Marking Machinery

Chapter 1: Overview of Marking Machinery

Marking machinery is industrial equipment that specializes in creating texts, graphics, labels, and codes on parts and products. Each type of marking machine has different mechanisms in modifying the properties of a material to create the desired mark. Some of these mechanisms are stamping, engraving, inking, and etching.

Marking is performed to provide identification, traceability, and decoration to a product or a part that is distinguishable by a wide class of individuals and even machines such as scanners, barcode readers, and 2D code readers. This is a robust process that has significantly improved the entire supply chain and the marketing and advertising of countless products.

The succeeding chapters enumerate the common marking methods and their machinery description, operating principles, and applications. The marking method suitable for a particular application depends on the physical and chemical properties of the material, return of investment, and value of the product.

Chapter 2: Physical Marking Methods

Dot Peen Marking

The dot peen marking machine uses a marking pin (or peen) made of rigid material, such as carbide, to engrave a series of small dots closely spaced to one another to form straight or curved lines. The engraving by the marking pin induces low stress in the material. The resulting mark is readable, permanent, and has a deep impression on the substrate.

Dot peen marking machines use a coordinate system to place the dots precisely. The marking pin is attached to the marking head, which is driven by a pneumatic or an electromechanical system. To adjust the contrast and depth of marking, several parameters can be adjusted such as clearance of the pin and the part, dot spacing, and pressure.

Dot peen marking is a fast, accurate, and reliable method of marking metals. This method can print logos, texts, and 2D codes in a wide class of materials of any size or orientation. Dot peen marking machines are low maintenance; marking heads and pins have a long service life.

Scribe Marking

The scribe marking machine uses a stylus with a tip made from a hard material such as carbide and diamond to produce a mark. The stylus tip gently pierces the substrate and is dragged along its surface to create lines or curves. The resulting mark is clear, continuous, permanent, and also has a deep impression on the substrate. Scribe marking is also known as “drop and drag” and “scratch" marking.

Scribe marking machines emit sounds at lower decibels than dot peen marking machines. The latter relies on repeated indentations of the pin on the substrate, which produces unwanted noise and vibrations at a rapid rate. Furthermore, since scribe marking machines produce continuous lines and curves, they have a higher marking resolution.

Scribe marking machines also use a coordinate system in directing the path of the stylus. The stylus can be adjusted to mark parts with concave, inclined, round, and irregular profiles.

Scribe marking machines are mechanically robust and require minimal maintenance. This machinery is used for marking metal workpieces used in the transportation, construction, farming, and automotive industries.

Die Marking

Die marking is one of the simplest marking techniques; it utilizes a marking die. The marking die may be a stroking or rolling die that features a raised, engraved surface that resembles the pattern to be printed. A die marking operation may be ink-based or it may be high-pressure marking.

Ink-based Die Marking

Inks made from dyes or pigments are consumed to create a print on the substrate. A sufficient amount of ink is applied to a marking die and is then transferred by contact on the surface of the substrate. The tip of the die is made of rubber. The quality of marking is influenced by the affinity of the ink to the substrate, amount of ink used, setting time, and contact of the die on the substrate.

Since ink-based marking does not induce stress, it is ideal for marking brittle substrates such as glass and ceramics.

The following are some examples of ink-based die marking devices:

Reciprocating Coders

These marking devices have a pneumatically- or electronically-powered marking head that transfers the ink by stroking. They are commonly used in traceability systems in the manufacturing and automotive industries. They are used to print information such as expiration dates, product codes, prices, and labels directly on the individual product. They may be installed in line with the processing equipment or may be portable or hand-held.

Pad Printers

These marking machines transfer a pattern from a flexible silicone rubber pad onto the surface of the substrate. The ink is transferred by carefully blanketing the substrate, which is held in place. This method is ideal for the ink marking of two-dimensional patterns into three-dimensional surfaces of all shapes and sizes.

Hot Stamping Machines

Hot stamping is the process of transferring ink from a carrier foil into the substrate by pressing a heated die. Hot stampers produce a lustrous and shiny mark which is suitable for decorative letterings and ornamentation purposes.

