2D Direct Parts Marking Guideline B-17

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1 B-17

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3 AIAG PUBLICATIONS An AIAG publication reflects a consensus of those substantially concerned with its scope and provisions. An AIAG publication is intended as a guide to aid the manufacturer, the consumer and the general public. The existence of an AIAG publication does not in any respect preclude anyone from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the publication. CAUTIONARY NOTICE AIAG publications are subject to periodic review and users are cautioned to obtain the latest editions. MAINTENANCE PROCEDURE Recognizing that this AIAG publication may not cover all circumstances, AIAG has established a maintenance procedure. Please refer to the Maintenance Request Form at the back of this document to submit a request. APPROVAL STATUS The AIAG Board of Directors approved this document for publication on February 25, Published by: Automotive Industry Action Group Lahser Road, Suite 200 Southfield, Michigan Phone: (248) Fax: (248) AIAG Copyright and Trademark Notice: The contents of all published materials are copyrighted by the Automotive Industry Action Group unless otherwise indicated. Copyright is not claimed as to any part of an original work prepared by a U.S. or state government officer or employee as part of the person s official duties. All rights are preserved by AIAG, and content may not be altered or disseminated, published, or transferred in part of such content. The information is not to be sold in part or whole to anyone within your organization or to another company. Copyright infringement is a violation of federal law subject to criminal and civil penalties. AIAG and the Automotive Industry Action Group are registered service marks of the Automotive Industry Action Group Automotive Industry Action Group B-17 1 Issue: 01 Dated: 2/03

4 FOREWORD This guideline was prepared by the 2D Direct Parts Marking (DPM) Work Group of the Automatic Identification Data Collection Work Group. AIAG believes that the use of this guideline will help maximize the benefits of auto ID as an industry-wide productivity tool. Without guidelines, industry use of auto ID technology would be encumbered by many different protocols and methodologies. The mission of the 2D DPM Work Group is to provide information on direct parts marking of Data Matrix and/or QR Codes using laser, dot-peen, and inkjet marking technologies. This guideline was developed to help educate end users on the most common marking methods used throughout the automotive supply chain. The team obtained input from automotive industry standards and companies, non-automotive industry standards and companies, parts-marking technology providers, codereading technology providers, label companies, and various industry experts. In developing this guideline, the project team considered current 2D symbology parts identification methods, the common needs of manufacturing and assembly locations, and the performance capabilities of various marking and scanning technologies. After much research and many deliberations, a consensus was developed. B-17 2 Issue: 01 Dated: 2/03

5 ACKNOWLEDGEMENTS The following individuals and companies were instrumental in the development of this guideline: Fred Ayar John Balint Dennis Barlow Garry Boyd** Steve Brian Ed De Costa John Druskinis Valjean Eckert Luis Figarella Larry Graham Marsha Harmon Orlan Hayes Doug Horst Bill Hoffman Bob Jansen**** Bill Leedy Forrest Morgeson*** Gary Niemenski Rick Scorey Michael Stover* Richard Tervo Yuji Tsujimoto Lowry Computer Products Visteon Chassis Systems Ford Motor Company Ford Motor Company Rofin-Baasel, Inc. Cognex Corporation Avery Dennison Corporation Advanced Identification Management, Inc. RVSI General Motors Corporation QED Systems Telesis Technologies, Inc. EDS Corporation Intermec VIA Information Tools, Inc. Dana Corporation Telesis Technologies, Inc. Rofin-Baasel, Inc. Freedom Technologies Corporation Advanced Identification Management, Inc. Daimler Chrysler Corporation Denso International America, Inc. *Chair ** Co-Chair *** Secretary **** Document Coordinator B-17 3 Issue: 01 Dated: 2/03

6 TABLE OF CONTENTS AIAG PUBLICATIONS... 1 FOREWORD... 2 ACKNOWLEDGEMENTS... 3 TABLE OF CONTENTS INTRODUCTION Scope DEFINITIONS GENERAL: 2D DIRECT PARTS MARKING (DPM) Project Considerations Mark Durability Part Characteristics INKJET MARKING Overview Mark Geometry Mark Quality Reading Considerations DOT-PEEN MARKING Overview Mark Geometry Mark Quality Reading Considerations LASER MARKING Overview Mark Geometry Mark Quality Reading Considerations READING AND VERIFICATION Fundamentals of Reading Symbol Quality Grading Quality Parameters and Grading for 2D Symbols Scan Grading Physical Issues REFERENCES ABOUT AIAG MAINTENANCE REQUEST B-17 4 Issue: 01 Dated: 2/03

7 FIGURES Figure 1. Comparator Showing Cast Surface Roughness Figure 2. Texture to Improve Readability Figure 3. Marking Curved Surfaces Figure 4. Sample Inkjet Marks Figure 5. Continuous Inkjet System Figure 6. White Inkjet Ink on Green PCB When Imaged with Red Light Figure 7. Ultraviolet Inkjet Mark Figure 8. Inkjet with White Background Added Figure 9. Single Dot Mark Geometry Figure 10. Multiple Dot Mark Geometry Figure 11. Cross Sections of Material Marked with Various Stylus Cone Angles Figure 12. Preferred Stylus-to-Target Configuration Figure 13. Mark Diameter Range Using 30 Stylus Figure 14. Data Matrix Dot-Peen Marking with and without Proper Illumination Figure 15. QR Code Dot-Peen Marking with and without Proper Illumination Figure 16. Photonic Spectrum and Laser Wavelengths Figure 17. Laser Etching/Engraving Figure 18. Laser Annealing Figure 19. Laser Discoloration Figure 20. Laser Marking Enhancers Figure 21. Galvonometer Beam Steering Figure 22. Flying Optic Beam Steering Figure 23. Mapping of Alphabetic and Numeric Overall Symbol Grades Figure 24. Results of Using Option A Figure 25. Results of Using Option B Figure 26. Angle Distortion Figure 27. Variation from Nominal Fill TABLES Table 1. Terms and Definitions... 7 Table 2. Marking Method Selection Table 3. Marking Method Test Specifications Table 4. Photonic Spectrum and Laser Wavelengths Table 5. Equivalence of Numeric and Alphabetic Quality Grades Table 6. Test Parameters and Values B-17 5 Issue: 01 Dated: 2/03

