On a flat-surface workpiece, the Pad can make relatively direct contact with the printing area. However, when the surface is curved, the contact points change according to the shape of the workpiece. If one part of the Pad contacts the surface first, another part may not pick up the ink completely, causing the logo to be incomplete or uneven in color intensity.

The jig used to support the workpiece must also be considered. If the workpiece tilts or rotates even slightly, the position where the Pad makes contact will also change, which may cause the printing results to differ in each cycle.

■　Begin by examining the pattern of the symptoms

Before changing the Pad or adjusting the machine, several NG workpieces should be compared to determine whether the symptom repeatedly occurs in the same position or changes between workpieces.

If part of the printed pattern is missing in the same area every time, begin by checking the Pad shape, contact area, and plate surface. However, if the logo position or the location of the symptom changes, the workpiece placement and jig should be inspected first because the symptom may be related to inconsistent holding.

Separating the symptoms into incomplete printing, unclear edges, positional deviation, or marks on the workpiece helps narrow down the inspection points without changing every component at the same time.

■　Check the shape and hardness of the Silicone Pad

Silicone Pads are available in several shapes. Different shapes can be assembled together or produced according to the characteristics of the workpiece. For curved-surface applications, check whether the Pad can fully reach the surface where the logo must be printed and whether any part of the Pad contacts an edge or protruding part of the workpiece before reaching the printing position.

Silicone Pads are available in N, LH, and AT materials with several Shore E hardness levels. Therefore, simply stating that a hard Pad or soft Pad is being used may not provide enough information. The material type, hardness value, shape, and Pad size should all be recorded so that the results can be compared clearly.

Each material has different properties related to ink compatibility, ink release, durability, and antistatic performance. When changing the Pad, one factor should be changed at a time. For example, keep the same material and compare the hardness, or keep the same hardness and compare the shape. This makes it possible to identify which change is related to the NG parts.

■　The jig must support the workpiece and allow repeatable positioning

For curved workpieces, the jig does not only prevent the workpiece from falling. It must also help maintain the same orientation and position in every cycle. If there is clearance around the workpiece, or if the workpiece can move or tilt, the logo position and the Pad contact path may change.

The inspection points therefore include the supporting areas, holding tightness, and differences between workpieces.

■　Check the plate before adjusting the printing conditions

A plate used for Pad Printing involves factors related to pattern depth, edge sharpness, holes on the plate surface, and rust. If no abnormalities are found in the Pad shape or jig, check whether the logo pattern on the plate still retains its intended shape and whether it can hold ink across the entire area.

After confirming the Pad, jig, and plate, adjust the printing conditions by changing one item at a time and keeping samples from each condition. Adjusting several settings simultaneously may make it difficult to determine which change improved or worsened the printing result.

■　A step by step approach to reducing NG parts

First, collect samples of acceptable and NG workpieces, and separate them according to the location and characteristics of the symptoms.

Next, check whether the Silicone Pad shape covers the logo area and whether the jig can hold the workpiece in the same position.

Then check the Pad material type, hardness value, and size, together with the condition of the pattern on the plate. Once these components are stable, compare the printing conditions one setting at a time and record the result of each cycle.

This method does not begin by assuming whether the cause lies in the Pad or the machine. Instead, it uses the pattern of the NG parts to determine the inspection sequence, allowing each change to be supported by comparison data.

■　Which parts of the problem Tokuabe (Thailand) can help inspect

Tokuabe (Thailand) offers Silicone Pads in several shapes and materials, including assembled shapes and shapes produced according to the characteristics of the application. The company also offers plates, jigs, inks, Pad Printing machines, technical training, assistance with setting conditions, and printing services.

When inspecting NG parts on curved workpieces, prepare samples of acceptable and defective workpieces, images showing the locations of the symptoms, the workpiece shape and dimensions, logo size, and information about the Pad, jig, plate, ink, and current settings. This information helps identify which equipment component should be addressed first.

The conditions used for consideration include the workpiece shape, logo position, NG symptoms, and information about the equipment currently in use. If the information is still incomplete, please contact us.

※For more details, please download the attached information or submit an inquiry through the form below.

■　FAQ

Q1：If the printed pattern is incomplete on a curved surface, should a softer Pad be used?
A1：The Pad shape and contact path should be checked first. If the Pad cannot reach the entire logo area or contacts another part of the workpiece, changing only the hardness may not solve the problem.

Q2：If the logo position differs between workpieces, which part should be checked first?
A2：Begin by checking the jig and the workpiece placement method to determine whether the workpiece can be held in the same position and orientation every time. If the workpiece moves, tilts, or rotates, the Silicone Pad contact path and logo position may also change.

Q3：What information should be prepared for analyzing NG parts?
A3：Prepare samples of acceptable and NG workpieces, images showing the locations of the symptoms, the workpiece dimensions and shape, logo size, and information about the Pad, jig, plate, ink, and printing settings.

■　Key terms for understanding this article

• Silicone Pad : A silicone rubber pad used to pick up ink from the plate and transfer the pattern onto the workpiece
• Jig : A device used to support and position the workpiece during printing
• Shore E : A unit used to indicate the hardness level of a Silicone Pad
• NG : A workpiece whose printing result does not meet the specified acceptance criteria

※For more details, please download the attached information or submit an inquiry through the form below.