High Pressure Marking

A die or punch marks a substrate by exerting enough pressure to leave an indentation on its surface. The tool contains the pattern to be imposed. The quality of marking is affected by the mechanical properties of both the substrate and the die and the pressure applied. The die should be made from a harder material than the substrate to induce deformation on its surface.

High pressure marking machinery includes:

Stamping Machines

These machines create an embossed or debossed surface by applying force to shape and deform the material. The force is applied by the downward stroke of a punch, which has engravings of the pattern to be printed on its tip.

An embossed mark has a portion of the material raised away from its surface. On the other hand, a debossed surface has a portion of the material pressed against its surface. The raised or depressed portions resemble the marking pattern.

Roll Die Marking Machines

These machines consist of a cylindrical die that has engravings of the pattern to be printed on its lateral surface. The cylindrical die rolls over the substrate in sheet form while applying force to produce the mark.

Thermal Inkjet Printing

Thermal inkjet printing is used to print text, graphics, and images on a continuous sheet of substrate made of paper and plastic. Thermal inkjet printers are equipped with thousands of nozzles that transfer the ink into the substrate. The ink is heated by elements present around the nozzle wall. As ink vaporizes, it is transformed into a bubble which collapses itself out from the nozzle tip.

The quality of inkjet printers may be predicted by the advertised dots per inch (DPI); higher DPI means more dots are fitted in one inch, hence, it has higher resolution.

Thermal inkjet printers feature low-cost operation and portability. They are highly valued for printing different colors and tones in the substrate, which other marking techniques are not capable of. However, the image produced is less durable and is prone to smudging and staining when exposed to moisture, heat, and continuous touching.

Chapter 3: Electrochemical Etching for Marking

Electrochemical etching is the process of transferring a marking pattern from a stencil to an electrically conductive substrate through an electrolytic reaction. The stencil is attached to the marking head or placed directly onto the component to be marked. The steps involved in electrochemical etching are as follows:

1. The metal to be etched is connected to the positive terminal of the electric source and acts as the anode. A base plate of the same material is connected to the negative terminal of the electric source and acts as the cathode. The marking head is connected to the electric source.
2. The stencil is placed above the component to be marked.
3. The electric source is switched on.
4. The marking head is moistened with the electrolyte solution and pressed onto the part to close the circuit. It is then held for a few minutes to complete the marking of the part.

The electrolyte solution may be slightly alkaline or acidic and does not require a neutralizing step to protect it from corrosion.

The electrolytic process can be performed using alternating or direct current, each of which affect the metal surface differently. The use of alternating current (AC) does not remove any material on the surface and results in a mark that has a darker tone than the substrate. The use of direct current (DC) strips away a portion of the material and leaves an engraved mark with a tone that is similar to the color of the substrate. Nevertheless, the resulting mark made from the two methods is durable and abrasion-resistant. The properties of the material underneath the topmost surface and outside the marking area remain unmodified.

Electrochemical etching devices are portable and produce a high-quality and precise mark. They can mark almost any electrically conductive metals such as aluminum, zinc, steel, stainless steel, and titanium. The only downside of this method is the use of consumables such as electrolytes, cathodes, and anodes, which augment the operating cost.

Chapter 4: Laser Marking

Laser marking is a marking process that incorporates laser technology to mark workpieces. Laser marking machines make use of focused, high-energy laser beams that strike the surface of the material to print the marking pattern, which becomes permanent.

Laser marking machines are highly automated and are controlled by software to precisely mark a pattern on numerous substrates quickly. No mechanical contact such as clamping and fixing is performed; this eliminates the risk of material deformation and damage. They also don’t rely on consumables like ink and electrolytes.

The Science of Laser Marking

The term laser is an abbreviation for “Light Amplification by the Stimulated Emission of Radiation.” A laser beam is created when the electrons that constitute an atom of the medium become excited with the energy they have absorbed from an electrical current or another laser. When the electrons are excited, they transfer to a higher energy level and give off photons (the particles of light) as they return to their original energy level. These photons excite other atoms, causing them to give off photons that make a high strength amplified light.