8 1.0 INTRODUCTION This two-dimensional (2D) Direct Parts Marking (DPM) Guideline provides information for the marking and reading of Data Matrix and/or QR Code symbols marked directly on parts using laser, dot-peen, and inkjet technologies. The three technologies noted in this document are currently the most common methods for marking variable data 2D codes directly on parts in the automotive industry. This 2D DPM guideline is intended as a supplement to the AIAG B-4 Parts Identification and Tracking Application Standard. As a guideline, this document is intended to provide general information in order to help users of DPM technology. This guideline was developed in part based on a review of many related standards, which are listed in Section 8.0 References. 1.1 Scope To make this guideline as comprehensive as possible, the document begins with the terms most commonly used in the auto ID industry and continues through the specialized characteristics of each technology. Items to consider when evaluating marking projects Features and benefits of laser, inkjet, and dot-peen Qualities of each symbology Decoding techniques All exhibits are for illustrative purposes only and may not be to scale or code print quality guidelines. B-17 6 Issue: 01 Dated: 2/03

9 2.0 DEFINITIONS There are several terms and definitions associated with the subject of this guideline that have special meaning to the automotive industry. Table 1. Terms and Definitions TERM Direct Part Marking Global Threshold Life of a Part Mark Permanent Mark Code Verification Code Validation Intrusive Marking Module Non-intrusive Marking Unused Error Correction Symbol Substrate Collimated Light DEFINITION The use of technology such as laser, dot-peen, and inkjet to create an image on an item. The reflectance value (usually the average of the maximum and minimum reflectance values in an image) that determines the boundary level above which pixels are considered white and below which they are considered black. Anticipated life cycle, as defined by the manufacturer. The result of lasering, dot-peening, or inkjetting. A mark on an item that can survive its intended environment and remain readable for the anticipated life cycle of the item. Confirmation that a symbol is printed correctly and conforms to a specific standard. Confirmation that data in a symbol is encoded using the correct semantics and syntax and the data is appropriate for the intended application. Markings that alter the part surface and are considered controlled defects. A single cell in a matrix symbology used to encode one bit of data. Markings that are produced without damaging the part. The amount of remaining error-correction available in a symbol after existing damage/errors have been compensated for in the default decode algorithm. A Data Matrix or QR Code. Material upon which a mark is placed. Columns of illumination in parallel. B-17 7 Issue: 01 Dated: 2/03

10 3.0 GENERAL: 2D DIRECT PARTS MARKING (DPM) This portion of the guideline describes some general reasons for direct part marking (DPM), factors to consider when starting a DPM project, and how to select the most appropriate DPM technique for a given application. The following are some reasons for using DPM: Traceability is required after the product is separated from its temporary identification. The part is too small to be marked with bar code labels or tags. The part is subjected to environmental conditions that preclude the use of add-on identification means. The use of DPM methods may be more cost-efficient than individual item labels. Identification is required for at least the anticipated life cycle of the part, as defined by the manufacturer. The use of DPM may also be beneficial in the following manufacturing related processes: Production Automation Inventory Management Traceability/Part Path History Lot Control Select Fit Error Proofing Serialization Product Identification Quality Control/Defect Containment B-17 8 Issue: 01 Dated: 2/03

11 3.1 Project Considerations Once the determination has been made to use DPM, the following implementation issues should be reviewed: Which marking methodology is most appropriate for the application? Where will the mark be placed and how much room is available for the mark? What and how much information do you need to mark? Will the amount of information required fit in the space allowed for marking? When possible important information should also be marked in human-readable form for use when code-reading devices are not available. Must the part be modified in order to accommodate the mark and how will this modification and the mark affect part appearance? When will the part be marked in the manufacturing process? How quickly do you need to mark the part (cycle time)? How will you integrate the marking device into the production process How will you communicate data to be marked to the marking device? How do you control the marking process? Correct mark on part proper information Part change over new identification What environmental conditions will the mark have to survive? Is a permanent mark required? At what points will the mark be read? What are the reading conditions where the mark must be read? What type of material is being marked? (See Table 2) What level of equipment maintenance is required for a given marking technology and given manufacturing environment? B-17 9 Issue: 01 Dated: 2/03

