This article presents all the information you need to know about Marking Machinery.
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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.
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.
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 uses a marking die and is the simplest marking technique. The marking die may be a stroking or rolling die with a raised, engraved surface that resembles the pattern to be printed. Die marking operation can be ink based or high pressure 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:
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.
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 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.
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:
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.
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 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.
Marking parts with a stain or ink is an easy way to see the difference between similar parts to determine a pass-fail status or confirm a process has been completed. The marking of parts during assembly is completed for several reasons from identifying approved parts to determining the machine used to produce them.
In some cases, parts are marked with invisible stains that can only be seen under an ultraviolet light. This type of marking is done to parts to determine if there has been any tampering with the part.
The three types of contact and non-contact marking are handheld markers, contact marking systems, and non-contact spray marking systems. Of the three systems, handheld marking systems are the simplest and are used to identify the completion of a task such as filling a radiator or injecting a fluid into a system.
Contact marking systems use ink or stain that has been placed in a reservoir. When a component or part is positioned for a process or test and the process or test is completed, an actuator causes a dauber to imprint a mark on the part to indicate its status.
Non-contact marking systems use a form of spray process to apply a colored spot, band, or stripe. The paint or stain is held in a reservoir from which it is applied at high pressure. The valve for the spray can be fixed mounted or connected to an actuator that positions it in relation to the part to be marked. In more complex processes, the part is rotated as the non-contact marker applies a band of color.
Marking stains for contact and non-contact marking are referred to as inks, staining colors, or paints and are either opaque or transparent.
Transparent marking stains have thinner viscosity and dry fast. They are used on light surfaces or in applications that require tight tolerances. The chemical structure of transparent stains prevents them from settling or separating.
Opaque marking stains have pigments designed to produce heavier and darker marks regardless of the type of surface. They are applied thicker and take longer to dry. The thickness of opaque marking stains is adjusted to fit the needs of a specific part or process.
Electrochemical etching is the process of transferring a marking pattern from a stencil to an electrically conductive substrate through an electrolytic reaction. It is one of the oldest permanent marking methods still used, is very easy to use, and extremely versatile with regard to the shape and geometry of the part being etched.
Electrochemical etching is the only method that does not alter the integrity of the metal being marked and does not create any stress points in the crystalline structure of the base metal. It is for this reason that it is the only marking method approved for use on flight critical parts (FCP).
Electrochemical marking is very flexible with regard to the shape of the part. Since the stencil is flexible and can be wrapped around any surface, it is possible to mark complicated geometries without the need for elaborate jigs or fixtures.
The process involves the following steps:
The electrolytic process can be performed using alternating or direct current, each of which affects the metal surface differently. The use of alternating current (AC) does not remove any material on the surface but produces a "native oxide" residue on the metal 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.
The resulting markings from the two methods are durable and abrasion-resistant. The properties of the material underneath the topmost surface and outside the marking area remain unmodified.
The electrolyte solutions may be slightly alkaline or acidic and require neutralizing and cleaning to prevent subsequent corrosion of the part. Some companies have developed and offer electrolytes that are corrosion resistant and do not require neutralizing. Parts that use these special electrolytes never "rust" when used on ferrous metals and alloys.
Electrochemical etching devices are portable and produce high-quality and precise marks of any legend such as alphanumeric characters, logos, and single or two dimensional bar codes such as the QR or data matrix codes. They can mark almost any electrically conductive metals such as aluminum, zinc, steel, stainless steel, and titanium.
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 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.
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:
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.
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.
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.
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.
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 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 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 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.
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).
Part marking plays several roles, which makes it a vital process:
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.
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.
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.
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.
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