The total reflector is positioned in one end of the laser tube to keep the photons bouncing back and forth through the medium. A partial reflector is positioned on the other end that allows some of the photons to escape. The escaping photons make the powerful laser light that gives off heat to modify the properties and appearance of the surface it strikes.

Laser beams may be pulsed or continuous. Pulsed lasers have energy output concentrated in short bursts occurring in regular intervals. The peak of the instantaneous energy emitted by a pulse laser can be extremely high. Continuous-wave lasers have a constant but lower energy output over an interval.

Laser Marking Processes

The energy produced by the laser marker introduces physical or chemical changes depending on the nature of the substrate and laser power. There are several laser marking processes that can accommodate different needs:

Laser Engraving

In laser engraving, powerful laser beams vaporize a portion of the material to expose a noticeable cavity underneath its surface. The resulting cavity forms the mark. To accomplish this, the laser engraver must generate enough heat to vaporize the material in milliseconds.

Laser engraving creates marking depths ranging from 0.0001 – 0.005 inches, while deep laser engraving creates depths greater than 0.005 inches. The depth is increased by repeating laser pulses. The mark produced is abrasion resistant and keeps its readability after post-process treatments.

This process is suitable for almost any kind of metal, plastic, wood, leather, glass, or ceramic. It has a smaller chance of damaging or deforming the material than the mechanical engraving process.

Laser Etching

In laser etching, the laser beam melts the material, which causes it to expand and form a noticeably raised cavity above its surface. The resulting cavity forms the mark. This process is faster than laser engraving because less energy is required to melt a material than to vaporize it. Hence, laser etching is a more economical option.

Laser etching creates high contrast marks with an elevation of up to 80 microns. However, the mark is prone to abrasion since it is raised against the surface. It is suitable for a variety of materials, which include aluminum, anodized aluminum, steel, lead, and magnesium.

Laser Annealing

In laser annealing, the heat effect of the laser beam causes color change due to the oxidation of the material. The contrasting tones give rise to the mark. The required energy for this process is relatively lower than laser engraving and laser etching, and no materials are being removed nor disintegrated. The marking depth created is usually 20 – 30 microns in depth. Depending on the marking temperature, different colors can be produced.

This process is suitable for substrates that are required to maintain their strength and material integrity after marking, which is beneficial for materials used in structural applications. It is also used for marking medical instruments. Commonly marked metals using this method are steel, stainless steel, and titanium. It is the only applicable marking process for stainless steel because it does not remove the protective chromium oxide layer on its surface.

Laser Carbonizing

In laser carbonizing, the heat given by the laser beam breaks the polymeric bond of the substrate that causes the area to darken and release hydrogen and oxygen gases. A noticeable contrast that defines the mark is observed after the reaction. Laser carbonizing is used in marking organic materials such as synthetic polymers, plastics, wood, paper, and leather. However, it is not recommended for marking dark-colored substrates because it only produces a tone darker than the color of the material, so this would result in a low contrast marking.

Laser Foaming

In laser foaming, the laser beam melts the polymeric material, and foam and gas bubbles are emitted as a response. The mark produced is raised away from the surface and is white, silver, or tan. The emitted bubbles change light refraction properties of the material; this makes a lustrous mark. Laser foaming is used in marking protective plastics in electronic devices, signages, and decorative letterings.

The types of laser marking machines, categorized by their capabilities and specifications, are as follows:

CO2 Laser Machines

CO2 laser machines produce laser gas by passing electric current in a gaseous mixture containing CO2 sealed in a chamber. The CO2 acts as the laser medium, and it emits infrared waves that are 10.64 microns in wavelength. These machines can perform many laser marking operations and can also cut materials. The piercing capability of CO2 lasers is suitable for deep engraving. However, they consume more power.

CO2 lasers are ideal for marking non-metallic materials such as wood, acrylic, paper, leather, glass, and ceramics; they are not applicable for some metallic substrates. Common applications are PVC pipes, electronic components, packaging materials, building materials, and furniture.

Fiber Laser Machines

Fiber laser machines produce solid-state lasers by passing electric current in an optical fiber doped with rare-earth elements. The optical fiber acts as the laser medium. It emits electromagnetic waves 1.064 microns in wavelength and has a much smaller focal distance, which brings the intensity up to 100 times that of CO2 systems with similar power output; this makes fiber laser machines ideal for harder and denser materials such as metals and plastics.