12 Material To Be Marked Marking Process Table 2. Marking Method Selection A L U M I N U M Metallics F E R R O U S M A G N E S I U M T I T A N I U M C E R A M I C S G L A S S Non-Metallics Dot-peen Laser Inkjet = Acceptable marking process for noted material F I B E R G L A S S P L A S T I C S R U B B E R 3.2 Mark Durability When selecting a marking method, testing parameters should be developed to determine if the mark can survive its intended environment and remain decodable. Testing such as accelerated weather testing should be structured to simulate expected conditions. Several standardized testing methods typically used for this purpose are listed in the table below. These are for reference only and are not mark survivability requirements. Table 3. Marking Method Test Specifications Test Abrasion Resistance Specification Number ASTM D Adhesion ASTM D Atmospheric Acid Pollution Resistance ASTM D1308 (with addition of sulfuric acid testing) Boiling Water ASTM D Specification Title Standard Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser Standard Test Methods for Measuring Adhesion by Tape Test Standard Test Method for Effect of Household Chemicals on Clear and Pigmented Organic Finishes Standard Practice for Testing Water Resistance of Coatings Using Water Immersion B Issue: 01 Dated: 2/03

13 Table 3. Marking Method Test Specifications (continued) Test Corrosion Resistance Specification Number ASTM B Specification Title Standard Practice for Operating Salt Spray (Fog) Apparatus Mar Resistance ASTM D Standard Test Method for Mar Resistance of Plastics Thermal ASTM D Ultraviolet Exposure ASTM G53-96 Water Resistance ASTM D Water Resistance ASTM Weathering ASTM G26-95 Standard Test Methods for Evaluating Coatings for High Temperature Service Standard Practice for Operating Light- and Water-Exposure Apparatus (Fluorescent UV-Condensation Type) for Exposure of Nonmetallic Materials Standard Practice for Testing Water Resistance of Coatings Using Water Immersion Standard Practice for Testing Water Resistance of Coatings in 100% Relative Humidity Standard Practice for Operating Light-Exposure Apparatus (Xenon-Arc Type) With and Without Water for Exposure of Nonmetallic Materials Note: ASTM Specifications can be acquired from the American Society for Testing and Materials. 3.3 Part Characteristics When selecting a marking method and symbol density, you must determine if the item requires additional surface preparation prior to marking. This analysis should address the following issues: Is the item flat in the area to be marked? How rough is the item s surface compared to required module size? Does the surface finish cause excessive amounts of shadowing and/or glare? Does the surface provide sufficient contrast for decoding? Will the surface be painted, coated, or treated at any point? The surface of an item to be marked should not be rougher than the minimum module size in the symbol. Symbol marking should be limited to a module size ratio of at least 5:1 of the surface roughness, regardless of the marking method selected. For example, cast surfaces present a unique symbol decoding challenge because the surface irregularities (pits) create shadows that can be misinterpreted by the decoding software as dark data modules. Consequently, individual data modules in the symbol must be larger than the surface irregularities so that the decoding software can differentiate between the two features. B Issue: 01 Dated: 2/03

14 Figure 1 is for illustrative purposes only and shows the effect of a surface on the readability of a symbol. Figure 1. Comparator Showing Cast Surface Roughness Painted and coated surfaces present special concerns when a mark is intended to be permanent. If the item is marked prior to coating, the coating may obscure the mark. If the item is marked after coating, the marking method may damage the coating s integrity. If a mark is placed on a coating, then the mark durability is equally dependent on the coating and marking method. Surface enhancement such as machining, texturing, or cleaning may be required to improve marking and reading quality. In most cases, a smooth matte, or dull finish is preferred over a shiny surface. The area of the finished surface should be greater than the mark itself. See Figure 2. Figure 2. Texture to Improve Readability Textured Area B Issue: 01 Dated: 2/03

15 Surface Curvature For marking and reading, flat surfaces are preferred over curved surfaces because the curvature of an item may prohibit proper marking and can distort the code. If the mark is made on a round/curved surface, the symbol height should be less than 16 percent of the part s diameter. For Data Matrix codes, a rectangular symbol may be considered to provide greater readability on smaller circumference parts. Use of rectangular form should only be used as a last resort and should be agreed upon by all trading partners. QR Code is not available in a rectangular form. Figure 3 illustrates the proper method for marking and lighting curved surfaces. Figure 3. Marking Curved Surfaces Improper marking Area of illumination Proper marking Thickness Part or surface thickness must be taken into account when applying intrusive markings to prevent deformation or excessive weakening of the part. The degree of thickness required for intrusive marking is directly related to the heat, depth, or force applied. In most applications, the marking depth should not exceed 1/10 the thickness of the part. Part thickness is generally not a concern when applying non-intrusive markings. B Issue: 01 Dated: 2/03

16 4.0 INKJET MARKING 4.1 Overview 2D Direct Parts Marking Guideline Inkjet technology sprays precisely controlled drops of ink through the air in a pattern capable of creating a symbol. These drops are made of pigment suspended in fluid that evaporates, leaving the colored dye on the surface of the item. Figure 4 shows an example of an inkjet mark. There are two primary methods for generating these drops: the Drop-on-Demand and Continuous. The Drop-on-Demand method uses valves or Piezo-electric technology to force ink through an orifice. This method has significant printing resolution advantages over the Continuous method. The distance the ink can be shot is usually limited to no more than 1/8 th of an inch. This limits the use of Drop-on-Demand in industrial DPM applications. The Continuous method is preferred over Drop-on-Demand for industrial DPM applications. In this method, a continuous single jet of ink is made to pass between two variable voltage plates whose voltage can be adjusted. The voltage changes adjust the vertical location at which the drops will land; the horizontal position is varied by movement of the target (or part) in reference to the print head. Figure 5 displays a typical system. When no marks are being formed, the drops circulate from the nozzle to the ink reservoir. Figure 4. Sample Inkjet Marks B Issue: 01 Dated: 2/03

17 Figure 5. Continuous Inkjet System An advantage of the Continuous Inkjet method for DPM is that the distance from the nozzle to the target item is significantly larger. It is more robust when dealing with non-porous surfaces and dirty environments. For the remainder of this document (unless specifically stated), inkjet will refer to Continuous Inkjet marking technology. In DPM applications (unlike in paper, where the ink fluid is absorbed by the paper), the ink is required to have an evaporation fluid. This fluid is normally referred to as the make-up fluid. The solvent-based fluid is used to keep the viscosity of the ink stream correct. This must be a fast evaporation fluid to prevent the mark smearing by either motion or handling. The evaporation of this fluid allows for the deposition of the ink dye on the surface. It is this ink dye that generates the contrast of the mark to the target surface. The fast evaporation of the fluid can also cause problems with the ink drying and clogging the marking head if proper maintenance is not performed. There are many solvent-based fluids available. They can be selected for very fast drying, pigmented, colored, UV curable, low odor, low solvent, alcohol based, water based, non-flammable, high gloss, thermochromic, boil resistant, and many other applications. Particular attention must be placed if a Methyl Ethyl Ketone (MEK) solvent-based fluid is selected. Consult your plant Safety Officer about related OSHA, environmental, and/or company mandates about the use of MEK. The issues involved in marking and reading inkjet symbols placed directly on parts are somewhat different from those of symbols printed on paper. Particular attention must be paid to the condition of the substrate on which the ink is to be deposited. Cleaning the part surfaces prior to marking with an abrasive pad to remove coatings, rust, and discoloration, or using an air knife to blow away excess machining fluids, debris, or oil can improve mark and adhesion reliability. B Issue: 01 Dated: 2/03

18 4.2 Mark Geometry Inkjet Modules (Dots) A single ink drop or spot is preferred to represent each module. Although multi-dot modules closely simulate a square module of a symbol, there are a number of reasons for using just one dot for each module. The most obvious advantage is the printing time, where using a single dot for a module takes only about a ninth of the time as using 3X3 dots for a module. As in dot-peen marking, the border of the Data Matrix code (the L bar finder) is represented by a series of nearly touching modules. Critical to the readability of inkjet data matrix codes are the shape, size and spacing of these individual modules. These modules should be round in appearance and be large enough to overcome any surface background noise. 4.3 Mark Quality Limitations Inkjet marking may not be considered a permanent marking method in some cases and is generally limited to parts that will not be exposed subsequently to harsh manufacturing, operational, and/or remanufacturing conditions. In particular, it should not be used on EDM, grit-blasted, machined, and shot-peened surfaces. Many of these conditions change surface properties and/or color and may make it necessary to reapply the mark. In addition, care must be exercised to ensure that the part will not go through any paint-dissolving fluid, as this may also wash out the mark. Another limitation to inkjet marking is that normally a part must be moving at a consistent speed in one direction past the marking head during the marking process. Some inkjet system suppliers can provide a modification where the marking head moves and the part being marked remains still. Inkjet Nozzle Selection Inkjet Module Size Various nozzle sizes can be used, depending on the desired module size. Typically the individual module size may be as small as (125 microns) and as large as (500 microns), although larger/smaller dimensions may be possible with specific equipment modifications. Other factors, such as the amount of data to be encoded, reading equipment and substrate, may limit actual module size. (See Reading Considerations for more on module size) If the marking head does not receive proper periodic cleaning and maintenance, it can clog, blocking part of the symbol s completion. 4.4 Reading Considerations Ink and Background Color Ink marking color must be selected to maximize symbol contrast. Contrast will depend on the interaction between the ink color, the part s natural background color, and the color of light used by the symbolreading device. Colors may appear different under various light sources and lighting conditions. Figure 6 illustrates the effect of white ink on a green surface under red lights (Black ink would offer almost no contrast under those circumstances). B Issue: 01 Dated: 2/03

19 Another option for improving symbol contrast is through the use of inks that fluoresce at a specific light wavelength such as near Infrared (IR) or Ultraviolet (UV). Most symbol reading devices use IR light sources for code reading so you could mark a symbol that is not visible to people but still reads without special equipment. Even if a symbol appears to have very low contrast visually, a symbol reader may see it as near white on black or black on white image quality. Figure 7 shows ultraviolet ink illumination. Mutual agreement between supplier and customer is necessary to ensure that compatible reading technologies are available when using special applications of IR or UV fluorescing inks. In some cases, symbol reading can be improved by applying a colored medium as a backdrop to the area where the code will be applied, as illustrated in Figure 8. Note: To ensure reading efficiency, a minimum contrast ratio of 20 percent is required between the reflectance value of the module and the surrounding substrate. Various densitometers can provide such measurements nondestructively. B Issue: 01 Dated: 2/03

20 Figure 6. White Inkjet Ink on Green PCB When Imaged with Red Light Figure 7. Ultraviolet Inkjet Mark Figure 8. Inkjet with White Background Added B Issue: 01 Dated: 2/03