Fiber laser machines require less maintenance and have a longer service life—up to 100,000 hours. Aside from marking hard metals, they are used on surfaces with plating, coating, ABS, epoxy resins, and inks. These machines are the most common today, and they are used in almost all industries. Some applications are IC chips, jewelry, automotive parts, electronic devices, components, etc.

Green Laser Machines

Green laser machines operate in the green visible spectrum. They emit a laser wavelength of 532 nm and a power of 5 – 10 watts. Green lasers give off energy at a much lower temperature, which eliminates heat stress in the substrate. They also have a narrower beam tip of up to 10 microns, which makes them ideal for tighter spot sizes and precision marking. They are used in marking highly sensitive materials such as silicon wafers, printed circuit boards, glass, ceramics, and thin plastics. However, they are not recommended for deep engraving.

Ultraviolet Laser Machines

UV laser machines emit long-wavelength UV rays ranging from 10 – 400 nm. UV lasers can be absorbed by the substrates faster and can also be used in marking highly reflective materials. UV laser marking is useful in cold marking applications where thermal stress is not tolerable; it eliminates the risk for glass and ceramics when marking. They are also used in precision marking of circuit boards, microchips, solar panels, and measuring equipment for medical applications (i.e., syringes and cylinders).

Chapter 5: Advantages of the Marking Process and Marking Machinery

Part marking plays several roles, which makes it a vital process:

Product Identification

Product identification and labeling are essential means of communication between the manufacturer and consumers. They share the brand name, the manufacturing company, and the product variant. Part marking differentiates one product from others.

Product Traceability

Traceability is the act of collecting and managing information along the product’s lifecycle from acceptance of raw materials to shipment of products. This activity is strictly enforced in automotive, electronics, medical devices, and food and pharmaceutical manufacturing. It is beneficial to the persons involved in the supply chain, and that includes the end consumers.

Critical information such as production batch, expiration dates, quality control stamps, and serial numbers can be easily seen in individual parts in the form of texts and graphics. 2D and bar codes are employed in advanced traceability systems.

Decorative Purposes

The application of marking can be as simple as adding artistic elements in products and workpieces to increase their aesthetic value. Marking for decorative purposes is usually performed on jewelry and crafts.

Advantages of Marking Machinery

Marking machinery is an industrially robust and highly profitable investment. It is equipped with highly automated and programmable features that reduce labor costs and increase marking quality and speed. Minimal intervention is needed as the operation of the equipment may be controlled by a single operator.

High-quality marking is assured when a manufacturer carefully evaluates and selects the correct machinery for his needs. All marking machinery offers distinct marking characteristics. Legibility of markings are guaranteed when the correct marking method is chosen for a specific material. Multiple parts can be marked precisely and with high repeatability.

Conclusion

• Marking machinery is industrial equipment that specializes in creating texts, graphics, logos, and codes in parts and products.
• Dot peen marking is a marking process of creating a series of small dots to form lines and curves in the substrate.
• Scribe marking is a marking process of drawing lines and curves in the substrate.
• Die-based marking is a collection of techniques that transfer the marking pattern from the die or punch into the substrate.
• In thermal inkjet printing, the heated ink is sprayed into the substrate through the thousands of nozzles inside the printer.
• Electrochemical etching is the process of transferring a marking pattern in the stencil to the surface of the substrate by an electrolytic reaction.
• Laser marking is a non-contact marking technique that incorporates laser technology. The energy given by the laser beam interacts with the substrate and modifies its properties.
• There are five laser marking processes that introduce physical and chemical changes depending on the nature of the substrate and laser energy level. These are laser engraving, laser etching, laser annealing, laser carbonizing, and laser foaming. The latter two are used for organic substrates.
• The types of laser-marking machines discussed were CO2 laser, fiber laser, green laser, and UV laser machines. They operate at different energy levels.
• Part marking plays a vital role in product identification, traceability, and aesthetics.
• Marking machinery is highly automated. They produce high-quality marking with high precision and repeatability, provided that a manufacturer selects the appropriate marking machine for the material.