21 5.0 DOT-PEEN MARKING 5.1 Overview Dot-peen marking technology typically produces round indentations on a part s surface with a pneumatically or electromechanically driven stylus, otherwise known as a pin. Critical to the readability of dot-peen marked symbols are the indented dot s shape, size, and spacing. The dot size and appearance are determined mostly by the stylus cone angle, marking force, and material hardness. The indented dot created should be suitable to trap or reflect light and large enough to be distinguishable from the parts surface roughness. It should also have spacing wide enough to accommodate varying module sizes, placement, and illumination. The issues involved in marking and reading dot-peen-marked symbols on metals are different than symbols printed on paper. The first fundamental difference is that the contrast between dark and light fields is created by artificial illumination of the symbol. Therefore, the module s shape, size, spacing, and part surface finish can all affect symbol readability. The key to a successful dot-peen marking and reading project is to tightly control the variables affecting the consistency of the process. Symbol reading verification systems can provide feedback of the process parameters to some extent. Marking system operating and maintenance procedures must be established to help ensure consistent symbol quality. Regular maintenance schedules should be established to check for issues such as stylus wear. Additional processes, like machining dedicated surfaces, may be necessary to improve the symbol readability. Cleaning the part surfaces prior to marking with an abrasive pad to remove coatings, rust, and discoloration, or using an air knife to blow away excess machining fluids, debris, or oil can also increase the symbol quality. 5.2 Mark Geometry Dot-peen markers create a round dot on an item s surface by striking the item with a pointed stylus. A single strike will create a dot. Single-strike dots or multiple-strike dots can be used to create a single data module. Since dot-peen marks produce round modules instead of square modules, multiple-strike modules can be used to create a more square-looking module, which may help in the decoding process. Multiplestrike modules are also used to create larger size symbols. Either single-strike modules or multiple-strike modules may provide for better symbol readability depending on the material type, the surface condition of the item being marked and the reading equipment used. In most cases, it is preferable to have a module fill ratio 80 percent - of the module size. This allows for adjustment of the module size with vision tools available in most readers. B Issue: 01 Dated: 2/03

22 Figure 9. Single Dot Mark Geometry Figure 10. Multiple Dot Mark Geometry 2 x 2 3X3 The greatest advantage to single-dot module marking is faster mark cycle time. Single-dot module marking may reduce marking time by more than 75 percent in some cases. Another mark geometry factor that can affect code readability is off-center marks resulting from fluctuations in throw force, stylus play, stylus deflections, or similar conditions such as drag. To some extent, these can be compensated for by decoding software. 5.3 Mark Quality The following surfaces should have mark parameters verified within the production environments: Dot-peen mark on coated or painted surfaces: After an item has been coated, the mark may damage the coating. For example, painted items may chip during the mark process. This can lead to compromising the integrity of the material (i.e., corrosion). It may also create uneven reflectivity and make the symbol unreadable. Dot-peen mark on items to be coated or painted: After the paint or coating is applied, the mark may or may not be readable. For example, the use of paint is a concern because paint may fill the dotpeened cavities and make the symbol unreadable. Dot-peen mark on surfaces treated additionally with abrasive methods: Surface treatments like shot peening, Sutton finish, or Tornado Sutton can affect the readability of a dot-peened symbol. Limitations of Dot-Peen Conditions that may affect the use of dot-peen marking are the following: Thin materials whose structural integrity might be compromised by a mark Parts not held firmly in place during the marking process B Issue: 01 Dated: 2/03

23 Nonmetallic materials that chip, shatter, or regain shape after impact High volume production metals hardened above 54 on the Rockwell Hardness C Scale Stylus Cone Angle Much independent testing has concluded that, in general, a 30 (120 included) stylus will create marks with the best light reflectivity for decoding. A 30 stylus creates a mark more forgiving to variations in illumination; however, certain surface roughness and resulting reflectivity may make other cone angles more desirable. Figure 11below shows the cross sections of the material marked with various stylus cone angles. Collimated light coming in vertically is demonstrated in the top and middle drawing. For a 30 stylus as described in the top drawing, the light reflects off the indented surface without any obstruction. For any stylus with 30 or smaller cone angles, most incident light is evenly reflected off the indented surface. When viewed in the image captured by the camera, the modules are solid dark on a light surface background, or vice versa, depending on the illumination scheme. Figure 11. Cross Sections of Material Marked with Various Stylus Cone Angles Incoming Light Reflected Light Marked Surface (30 Pin) Included Angle 30 Angle Marked Surface (45 Pin) Marked Surface (45 Pin) B Issue: 01 Dated: 2/03

24 Mark Depth The minimum depth requirement for dot-peen marking is inches. For pneumatic markers, adjusting air pressure and/or the gap between the stylus and the substrate can control depths. This distance is variable and ranges from 0.05" to 0.5". The greater this distance, the deeper the mark given equal air pressures. For electromechanical markers, adjusting the current and/or the gap between the stylus and the substrate can control depths. Mark depth also depends on material hardness and stylus type. Figure 12. Preferred Stylus-to-Target Configuration Stylus Cartridge Stylus cartridge to stylus tip distance inch to 0.5-inch in the retracted state Stylus Stylus tip to target distance inch to 0.5-inch =.0056 Markin Depth g Surface Figure 13. Mark Diameter Range Using 30 Stylus B Issue: 01 Dated: 2/03

25 0.022 Mark Dia Mark Dia Depth Dia. Stylus Illustrated Depth Depth Machine Parameters It is important to control marking system parameters. The following situations can lead to reading failure: improper setup, lack of maintenance on stylus drive air pressure, stylus stroke, and stylus return pressure (or in the case of spring stylus return systems, spring fatigue ). Along with marking system parameters, the following elements can cause variations in module size, shape and placement: marking head fixtures, part fixtures, machine settings and operator error. It is recommended that marking and reading systems be incorporated into automatic stations whenever possible or that dedicated fixtures be used for aligning the part to the marking head. With all machine setup parameters, auxiliary equipment can be added to provide greater control of operator variables on the factory floor. Fixed-mount single or multiple stylus markers are preferred. Handheld markers are acceptable but must be clamped to the surface to prevent unwanted movement during the marking operations. Machine setup operations must be checked to ensure that the stylus is positioned at a 90-degree angle (perpendicular) to the marking surface. Stylus projection from the stylus nose guide should not exceed 0.5-inches in the retracted state to prevent deflection upon impact and its resulting oscillations. See Figure 12. B Issue: 01 Dated: 2/03

26 5.4 Reading Considerations Variable or multiple lens readers can be used in applications requiring the use of different sized 2D symbols. Because dot-peening produces a low contrast mark, successful reading could be improved by the application of colored backfill media or by using a lighting solution that produces artificial contrast. When selecting the location for the symbol, illumination of the mark must be taken into consideration. If the symbol is recessed or adjacent to a protruding surface, lighting becomes more difficult. Figures 14 and 15 illustrate a properly applied and illuminated dot-peen mark. The lighting setup used with the fixed station reader must be forgiving enough to compensate for normal production variation in surface roughness and stylus wear. B Issue: 01 Dated: 2/03

27 Figure 14. Data Matrix Dot-Peen Marking with and without Proper Illumination Proper Illumination Improper Illumination Figure 15. QR Code Dot-Peen Marking with and without Proper Illumination Proper Illumination Improper Illumination B Issue: 01 Dated: 2/03

28 6.0 LASER MARKING 6.1 Overview 2D Direct Parts Marking Guideline Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. Some lasers can be used to create a mark on some materials. This is done by directing a beam of coherent, collimated, focused light energy onto an item s surface. In general, when a laser s beam comes into contact with an item, its light energy is converted into heat energy, which creates a mark either by melting, ablation, carbon migration, or chemical reaction. Various materials may react differently to each type of laser and/ or laser marking technique. All lasers will not create readable marks on all substrates. When considering a laser marking system, the following factors should be taken into consideration: Type of material to be marked Laser type and marking process type Laser power Cycle time Information (volume of data) to be marked Laser safety Different materials absorb or reflect specific laser wavelengths at different rates. The amount of absorption is directly proportional to the laser s ability to heat the material and cause a change in its appearance. The type of lasing medium will determine a laser s light wavelength. Laser marking systems typically derive their name from their lasing medium. For example, CO 2 lasers use carbon dioxide gas as a medium. B Issue: 01 Dated: 2/03

29 Common Laser System Types Figure 16. Photonic Spectrum and Laser Wavelengths Table 4. Photonic Spectrum and Laser Wavelengths Laser Type Wavelength (nm) Nd:Yag (neodymium: yttrium-aluminum garnet) 1064 CO 2 gas (carbon dioxide) 10,600 Nd:YVO 4 (neodymium: yttrium-vanadate) 1060 Nd:Yag Green (frequency doubled neodymium: yttrium-aluminum garnet) 532 Below are the generally accepted major classifications of lasers. Solid-State Lasers The solid-state laser medium is a crystal or glass which has an impurity (the lasing material) distributed (doped) throughout its solid matrix There are a variety of beam generation techniques, but all solid-state lasers require a high intensity light source in a reflective chamber to drive light energy into the crystal to excite the molecules. The light source can be pulsed or operated in the continuous wave (CW) mode. Examples of this type of laser would be the Nd:YAG and the Nd:YVO 4 lasers. B Issue: 01 Dated: 2/03

30 YAG lasers and YVO 4 are the most common type of industrial solid-state lasers. Beam generation techniques include CW, Q-Switching, Pulsing, and Diode Pumping. Semiconductor Lasers Sometimes called direct diode lasers, these are not to be confused with solid-state lasers. These are electronic devices and are generally very small and emit very low power. They may be built into larger arrays; however, as of this writing output power has been limited to fewer than 20 watts. Gas Lasers As the name implies, gas lasers rely on a reactant gas contained in some form of enclosure or tube and are often pumped or induced to laser by passing an electric discharge through the gas medium itself. Excimer and CO2 lasers are examples of gas lasers. Excimer lasers are a notable exception to the name-implies-the-lasing medium nomenclature rule of gas lasers. The excimer name is derived from combining and shortening the terms excited and dimmers. Excimer uses reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton, or xenon combined in a sealed tube. When electrically stimulated, a pseudo molecule (dimmer) is produced. The dimmer produces laser light in the ultraviolet range. CO2 laser manufacturers can use several different approaches to gas handling and electrical power input: Sealed Tube/Waveguide Slow-axial flow Diffusion cooled/waveguide Fast-axial flow (FAF) Laser Safety Standards Classifications In the United States laser safety is regulated by the Center for Devices and Radiological Health (CDRH), part of the Food and Drug Administration (FDA). Regulation 21 CFR Subchapter J Parts 1002, 1010, and 1040 applies to laser manufacturers. These standards classify lasers into four broad areas depending on how they are shielded and the potential for causing biological damage during operation. All laser systems should be clearly labeled with one of four class designations (Class I, II, III, or IV). Laser safety classification is based on laser power level and whether the laser beam is enclosed to prevent possible injury. Laser systems with a power output of greater than 5 milliwatts must be registered with the CDRH. Laser marking system manufacturers are required by the CDRH to certify compliance with whichever class of safety the laser system has been manufactured in compliance with. The two most common types of laser safety rating used for laser marking devices are Class I and Class IV. Class I laser safety is the most safe and Class IV is the least safe. Class I laser systems require laser beam shielding to prevent injury from contact with the laser beam. This is normally accomplished by conducting the laser marking process in what is sometimes call a light tight box. Beam shield boxes can be designed for install directly into production lines or can be made for manual loading and unloading. These boxes will have interlock safety devices to prevent the laser from B Issue: 01 Dated: 2/03

31 firing when the box is open much like a microwave oven has an interlock in its door to prevent use with the door open. In some cases, parts can run through a production line on a track through a series of angled turns that prevent the laser beam from reflecting more than three times instead of needing an enclosed box. Class IV laser marking systems are the least safe and may not block against accidental contact with the laser beam. The laser light wavelengths used for laser marking systems (except for some green wavelength lasers) are not visible to the human eye, so you cannot see a laser beam when it is present to avoid accidental contact. The power level of lasers used for laser marking is strong enough to easily burn a person s skin. The hazard of most concern is damage that could occur from a laser beam striking a person in the eye, which could cause permanent blindness. Companies that produce laser marking systems are required to create safety-reporting documents and submit them to the CDRH for approval on all new and/or modified laser marking systems. Once approved for a specific classification of laser safety, the CDRH will assign that particular laser system an Ascension Number. If a laser is manufactured by one company but integrated by another company, then the integration company becomes responsible for laser safety and is considered the system manufacturer. The integration company would be required to file with the CDRH for a new Ascension Number for each different system configuration they install. Caution should be taken when selecting a laser system integration company since many standard equipment integrators may not have experience in laser safety requirements. Laser Safety and OSHA At this writing, OSHA has not created a laser safety related requirements document. Instead, OSHA has cited some companies for operating under seriously unsafe practices under the General Duty clause 5 [a][1], of Public Law , the Occupational Safety & Health Act of Laser Safety Standards ANSI B Machine Tools Using Lasers for Processing Materials ANSI Z for end users of industrial lasers OSHA Instructional Publication 8.17 (5 August 1991) ISO safe use standard for industrial laser machines IEC 825 (Cenelec EN 60825) Radiation Safety of Laser Products B Issue: 01 Dated: 2/03

32 6.2 Mark Geometry Laser Etching/Engraving This process uses heat created by a laser beam to remove material through vaporization. Marks produced by this method may have limited contrast from non-marked areas since the mark color and background color are normally the same and contrast is created by depth shadows or a difference in surface finish. Higher power laser systems and longer marking cycle times may be required depending on the material of the items being marked and mark depth requirements, etc. Lasers can also be used to remove coatings from items to produce a mark. Many times metal items are coated to protect them so using a laser to remove a coating may cause the item to rust in marked areas. Many paints and other coatings will burn off where contacted by high-power marking lasers. Figure 17. Laser Etching/Engraving Area of material vaporization Laser Annealing Heat created by a laser beam can be used to perform very controlled heat-treating. In this case metal parts containing carbon are affected by the laser s heat, which will produce a mark due to a localized metallurgical change by carbon migration. Metals containing higher concentrations of carbon can produce a darker mark easier than metals containing less carbon, which may produce a lighter brown mark. Marks created with this method will not necessarily be raised or depressed but instead be flush or smooth with the rest of the items surface. Mark depth will depend upon the material s carbon content and laser energy/heat applied for a given time period. Figure 18. Laser Annealing Metal Substrate Area of Mark B Issue: 01 Dated: 2/03

33 Laser Discoloration Some lasers can be used to discolor or bleach the color out of certain items and coatings. This process can also be used to mark some plastics. In plastic marking, a laser can cause the plastic to burn/char, foam, or bubble, causing contrast with the original color of the part. Figure 19. Laser Discoloration Marked Surface Surface Coating Laser Marking Enhancers Materials and methods exist that can assist in laser marking by the following: Increase mark contrast Allow for marking a wider range of items Improve laser marking cycle time Reduce the amount of laser power required Chemicals can be added in small amounts to some plastics that will react by changing color when contacted with a laser. Special coatings can also be applied to the surface of an item that will fuse to the item when heated by a laser. This also allows for the marking of many different kinds of materials while needing only one type of laser. Figure 20. Laser Marking Enhancers Bonded/Fused Material Substrate B Issue: 01 Dated: 2/03

34 6.3 Mark Quality Laser marking quality is mainly affected by and dependent on the item being marked and the laser marking method selected. Marking resolution can be far greater than with inkjet or dot-peen. Laser marking resolution is based on laser beam diameter or spot size and how closely in focus the marking area is. The marking area of an item should be perpendicular to the laser beam and the focal distance or item shape should not vary by more than ¼ or the mark may appear out of focus. Manufacturing process and material property variations in the item being marked can also affect mark consistency; for example: Differences in metallurgy between lots or between suppliers Variations in coating thickness Consistency of surface finish Laser Beam Steering Control Two common methods for laser beam control and delivery are galvanometer and flying optics. Galvanometer or beam steered laser marking systems are most common for in-production-line use and are normally driven by computer-controlled mirrors that move the beam by reflecting it to a specific location. Figure 21depicts the laser beam emanating from the laser medium chamber, which by hitting one mirror that draws in one direction then hitting another mirror that draws in the other direction, the beam finally travels through a focusing lens onto the item to produce a mark. Galvanometer steered systems are much faster than flying optic systems. B Issue: 01 Dated: 2/03

35 Figure 21. Galvonometer Beam Steering Flying optics, as shown below in Figure 22, work much like a plotter. These laser marking systems are controlled by belt-or gear-driven motors that move fixed mounted mirrors along x and y coordinates. Figure 22. Flying Optic Beam Steering B Issue: 01 Dated: 2/03

36 6.4 Reading Considerations Laser marking is considered to have the highest marking resolution allowing for greater code densities than other marking methods. This allows for the ability to encode more information or to create smaller sized marks. The ability to read small and/or higher density marks depends on the pixel resolution of the reading device. Laser marked Data Matrix and QR codes are normally marked with square modules, which can also help improve code readability. Laser marking is considered the highest precision and most consistent marking method. The ease of reading laser marks is also primarily based on the amount of contrast created, as noted in types of marking methods in Section 6.2. B Issue: 01 Dated: 2/03

37 7.0 READING AND VERIFICATION In this section, we discuss factors related to the reading and verification of 2D DPM symbols. The two choices for 2D DPM are Data Matrix and QR Code as spelled out in the AIAG B-4 Part Identification and Application Standard. The international standard for Data Matrix is ISO and the one for QR code is Fundamentals of Reading Many people are confused about the differences between readers and verifiers. Reading can best be described as the action of extracting data from a symbology. Verification includes reading but goes further into quantifying the quality of a symbol. The typical components of a reading and/or verification system are similar. They include sensors, optics, illumination, and processing unit. Sensors Both of the symbologies recommended here are matrix-type 2D barcodes. Reading them requires the simultaneous capture of the symbol, usually accomplished via an image capture device such as Charged- Coupled Device (CCD) or Complementary Metal Oxide Semiconductor (CMOS) sensors. CCD/CMOS sensors generate an image map of what they see. This is typically referred to as the captured image. This captured image is then transferred to the processor memory in order for its algorithms to generate the information. Optics Because the sensor will capture an image, an optical system capable of projecting the symbol image into the sensor is required. Typically this is done by placing optics in the path between symbol and sensor. The selection of these optics is specific to the application (whether hand-held or fixed). Illumination Because these sensors are passive (as opposed to laser sensors, which provide their own illumination), illumination must be provided. In most cases, the marking method and reading condition will dictate the type of illumination used. The two major types of illumination are termed Bright Field and Dark Field. While some marking methods self-generate contrast (e.g., laser marking may generate dark modules and inkjet may have a specific ink color), methods such as dot-peening are not color specific. Instead, the mark will assume a color based on the illumination. Bright field illumination is usually located close to the image capture sensor and produces an image in which the background is bright (or light), with the marked modules taking a dark color. Dark Field is its opposite. The lighting is generated very close to the surface, at extremely low angles, generating an image that displays light modules on a dark background. As with other methods of marking, readers can have difficulty reading symbols that are placed near obstructions that can block illumination. Additional illumination and filters can be used to increase code contrast. Consequently, when considering mark locations, an engineering evaluation must be conducted B Issue: 01 Dated: 2/03

38 prior to placing symbols within recesses or adjacent to structures that protrude above the marking surfaces. Intensity of the light source must be high enough to easily create a contrast of the module relative to the part surface and also to overcome the effects of changing ambient light conditions. The illumination source must be diffused lighting to avoid hot spots (glare areas) on the part surface. Florescent lights are an excellent source of diffused light. Light sources such as light-emitting diodes (LEDs) with a diffusing filter can also be used. Red light sources are often used instead of white to reduce glare on shiny parts. A red light filter can also be placed on the camera system to allow in only red light. Processing Unit Once an image of a marked symbol is acquired, this information is provided to a processor. Herein lies one of the major differences between reading and verifying. Whereas readers are primarily interested in extracting the information from the symbol, verifiers are designed to quantify a number of quality factors related to the symbol. For that reason, readers are free to implement the most advanced decoding algorithms that a respective manufacturer can devise, whereas verifiers must implement a reference decode algorithm specified by international agreement. For this reason, ISO was developed. Note that beyond these standardized metrics, manufacturers are free to expand their offerings to include tools further tailored to specific marking methods. 7.2 Symbol Quality Grading The measurement of two-dimensional bar code symbols is designed to yield a quality grade indicating the overall quality of the symbol. This quality grade can be used by producers and users of the symbol for diagnostic and process control purposes and are broadly predictive of the read performance to be expected of the symbol in various environments. The process requires the measurement and grading of defined parameters, from which a grade for an individual scan (scan reflectance profile grade or scan grade) is derived; the grades of multiple scans of the symbol are averaged to provide the overall symbol grade. Expression of Quality Grades International Standards specify a numeric basis for expressing quality grades on a descending scale from 4 to 0, with 4 representing the highest quality. However, in application standards with an historical link to ANSI X3.182, individual parameter grades and individual scan grades may also be expressed on an equivalent alphabetic scale from A to F, with A representing the highest grade. B Issue: 01 Dated: 2/03

39 Table 5. Equivalence of Numeric and Alphabetic Quality Grades Numeric Grade Alphabetic Grade 4 A 3 B 2 C 1 D 0 F Overall Symbol Grade Where a specification defines overall symbol grades in alphabetic terms, the relative mapping of the alphabetic and numeric grades is as illustrated in Figure 23 below. For example, the range of 1.5 to immediately below 2.5 corresponds to grade C. Figure 23. Mapping of Alphabetic and Numeric Overall Symbol Grades The overall symbol grade shall be the arithmetic mean of the scan grades for all images. If any two scans of the same symbol yield different decoded data, then the overall symbol grade, irrespective of individual scan grades, shall be 0. Overall symbol grades shall be expressed to one decimal place on a numeric scale ranging in descending order of quality from 4.0 to 0.0. B Issue: 01 Dated: 2/03